| Summary: | Residential expansion into traditionally rural areas, environmental issues and increasing integration and farm sizes, have placed steadily increasing pressure and demands on the modern pork producer. Waste management and odor control have become important priority issues.
In this research, a controllable field scale biological treatment system was designed, constructed and investigated. The anoxic/aerobic (A/A) system consisted of an anoxic reactor, which receives the raw swine waste, in series with an aerobic reactor. The design of the system require the heterotrophic bacteria in the anoxic reactor to oxidize the organic carbon to carbon dioxide utilizing nitrate as the terminal electron acceptor and producing nitrogen gas through denitrification. Also, in the aerobic reactor autotrophic bacteria oxidize the ammonia to nitrate and a recirculation stream is fed back to the anoxic reactor to supply the needed nitrate.
Over the course of the investigation, the hydraulic retention times of the anoxic and aerobic reactors were increased from 35 and 36 hours to 105 and 108 hours respectively in order to establish steady state conditions. A recirculation ratio of 1 was maintained throughout the experiment. Chemical Oxidation Demand (COD), ammonia-N and nitrate-N were tracked through the system during the study.
At steady state, COD was reduced from 10,163 to 5,023 mg/L; ammonia-N was reduced from 1,209 to 633 mg/L; and nitrate-N held steady at 95 mg/L, which was the sample detection limit. It is believed that partial nitrification was achieved in the aerobic reactor, which supplied nitrite as opposed to nitrate to the anoxic reactor for organic decomposition resulting in the unexpected low nitrate-N results. An acceptable 67% of the overall 51% COD reduction was accomplished in the anoxic reactor. These results show the field scale system reduced both the organic carbon and ammonia in the swine wastewater and prove the feasibility of the system. The reduction in ammonia indicates that the A/A system may have potential to address odor related problems of swine wastewater. Further research and study to optimize the controlling parameters and achieve more efficiency from the system is warranted and will be easily implemented utilizing the effective controls built in.
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