Sludge minimisation technologies

Abstract

The treatment and disposal of excess sludge represents a bottleneck of wastewater treatment plants all over the world, due to environmental, economic, social and legal factors. There is therefore a growing interest in developing technologies to reduce the wastewater sludge generation. The goal of this paper is to present the state-of-the-art of current minimisation techniques for reducing sludge production in biological wastewater treatment processes. An overview of the main technologies is given considering three different strategies: The first option is to reduce the production of sludge by introducing in the wastewater treatment stage additional stages with a lower cellular yield coefficient compared to the one corresponding to the activated sludge process (lysis-cryptic growth, uncoupling and maintenance metabolism, predation on bacteria, anaerobic treatment). The second choice is to act on the sludge stage. As anaerobic digestion is the main process in sewage sludge treatment for reducing and stabilising the organic solids, two possibilities can be considered: introducing a pre-treatment process before the anaerobic reaction (physical, chemical or biological pre-treatments), or modifying the digestion configuration (two-stage and temperature-phased anaerobic digestion, anoxic gas flotation). And, finally, the last minimisation strategy is the removal of the sludge generated in the activated sludge plant (incineration, gasification, pyrolysis, wet air oxidation, supercritical water oxidation).

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“…This sludge contains volatile solids and retains about 95% of water resulting in a large volume of residual solids produced. The biological sludge production in conventional wastewater treatment plants can be minimized using different strategies (Pérez-Elvira et al 2006), such as endogenous metabolism and maintenance metabolism. In this last approach part of energy source is used for maintaining living functions, in this phase the substrate consumption is not used for cellular synthesis.…”

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“…The activated sludge process is the most widely used for biological waste water treatment in the world, but it results in the generation of a considerable amount of excess sludge that has to be disposed of (Pérez-Elvira et al, 2006). The cost of the excess sludge treatment and disposal can represent up to 60% of the total operating costs.…”

“…Therefore, current legal constraints, rising costs and public sensitivity towards sewage sludge disposal necessitate the development of strategies for the reduction and minimisation of excess sludge production. Reducing sludge production in waste water treatment instead of post-treating the sludge that is produced appears to be an ideal solution to this issue, because the problem would be treated at its roots (Pérez-Elvira et al, 2006). The biological sludge production in conventional wastewater treatment plants can be minimised in a number of ways.…”

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“…Likewise the pathogen reduction was similar in the two stage system. More recently Dareioti [57], Sakar et al [58]; Kara et al [59]; Parawira et al [60]; Nishio and Nakashimada [61]; Perez-Elvira et al [62]; Alatriste-Mondragon et al [63] and Ke ShuiZhou et al [64] have reported on the role of and variations to approaches in two stage anaerobic digestion in treating a range of organic wastes. Kumar [49] used two stage anaerobic digestion on piggery effluent.…”