| Summary: | The chemical aspects of the aerobic treatment of pig waste were investigated in farm scale systems associated with an intensive pig production unit. Changes in chemical composition were monitored over extended periods of aeration of liquid manure in oxidation ditches. Transformations of inorganic nitrogen in farm waste demonstrated considerable controlling influence over the mixed liquor pH and dissolved oxygen. Loss of soluble nitrogen (about 50% of the total nitrogen) appeared to be an inevitable consequence of aerobic treatment; the loss being sustained either by desorption of ammonia gas at high pH, or by nitrification and denitrification, which, may occur simultaneously even under apparently aerobic conditions. A two stage nitrification-denitrification sequence could eliminate almost all the soluble nitrogen from the mixed liquor. Incomplete nitrirication, as evidenced by nitrite and ammonium accumulation, resulted from the inhibition of nitrite oxidation by molecular ammonia and/or undissociated nitrous acid. This process, once initiated, became self-promoting. The chemical composition of farm waste slurries, mixed liquors and solids was investigated in detail. The partitioning of chemical species between solid and liquid phases was examined before and after treatment. Solids consisted of a mixture of coarse fibre and fine microbial sludge, the nitrogen and fibre contents being inversely related. The microbial solid contained 5 to 7% organic nitrogen most of which could be recovered as amino acids following hydrolysis. However methionine and isoleucine were found to be deficient. Mass balances in flow systems were analysed by a kinetic approach and an attempt was made to explain the inter-relationships between operating parameters.
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