Increasing environmental awareness coupled with more stringent regulation standards has triggered various industries to challenge themselves in seeking appropriate wastewater treatment technologies. Coagulation−flocculation process is regarded as one of the most important and widely used treatment processes of industrial wastewaters due to its simplicity and effectiveness. This paper provides a critical review on recent studies of coagulation−flocculation treatment processes of various industrial wastewaters. The limitations and challenges for the coagulation−flocculation process such as the toxicity and health hazard posed by inorganic coagulants, production of large amount of toxic sludge, ineffectiveness in removing heavy metals and emerging contaminants, increase in effluent color, inefficient pollutant removal using natural coagulants, and complexity of scaling up procedure are presented. In addition, an overview on the influence of process parameters on treatment efficiency is included in this review. Finally, this review concludes with recommendations for improvements and new directions for this long-established process.

The growth of Rhodobacter sphaeroides NCIMB8253 was investigated under photoanaerobic conditions with different concentrations of palm oil mill effluent in a dual effluent growth medium. The influence of pulp and paper mill effluent as an alternative diluting agent on the bacterial growth was also investigated. During this study, it was determined that the use of pulp and paper mill effluent as a diluting agent promoted bacterial growth compared with the use of raw palm oil mill effluent medium alone. The cell growth data for all experimental sets were well-fitted to the logistic and modified Gompertz models. The results revealed that 25% (v/v) palm oil mill effluent medium with pulp and paper mill effluent as a diluting agent, namely G5 medium, can be applied as a suitable growth medium. A maximum colony-forming-units (CFU) number of 360 × 10 8 CFU/mL was achieved in G5, which was higher than that for raw palm oil mill effluent and comparable with that for water-diluted palm oil mill effluent medium. Furthermore, chemical oxygen demand level (COD total and COD soluble ) reductions were observed in all treatments.

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