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Environ Sci Pollut Res (2014) 21:1040710418 DOI 10.1007/s11356-014-2900-1
RESEARCH ARTICLE
Coagulant recovery from water treatment plant sludge and reuse in post-treatment of UASB reactor effluent treatingmunicipal wastewater
Abhilash T. Nair & M. Mansoor Ahammed
Received: 22 January 2014 /Accepted: 7 April 2014 /Published online: 29 April 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract In the present study, feasibility of recovering the coagulant from water treatment plant sludge with sulphuric acid and reusing it in post-treatment of upflow anaerobic sludge blanket (UASB) reactor effluent treating municipal wastewater were studied. The optimum conditions for coagulant recovery from water treatment plant sludge were investigated using response surface methodology (RSM). Sludge obtained from plants that use polyaluminium chloride (PACl) and alum coagulant was utilised for the study. Effect of three variables, pH, solid content and mixing time was studied using a BoxBehnken statistical experimental design. RSM model was developed based on the experimental aluminium recovery, and the response plots were developed. Results of the study showed significant effects of all the three variables and their interactions in the recovery process. The optimum aluminium recovery of 73.26 and 62.73 % from PACl sludge and alum sludge, respectively, was obtained at pH of 2.0, solid content of 0.5 % and mixing time of 30 min. The recovered coagulant solution had elevated concentrations of certain metals and chemical oxygen demand (COD) which raised concern about its reuse potential in water treatment. Hence, the coagulant recovered from PACl sludge was reused as coagulant for post-treatment of UASB reactor effluent treating municipal wastewater. The recovered coagulant gave 71 % COD, 80 % turbidity, 89 % phosphate, 77 % suspended solids and 99.5 % total coliform removal at 25 mg Al/L. Fresh PACl also gave similar performance but at higher dose of 40 mg Al/L. The results suggest that coagulant can be recovered from water treatment plant sludge and can be used to treat UASB reactor effluent treating municipal wastewater which
can reduce the consumption of fresh coagulant in wastewater treatment.
Keywords Coagulant recovery . BoxBehnken design . Recovered coagulant reuse . Response surface methodology . Water treatment plant sludge
Introduction
Coagulation is the most common process used to remove suspended particles, colloids, organics, colour and microorganisms from the drinking water supplies (Duan and Gregory...