Evaluation of the efficacy of cactus-banana peels composite as a natural coagulant for surface water treatment

Abstract

Approximately two billion people in the world lack access to safely managed drinking water. This constitutes a challenge that needs to be overcome by the realization of the sixth Sustainable Development Goal (SDG 6) on attainment of access to clean and safe water for all. To achieve SDG 6, it is important to adopt sustainable water treatment practices. The practices should be of low cost, which is why locally available materials need to be exploited to contribute to the attainment of the goal. Aluminium and ferric salts continue to be used as coagulants in drinking water treatment. Natural coagulants can be used for the same purpose because they are cheap, locally accessible and environmentally friendly. Low production yields and low molecular weight affect commercial adoption of natural coagulants from individual plants, hence the exploration of performance of their composites. This study evaluated the performance of a cactus-banana peels composite as a natural coagulant for surface water treatment as they are locally available and contain chemical functional groups responsible for their zeta potential in water coagulation. Design Expert Software was used to design jar test experiments for attainment of optimum mixing ratio, dosage, pH and extraction time of the composite and development of performance models. Performance of the coagulant was evaluated based on removal efficiencies of turbidity, total suspended solids (TSS) and Escherichia coli (E.coli). The goodness of fit for developed models was evaluated using R2 values and adequate precision. The optimal composition of the composite was cactus to banana peels ratio of 1:0.6. The optimally mixed powder had a bulk density of 590kg/m3 while the extracted liquid coagulant had pH and electrical conductivity of 7.05 and 1123 µS/cm, respectively. The optimum dosage, pH and extraction time were 11 mL/L, 7 and 28 mins, respectively. Turbidity, TSS and E.coli removal efficiencies were 87.02, 82.07 and 81.07%, respectively. These results indicated good performance of the composite coagulant in water treatment when compared to 82-99% for alum, the most commonly used commercial coagulant. The study recommends further investigation of the coagulant’s performance on other water types and quality parameters.