Abstract
Abstract In order to optimize the operating conditions for a combined polyaluminum chloride (PACl) coagulation/flocculation and ultrafiltration process for treating potable water, the main, second order and interaction effects of PACl dose and flocculation retention time (FRT) on permeate turbidity, UV254 and membrane permeability were investigated using a 100 kDa hollow fiber membrane operated in the dead-end mode. A multilevel factorial design was used to determine the relevant ranges of the two factors for optimization. A 22 central composite design (CCD) was then used to develop mathematical correlation models for the optimum operating conditions. The main effect of PACl dose was the most significant factor on all the responses. For permeability, both the main effect of FRT and FRT–PACl dose interactions were found to be insignificant. The optimum PACl dose and FRT for the feed water were 20 mg/L and 14 min, respectively. Corresponding permeate turbidity, UV254 and permeability were 0.15 ± 0.01 NTU, 0.003 ± 0.001 cm−1 and 62.0 ± 9.52 Lm−2 h−1 bar−1, respectively. Experimental validation runs confirmed the reliability of the predicted optimal conditions thus implying that CCD models can be used to predict/optimize the quality and quantity of permeate from hybrid coagulation–ultrafiltration systems for potable water treatment.
Highlights
Ultrafiltration (UF) is widely applied as an effective technique for removing a diverse array of waterborne pathogens such as protozoa, bacteria and viruses from drinking water (Hill et al ; Mull & Hill )
The statistical significance of polyaluminum chloride (PACl) dose and flocculation retention time (FRT) on turbidity, UV254 and color of the feed water was investigated and their relevant experimental ranges to consider for optimization were determined
A similar observation was reported by Li et al ( ) who claimed that among the factors affecting the hybrid coagulation – UF process, coagulant dose and retention time are two crucial factors that can impact on floc formation and size distribution as well as permeability of UF membranes
Summary
Ultrafiltration (UF) is widely applied as an effective technique for removing a diverse array of waterborne pathogens such as protozoa, bacteria and viruses from drinking water (Hill et al ; Mull & Hill ). ). Compared with conventional sand filtration, UF has several advantages which include a higher treatment efficiency, smaller footprint, fewer chemicals demand, less sludge production and easy automation. Recent advances in membrane technology have made UF a cost-effective alternative to other filtration techniques (Jeong et al ; Mull & Hill ). It is seen by communities as a safer treatment alternative (Guo et al )
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