ReviewSustainable management of water treatment sludge through 3‘R’ concept
Introduction
The trend of urbanization and rapid growth of population have exerted the portable water demand, which requires exploration of raw water sources, developing treatment and distribution systems. In order to meet the increasing demand, the production of potable water from the water treatment plants (WTPs) has to be increased. Surface water mainly from river carries suspended as well as colloidal solids and other impurities. Therefore, requires proper treatment, depending on the quality of available raw water and quality needed at the users end. The conventional WTPs involve the process of coagulation, flocculation, sedimentation, filtration and disinfection. During these treatment processes large quantity residues or wastes are generated known as water treatment sludge (WTS) and a typical WTP produces about 100,000 ton/year of sludge whereas, on a global scale, available literature estimates that at present the daily production of sludge exceeds 10,000 ton (Babatunde and Zhao, 2007). The WTS is of environmental concern and requires careful consideration if it is to be managed in an environmentally acceptable and sustainable manner.
In India, WTS from most of the WTPs are being discharged into nearby drains, which ultimately meet the water source on downstream side of intake. In some of the WTPs, clarifiers are cleaned once in a year and the sludge is disposed off on nearby open lands (CPCB report, 2011). The simple method of final disposal, although a less expensive, is not a proper solution due to the possibility of contamination of water bodies and soil from the chemical products used in the treatment. Proper handling of increasing residual sludge from WTPs in an economical and environmentally friendly manner remains a very important issue. The recovery, recycling and reuse, 3‘R’ may provide a sustainable solution to the WTS management problems under stringent environmental laws. Therefore, the main objective of this paper is to present a comprehensive review of sustainable approaches and prospective trends in sludge handling that contributes to the WTS reuse.
Section snippets
Methods and scope
Current study focuses the developments on WTS management approaches identified and investigated worldwide. However the subject is still in developing stage in some countries but with the realization of adverse environmental impact, strict legislation may be implemented soon for the safe disposal of WTS. A comprehensive review of different methods reported in peer-reviewed journals, conference proceedings, published reports and other documents presenting, sustainable sludge management through
Physicochemical characterization
The term “water treatment sludge (WTS)” covers all wastes produced during treatment of water in a WTP and the properties of the WTS depend typically on the quality of raw water and the treatment method applied. If the groundwater, generally having stable quality is treated, the quantity and quality of the WTS fluctuate very little. On the other hand, the treatment of surface water sometimes results noticeable change in the sludge production in terms of quality and quantity. It may occur due to
Toxicity and environmental challenges
Literature over the potential toxicity of the WTS is very limited and also the available literature is somewhat contradictory, therefore there is need of detailed study to find the toxicity of inorganic especially metallic contaminants as well as organic contaminants present in the WTS when exposed to land and water environment (Babatunde and Zhao, 2007). The toxicity of alum sludge was studied by George et al. (1995) and concluded that the alum sludge may affect the algal growth in the
Sustainable reuse options
The physicochemical characteristics of WTS as reported in the literature permit the constructive utilisation of sludge in various ways. Hence, some of the prominent reuse options identified across the globe have been documented with past findings and recent development in the consequent sections.
Discussion
Reuse of WTS provides a unique and sustainable end point solution to sludge disposal problem. Fig. 3 presents the summary of the reuse options with associated advantages and disadvantages. Different applications of WTS in wastewater treatment would provide some significant chemical savings through resource recovery and reuse; enhance the treatment efficiency and reduce the sludge volume. However, it is unlikely that the wastewater treatment plant would be cited close to a WTP. But it could be a
Conclusions
Safe sludge disposal has emerged as a significant element of water resource planning and management. Currently practised sludge disposal method poses danger to the environment and public health. Therefore, finding beneficial reuse options became paramount for sustainable sludge management. Such reuses of the WTS should have a multi dimensional approach, offering both economic and environmental sustainability. Several reuse options investigated globally would positively contribute in developing
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