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Flue gas desulfurization-derived wastewater sludge (FGD-WWS) has been produced increasingly in China and India etc., and its content of heavy metals (HMs) including Cd, Cr, Cu, Hg, Ni and Zn seriously exceeds the limits allowed. Developing the suitable disposal of FGD-WWS is therefore significantly important and necessary. The novel process of electrokinetic treatment combined with chemical pretreatment of HMs in FGD-WWS were proposed here to improve the removal efficiency. Results indicate that the effects of different pretreatment agents (citric acid (CA), ammonia, tetrasodium of N, N-bis (carboxymethyl) glutamic acid (GLDA), and rhamnolipid) on the ET of HMs were different. To investigate the mechanism of combined process, the transformation potential (TP), exchange potential (EP) and removal potential (RP) were calculated. Correlation analysis shows the correlation between TP and RP was higher than that between EP and RP, indicating that the removal efficiency is mainly affected by the fraction transformation of HMs. Electric field, pH and pretreatment agents are main factors causing fraction transformation and affecting TP. Focusing on fraction transformation is an efficient way to improve further the removal efficiency. The work is promisingly valuable for developing the technology of treating FGD-WWS. [Display omitted] • The electrokinetic treatment and chemical pretreatment improve removal efficiency. • Chemical pretreatment with different agent has totally different effect. • The removal efficiency is mainly affected by the fraction transformation. • Adding different pretreating agents facilitate the fraction transformation. [ABSTRACT FROM AUTHOR]

Abstract: In India, over the last few decades, there has been a remarkable increase in sewage sludge production due to population increase and unplanned urbanization. The aim of the present study was to investigate the ability of an epigeic earthworm Eisenia foetida to transform primary sewage sludge (PSS) amended with cow dung (CD) into value added product, i.e., vermicompost in laboratory scale experiments. Two approaches investigated in the study were: (1) evaluation of vermistabilization of PSS and CD mixtures after 15 weeks in terms of fertilizer quality of the products and; (2) growth and reproduction of Eisenia foetida up to 11 weeks in different vermireactors. In all the PSS and CD mixtures, a decrease in pH, TOC and C:N ratio, but increase in EC, TKN, TK and TP was recorded. The heavy metals’ content in the vermicomposts was higher than initial mixtures. Maximum worm biomass was attained in 10% PSS+90% CD mixture while, the worm growth rate was highest in 30% PSS+70% CD feed mixture. It was inferred from the study that addition of 30–40% of PSS with CD had no adverse effect on the fertilizer value of the vermicompost as well as growth of Eisenia foetida. The results indicated that PSS could be converted into good quality manure by vermicomposting if mixed in appropriate ratio (30–40%) with cow dung. [Copyright &y& Elsevier]