Determination of the progression in soil microbial response, and changes in soil permeability, following application of meat processing effluent to soil

Abstract

Irrigation of primary-treated meat processing plant effluent onto soils may cause a decrease in soil permeability. The microbial response, and the decrease and subsequent recovery in soil permeability, following application of primary-treated meat processing effluent to soils was investigated. soil permeability was measured on repacked soil-columns following a surface application of effluent or water and storage at either 13 or 25°C. The microbial response to effluent application was examined, using a scanning electron microscope (SEM), in samples from the effluent and water treated soil-columns, and also in samples from field sites where meat processing effluent had been regularly irrigated. There was a strong microbial response to addition of primary-treated meat processing effluent to the soil, which initially resulted in the formation of a semi-continuous film on the soil surface. The surface film, which was observed under both laboratory and field conditions, formed and decomposed two to three times faster at 25°C than at 13°C. The surface film appeared to consist of polysaccharide slime, within which bacterial forms became evident. The surface film gradually disintegrated, leaving only the bacterial forms. Over time, a diversity of microorganisms developed, with fungi, actinomycetes and a range of colonial bacteria appearing. It took 44 days at 25°C and 155 days at 13°C, for all evidence of microbial material to disappear. At 25°C, soil-column permeability dropped by a mean of 70%v four days after effluent application, but recovered to the initial permeability after 23 days. At 13°C soil permeability dropped by a mean of 50%, four days after effluent application, and took over 50 days to return to the initial permeability. The total permeability recovery period was similar to that observed for microbial diversification and the degradation of the initial surface film coating to occur. It is suggested therefore, that the progression of microbial response is a major factor determining soil permeability recovery following application of effluent from the meat processing industry.