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Land problems in sewage sludge DISPOSAL - IMPLEMENTATION OF THE ENVIRONMENT - AN OVERVIEW

Md. Wasim Aktar

Pesticide Residues Laboratory, Department of Agricultural Chemicals,
Bidhan Chandra Krishi Viswavidyalaya, Mohanpur-741252, Nadia, West Bengal, India

1. Introduction
Most wastewater treatment processes produce a sludge that must be eliminated. Conventional secondary treatment plants typically generate primary sludge in the settling phase of primary and secondary treatment, biological sludge final settling after the biological process. The characteristics of secondary sludge vary with the type of biological processes, and often it is mixed with primary sludge before treatment and disposal. About half of the operating costs of secondary treatment plants in Europe may be associated with treatment and sludge disposal. The application of raw or treated sewage sludge can significantly reduce the component cost of disposing of sewage sludge from wastewater and provide much of the nitrogen and phosphorus from many cultures. Very rarely sewer systems that transport the sewage treatment plants, industrial effluents and stormwater runoff from roads and other paved areas are often dumped into sewers. Thus, the sewage sludge contains, in addition to organic waste, traces of many pollutants used in our modern society. Some of these chemicals may be phytotoxic and some are toxic to humans and / or animals so it is necessary to control soil concentrations of potentially toxic elements (EFA) and their rate of application to soil. The health risk of chemicals in sewage sludge spread on land has been reviewed by Dean and Suess1
Sewage sludge also contains pathogenic bacteria, viruses and protozoa and other parasitic helminths, which can result in hazards to human health, animals and plants. A WHO (1981) Report on risk to health of microbes in sewage sludge spread on land identified as salmonella and Taenia giving rise to greater concern. The number of parasites and pathogens in sludge can be significantly reduced before application to land by the appropriate sludge treatment and the potential risk to health is further reduced by the effects of climate, soil and micro- bodies after the mud is applied on the ground. However, in the case of certain crops, restrictions on planting, grazing and harvesting are required.
Apart from these concerns, sewage sludge also contains useful concentrations of nitrogen, phosphorus and organic matter. The availability of phosphorus contained in the application year is about 50% and is independent of any treatment of sludge before. nitrogen availability is more dependent on sludge treatment, slurry untreated and dehydrated sludge treated releasing nitrogen slowly with benefits for the crops being implemented on a relatively long period. Liquid-anaerobic digested sludge has a high content of ammonia nitrogen that is readily available to plants and can be particularly beneficial to the grasslands. Organic matter in sludge can improve the water holding capacity and structure of some soils, particularly when applied in the form of dewatered sludge cake.
2. What is sludge?
Residues, biosolids, sludge, wastewater, sewage by-product, compost: there are many names for the sludge and sludge products. The term "sludge" is used as most people understand: the solid, sometimes, sometimes liquid material produced by treatment facilities and wastewater used as fertilizer on fields, gravel pits, and the forest lots statewide. The sludge can be classified as "Class A" if it has been treated to reduce germs in the background.