DETERMINATION OF THE PROGRESSION IN SOIL MICROBIAL RESPONSE, AND CHANGES IN SOIL PERMEABILITY, FOLLOWING APPLICATION OF MEAT PROCESSING EFFLUENT TO SOIL

Irrigation of primary-treated meat processing plant effluent onto soil s may cause a decrease in soil permeability. The microbial response, a nd the decrease and subsequent recovery in soil permeability, followin g 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 e ither 13 or 25 degrees C. The microbial response to effluent applicati on was examined, using a scanning electron microscope (SEM), in sample s from the effluent and water treated soil-columns, and also in sample s from field sites where meat processing effluent had been regularly i rrigated. There was a strong microbial response to addition of primary -treated meat processing effluent to the soil, which initially resulte d in the formation of a semi-continuous film on the soil surface. The surface film, which was observed under both laboratory and field condi tions, formed and decomposed two to three times faster at 25 degrees C than at 13 degrees C. The surface film appeared to consist of polysac charide slime, within which bacterial forms became evident. The surfac e film gradually disintegrated, leaving only the bacterial forms. Over time, a diversity of microorganisms developed, with fungi, actinomyce tes and a range of colonial bacteria appearing. It took 44 days at 25 degrees C and 155 days at 13 degrees C, for all evidence of microbial material to disappear. At 25 degrees C, soil-column permeability dropp ed by a mean of 70% four days after effluent application, but recovere d to the initial permeability after 23 days. At 13 degrees C soil perm eability dropped by a mean of 50%, four days after effluent applicatio n, and took over 50 days to return to the initial permeability. The to tal permeability recovery period was similar to that observed for micr obial diversification and the degradation of the initial surface film coating to occur. It is suggested therefore, that the progression of m icrobial response is a major factor determining soil permeability reco very following application of effluent from the meat processing indust ry. (C) 1997 Elsevier Science B.V.