Environmental impact and removal of phosphates in swine farm effluent

H.K. Ong, Y.S.Lim and M. Suhaimi

Abstract

This article describes the results of: a) a case study to determine the loading of excess phosphates to the environment from pig industry in Malaysia; b) an experiment on the effect of phosphorus (P) concentration on turbidity of wastewater; c) field study on effect of waste stabilization ponds on P retention; d) laboratory study on efficacy of biological P removal. Total consumption of P was about 6,145 t of which about 1,255 t originated from inorganic supplements. This amount was about 1.1% of the total amount of phosphatic fertilizers of about 550,000 t used annually in Peninsular Malaysia. Apparent excretion of P was found to be 4,618 t/year or equivalent to approximately 10,566 t of P2O5 per year. The feed supplements used were tricalcium phosphate (TCP), dicalcium phosphate (DCP), monocalcium phosphate (MCP) and MDCP (a mixture of DCP and MCP). The proportions of farmers using TCP, DCP, MCP and MDCP were 25, 33, 9 and 33%, respectively. The apparent digestibilities of TCP, DCP, MCP and MDCP were 48, 66, 81 and 73%, respectively. The P source with the highest digestibility, i.e. MCP was least used by farmers. Turbidity of wastewater was found to increase with increasing total P (TP) concentration. Only 16.5% of TP in raw slurry was in dissolved form. Approximately 90% of TP were retained in the series of anaerobic, facultative and aerobic ponds. The efficacy of TP removal via sequential anaerobic and aerobic digestion under laboratory conditions was found to be 66.4%, while soluble P was almost completely removed.

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