FATE OF BIOLOGICAL AND CHEMICAL CONTAMINANTS FROM ON-SITE DISPOSAL OF LIQUID PIGGERY WASTES - RESULTS FROM A SOIL COLUMN STUDY

To assess the feasibility of the soakaway system in treating piggery wastes, eight columns of 3 m length were packed with five commonly occurring soils from Hong Kong and were dosed with pig slurry daily for a period of four months. Infiltration rates of the columns were monitored daily while slurry and soil solution were sampled weekly or fortnightly and analyzed for the major bacterial, organic and inorganic contaminants. Purification efficiency was higher in the volcanic soils than in the coarser granitic soils. Most of the contaminants were removed in the top 1 m unsaturated zone of the columns. Analysis of the effluent collected at the end of the 3 m columns packed with granitic and volcanic alluvial soils indicated purification efficiencies of 100% for E. coli and more than 95% for. BOD5, total-P, total-N, PO4, NH4-N and NO3-N. The purification efficiencies of footslope deposits and in-situ weathered materials were significantly lower.