- Email: [email protected]
aerobic treatment system for dairy shed wastewater
J. agric. Engng Res. (1981) 26, 499-507
An Anaerobic/Aerobic
Treatment
System for Dairy Shed
Wastewater 1. Design
and Overall
System Performance
D. J. WARBURTON*; H. MELCER~; R. M. CLARKE*
A 2-stage system was developed for the treatment of dairy shed wastewater.’ It consisted of an unmixed uninsulated anaerobic tank of 5-10 days hydraulic residence time followed by a stone media trickling filter over which the waste was circulated for periods of l-3 days. One field-scale and 2 laboratory-scale plants were constructed to facilitate comparison between treatments. This paper, which is the first in a series of three, describes the plants and discusses the experimental design. The characteristics of the dairy shed wastewater are presented and a summary of overall plant performance is given. The second and third papers describe the performance of the anaerobic and aerobic phases, respectively. The experiment shows that an average COD removal of 70% in the anaerobic phase was unaffected by loading rate. The aerobic phase removed 66% COD at the optimum experimental conditions. The final discharge from the aerobic tank, under these conditions, was 700 mg/l COD. This provided an overall treatment efficiency of 89.5 %. Changes in plant operating conditions altered its treatment efficiency. 1.
Introduction
The high organic loading of dairy shed (milking parlour) wastewater has precluded its direct discharge to natural receiving waters in New Zealand. Typical COD values range from 5000 to 8000 mg/l. Spray disposal directly on to pasture has been widely practised,* but high maintenance, labour and management requirements have generated adverse criticism and farmer resistance. The main alternative, anaerobic/aerobic lagooning, is being used increasingly, but the area of land removed from grazing, and the lack of any return from the wastewater for irrigation or fertilizer, may impose high opportunity costs. These problems prompted this investigation into a more compact system with the potential for recycle of the treated wastewater, but without significantly increasing the complexity of treatment. A 2-stage anaerobic/aerobic system, comprising an unmixed, unheated anaerobic phase followed by trickling filtration was selected for study. Reported work on anaerobic lagoons3-* and sedimentation studies9-‘* indicate that loading rate has little influence on treatment efficiency and that settling alone can remove 60% of the COD. This suggests that unmixed ponds could be loaded at high rates (greater than 0.6 kg COD m- 3 d-l) with low mean hydraulic residence times (less than 10 days) without significantly reducing performance and that lagoon sizes could be reduced to save productive land. A second, aerobic phase was considered essential since anaerobic lagoon discharges contain too great an organic loading for direct release to a natural water-course and often present odour and salt accumulation problems when used for recycle cleaning and spray irrigation!3 Trickling filtration was selected over other aerobic processes because resilience to shock loading, low maintenance and minimum land use14-16 make it suitable for a dairy farm. A final clarifier was not included in the treatment sequence to minimize the complexity of operation. * Agricultural Engineering Department, Massey University, Palmerston North, New Zealand t Biotechnology Department, Massey University, Palmerston North, New Zealand Received
11 December
1978; accepted in revised form 26 August
1981
499 0021~8634/81/060499+09
$02.00~0
0 1981 The British Society for Research in Agricultural
Engineering
TREATMENT
500
COD BOD TS vs DO NO,-N NH,-N DKN TKN DIP TDP TP TDN TPN TN DOP TPP
FOR
DAIRY
SHED
WASTEWATER.
I
ABBREVIATIONS Total Chemical Oxygen Demand Total 5-day Biochemical Oxygen Demand at 20°C (no soluble fractions were analysed) Total Solids Volatile Solids Dissolved Oxygen Nitrate Nitrogen Ammoniacal Nitrogen Dissolved Kjeldahl Nitrogen Total Kjeldahl Nitrogen Dissolved Inorganic Phosphate Total Dissolved Phosphate Total Phosphate Total Dissolved Nitrogen = DKN + NO 8-N Total Particulate Nitrogen = TKN-DKN Total Nitrogen = TKN + NO,-N Dissolved Organic Phosphate = TDP - DIP Total Particulate Phosphate = TP-TDP
2.
Experimental design
The main control variables for this type of wastewater treatment system were identified as: (1) anaerobic residence time (A); (2) aerobic residence time (B) and (3) trickling filter recycle ratio (C). Initial studies were conducted to assess the effect of these factors on each experimental setting.’ The rate of biological film growth and COD removal indicated that 3 weeks would be required to reach equilibrium in the aerobic section and that 5-8 weeks would be required to reach equilibrium in the anaerobic tank. A totally randomized experimental design, using a minimum of 3 treatment levels for each variable and incorporating these stabilization periods between each set of variables, required an TABLE I
Treatment combinations for a J-level nested factorial design experiment for laboratory plants Blocks Treatment variable
-______ Z AZ
Anaerobic holding time (A) Aerobic hording time (B) Recycle rate (C)
cz czz
czzz
I
BZ -___ &Cl BIG
B,C,
zz
I
HZ
AIZ
AZZZ
BZZ
BZZZ
BG B&z
B&I BaCz
As
AS
B,C,
f&S,
YZ
f4"I
D.
J.
WARBURTON;
H.
MELCER;
R.
M.
501
CLARKE
unacceptably long time and a 3-level nested factorial design was therefore used. The anaerobic residence times formed the three main blocks, with the aerobic residence time and recycle rate confounded within each block (Table 1). This design allowed anaerobic residence time to be held constant over longer periods without affecting the time required for each treatment. The procedure did not, however, allow separation of anaerobic treatment effects from block effects due to blocking over time. Consequently it was not statistically possible to confirm whether the differences in results between anaerobic settings were due to the loading rates or other variables. Uncontrolled factors such as climate, raw wastewater composition and animal feed composition were monitored but the changes in these characteristics were not large enough to affect overall performance significantly. Allowing 3 weeks for aerobic acclimatization and 1 week for monitoring, a total of 4 weeks was required per setting. To reduce the experimental period further and to allow comparison between the performance of similar systems, 2 identical laboratory-scale plants were constructed. The 9 aerobic treatment variables (3 x 3) within each block, plus 1 repeat treatment, were randomly divided between each laboratory plant. The 5 aerobic treatments per anaerobic setting in each of the laboratory plants gave a total experimental period of 60 weeks. A field-scale pilot plant was also constructed to enable scale effects to be assessed. However, with 2 laboratory plants being used to test all the experimental variables, it was necessary to select treatments for the field-scale plant so that the variables would be confounded. The procedure was based on Snedecor and Cochran19 and is shown in Table II. Detailed statistical analysis of the data defining the performance of the trickling filter is presented in Paper III. Anaerobic treatment data is examined in Paper II but is not subjected to the same statistical analysis in view of limitations in the experimental design. TABLE II
Confounding of field plant treatments AI
I
AII
AI11
Note: Confounding aerobic treatments (Table I) into 3 groups allowed each to be randomly allocated to one of the anaerobic treatment blocks
3.
Plant design and construction
On the basis of earlier work,‘, 16-20 the following values of control variables A, B and C were selected. A-Anaerobic residence time (days) 5.0, 7.5, 10.0 B-Aerobic residence time (days) 1.0, 2.0, 3.0 C-Recycle ratio (daily volume pumped over the filter/total daily input to the 5 : 1 (2.8) system). Corresponding hydraulic loading rates (m3 wastewater/m2 filter 20 : 1 (10.0) cross-sectional area/day) are given in parentheses. 35 : 1 (18-4) Fig. I is a schematic diagram of the laboratory plants and Fig. 2 is a photograph of 1 of the 2 plants. A proportional sampler was used at the cowshed to obtain wastewater for the 3 plants.’ The laboratory plants were loaded by hand and a hydraulic loading rate of approximately O*OOlfullscale was selected for them to allow convenient sample size and plant dimensions. This required
502
TREATMENT
FOR
DAIRY
SHED
WASTEWATER.
I
ROW wastewater
Trickling filk.,
Recycle
-
c
Final discharge F
t I’
I Aerobic tank C
* Multiple
outlets
Fig. I. Schematic diagram of laboratory treatment plant
twice-daily loadings of 0.004 m3 (Fig. 2,A), and called for anaerobic tank dimensions of 0.50~ 0.32 x0.56 m (Fig. 2,B). At the maximum detention time of 10 days an operating volume of 0.08 m3 resulted. The tanks were constructed from galvanized sheet metal with a clear plastic front to allow visual inspection of the accumulating solids. Discharge tappings were made to prevent discharge of floating solids. A 1.8 x 0.14 m diameter plastic tube was used to house each of the laboratory-scale trickling filters to allow visual inspection of the biological film and fluid flow (Fig. 2,D). The filter was covered with foil to prevent algal growth by maintaining light-free conditions in the filter. The tubes were mounted above the aerobic tanks and a medium of 19 mm stones was selected for economic reasons. Aerobic tank construction was similar to the anaerobic tank with dimensions of 0.35 x0.25x0*30 m (Fig. 2,C). The recycle intakes were in the upper half of the aerobic
Fig. 2. Anaerobic/aerobic laboratory treatment plant
D.
.I.
WARBURTON;
H.
MELCER;
R.
M.
503
CLARKE
holding tank to minimize the intake of settled solids. The flow through the treatment plants was achieved by displacement. Multiple discharge outlets in both anaerobic and aerobic tanks allowed control of detention time. A 4.5 m3 concrete tank was used for the anaerobic phase in the field-scale plant and this gave a scale factor of approximately 56 times that of the laboratory plants. All other design criteria were scaled to maintain similar operating conditions and to utilize available materials. Fig. 3 is a schematic diagram of the field plant, a photograph of which appears in Fig. 4. TrCe~ling Anaerobic tank R
n-
* Multiple outlets
Final discharge
??
Aerobic tank C
Fig. 3. Schematic diagram offield treatment plant
Fig. 4. Anaerobic/aerobic
4.
field treatment plant
Results
Samples were taken for analysis from the raw wastewater, the anaerobic outlet, the top of the trickling filter, the bottom of the trickling filter, and the final discharge. This sampling enabled each phase to be analysed separately, as well as allowing the performance of the whole plant to be determined.
504
TREATMENT TABLE
FOR
DAIRY
SHED
WASTEWATER.
I
111
Dairy shed wastewater characteristics
Parameter * COD BOD TV%) VS (%TS) DO NO,-N NH,-N DKN TKN DIP TDP TP TDN TPN TN DOP TPP
* Abbreviations
Mean,
trig/l unless statea
Standard deviation
Range
1326 3000-l 1,000 1510 469 9.50-3200 0.72 0.176 0.24-1.17 68.3 5.12 53-75 1.41 5.0 1.1-6.8 2.9 1.75 1.1-3.1 9.86 26.4 14.2-45.6 115.0 294-228.5 60 208.0 79 81.5-360.0 4.5 1.59 2.8-7.4 6.5 3.15 3.0-12.3 11.38 35.2 21 d-54.4 1lCulated values based on the above d;ata) Cc;, 117.9 90.0 207.9 I 1.98 28.71 6600
I
are defined in the text
Twice-daily milking at the dairy shed generated approximately 35 1 of wastewater per cowmilking over a 20-30 min cleaning period .’ The wastewater consisted of mud (carried in by the cows from the pasture), dung and urine washed from the holding yards, and milking machine washings. This wastewater discharge exerted an intermittent organic and hydraulic load on the treatment plants. Average values of measured parameters, which varied during the season*’ are presented in Table III. The range of values and standard deviations indicates the extent of the variations experienced on a daily basis and suggests the need for a significant factor of safety to accommodate these variations in a full-scale plant. Laboratory procedures were in accordance with standard methods.**-*’ The quality of the final discharge is indicated in Table IV. The pH of the wastewater and final discharge did not vary greatly with average values of 8.2 units and 7.3 units, respectively. Although influenced by treatment settings the data show the degree of treatment that was achieved. The 90 % reduction in oxygen demand is generally sufficient to allow stream discharge. The relatively low volumes (approximately 70 1 cow-l d-l) and the intermittent discharge are compatible with legal requirements for liquid discharges in New Zealand.26 The high DO for the wastewater reflects the high pressure hose yard cleaning used at the dairy. The DO levels in the final discharge indicate the degree of organic removal. This is verified by the extent of nitrification achieved. The nutrient levels, particularly the dissolved fractions, are considered high. At present there are no specific guidelines for controlling nutrient discharges in New Zealand. However, land application of the final discharge or re-use of the discharge for yard cleaning, would provide some economic returns and avoid stream pollution. Table V presents the COD and TS results from the field and laboratory plants. The 2 identical laboratory plants gave similar results with the greatest discrepancy occurring at a 3 day aerobic residence time and a 20 : 1 recycle ratio. The variation of 55’A was not significant, and similarly designed and operated plants may be expected to provide similar treatment.
D.
J.
WARBURTON;
H. MELCER;
R.
M.
505
CLARKE TABLE IV
Effluent quality in the haI discharge*
Parametert
Mean, mgll unless stated
COD 640 BOD 145 TS(%) 0.15 VS (%TS) 45.4 DO 3.7 NO,-N 77.0 NH,-N 7.1 DKN 27.4 TKN 44.4 DIP 19.2 TDP 21.2 TP 23.8 (Calculated values based on TDN 104.3 TPN 17.0 TN 121.3 DOP 2.0 TPP 2.6
Range 48&850 110-215 0~11-0~19 41448.4 2.0-6.0 36-122 24-15.1 17.2-37.5 29.2-64.7 14.8-27.0 16.1-31.0 19.8-34.5 he above)
-
* The data are based on maximum aerobic detention times, a 35 : 1 recycle ratio and the results from laboratory and fieldtreatmentplants. The 3 anaerobic treatment blocks were combined together t Abbreviations are defmcd in the text
TABLE V
Plant comparisons for aerobic treatment
Aerobic residence time
Recycle ratio
Plant
.-
LA * LB Ft
20
35
:1
:1
wll
I
2 days
1 day COD FD:,
5:l
_-
-TS FD, %
541 -
0.127
547
oG5
-COD FD, mgll
TS FD, %
715 714 614
0.108 0.104 0.101
3 days
--
COD FD, mgll 633 641
0.113 0.107 0.155 0.161 0.152 0.190 -
1618 -
0.173 -
1650 -
0.232
F
1138
0.144
985
0.209
885 938 939
LA LB
1381 1312 849
0.187
536
0.093
484
,0.194 554
0.102
603
LA LB
F
0.150
_-
TS FD, %
0.161
* 15, and LB are the 2 laboratory plants. The experimental design (1) only allowed one duplicate per recycle setting between the laboratory plants t F= field plant t FD = final effluent discharge
506
TREATMENT
FOR
DAIRY
SHED
WASTEWATER.
I
A comparison of the laboratory and field plant data shows acceptable agreement, except at low residence times and high recycle ratios. The 30% improvement in discharge COD concentrations of the field plant with a 1 day residence and 35 : 1 recycle ratio (Table V) was significant. The greater distance between the filter outlet and final discharge gives improved settling, and the size of the plant makes it less susceptible to small changes. Similar trends were observed with the other data, suggesting that unless operated at low aerobic residence times and high recycle ratios the laboratory and field plants may be considered to achieve similar results. Plant operation presented no problems and labour requirements for operation and maintenance were minimal. 5.
Conclusions
1. Monitoring of the dairy shed wastewater showed large daily variations but mean concentrations were 6600 mg/l COD, 7200 mg/l TS, 208 mg/l TN and 35 mg/l TP with an average discharge volume of 70 1 cow-l d-l. 2. The final discharge from the treatment system was of sufficient quality to allow stream discharge in most cases. However, the level of dissolved nutrients (77 mg/l NO,-N) suggests that the final discharge could be effectively used on the land. 3. Comparison between similarly designed systems showed no significant difference in treatment efficiencies. A scale difference of 56 times between treatment plants also produced effluents of similar quality, except under conditions of low aerobic residence time and high recycle ratios. Since this operating condition did not achieve high treatment efficiencies the difference in treatment with scale is of no practical significance and full-scale performance may be predicted from the data obtained. 4. Labour and maintenance requirements were low during the 15 months of operation. Acknowledgements
The authors wish to acknowledge the assistance of: (1) Messrs Tyler, Compton and Bolter of the Agricultural Engineering Department, Massey University, for the construction of the treatment plants; (2) Professor Townsley of Agricultural Economics and Farm Management Department, Massey University for assistance with the experimental design and (3) Soil Science Department, Massey University, for the Nitrogen and Phosphorus analyses. REFERENCES ’
Warburton, D. J. Studies in anaerobic/aerobic treatment of dairy shed effluent. Ph.D. Thesis, Massey
University, 1977 2 Clarke, R. M. The design and operation of spray disposal systems for dairy farms in New Zealand. Agric. Engng Aust., 1977 6 (1) 10-18 3 Lo&r, R. C. Efluent quality from anaerobic lagoons treating feedlot wastes. Wat. Pollut. Control Fedn Jl, 1967 39 384-391 4 Loelu, R. C.; Ruf, J. A. Anaerobic lagoon treatment of milking-parlour wastes. Wat. Pollut. Control Fedn Jl, 1968 40 83-94 5 Bhagat, S. K.; Proctor, D. E. Treatment of dairy manure by lagooning. Wat. Pollut. Control Fedn Jl, 1969 41 785-795 ’ Nordstedt, R. A.; Baldwin, L. B.; Hortenstine, C. C. Multistage lagoon systems for treatment of dairy farm waste. Proc. Int. Symp. Livestock Waste (Am. Sot. agric. Engrs Pub]. PROC-271), 1971 77-80 ’ Nordstedt, R. A. ; Baldwin, L. B. Sludge accumulation and stratification in anaerobic dairy waste lagoons. Trans. Am. Sot. agric. Engrs, 1975 18 312-315 8 Nordstedt, R. A.; Baldwin, L. B. Sludge management for anaerobic dairy waste lagoons. Proc. 3rd Int. Symp. Livestock Wastes (Am. Sot. agric. Engrs Publ. PROC-275), 1975 535-536 ’ Witzel, S. A.; McCoy, E.; Polkowski, L. B.; Attoe, 0. J.; Nichols, M. S. Physical, chemical and bacteriologicalproperties offarm wastes (bovine animals). Proc. Natn. Symp. Animal Waste Management (Am. Sot. agric. Engrs Publ. SP-0366), 1966 10-14
D.
J.
WARBURTON;
H.
MELCER;
” Sobel, A. T. Physicalproperties
R.
M.
CLARKE
507
of animal manures associated with handling. Proc. Natn. Symp. Animal Waste Management (Am. Sot. agric. Engrs Publ. SP-0366), 1966 27-31 ” Moore, J. A.; Hegg, R. 0.; Scholz, D. C.; Strauman, E. Settling solids in animal waste slurries. Trans. Am. Sot. agric. Engrs, 1975 18 694-698 ” Dugan, G. L.; Young, R. H. F.; Takamiya, G. Animal waste management in Hawaii. Wat. Pollut. Control Fedn Jl, 1973 45 742-750 l3 Missouri Basin Engineering Health Council Waste treatement lagoons-state of the art. E.P.A.17090EHX07/71 ” Bruce, A. M. Percolatingfilters. Process Biochem., 1969 4 19-23 ‘5 National Research Council Sewage treatment at military installations. Sewage Wks Jl, 1946 18 897-982 lb Dow Chemical Company Literature search and critical analysis of biological trickling filter studies. E.P.A.-17050DDY12/71 ’’ Hart, S. A. Digestion tests of livestock wastes. Wat. Pollut. Control Fedn Jl, 1963 35 748-757 ‘* Gramms, K. C.; Polkowski, L. B.; Witzel, S. A. Anaerobic digestion of farm animal wastes (dairy bull, swine andpoultry). Trans. Am. Sot. agric. Engrs, 1971 14 7-13 I9 Snedecor, G. W.; Co&ran, W. G. Statistical Methods (6th edn). Iowa University Press, 1974 593 pp 2o Warburton, D. J.; Clarke, R. M.; Melter, H. Development of an anaerobic/aerobic treatmentplant for dairy shed efluent. Proc. Biotechnol. Conf., Massey University, May 1975 14 pp ” Warburton, D. J.; Clarke, R. M.; Melter, H. Characteristics of dairy shed wastewater for the design of treatment systems. This article was accepted about 12 mths ago with the Australian Ag Engng J. Unfortunately they have run into publication difficulties and we await the outcome. ” A.P.H.A., A.W.W.A. and W.P.C.F. Standard Methods for the Examination of Water and Wastewater (14 edn). Washington, D.C. A.P.H.A. ” Tebutt, T. H. Y.; Berkun, M. Respirometric determination of BOD. Wat. Res., 1976 10 613-617 24 Bremner, J. M.; Keeny, D. R. Steam distillation methods for determination of ammonia, nitrite and nitrate. Analyt. chim. acta, 1965 32 485-495 ” Murphy, J.; Riley, J. P. A modified single solution method for determination of phosphate in natural waters. Analyt. chim. acta, 1962 27 31-36 26 New Zealand Government, N.Z. Water & Soil Conservation Act plus Amendments, Government Legislation, Wellington, 1974 102 pp
An Anaerobic/Aerobic
Treatment
System for Dairy Shed
Wastewater 1. Design
and Overall
System Performance
D. J. WARBURTON*; H. MELCER~; R. M. CLARKE*
A 2-stage system was developed for the treatment of dairy shed wastewater.’ It consisted of an unmixed uninsulated anaerobic tank of 5-10 days hydraulic residence time followed by a stone media trickling filter over which the waste was circulated for periods of l-3 days. One field-scale and 2 laboratory-scale plants were constructed to facilitate comparison between treatments. This paper, which is the first in a series of three, describes the plants and discusses the experimental design. The characteristics of the dairy shed wastewater are presented and a summary of overall plant performance is given. The second and third papers describe the performance of the anaerobic and aerobic phases, respectively. The experiment shows that an average COD removal of 70% in the anaerobic phase was unaffected by loading rate. The aerobic phase removed 66% COD at the optimum experimental conditions. The final discharge from the aerobic tank, under these conditions, was 700 mg/l COD. This provided an overall treatment efficiency of 89.5 %. Changes in plant operating conditions altered its treatment efficiency. 1.
Introduction
The high organic loading of dairy shed (milking parlour) wastewater has precluded its direct discharge to natural receiving waters in New Zealand. Typical COD values range from 5000 to 8000 mg/l. Spray disposal directly on to pasture has been widely practised,* but high maintenance, labour and management requirements have generated adverse criticism and farmer resistance. The main alternative, anaerobic/aerobic lagooning, is being used increasingly, but the area of land removed from grazing, and the lack of any return from the wastewater for irrigation or fertilizer, may impose high opportunity costs. These problems prompted this investigation into a more compact system with the potential for recycle of the treated wastewater, but without significantly increasing the complexity of treatment. A 2-stage anaerobic/aerobic system, comprising an unmixed, unheated anaerobic phase followed by trickling filtration was selected for study. Reported work on anaerobic lagoons3-* and sedimentation studies9-‘* indicate that loading rate has little influence on treatment efficiency and that settling alone can remove 60% of the COD. This suggests that unmixed ponds could be loaded at high rates (greater than 0.6 kg COD m- 3 d-l) with low mean hydraulic residence times (less than 10 days) without significantly reducing performance and that lagoon sizes could be reduced to save productive land. A second, aerobic phase was considered essential since anaerobic lagoon discharges contain too great an organic loading for direct release to a natural water-course and often present odour and salt accumulation problems when used for recycle cleaning and spray irrigation!3 Trickling filtration was selected over other aerobic processes because resilience to shock loading, low maintenance and minimum land use14-16 make it suitable for a dairy farm. A final clarifier was not included in the treatment sequence to minimize the complexity of operation. * Agricultural Engineering Department, Massey University, Palmerston North, New Zealand t Biotechnology Department, Massey University, Palmerston North, New Zealand Received
11 December
1978; accepted in revised form 26 August
1981
499 0021~8634/81/060499+09
$02.00~0
0 1981 The British Society for Research in Agricultural
Engineering
TREATMENT
500
COD BOD TS vs DO NO,-N NH,-N DKN TKN DIP TDP TP TDN TPN TN DOP TPP
FOR
DAIRY
SHED
WASTEWATER.
I
ABBREVIATIONS Total Chemical Oxygen Demand Total 5-day Biochemical Oxygen Demand at 20°C (no soluble fractions were analysed) Total Solids Volatile Solids Dissolved Oxygen Nitrate Nitrogen Ammoniacal Nitrogen Dissolved Kjeldahl Nitrogen Total Kjeldahl Nitrogen Dissolved Inorganic Phosphate Total Dissolved Phosphate Total Phosphate Total Dissolved Nitrogen = DKN + NO 8-N Total Particulate Nitrogen = TKN-DKN Total Nitrogen = TKN + NO,-N Dissolved Organic Phosphate = TDP - DIP Total Particulate Phosphate = TP-TDP
2.
Experimental design
The main control variables for this type of wastewater treatment system were identified as: (1) anaerobic residence time (A); (2) aerobic residence time (B) and (3) trickling filter recycle ratio (C). Initial studies were conducted to assess the effect of these factors on each experimental setting.’ The rate of biological film growth and COD removal indicated that 3 weeks would be required to reach equilibrium in the aerobic section and that 5-8 weeks would be required to reach equilibrium in the anaerobic tank. A totally randomized experimental design, using a minimum of 3 treatment levels for each variable and incorporating these stabilization periods between each set of variables, required an TABLE I
Treatment combinations for a J-level nested factorial design experiment for laboratory plants Blocks Treatment variable
-______ Z AZ
Anaerobic holding time (A) Aerobic hording time (B) Recycle rate (C)
cz czz
czzz
I
BZ -___ &Cl BIG
B,C,
zz
I
HZ
AIZ
AZZZ
BZZ
BZZZ
BG B&z
B&I BaCz
As
AS
B,C,
f&S,
YZ
f4"I
D.
J.
WARBURTON;
H.
MELCER;
R.
M.
501
CLARKE
unacceptably long time and a 3-level nested factorial design was therefore used. The anaerobic residence times formed the three main blocks, with the aerobic residence time and recycle rate confounded within each block (Table 1). This design allowed anaerobic residence time to be held constant over longer periods without affecting the time required for each treatment. The procedure did not, however, allow separation of anaerobic treatment effects from block effects due to blocking over time. Consequently it was not statistically possible to confirm whether the differences in results between anaerobic settings were due to the loading rates or other variables. Uncontrolled factors such as climate, raw wastewater composition and animal feed composition were monitored but the changes in these characteristics were not large enough to affect overall performance significantly. Allowing 3 weeks for aerobic acclimatization and 1 week for monitoring, a total of 4 weeks was required per setting. To reduce the experimental period further and to allow comparison between the performance of similar systems, 2 identical laboratory-scale plants were constructed. The 9 aerobic treatment variables (3 x 3) within each block, plus 1 repeat treatment, were randomly divided between each laboratory plant. The 5 aerobic treatments per anaerobic setting in each of the laboratory plants gave a total experimental period of 60 weeks. A field-scale pilot plant was also constructed to enable scale effects to be assessed. However, with 2 laboratory plants being used to test all the experimental variables, it was necessary to select treatments for the field-scale plant so that the variables would be confounded. The procedure was based on Snedecor and Cochran19 and is shown in Table II. Detailed statistical analysis of the data defining the performance of the trickling filter is presented in Paper III. Anaerobic treatment data is examined in Paper II but is not subjected to the same statistical analysis in view of limitations in the experimental design. TABLE II
Confounding of field plant treatments AI
I
AII
AI11
Note: Confounding aerobic treatments (Table I) into 3 groups allowed each to be randomly allocated to one of the anaerobic treatment blocks
3.
Plant design and construction
On the basis of earlier work,‘, 16-20 the following values of control variables A, B and C were selected. A-Anaerobic residence time (days) 5.0, 7.5, 10.0 B-Aerobic residence time (days) 1.0, 2.0, 3.0 C-Recycle ratio (daily volume pumped over the filter/total daily input to the 5 : 1 (2.8) system). Corresponding hydraulic loading rates (m3 wastewater/m2 filter 20 : 1 (10.0) cross-sectional area/day) are given in parentheses. 35 : 1 (18-4) Fig. I is a schematic diagram of the laboratory plants and Fig. 2 is a photograph of 1 of the 2 plants. A proportional sampler was used at the cowshed to obtain wastewater for the 3 plants.’ The laboratory plants were loaded by hand and a hydraulic loading rate of approximately O*OOlfullscale was selected for them to allow convenient sample size and plant dimensions. This required
502
TREATMENT
FOR
DAIRY
SHED
WASTEWATER.
I
ROW wastewater
Trickling filk.,
Recycle
-
c
Final discharge F
t I’
I Aerobic tank C
* Multiple
outlets
Fig. I. Schematic diagram of laboratory treatment plant
twice-daily loadings of 0.004 m3 (Fig. 2,A), and called for anaerobic tank dimensions of 0.50~ 0.32 x0.56 m (Fig. 2,B). At the maximum detention time of 10 days an operating volume of 0.08 m3 resulted. The tanks were constructed from galvanized sheet metal with a clear plastic front to allow visual inspection of the accumulating solids. Discharge tappings were made to prevent discharge of floating solids. A 1.8 x 0.14 m diameter plastic tube was used to house each of the laboratory-scale trickling filters to allow visual inspection of the biological film and fluid flow (Fig. 2,D). The filter was covered with foil to prevent algal growth by maintaining light-free conditions in the filter. The tubes were mounted above the aerobic tanks and a medium of 19 mm stones was selected for economic reasons. Aerobic tank construction was similar to the anaerobic tank with dimensions of 0.35 x0.25x0*30 m (Fig. 2,C). The recycle intakes were in the upper half of the aerobic
Fig. 2. Anaerobic/aerobic laboratory treatment plant
D.
.I.
WARBURTON;
H.
MELCER;
R.
M.
503
CLARKE
holding tank to minimize the intake of settled solids. The flow through the treatment plants was achieved by displacement. Multiple discharge outlets in both anaerobic and aerobic tanks allowed control of detention time. A 4.5 m3 concrete tank was used for the anaerobic phase in the field-scale plant and this gave a scale factor of approximately 56 times that of the laboratory plants. All other design criteria were scaled to maintain similar operating conditions and to utilize available materials. Fig. 3 is a schematic diagram of the field plant, a photograph of which appears in Fig. 4. TrCe~ling Anaerobic tank R
n-
* Multiple outlets
Final discharge
??
Aerobic tank C
Fig. 3. Schematic diagram offield treatment plant
Fig. 4. Anaerobic/aerobic
4.
field treatment plant
Results
Samples were taken for analysis from the raw wastewater, the anaerobic outlet, the top of the trickling filter, the bottom of the trickling filter, and the final discharge. This sampling enabled each phase to be analysed separately, as well as allowing the performance of the whole plant to be determined.
504
TREATMENT TABLE
FOR
DAIRY
SHED
WASTEWATER.
I
111
Dairy shed wastewater characteristics
Parameter * COD BOD TV%) VS (%TS) DO NO,-N NH,-N DKN TKN DIP TDP TP TDN TPN TN DOP TPP
* Abbreviations
Mean,
trig/l unless statea
Standard deviation
Range
1326 3000-l 1,000 1510 469 9.50-3200 0.72 0.176 0.24-1.17 68.3 5.12 53-75 1.41 5.0 1.1-6.8 2.9 1.75 1.1-3.1 9.86 26.4 14.2-45.6 115.0 294-228.5 60 208.0 79 81.5-360.0 4.5 1.59 2.8-7.4 6.5 3.15 3.0-12.3 11.38 35.2 21 d-54.4 1lCulated values based on the above d;ata) Cc;, 117.9 90.0 207.9 I 1.98 28.71 6600
I
are defined in the text
Twice-daily milking at the dairy shed generated approximately 35 1 of wastewater per cowmilking over a 20-30 min cleaning period .’ The wastewater consisted of mud (carried in by the cows from the pasture), dung and urine washed from the holding yards, and milking machine washings. This wastewater discharge exerted an intermittent organic and hydraulic load on the treatment plants. Average values of measured parameters, which varied during the season*’ are presented in Table III. The range of values and standard deviations indicates the extent of the variations experienced on a daily basis and suggests the need for a significant factor of safety to accommodate these variations in a full-scale plant. Laboratory procedures were in accordance with standard methods.**-*’ The quality of the final discharge is indicated in Table IV. The pH of the wastewater and final discharge did not vary greatly with average values of 8.2 units and 7.3 units, respectively. Although influenced by treatment settings the data show the degree of treatment that was achieved. The 90 % reduction in oxygen demand is generally sufficient to allow stream discharge. The relatively low volumes (approximately 70 1 cow-l d-l) and the intermittent discharge are compatible with legal requirements for liquid discharges in New Zealand.26 The high DO for the wastewater reflects the high pressure hose yard cleaning used at the dairy. The DO levels in the final discharge indicate the degree of organic removal. This is verified by the extent of nitrification achieved. The nutrient levels, particularly the dissolved fractions, are considered high. At present there are no specific guidelines for controlling nutrient discharges in New Zealand. However, land application of the final discharge or re-use of the discharge for yard cleaning, would provide some economic returns and avoid stream pollution. Table V presents the COD and TS results from the field and laboratory plants. The 2 identical laboratory plants gave similar results with the greatest discrepancy occurring at a 3 day aerobic residence time and a 20 : 1 recycle ratio. The variation of 55’A was not significant, and similarly designed and operated plants may be expected to provide similar treatment.
D.
J.
WARBURTON;
H. MELCER;
R.
M.
505
CLARKE TABLE IV
Effluent quality in the haI discharge*
Parametert
Mean, mgll unless stated
COD 640 BOD 145 TS(%) 0.15 VS (%TS) 45.4 DO 3.7 NO,-N 77.0 NH,-N 7.1 DKN 27.4 TKN 44.4 DIP 19.2 TDP 21.2 TP 23.8 (Calculated values based on TDN 104.3 TPN 17.0 TN 121.3 DOP 2.0 TPP 2.6
Range 48&850 110-215 0~11-0~19 41448.4 2.0-6.0 36-122 24-15.1 17.2-37.5 29.2-64.7 14.8-27.0 16.1-31.0 19.8-34.5 he above)
-
* The data are based on maximum aerobic detention times, a 35 : 1 recycle ratio and the results from laboratory and fieldtreatmentplants. The 3 anaerobic treatment blocks were combined together t Abbreviations are defmcd in the text
TABLE V
Plant comparisons for aerobic treatment
Aerobic residence time
Recycle ratio
Plant
.-
LA * LB Ft
20
35
:1
:1
wll
I
2 days
1 day COD FD:,
5:l
_-
-TS FD, %
541 -
0.127
547
oG5
-COD FD, mgll
TS FD, %
715 714 614
0.108 0.104 0.101
3 days
--
COD FD, mgll 633 641
0.113 0.107 0.155 0.161 0.152 0.190 -
1618 -
0.173 -
1650 -
0.232
F
1138
0.144
985
0.209
885 938 939
LA LB
1381 1312 849
0.187
536
0.093
484
,0.194 554
0.102
603
LA LB
F
0.150
_-
TS FD, %
0.161
* 15, and LB are the 2 laboratory plants. The experimental design (1) only allowed one duplicate per recycle setting between the laboratory plants t F= field plant t FD = final effluent discharge
506
TREATMENT
FOR
DAIRY
SHED
WASTEWATER.
I
A comparison of the laboratory and field plant data shows acceptable agreement, except at low residence times and high recycle ratios. The 30% improvement in discharge COD concentrations of the field plant with a 1 day residence and 35 : 1 recycle ratio (Table V) was significant. The greater distance between the filter outlet and final discharge gives improved settling, and the size of the plant makes it less susceptible to small changes. Similar trends were observed with the other data, suggesting that unless operated at low aerobic residence times and high recycle ratios the laboratory and field plants may be considered to achieve similar results. Plant operation presented no problems and labour requirements for operation and maintenance were minimal. 5.
Conclusions
1. Monitoring of the dairy shed wastewater showed large daily variations but mean concentrations were 6600 mg/l COD, 7200 mg/l TS, 208 mg/l TN and 35 mg/l TP with an average discharge volume of 70 1 cow-l d-l. 2. The final discharge from the treatment system was of sufficient quality to allow stream discharge in most cases. However, the level of dissolved nutrients (77 mg/l NO,-N) suggests that the final discharge could be effectively used on the land. 3. Comparison between similarly designed systems showed no significant difference in treatment efficiencies. A scale difference of 56 times between treatment plants also produced effluents of similar quality, except under conditions of low aerobic residence time and high recycle ratios. Since this operating condition did not achieve high treatment efficiencies the difference in treatment with scale is of no practical significance and full-scale performance may be predicted from the data obtained. 4. Labour and maintenance requirements were low during the 15 months of operation. Acknowledgements
The authors wish to acknowledge the assistance of: (1) Messrs Tyler, Compton and Bolter of the Agricultural Engineering Department, Massey University, for the construction of the treatment plants; (2) Professor Townsley of Agricultural Economics and Farm Management Department, Massey University for assistance with the experimental design and (3) Soil Science Department, Massey University, for the Nitrogen and Phosphorus analyses. REFERENCES ’
Warburton, D. J. Studies in anaerobic/aerobic treatment of dairy shed effluent. Ph.D. Thesis, Massey
University, 1977 2 Clarke, R. M. The design and operation of spray disposal systems for dairy farms in New Zealand. Agric. Engng Aust., 1977 6 (1) 10-18 3 Lo&r, R. C. Efluent quality from anaerobic lagoons treating feedlot wastes. Wat. Pollut. Control Fedn Jl, 1967 39 384-391 4 Loelu, R. C.; Ruf, J. A. Anaerobic lagoon treatment of milking-parlour wastes. Wat. Pollut. Control Fedn Jl, 1968 40 83-94 5 Bhagat, S. K.; Proctor, D. E. Treatment of dairy manure by lagooning. Wat. Pollut. Control Fedn Jl, 1969 41 785-795 ’ Nordstedt, R. A.; Baldwin, L. B.; Hortenstine, C. C. Multistage lagoon systems for treatment of dairy farm waste. Proc. Int. Symp. Livestock Waste (Am. Sot. agric. Engrs Pub]. PROC-271), 1971 77-80 ’ Nordstedt, R. A. ; Baldwin, L. B. Sludge accumulation and stratification in anaerobic dairy waste lagoons. Trans. Am. Sot. agric. Engrs, 1975 18 312-315 8 Nordstedt, R. A.; Baldwin, L. B. Sludge management for anaerobic dairy waste lagoons. Proc. 3rd Int. Symp. Livestock Wastes (Am. Sot. agric. Engrs Publ. PROC-275), 1975 535-536 ’ Witzel, S. A.; McCoy, E.; Polkowski, L. B.; Attoe, 0. J.; Nichols, M. S. Physical, chemical and bacteriologicalproperties offarm wastes (bovine animals). Proc. Natn. Symp. Animal Waste Management (Am. Sot. agric. Engrs Publ. SP-0366), 1966 10-14
D.
J.
WARBURTON;
H.
MELCER;
” Sobel, A. T. Physicalproperties
R.
M.
CLARKE
507
of animal manures associated with handling. Proc. Natn. Symp. Animal Waste Management (Am. Sot. agric. Engrs Publ. SP-0366), 1966 27-31 ” Moore, J. A.; Hegg, R. 0.; Scholz, D. C.; Strauman, E. Settling solids in animal waste slurries. Trans. Am. Sot. agric. Engrs, 1975 18 694-698 ” Dugan, G. L.; Young, R. H. F.; Takamiya, G. Animal waste management in Hawaii. Wat. Pollut. Control Fedn Jl, 1973 45 742-750 l3 Missouri Basin Engineering Health Council Waste treatement lagoons-state of the art. E.P.A.17090EHX07/71 ” Bruce, A. M. Percolatingfilters. Process Biochem., 1969 4 19-23 ‘5 National Research Council Sewage treatment at military installations. Sewage Wks Jl, 1946 18 897-982 lb Dow Chemical Company Literature search and critical analysis of biological trickling filter studies. E.P.A.-17050DDY12/71 ’’ Hart, S. A. Digestion tests of livestock wastes. Wat. Pollut. Control Fedn Jl, 1963 35 748-757 ‘* Gramms, K. C.; Polkowski, L. B.; Witzel, S. A. Anaerobic digestion of farm animal wastes (dairy bull, swine andpoultry). Trans. Am. Sot. agric. Engrs, 1971 14 7-13 I9 Snedecor, G. W.; Co&ran, W. G. Statistical Methods (6th edn). Iowa University Press, 1974 593 pp 2o Warburton, D. J.; Clarke, R. M.; Melter, H. Development of an anaerobic/aerobic treatmentplant for dairy shed efluent. Proc. Biotechnol. Conf., Massey University, May 1975 14 pp ” Warburton, D. J.; Clarke, R. M.; Melter, H. Characteristics of dairy shed wastewater for the design of treatment systems. This article was accepted about 12 mths ago with the Australian Ag Engng J. Unfortunately they have run into publication difficulties and we await the outcome. ” A.P.H.A., A.W.W.A. and W.P.C.F. Standard Methods for the Examination of Water and Wastewater (14 edn). Washington, D.C. A.P.H.A. ” Tebutt, T. H. Y.; Berkun, M. Respirometric determination of BOD. Wat. Res., 1976 10 613-617 24 Bremner, J. M.; Keeny, D. R. Steam distillation methods for determination of ammonia, nitrite and nitrate. Analyt. chim. acta, 1965 32 485-495 ” Murphy, J.; Riley, J. P. A modified single solution method for determination of phosphate in natural waters. Analyt. chim. acta, 1962 27 31-36 26 New Zealand Government, N.Z. Water & Soil Conservation Act plus Amendments, Government Legislation, Wellington, 1974 102 pp