Water saving and reuse strategies for a local South African fresh-produce bulk market

Abstract

This research addresses water conservation and wastewater reuse strategies at the Clairwood fresh produce bulk market in Durban, South Africa. The research aims to optimise wastewater treatment processes through a comparative evaluation focusing on three technologies: electrocoagulation (EC), dissolved air flotation (DAF), and slow sand filtration (SSF). Effluents from three sources – Trader’s Hall, Distribution Centre, and Final Effluent were characterised based on physical, chemical, and biological parameters, including chemical oxygen demand (COD), turbidity, suspended solids, and microbial content. Results revealed high pollution levels, with COD concentrations ranging from 300 to 1200 mg/L, turbidity reaching 150 NTU, and suspended solids up to 500 mg/L. To address these challenges, wastewater samples were collected from the Trader’s Hall, Distribution centre, and Final Effluent and were analysed for key physical, chemical, and biological parameters. The samples were treated using EC, DAF, and SSF under controlled laboratory conditions. Optimisation of the processes was performed using Response Surface Methodology (RSM), considering operational parameters such as induced voltage, agitation speed, and retention time on treatment performance. The effectiveness of each technology was assessed based on pollutant removal efficiencies, including COD, turbidity, suspended solids, and microbial reduction. EC emerged as the most effective treatment, achieving 95% COD removal, 98% turbidity reduction, and significant decreases in conductivity. In comparison, DAF achieved 85% COD removal, while SSF demonstrated limited effectiveness, achieving only 60% COD removal. The optimised EC process showed scalability potential and was validated against the South African National Water Act and South African National Standards for applications such as cleaning the skip area, ablution systems, and process water. The study concluded that up to 27% of the market’s municipal water demand could be offset by reusing treated wastewater, based on a comparison between the volume of treated effluent meeting reuse standards and market’s recorded municipal water consumption. This research underscores the viability of EC as a cost-effective and environmentally sustainable technology, particularly for regions grappling with water shortages. Although a detailed economic analysis was not conducted, the high treatment efficiency and relatively low operational requirements suggest potential cost benefits. Beyond its technical contributions, the study highlights broader implications for optimising wastewater treatment and reuse processes in the fruit and vegetable process industry (FVPI). These findings align with global sustainability goals (in particular, #6 Clean water and sanitation), offering a replicable model for integrating wastewater reuse into industrial systems to mitigate water scarcity and promote environmental stewardship.