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Experimental study of high rate pond system treating piggery wastewater
8
Pergamon
Wat. Sci. Tech. Vol. 34, No. II, pp, 125-132,1996. CopyrightC 1996IAWQ.Publishedby ElsevierScience Ltd. Printedin Great Britain.All rightsreserved. 0273-1223/96 SI~'OO + l}OO
PU: 80273-1223(96)00920-1
EXPERIMENTAL STUDY OF HIGH RATE POND SYSTEM TREATING PIGGERY WASTEWATER Baozhen Wang, Wenyi Dong, Jinlan Zhang and Xiangdong Cao Water Pollution Control Research Centre, Harbin University ofArchitecture and Engineering, 144 DazhiStreet, Harbin 150006, China
ABSTRACf The results of an experimental study conducted in a full-scale high rate pond system treating piggery wastewater at Jianfengshan Piggery. Panyu City. Guandong Province. are presented. The systemconsistsof twoadvanced anaerobic ponds(AAP) in parallel, followed by an anaerobic transformation pond(ATP) and a five-cell algae-bacterial pond (ABP). The mechanism of the AAP is described and the hydraulic flow pattern analyzed. Fermentation pits (FP) built on the bottom performed very efficiently. operating like UASB in principle. A newconceptof ATP is advanced, basedon its abilityto transform poorlydegradable materials to moreeasilydegradable ones.It wasfound in the studythat the HRPsystemwasmore efficient, morereliable and saved 40% land area compared witha conventional pondsystem. Economic analysesof both the energy consumption and the benefitto the pond systemof fish farming are also included in the paper.Copyright e 1996IAWQ. Published by ElsevierScienceLtd.
KEYWORDS Advanced anaerobic pond (AAP); anaerobic fermentation pit; anaerobic transform pond (ATP); algae/bacterialpond (ABP); piggery wastewater. INTRODUCfION With the rapid development of large-scale piggeries in South China, highly organic piggery wastewater has become an increasingly serious pollution source. As the wastewater is rich in organic and nutrient materials, it is easy to over-fertilize the farmland when applying it and make receiving waters eutrophic. Therefore, it is imperative to find a way to treat the piggery wastewater efficiently and economically. The characteristics of piggery wastewaters vary widely owing to the different methods for manure cleaning, and hence the treatment methods are different as well. In China, although there are many methods employed for piggery wastewater treatment, such as digestion pits in rural areas, two-step fermentation (Zhang, 1989), and activated sludge processes (Xu, 1993), the treatment efficiencies are usually very low, or they consume too much energy. Land treatment (EPA, 1979) is an appropriate method to return nutrients to farmland; however, the soil will get saturated for a certain time, and the underground water will probably be polluted through percolation.
125
B. WANGetaL
126
Considering that the annual average temperature in Pearl River Delta area is over 21°C, and that there are over 2000 h of sunshine annually, the application of a pond system for piggery wastewater treatment is attractive due to lots of advantages, such as low capital and operating/maintenance costs, low energy consumption, simplicityand ease of operation and maintenance, and stability in performance (Wang, 1984, 1991). However, the rapidly increasing cost of land has greatly hindered the popularization and application of conventional pond systems which occupy too much land area. The high rate pond system developed by the authors performsmuch better than conventional pond systemsby means of a much higherconcentration of more active biomass in the form of anaerobic sludge in advanced anaerobic pond submerged biofilm in anaerobic transformation pond as well as better flow regime close to plug flow, which make the system operate at higher hydraulic and organicloadingrates, thus reducing the land area. The high rate pondsystem consists of advanced anaerobic pond(AAP) (Oswald, 1967), anaerobic transform pond(ATP), AlgaelBacterial pond and fish pond. It is shown from the study that HRPScan treat piggerywastewater very efficiently and economically. Compared with ordinary stabilization pond system, it saved land area by 50 percent. EXPERIMENTAL SITE AND METHOD
Experimental site. This was a full-scale experiment, carried out at Jianfengshan Piggery in Panyu City, Guangdong Province. The piggery was originally built in 1988, located on the Jianfengshan Hill. Near the foot of the hill, there is a reservoir with 3 ha of water surface for farmland irrigation. The wastewater from the piggery (140 m3 per day) was discharged into the reservoir without any treatment before the plant was built, and thus all the fish and shrimp died of heavy pollution, and the farmland got over-fertilized when irrigated by the polluted water, and once became black, with an offensive smell. The quality of the piggery wastewateris shown in Table 1. Table 1. Analytical results of piggery wastewater in the test Parameter
COD..
BODs
55
TN
TP
pH
(mgll)
11000-17000
5000-8000
2000-8000
420-700
80-130
7-8.5
In order to control and tackle the above-mentioned pollution, a high rats pond system was built with a total treatmentcapacity of 140 mlfd. All of the unit ponds in the system were constructed with stone blocks and waterproof cement-sand grout as binder. The final flow sheet is: Pre-treatment including primary settling basins and equalization basin ~ Advanced Anaerobic Ponds(AAP) ~ Anaerobic Transformation ponds(ATP) ~ Symbiotic AIgaelBacterial ponds(ABP) ~ Effluent to reservoir as fish pond. The plan and flow chart are shown in Figures I and 2 respectively, and the design parameters of the unit ponds in the system are shown in Table 2. Table 2. The main design parameters on the pond system Pond Type Organic Loading Rate(KgBODslm'.d) Pond Depth (m) Retention Time (d) Occupied Area (m') Effective Volume (m')
AAP
ATP
ABP
3.3
0.24 3.80 2.2 120 300
1.20 7.1 950
4.00 (+ 1.0 in pits) 2.2 90
300
3
1000
The pond system was characterized by the following: (i) some fermentation pits were built on the front part of the bottom in the AAT and the inlets werejust built on the bottomof the fermentation pits, whichoperate like UASB in principlewith upflowpattern; (ii) fibrous carriers fixed on circular plates were packedin front
Highrate pondsystemtreatingpiggerywastewater
127
part of ATP for the purpose of the increase and even distribution of biomass in the form of submerged biofilm growing on the fibrous carriers in the ATP; (iii) a surface aerator was placed in the first or second cell of the ABP, which made the flow circulate in cells 1 and 2, operating like an oxidation ditch. This increased the oxygen supply and enhanced the aerobic biodegradation and assimilation, which in turn promoted the growth of plankton as foodstuffs for fish in the following fish pond.
outlet
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....0
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Algae-bacteria Pond
~
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lnle dlstrbulion
~
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,C.Cl
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ATP
~
2000
ra
III
;.:;
2500
Figure. I. Planof high rate pondsystem.
1.60
fermentatio pit
\.= 0.40
4 U
AAP
ATP
ABP
'~o~
Figure.2. Schematic diagramof high rate pondsystem.
Operation ofHigh Rate Pond System (HRPS). Operating results of HRPS are listed in Table 3. It can be seen that effluent CODer and BODs values reached the standards as shown in Table 4, close to the national standards. The nitrogen and phosphorus concentrations were still very high; however, they could be further removed through nitrogen volatilization, phosphate precipitation, uptake by algae and other aquatic plants for photosynthesis to produce new cells when discharged into the reservoir as flsh pond. The surplus algae were eaten by fishes, and the surplus aquatic plants were cleaned periodically. It was found that fifty thousand fish fries put into the reservoir grew very fast, i.e. from 0.1-0.1 S kg to 1.0-1.2 kg for each fish just in three months farming. Operation and analysis of Advanced Anaerobic Pond (AAP). It can be found from Table 3 that BOD removal rate in AAP was over 90%, much higher than traditional anaerobic pond, and close to that of som:
B. WANOetaL
128
high rate anaerobic reactors, which is mainly attributedto the fermentation pits that perform in principlejust like a UASBreactor. Table 3. Operatingresultsof high rate pond system (Averagein June- November, 1992) Effluent Parameter
Dis. BOD, Dis. COD.. Total COD.. SS NH]-N Total N PO.-p Total P pH
Pretreat. mg/I
2110 3700 5590
AAP
ATP
mg/], %
mg/I, %
203 546 796 384 630 646 59.5 70.6 7.51
904
590 659 72.7 101 7.21
90.4 187 85.2 468 85.7 652 57.6 137 -6.7 559 1.9 571 17.6 57.1 30.1 68.7 7.59
ABP mg/l, %
8.0 14.3 18.0 64.2 11.2 11.6 4.0 2.7
51.4 212 306 224 197 211 24.9 29.8 7.94
72.5 54.7 53.0 63.7 64.3 63.0 56.5 56.6
FP mg/I, %
26.8 127 175 53.6 U.8 32.6 7.3 2.8 7.75
47.9 40.1 42.8 76.1 94.0 84.5 75.5 88.8
Table 4. Local discharge standards for piggery wastewater Parameter
COD..
BOD,
55
pH
Concentration
5OOmg/1
2oomg/1
lOOmg/1
6.5-8.5
The advanced anaerobic pond with sludge pits was developed from a traditional anaerobic pond, increasing sludge age and micro-organisms' population by means of recycling inside the reactor, or self sludge recycling like that in UASB. The anaerobic fermentation pit was set up to form an upflow anaerobic sludge bed (UASB), in which the generated biogas flowed upwards through.the sludge bed in the fonn of fine bubbles, which promoted the mixing of organic substrate with granular sludge particles. The fermentation pits are square-shaped and the inlet pipe is put into the bottomof the pits, as shown in Figure 2. The pits were 1.0m deep, but the pond bottom was 5.0 m below the water surface. It was made with a slope of 5% to let the latter part of the sludge slide into the pits, thus improving the sludge collection in the pits, and allowingthe sludgeto be digested inside the pond.
90 Terrp.
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27
/ ~"
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84
./
Aug. Sept. Oct.
-p
21
, 19
17 Nov.
Month
Figure.3. The variationof COD removal in AAP with operatingtime.
Highrate pondsystemtreating piggery wastewater
129
On the other hand, the fermentation pits provided a very favourable hydraulic flow regime mainly caused by biogas bubbling which promoted the even distribution and completed mixing of the influent organisms with sludge. In the fermentation pit. it was very close to completely mixed mode due to the gas mixing; it could hold high organic load and keep stable operation at shock load. The other part of the pond was in diffusion state. and close to plug flow mode. In terms of biodegradation kinetics. it has greater degradation capacity and most of the organic load was degraded and removed in the AAP; the CODer removal is shown in Figure
3. Operation ofAnaerobic Transform Pond (ATP). It was 20 m long. and was separated into two parts, 12 m and 8 m, by a perforated wall. The packing arrangement of biofilm carriers was in the form of synthetic fibers fixed on plastic circular plates hung on ropes. as shown in Figure 4. and set in the front part. The distance between the plate-formed fibrous carriers on the rope was 100 mm. The package density was 28.3%. The fabric was made from hydrophilic synthetic material. so that is was quickly coated with biofilm. After about one month's operation the biofilm developed to give full coverage of the carriers and the biomass was measured to be 20 gil.
-j Figure. 4. The package arrangement of biofilm carriers.
It can be seen from Table 3 that CODerremoval in ATP was very low. only 10-20%. but suspended solids (SS) was removed significantly. up to 64.2%. and the organic removal in the following aerobic (algae) pond greatly increased in comparison with conventional stabilization ponds; BOD 5 removal reached 72.S% ; As shown in Table 5, the BOD/CODer ratio of the ATP effluent was on average more than 10% than that of the influent, which shows that the biofilm can transform poorly degradable organic compounds existing in the AAP into easily biodegradable ones. and hence increase the biodegradability of the substrate Table S. The influent and effluent BOD/CODer values of ATP.
Infl. Effl.
June
July
August
September
OCtober
November
December
0.229 0.263
0.267 0.280
0.2S4
0.247 0.283
0.260 0.301
0.27S
O.2SS
0.308
0.283
0.281
Operation ofAlgae-Bacterial Pond (ABP). The reformed algae-bacteria symbiotic pond consisted of S cells in series and was divided into two parts. The rust part contained two cells of 1.2 m in depth. and the second part three cells of 0.8 m in depth. as shown in Figure 1. A surface aerator (1.1 kW) was installed in the second cell. which gave a circulated flow in the rust and second cells when operated in winter season because of the shortage of oxygen from low rate photosynthesis. just as in the oxidation ditch. where the organic loading rate and low temperature affected the performance significantly.
B. WANGetaL
130
It is shown in Table 5 that the efficiency of the algae-bacterial pond is quite high, i.e. the dissolved BODs removal reached 72.5%, and average effluent concentration was 51.4 mgIJ. Since algae photosynthesis and bacteria metabolism are affected by temperature, the treatment efficiency was correspondingly variable with season as can be seen in Figure 5. Accordingly, to compensate for the effects of the temperature variation, use of the aerator was judged to be necessary in January and February.
85
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80
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~--t--- .......... I
29 Terrp. I'. -
' ...
r-B005.,.-"'"" ..... V
25
.e-
23
\
§ :: 55 ...Lr1
27
\
21 19 17
..!..l
Aug
Sap
Oct
Nov
Month
Figure. 5. The variation of BOOs removal in ABP with operation time.
The effluent SS concentration was comparably high, owing to the photosynthesis of algae, which contributed to a large part of TSS, which also varied with season. Since the algae can be consumed by fish in the reservoir as foodstuff, they can be removed through food chains in this way.
Performance of the fish pond. Originally a smaJl reservoir for farmland irrigation fiJled by storm runoff water, the fish pond purified the influent (effluent from ABP) in two ways: one was the dilution of influent with the water stored in it; the other was purification through food chains resulting from fish farming, by means of which the influent was purified very efficiently, in particular various nutrients were removed at very high efficiencies; the TN, NH 4-N, TP and P04-P were removed by 84.5%. 94.0%. 75.5% and 88.8% respectively. The effluent was good enough in quality for farmland irrigation. Nitrogen and phosphorus removal. It is found from Figure 6 that the removal of total N and total P are high in the pond system, and this occurred mainly in the algae-bacterial symbiotic pond, ammonia nitrogen concentration was even increased in both the AAP and ATP, but more obviously in the AAP; this was ascribed to the high concentration of organic N and P, i.e. urine, protein and fat, contained in piggery wastewater, which was converted to ammonia nitrogen by anaerobic processes. Only a small part of it was volatilized and participated in the synthesis of new cell of bacteria, the rest dissolved and remained in the water (Boller, 1987). There was the same case in the second pond (ATP), but it was less evident due to the decrease of influent organic N and P. Phosphorus was removed evidently in AAP through the precipitation of phosphate with metal ions in the influent such as FE2+1FE3+, Ca 2+, etc. The algae-bacterial pond has a very large water surface, and high pH value, which promoted the ammonia volatilization and uptake by algae with seasonal temperature variation.
Highrate pond systemtreatingpiggerywastewater
BOO 700
i
]
600
,
TP
400
300
z 200
160
TN --::::::=I"=t - - NH 'l:o 3-N
500
po:-p
100
\
t31
140 100
j
eo
~
120
~~
0
8
60 40
Q.
20 0
RavPre-treatAAP AlP ASP Pord System
FP
Figure6. The variation of Nand P concentration in the High Rate PondSystem.
COMPREHENSIVE BENEm ANALYSIS OF THEHIGH RATE POND SYSTEM
Technical parameters. The technical parameters of HRPS and the conventional pond system are compared in Table 6. Table6. The comparison of HRPS and Conventional PondSystem
Anaerobic
Aerobic
BOD, loading rate (KgBOD/M] d)
HRT
CPS
0.09-0.26
HRPS CPS
Water depth
BODs removal
(m)
(%)
10-15
2.5-4
70-80
1.5-2.1
2.1
4-5
90-92
0.015-0.08
> 10-40
0.45-0.9
60-90
0.8-1.2
75-80
(d)
HRPS 0.03-0.05 7.1 Note: CPS stands for ConventlonaI pond system
It can be seenthatorganic loading rate in HRPS was 10timeshigherthanthatof a conventional one, and the hydraulic retention time wasonly 115 to that of conventional pond, which means that HRPS occupies much less landarea.
Economical benefit. The performance of the HighRate Pond System fully depends on microorganisms and natural resources to treat wastewater, it consumes much less energy than conventional treatment plans. Besides, the system is easy to operate and demands littlemaintenance. The total treatment cost is only 0.07 Yuan(RMB)/m3• In the pre-treatment step, the sedimentation particles were mainly the uneaten foodstuff of pigs, and were reused to feed fish farmed in the nearby fish ponds. Since the pollution was controlled by the HRPS, the reservoir was recovered and used to farm fish, from which the income is about 100,000 yuan (RMB) a year (l US$. 8.4RMB Yuan in 1995).
B. WANG et al.
132
CONCLUSIONS The high rate pond system developed in this study has been shown to be very efficient and economical for treating piggery wastewater, with high removal efficiencies for various polIutants, such as TSS, COD, BOD 5, TN, NH4-N, and TP. The HRPS consists of advanced anaerobic pond (AAP), anaerobic transformation pond (ATP) a1gaelbacterial pond (ABP) and fish pond. The AAP has shown very high removal efficiencies both for COD and BOD 5 with typical values of 85% and 90% respectively, which can be mainly ascribed to the fermentation pits on the bottom, which perform like UASB in principle. The ATP, packed with synthetic fibrous carriers, exhibited a unique performance characteristic that improved the biodegradation of substrate by transforming some poorly degradable organic compounds into easily degradable ones. The ABP removed organics and nutrients at significantly high efficiencies by virtue of its symbiotic a1gaelbacterial. An ecological system was formed through fish farming in the fish pond and consisted of various food chains through which various polIutants were removed efficiently, with a final effluent either meeting local discharge standards or available for irrigation on farmland. The HRPS was shown superior to CPS in various aspects: the organic loading rate in HRPS is 10 times that of the CPS, HRT in HRPS only 1/5 that of CPS, and organics and nutrients removal in HRPS much higher than those in CPS. The area needed for the HRPS is about 1/2 or even less than that of CPS. REFERENCES Boller,M. (1987). Nutrient Removal from Wastewater. 7th European Sewageand RefuseSymposium, EWPCA·/FATMunich. pp, 19-22. EPA (1979).A History of Land Application as a Treatment Alternative. Technical Report. EPA43019·79·0/2. Oswald.WJ. (1967). Integrated PondSystemsfor Subdivisions, Journal WPCF 1289-1304. Wang,B.Z.(1984). The Design, Construction, Operation and Maintenance of Ecological PondSystem. China, SecondSeminaron Pond Technology (in Chinese). Wang,B.z. (1991). WaterPollution ControlEngineering. Chapter9, High Education Publisher(in Chinese). Xu. I. W.(1993).Piggery Wastewater Treatment Technique. Shanghai Environmental Science(March. in Chinese). Zhang. L., Xu. J.Q., Wu. Y.Y. (1989). Research on Mirco-organic Biology of Methane Two Step Fermentation Process. China Me/hane (February. in Chinese).
Pergamon
Wat. Sci. Tech. Vol. 34, No. II, pp, 125-132,1996. CopyrightC 1996IAWQ.Publishedby ElsevierScience Ltd. Printedin Great Britain.All rightsreserved. 0273-1223/96 SI~'OO + l}OO
PU: 80273-1223(96)00920-1
EXPERIMENTAL STUDY OF HIGH RATE POND SYSTEM TREATING PIGGERY WASTEWATER Baozhen Wang, Wenyi Dong, Jinlan Zhang and Xiangdong Cao Water Pollution Control Research Centre, Harbin University ofArchitecture and Engineering, 144 DazhiStreet, Harbin 150006, China
ABSTRACf The results of an experimental study conducted in a full-scale high rate pond system treating piggery wastewater at Jianfengshan Piggery. Panyu City. Guandong Province. are presented. The systemconsistsof twoadvanced anaerobic ponds(AAP) in parallel, followed by an anaerobic transformation pond(ATP) and a five-cell algae-bacterial pond (ABP). The mechanism of the AAP is described and the hydraulic flow pattern analyzed. Fermentation pits (FP) built on the bottom performed very efficiently. operating like UASB in principle. A newconceptof ATP is advanced, basedon its abilityto transform poorlydegradable materials to moreeasilydegradable ones.It wasfound in the studythat the HRPsystemwasmore efficient, morereliable and saved 40% land area compared witha conventional pondsystem. Economic analysesof both the energy consumption and the benefitto the pond systemof fish farming are also included in the paper.Copyright e 1996IAWQ. Published by ElsevierScienceLtd.
KEYWORDS Advanced anaerobic pond (AAP); anaerobic fermentation pit; anaerobic transform pond (ATP); algae/bacterialpond (ABP); piggery wastewater. INTRODUCfION With the rapid development of large-scale piggeries in South China, highly organic piggery wastewater has become an increasingly serious pollution source. As the wastewater is rich in organic and nutrient materials, it is easy to over-fertilize the farmland when applying it and make receiving waters eutrophic. Therefore, it is imperative to find a way to treat the piggery wastewater efficiently and economically. The characteristics of piggery wastewaters vary widely owing to the different methods for manure cleaning, and hence the treatment methods are different as well. In China, although there are many methods employed for piggery wastewater treatment, such as digestion pits in rural areas, two-step fermentation (Zhang, 1989), and activated sludge processes (Xu, 1993), the treatment efficiencies are usually very low, or they consume too much energy. Land treatment (EPA, 1979) is an appropriate method to return nutrients to farmland; however, the soil will get saturated for a certain time, and the underground water will probably be polluted through percolation.
125
B. WANGetaL
126
Considering that the annual average temperature in Pearl River Delta area is over 21°C, and that there are over 2000 h of sunshine annually, the application of a pond system for piggery wastewater treatment is attractive due to lots of advantages, such as low capital and operating/maintenance costs, low energy consumption, simplicityand ease of operation and maintenance, and stability in performance (Wang, 1984, 1991). However, the rapidly increasing cost of land has greatly hindered the popularization and application of conventional pond systems which occupy too much land area. The high rate pond system developed by the authors performsmuch better than conventional pond systemsby means of a much higherconcentration of more active biomass in the form of anaerobic sludge in advanced anaerobic pond submerged biofilm in anaerobic transformation pond as well as better flow regime close to plug flow, which make the system operate at higher hydraulic and organicloadingrates, thus reducing the land area. The high rate pondsystem consists of advanced anaerobic pond(AAP) (Oswald, 1967), anaerobic transform pond(ATP), AlgaelBacterial pond and fish pond. It is shown from the study that HRPScan treat piggerywastewater very efficiently and economically. Compared with ordinary stabilization pond system, it saved land area by 50 percent. EXPERIMENTAL SITE AND METHOD
Experimental site. This was a full-scale experiment, carried out at Jianfengshan Piggery in Panyu City, Guangdong Province. The piggery was originally built in 1988, located on the Jianfengshan Hill. Near the foot of the hill, there is a reservoir with 3 ha of water surface for farmland irrigation. The wastewater from the piggery (140 m3 per day) was discharged into the reservoir without any treatment before the plant was built, and thus all the fish and shrimp died of heavy pollution, and the farmland got over-fertilized when irrigated by the polluted water, and once became black, with an offensive smell. The quality of the piggery wastewateris shown in Table 1. Table 1. Analytical results of piggery wastewater in the test Parameter
COD..
BODs
55
TN
TP
pH
(mgll)
11000-17000
5000-8000
2000-8000
420-700
80-130
7-8.5
In order to control and tackle the above-mentioned pollution, a high rats pond system was built with a total treatmentcapacity of 140 mlfd. All of the unit ponds in the system were constructed with stone blocks and waterproof cement-sand grout as binder. The final flow sheet is: Pre-treatment including primary settling basins and equalization basin ~ Advanced Anaerobic Ponds(AAP) ~ Anaerobic Transformation ponds(ATP) ~ Symbiotic AIgaelBacterial ponds(ABP) ~ Effluent to reservoir as fish pond. The plan and flow chart are shown in Figures I and 2 respectively, and the design parameters of the unit ponds in the system are shown in Table 2. Table 2. The main design parameters on the pond system Pond Type Organic Loading Rate(KgBODslm'.d) Pond Depth (m) Retention Time (d) Occupied Area (m') Effective Volume (m')
AAP
ATP
ABP
3.3
0.24 3.80 2.2 120 300
1.20 7.1 950
4.00 (+ 1.0 in pits) 2.2 90
300
3
1000
The pond system was characterized by the following: (i) some fermentation pits were built on the front part of the bottom in the AAT and the inlets werejust built on the bottomof the fermentation pits, whichoperate like UASB in principlewith upflowpattern; (ii) fibrous carriers fixed on circular plates were packedin front
Highrate pondsystemtreatingpiggerywastewater
127
part of ATP for the purpose of the increase and even distribution of biomass in the form of submerged biofilm growing on the fibrous carriers in the ATP; (iii) a surface aerator was placed in the first or second cell of the ABP, which made the flow circulate in cells 1 and 2, operating like an oxidation ditch. This increased the oxygen supply and enhanced the aerobic biodegradation and assimilation, which in turn promoted the growth of plankton as foodstuffs for fish in the following fish pond.
outlet
JianFengShan Mountain (Bamboo)
....0
~
'E
Ul II) ___
Algae-bacteria Pond
~
~
II)~
D:: l:l 0 I=lll. III
r-aerator
lnle dlstrbulion
~
(UInr)
,C.Cl
~.!!l
=e II)
ATP
~
2000
ra
III
;.:;
2500
Figure. I. Planof high rate pondsystem.
1.60
fermentatio pit
\.= 0.40
4 U
AAP
ATP
ABP
'~o~
Figure.2. Schematic diagramof high rate pondsystem.
Operation ofHigh Rate Pond System (HRPS). Operating results of HRPS are listed in Table 3. It can be seen that effluent CODer and BODs values reached the standards as shown in Table 4, close to the national standards. The nitrogen and phosphorus concentrations were still very high; however, they could be further removed through nitrogen volatilization, phosphate precipitation, uptake by algae and other aquatic plants for photosynthesis to produce new cells when discharged into the reservoir as flsh pond. The surplus algae were eaten by fishes, and the surplus aquatic plants were cleaned periodically. It was found that fifty thousand fish fries put into the reservoir grew very fast, i.e. from 0.1-0.1 S kg to 1.0-1.2 kg for each fish just in three months farming. Operation and analysis of Advanced Anaerobic Pond (AAP). It can be found from Table 3 that BOD removal rate in AAP was over 90%, much higher than traditional anaerobic pond, and close to that of som:
B. WANOetaL
128
high rate anaerobic reactors, which is mainly attributedto the fermentation pits that perform in principlejust like a UASBreactor. Table 3. Operatingresultsof high rate pond system (Averagein June- November, 1992) Effluent Parameter
Dis. BOD, Dis. COD.. Total COD.. SS NH]-N Total N PO.-p Total P pH
Pretreat. mg/I
2110 3700 5590
AAP
ATP
mg/], %
mg/I, %
203 546 796 384 630 646 59.5 70.6 7.51
904
590 659 72.7 101 7.21
90.4 187 85.2 468 85.7 652 57.6 137 -6.7 559 1.9 571 17.6 57.1 30.1 68.7 7.59
ABP mg/l, %
8.0 14.3 18.0 64.2 11.2 11.6 4.0 2.7
51.4 212 306 224 197 211 24.9 29.8 7.94
72.5 54.7 53.0 63.7 64.3 63.0 56.5 56.6
FP mg/I, %
26.8 127 175 53.6 U.8 32.6 7.3 2.8 7.75
47.9 40.1 42.8 76.1 94.0 84.5 75.5 88.8
Table 4. Local discharge standards for piggery wastewater Parameter
COD..
BOD,
55
pH
Concentration
5OOmg/1
2oomg/1
lOOmg/1
6.5-8.5
The advanced anaerobic pond with sludge pits was developed from a traditional anaerobic pond, increasing sludge age and micro-organisms' population by means of recycling inside the reactor, or self sludge recycling like that in UASB. The anaerobic fermentation pit was set up to form an upflow anaerobic sludge bed (UASB), in which the generated biogas flowed upwards through.the sludge bed in the fonn of fine bubbles, which promoted the mixing of organic substrate with granular sludge particles. The fermentation pits are square-shaped and the inlet pipe is put into the bottomof the pits, as shown in Figure 2. The pits were 1.0m deep, but the pond bottom was 5.0 m below the water surface. It was made with a slope of 5% to let the latter part of the sludge slide into the pits, thus improving the sludge collection in the pits, and allowingthe sludgeto be digested inside the pond.
90 Terrp.
i
88
l
86
~
'1'*
>---
lo" ...
/ ~/'
§:
~'
25
"
..lJt.
23
" \
\
78
...In
29
27
/ ~"
/
84
./
Aug. Sept. Oct.
-p
21
, 19
17 Nov.
Month
Figure.3. The variationof COD removal in AAP with operatingtime.
Highrate pondsystemtreating piggery wastewater
129
On the other hand, the fermentation pits provided a very favourable hydraulic flow regime mainly caused by biogas bubbling which promoted the even distribution and completed mixing of the influent organisms with sludge. In the fermentation pit. it was very close to completely mixed mode due to the gas mixing; it could hold high organic load and keep stable operation at shock load. The other part of the pond was in diffusion state. and close to plug flow mode. In terms of biodegradation kinetics. it has greater degradation capacity and most of the organic load was degraded and removed in the AAP; the CODer removal is shown in Figure
3. Operation ofAnaerobic Transform Pond (ATP). It was 20 m long. and was separated into two parts, 12 m and 8 m, by a perforated wall. The packing arrangement of biofilm carriers was in the form of synthetic fibers fixed on plastic circular plates hung on ropes. as shown in Figure 4. and set in the front part. The distance between the plate-formed fibrous carriers on the rope was 100 mm. The package density was 28.3%. The fabric was made from hydrophilic synthetic material. so that is was quickly coated with biofilm. After about one month's operation the biofilm developed to give full coverage of the carriers and the biomass was measured to be 20 gil.
-j Figure. 4. The package arrangement of biofilm carriers.
It can be seen from Table 3 that CODerremoval in ATP was very low. only 10-20%. but suspended solids (SS) was removed significantly. up to 64.2%. and the organic removal in the following aerobic (algae) pond greatly increased in comparison with conventional stabilization ponds; BOD 5 removal reached 72.S% ; As shown in Table 5, the BOD/CODer ratio of the ATP effluent was on average more than 10% than that of the influent, which shows that the biofilm can transform poorly degradable organic compounds existing in the AAP into easily biodegradable ones. and hence increase the biodegradability of the substrate Table S. The influent and effluent BOD/CODer values of ATP.
Infl. Effl.
June
July
August
September
OCtober
November
December
0.229 0.263
0.267 0.280
0.2S4
0.247 0.283
0.260 0.301
0.27S
O.2SS
0.308
0.283
0.281
Operation ofAlgae-Bacterial Pond (ABP). The reformed algae-bacteria symbiotic pond consisted of S cells in series and was divided into two parts. The rust part contained two cells of 1.2 m in depth. and the second part three cells of 0.8 m in depth. as shown in Figure 1. A surface aerator (1.1 kW) was installed in the second cell. which gave a circulated flow in the rust and second cells when operated in winter season because of the shortage of oxygen from low rate photosynthesis. just as in the oxidation ditch. where the organic loading rate and low temperature affected the performance significantly.
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It is shown in Table 5 that the efficiency of the algae-bacterial pond is quite high, i.e. the dissolved BODs removal reached 72.5%, and average effluent concentration was 51.4 mgIJ. Since algae photosynthesis and bacteria metabolism are affected by temperature, the treatment efficiency was correspondingly variable with season as can be seen in Figure 5. Accordingly, to compensate for the effects of the temperature variation, use of the aerator was judged to be necessary in January and February.
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Figure. 5. The variation of BOOs removal in ABP with operation time.
The effluent SS concentration was comparably high, owing to the photosynthesis of algae, which contributed to a large part of TSS, which also varied with season. Since the algae can be consumed by fish in the reservoir as foodstuff, they can be removed through food chains in this way.
Performance of the fish pond. Originally a smaJl reservoir for farmland irrigation fiJled by storm runoff water, the fish pond purified the influent (effluent from ABP) in two ways: one was the dilution of influent with the water stored in it; the other was purification through food chains resulting from fish farming, by means of which the influent was purified very efficiently, in particular various nutrients were removed at very high efficiencies; the TN, NH 4-N, TP and P04-P were removed by 84.5%. 94.0%. 75.5% and 88.8% respectively. The effluent was good enough in quality for farmland irrigation. Nitrogen and phosphorus removal. It is found from Figure 6 that the removal of total N and total P are high in the pond system, and this occurred mainly in the algae-bacterial symbiotic pond, ammonia nitrogen concentration was even increased in both the AAP and ATP, but more obviously in the AAP; this was ascribed to the high concentration of organic N and P, i.e. urine, protein and fat, contained in piggery wastewater, which was converted to ammonia nitrogen by anaerobic processes. Only a small part of it was volatilized and participated in the synthesis of new cell of bacteria, the rest dissolved and remained in the water (Boller, 1987). There was the same case in the second pond (ATP), but it was less evident due to the decrease of influent organic N and P. Phosphorus was removed evidently in AAP through the precipitation of phosphate with metal ions in the influent such as FE2+1FE3+, Ca 2+, etc. The algae-bacterial pond has a very large water surface, and high pH value, which promoted the ammonia volatilization and uptake by algae with seasonal temperature variation.
Highrate pond systemtreatingpiggerywastewater
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600
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300
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Figure6. The variation of Nand P concentration in the High Rate PondSystem.
COMPREHENSIVE BENEm ANALYSIS OF THEHIGH RATE POND SYSTEM
Technical parameters. The technical parameters of HRPS and the conventional pond system are compared in Table 6. Table6. The comparison of HRPS and Conventional PondSystem
Anaerobic
Aerobic
BOD, loading rate (KgBOD/M] d)
HRT
CPS
0.09-0.26
HRPS CPS
Water depth
BODs removal
(m)
(%)
10-15
2.5-4
70-80
1.5-2.1
2.1
4-5
90-92
0.015-0.08
> 10-40
0.45-0.9
60-90
0.8-1.2
75-80
(d)
HRPS 0.03-0.05 7.1 Note: CPS stands for ConventlonaI pond system
It can be seenthatorganic loading rate in HRPS was 10timeshigherthanthatof a conventional one, and the hydraulic retention time wasonly 115 to that of conventional pond, which means that HRPS occupies much less landarea.
Economical benefit. The performance of the HighRate Pond System fully depends on microorganisms and natural resources to treat wastewater, it consumes much less energy than conventional treatment plans. Besides, the system is easy to operate and demands littlemaintenance. The total treatment cost is only 0.07 Yuan(RMB)/m3• In the pre-treatment step, the sedimentation particles were mainly the uneaten foodstuff of pigs, and were reused to feed fish farmed in the nearby fish ponds. Since the pollution was controlled by the HRPS, the reservoir was recovered and used to farm fish, from which the income is about 100,000 yuan (RMB) a year (l US$. 8.4RMB Yuan in 1995).
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CONCLUSIONS The high rate pond system developed in this study has been shown to be very efficient and economical for treating piggery wastewater, with high removal efficiencies for various polIutants, such as TSS, COD, BOD 5, TN, NH4-N, and TP. The HRPS consists of advanced anaerobic pond (AAP), anaerobic transformation pond (ATP) a1gaelbacterial pond (ABP) and fish pond. The AAP has shown very high removal efficiencies both for COD and BOD 5 with typical values of 85% and 90% respectively, which can be mainly ascribed to the fermentation pits on the bottom, which perform like UASB in principle. The ATP, packed with synthetic fibrous carriers, exhibited a unique performance characteristic that improved the biodegradation of substrate by transforming some poorly degradable organic compounds into easily degradable ones. The ABP removed organics and nutrients at significantly high efficiencies by virtue of its symbiotic a1gaelbacterial. An ecological system was formed through fish farming in the fish pond and consisted of various food chains through which various polIutants were removed efficiently, with a final effluent either meeting local discharge standards or available for irrigation on farmland. The HRPS was shown superior to CPS in various aspects: the organic loading rate in HRPS is 10 times that of the CPS, HRT in HRPS only 1/5 that of CPS, and organics and nutrients removal in HRPS much higher than those in CPS. The area needed for the HRPS is about 1/2 or even less than that of CPS. REFERENCES Boller,M. (1987). Nutrient Removal from Wastewater. 7th European Sewageand RefuseSymposium, EWPCA·/FATMunich. pp, 19-22. EPA (1979).A History of Land Application as a Treatment Alternative. Technical Report. EPA43019·79·0/2. Oswald.WJ. (1967). Integrated PondSystemsfor Subdivisions, Journal WPCF 1289-1304. Wang,B.Z.(1984). The Design, Construction, Operation and Maintenance of Ecological PondSystem. China, SecondSeminaron Pond Technology (in Chinese). Wang,B.z. (1991). WaterPollution ControlEngineering. Chapter9, High Education Publisher(in Chinese). Xu. I. W.(1993).Piggery Wastewater Treatment Technique. Shanghai Environmental Science(March. in Chinese). Zhang. L., Xu. J.Q., Wu. Y.Y. (1989). Research on Mirco-organic Biology of Methane Two Step Fermentation Process. China Me/hane (February. in Chinese).