Optimization of agro-industrial wastewater treatment using unmodified rice starch as a natural coagulant

• Unmodified rice starch could be used as a natural coagulant in POME treatment.
• Rice starch as a coagulant aid was able to reduce alum dosage in POME treatment.
• RSM enabled TSS removals from POME up to 86.65% using alum plus rice starch.
• RSM enabled COD removals from POME up to 49.23% using alum plus rice starch.
• Addition of rice starch as a coagulant aid reduced the cost of chemicals by 33.8%.

There have been increasing interests on the use of organic starch derivative coagulants such as cationic starch in coagulation-flocculation process due to environment and health concerns regarding the use of inorganic coagulants. However, studies on the potential utilization of unmodified starch in wastewater treatment remain limited. In this study, treatment performance of unmodified rice starch and alum was tested on agro-industrial wastewater produced from crude palm oil extraction, namely palm oil mill effluent (POME). Response surface methodology (RSM) showed that an addition of unmodified rice starch not only enhanced total suspended solids (TSS) and chemical oxygen demand (COD) removals; but it also significantly improved the process by reducing both the dosage of alum (−47.95%) and settling time (−58.66%), while shifting the operating pH closer to the natural pH of POME. The treatment enabled TSS and COD removals up to 86.65 and 49.23%, respectively under the optimum conditions of 0.38 g/L alum, 0.28 g/L unmodified rice starch, pH 4.45 and settling time of 5.54 min. An addition of unmodified rice starch to alum also resulted in 33.8% reduction of chemical cost as compared to the treatment using alum alone.