2008:104 PB MASTER’S THESIS
Fellingsdams An investigation of wastewater treatment by chemical precipitation in ponds in northern Sweden
Wen Zhang
M.Sc. in Environmental Engineering CONTINUATION COURSES
Department of Civil and Environmental Engineering Division of Sanitary Engineering
Universitetstryckeriet, Luleå 2008:104 PB • ISSN: 1653 - 0187 • ISRN: LTU - PB - EX - - 08/104 - - SE
Luleå University of Technology
MASTER THESIS
Fellingsdams - An investigation of wastewater treatment by chemical precipitation in ponds in northern Sweden
WEN ZHANG
Master of environmental engineering Department of Civil, Mining and Environmental Engineering Luleå University of Technology
Abstract Fellingsdams are widely used in northern Sweden as an economical and easy operating method to treat the wastewater. They are divided into in-pond and pre-pond systems by different locations of dosage. Aluminium salts, iron salts and slaked lime are the most common coagulants that have been used, since they are cheap and easy to react with water.
Turbidity and detention time are two important factors in fellingsdams. Turbidity is mainly influenced by precipitation and algae. From the perspective of actual detention time, the pond geometry should be long and narrow.
When using slaked lime as coagulant, there is usually a large amount of sludge accumulated around the influent pipe because of fast precipitation. In the fellingsdam at Nyliden, 90% of the total sludge was found accumulated in about 20 meters. Aluminium salts and iron salts react slower with water, so the formed sludge curves are modest. To remove the sludge, excavation and pumping are the choices but differs due to different conditions. Dewatering is the main way to treat the sludge.
The main task for a fellingsdam is to remove the organic carbon, nitrogen and phosphorus. The effluent values from yearly environmental reports 2001-2007 were analyzed, most values were below the demands. The coliform bacteria concentration is a problem in the effluent water. A high pH environment guarantees low bacteria concentration in the effluent. Laboratory analyses were made on samples from a few aluminium fellingsdams and iron fellingsdams, only the pond in Hede reduced the coliform bacteria concentration below 10 cfu/100ml. Mellansel fellingsdam, an iron pond, had a high value of 6600 cfu/100ml in the effluent.
Future utilization of the effluent water is also discussed; irrigation is one of the uses. The energy forest in Vika Strand, Falun is a good example. Luleå University of Technology
Acknowledgements The investigation includes lots of field work and data analysis, thus the field cooperation and data collection are very important. I would like to express my gratitude to all the managers and operators at Örnsköldsvik, Härjedalen, Östersund, Ljusdal and Bollnäs municipalities; they provided a detailed background information of each fellingsdam during the field investigation, and also presented the environmental reports.
I appreciate my supervisor Professor Jörgen Hanaeus for offering me this opportunity to work with him. I improved a lot through this study, the theoretical knowledge I learned at the university became practical. We visited a lot of fellingsdams to get water and sludge samples. It was hard to take samples from the frozen ponds in cold winter, and sometimes we need to row a rubber boat to get samples in the ponds. But I realised that I have never learned that much, the theoretical knowledge is important but not enough, whereas practical experience can be harder and challengeable. And also I am grateful to his patient guidance and unconditional support.
Finally, I would like to give my special thanks to my parents whose patient love enabled me to complete this work.
Wen Zhang Nov. 2008 Luleå
Luleå University of Technology
TABLE OF CONTENT 1. BACKGROUND INFORMATION………………………………………………1 1.1 Fellingsdams..…………………………………………………………………..1 1.2 Fellingsdams in Sweden………………………………………………………..1 1.3 Aim and method of this investigation………………………………………….1
2. CHEMICAL PRECIPITATION IN FELLINGSDAMS………………………….3 2.1 Pre-pond and in-pond systems…………………………………………………3 2.2 Transporting process…………………………………………………………...4 2.3 Chemical precipitation…………………………………………………………6 2.3.1 Aluminum salts……………………………………………………………6 2.3.2 Iron salts………………………………………………………………....7 2.3.3 Slaked lime …………………………………………………………..….8 2.4 Turbidity………………………………………………………………………..9 2.5 Detention time………………………………………………………………...14 2.6 Investigated fellingsdams……………………………………………………..15 2.6.1 Lime fellingsdams………………………………………………………..15 2.6.2 Aluminum fellingsdams……………………………………….…………20 2.7 Suggestions……………………………………………………………………24
3. SLUDGE ACCUMULATION…………………………………………………….26 3.1 Sludge quantities……………………………………………………………...26 3.1.1 Sludge depth in fellingsdams…………………………………………….26 3.1.2 TS and organic content of the sludge…………………………………….32 3.2 Sludge removal and treatment………………………………………..……….38
4. REMOVAL OF ORGANIC MATTER, PHOSPHORUS, NITROGEN AND BACTERIA…………………………………………………………………….…….43 4.1 Organic matter………………………………………………………...………43 4.2 Phosphorus…………………………...……………………………………….46 4.3 Nitrogen……………………………………………………………………….47 4.4 Bacteria…………………………………………………….………………….49
5. FUTURE DEVELOPMENT……………………………………………………....50
CONCLUSIONS…………………………………………………………………....51 REFERENCE……………………………………...…………………………………52
APPENDIX Luleå University of Technology
1. Background information 1.1 Fellingsdams
A fellingsdam also called “a pond or a lagoon using chemical precipitation”, is a pond system to separate nutrient and organic matter by adding coagulant. The main process of this wastewater treatment method is chemical precipitation.
Compared with most other methods of treating wastewater, a pond system provides several advantages. It is a simple process which is easy to operate and inexpensive. Meanwhile the drawback of fellingsdam is that to achieve certain discharging water quality, a reasonably large area is necessary. So the method is not suitable to apply in cites of high population density. The treatment of sludge which is generated during the chemical precipitation should also be considered.
The difference between fellingsdam and common wastewater stabilisation ponds system or lagoons is the chemical dosage. Sunshine is an important driving factor for a pond system, so during winter time, when the pond is covered by snow and ice, it will not work. Since the operation of a fellingsdam mainly relies on a chemical reaction, it can work quite well during a winter period.
1.2 Fellingsdams in Sweden
The use of ponds or lagoons for wastewater treatment can be traced back to centuries ago. For instance, ponds have been used in China for more than 2000 years (Baozhen, 1987). A use of the fellingsdam method to treat the wastewater is rather common in northern Sweden, because the population in the north is small and the area is huge. In cold region, lagoons do not work well in winter; add chemical coagulant can help to precipitate organics, nitrogen and phosphorus. The population density in these areas is small and most of these regions are covered by forest which makes fellingsdam a better solution to treat wastewater compared with a compact wastewater treatment plant. Besides, it is also more economical.
A number of fellingsdams were built several decades ago in Sweden. Most of them are in good condition and still in operation.
1.3 Aim and method of this investigation
To investigate the operation conditions of the existing fellingsdams and to find out any latent problem are the aims of this task. Some suggestions and ideas for both existing fellingsdams and future constructions.
Fellingsdams from 5 municipalities were investigated namely Örnsköldsvik, Härjedalen, Östersund, Ljusdal and Bollnäs. In a total of 16 fellingsdams turbidity and
- 1 - Luleå University of Technology sludge samples were taken for laboratory analysis. 6 of them were lime ponds, and 10 of them were aluminium ponds. One iron pond located at Mellansel, was also investigated regarding the effluent quality. More of fellingsdams information was collected from yearly reports of each municipality.
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2. Chemical precipitation in fellingsdams
2.1 Pre-pond system and in-pond system
According to the location of dosage, fellingsdams can be divided into two different groups: pre-pond systems and in-pond systems. These two different fellingsdam systems are shown in figure 1.
Influent Influent
Dosage
Dosage
Effluent Effluent
a) Pre-pond system b) In-pond system
Figure1. Location of dosage at fellingsdams
Pre-pond system is to add the chemical close to the inlet of the first pond. There is sometimes no pre-sedimentation tank, all the precipitation will occur in the ponds.
In-pond system is to add the chemicals within the ponds. There can be one or more pre-settling ponds before dosing. Use of the pre-settling pond is to remove big particles from the wastewater and achieve a better treatment result.
There are advantages and drawbacks for both of these two different fellingsdams. For the pre-pond system it is easier to mix the chemicals into the wastewater without any installation of specific mixing facilities by using the kinetic energy of the water at a pumping station or in a sloping inlet pipe. It is also easier to include organic matter in the precipitation since it may be less dissolved at the inlet end of the pond. Furthermore, when lime is used as the coagulant, a high pH can be kept throughout
the pond system which prevents the formation of hydrogen sulfide (H2S). H2S create an unpleasant odour to the neighborhood. Another advantage is since all the sludge accumulates at one location; sludge removal will be comparably easy. (Hanaeus, 1991)
In-pond systems may require smaller amounts of coagulant, because most of the big particles will settle already in the sedimentation pond. Another utilization of the
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pre-settling pond is to adjust the flow. It can be used as a reservoir to provide a constant flow rate for the next treatment step. Concerning the sludge problem, in-pond system can divide biological sludge and chemical sludge at different locations which may be an advantage if the sludge should be recycled. (Hanaeus, 1991)
2.2 Transports
Wastewater is transported to the silo and mixed with coagulant, then discharged to the pond. Usually there is a mixer near the influent to stir the water. After precipitation for a few days, the treated water is discharged to a nearby receiving water body .
Figure2. Dosage buildings at fellingsdams: Ånge and Björnrike.
Figure 2 shows two normal dosage buildings for fellingsdams, located at Ånge and Björnrike respectively. After transportation through the silos, the coagulant will be mixed with clean water and finally meet wastewater in the ponds.
Figure 3 shows the lime dosing process to the fellingsdam at Bredbyn. Lime was dosed to the wastewater after passing a septic tank.
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(a) (b) Figur3. Lime dose at Bredbyn.
A mixing device is shown in figure 3a. The coagulant lime was mixed with clean water periodically in the funnel reactor, and then discharged through a pipe to the pond. The erosion area at the wall of the silos was caused by pounding with a hammer. Because part of the coagulant could clog on the inside wall, pounding can release the clogged chemical to make the dosing process work well. Figure 3b shows the pipe when discharging the lime solution to the wastewater pond.
Figure4. Coagulant transporting pipes to ponds at Hede.
In figure 4 is shown the aluminum transporting pipes in the pond system at Hede. Aluminum salt was first mixed with water then transported to a small well where it was mixed with wastewater and discharged to the ponds. It is wise of the operator to cut some rectangle holes on the pipes. That makes it easier to find out the clogging
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problem and clean the pipe in time.
Figure5. Mixing device in the first pond at Glössbo
Figure 5 shows a common mixer in fellingsdam, it is driven by electricity and stirs water periodically. There was no obvious sludge layer around the mixer; the entire first pond was turbid when the mixer worked. The use of a mixer is to prevent the fast settling sludge to clog the transporting pipe.
2.3 Chemical precipitation
Currently, aluminum salts, iron salts and slaked lime which are reasonably cheap and easy to react are widely used as coagulants in fellingsdams.
2.3.1 Aluminum salts
Addition of aluminum salts in ponds produces aluminum hydroxide (Al(OH)3), which is insoluble in water and precipitates as flocs. The aluminum hydroxide flocs have a high sorption capacity and therefore both phosphate and heavy metals will be adsorbed on the surface when the precipitates settle and form sludge. But the solubility of aluminum hydroxides will increase at increased pH values, which means that the adsorbed substances will be released at high pH values. So the most suitable pH for Al-precipitation in a pond is 6.0-6.5. This pH-range is favourable for biological life in the wastewater, so subsequent biodegradation is not impeded (Hanaeus, 1991).
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If the salt anion is sulphate, the combined effect of acidification and an increase in the sulfur content will produce more hydrogen sulfide during anaerobic pond conditions which are common in winter (Hanaeus, 1991).
Table1. Dosage and daily flow in Al-ponds Billsta Ånge Björnrike Hede Ytterhogdal Dosage 2.8 9.2 38.3 28.8 13.1-14.8 (gAl/m3) Flow (m3/day) 350 4326 184 602 / Bruksvallarna Norrfällsviken Tandsjöborg Los Falun Dosage 10.9 18 / 51.7 / (gAl/m3) Flow (m3/day) 250 37 96 850 /
Except for Norrfällsviken, Tandsjöborg and Falun, the coagulant used in these fellingsdams was AVR. It is ferric aluminum sulphate, its molecular formula is
Al1.5Fe0.5(SO4)3·18H2O. Aluminum sulphate has been widely used for drinking water purification for a long time. It will unquestionable to precipitate the phosphorus, but also the bacteria issue needs to be concerned. As Al is dosed by different chemicals with different compositions it is suitable to give the dose in g Al/m3. From table 1, we can see the dosage of aluminum varies a lot, a common dosage of Al in fellingsdam should be 12-25gAl/m3. Higher dosage will lead to a higher cost and higher sludge formation, but too low dosage can not reach the treatment goals.
PAX, poly aluminum chloride, was used at the fellingsdam in Norrfällsviken. The coagulant that has been used in Tandsjöborg is called Ecofloc. At the ponds in Falun, aluminum chloride was used: “Pluspac1800 (Ciba)”. Aluminum chloride is
very easy to react with hydroxide and precipitate phosphorus as Al(H2PO4)3. The operator only dosed coagulant in one pond in winter to treat the wastewater which was then discharged to a nearby water body. 4 other ponds were used during summer and their effluent irrigated energy forest.
2.3.2 Iron salts
Similar to the aluminum salts, iron salts also precipitate and form hydroxide flocs when in contact with water. However, optimum pH for precipitation of phosphorus with iron ranges from 5.0 to 5.5. One important fact which needs attention is that the ferric iron will be converted to ferrous iron when losing contact with oxygen, and may then release combined phosphorus. The long-term stability of the iron-phosphate-hydroxide sludge during periods of anaerobic conditions in the ponds is not well known (Hanaeus, 1991).
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Figure6. Fellingsdam at Mellansel
Aluminum was the coagulant before 2001 at the fellingsdam in Mellansel. The operator closed the dosage of aluminum and added iron salt in 2001. From 2001 till now, the coagulant was iron salt. The red color from iron can be seen from the surface, figure 6. Mellansel was a one pond system with a daily flow around 500m3/day; the dosage of iron salt was 430g/m3.
2.3.3 Lime
Use of slaked lime as coagulant can create an extreme chemical environment where pH ranges from 10.5 to 12.0. Most living matter can not survive in such alkaline water except some specialized microorganisms. Even though it is not favourable for biodegradation, most pathogenic bacteria can be killed by liming. Since lime has a strong reaction when in contact with water, a large quantity of sludge accumulates in the very beginning of the first in a pond system, and then sludge accumulation rapidly decreases. Concerning operational problems, the fast settling of heavy particles may block the transporting pipe.
Table2. Dosage and daily flow in lime-ponds Bredbyn Nyliden Långviksmon Funäsdalen Tänndalen Glössbo Dosage 650 170 773 1000 1012 1000 3 (gCa(OH)2/m ) Flow 712 200 75 406 332 37 (m3/day) pH 12.0 10.7 11.2 12.5 12.3 12
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The dosage of lime varied from 170g/m3 to 1012g/m3, which made pH vary from 10.7 to 12.5. The cleanness of Ca(OH)2 is at least 90%, a normal interval dosage is 3 500-1200g/m . When at moderately high pH values, the precipitate is CaCO3, and at high pH-values, >11, the precipitate is dominated by Ca10(PO4)6(OH)2 (Hanaeus, 1991).
2.4 Turbidity
Turbidity is considered as a good measure of the water quality as it refers to how clear the water is. The units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU).
There are several parameters influencing the water turbidity, such as - Phytoplankton - Sediments from erosion - Resuspended sediments from the bottom (frequently stir up) - Algae growth - Urban runoff
Precipitation and algae are the two main reasons for turbidity in fellingsdams, as shown in figure 7.
Figure7. Turbidity changes by depth in fellingsdams.
The black curve represents the turbidity changes due to precipitates at different depths of a fellingsdam. Turbidity slowly increases when close to the bottom. At suitable conditions, algae vegetate very fast and wide. They have big effect on turbidity, but they only grow close to the surface, so the turbidity curve will be modified as shown
- 9 - Luleå University of Technology by the dotted curve. The following part will explain in detail how the precipitant and algae influence the turbidity. a. Turbidity caused by precipitation
Figure8. Turbidity due to sediment
During sedimentation or precipitation, turbidity will be influenced a lot, as exemplified by figure 8 Turbidity is usually high at the influent where the coagulant reacts with wastewater and produces large amounts of precipitate in terms of small particles that makes the water turbid. As the water passes through the ponds, precipitates will settle down to form bottom sludge and the water will be cleaner and less turbid.
At the fellingsdams of Los, turbidity changes were detected from the influent to the effluent. The fellingsdam at Los is a pre-pond system. There are two ponds which were cleaned in 2003. Aluminum sulphate was used as a coagulant and the dosage was 51.7gAl/m3. Plan view and sampling points are shown in figure 9.
6
7 5
8
84m 4
3
2 Dosing Effluent 1 building
50m 52m Figure9. Sampling points in the fellingsdam at Los.
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Turbidity samples were taken following the water passage, from point 1 to point 8 and to the effluent. There were large amounts of sludge accumulated around the inlet pipe. Points 1, 2 and 3 were sampled close to the high accumulated sludge area. Two different depths of sampling were used: 15cm and 50cm. Results of the instrument readings are represented in table 3.
Table3. Turbidity values at different depths in fellingsdam at Los. Sampling points 1 2 3 4 5 6 7 8 Effluent Turbidity at 15cm depth 4.01 5.3 4.63 4.53 7.43 4.4 4.21 3.48 3.85 (NTU) Turbidity at 50cm depth 5.05 * * 4.82 5.2 4.83 4.53 3.54 3.75 (NTU) * Turbidity samples could not be taken at 50cm depth due to sludge accumulation. Free water depth was less than 50cm.
Turbidity curves of these two different depths are shown in figure 10. As turbidity at 50cm depth was not detected at point 2 and 3, they are not included.
Actual detention time (days) 012345 8 8
15cm depth 50cm depth 7 7
6 6
5 5 Turbidity (NTU) 4 4
3 3 0 20 40 60 80 100 120 140 160 180 200 220 Estimated distance (m)
Figure10. Turbidity curves in ponds at Los.
Turbidity at 15cm depth at point 5 was 7.43NTU which is surprisingly high. No obvious reason was found. Except for this point, the turbidity curve of 15cm is below the 50cm curve. If there is no appearance of algae in the fellingsdam, normally, turbidity will increase with the increasing depth.
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b. Turbidity caused by algae
Figure11. Turbidity due to algae
The appearance of algae is another important factor that affects turbidity, figure 11. During summertime algae are quite common in fellingsdams. Wastewater is rich in bacteria and organic nutrients which provides a favorable growth environment for algae. Plenty of sunshine is also necessary. The algae will increase the water turbidity, and also change its colour. Chlorophyll is the main reason of the colour change.
The fellingsdam at Ytterhogdal is a 6 pond system with 2 pre-sedimentation ponds and 4 chemical precipitation ponds. It was constructed in 1994; aluminum sulphate is the coagulant. Two pre-sedimentation ponds worked in parallel. Pond 1 was emptied to remove the sludge during the investigation in March; pond 2, 3, 4 were in use. The plan view and sampling points in the ponds are shown in figure 12.
32m 65m
Pond 1 1 Pond 2 2 3 9.5m Dosing building 6 5 Pond 3 4 7m
Pre-pond 1 18m 7 8 9 7.5m Pond 4 10 6m 7m Pre-pond 2 19m Effluent 100m
24m
Figure12. Sampling points in the ponds at Ytterhogdal.
Algae were found rich in the chemical precipitation ponds here. The colour due to algae could easily be seen by the eyes. At sampling point 9, the water was very green and the water sample at 15cm depth was much greener than the one at 50cm depth. Turbidity values are shown in table 4.
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Table4. Turbidity values at different depths in the fellingsdam at Ytterhogdal. Sampling point 1 2 3 4 5 6 7 8 9 10 Effluent Turbidity 11.4 14.1 * 9.1 8.8 8.7 7.0 6.8 9.7 13.3 10.3 15cm depth (NTU) Turbidity 13.3 12.5 * 9.0 8.7 7.7 7.1 6.6 8.3 12.4 10.3 50cm depth (NTU) * Sludge accumulated to the surface at sampling point 3, so turbidity samples could not be taken.
Actual detention tim e (days) 0 4 8 12 16 20 24 28
14 15cm depth 14 50cm depth
12 12
10 10
Turbidity (NTU) 8 8
6 6
0 100 200 300 400 500 Estim ated distance (m )
Figure13. Turbidity curves for the fellingsdam at Ytterhogdal.
In this case, turbidity value decreased by the increasing depth. Except for the first sampling point, turbidity at 50cm depth was higher than the 15cm depth one. One important reason for this phenomenon was the appearance of algae. Algae grew close to the water surface; therefore the turbidity at 15cm was high. However, the growth of algae requires sunlight, for this reason the number of algae was lower at 50cm. Algae didn’t grow at point 1 where close to the influent pipe, due to the hydrodynamic force. Whereas wildly spread in the rest of the fellingsdam.
Wastewater provides a warm temperature and a rich nutrient environment for algae. Under such conditions, algae grow very easily and are widely spread in the ponds in summer time. It is also possible that more than one specie of algae exist at one pond system at a time. Since the main process in fellingsdam is chemical precipitation, the occurrence of algae is of secondary interest, but it will carry nutrients and organic matter to the effluent. So from this point of view algae should be removed.
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2.5 Detention time
Detention time measures how long time a water molecule resides within a pond before being discharged. After addition of coagulant, the precipitate needs a certain time to settle before the water leaks to a receiving water body. This settling time put demands on the detention time.
Theoretical detention time is the time it takes for the water molecules to pass the pond in order; e.g. no mixing takes place. The actual value however is always lower and it can be adjusted by a coefficient, here denoted α. α is a hydraulic efficiency factor and ranges from 0 to 1. V TT ⋅=⋅= αα Equation (1) actual ltheoretica Q Where V is the volume of the pond and Q is the flow rate. The α value can be affected by several factors, for instance, a long narrow pond will increase the α value, and on the contrary, a square or round pond will bring the value down. A system consisting of several ponds can also work more efficiently than a one pond system with a higher α value. In a perfect plug flow state, α is 1 which means actual detention time is equal to theoretical detention time.
Figure14. Effective utilization areas in different pond geometries.
In figure 14, there are 3 different pond figures. The white parts are the effective utilization areas. Water passes the shortest way through the pond, so the shadowed part can not be utilized. For a square pond like pond (a), the effective utilization is only 10%. But if separate the pond to two ponds as (b), the efficiency will raise to 20%. For a long rectangular pond, figure (c), the effective utilization of the fellingsdam area will be about 50%. The corresponding α values are 0.1, 0.2 and 0.5,
then the actual detention time of the three pond systems are 0.1Ttheoretical, 0.2Ttheoretical and 0.5Ttheoretical respectively.
The coefficients are set out of tracer experiments, some of which are presented by Hanaeus, 1991. A high energy input to the water also will reduce the participating
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area of a pond.
a)
b)
Figure15. Efficient utilization of a fellingsdam.
Figure 15a shows an ideal pond system for a fellingsdam. The effective utilization may reach 95%, and the actual detention time approaches the theoretical detention time. Another method to increase the utilization rate is to insert curtains to divide the pond. Then the water is forced to go a longer distance which increases the detention time. Several fellingsdams use curtains at present, such as Ånge, Funäsdalen and Ytterhogdal. One operational problem of the curtains is once they break down, water goes directly across them. If a pond is covered by ice and snow, the pressure may press the curtain down, and water passes above the curtain. The effluent quality of wastewater from this period may be lower than usual.
2.6 Investigated fellingsdams
2.6.1 Lime ponds
Glössbo
Glössbo is a two pond system with slaked lime as coagulant. There were no pre-sedimentation ponds, but there was a separation screen in the dose building to remove big particles. It was constructed in 1985. The flow is only 37m3/day and the 3 chemical dosage reaches 1000gCa(OH)2/m . The high lime dose created a high pH value, above 12.0.
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a)Pond 1 with mixers below each platform. b) Pond 2 Figure16. Fellingsdam in Glössbo
There are two mixers in the first pond in Glössbo under the metallic platforms as shown in figure 16a. Because of the high lime dose and no pre-sedimentation, the chemical precipitation is very fast and sludge accumulated to a quite high level in the first pond. To distribute the lime solution in the wastewater, mixing is considered useful. However due to a high turbulence and energy consumption, the operator had stopped one of the mixers. The one at the influent was still in operation (to get an actual turbidity result, during sampling, both mixers were turned off). Even though the first pond was cleaned at 2006, sludge accumulated to the water surface at the edges of the pond.
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Dose building
7 8
5 6 5 9
30m 2 3 4
1 10 50m Influent
20.5m
24m
11
Effluent
10m 22m
Figure17. Sampling points in the fellingsdam at Glössbo.
Figure 17 is the plan view with sampling points in the fellingsdam at Glössbo. The volume of the ponds is 2250m3, and its’ α value is estimated to be 0.35. The calculated actual detention time then is 20.7 days.
Turbidity and pH values are represented in table 5. The turbidity curve in Glössbo is shown in figure 18.
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Table5. Turbidity and pH value at the sampling points in ponds at Glössbo. Sampling points 1 2 3 4 5 6 Estimated distance (m) 5 10 14 18 26 23 Turbidity at 15cm (NTU) 20 14.1 13.2 12.3 12.5 12.3 Turbidity at 50cm (NTU) * * * * * * pH 12.3 12.3 12.3 12.3 12.3 12.3 Sampling points 7 8 9 10 11 Effluent Estimated distance (m) 30 37 51 64 82 92 Turbidity at 15cm (NTU) 11.7 4.0 3.64 3.64 4.24 4.24 Turbidity at 50cm (NTU) * * 3.96 3.80 4.50 3.54 pH 12.3 12.0 12.0 12.0 12.0 12.0 *Turbidity at 50cm in the first pond was not detected, because the sludge accumulated to a very high level that closed to the water surface.
Actual detention tim e (days) 048121620
20 20 15cm depth
16 16
12 12
8 Turbidity (NTU) 8 4 4 0 0 20406080100 Estim ated distance (m )
Figure18. Turbidity curve in ponds at Glössbo.
Turbidity values in the first pond are quite similar at different locations, all above 10 NTU due to the mixer. As soon as the water entered the second pond, from point 8, turbidity became reduced below 5 NTU. The water turbidity became quite stable after about 10 days and 40 meters.
Nyliden
The following figure 19 presents another lime pond, located at Nyliden. The fellingsdam at Nyliden was also a one pond system with a daily flow about 200m3. This is an occasional big flow due to a leakage-in at the sampling time. According to
- 18 - Luleå University of Technology the operator the average flow was 25m3/day. Slaked lime was the coagulant and the 3 dosage was 170gCa(OH)2/m . From the pond geometry and the sludge accumulated, we can assume its’ α value to be 0.35. The pond volume is about 2380m3 and as the daily flow was 200m3/day. Then the theoretical detention time is 12 days. The actual detention time was calculated to be 4.2 days.
Effluent
6 4 5
31m
3 7
2
1 14m Influent
38m 11.5m
Figure19. Sampling points of the fellingsdam at Nyliden.
Turbidity at different depth and pH values are listed in table 6 and turbidity curves are plotted in figure 20.
Table6. Turbidity and pH value at the sampling points of Nyliden. Sampling points 1 2 3 4 5 6 7 Effluent Estimated distance (m) 0 7 31 34 45 50 55 65 Turbidity/15cm (NTU) 28.7 36.9 18.4 14.4 12.2 6.9 5.6 6.0 Turbidity/50cm (NTU) 26.7 * 15.0 14.9 11.0 7.2 8.2 6.0 pH 10.6 10.6 10.6 10.4 10.6 10.7 10.7 10.7 * Turbidity can not be detected due to the sludge accumulation at point 2.
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Actual detention time (days) 012345 40 40
35 15cm depth 35 50cm depth 30 30
25 25 20 20 15
Turbidity (NTU) Turbidity 15 10 10 5 5 0 -10 0 10 20 30 40 50 60 70 Estimated distance (m)
Figure20. Turbidity curve in pond at Nyliden.
Turbidity near the influent was about 30 NTU, and ended up with 6 NTU at the effluent. Compared with the fellingsdam at Glössbo, the lime dosage was much smaller in Nyliden, probably due to the occasional high flow. The pH value, which reached 12.3 in Glössbo, thus became 10.6 in Nyliden. Turbidity became stable after 3.6 days. A similar phenomenon appears in the turbidity curves of these two fellingsdams; the turbidity decreased quickly below 10NTU at a short distance within 50 meters.
2.6.2 Aluminum ponds
Norrfällsviken
Norrfällsviken is a three pond system with Aluminum sulphate as coagulant. The flow during May, 2008 was around 37m3/day and the dosage was about 180ml/m3. During summer time, Norrfällsviken is a tourist area; the daily flow may be much higher than 37m3.
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110m
12m Pond 3 Effluent
Well 2
12m 5 6 Pond 2
Well 1
12m 4 3 2 Pond 1 1
Dosage (500 meters away)
Figure21. Sampling points at the ponds of Norrfällsviken.
The volume of the pond is about 4690 m3 and the α value can be estimated to 0.65 with this geometry, then the actual detention time is 82.4 days. 6 points were sampled in the first two ponds of the fellingsdam. There was almost no flow in the third pond and at the effluent of well 2 was seriously clogged by water born plants. So the third pond is not possible to analyse.
Table7. Turbidity and pH value at the sampling points in Norrfällsviken. Sampling points 1 2 3 4 5 6 Estimated distance (m) 7 37 67 100 120 165 Turbidity (NTU) * 11.9 9.28 9.46 3.24 2.26 pH * 7.9 8.0 8.0 7.25 7.25 *No turbidity samples were taken from point 1, because the sludge accumulated to the water surface.
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Actual detention time (days) 0 1020304050607080 10 12 15cm depth 50cm depth 8 10
8 6
6 4 Turbidity (NTU) Turbidity 4 2
2 0 20 40 60 80 100 120 140 160 180 Esitimated distance (m)
Figure22. Turbidity curves in ponds at Norrfällsviken.
From table 7 and figure 22 can be seen, turbidity became stable after 120 meters and about 55 days.
Hede
Hede is an in-pond aluminum fellingsdam. It is a 12 ponds system in which 7 of the ponds work after dosage; the remaining 6 ponds work in two groups in parallel as pre-sedimentation ponds. Aluminum sulphate was used as coagulant and the dosage was about 21gAl/m3. The flow during the time of investigation was 602m3/day. The pond geometry is shown in figure 23. There is a gravel filter precedes the effluent well.
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Influent Pre-pond 3 5 7 system 1 1
2 3 4 5 6 7 Dosing 1 building 90m
Pre-pond system 2
2 4 6 Effluent
8m 8m 8m 8m 8m 8m 8m
Figure23. Fellingsdam at Hede
8 turbidity samples, include the effluent, were taken in the fellingsdams at Hede. The fellingsdam volume is about 7050 m3. For a fellingsdam like Hede, its’ α can be estimated to 0.9 or even higher, the ponds were highly utilized. The actual detention time was 10.6 days. The measured values of each sampling points are listed in table 8. Figure 24 presents the turbidity curve.
Table8. Turbidity and pH value at the sampling points in Hede. Sampling points 1 2 3 4 5 6 7 Effluent Estimated distance (m) 15 90 180 270 360 450 540 630 Turbidity (NTU) 21.1 15.5 7.9 5.5 5.7 3.3 3.5 2.5 pH 5.5 5.4 5.6 5.6 5.6 5.7 5.7 5.6
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Actual detention time (days) 024681012 25 25
15cm depth 20 20
15 15
10 10 Turbidity (NTU) Turbidity
5 5
0 0 0 100 200 300 400 500 600 700 Estimated distance (m)
Figure24. Turbidity curve in ponds at Hede.
After 5 days and 260m, the turbidity became low, about 5 NTU. After about 8 days and 450 meters, the turbidity was still lower, 3.5 NTU.
From figures 18-24 it can be seen that, when the coagulant is slaked lime, the water turbidity curves become stable after a short distance while aluminum sulphate takes longer distance. The turbidity in Glössbo was reduced from 20 NTU to 4 NTU in 40 meters. Water turbidity in Nyliden was reduced from 36.9 NTU to 7 NTU in a distance of 50 meters. But the aluminum ponds in Norrfällsviken and Hede needed 120 meters and 450 meters respectively. It doesn’t mean aluminum fellingsdam requires longer distance to reach a constant turbidity value; the turbidity is also influenced by other objective reasons, such as pond geometry.
From the turbidity curve, an appropriate detention time can be suggested. The rest of the pond area represents an excess capacity with respect to the turbidity. Ponds in Nyliden and Norrfällsviken were about the right size to solve the current flow, though Glössbo can decrease its second pond size and 6 precipitation ponds should be enough for Hede pond system.
2.7 Suggestions
From the actual detention time point of view, it is easy to define the pond size, related to the turbidity curves above. A few suggestions are given.
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a) Sludge cleaning From equation 1, it follows that the larger acceptable water volume of a pond, the longer detention time it gives. Sludge accumulation in a pond will shorten the detention time and became a problem for the operation. Even though sludge accumulation is a slow process, to get a longer detention time and good treatment of the wastewater, removal of the sludge in pond periodically is necessary and suggested.
b) High dosage A high dosage of lime leads to a high pH value and also to a large quantity of sludge. From the analysis of the turbidity curves, higher dosage achieved a better result in a shorter distance. If the pond volume is set, more water can be treated with a higher dosage. Drawback of a high dosage is a higher sludge production, especially around the inlet pipe. Effective maintenance and cleaning should be carried out.
c) Pond geometry Pond geometry is very important for the treatment results. For long narrow ponds, the α value will be close to 1, then the utilization of the pond will be high. For a large square pond, plastic curtains or soil walls can be used to divide the pond tinto several channels or small ponds.
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3. Sludge accumulation
3.1 Sludge quantities Fellingsdams will produce large quantities of sludge due to the chemical precipitation. The formation and accumulation of sludge is influenced by the different coagulant and pond system.
3.1.1 Sludge depth All the sludge samples are collected from different municipalities in Sweden. In this project, 17 fellingsdams were investigated and 6 of them were lime ponds. a. Lime ponds There is an obvious fact that can distinguish a lime pond from the others: there is usually a large accumulation of sludge around the influent pipe.
Nyliden
Fellingsdam at Nyliden is a one pond system; the following figure 3.1 is a photograph from the influent. There was a mixer at the influent stirring wastewater during dosing, preventing the fast precipitating lime sediments clogging the pipe. At some distance to the mixer, it was easy to see that the sludge accumulated up to the water surface.
Figure25. Fellingsdam at Nyliden
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Pond geometry with sampling points is presented before, see figure 19. Sludge depths at different location are in table 9. The sludge accumulation curve in Nyliden is shown in figure 26.
Table9. Sludge thickness in the fellingsdam at Nyliden. Sampling point 1 2 3 4 5 6 7 Estimated distance (m) 0 7 31 34 45 50 55 Sludge thickness (m) 0.38 1.07 0.11 0.17 0.06 0.29 0.15
Sludge accumulation in Nyliden
1,2
) 1 0,8 0,6 0,4
Sludge depth (m depth Sludge 0,2 0 0 102030405060 Estimated distance (m)
Figure26. Sludge accumulations at Nyliden
As shown in figure 26, sludge accumulation curve of the fellingsdam at Nyliden, a great portion of sludge accumulated in 20 meters distance. At sampling point 2, the sludge accumulated to more than 100cm depth, then decreased rapidly to 20cm. As can be seen from figure 26, lime sludge didn’t accumulate largely around the mixer, point 1. The fellingsdam has never been cleaned since constructed; the sludge has accumulated for almost 20 years. Still, most of the sludge is located near the inlet area. This indicates that lime precipitation is a fast process. b. Aluminum ponds
Compared with slaked lime, the chemical reaction is slower when the coagulant is aluminum salt. So the precipitated sludge forms a modest slope from the dosage point.
Bruksvallarna
At the fellingsdam at Bruksvallarna, there was a three ponds system and one of the ponds was a pre-sedimentation pond. The coagulant was AVR (ferric aluminum sulphate). The dose was about 8gAl/m3, and the daily flow was 250m3/day when investigated. Figure 27 shows a plan view and the sampling points in the ponds.
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120m
Pond 2 20m 4 Pre-pond 1 3 40m 65m 66m 2 Influent 1 Dosing 43m building 58m 5 6
Pond 3 Effluent
Figure27. Sampling points at the ponds of Bruksvallarna.
The sludge depth at the point 1 was quite high, and was then slowly reduced towards to the effluent. The origin of the Bruksvallarna ponds is a wetland, so vegetation was found to be quite common here. The sludge samples at point 3 and 4 are very thin and of low density. At sampling point 5, the sludge sample taken from the bottom was not only sludge; it was a mixture of sludge, plants and clay. There was almost no sludge at point 6; when tested with a metallic stick, the bottom felt like consisting of aquatic roots or weeds.
Table10. Sludge thickness in the fellingsdam at Bruksvallarna. Sampling point Influent 1 2 3 4 5 6 Estimated distance (m) 0 25 45 62 77 94 105 Sludge thickness (m) 1.05 0.97 0.62 0.51 0.39 0.42 0.29
Sludge accumulation in Bruksvallarna
1,2
) 1 0,8 0,6 0,4
Sludge depth (m depth Sludge 0,2 0 0 20 40 60 80 100 120 Estimated distance (m)
Figure28. Sludge accumulation curve in pond 2 of the fellingsdam at Bruksvallarna
The pre-sedimentation pond was not investigated this time; the sludge accumulation
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curve concerned the chemical sludge in pond 2 and pond 3. The biological sludge in the pre-pond was not considered. The gradient of the sludge accumulation curve is obviously lower than at the lime ponds in Nyliden which indicates that the precipitation of aluminum is slower.
c. Pre-pond system
Långviksmon
In the fellingsdam at Långviksmon, there was a 4 ponds system for which the coagulant was slaked lime. There is no pre-sedimentation pond, but a separate tank before the dosage to remove the floating particles. Coagulant was added without 3 3 pre-sedimentation. The daily flow was 75m and the lime dose was 773 gCa(OH)2/m at the investigation. Sludge had never been removed from this pond system, so the accumulated sludge in the first two ponds reached a high level, which provided a good growing environment for the vegetation as can be seen in the figure 29a. It was in early April when investigated the fellingsdams, except the first pond, the other three ponds were still covered by snow and ice.
a) The 1st pond b) The 4th pond Figure29. Fellingsdam at Långviksmon
A plan view of the ponds and sampling points are shown in figure 30.
3.5m
1 28m 2 3 4
Influent Effluent 3.5m 24m 5m 26m 6m 15m 10m 14m
Figure30. Sampling points in the fellingsdam at Långviksmon.
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The sludge accumulation curve is shown in figure 31.
Table11. Sludge thickness in the fellingsdam at Långviksmon. Sampling point 1 2 3 4 Estimated distance (m) 2 45 80 125 Sludge thickness (m) 1.6 0.7 0.38 0.3
Sludge accumulation in Långviksmon
2 ) 1,5
1
0,5 Sludge depth (m depth Sludge
0 0 20406080100120140 Estimated distance (m)
Figure31. Sludge accumulation curve in the fellingsdam at Långviksmon
Half of the total sludge had accumulated in the first pond which also can be seen from figure 31; the first pond was almost filled by sludge. Sludge was floating at the surface and vegetation covered part of the pond. The currently influent wastewater goes through the vegetation to the channel and then flows to the second pond. As shown in figure31, the sludge level in the third and fourth ponds was kept below 40cm. Most sludge precipitated in the beginning.
d. In-pond system
Tänndalen
Refer to figure 32, the fellingsdam at Tänndalen was a two pond system. The first pond was a pre-sedimentation pond which was also a sludge storage pond. The origin of this area was wetland. There was an island and a curtain that divided the pond into two smaller ponds. This separation forced water to go inside the island, thus increasing the detention time.
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From the sludge storage pond Dosing a b Effluent building c 1 d Influent 2 5
3 4 150m Wetland Island
50m
80m 20m 90m
Figure32. Sampling points in the fellingsdam at Tänndalen.
It was April, 17th when investigating the pond at Tänndalen. The pond was covered by snow and ice. The sampling points 1-5 were first used to find out the water flow direction. But when tested, the pH values at point 2 and 4 were lower than 10 and hence the water most likely did not follow this way.
Ice was found to be not that solid along the line a, b, c and d. The curtain didn’t work by reason of ice cover, the ice pressed the curtain down at point b and the wastewater went through above the curtain directly to the effluent. The tested pH values along the c, d line were around 12 which indicated a reasonable flow direction. However sludge accumulated to a high level also at point 2. Thus the partition worked during summer when the water moved around the island to the effluent. Previous measurements have defined that summer route (Cripps and Hanaeus, 1991).
Table 12 represents the pH values and sludge depths in fellingsdams at Tänndalen and figure 33 shows the sludge accumulation curve.
Table12. pH value at sampling points in the fellingsdam at Tänndalen. Sampling points 1 2 3 4 5 a b c d Effluent pH value * 10.0 11.6 9.8 11.0 * * 11.9 12.0 12.1 Estimated 35 # # # # 75 128 158 178 190 distance (m) Sludge depth(m) 1.17 1.30 0.25 0.14 0.24 0.52 0.48 0.19 0.05 * Water samples were impossible to get at point 1, a and b. Sludge accumulated to the free water surface. # Not transport route.
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Sludge accumulation in Tänndalen
1,4
) 1,2 1 0,8 0,6 0,4 Sludge depth (m depth Sludge 0,2 0 0 50 100 150 200 Estimated distance (m)
Figure33. Sludge accumulation curve in the fellingsdam at Tänndalen.
Figure 33 shows the sludge accumulation curve along line 1-a-b-c-d, the sludge accumulated mostly in the beginning, and then was suddenly reduced, common for a lime pond. The sludge depth is not very much related to pre or in-pond, the gradient of the turbidity is more related to the use of coagulant. Also, depends on the removal frequency and the water inflow energy.
3.1.2 Total solid and organic content of the sludge
To get a better understanding of the sludge dynamics, sludge samples were taken from each fellingsdam for analysis of the total solid content and organic content. Total-solid represents the dry content of sludge samples and organic content is the percentage organic matters out of total solids. All sludge samples were put into an oven to remove the water content at 110 ºC for 24 hours. Then, after cooling and weighting, they were put them into a 550 ºC oven for two hours to remove the organics.
All the sludge samples were planned to be taken from the pond bottoms. There were sometimes practical problems; somewhere the depth was too high for the equipment to reach the bottom. At some occasions the samples were mixed with bottom clay minerals. Usually, the total solids content is high near the bottom and low near the surface. In some of the ponds, such as Nyliden and Långviksmon, the sludge had never been removed, the bottom sludge was more than 10 years old, and had a very high TS. The sludge of Ånge fellingsdam was comparable low in TS since the ponds were cleaned every year.
a. Lime ponds
Nyliden
The pond geometry and the sampling points are represented in figure 19. Results of
- 32 - Luleå University of Technology total solids and organic content from laboratory analyses are shown in table 13 and figure 34.
Table13. TS and organic content in ponds at Nyliden Sampling points 1 2 3 4 5 6 7 Estimated distance (m) 0 7 31 34 45 50 55 TS (%) 38.58 75.44 23.81 18.19 18.37 46.53 32.84 Organic content (% of TS) 4.53 1.09 8.00 6.55 6.24 1.80 7.92
TS and organic content in ponds at Nyliden
TS Organic content
) 80% 60% 40% TS; 20%
Organic content(% Organic 0% 0 102030405060 Estimated distance (m)
Figure34. TS and organic content of the sludge in ponds at Nyliden
The organic content of the sludge in the fellingsdam at Nyliden was lower than 10%. A main reason for such a low value is the slaked lime coagulant which contributes with a high amount of inorganic matter.
Another example of a lime fellingsdam is the one at Långviksmon. In table 14 and figure 35, the TS and organic content results are shown. Pond geometry and sampling points were presented in figure 30.
Table14. TS and organic content in ponds at Långviksmon Sampling points 1 a 2 3 4 Estimated distance (m) 2 25 50 100 145 TS (%) 41.72 20.56 62.82 51.51 51.72 Organic content (% of TS) 8.41 6.70 2.24 3.00 3.88 * Point a was at the channel from the first pond to the second pond.
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TS and organic content in ponds at Långviksmon
TS Organic content ) 80% 60%
TS; 40% 20%
Organic content (% content Organic 0% 0 20406080100120140160 Estimated distance (m)
Figure35. TS and organic content of the sludge in ponds at Långviksmon
The organic content of the sludge TS in the fellingsdam at Långviksmon was lower than 10%. Even the total solids content was much different compared with ponds at Nyliden.
Funäsdalen
Previous two fellingsdams were pre-pond systems. Here the in-pond system at Funäsdalen will be described. Funäsdalen pond system is a 4-pond system and contains one pre-sedimentation pond and 3 precipitation ponds. Pond 4 was to a large extent separated by plastic curtains to form the wastewater flow direction. Daily flow 3 3 was about 406m /day and the dosage was 1000 gCa(OH)2/m . A plan of the ponds and sampling points is shown in figure 36.
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Effluent 100m
6
7 5 30m
4
3
Pond 4 1 2 Pond 2 Pond 3
Dosing building From the pre-sedimentation pond
Figure36. Sampling points in the fellingsdam at Funäsdalen
Results of the laboratory experiments are presented in table 15.
Table15. TS and organic content in ponds at Funäsdalen Sampling points a 1 2 3 4 5 6 7 Estimated distance(m) * 5 10 110 310 510 710 610 TS (%) 19.76 22.14 14.01 28.57 25.70 37.46 33.97 34.19 Organic content 40.01 9.63 8.37 8.93 7.43 5.91 4.76 5.47 (% of TS) * a was taken from the side of pre-sedimentation pond.
The organic content of the sludge TS was above 40% in the pre-sedimentation pond. The sludge after dosage had a value less than 10% due to the added lime. b. Aluminum ponds
At the use of aluminum as coagulant, the suitable pH value for precipitation is about 6.0 to 6.5. The way to remove organic matter is sediment the organic particles or, possibly, biodegradation.
The fellingsdam at Ånge was a six-pond system without pre-sedimentation ponds. The daily flow during investigation was 4326m3/day and the AVR dosage was 9.2gAl/m3. It was constructed in 1991 and slaked lime was used in the beginning. In late 90th, the manager changed to aluminum as coagulant. As shown in figure 37, ponds 1, 2, 5 constituted one pond-system, while ponds 3, 4, 6 formed another
- 35 - Luleå University of Technology pond-system. They worked in turns and each of them operated one year. Ponds 1 and 2 were cleaned when ponds 3, 4 and 6 were on operation. The other way round, pond 3 and 4 were cleaned when ponds 1, 2 and 5 were on operation. The removed sludge was put in a sludge dewatering pond for periods and after dewatering by freezing and thawing, transported for further treatment or usage.
93m Dosing 1 2 3 4 pond 3 building pond 1 22m
Influent pond 4 pond 2 22m
Effluent
pond 5
pond 6 sludge 5 6 7 6 5 50m dewatering pond
97m
Figure37. Sampling points in the fellingsdam at Ånge.
Sludge samples were taken from pond 1 and 5 since they were on operation when investigated. Pond 2 was also on operation when investigated, but since pond 1 and 2 worked in parallel, the sludge quality could be quite similar, and no samples were taken from pond 2. The analyses results from the laboratory are presented in table 16 and figure 38.
Table16. TS and organic content in ponds at Ånge Sampling points 1 2 3 4 5 6 7 Estimated distance (m) 13 38 58 75 12 0 17 0 22 0 TS (%) 2.94 2.46 14.3 218.1 0 42.92 41.81 24.39 Organic content (% of TS) 64.31 55.66 49.00 46.31 5.33 3.19 2.79
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TS and organic content in ponds at Ånge
TS Organic content
70% 60% 50% 40%
TS; 30% 20% 10%
Organic content(%)Organic 0% 0 50 100 150 200 250 Estimated distance (m)
Figure38. TS and organic content of the sludge in ponds at Ånge
The organic content was higher than 60% in the beginning of the first pond, and then decreased to less than 3% with distance. Though the average measured pH value at Ånge was about 7.1 which was a little higher than the suitable pH value for precipitation, biological life can live in this environment and makes biodegradation by bacteria and algae possible. It is however very dependent of radiation into the water.
Hede
Another aluminum pond, an in-pond system, will be analyzed to compare the differences in organic content. Sludge samples were taken from the fellingsdam in Hede. Samples were taken from the precipitation ponds 1 and 2. Pond geometry with sampling points was presented in figure 23. Ponds 1 and 2 were cleaned every two years; the other 5 ponds had never been cleaned. During the cleaning period, the first two ponds were cut off; wastewater was transported to pond 3 and went through the rest of the ponds to the effluent. So when investigated, most sludge accumulated at ponds 1, 2 and 3. There was almost no sludge in ponds 4 to 7, only a small quantity of sludge accumulated around the inlet pipe in pond 4. Sludge samples were for that reason only taken from ponds 1 and 2.
Table17. TS and organic content in ponds at Hede Sampling points 1 2 TS (%) 15.67 15.62 Organic content (% of TS) 46.34 42.80
As can be seen from table 17, organic content shortly after dosage was 46.34% which is much less than the value at Ånge. Because the pre-sedimentation pond at Hede has already removed part of the organic matter, the subsequent precipitation will precipitate less organics.
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Bruksvallarna
According to specific conditions of each pond, there are exceptions concerning the organic content. Sampling gave quite different results in fellingsdam at Bruksvallarna. See table 18 and figure 39. Pond geometry and sampling points are shown in figure 27.
Table18. TS and organic content in ponds at Bruksvallarna Sampling points 1 2 3 4 Estimated distance (m) 25 45 62 77 TS (%) 63.67 3.05 3.73 4.62 Organic matter (% of TS) 0.68 44.91 37.96 22.40
TS and organic content in ponds at Bruksvallarna
TS Organic content ) 80% 60% 40% 20% 0% TS;Organic content (% 0 102030405060708090 Estimated distance (m)
Figure39. TS and organic content curves in the ponds at Bruksvallarna.
The fellingsdam at Bruksvallarna was also an in-pond system. Except the first sampling point, the other values were reasonable. Possible explanation for the low organic content and high TS at the first sampling point is that the sludge sample was mixed with clay. The equipment got too deep down through the sludge and into the bottom clay. Clay contains almost no organic matter which brings the value down. The values at point 3 and 4 were most likely due to the plants residue in sludge. Actually, there was very little sludge accumulated at these two points, samples were mixtures of sludge and roots of water plants. The reason they kept a high organic content is the water born vegetation residue in sludge samples.
3.2 Sludge removal and treatment
No outstanding way to remove the sludge from pond system has been demonstrated; pumping and excavation are the most common methods, but there are also risks and disadvantages. After having removed wastewater from the ponds, the low density
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sludge can be pumped out by a high power pump. It is easy to implement, but can not be applied at every case. If the sludge is very dense, excavator can be used, but sludge can only be removed at the area the equipment can reach.
During the investigation trip, five fellingsdams at Ö-vik municipality were visited, that had never been cleaned since constructed. Sludge accumulated to the surface at some ponds. Sludge management in Härjedalen municipality was more frequent. Once sludge has accumulated to a high level, it becomes a problem for the regular operation. Sludge takes lots of space in a fellingsdam and in addition the volume of the pond for precipitation becomes reduced and the actual detention time shortened. In Långviksmon the sludge fully occupied accumulated the first pond and the water passed above the sludge to the second pond; there was almost no space for precipitation in the first pond. The utilization ratio of the fellingsdams was about 40%. Table 19 shows the construction year and cleaning frequency for several of the pond system.
Table19. Year of construction and last cleaning time Al-ponds Billsta Ånge Björnrike Hede Bruksvallarna Constructed 1986 1991 1976 1999 1979 year Last cleaning Never 2007 never 2007 Never time /2007 * Norrfällsviken Ytterhogdal Tandsjöborg Los Falun Constructed 1985 1994 / / 2001 year Last cleaning 2000 2008 Never 2003 Never time
Lime-ponds Bredbyn Nyliden Långviksmon Funäsdalen Tänndalen Glössbo Constructed / 1989 1975 1986 1985 1985 year Last Never Never Never 2008 Never 2006 cleaning /2007 * time *Björnrike 1st and 3rd ponds have never been cleaned, 2nd was cleaned in 2007. Glössbo 1st pond was cleaned in 2006, 2nd was cleaned in 2007
The view of the cleaned ponds was nicer than for a pond which has never been cleaned. Birds perched in some ponds, and interesting was that beaver was found at the ponds of Bruksvallarna. Some fellingsdams are constructed at tourist sites, and then the ambient environment becomes an important yardstick to measure a good performance of a fellingsdam. The treatment ability is important to a fellingsdam, but at present, the aesthetic impression becomes important too. For both operational and environmental reasons, sludge should be cleaned periodically.
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The removed sludge can be discharged or deposited for natural dewatering. Dewatering is to remove the water content from sludge. The volume of liquid sludge reduces a lot after dewatering. Naturally freezing, thawing and drying is useful but demands a long period. Machine processes, such as pressing and centrifugation, are faster but costly. The mechanical treatment is mostly used in compact wastewater treatment plants; natural freezing and drying is widely used at fellingsdams. Sludge was often piled up at a side of the ponds to dry. Figure 40 shows pictures of the sludge heaps in Hede and Ytterhogdal respectively. Vegetation was found on both the sludge heaps.
a) Sludge heaps in Hede b) Sludge heaps in Ytterhogdal Figure40. Sludge heaps
Differently, a sludge dewatering pond was well used in the fellingsdam at Ånge. The operator cleaned a dewatering pond every year, and put the sludge for drying in another sludge pond, after which the dewatered sludge was transported for further treatment or utilization.
Hede
As shown in figure 23 at the fellingsdam of Hede, three ponds constitute a pre-sedimentation system and work in parallel with three other ponds. One of these pre-sedimentation ponds system functioned when the other three were emptied and cleaned. Water then flowed to the precipitation ponds after dosing. The first two ponds have been emptied twice since constructed 1999; the other five have never been cleaned. All the sludge was disposed at the side of the pond and built up sludge heaps
- 40 - Luleå University of Technology as shown in figure 3.16a. Besides the sludge from the Hede ponds themselves, about 1000m3/year external sludge from the other wastewater plants in Härjedalen municipality was transported here and became added to the sludge heaps.
A plan-view of the sludge heaps is presented in figure 41.
Figure41. Plan-view of sludge heaps at the fellingsdam of Hede.
The average height of the sludge heap is about 2.4m; the calculated sludge amount is 556m3. The small sludge heap is 5% of the big heap, 28m3. The total amount of sludge is 584m3. The tested mean value of sludge TS content in pond was 15%. Assuming a TS content in the sludge heaps of 60%, then the original sludge volume that build-up the heaps was 2336m3. 25% of the sludge is from the primary settling pond and 25% is the external sludge from the other nearby pond systems. Only 50% of the sludge is chemical sludge from Hede fellingsdam and the volume of the sludge is 1168 m3.
Another sludge heap was located at Ytterhogdal. It was a 6 ponds system with slaked lime dosing chemical as shown in figure 12. Pond 1 was empty to remove the accumulated sludge during March 2008 and pond 2 was in use. These two ponds were initially combined, and had been cleaned twice before separation. 25cm sludge layer was removed each time. One of the pre-precipitation ponds had been cleaned once; another had been cleaned twice since 1994. All the sludge was accumulated at the nearby sites. There were three sludge-heaps in this area. Figure 40b is a photograph from one of the sludge heaps. Figure 42 is a plan view.
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7m
7.2m
27m
a)
75m
14m
15m
4m 9m 9.6m
b) c)
Figure42. Sludge heaps at the fellingsdam of Ytterhogdal
The average heights of each sludge heap are 1m, 0.3m and 0.35m respectively. The sludge quantity in Ytterhogdal was 430m3 totally, the tested total solid content at the sludge heaps was 56% and the TS content in the pond was about 30%. Then the original volume of the sludge was around 800m3.
Dewatering by natural freezing and drying can reduce the sludge volume a lot, such as in the two cases above. It is definitely an easy and economic sludge treatment method.
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4 Removal of organic matter, phosphorus, nitrogen and bacteria
Organic carbon, nitrogen and phosphorus are the major nutrients in treated wastewater discharges. Nutrients such as nitrogen and phosphorus may cause eutrophication in the water receiving body. Moreover, it may stimulate the growth of algae and rooted aquatic plants in shallow streams (Metcalf & Eddy, 2001). To remove the organic matter and nutrients is the main task for a fellingsdam.
4.1 Organic matter
The organic matter is usually measured by the values of BOD or COD. BOD is the biological oxygen demand; COD is the chemical oxygen demand. The basic principles to remove the organic carbon are either to separate particulate organic matter into the bottom sludge or to convert dissolved organic matter into carbon dioxide.
As an optional step of treatment procedure, pre-sedimentation may separate large particles which removes a part of the organic matter. Particulate organic matter will settle down either in a pre-sedimentation pond or in a precipitation pond. Bacteria may break down organic matter and degrade them to carbon dioxide at aerobic conditions or convert organic matter to methane and carbon dioxide in anaerobic conditions. The formed carbon dioxide can be utilized to generate algae at a certain temperature and enough solar radiation, thus providing oxygen to the bacteria.
When using slaked lime as coagulant, the concomitant high pH value approaches 10.5-12.0. Most microorganisms can not survive in such environment. Therefore biodegradation is not efficient especially not at winter with low temperature in the wastewater and with a limited solar radiation. So a lower removal of dissolved organic matter could be the result of using slaked lime.
The following table 20 shows the mean effluent BOD7 and COD values of different lime fellingsdams from year 2001 to 2007.
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Table20. Effluent BOD7 and COD values from fellingsdams using lime precipitation. Location of plant 2001 2002 2003 2004 2005 2006 2007 PE
BOD7 (mgO2/l) Gottne 31 87 94 74 82 66 / 226 Skorped 14 29 47 25 26 25 / 261 Bredbyn 26 41 63 53 30 68 / 1352 Funäsdalen 27 32 30 31 33 28 25 3978 Tänndalen 16 19 23 26 15 28 22 3914 Annual mean 23 40 51 42 37 43 24 /
COD (mgO2/l) Gottne 64 156 154 127 136 117 / 226 Skorped 45 66 96 65 67 86 / 261 Bredbyn 56 79 121 110 78 135 / 1352 Funäsdalen 66 66 73 69 73 73 82 3978 Tänndalen 46 64 77 74 63 95 90 3914 Annual mean 55 86 104 89 83 101 86 / “/” = no data available
The annual values differs from each pond and each year, the total mean BOD7 value was about 39mgO2/l and COD was about 86 mgO2/l. From the individual felingsdams, the yearly mean BOD7 values varied between 14mgO2/l to 94mgO2/l. Even in a certain pond system, values changed a lot between different years. This is because the effluent concentration largely depends on the influent concentration of organics. With a high oxygen demand at the influent, the effluent oxygen demand could be comparably higher than with a low oxygen demand in the influent. Since there was no available data for influent BOD7 and COD, it is not easy to compare the differences. But from data in a previous investigation (Hanaeus, 1991), table 21, the influent and effluent values are clearly analyzed.
Table21. Values of COD Cr and BOD7 tested in 1991 (Hanaeus, 1991).
Precipitant Location of plant CODCr (mgO2/l) BOD7 (mgO2/l) Infl. Effl. Infl. Effl. Al Östersund (3 plants) / / 41 18 Ähtäri / / 201 50 Losby 426 136 234 59 Nordsäter 265 83 130 29 Lime Örnsköldsvik (8 plants) / 72 / 25 Funäsdalen 213 104 / / Edsåsdalen 401 126 / / “/” = no data available
More concentrated influents thus are likely to generate more concentrated effluents
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(Hanaeus, 1991). Even the effluent BOD7 was 50mgO2/l in ponds at Ähtäri which is higher than 18mgO2/l in Östersund, the removal ratio was 75% at Ähtäri and higher than 54% in Östersund.
The average BOD7 and COD values from individual fellingsdams using aluminum precipitation are shown in table 22.
Table22. Effluent BOD7 and COD values from fellingsdam using aluminum precipitation. Location of plant 2001 2002 2003 2004 2005 2006 2007 Pe
BOD7 (mgO2/l) Solberg 4 4 6 4 4 5 / 157 Björnrike 41 65 64 66 45 60 59 2137 Bruksvallarna 9 12 12 19 17 14 / 2000 Hede 13 27 33 33 25 23 26 2156 Ytterhogdal / / / / / / 39 / Annual mean 17 27 29 31 23 26 41
COD (mgO2/l) Solberg 27 34 32 30 30 31 / 157 Björnrike 73 107 109 120 85 120 113 2137 Bruksvallarna 38 36 33 45 55 37 / 2000 Hede 33 52 62 58 58 55 62 2156 Ytterhogdal / / / / / / 78 / Annual mean 43 57 59 63 57 61 84 “/” = no data available
Total mean value of BOD7 was 28mgO2/l and COD was about 61mgO2/l. These are a little lower than for the lime precipitation ponds. The reason is complicated. Low micro-organism activity in lime pond could be one and the influent concentration is another influence factor. Population that connected to the plant can also impact the effluent. In Björnrike, for instance with ponds located at a tourist site. People come and ski in this area which produces a lot more wastewater during winter time. The following phenomenon is a higher oxygen demand in ponds. To treat the big inflow, addition of more coagulant is necessary.
Fellingsdams using iron as coagulant is not quite common, there was only one pond in Mellansel using iron precipitation during this study trip. It is a one pond system with an inflow of about 500m3/day. Dosage of ferric sulphate was 430g/m3. The mean
BOD7 value was 28mgO2/l and COD was 81mgO2/l and overall values from each year are represented in table 23.
.
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Table23. Effluent BOD7 and COD values from a fellingsdam using iron precipitation. Location of plant 2003 2004 2005 2006
BOD (mgO2/l) Mellansel 26 21 24 25
COD (mg O2/l) Mellansel 75 66 70 84
4.2 Phosphorus
When discharging treated wastewater to a receiving water body, high phosphorus concentration in the effluent could generate plentiful algae and aquatic plants at favorable conditions. Excess vegetation consumes much oxygen at degradation which may cause fish dead. To remove phosphorus is one of the main objectives of a fellingsdam.
The main idea to remove phosphorus from wastewater is by the precipitation of the hydroxo-phosphates of aluminum, iron or calcium. The species differ for the different coagulants.
The phosphorus concentrations in fellingsdams using lime precipitation are shown in table 24.
Table24. Effluent concentration of phosphorus (mgP/l) in ponds using lime precipitation. Location of plant 2001 2002 2003 2004 2005 2006 2007 Gottne 0.22 0.75 0.25 0.21 0.16 0.20 / Skorped 0.10 0.09 0.13 0.21 0.21 0.29 / Bredbyn 0.16 0.12 0.31 0.21 0.29 0.55 / Funäsdalen 0.22 0.23 0.18 0.15 0.17 0.20 0.12 Tänndalen 0.23 0.16 0.21 0.25 0.16 0.28 0.27 Annual mean 0.19 0.27 0.22 0.21 0.20 0.30 0.20 “/” = no data available
The average effluent value of phosphorus from year 2001 to 2007 was about 0.23mgP/l. As there was no data from the influent, an assumed influent concentration of phosphorus is 6mgP/l, which gives the removal proportion 96%. Thus the chemical precipitation worked well in these fellingsdams. For a high value in 2006 at Bredbyn, the reason could be a high inlet phosphorus or low lime addition. Since chemical dosage was set, a concentrated inlet wastewater is possible.
Table 25 gives the phosphorus concentration of the ponds effluents when aluminum is used as coagulant.
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Table25. Effluent concentration of phosphorus (mgP/l) in ponds using aluminum precipitation. Location of plant 2001 2002 2003 2004 2005 2006 2007 Solberg 0.10 0.06 0.11 0.09 0.16 0.10 / Björnrike 0.16 0.46 0.15 0.16 0.10 0.23 0.20 Bruksvallarna 0.16 0.12 0.14 0.15 0.38 0.07 0.08 Hede 0.05 0.07 0.04 0.04 0.03 0.04 0.05 Ytterhogdal / / / / / / 0.061 Annual mean 0.12 0.18 0.11 0.11 0.17 0.11 0.10 “/” = no data available
The average value of phosphorus in the effluents was about 0.13mgP/l. The ponds in Hede kept a high removal ratio of phosphorus these years, which may be credited to the well designed pond system, which assures a long detention time, and to a high aluminum dosage. As shown in table 1, the dosage of aluminum in Hede was 28.8gAl/m3.
Values of phosphorus concentration in the effluent using iron precipitation are shown in table 26.
Table26. Effluent concentration of phosphorus (mgP/l) in ponds using iron precipitation. Location of plant 2003 2004 2005 2006 Mellansel 0.70 0.20 0.29 0.43
4.3 Nitrogen
Nitrogen removal methods in wastewater treatment can be divided into physicochemical method and biological method.
When using chemical precipitation, different results can be expected. Among the three most common coagulants, slaked lime is the most preponderant one. Lime increases pH to 10.5-12.5. Most of the soluble ammonia present will be converted to gaseous ammonia at such a high pH (Hanaeus, 1991). However, the rate of ammonia release is very slow, and a long detention time in ponds is required. In practice some kind of stripping is necessary to achieve a greater nitrogen removal by this reaction (Hanaeus, 1991), for example, air stripping.
Table 27, 28 and 29 show the nitrogen concentration in ponds using different coagulants.
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Table27. Effluent concentration of nitrogen (mgN/l) in ponds using lime precipitation Location of plant 2001 2002 2003 2004 2005 2006 2007 pH Gotten 12 25 29 25 25 23 / 12.5 Skorped 7 12 16 11 12 10 / 12.0 Bredbyn 8 13 17 15 10 16 / 12.0 Funäsdalen 19 23 25 27 30 26 27 12.2 Tänndalen 12 13 17 17 11 19 15 12.0 Annual mean 11.6 17.2 20.8 19 17.6 18.8 21 “/” = no data available
Table28. Effluent concentration of nitrogen (mgN/l) in ponds using aluminum precipitation Location of plant 2001 2002 2003 2004 2005 2006 2007 pH Solberg 4 6 6 4 7 5 / / Björnrike 24 33 32 43 35 42 41 6.1 Bruksvallarna 13 13 13 18 18 18 / 6.3 Hede 17 22 26 26 24 20 21 5.6 Ytterhogdal / / / / / / 33 7.5 Annual mean 14.5 18.5 19.3 22.8 21 21.3 31.7 “/” = no data available
Table29. Effluent concentration of nitrogen (mgN/l) in ponds using iron precipitation Location of plant 2001 2002 2003 2004 2005 2006 pH Mellansel 12 14 15 19 16 15 8
The average value in the effluent from lime fellingsdams is 18mgN/l, and the mean effluent concentration of nitrogen in aluminum fellingsdams is 21.3mgN/l. Effluent nitrogen concentrations using aluminum precipitation was higher than using lime precipitation, this is reasonable and understandable. But there is not much difference between the two values, which indicates that nitrogen removal is slow.
Nitrogen can also be removed by nitrification which is a biological process. It is an initial conversion of ammonium to nitrite.
+ − + 24 2 +→+ 4HNOONH
− − + 22 3 +→+ 2HNOOHNO Since this reaction is sensitive to temperature and pH of the water, conversion of ammonium to nitrite will be slow in cold season and in an improper pH value environment. The optimum pH value is about 8.4, so in many cases, nitrogen removal through nitrification is not possible. This can be achieved with a neutral pH and during summer period. Bacterial work is basic for this process.
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4.4 Coliform bacteria in fellingsdams
Pathogenic bacteria in wastewater are harmful for human health. If the wastewater is not well treated before discharge, it will pollute the receiving water body and may cause water born disease.
A high pH environment guarantees a low bacteria concentration in the effluent. As mentioned before, pH ranges from 10.5 to 12 in lime fellingsdams. Most microorganisms can not survive and most pathogenic bacteria are killed at such a high pH. Aluminum and iron fellingsdams have lower pH, and the bacteria removal should be analyzed. Bacteria analyses from aluminum and iron ponds are presented in table30. Mellansel is an iron fellingsdam, the other three fellingsdams are aluminum ponds.
Table30. Analyses of pathogenic bacteria from fellingsdams. (cfu/100ml) Locations Testing Temperature Intestinal Coliform Thermotolerant date at sampling Enterococci bacteria, Coliform 35 ºC bacteria, 44ºC Hede 2008.05.13 5 ºC <10 <10 <10 Orrviken 2008.05.14 5 ºC 60 400 120 Billsta 2008.04.02 0.4 ºC 690 510 10 Mellansel 2008.03.31 0.4 ºC / 6600 300 “/” = no data available.
All indicator bacteria concentrations are less than 10cfu/100ml at the effluent of the fellingsdam at Hede. The fellingsdams at Billsta and Mellansel were at a low temperature and had been covered by snow and ice for half a year when sampled; low biodegradation should be expected, resulting in a higher bacteria concentration. The coliform bacteria concentration in Mellansel was 6600cfu/100ml, was high and need may need further investigation.
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5. Future development
Fellingsdams owns a long history over the world. As the compact wastewater treatment plant costs a lot, in rural area and in less developed countries, where there is enough area and less population, the fellingsdam is a recommended alternative. Further more, it may be possible to find further use of effluent water.
Energy forest in Falun
The fellingsdam at Vika Strand, Falun is a combined system. During winter time, the operator dose coagulant to one of the ponds, to solve the wastewater. When in summer dosing is shut off and the other ponds are operating. The effluent of the treated water is transported through a pipe to a nearby energy forest, as shown in figure 43.
Figure43. Energy forest at the fellingsdam of Vika Strand
Energy forest is shrubbery forest. The fast growing shrubs are used for combustion. The wood can not be utilized for advanced wooden wares, but they require short time to grow compared with the surrounding forest. A part of energy forest, irrigated by treated wastewater, became obviously higher and thicker than the natural growing one. Due to the nutrients in the wastewater, the energy forest grows very quick and big.
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Conclusions Where algae grew in the ponds, turbidity was high close to the water surface, then decreased with depth, and finally increased again when near the bottom.
Sludge accumulated to the water surface, more than 1.2 meters at some fellingsdams. A few fellingsdams at Örnsköldsvik have never been cleaned; the future cleaning can be very difficult since the bottom sludge was very old and dense, thus hard to remove.
The organic content of the sludge in lime fellingsdams is sometimes lower than 3% of TS according to the laboratory analyses. And in aluminum ponds, it is more than 40% of TS in the beginning and decreases a lot near the effluent. In the chemical sludge organic matter was always found.
The mean value of BOD7 was about 39mgO2/l and the mean value of COD was 86mgO2/l in the effluents of the lime fellingsdams. In aluminum fellingsdams, the mean effluent BOD7 and COD values were 28mgO2/l and 61mgO2/l respectively. The average effluent concentration of phosphorus in ponds using lime precipitation from year 2001 to 2007 was 0.23mgP/l. The value was 0.13mgP/l when using aluminum precipitation. The nitrogen concentration in the effluents of lime ponds was 18mgN/l and 21.3mgN/l in aluminum ponds. From these values can be seen that the phosphorus has been well removed and that the treatment ability of lime and aluminum fellingsdams to remove organic matter and nitrogen was acceptable. Only one iron fellingsdam was investigated, so it is hard to evaluate and give a conclusion, but the effluent values of BOD7, phosphorus and nitrogen from the individual fellingsdam were acceptable.
The coliform bacteria removal in aluminum fellingsdams at Hede was excellent, but not efficient at two other investigated ponds. At the iron pond in Mellancel, the effluent concentration was 6600cfu/100ml which is too high and need to be further investigated.
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References Metcalf&Eddy, Inc. (2003). Wastewater Engineering: Treatment and reuse. Fourth edition
Reinosdotter, K. & Sjöbohm, L. (2000). Wastewater treatment in ponds, Brazil. Master thesis, 2000:242CIV, Luleå University of Technology
Cripps, S.J. & Hanaeus, J. (1993). The effects of chemical precipitation by slaked lime on suspended particle dynamics in wastewater ponds. Water Science and Technology.Vol.28. No. 28, No.10, pp.215-222.
Hanaeus, J. (1991). Wastewater treatment by chemical precipitation in ponds. Dissertation, 1991:095D, Luleå University of Technology.
Environmental reports from 2001 to 2007 for the fellingsdam at Björnrike
Environmental reports from 2001 to 2007 for the fellingsdam at Bruksvallarna
Environmental reports from 2001 to 2007 for the fellingsdam at Funäsdalen
Environmental reports from 2001 to 2007 for the fellingsdam at Hede
Environmental reports from 2001 to 2007 for the fellingsdam at Tanndalen
Environmental report in 2007 for the fellingsdam at Ytterhogdal
Environmental reports from 2001 to 2006 for the fellingsdam at Mellansel
Environmental reports from 2001 to 2006 for the fellingsdam at Gottne
Environmental reports from 2001 to 2006 for the fellingsdam at Solberg
Environmental reports from 2001 to 2006 for the fellingsdam at Skorped
Environmental reports from 2001 to 2006 for the fellingsdam at Bredbyn
Environmental reports from 2001 to 2006 for the fellingsdam at Kubbe
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APPENDIX Measured values in fellingsdams at Norrfällsviken……………………..…………….1 Measured values in fellingsdams at Ytterhogdal…………………...………………….2 Measured values in fellingsdams at Tandsjöborg…………………….……..………....3 Measured values in fellingsdams at Los………………...……………………………..4 Measured values in fellingsdams at Glössbo…..……………………………………...5 Measured values in fellingsdams at Falun……………………..……………………...6 Measured values in fellingsdams at Bredbyn...... 7 Measured values in fellingsdams at Nyliden……………………..…………………....8 Measured values in fellingsdams at Långviksmon………………..…………………...9 Measured values in fellingsdams at Billsta…………………………………………..10 Measured values in fellingsdams at Ånge…………………..…………………..……11 Measured values in fellingsdams at Björnrike…………………..………………..….12 Measured values in fellingsdams at Hede……………………………………………13 Measured values in fellingsdams at Funäsdalen……………………………………..14 Measured values in fellingsdams at Tänndalen………………………………………15 Measured values in fellingsdams at Bruksvallarna...... 16 Luleå University of Technology
Norrfällsviken
Sampling point Water Sampling point Oxygen concentration Sludge depth turbidity pH number temperature number ( ºC ) (mg/l) (m) (NTU) 1 1,64 2 15 5 1,09 2,1 11,9 7,9 3 14 11,2 0,28 3,1 9,07 8 3,2 9,49 8 4 13 0,7 0,59 4,1 8,72 8 4,2 10,2 8 5 14,5 6,7 0,22 5,1 3,41 7,3 5,2 3,06 7,2 6 14,5 7,2 0,06 6,1 2,25 7,3 6,2 2,27 7,2 Well from pond 1-2 8,69 7,9 Well from pond 2-3 2,1 7,2 Effluent drainage 5,4 6,2 Effluent from pond 2 8,62 6,5 Effluent 7,2 6,3
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Ytterhogdal
Sampling Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH point number number (ºC) (mg/l) (m) (NTU) 1 7,9 0,8 0,2 1,1 11,4 7,1 1,2 13,3 7 2 8,6 0,75 0,2 2,1 14,1 7,1 2,2 12,5 7,1 3 9,2 0,9 0 4 10 3,2 0,84 4,1 9,09 7,2 4,2 9,04 7,2 5 10,2 3,8 0,57 5,1 8,77 7,2 5,2 8,67 7,2 6 10,1 3,4 1,09 6,1 8,67 7,3 6,2 7,67 7,3 7 10,5 4,6 0,39 7,1 6,98 7,3 7,2 7,05 7,3 8 10,7 6,4 0,27 8,1 6,78 7,4 8,2 6,58 7,4 9 11,3 9,7 0,15 9,1 9,68 7,8 9,2 8,25 7,6 10 11,4 18,5 0,06 10,1 13,3 9,3 10,2 12,4 9,3 Effluent 1 10,3 9,2 Effluent 2 10,3 9,1
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Tandsjöborg
Sampling point Water Sampling point Oxygen concentration Sludge depth Turbidity pH number temperature number (ºC) (mg/l) (m) (NTU) 1 6,7 6,9 0,97 7,16 7,1 2 6,8 6,8 1,22 7,26 7 3 7,3 6,7 0,47 5,88 6,9 4 7,3 5,6 0,75 5,69 6,8 5 6,5 6,3 0,82 5,64 6,8 6 7,2 6,8 0,75 4,5 6,8 7 7,2 6,4 0,55 4,56 6,7 8 7,9 6,6 0,39 4,73 6,7 Effluent1 4,88 6,4 Effluent2 4,53 6,5
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Los
Sampling point Water Sampling point Oxygen concentration Sludge depth Turbidity pH number temperature number (ºC) (mg/l) (m) (NTU) 1 9 8,7 0,71 1,1 4,01 8,2 1,2 5,05 8,2 2 9,1 6,2 1,03 2,1 5,3 8,1 3 9 8,7 0,47 3,1 4,63 8,2 4 9 9 0,22 4,1 4,53 8,2 4,2 4,82 8,3 5 9,3 9 0,17 5,1 7,43 8,5 5,2 5,2 8,4 6 9,4 9,2 0,19 6,1 4,4 8,4 6,2 4,83 8,4 7 9,3 8,3 0,12 7,1 4,21 8,4 7,2 4,53 8,3 8 9,6 8,8 0,06 8,1 3,48 8,7 8,2 3,54 8,7 Well 1 4,38 8,4 Well 2 4,18 8,4 Effluent 1 3,85 9 Effluent 1 3,75 9
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Glössbo
Sampling point Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number number (ºC) (mg/l) (m) (NTU) 1 10 2,6 0,17 1 20 12,2 2 10 2,6 0,69 2 14,1 12,3 3 10 3 1,43 3 13,2 12,3 4 10 2,8 0,59 4 12,3 12,3 5 10 2,8 0,85 5 12,5 12,3 6 10,1 2,7 1,28 6 12,3 12,3 7 10,1 2,7 0,7 7 11,7 12,3 8 11,7 0,7 0,86 8 4 12 9 11,7 0,7 0,29 9,1 3,64 12 9,2 3,96 12 10 11,8 0,7 0,11 10,1 3,64 12 10,2 3,8 12 11 11,8 0,7 0,07 11,1 4,24 12 11,2 4,5 12 Effluent 1 4,24 12 Effluent 2 3,54 12
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Falun
Sampling point Water temperature Oxygen concentration Turbidity pH sludge depth number (ºC) (mg/l) (NTU) (cm) 1 12,4 4,3 8,52 7,5 213 2 12,4 4,3 8,12 7,5 61 3 / / / / 17 4 / / / / 148
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Bredbyn
Sampling point Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number number (ºC) (mg/l) (m) (NTU) 1 1,0 7,5 0,14 1,1 20,8 11,9 1,2 18,8 11,9 2 1,0 7,5 0,98 2,1 16,7 11,9 2,2 15,6 11,9 3 1,1 7,8 1,48 3,1 13,6 11,9 3,2 12,2 11,9 4 1,1 8,0 1,58 4,1 78,0 12,2 4,2 32,2 12,0 5 1,2 7,6 1,15 5,1 15,7 12,0 5,2 15,8 12,0 6 1,0 8,0 6,1 12,5 12,0 6,2 9,6 12,0 Effluent 0,6 6,7 Effluent 6,0 12,0
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Nyliden
Sampling point Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number number (ºC) (mg/l) (m) (NTU) 1 3,7 7,3 0,38 1,1 28,7 10,5 1,2 26,7 10,7 2 3,9 6,9 1,07 2,1 36,9 10,6 3 2,5 5,7 0,11 3,1 18,4 10,6 3,2 15 10,5 4 2,7 6,5 0,17 4,1 14,4 10,4 4,2 14,9 10,4 5 1,9 6,9 0,06 5,1 12,2 10,6 5,2 11 10,6 6 1 8 0,15 6,1 5,63 10,6 6,2 8,2 10,7 7 0,9 10,1 0,29 7,1 6,87 10,6 7,2 7,2 10,7 Effluent 1 6,1 10,7 2 5,88 10,7
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Långviksmon
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) 1,1 4,1 8,5 >1.6 51,8 11,4 1,2 52,4 11,5 2,1 / / / 8,87 10,5 3,1 3,3 5,8 0,7 3,13 11,5 4,1 / / / 11,5 11,3 5,1 1,7 2,4 0,38 8,11 11,7 6,1 1,5 2,2 0,3 10,9 11,1 Effluent 1 7,33 11,2 Effluent 2 6,74 11,2
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Billsta
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) 1,1 0,4 7,5 0,29 40,5 6,6 1,2 37,5 6,5 2,1 0,2 7 0,98 34,2 6,4 3,1 0,4 2,2 0,45 28,5 6,4 4,1 2,6 1,9 0,36 15,2 6,6 Effluent 1 23,8 6,6 Effluent 2 23,8 6,5
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Ånge
Sampling point Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number number (ºC) (mg/l) (m) (NTU) 1 6,2 1,5 1,49 1,1 17,5 7,1 1,2 26 7 2 6,2 1 0,83 2,1 20 7,1 2,2 18,1 7,1 3 6,6 1 0,37 3,1 17 7,1 3,2 17,1 7,1 4 6 1 0,39 4,1 16,8 7,1 4,2 16,5 7,1 5 8,6 3 0,88 5,1 16,7 7,2 6 8,3 1,2 0,39 6,1 17,7 7,2 6,2 22 7,2 7 8 1,1 0,22 7,1 17,9 7,3 7,2 18,5 7,3 Channel 1-2 left side 17,4 7,2 Channel 2-3 16,7 6,9 Channel 1-2 right side 17,3 7 Channel 2-3 16,8 7 Effluent 1 16 7,1 Effluent 2 15,6 7,1
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Björnrike
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) 1 5 1,6 0,64 64,1 6,5 2 4,9 1,4 0,69 67,5 6,5 3 4,1 1,5 0,59 77,5 6,6 4 3,2 1,5 1,25 69,1 6,7 5 1,5 2,2 1,65 32 5,8 6 3,3 1,2 1,22 22,7 5,7 7 2,4 1,5 0,43 36,4 5,8 8 2,3 2 0,89 21,5 5,8
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Hede
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) Pre-pond 1 5,5 3,6 Pre-pond-2 5,3 3,4 1 4,7 half pond covered by sludge 21,1 5,5 2 4,7 3,8 0,7 15,5 5,4 3 3,7 3,6 1 7,85 5,6 4 3,6 3,6 0,5 5,48 5,6 5 2,8 3,3 5,66 5,6 6 2,4 3,5 3,28 5,7 7 1,6 3,3 3,45 5,7 Effluent 1 2,6 5,6 Effluent 2 2,48 5,6
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Funäsdalen
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) 1 2,4 4,4 around 1.4m 1,26 12,1 2 can be seen at the surface 1,46 12,2 3 1,1 3,3 0,13 11,5 12,2 4 2,7 3,2 0,17 7,04 12,2 5 1,4 3,5 0,1 7,84 12,2 6 0,5 3,2 0,19 9,68 12,2 7 2,4 3,3 0,26 2,46 12,5 Effluent 1 1,26 12,5 Effluent 2 2,46 12,5
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Tänndalen
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) raw water 61,2 6,9 1 0,1 1,9 1,17 2 0 1,6 <1.32 217 10 3 0,5 1,8 0,25 11,5 11,6 4 0,4 1,6 0,14 67,1 9,8 5 0,5 1,6 0,24 12,7 11 a 0 2,8 0,52 b 0,1 2,4 0,48 c 0,1 2,4 0,19 10,3 11,9 d 0,1 4,1 / 182 12 Effluent 1 5,26 12 Effluent 2 4,69 12,3
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Bruksvallarna
Sampling point Water temperature Oxygen concentration Sludge depth Turbidity pH number (ºC) (mg/l) (m) (NTU) 1 0,5 3,3 0,97 16,3 6,3 2 0,4 3,1 0,62 13,3 6,3 3 1,1 2,5 0,51 11,4 6,3 4 0,3 2,8 0,39 10,6 6,3 Effluent from pond 2 to 3 12 6,3 11,8 6,3 5 0,1 1,4 0,42 15,6 6,3 6 0,8 2,3 0,29 17,8 6,3 15 6,3 Effluent from pond 3 14,6 6,3
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