A strategy for coupling municipal wastewater treatment using the Sequencing Batch Reactor with effluent nutrient recovery through aquaculture

e:>

Pergamon

Waf. Sci. T.ch. Vol. 35. No. I. pp. 177-184. 1997. Copyrisht e 1996 IAWQ. Published by Elsevier SCIence Ud Prinled in areal Brilain. All riShlS reset'Ved.

PII:

S0273-1223(96~894-3

0273-1223197 517'00 + 0110

A STRATEGY FOR COUPLING

MUNICIPAL WASTEWATER TREATMENT USING THE SEQUENCING BATCH REACTOR WITH EFFLUENT NUTRIENT RECOVERY THROUGH AQUACULTURE A. K. Umble and L. H. Ketchum, Jr Department ofCivil Engineering and Geological Sciences. University ofNotre Dame. Notre Dame. IN 46556. USA

ABSTRACf Recovering inorganic nutrients from treated municipal wastewaters prior to discharge, can not only minimize deterioration of receiving water quality, but can also be used to culture fish. Recovery can be achieved by integrating an ecological component, aquaculture, into the treatment scheme. Because of its operating flexi• bility, a Sequencing Batch Reactor was used to provide biological treatment of a municipal wastewater for oxidation of organic matter, removal of suspended solids, and nitrification. Performance of the reactor's 12• hour cycle for CBODs , TSS, and NHrN removals was 98%, 90%, and 89%, respectively. To recover inor• ganic nutrients, effluents were used to fertilize growth of desirable algal groups in an aquaculture component. Desirable algal groups are those which are preferred food sources for those zooplankton considered preferred prey for fish. DesiraQle algal response is influenced by the ratio of inorganic nutrients put into the system. An SBR's operational strategy was developed to produce effluents with acceptable N:P ratios ranging from 16 to 23. Though wide variation of this ratio resulted from this fertilization in the aquaculture tanks, the resulting algal response throughout the culture period was dominance of edible algal greens. Copyright@ 19961AWQ. Published by Elsevier Science Ud KEYWORDS Algae; aquaculture; fish; nutrients; phytoplankton; planktivore; wastewater; zooplankton INTRODUCfION Treating municipal wastewaters to meet increasingly stringent effluent quality standards is an ongoing chal• lenge. In recent years, regulatory scrutiny has focused on effective removal of excessive concentrations of inorganic nutrients often remaining in effluents of conventional biological treatment processes. Subsequent discharge of these excesses can threaten the quality of the receiving waters (Vymazal, 1989). Regulatory com• pliance has been especially challenging for existing facilities due to the significant capital investment and operational expertise required for tertiary process expansions (Jewell, 1994). Therefore, development of alter• native,low-cost, treatment technologies that address these constraints is essential. This paper summarizes the initial phases of work currently underway at the University of Notre Dame which couples the Sequencing 177

\78

A. K. UMBLE and L. H. KETCHUM, JR

Batch Reactor with an aquaculture component to investigate the objectives of treatment performance and recovery of inorganic nutrients for beneficial use, that of game fish production. Using nutrients in wastewaters to stimulate primary productivity for the production of fish is not a new idea. For centuries, many have relied on this process for supplementing basic nutritional protein. However, typi• cally raw wastewaters are applied as an organic fertilizer with emphasis on fish production, and not necessar• ily on treatment of wastewaters. Little control is exercised over the ecological response of the culture facility, and the high net primary productivity often results in effluents from these aquaculture facilities being of less quality than that of the initial wastewater (Schroeder et aI., 1991). Consequently, these water quality condi• tions generally favor culturing only detrital and filter feeding, as opposed to planktivorous, or gamefish spe• cies desired by sports fishing enthusiasts (Perschbacher, 1995). Generally, pond culturing of desirable game fish in North America has not utilized either raw or treated domestic wastewaters as the primary fertilizing source. Instead, culturing is often more successful when liq• uid inorganic, as opposed to organic fertilizers are used to stimulate phytoplankton production (Qin and Cul• ver, 1992). Such nutrient fertilizers are applied at predetermined ratios in specific volumes and frequencies necessary to sustain adequate desirable food availability for the fish being reared. These "bottom-up" mea• sures (i.e., controlling nutrient resource availability) permit some degree of control over the ecology of the system because it tends to "force" a predicted, and desirable, baseline food source for the system's "top• down" response (i.e., planktivory grazing pressure). Thus, desirable planktivorous fish from the Percidae and Centrarchidae (e.g., walleye, perch, and bass) families can be successfully reared. Current research results indicate that in order to sustain the preferred baseline food sources for optimal plank• tivory production, not only are the nutrient ratios in the fertilization critical, but specific concentration levels of these nutrients in the culture water must be maintained throughout the culture period. For example, in work done with culturing Walleye (Stizostedion vitreum), Helal and Culver (1992) found that applying a fertiliza• tion ratio of inorganic nitrogen to phosphorus of 16-32: 1, applied weekly to maintain concentration levels of 600-900 J.1g/L, and 30 J.1g/L of these respective nutrients, resulted in production of edible algae for those zoop• lankton, primarily Daphnia spp., considered preferred prey for maximum growth and yield of planktivorous fish. When fertilizing with treated wastewaters, the presence of residual suspended solids introduces organic mate• rial, minerals, and other metabolites that may influence the system's nutrient levels, and in tum, the system's ecological response. The operational flexibility of the SBR, based on temporal rather than spatial parameters (Irvine, 1989), provides an opportunity to develop a treatment strategy that results in acceptable treatment performance concomitant with effluents containing appropriate nutrient ratios. These effluents can then be applied as a nutrient fertilizer for an aquaculture component for rearing desirable fish species. In addition, its proven cost-effectiveness makes the SBR an attractive treatment alternative for both public and private sector users (Ketchum et ai., 1979). METHODS A 3,800 L, fiberglass, egg-shaped Sequencing Batch Reactor was used in this study. It is located at the Elkhart Municipal Wastewater Treatment Plant in Elkhart, Indiana. It stands 2.9 meters high and has a maximum diameter of 1.4 meters. It treats approximately 1900 L daily through two 12-hour cycles. The operational sequence is outlined in Table 1. This reactor includes a diffused aeration system at a discharge pressure of 275 kPa (gage), and a coarse bubble air diffuser (driven by a 0.25 kW air pump) providing mixing and aeration of the mixed liquor. No dedicated mixing unit is used. A fixed submersible 0.25 kW pump decants the treated effluent and removes waste activated biomass. The effluent volume withdrawn during the DRAW sequence is controlled by a mechanical float switch. Throughout the study period, mixed liquor suspended solids concen• tration in the reactor ranged from 2500 to 3500 mg/L. Mixed liquor wasting occurred during the REACf I /

A strategy for coupling municipal wastewater treatment

179

period at a rate of 135 Uday. Under these conditions, the reactor operated with a hydraulic retention time of 48 hours and a mean cell residence time of 28 days. Raw, degritted wastewater from the Elkhart plant was treated with this reactor. The influent wastewater is relatively high strength, particularly in ammonia due to industrial discharges. The characteristics are described in Table 2. Six aquaculture tanks having a volume of 550 L were used to monitor the ecological response to the SBR's effluent fertilization. These were arranged in three pairs of two. Each tank was equipped with a limestone fil• ter (average volume of 0.03 cubic meters with rock averaging 20-25 mm in diameter) through which approx• imately one tank volume per hour is circulated to nitrify ammonia and neutralize pH. Suspended 0.75 meters above each tank was a 400-watt metal halide lamp providing simulated sunlight to drive photosynthetic activ• ity. These operated on a 12-hour diel cycle. TABLE 1: SBR OPERATIONAL STRATEGY Reactor Sequence

Time,Drs.

STATIC FILL

0.5

AERATED REACT

8.5

SETTLE

1.0

DRAW

0.5

IDLE

1.5

Total Cycle

12.0

TABLE 2: RAW WASTEWATER CHARACTERISTICS COD, mgIL

CBODs , mgIL

TSS, mgIL

NH 3-N, mgIL

TP, mgIL

Ave. Month

501

240

122

41

4.4

Max. Daily

954

387

239

103

9.5

Min. Daily

293

78

43

14

2.6

Tracking studies were conducted on the SBR to observe the changes in the nitrogenous and phosphorus spe• cies throughout a reaction cycle. The REACT period of the SBR was divided into three intervals. Settled, par• tially treated effluent volumes were withdrawn from these intervals according to the following schedule: 0.5 hours, 3.5 hours, and 8.5 hours, all measured from the beginning of the REACT period. These fertilizing effluents were discharged weekly into the three corresponding aquaculture tank pairs. The fertilizing volumes were determined from the tracking studies based on the mass loadings which would provide 20: 1 nutrient ratios in the tanks at theoretical concentration levels between 350-550 ~gIL and 15-30 ~gIL of inorganic nitrogen and phosphorus, respectively. (The culture waters contained approximately 3 mgIL of residual nitrate and 0.01 mgIL of residual phosphorus prior to initial fertilization). Each pair of tanks were monitored for nutrient levels and algal dominance and abundance responses throughout the culturing period reflecting the level of productivity of the system. Sampling of the aquaculture tanks was done weekly prior to each fer• tilization using a #25 (63 IJ.m) nylon plankton net. Nutrient levels in both the reactor and the aquaculture units were monitored using Standard Methods for the Examination of Water and Wastewater (1992) for determination of ammonia nitrogen, and phosphorus. Field colorimetric kit methods were used to monitor nitrite and nitrate levels. Phase contrast microscopy at 20x power was used to identify and enumerate the algal consortia present.

180

A. K. UMBLE and L. H. KETCHUM. JR

RESULTS Start-up of the SBR took place in April of 1995, and its treatment performance monitored from that time throughout the algal culturing period during the fall of 1995. Performance data are summarized in Table 3. The average removal rates demonstrate that the SBR performed to within the compliance standards required by the City of Elkhart's regulatory discharge permit. The nutrient dynamics occurring within the REACT period from the SBR and their corresponding relative ratios are illustrated in Figure I. Despite the nitrogenous transformation of ammonia to nitrate during the reaction period. concentration of total inorganic nitrogen in the effluents remained within the same order of magnitude. The treatment strategy utilized resulted in a N:P ratio between 16 and 23, well within the ranges recommended by Helal and Culver (1992). The N:P ratio's sensitivity, then, results from the reduction of total phosphorus during the cycle. TABLE 3: SBR PERFORMANCE DATA: CONSTITUENT REMOVAL, IN PERCENT COD,

CBOD 5 ,

TSS,

NH 3-N,

TP,

%

%

%

%

%

Average

90.4

98.5

90.0

88.9

75.2

Maximum

95.5

99.7

97.7

99.9

97.4

Minimum

84.0

9\.9

34.9

36.1

46.9

4OT-----------------, c NH3-N, mgIL o N03-N, mgIL 02-N, mgIL 3 Total P, mgIL N:P Ratio

••

Cone., mglL, 20 or :PRatio

.......

.......

O,.u.;~-fII---"""""''''--..,..---..'''"''''

0.5

I

.....t__-..

I

1st Pair 2nd Pair 3rd Pair Time from Beginning of REACT, Hrs. Fig. I. Nutrient levels and ratios in SBR effluents The nutrient ratios sustained in the aquaculture tanks, and their respective concentrations measured one week and three weeks following the first fertilization inputs arc shown in Figures 2 and 3. Significant variability occurred in the nutrient ratios in each tank pair, as well as in each tank within the pair. After the first week, the ratios averaged 34 but varied from 25 to 44. After the third week, the ratio averaged 49, but again showed sig-

A strategy for coupling municipal wastewaler Irealmenl

181

nificant variability ranging from 22 to 102. TOlal nitrogen and phosphorus concentration levels averaged near 3000 Ilg/L and 100 IlglL, respectively after one week, and similarly after 3 weeks. Interestingly, despite the variability in ratio, there remained a relative degree of constancy over time in the amount of inorganic nitro• gen present in all tanks. The ratio, then, appears sensitive to the level of phosphorus present. These results suggest that despite the controlled input of nutrients into the system. the system's ecological assimilatory response to those resources was not controllable.

60.-----------..., Cone., mgIL N:P 40 Ratio 20

~ IJ

IJ

•

4

o

Total ,mgIL Tot. Inorg.- ,mg/L TP, mgIL

o •

4

Cone., mgIL 2

0

N:P 50 Ratio

Cone., mgIL 2

1 ~~

:

::

,3

41

12

51,1

6,

I

Tank o. & Pairings Fig. 2. Nutrient levels in culture waters after I week

100

T tal ,mgIL Tot. Inorg.-N, mg/L TP, mg/L

c % Scenede mu a % ChIarella • % Diatoms

75

3

41 I 2 5, I I 61 Tank o. & Pairings Fig. 3. Nutrient levels in culture waters after 3 week

100..------------....., % Scenede mu c % Chlorella • % Diatoms D

75 '.'

%of Total 50 Cells

%of Total 50 Cell

25

25

13

41 ,2 51 L.,..:.I_~~ Tank No. & Pairings Fig. 4. Algal response after I week

o

'.'

.'

:::

.. h

I::::.:,

.;

. . , •:•:. •

i

II. ';;.

lo.

,L.,;3:.-_4,,-,1 ,2 5, II 61 Tank No. & Pairings Fig. 5. Algal response after 3 week

The influence of nutrient ratios was gauged by the resulting dominant algal consortiums and their relative abundances occurring in each tank. These results are shown in Figures 4 and 5. It was readily observed that despite the varying nutrient ratios and higher nutrient concentrations than the targets discussed above, each tank exhibited a predominance of Scenedesmus, Chlorella. and Diatom groups throughout the culturing

A. K. UMBLE and L. H. KETCHUM. JR

182

period. At the beginning of the culture period, Scenedesmus made up nearly 75% of the algae observed, with Chlorella and Diatoms comprising approximately the remaining 25%. Near the end of the culture period, the same groups dominated but with the Scenedesmus forming :learly 60% of the total and Chlorella increasing to nearly 30%, and Diatoms the approximate remainder. In particular, Scenedesmus has been found to be a preferred food source for the growth and reproduction of groups of Crustaceans, i.e., zooplankton, known to be preferred prey for the growth of larval and fry planktivorous fish (Helal and Culver, 1992). DISCUSSION The challenge facing the fish-culturist rearing planktivorous species is providing consistent conditions that favor development of preferred food sources for these fish. This task is often undertaken by imposing "bot• tom-up" controls on the ecological system, i.e., controlling the input, and thereby the availability, of nutrient resources. Research has shown that this method of control can influence dominance and abundance of those algal groups most edible for those zooplankton organisms which planktivorous fish species prefer to con• sume. Successful fertilization of inorganic nutrients has been achieved using liquid inorganic fertilizers applied at nitrogen to phosphorus ratios of 16-32: 1 in frequencies necessary to sustain concentrations of 600• 900 JlgIL, and 30 JlgIL of nitrogen and phosphorus, respectively, in the culture waters (Helal 1992). In this study, treated wastewaters were used as the fertilization source. The treatment reactor was monitored to deter• mine if such nutrient conditions could be generated, and the aquaculture waters monitored to determine if the nutrient levels could be sustained, and if preferred edible algal groups would dominate using this fertilization approach. The significance of these parameters were gauged by the ecological response of the system. The results of this study indicate that defining a specific interval within the SBR's REACT period to withdraw partially treated effluents for fertilization may nol be as significant as the nutrient ratio itself. Throughout the duration of the aerobic REACT sequence, the total nitrogen within the reactor remained relatively constant. While the concentration of ammonia declined during nitrification, the oxidized forms of nitrogen simply replaced the ammonia. Therefore. fertilizing with effluents from within particular intervals of the REACT period may not be necessary since each interval results in an acceptable ralio. But, it may indeed be a neces• sary procedure if the varying concentrations of the different nitrogenous species present within any given interval influence the algal response of the aquaculture system. This, however, was not found to be true in this study. Despite consistent inputs from the SBR, little uniformity in nutrient ratio occurred in the tanks throughout the culture period. This was true even for both tanks within each pair fertilized with the same effluents. The fac• tor controlling this ratio variability was the concentration of phosphorus, indicating that phosphorus was the limiting nutrient throughout the culture period. Though the nutrient ratio varied in each tank throughout the culture period, the dominant algal response in each tank consisted of those groups considered preferred food sources for zooplankton. This occurred even though the relative concentrations of the nutrients were significantly higher than the targets suggested by Helal and Culver (1992). This implies that edible algal dominance may be most sensitive to nutrient ratio inputs and concomitant nutrient levels during initial productivity stages. But once dominance is established, the algae may be less sensitive to narrow nutrient ratio ranges and the actual magnitude of nutrient levels present. Indeed, they may become able to tolerate broader ranges in both parameters. This may hold until an algal crash occurs. If, however, top-down grazing pressures, in the fonn of zooplankton and fish, are imposed on the system prior to the crash, conceivably, this grazing pressure could provide ecological balance. This bal• ance would in turn permit the edible algal groups to maintain dominance throughout a prolonged culture period. This hypothesis is being investigated in studies now underway.

A strategy for coupling municipal wastewater treatmenl

183

CONCLUSION The SBR is a flexible, bigh-perfonnance treatment system for the removal of organic material and suspended solids. In this study, instead of utilizing the SBR to remove inorganic nutrients, these were recovered through aquaculture. Operating strategies can be developed to assure that the SBR will deliver acceptable relative ratios, and ranges of mass loadings of inorganic nutrients in the effluents, necessary for fertilization of an aquaculture system. The consistent dominant edible green algal response of the aquaculture component indicates that the SBR's effluent fertilizer sustained desired food sources, and that the response is not sensitive to effluents from differ• ent intervals within the REACf sequence. This implies that fertilization can be readily incorporated and auto• mated into the overall SBR operational strategy thereby reducing capital cost and labor inputs. The fertilization parameters of N:P ratios between 16-32 to maintain nutrient concentrations of between 500- lOOO ~gIL and 30 ~gIL of nitrogen and phosphorus, respectively, until preferred edible algal dominance is estab• lished appear appropriate. Fertilization frequency thereafter depends on whether the same nutrient ratio and mass inputs sustain the dominance of the edible greens. In this study, weekly fertilizations were adequate. ACKNOWLEDGEMENTS The authors wish to thank the University of Notre Dame and the U.S. Department of Education for their sup• port in this work. In addition, the City of Elkhart has provided substantial "in-kind" contributions to this project by providing facilities, utilities, analytical support, and personnel. REFERENCES Helal, H. A., Culver, D.A. (1992). Effects of manipulation of the nitrogen to phosphorus ratio in inorganic fer• tilization of fish rearing ponds. Federal Aid in Fish Restoration Project F-57-R·8-14. Ohio Depart• ment of Natural Resources, Division of Wildlife. March I, I987-June 30, 1992, pp. 11.1-11.61. Irvine, R. L., Ketchum, Jr., L. H. (1989). Sequencing batch reactors for biological wastewater treatment. CRC Critical Reviews in Environmental Control, 18, 255-294. Jewell, W. 1. (1994). Resource-recovery wastewater treatment. American Scientist, 82, 366-375. Ketchum, Jr., L.R., Irvine, R.L., Liao, P.C. (1979). First cost analysis of sequencing batch biological reactors. Journal Water Pollution Control Federation. 51,288-297. Perschbacher, P.W. (1995). Algal management in intensive channel catfish production trials. World Aquacul• ture, 26(3), 65-68 Qin, J.G., Culver, D.A. (1992). The survival and growth of larval Walleye, Stjzostedjon vjtreum, and trophic dynamics in fertilized ponds. Federal Aid in Fish Restoration Project F-57·R·8·J4. Ohio Department of Natural Resources, Division of Wildlife. March I, 1987-June 30,1992, pp. III.I-rn.43. Schroeder, G.L., Alkon, A., Laber, M. (1991). Nutrient flow in pond aquaculture syslems. In: Aquaculture and Water Quality, Brune, D.E., Tomasso, J.R. (Eds.), World Aquaculture Society, Baton Rouge, LA, pp. 489-505.

184

A. K. UMBLE and L. H. KETCHUM. JR

Standard Methods for the Examination ofWater and Wastewater (1992). Greenberg, AE., Clesceri, L.S., Eaton, AD., (Eds.), American Public Health Association, American Water Works Association, Water Environment Federation, pp. 2.57. 4.81, 4.112 Vymazal, J. (1989). Use ofperiphyton for nutrient removal from waters. In: Constructed Wetlands for Waste• water Treatment: Municipal, Industrial and Agricultural. D.A Hammer, (Ed.), Lewis Publishers, Inc., Chelsea, Michigan, pp. 558-564.