Bacteriological studies of land disposal of piggery effluent.

Abstract

Proc. Aust. Soc. Anim. Prod. (1978) 12: 158 BACTERIOLOGICAL STUDIES OF LAND DISPOSAL OF PIGGERY EFFLUENT D.S. CHANDLER* and J.A. CRAVEN* In Australia, most piggery effluent is discharged to land with little or no treatment. The maximum safe loading level for soils has not been established and the work reported in this paper is part of an evaluation of the extent to which the microorganisms in effluent limit the amount of effluent that can be spread on a given area. Effluent contains a number of organisms that have the ability to cause disease in animals and man. The persistence of some of these organisms has been studied at a number of sites at Werribee and elsewhere in Victoria. Escherichia cozi is widely used as an indicator organism in water pollution studies and much of the present investigation has concentrated on the behaviour of this organism. Analysis of fifty partially treated or aw effluen s showed E. COZY 5 t number 5 in the effluents ranged from 2 x 10 to 2 x 10 per ml (mean 5 x lo7 per m&). The total number of aerobic mesophiles ranged from 5 x 10 to 10 bacteria per ml. SahoneZZa spp were isolated from one effluent sample and ErysipeZothrix rhusiopathiae was present in 17 of 40 samples examined. Soils qnd pas ures sampled 24 hours after efgluent reparation have k T: yielded 10 to 10 E. coli/g d.m. in soil and 10 to 10 /g of pasture cut 3Omrn 3bove ground level. Numbers in the surface soil generally declined to 10 /g d.m. three to six weeks after application. E. coli numbers on pasture declined faster than in soil, and were often not detectable on pasture cut 30mm above the ground when sampled two weeks after effluent application. Profile studies on the grass sward have shown persistence on grass to be greatest near the soil surface. Persistence of E. coli on both grass and surface soil was found to be enhanced in the late summer and autumn applications of 1976 (eight months survival on surface soil, 'six months on pasture). The autumn and winter of 1976 was a period of exceptionally low rainfall. Profiles dug in the clay loam soil of the plot 3 during this period showed large numbers of k2~oZi in the subsoil (10 /g six months after application at 20-30cm, Subsequent profile studies have indicated (i) lower 10 /g at 45-55cm). persistence in sub soils as the soil dried in late spring, with few E. COzi surviving in subsoils by 'mid summer (ii) little evidence of lateral movement in the Werribee Deutgam clay-loam soil with a surface slope less than 1% (iii) rapid downwards movement of E. coli through the soil after application, particularly in late summer whensoil cracking enabled unrestricted downward movement to depths of over one metre. Preliminary studies of runoff waters from plots with low surface slope indicate that although only a small percentage of applied E. coli cells may be retrieved in surface runoff waters, the numbers of cells 'eluted could pollute large volumes of water to beyond acceptable E. b02i counts. It is possible that the ability to control runoff water from disposal areas, at least in the period immediately following spreading, may be an important consideration in planning land disposal systems. * Department of Agriculture, 'Attwood' Veterinary Research Laboratory, Westmeadows, Vic. 3047. 158. --