Salmonid hatchery wastewater treatment

By Paul B. Liao* nature of hatchery operating procedures, both The characteristics of wastewater must be un- quantity and quality of wastewater vary from derstood before the methods treating that waste time to time. Accordingly, a treatment method can be discussed. The nature of salmonid for salmonid hatchery wastes must be eco- hatchery wastes and their pollution potential nomical, flexible and efficient in terms of the have recently been discussed by Liao." In degree of treatment required. Therefore, de- general, salmonid hatchery wastes can be velopment of an alternate treatment method classified into three groups dependent on type for hatchery effluent water control appears de- of hatchery and type of water supply system. sirable. They are normal hatchery effluent, raceway The degree of treatment required for a cleaning wastes and reuse filter effluent.** For hatchery effluent depends upon several factors reference, Table 1 summarizes salmonid hatch- including wastewater quality, receiving water ery wastewater characteristics. conditions, receiving water quality standards For normal hatchery effluent and reuse filter and effluent water quality standards. The con- overflow waters, the potential pollution prob- trol of pollution from a hatchery can be ac- lems involve depletion, nutrient en- complished by both in-hatchery operation richment and taste and odor in cases where improvements and effluent water treatment. the receiving water flow is low. Raceway clean- The former has been recently discussed in ing water and reuse filter backwashing wastes detail by the author.' This paper will discuss are potential sources of pollution comparable the results of the treatment methods studied. to domestic sewage. Therefore, no matter where the hatchery is located, effective control Methods studied. The treatment methods of these wastes is necessary. studied were stabilization , primary Generally, conventional wastewater treat- settling and aeration (combination of a short ment methods are applicable for hatchery term aeration tank and sedimentation ). wastes control. However, since hatchery flows The investigations covered all the above men- are extremely high (with an annual produc- tioned categories of wastewater. Each treat- tion of 300,000 lb of trout the total flow is ment method is described briefly in the fol- about 45 mgd) conventional methods of treat- lowing paragraphs. ing hatchery wastes would cost several times that of a domestic system for the same degree Stabilization ponds. A study using stabiliza- of treatment. This would, in most cases, upset tion ponds was conducted at Cowlitz Trout the fisheries system planning. Also, due to the Hatchery in the State of Washington in the late and summer of 1969. Four natural rearing ponds of about 4.5 acres each, with an average water depth of about 8.2 ft, were This article answers a number of questions raised after publication of Paul Liao's article in the August 1970 issue selected for the study. Wastewater from the of Water & Sewage Works. —Ed. hatchery flowed to a distribution channel where the water was introduced to each test *Predoctoral Research Associate, Water and Air Resources Div., University of Washington, Seattle; and Consultant pond by a slide gate. The flow through each for Kramer, Chin & Mayo Consulting Engineers, 1917 pond was measured at the outlet weir. During First Ave., Seattle, Wash. 98101. the test period the water was maintained at a

**In some hatcheries where filter beds are used to recon- control depth of 8.2 ft. The detention time was dition water for reuse about 5 to 10 percent of the varied by adjusting the amount of water to total hatchery flow over the beds is bypassed continu- the pond with the help of inlet slide gates. ously. The filters, consisting of crushed oyster shells and For each variation in flow or quality of waste- rocks, are backwashed every 3 to 6 days. Backwash water, samples were collected for chemical flow through each filter involves passing 1.5 to 2.0 mgd through each unit with a duration of 100 to 120 min analysis at the inlet and outlet at intervals of per unit. 5 hr for a period of 24 hr. Tests were made 9 WATER & SEWAGE WORKS, December, 1970 IGO on individual samples and the average results ASIMOVINE 2.5.5 2242 are summarized in Table 2 and Figure 1. % SO Primary settling. To evaluate the primary settling characteristics of the hatchery waste- EFFICIENCIES

water, samples were collected from the race- way effluent during the period that the raceway NESIOVAL

was being cleaned. These samples were trans- SS ported to the laboratory and after complete

AND mixing were subjected to a 2 hr Imhoff cone

SOD settling test. The BOD and solid tests were 0 -POD o -$ made on samples before and after settling. The results of these tests are reported in Table O 20 40 SO SO 100 3. No similar tests were made on normal BOD LOADING lb DOD/ oao / doy hatchery effluent water because of its low Figure BOD and suspended solids removal efficiencies of plain detention pond. solids content.

Aerated system. This system, as illustrated by Figure 2, consists of an aeration tank and detention pond. Wastewater enters the aeration tank and is aerated for a fairly short period (about 1/3 of total retention time). Aeration is accomplished using plastic tubing installed on the tank bottom to bubble air into the waste- water. Aeration raises the dissolved oxygen level, increases the contact between organisms and organic materials and activates the or- ganisms, thus enhancing biological oxidation. The aerated wastewater and activated or- ganisms flow by gravity to the detention pond where the solids settle out by gravity and the organic matter is further broken down by biological activity. The effluent is clear, with a low organic and solids content. This system of treatment was used for normal Figure 2: Pilot plant showing mixing pail, aeration tank and . hatchery effluent water at the Seward Park

Table 1: Characteristics of salmonid hatchery wastewater Average increase and range mg/I Pollutants A BOD 5.36 (0.12-36.5) 33.6 (18-49) 48 (36-69) 5.3 (2.2-9.9) COD 21.3 (3-125) - - 158 (60-296) 25 (16-40) Ammonia (NHs) 0.532 (0-2.55) - - 1.34 (0.85-1.61) 1.0 (0.85-1.37) Nitrate (NO.) 1.676 (0.045-3.1) - - 1.03 (0.44-1.76) 1.35 (0.44-2.66) Phosphate (PO4) 0.077 (0.01-0.262) - - 0.99 (0.71-1.35) 0.83 (0.6-1.11) Suspended solids 7.0 (0-55) 96 (85-104) 145 (104-224) 14 (7-18) Settleable solids 3.5 (0-35) 85 (78-89) 5 m1/I (2-15 m1/1) - Dissolved solids 78 (25-186) 78 (70-81) 80 76 Total solids 85 (30-190) 174 (166-185) 275 (202-294) 90 (76-120) Volatile solids 29 (5-100) 108 (90-125) 108 (84-149) 34 (32-40) A - Normal hatching effluent B - Ponds being cleaned C - Filter backwash water D - Filter bypass water (filter normal overflow)

Table 2: Summary of Cowlitz stabilization pond tests Test Temperature *F pH Retention BOD loading Percent removal No Flow, mgd air water in out time, days lb/acre-day BOD Nits NOB PO4 TS 1* 2.27 48 58 7.1 7.1 4.0 9.1 35 44 43 19 6 2* 4.66 48 56 7.1 7.0 2.0 18.6 32 52 36 0 17 3 3.98 48 58 7.1 7.5 2.3 46.0 56 77 41 86 6 4 1.54 48 60 7.1 7.7 6 70.1 48 78 58 87 14 5 2.17 54 60 7.3 7.8 4.2 38.0 68 - - - 27 6 4.63 54 60 7.3 7.1 2.0 65.5 54 - - - 32 7 3.30 54 63 7.3 8.5 2.8 46.6 61 - - - 24 8 1.68 54 59 7.3 7.1 5.5 24.0 62 - - - 24 *Ponds tested not stabilized yet Tests not conducted 10 - 440 WATER & SEWAGE WORKS, December, 1970 Trout Hatchery from fall 1969 through winter 1 00 o 1970 and later studied at the Dworshak Na- • o • t tional Steelhead Hatchery in the State of Idaho GO .1 - 7 • 1 : ( 0 • CO for the treatment of combined wastes of re- 0 , 0 - _, , , r { -1-- use filter backwash water and reuse raceway i 1 1 1 • • 4- effluent waters. A summary of the results is 60 --. • _ i i given in Figures 3-5. ' • I 4 ao•i - - -f -- ■ • , • 0 AND S REMOVALS

Discussion. Stabilization pond: Although the DOD % o - • 20 BOD loading rates were low and the deten- • NORMAL HATCHERY EFFLUENT (DETENTION TOM 10 NIS OR NORM tion time was fairly high, the BOD removal • - NORMAL FILTER OVERFLOW (SHORTER D(TIF•TION TIME) { efficiencies of unstable ponds were low (less • - FILTER SACKWASHING WATER than 50 percent). The suspended solids remov- 125 250 375 500 625 750 875 1 000 al efficiency for these ponds ranged between SOD LOADING. lb BOD /am / day

40 and 50 percent. When compared to the con- Figure 3: BOD and suspended solids removal efficiencies vs. loading rate (aerated ventional sedimentation ponds, this removal system). efficiency seemed to be too low. However, when the initial pollutant concentrations are low, they tend to be more difficult to remove.

As shown in Table 1, the initial concentrations • o ' 0 ot of BOD, NH3, NO3, PO4 and solids were very low. However, nutrient removals were fairly SO high. This can be attributed to biological activ- ity and settlement. When the ponds were stab- SO ilized, the pollutant removal efficiency was im- ( proved. With BOD loading rates ranging from 4 '

25 to 65 lb/acre-day and detention time 2 to DOD REMOVED 40

5.5 days, the BOD removal efficiencies ranged % from about 55 to 70 percent. The suspended 0- NORMAL FILTER OVEIWLOW. SO solids removal was parallel to that of BOD. • -FILTER RACKWASPIIN0 This indicates that the BOD is probably associ- WATER. G■ -NORMAL HATCHERY ated with the suspended solids. EFFLUENT. From the test results it appears that when O 1 0 20 30 40 50 GO 70 the ponds are stabilized, they are sufficient DETENTION TINE. 606,2 for pollution control. It is interesting to note Figure 4: BOD removal efficiencies vs. detention time (aerated system). that at the Cowlitz Hatchery the four ponds tested were used for rearing fingerling trout during peak season. The pollutant removal effi- ciency with in ponds was comparable to , that without fish in ponds. Therefore, they serve not only as pollution control systems but also as rearing units. This makes them even more attractive when the land for such construction

is available because the cost is low and the REMOVAL EFFICIENCY operation is simple. BOO Primary settling of raceway cleaning wastes: The results of Imhoff cone tests reveal that about 80 percent of the waste strength can O 5 i0 IS 30 U be removed within two hours (Table 3). It must INITIAL 1100 CONCENTRATION MI II. be noted that this is true for pond cleaning Figure 5: BOD removal vs. initial concentration (aerated wastes only. After the fish fecal wastes and system). unconsumed foods settle out, they remain on the raceway bottom for one day to one week until the raceways are cleaned. During this period a portion of the organic matter is de- composed by the organisms in the ponds. When that found in conventional sewage. This can the raceways are being cleaned, both solids be attributed to their longer retention in the and residual organic matter are carried away raceways and the biological acitvities. Be- by the outgoing water. Because of the affilia- cause settlement in an Imhoff cone represents tion of organic matter with solids, when the an ideal condition, when application is made solids are removed the organic material is for prototype construction, longer detention removed too. The settleability of solids con- time (greater than 2 hr) must be provided if tained in pond cleaning wastes is higher than the same removal efficiency is desired.

WATER & SEWAGE WORKS, December, 1970 441 Aerated system: The pollutant removal effi- an increase of initial BOD concentration. This ciency of the aeration system studied depends is similar to domestic sewage treatment. on many factors, mainly water temperature, Suspended solids removal by the system is initial pollutant concentrations, BOD loading parallel to the BOD removal as shown in Figure rates, retention time, and the manner and 4. This is similar to the stabilization ponds quantity of the air supply. Because of the na- studied. No plots of nutrient removal have been ture of hatchery wastewater, BOD removal is prepared. However, it appears from the results not greatly affected by the BOD loading rate. obtained that the percent removal is, in gen- As indicated in Figure 3, when the detention eral, lower than that of stabilization ponds. time remains fairly constant the BOD removal This could be attributed to the greater nutrient efficiency decreases slightly with an increase uptake by the algae and other organisms in of BOD loading. During the period of this the ponds. study, the most significant factor affecting the In short, the aerated system varies from other BOD removal was total detention time. When aeration processes primarily in detention time total detention time was reduced from 10 to and its suitability for hatchery effluent. As 4 hr, the efficiency dropped from around 80 compared to other wastes, hatchery effluent percent to about 60 percent or less. The opti- water appears more amenable to simple sec- mal detention time was around 10 hr during ondary treatment. In general, this system is this study (Figure 4). This confirms most of that simple, more flexible and more economical batch unit study results. The author conducted than the other methods in terms of the degree batch unit studies utilizing pure cultures to of treatment. remove substrate from the liquid. In most cases more than 80 percent of the total substrate was removed in 8 hr.3 Conclusions and suggestions. The results of The air requirement for optimum BOD re- this study support the following conclusions: moval was about 0.15 to 0.25 cu ft/gal of 1. The reuse filter backwash water quality water, which is lower than that used in the is similar to that of raceway cleaning wastes. process of 0.5 to 2.0 cu ft/gal. The pollution potential of both wastes is com- However, due to the lower initial BOD concen- parable to domestic sewage and thus requires tration, the ratio of cu ft of air per lb of BOD effective control. removed is about 2000 to 4000. This value is 2. A stabilization pond, properly designed, higher than that used in a conventional acti- can provide BOD and suspended solids reduc- vated sludge process, where about 1000 to tion on the order of 60 percent or more at 2000 cu ft of air per lb of BOD removed is BOD loading rates of 50 lb/acre-day with used. It was observed that the increase in air detention time of about 3 days. supply did not increase the BOD removal effi- 3. Nitrate and phosphate removal in the ciency significantly, but this excess air supply stabilization ponds is fairly high, although the did raise dissolved oxygen values to near results were somewhat random. This is consis- saturation. Also, it was thought that the man- tent, however, with detention ponds used for ner of air supply and the water depth of aera- other types of organic waste treatment. tion would have significant effect on BOD 4. Sedimentation ponds providing in excess removal efficiency. However, the results of the of two hr detention time can be expected to air supply tests did not suggest this.4 reduce the BOD and solids removal from the Figure 5 illustrates the relationship between effluent of raceways being cleaned by about BOD removal efficiency and initial BOD con- 80 percent. centrations. When the loading rates and air 5. A combination of short term aeration supply rates were kept fairly constant, it was (an air supply rate ranging from 0.15 to 0.25 found that removal efficiency increased with cu ft/gal) and an adequate detention time

Table 3: BOD and solids removal by sedimentation (raceway cleaning waste) Temper- Total solids Volatile Suspended ature BOD, mg/I mg/I solids mg/I solids mg/I Time °F pH Before After Before After Before After Before After Sample 1 0830 as 7.4 48.2 9.7 185 42 125 25 104 15 Scrnple 2 0830 48 7.0 17.9 3.5 166 47 90 30 85 7 Sample 3 0830 48 7.3 34.9 6.5 170 34 110 22 104 11 Average 48 7.2 33.6 6.6 174 41 108 26 96 11 Percent reduction 80.3 74.4 76.0 88.6 1) Samples taken at effluent of rearing pond number CZ of Cowlitz Trout Hatchery on June 19, 1969 when the pond was being cleaned. IEI 2) Before and after means before and after 2 hr of settling in an Imhoff cone. 442 WATER & SEWAGE WORKS, December, 1970

with (4 to 10 hr) can reduce hatchery pollution advantageous than the methods presented loads by 50 to 90 percent. here. Based on the above individual conclusions it is suggested that: Acknowledgments. This study was partially supported by the State of Michigan, the U. S. 1. If local pollution control codes for hatch- Army Corps of Engineers of Walla Walla Dis- ery wastewater are not stringent, a settling trict and Kramer, Chin & Mayo, Consulting basin with 2 to 3 hr detention time should be Engineers. Special thanks are due to the per- provided for raceway cleaning wastes and/or sonnel at the Cowlitz Trout Hatchery and the reuse filter backwash waste control. If volume Seward Park Trout Hatchery in the State of of the control facility, based on 2 to 3 hr Washington, the Dworshak National Stee!head detention time, is too large because of ex- Hatchery in the State of Idaho, James Vail and tremely high hatchery flow, the volume can be Victor Oblas of Kramer, Chin & Mayo for their reduced by separating raceway cleaning assistance throughout the study. wastes from normal hatchery effluent. 2. If local pollution control codes for hatch- References ery wastewater are stringent, and where land I. Liao, P. B. Pollution Potential of Solmonid Fish Hatch- is available, stabilization pond(s) may be eries. Water & Sewage Works, 117=81291 (1970). adopted. They could serve as pollution control 2. A Process Design For Effluent Treatment Facilities At Spring Creek And Bonneville Solmonid Hatcheries. A facility as as rearing unit during peak Report prepared by Liao, P. B. and Mayo, R. D. of season. When land availability is limited, the Kromer, Chin & Mayo, Consulting Engineers, Seattle, aerated system studied with total detention Washington (August 1970). time of 4 to 10 hr (depending on the degree 3. Liao, P. B. Bacterial Flocculation. Masters Thesis, Okla- University, August 1967 (unpublished). of treatment required) may be utilized. homa State 4. A Study of Salmonid Hatchery Wastewater Control 3. Other methods, either conventional or un- For The Platte Hatchery In Michigan. A Report pre- pared by Liao, P. B. and Mayo, R. D. of Kramer, Chin conventional, can be used if, after being & Mayo, Consulting Engineers, Seattle, Washington studied in depth, they are considered more (May 1970).

ED WATER & SEWAGE WORKS, December, 1970 443