Treatment of greywater by adsorption and coagulation with Hibiscus Sabdariffa as the natural coagulant

Abstract

Greywater refers to wastewater from showers, baths, basins and washing machines. Recycled greywater can be used for crops irrigation, toilet flushing, and other activities that does not require fresh water. Coagulation is an effective, simple, and cheap process to treat greywater with the use of coagulants. The studies show that the use of chemical coagulants pose threat to the environment, produce large amount of sludge and have severe effect on human health. This study uses Hibiscus Sabdariffa seeds as natural coagulant, as they are biodegradable, non-toxic, and safe for human health. The seeds of Hibiscus Sabdariffa are usually discarded, thus using them as natural coagulants makes it cost-effective. Another process of adsorption was also studied in this work due to its effectiveness in treating wastewater. Activated carbon have been studied as an adsorbent due to its low-cost and sustainability. The aims of this paper are to investigate the performance of the seeds and adsorbent by differing pH, coagulant dosage, and adsorbent dosage. Jar test was carried out by varying pH of 2-12, coagulant dosage of 20-120 mg/L and adsorbent dosage of 0.5-5g. The process involved rapid mixing for 4 minutes, slow mixing for 25 minutes and 30 minutes of sedimentation time. By carrying out the experiment, it was found out the seeds of Hibiscus Sabdariffa showed best performance at pH 2, coagulant dosage 20 mg/L with the turbidity removal and COD removal of 91.3% and 43%, respectively. For the process of adsorption, highest turbidity and COD removal were determined to be 98.6% and 61.6% respectively with the pH 2 and adsorbent dosage of 3g. The combined process of adsorption-coagulation shows best performance at pH 2, coagulant dosage 4 mg/L and adsorbent dosage of 1.6g with the turbidity and COD removal of 98.3% and 85% respectively. This study shows the potential in Hibiscus Sabdariffa seeds and activated carbon to treat greywater for reuse.