Fouling and Energy Consumption Impede Electrochemical Disinfection of Constructed Wetland Effluents

Electrochemical disinfection (ECD) of constructed wetlands (CWs) effluents via in situ chlorine electrogeneration has been proposed for decentralised water treatment and reclamation. Studies demonstrating the feasibility of continuous ECD of CW effluents in field conditions for several weeks are scarce. Here, a pilot-scale CW was operated for 28 weeks to treat a calcium-rich wastewater stream (131 ± 42 mg L−1) for reclamation. Five electrochemical cell configurations were designed to continuously disinfect the effluent from the pilot-scale CW, differing in the water route, membrane type and catholyte. All configurations inactivated pathogens to levels considered safe for water reclamation. For four configurations, the maximum operating times without maintenance were short (< 1 week) due to calcium-based precipitates inducing membrane and cathode scaling. An additional configuration used rainwater as a cathodic influent for producing an alkaline stream to precipitate mostly calcium carbonate upstream from the ECD system. This avoided premature reactor failure, allowing 21 weeks of operation without apparent scaling. However, the alkaline stream demanded higher charge densities to be neutralised at the anode via water oxidation before a sufficient chlorine evolution. Thus, the flow rate of water treated (1.8 L h−1) was 4.6 times lower than for the other configurations. The resulting energy consumption (5.9 kWh m−3) was considered high for water reclamation. This work illustrates the practical aspects impeding stability and efficiency for ECD of hard waters and highlights possible strategies to deal with adverse scaling.