Sludge Management. The treatment and disposal of industrial and residential sludge is an environmentally sensitive problem. Some traditional disposal routes, such as disposal at sea, are coming under pressure which necessitates finding alternatives. This sludge management ebook describes the effect of composted sludge on the growth of Acacia auriculiformis and Swietenia mahagoni seedlings in the nursery.
Application of sludge to land has been practiced in an attempt to dispose of industrial and residential waste and to gain potential fertilizer value from the application. Since, it contains many essential plant nutrients, sludge can be used as a plant growth medium. Several studies have shown that sludge addition provide significant benefit to crop growth (Gaynor and Halstead, 1976; Beckett et al., 1977). This is not surprising in view of elevated nitrogen, phosphorous and other nutrients levels in sludge (Sommers, 1977). Besides benefiting plant growth, sludge addition can change soil physical and chemical properties (Peles et al., 1996; Ramachandran and D’Soura, 1998; Gardiner et al., 1995; Jobra and Andres, 2000; Hossain and Miller, 2004). Pathogen levels can be reduced through decomposition (Zasoski, 1981). As forests are not food chain crops, many of the public health concerns and land application regulations should not be as critical as those associated with agricultural site (Cole et al., 1983). These changes will depend on the properties of the applied sludge and the quality of sludge applied (Zasoski, 1981). However, the moist, anaerobic qualities of sludge are not conducive to plant growth. These qualities can be alleviated by mixing sludge with a bulking agent and allowing the mixture to compost (Bledsoe, 1983).
Some countries move forward significantly in using industrial and residential sludge in agriculture and forest crops. This is one of the important safe disposal systems, becoming popular in some other countries. It has been found that everyday 300 to 350 tons garbage is generated in Dhaka (Bhuiyan, 1991). About 3,000 tons of garbage is generated in all metropolitan cities a day. Management of this waste costs about Tk. 200 million a year as against the collection of conservancy tax to the tune of Tk. 120 million a year (Majumder, 1996). Except for large cities like Dhaka and Chittagong, there is hardly any proper arrangement of collection and disposal of garbage in urban areas. Not only can the existing unhygienic crude dumping of garbage be avoided but the waste can be converted in to organic manure on a large scale.
Advantages of sewage sludge application in forestry over agriculture are because extensive areas of forest land and nurseries are available, sludge may be applied throughout the year unconstrained by the crop (Bayes et al., 1991), forests and nurseries are typically located in better drained sites and are not subject to the periodic flooding of alluvial agricultural areas, many of the forest areas and nursery soils are markedly deficient in the major nutrients that are found in the industrial sludge and wastewater, particularly nitrogen and phosphorous. Since the forests are not food chain crops, many of the public health concerns and land application regulations should not be as those associated with agricultural sites (Cole et al., 1983). Theoretically forest soils in the nursery have properties well suited to receive sludge and waste water additions, including high organic carbon content which will immobilize available nitrogen, a high infiltration rate which should minimize the potential for surface run off, and a perennial root system which should allow for year round uptake of available nutrients (Cole et al., 1983).