Vol. 37(2), pp. 137-154, Dec. 2018 Tanzania Journal of Engineering and Technology ISSN 1821-536X (print) Copyright © 2018 College of Engineering and ISSN 2619-8789 (electronic) Technology, University of Dar es Salaam

Full Length Research Paper Creative commons licence type CC BY-NC-ND

The Fate of Nitrogen and Faecal Coliform in the Wetland in

John K. Kayima1*, Aloyce W. Mayo2 and Joel K. Nobert2

1Engiplan Consultants, Plot 697, Kitakule/Bishop Crescent off Balintuma Road, P. O. Box 3504, Kampala, Uganda. 2Department of Water Resources Engineering, University of Dar es Salaam, P.O. Box 35131, Dar es Salaam, Tanzania. E-mail: [email protected] *Corresponding author: [email protected]

ABSTRACT

The capacity of the Lubigi wetland to reduce nitrogen and faecal coliform pollution entering Lake Kyoga in Uganda was investigated. Three transects with 5 sampling points in each, were established in the wetland. Wetland plants samples were collected from the specific locations along the transects, and laboratory tests and analyses were carried out for plants biomass and nitrogen contents determination. Samples of wetland sediments were also collected, and laboratory tests and analyses were done for determination of nitrogen content in the sediments. Wetland water samples were taken from the main wetland inlet and the main outlet from the wetland main study area. At the same time, wetland water pH, dissolved oxygen and temperatures were measured in-situ. Laboratory tests and analyses for ammonia-nitrogen, nitrate-nitrogen, total Kjeldahl nitrogen, total nitrogen and faecal coliforms were carried out on the wetland water samples. The results indicate that the Lubigi wetland received about 16 to 173 mg/l of total nitrogen, largely in form of organic- nitrogen (64.7%) and ammonia-nitrogen (35.2%). Nitrate-nitrogen and Nitrite-nitrite accounted for only 0.1% of the total nitrogen in the inlet. The wetland removed about 24.9% of this nitrogen, which is equivalent to removal of about 1,672 tons of nitrogen annually. About 67.5 gN/m2 and 0.30 gN/kg of dry sediments were sequestered in the wetland plants biomass and the benthic layer respectively. The Lubigi wetland main study area also receives faecal coliform concentrations with the wetland inlet mean value of 653,509 CFU/100ml and its outlet mean value is 218,676 CFU/100ml. These values give a faecal coliform (FC) overall removal efficiency of approximately 66.5%. It was thus concluded that the Lubigi wetland has considerable capacity to buffer and protect Lake Kyoga, by reducing nitrogen and faecal coliform pollution entering the lake.

Key words: Faecal coliform pollution, Lubigi wetland, Nitrogen removal.

INTRODUCTION drainage channel with an average capacity of approximately 220,000 m3/day. The The Lubigi wetland, which is located in channel collects municipal and industrial the north-western part of Kampala, is one wastewater, storm water run-off and sub- of the largest Lake Kyoga drainage basin surface water flow from the upstream wetlands (Kayima and Mayo, 2018). The densely populated and unsewered slums. wetland receives discharges from a In addition, the stream receives effluent canalized stream and the Nsooba-Lubigi discharges from the Lubigi sewage

Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 137 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda treatment plant, with a design capacity of in infants and increased cancer risks in 5,400 m3/day (Watebawa, 2012; National human beings (Senzia, 2003; Rogan and Water and Sewerage Corporation, 2015). Brady, 2009; Karr, 2012; Brender et al., Therefore this wetland is practically used 2013). On the other hand, pathogenic for disposal of municipal wastewater organisms present in wastewater can cause (Kayima et al., 2018a). diseases and severe public health problems, and are considered to be Natural wetlands, Lubigi inclusive, have responsible for most of the morbidity and capacities to remove toxins and nutrients mortality in developing countries (WHO, from water bodies (Marwa, 2013; Kayima 2015). et al., 2018a; Masawe et al., 2018). Therefore they act as ecological transition Wetlands are not only effective for zones that protect the quality of water in removal of chemical pollutants, but they downstream fresh water bodies such as are also effective in reduction of pathogens rivers and lakes (Terer et al., 2005; Henry (Mayo and Kalibbala, 2007; Kalibbala et and Semili, 2005; Mayo et al., 2018). At al., 2008), which is vital for protection of present, there are serious concerns that the human health against diseases. However, Lubigi wetland will not only become the knowledge on the fate and removal of degraded, but will also pass on pollutants bacteria in wetlands is still unclear owing from upstream discharges, to the to the complexity of influencing factors downstream fresh water bodies of the and bacterial removal mechanisms (Weber and Lake Kyoga (Kayima and Legge, 2008; Wu et al., 2016). et al., 2018). This could lead to excessive Wetlands receive bacterial pollution from concentrations of, among other pollutants, multiple sources including inlet nitrogen and faecal coliforms (FC) wastewater and animals that live in or (Kayima et al., 2018) leading to serious around the wetland. Their performance is problems for people who rely on these also highly dependent on the type and water bodies for various uses (Gumm, density of macrophytes, hydrology, 2011). hydraulic regime, retention time and various physical-chemical factors that Nitrogen is among the major pollutants influence natural die-off of bacteria found in raw or partially treated (Kalibbala et al., 2008; Weber and Legge, wastewater (Metcalf and Eddy Inc., 2003). 2008). Excessive concentrations of nitrogen can stimulate eutrophication (Bricker et al., While it is known that wetlands receiving 2008), which can lead to production of wastewater have capacities to transform greenhouse gases (Kinney and Valiela, and remove the pollutants contained in the 2013), blockages of receiving fresh water wastewater (Mitsch and Gosselink, 2007; bodies, and interference with navigation Bavor and Waters, 2008; Mayo et al., (UNEP, 2013). The exposure to excessive 2014), the performance of wetlands differ concentration of ammonia can lead to because of aforementioned factors. toxicity to aquatic life and depletion of Therefore, it is important to investigate the dissolved oxygen, which can cause the fate of nitrogen and faecal coliforms in the death of fish, damage coral reefs and Lubigi wetland, with a view to assessing render water septic and odorous and the capacity of the wetland to reduce therefore unfit for human and animal use nitrogen and faecal coliform pollution (Morrow, 2009; Baker et al., 2013; Li et entering the downstream Mayanja River al., 2014; Shin et al., 2016). Excessive and Lake Kyoga. To achieve this nitrate in drinking water is known to cause objective, it was necessary to investigate methamoglobinaemia (blue baby disease) the effectiveness of Lubigi wetland in

138 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert reduction of nitrogen and faecal bacteria, sources. This zone is closest to the wetland which is the main objective of this main wastewater inlet and is dominated by research study. Echinochloa pyramidalis and Paspalum scrobiculatum, with abundance of other MATERIALS AND METHODS assorted types of plant species. Hence, transect T1 was established in this section The Main Study Area about 700 m downstream of the wetland main wastewater inlet. The middle zone Figure 1 shows the main study area, which was observed to be dominated by Cyperus is delineated in the north-east of Kampala papyrus and Typha capensis, with city by the Hoima Road, with the main abundance of other assorted types of plant wastewater inlet located at latitude species. Hence, transect T2 was 00˚20’48” N and longitude 32˚32’28” E; established in this section about 1,440 m and in the south-west by the Sentema Road downstream of the wetland main with the main wetland outlets located at wastewater inlet. The zone closest to the latitude 00˚19’56” N and longitude main study area outlets was observed to be 32˚31’34” E. This section of the wetland dominated by Cyperus papyrus and covers an area of about 1.1 km2, at an Thelypteris acuminata, with abundance of altitude of approximately 1,158 m above other assorted types of plant species. sea level, with a total catchment area of Hence, transect T3 was established in this about 40 km2. This is the section of the section about 1,930 m downstream of the wetland, which receives direct impact of wetland main wastewater inlet (Figure 1). polluted wastewater from upstream

Figure 1: Map of the Lubigi Wetland Main Study Area

In each of the 3 transects, 5 sampling follow the spatial variability across the points were established in order to closely widths of the wetland, as one moves from

Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 139 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda the main central drainage channel away and Biotechnology laboratory, in Uganda. towards the edges of the wetland on either The sun-dried samples of each plant part side of the channel. The transects and were thereafter oven-dried at 105 oC. The sampling points were geo-referenced using dry weight to wet weight ratio of the 500 g a Garmin Global Positioning System sub-sample, was used to calculate the total (GPS) device, in order to determine and dry weight in the 1mx1m quadrats in the record the co-ordinates of their locations. transects. Then they were transferred to a digitized map of the area, to ensure that the same Determination of nitrogen content in the transects and points are used every time plants sampling is done. To facilitate movements and work within the transects, Cyperus Total-nitrogen (TN) was chosen as the papyrus culms were cut and tied in bundles basic element for nitrogen used up by which were laid down to make accessible plants. The total-nitrogen content of the paths. Life rafts and jackets and other dried plant parts was determined according safety precautions and measures, were to the methods used by Novozamsky et al. used throughout the research field work. (1983). Fine materials out of every plant part were obtained by grinding a portion of Field and Laboratory Tests the dried plant parts in a manual grinder. Then the fine materials were sieved Determination of plants biomass through a 0.5 mm sieve in the Kawanda National Agricultural Research The sampling of plants for biomass Organization laboratory in Uganda, and determination was done in October and the ensuing powder was preserved November 2016. The 5 most dominant following the preparation methodology plants species namely Cyperus papyrus, devised by Muthuri and Jones (1997). Echinochloa pyramidalis, Typha capensis, Rottboellia cochinchinensis and Thereafter, portions of the dried powder Oldenlandia lancifolia were analyzed. were scooped up, and transferred These most dominant plant species were quantitatively into the destruction tubes in harvested; from the already established which digestion was done in a block, using 1mx1m sampling quadrats in transects T1, a concentrated Sulphuric-salicylic mixture T2 and T3. The above-ground biomass with Selenium as a catalyst. The analysis was cut and separated into leaves/umbels of total nitrogen in the digested samples and stalks/culms depending on the plant was then carried out, in accordance with type. Then these parts were weighed using the Standard Methods for the Examination a digital balance in the field, in order to of Water and Wastewater (APHA et al., obtain the total wet weight of each plant 2012). Finally, nitrogen content in plants part. The below-ground biomass was was determined following the approach removed by digging up all roots/rhizomes described by Muraza (2013). In this in the 1mx1m quadrats, and carefully approach, the plants biomass content in washing off all the dead materials and kilograms of plants dry weight per square soil/peat. The roots/rhizomes were also meter of wetland (kgDWm-2), and the weighed in the field, in order to obtain plants nitrogen content as a percentage of their total wet weight. From the whole plants Dry Weight (%DW) were first sample of each plant part in a 1mx1m determined. Then the plants nitrogen quadrat, a sub-sample weighing 500 g was content in g N.m-2 was determined as the taken for sun-drying in the Makerere product of the plants biomass content and University Plant Sciences, Microbiology the plants nitrogen content as a percentage.

140 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert

Determination of nitrogen content in the from the main wetland inlet and the main sediments wetland outlet. Samples of 2.0 liters each were collected from a depth of 10 cm to 20 The collection of wetland sediments was cm below the water surface, into sterilized done simultaneously with the plants plastic containers. The samples were sampling. The sediments were collected stored in cool boxes, and then transported from 3 of the 5 sampling quadrats, in each to the National Water and Sewerage of the 3 transects T1, T2 and T3. The Corporation laboratory in Uganda, and sediments samples were packed in cool examined within a period of 4 hours. At boxes and transported to the Makerere the same time, in situ wetland water University Plant Sciences, Microbiology temperatures were measured with portable and Biotechnology laboratory in Uganda, thermometer WTW 3310. The pH values where they were-oven dried at 105 ºC. were measured with a pH electrode SenTix After drying, the samples were ground in a 21 WTW, connected to a portable pH manual grinder and sieved through a 0.5 meter WTW 3310. Dissolved oxygen (DO) mm sieve size in the Kawanda National was measured with a dissolved oxygen Agricultural Research Organization electrode CellOx 325 WTW, connected to laboratory in Uganda, in order to obtain a portable DO meter WTW 3310. the dry powder. Laboratory tests and analyses for To analyze the sediments for nitrogen ammonia-nitrogen (NH3-N), nitrite- contents, sub-samples of appropriate nitrogen (NO2-N), nitrate-nitrogen (NO3- weights were taken and digested in a N), Total Kjeldahl Nitrogen (TKN), Total block, using a concentrated Sulphuric- Nitrogen (TN) and faecal coliforms (FC) salicylic mixture with Selenium as a were carried out on the wetland water catalyst. The analysis of nitrogen in the samples, in accordance with the standard digested samples was then carried out methods for the examination of water and following the total nitrogen determination wastewater (APHA et al., 2012). Wetland procedures, in accordance with the water samples were kept under Standard Methods for the Examination of refrigeration at about 4 oC during storage. Water and Wastewater samples (APHA et Chemical preservation was done by adding al., 2012). The determination of the 1 ml of sulphuric acid (H2SO4) to 1 liter of nitrogen content in the sediments in gm-2, the sample to achieve a pH below 2 for was done by multiplying the sediments preservation of samples for determination nitrogen content in grams of nitrogen per of ammonia-nitrogen. Ammonia-nitrogen kilogram of sediments by the density of was analyzed using the Turbidmetric sediments in kgm-3 and then by 0.5m. This method, and the Nessler reagent. Nitrate- was based on the consideration that the nitrogen (NO3-N) was analyzed using the effective sediments depth for nitrogen Spectrophotometer with Cadmium sedimentation is 0.5m. At depths in the method, and the Nitra Version 5 reagent. sediments exceeding 0.5 m, layers of stiff TKN was analyzed using the Semi-Micro and almost impermeable clay soils are Kjeldahl method. The organic-nitrogen encountered in the wetland. (Org-N) was determined by calculating the difference between TKN and ammonia- Determination of wetland water nitrogen. Faecal coliforms were characteristics enumerated using membrane filtration technique using M-FC agar base solution Seventy two (72) wetland water samples as the medium in accordance with were collected at bi-weekly intervals from Standard methods for the examination of August 2016 to February 2018 inclusive,

Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 141 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda water and wastewater samples (APHA et performed using Spearman’s rank-order al., 2012). linear relationships, by examining the coefficients of correlation R and the Data processing coefficients of determination R2, which range between -1.0 and +1.0. The stronger All data generated in this research study the relationship between the were preliminarily examined to check for variables/parameters, the higher the their correctness. Those found to be coefficient of correlation R and the obviously erroneous, by virtue of coefficient of determination R2. appearing to be incongruous with the rest Coefficients of correlation R of -1.0 and of the data in their respective sets, were +1.0 represent perfect correlation between discarded. Subsequently, Microsoft the variables/parameters under EXCEL 2008 spreadsheet and MINITAB examination. Coefficients of correlation of Release 15 for Windows software were ≤ (-0.5) and (+0.5) were regarded as used to analyze the remaining data. The indicating variables/parameters having a Anderson-Darling test was used for testing strong correlation and relationship. normality. Comparisons of variables were Variables/parameters having coefficients performed using the Analysis of Variances of correlation R ≥ (-0.5) and (+0.5), were (ANOVA) technique. Multiple regarded as having poor correlation and comparisons were performed using relationship. Tukey’s HSD tests. Analyses of the data also included statistical correlations and RESULTS AND DISCUSSIONS statistical differences between related variables. Variation of physical-chemical characteristics Spearman’s correlation tests were performed on various data sets, in order to Table 1 summarizes the values of the examine the relationships between the observed Lubigi wetland water inlet and corresponding variables. These tests outlet nitrogen, faecal coliforms and assessed the linear relationships between related physical-chemical parameters. variables/parameters, and they were

Table 1: Variation of physical parameters in Lubigi Wetland

Parameter Inlet Values Outlet Values Min – Max Mean SD Min – Max Mean SD pH 6.60- 8.10 7.22 0.34 6.80-8.00 7.24 0.29 Temperature (ºC) 19.7-22.4 21.2 0.71 20.5-24.8 22.6 1.06 Dissolved Oxygen (mg/l) 0.06 – 2.43 0.30 0.37 0.07-0.64 0.23 0.10 Min-minimum and Max-maximum

showed that at the 95% confidence interval The pH (α = 0.05), there was no significant difference between the wetland inlet and Table 1 shows that in the wetland main outlet pH values (p = 0.143) although there inlet zone, the pH of the water ranged from is a positive linear correlation (R2= 0.391), 6.7 to 8.1 with a mean value of between the wetland outlet and inlet pH 7.22 0.34, while in the outlet zone, the values. The range of the observed outlet pH varied from 6.8 to 8.0 with a mean pH values suggests that microbial value of 7.24 0.29. Statistical analyses activities in the wetland are favored, since

142 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert these values fall within the optimum the high Biochemical Oxygen Demand functioning pH range of microbes (Kadlec, (BOD) related to the biogeochemical 2009). activities taking place in the wetland, including nitrification and the In particular, mineralization having the biodegradation by microorganisms of optimum pH range of 6.5 to 8.5 (Patrick organic matter in the wastewater, and the and Wyatt, 1964), and denitrification by decaying plant litter/detritus. Pseudomonas bacteria having the optimum pH range of 7.0 to 8.0 (Delwiche and Algal photosynthesis, which contributes to Bryan, 1978; Muller et al., 1999) are the oxygenation of wetlands, does not favored to occur at appreciable rates. appear to be playing a major role in the However, nitrification by Nitrosomonas Lubigi wetland although wetland received bacteria having the optimum pH range of 469 to 578 cal/m2/d of solar intensity 8.5 to 8.8, and by Nitrobacter bacteria (Mean = 525 cal/m2/d). It is worth to having the optimum pH range of 8.3 to 9.3 report that the average plant density in (Halling-Sorensen and Jorgensen, 1993), Lubigi wetland is 10.2 plants/m2 (Kayima appears to be less favored to occur at high and Mayo, 2018), which is about three rates. The range of the observed outlet pH times higher than 3.2 plants/m2 in Mara values, also favors ammonia-nitrogen to River Basin wetlands in Tanzania (Muraza exist predominantly in the ionized- et al., 2014). The thick canopy of the + ammonium (NH4 ) form, rather than in the dense emergent macrophytes prevalent in volatilized un-ionized-ammonia gas the Lubigi wetland has a sheltering and (NH3(g)) form, which starts to become shadowing effect, obstructing sunlight predominant at pH values above 9.0 from reaching the wetland water column (Konig et al., 1987). and thus curtailing the growth of algae, photosynthesis and oxygen production. In Dissolved oxygen addition, dense emergent macrophytes tend to reduce wind velocities and the From Table 1, the dissolved oxygen related physical re-aeration and concentrations in the main inlet zone, oxygenation actions on the wetland waters. ranged from 0.06 to 2.43 mg/l, with a Hence in general, nitrification by mean value of 0.32 mg/l, whereas in the Nitrosomonas bacteria having the outlet zone, the dissolved oxygen optimum dissolved oxygen concentration concentrations ranged from 0.07 to 0.64 range of 2.0 to 7.5 mg/l, and Nitrobacter mg/l, with a mean value of 0.24 mg/l at the bacteria having the optimum dissolved 95% confidence interval (α = 0.05). oxygen concentration of 4.0 to 7.5 mg/l Further statistical analyses showed that (Knowles et al., 1965; Senzia, 2003) is not there is a statistically significant difference favored to occur at high rates. However, between the inlet and outlet dissolved denitrification by Pseudomonas bacteria oxygen concentrations (p = 0.014) and a having the optimum dissolved oxygen very weak and positive linear correlation concentration range of less than 0.5 mg/l (R= 0.23), between the wetland outlet and (Halling-Sorensen and Jorgensen, 1993) is inlet pH values. The observed dissolved favored to occur at appreciable rates. oxygen (DO) concentration values, suggest that the Lubigi wetland has very low levels Water temperatures of aeration and oxygenation, and it is therefore by and large anoxic. The From Table 1, water temperatures in the dissolved oxygen concentrations decreased main inlet zone range from 19.7ºC to by 26.7% in the wetland, suggesting that 22.4ºC, with a mean value of 21.2 0.71 the water is significantly de-oxygenated by oC, whereas in the outlet zone, water

Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 143 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda temperatures range from 20.5ºC to 24.8ºC, mineralization having a limiting minimum with a mean value of 22.6 1.06 ºC. temperature of about 11oC to 14oC (U.S. Figure 2 shows that there is a positive, but Environmental Protection Agency, 2000) low linear correlation (R= 0.49), between is favored to occur at appreciable rates. outlet and inlet water temperatures, which However, nitrification by Nitrosomonas suggests that wetland temperature is bacteria having the optimum temperature relatively independent of inlet temperature. range of 28oC to 36oC, and Nitrobacter On average, wetland temperature increased bacteria having the optimum temperature by 1.4oC, although statistical analysis at range of 28oC to 42oC (Painter, 1970), is the 95% confidence interval (α = 0.05), not favored to occur at a high rate. On the suggests that there is no significant other hand, denitrification by difference between the inlet and outlet Pseudomonas bacteria having the optimum temperatures (p = 0.161). The observed temperature range of 3oC to 35oC can water temperature values suggest that proceed at appreciable rates.

Figure 2: Correlation between wetland outlet and inlet water temperatures

Ammonia-nitrogen in the wetland nitrogen concentrations (p = 0.037). These high ammonia-nitrogen concentration The concentration of ammonia-nitrogen in values can be attributed to the presence of the inlet ranged from 1.23 mg/l to 73.6 wastewater discharged into the Lubigi mg/l, with a mean value of 29.1 18.3 wetland. In particular, the process of mg/l. However, the concentration of mineralization of organic-nitrogen to ammonia-nitrogen in the wetland outlet ammonia-nitrogen appears to be varied from 0.71 to 61.0 mg/l with a mean proceeding at significant rates due to the value of 21.9 14.0 mg/l. Further pH and temperature conditions which statistical analyses showed that there is a favor this process, as already discussed. statistically significant difference between There is also the indication that the the wetland inlet and outlet ammonia- originally settled organic-nitrogen is being

144 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert regenerated back into the water column as very strong and positive linear ammonia-nitrogen, especially during the correlation/relationship (R= 0.88), between rainy and flash floods periods when the wetland outlet and inlet ammonia- conditions of hydraulic turbulence are set nitrogen. The observed mean value of in motion. outlet ammonia-nitrogen of 21.9 mg/l is more than double the recommended It was observed that the average ammonia- Uganda National Effluent Discharge nitrogen removal efficiency was 24.7%. Standard of 10.0 mg/l (Uganda National This relatively low overall removal Environmental Management Authority efficiency appears to be due to low rates of (NEMA), 2016). This implies that the nitrification as a result of unfavorable overall ammonia-nitrogen (NH3-N) dissolved oxygen levels. It is possible that removal capacity of the Lubigi wetland due to the high plants densities, plant main study area, does not meet the uptake may be the major process recommended standards, before disposing governing ammonia-nitrogen removal in effluents into the environment. the wetland. Figure 3 shows that there is a

Figure 3: Correlation between wetland outlet NH3-N and inlet NH3-N

Nitrate-nitrogen in the Lubigi Wetland inlet ranged from 0.01 to 1.64 mg/l, with a mean value of 0.15 0.20 mg/l, and in Figure 4 shows that there is a very strong the outlet it varied from 0.01 to 0.81 mg/l, linear correlation/relationship (R= 0.74) with a mean value of 0.09 0.14 mg/l. between the wetland outlet and inlet Statistical analysis revealed that there is a nitrate-nitrogen. The concentration of significant difference between the inlet and nitrate-nitrogen (NO3-N) in the wetland outlet ammonia-nitrogen concentrations (p Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 145 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda

= 0.024). It was noted that the mean outlet dissolved oxygen and temperature nitrate-nitrogen concentration of 0.09 mg/l conditions in the wetland. There is also was well below the recommended Uganda indication that due to the high plants National Effluent Discharge Standard of densities, the process of plant uptake is 10.0 mg/l (Uganda NEMA, 2016), also playing a significant role in the implying that the overall nitrate-nitrogen removal of nitrate-nitrogen. removal capacity of the Lubigi wetland main study area, meets the recommended The average nitrate-nitrogen removal standards, before disposing effluents into efficiency of 40.0% provides further the environment. evidence that denitrification may be proceeding and removing nitrate-nitrogen, The noticeably low nitrate-nitrogen at considerable rates. This denitrification concentration values appear to confirm the would be well supported, especially due to earlier observations and discussions, that the presence of the abundant labile organic the process of nitrification to form nitrate- carbon sources in the wastewater and the nitrogen is constrained by the dissolved decaying plant detritus, acting as electron oxygen level in the wetland. Furthermore, donors in favor of this process. In addition, this may be confirming the earlier it is possible that plant uptake is also observations that denitrification may be playing a significant role in the removal of proceeding and removing nitrate-nitrogen nitrate-nitrogen. at considerable rates due to favorable pH,

Figure 4: Correlation between wetland outlet NO3-N and inlet NO3

wetland inlet ranged from 4.4 to 134.2 Organic-nitrogen in the Lubigi wetland mg/l, with a mean value of 53.6 37.3 mg/l. In the wetland outlet zone, the Measurements of organic-nitrogen concentration of organic-nitrogen varied revealed that its concentration in the from 1.6 mg/l to 110 mg/l, with a mean

146 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert value of 40.1 33.8 mg/l. It was further The organic-nitrogen concentration in the observed that there is a statistically wetland inlet was noticeably high and can significant difference between the wetland be attributed to the presence of wastewater inlet and outlet ammonia-nitrogen discharged into the Lubigi wetland. concentrations (p = 0.013). Figure 5 also Furthermore, there is suggestion that due shows that there is a strong linear to the high plant densities, the leaching of correlation/relationship (R= 0.78) between the abundant decaying dead plant detritus the wetland outlet and inlet organic- makes a significant contribution to the nitrogen. The observed mean value of recycling of organic-nitrogen (Org-N) outlet organic-nitrogen of 53.6 mg/l, is back into the water column. The average more than double the recommended organic-nitrogen removal efficiency was Uganda National Effluent Discharge 25.1%, which might have been attributed Standard of 20.0 mg/l (Uganda NEMA, to the process of mineralization of the Org- 2016), implying that the overall organic- N to NH3-N. In addition, the sedimentation nitrogen removal capacity of the Lubigi of organic-nitrogen into the wetland wetland main study area, does not meet the benthic layers, may also be contributing recommended standards, before disposing significantly to the overall removal of effluents into the environment. organic-nitrogen from the water column.

Figure 5: Correlation between wetland outlet Org-N and inlet Org-N

Total nitrogen in the Lubigi wetland and from 10 to 167 mg/l, with a mean value of 62.4 36.8 mg/l in the outlet In accordance with the data collected, the zone. Further statistical analyses show that concentration of total-nitrogen varied from there is a statistically significant difference 16 to 173 mg/l, with a mean value of between the wetland inlet and outlet 83.1 44.7 mg/l in the wetland inlet zone, ammonia-nitrogen concentrations (p =

Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 147 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda

0.035). The average total-nitrogen removal in the sediments was 0.30±0.15 gN/kg efficiency was 24.9%, which is an sediments, which translates to 157.5 gN.m- appreciable amount considering that the 2 of wetland. It is evident that there is a mean hydraulic residence time is only general trend of more nitrogen about 2.0 days (Kayima et al., 2018b). accumulating in the sediments as the This removal is largely through net-loss by wetland water flows from wetland inlet to sedimentation, plants uptake and the outlet. This can be attributed to the denitrification. simultaneous trend of increase in plants densities from wetland upstream zones Figure 6 also shows that there is a strong towards the downstream ends. Table 2 linear correlation (R= 0.81) between the summarizes the results of the Lubigi wetland outlet and inlet total-nitrogen. The wetland plants biomass and nitrogen observed mean value of outlet total- contents. The corresponding increase in nitrogen of 83.1 mg/l, is more than double the below-ground roots and rhizomes the recommended Uganda National structures of these plants is responsible for Effluent Discharge Standard of 20.0 mg/l the trapping of increasing sediments (Uganda NEMA, 2016), implying that the quantities, which in turn determine the overall total-nitrogen removal capacity of increasing quantities of nitrogen trapped in the Lubigi wetland main study area, does the sediments. not meet the recommended standards, before disposing effluents into the Nitrogen content in wetland sediments environment. Sediment samples indicate that at transect This section of the wetland has removed T3 the concentration of nitrogen was 20.7 mg/l of nitrogen. With the average 0.60±0.22 gN/kg sediments. However, at flow rate of 221,357 m3/d (Kayima et al., transects T1 and T2, the samples 2018), the wetland has a capacity to concentration of nitrogen was 0.16±0.12 remove 4,582 kgN/d, which is equivalent and 0.14±0.12 gN/kg sediments, to 1,672 tons/year. Although substantial respectively. The average nitrogen content amount of nitrogen is removed in this in the sediments was 0.30±0.15 gN/kg section of the wetland, about 5,040 sediments, which translates to 157.5 gN.m- tons/day of nitrogen is discharged at the 2 of wetland. It is evident that there is a outlet end of the wetland, which suggests general trend of more nitrogen that significant quantity of nitrogen accumulating in the sediments as the received from the upstream is discharged wetland water flows from wetland inlet to at the downstream end without removal. the outlet. This can be attributed to the This could lead to pollution of water simultaneous trend of increase in plants bodies downstream of Lubigi wetland. densities from wetland upstream zones towards the downstream ends. Table 2 Nitrogen content in wetland sediments summarizes the results of the Lubigi wetland plants biomass and nitrogen Sediment samples indicate that at transect contents. The corresponding increase in T3 the concentration of nitrogen was the below-ground roots and rhizomes 0.60±0.22 gN/kg sediments. However, at structures of these plants is responsible for transects T1 and T2, the samples the trapping of increasing sediments concentration of nitrogen was 0.16±0.12 quantities, which in turn determine the and 0.14±0.12 gN/kg sediments, increasing quantities of nitrogen trapped in respectively. The average nitrogen content the sediments.

148 Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 John K. Kayima, Aloyce W. Mayo and Joel K. Nobert

Figure 6: Correlation between wetland outlet TN and inlet TN

Table 2: Lubigi Wetland Plants Biomass and Nitrogen Contents

Item Cyperus Echinochloa Typha Rottboellia Oldenlandia Average±SD Papyrus pyramidalis capensis cochinchinensis lancifolia Biomass AG 0.55±0.48 0.14±0.10 0.21±0.16 0.023±0.015 0.28±0.28 0.24±0.09 (kgDW/m2) BG 0.46±0.23 0.03±0.02 0.05±0.03 0.005±0.003 0.09±0.09 0.13±0.08 Total 1.01±0.05 0.17±0.06 0.26±0.08 0.028±0.009 0.37±0.01 0.37±0.17 Nitrogen AG 0.22±0.14 0.56±0.31 0.17±0.10 0.038±0.038 0.03±0.03 0.20±0.09 Contents BG 0.19±0.11 0.1±0.09 0.04±0.02 0.004±0.004 0.01±0.01 0.07±0.03 (%DW) Total 0.41±0.12 0.66±0.23 0.21±0.07 0.042±0.017 0.04±0.01 0.27±0.12 Nitrogen AG 121.0 78.4 35.7 0.9 8.4 48.89±22.57 Contents BG 87.4 3.0 2.0 0.0 0.9 18.66±17.19 (gm-2) Total 208.4 81.4 37.7 0.9 9.3 67.54±37.91 BG= Below-Ground plant organs; AG= Above-Ground plant organs; DW = Dry Weight; SD = Standard deviation

Faecal Coliforms in the Lubigi Wetland However, the quality of effluent is far above the recommended Uganda National The concentration of faecal coliform in the Effluent Discharge Standard of 5,000 wetland inlet ranged from 60 to 4,800,000 CFU/100ml (Uganda National cfu/100ml with a mean value of Environmental Management Authority 653,509 2,182 cfu/100ml. In the wetland (NEMA), 2016). This implies that the outlet zone, faecal coliform counts varied wetland outlet faecal coliform (FC) from 20 to 740,000 cfu/100ml, with a concentrations of the Lubigi wetland main mean value of 218,676 157 cfu/100ml. study area, do not meet the recommended Therefore, this gives an average faecal faecal coliform (FC) standards. However, coliform removal efficiency of 66.5%. when the logarithm values of the wetland inlet and outlet faecal coliform was Tanzania Journal of Engineering and Technology, (Tanz. Journ. Engrg. Technol.) Vol. 37 No. 2, Dec.2018 149 The Fate of Nitrogen and Faecal Coliform in the Lubigi Wetland in Uganda plotted, a strong correlation was observed done in Lubigi sewage treatment plant the (R = 0.95). The high faecal coliform (FC) effluent quality is still poor. In several concentration in the inlet can be attributed occasions raw sewage is directly by-passed to the wastewater discharged into the into the wetland when the plant is Lubigi wetland from the open channel overloaded or when it is undergoing drains and from Lubigi sewage treatment maintenance and repairs. plant. Although treatment of wastewater is

Figure 7: Correlation between the wetland outlet FC and inlet FC

In a study carried out by Kansiime and zone. This reduction is equivalent to a Nalubega (1999) in the Nakivubo swamp mean faecal coliform removal efficiency in Uganda, a relatively higher faecal of 38.3%. For comparison, Kalunde (2007) coliform removal efficiency of 90.9% was reported removal efficiency of faecal reported. This wetland receives wastewater coliform of 96.0% in a horizontal sub- from the Nakivubo storm water channel surface flow constructed wetland at the and effluents from the Bugolobi sewage University of Dar es Salaam wastewater treatment plant was reported to contain treatment facility. It is evident that faecal mean faecal coliform (FC) concentrations coliform removal efficiency varies from of 110,000 26,000 cfu/100 ml in the one system to another depending on the inlet and 10,000 2,400 cfu/100 ml in the type of wetland and variations of physical, wetland outlet zones. In another study by environmental and forcing functions Mayo and Kalibbala (2007) in constructed affecting each system. water hyacinth ponds in the University of Dar es Salaam in Tanzania, which received sewage effluents from the waste stabilization ponds, faecal coliform (FC) concentrations was reduced from 136,000 16,600 cfu/100ml in the wetland inlet zone, to a mean value of 83,900 10,200 cfu/100ml in the outlet

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CONCLUSIONS REFERENCES

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