Development Of Aerobic-microaerobic Two-stage SBR Process Treating Swine Wastewater

Swine wastewater is characterized by high ammonium and and low carbon-to-nitrogen ratio.It is very difficult for traditional biological denitrification processes to remove nitrogen from the low carbon-to-nitrogen ratio swine wastewater,along with the long technological process and high cost.Thus,there is a pressing need to to develop novel biological processes for the treatment of swine wastewater more efficiently and economically.Based on the previous researches,a novel aerobic-microaerobic two-stage sequential batch reactors（SBRs）process was suggested to treat manure-free piggery wastewater for the synchronous removal of organic carbon and ammonium.The first aerobic SBR involved in the two-stage SBRs process was designed to remove most of the chemical oxygen demand（COD）from the swine wastewater.With few COD in the wastewater,heterotrophic microorganisms would be restricted in the second microaerobic SBR,allowing autotrophic denitrification microorganisms such as aerobic ammonium oxidation and anaerobic ammonia oxidation（ANAMMOX）bacteria to thrive.The synergism of partial nitrification and ANAMMOX would make the second microaerobic SBR very powerful in ammonium and total nitrogen removal.Inoculated with the excess activated sludge collected from a local sewage treatment plant,the first aerobic SBR was started up at 30±1℃ with a dissolved oxygen（DO）ranged from 3.0-5.0 mg/L,and a steady state was reached since the 10 th day with a favorable nutrients removal.After the startup process,a programmable logic controller was introduced to control the aeration time to be 145 or 205 min following the influent COD concentration.With the concentration of COD,NH₄⁺-N and total nitrogen（TN）averaged 1187,526.7 and 528.8 mg/L in influent,a removal ratio averaged 67.4%,7.7% and 8.3% was obtained in the SBR with a residue of about 376,485.5 and 494.5 mg/L in effluent,respectively.The COD/TN ratio as low as about 0.8 was favorable for the enrichment of aerobic ammonium oxidation and ANAMMOX bacteria in the secondary microaerobic SBR.Inoculated with microaerobic activated sludge and operated at DO 0.2-0.3 mg/L,the secondary microaerobic SBR was started up with a total cycle length of 8 h that gave an intermittent aeration extending to 450 min.The inoculated sludge was acclimated by the gradually increased NH₄⁺-N in influent and an excellent nitrogen removal was kept at last.With the COD,NH₄⁺-N and TN of about 262,415.2 and 416.5 mg/L in influent,a removal ratio averaged 73.5%,93.0% and 83.8% was kept in the SBR with a residue of about 67,29.3 and 67.6 mg/L in effluent,respectively.△ NO3--N/ △ NH₄⁺-N indicated that partial ammonia oxidation coupled with ANAMMOX was the dominant approach to nitrogen removal,contributing more than 80.3% to the total TN removal in the secondary SBR.Fed with raw manure-free piggery wastewater characterized by the COD,NH₄⁺-N and TN averaged 963,443.6 and 445.2 mg/L,the removal ratio of 93.0%,93.4%,and 84.8% was kept by the aerobic-microaerobic two-stage SBR process,respectively.The effluent with the COD,NH₄⁺-N and TN of about 67,29.3,and 67.6 mg/L,respectively,well met with the emission standard of Pollutant Emission Standard for Livestock and Poultry Industry（GB 18596-2001）.Based on the above research results,an engineering technical proposal was worked out for the wastewater treatment of a pig farm in the north of China.Grid filtration,aerobic SBR,microaerobic SBR,coagulation and sedimentation,and disinfection were involved in the technological process in sequence.The designed treatment load was up to 200 m³/d,with the effluent meeting the emission standard of GB 18596-2001.Technical and economic analysis showed that the total investment of the project was about 1.572 million Yuan（RMB）,while with he processing cost of about 2.33 ￥/m³.The annual environmental protection fees would be cut by 1.22 million Yuan,resulted in the reduction of COD,BOD,NH₄⁺-N,TP and SS of 111.0,82.6,37.2,1.9 and 173.0 tons,respectively,by the wastewater treatment engineering.