Control of metal application rates from sewage sludge utilization in agriculture

During the treatment of sewage, a sludge is produced, which must be disposed. For many treatment works, agricultural use of the sludge is the most cost‐effective disposal option. In using sludge as a fertilizer replacement or soil conditioner in agriculture, the environment must not be endangered. In this objective, toxic metal accumulation is of special interest because excessive concentrations in sludged soil can reduce crop yields or result in unacceptable accumulations of toxic metals in crops with consequent hazard to the food chain. Although sewage sludge contains certain quantities of metals from natural sources, there are significant amounts derived from industrial effluents discharged to sewers. The paper will review all of these aspects and will examine critically the various policies of controlling metal accumulation in sludged soil with particular reference to the soil quality criteria (maximum permissible concentrations) which have been adopted.