Changes in the short‐chain carboxylic acid content and chemical oxygen demand of stored pig slurry

Abstract

Abstract The effects of sample size, temperature and duration of storage on the concentrations of short‐chain carboxylic acids (C 2 ‐C 5 ) and the chemical oxygen demand (COD) of pig slurry were determined. After initial maximum values shortly after storage commenced, the concentrations of acids declined to low steady values. The relative proportions of the acids present remained constant during storage possibly indicating a step‐wise decomposition process. Following agitation during the sampling procedure, the COD values remained fairly constant with greater oxygen depletion in the larger sub‐samples. Filtration of the supernatants of slurry sub‐samples produced marked decreases in both COD and acid content of the filtrate. The rate of oxygen loss and the production of maximum acid concentrations increased at higher temperatures. Changes in small storage samples (<500cm 3 ) did not reflect the changes likely to occur under normal farm storage conditions.