Optimisation of Electrocoagulation Flocculation Treatment of Laundry Greywater with Design of Experiment Methodology

Abstract

It is becoming increasingly more important to relook at the impact that greywater has on the environment and the opportunities that it can provide for water re-use. More especially that the sewer pipelines are often over flooded and overflowing onto the streets in most townships in South Africa due to sewer blockages, population, and wastewater treatment plants (WWTP) overcapacity. To cope with current and future wastewater treatment (WWT) demands, developments of alternative efficient and ecological safe WWT methods are required. Treatment of greywater with electrocoagulation-flocculation (ECF) techniques is one of the promising technologies. However, ECF applications seem to be heuristically approached due to the complexity of a multitude of ECF process control variables and a lack of understanding of their interactions. These variables may not only have a single effect on output but multiple inter-variable effects that need multi-parameter factor analysis. The statistical techniques Design of Experiment (DoE) and Response Surface Methodology (RSM) can be used to evaluate the interaction of factors on the ECF's treatment efficiency.

            In this research, the ECF efficacy was investigated by varying ECF process variables such electrodes types (stainless steel and aluminum, alternatively as anodes) in 800 mL and 2000 mL reactors to treat laundry greywater (LGW) under varying operating conditions of initial pH (3.5 to 8.5), voltage (10 to 15 V) and Mixing speed (0 to 500 rpm) that were carefully planned with DoE.

The optimum operating conditions were discovered to be between 4.5 and 5.75 pH at the start.; applied voltage (10V to 13.5 V), at mixing speeds between 125 and 350 rpm. There were varied successes with electrode type but iron seemed to favor affluent with more chlorides that ambient in LGW than that aluminum electrode, therefore the addition of chloride may improve iron ECF but this was not a variable. In this study, the results revealed that the only volume of the effluent can be increased in further studies to values beyond 2000 mL, which suggests that this ECF method can be scaled-up for the treatment of LGW with high TSS, pH out, turbidity, and color removal efficiency.