ABSTRACT
Sewage sludge is a proven fertilizer and soil conditioner and can be reused beneficially in agriculture without detriment to the environment or human health. The technical database on the fate of sewage sludge in soil is extensive, enabling management practices to be defined that protect the environment to ensure safe and secure reuse of sludge for crop production. Hygiene is the principal concern, particularly where agricultural practices are labour intensive and farm workers may come into direct contact with sludge. Under these circumstances, biosolids are supplied to the farm gate after treatment to eliminate pathogens. A dual barrier approach, employing treatment and land use restrictions, is effective in controlling the potential transmission of enteric disease when sludge is applied in mechanized farming systems. Potentially toxic elements (PTEs) slowly accumulate in sludge-treated soil, but this can be controlled to avoid deleterious effects on crops, soil microbial processes or the food chain. Organic contaminants sorb strongly to soil, volatilize or readily biodegrade, providing barriers to their transmission to the food chain; the consensus of scientific data is that they are not hazardous to human health or the environment in sludge. Effective trade effluent and source controls on contaminants are critical to sustainable recycling programmes.
