Anode substrate tailoring in fed-batch photosynthetic microbial desalination cell for industrial and domestic wastewater treatment

Abstract

Photosynthetic microbial desalination cells (PMDCs) have recently been valued for their dual capabilities in desalination and effluent treatment, coupled with energy generation. As a green technology, they leverage photosynthetic microbes to continuously supply in-situ oxygen at the cathode, which enhances reduction reactions. PMDCs also aid in nutrient removal and algal biomass production. While substrate concentration is a crucial factor influencing PMDC performance, especially with high-strength wastewater, it remains underexplored. Most studies have used anodic wastewater concentration typically ranging from 75 to 3000 mgL^-1, with only one study focused on examining the impact of substrate concentration on PMDC using 500 and 1000 mgL^-1. Therefore, this research addresses this gap by evaluating the PMDC performance at 2000, 4000, and 6000 mgL^-1 anode substrate concentrations. The study employed Scenedesmus obliquus as a biocatalyst for domestic wastewater treatment at the cathode. It was found that MDCs exhibited better performance at a substrate concentration of 4000 mgL^-1, with PMDC achieving the highest efficiency owing to the availability of the substrate and the lowest internal resistance. PMDC achieved an average working voltage, anode COD removal, and desalination of 276 mV, 83%, and 27%, respectively, which were 38%, 6%, and 17% higher than MDC control at 4000 mgL^-1 substrate concentration. Additionally, PMDC at the cathode demonstrated a notable reduction in COD at 72%, NH₄⁺-N at 62%, and PO₄^3-- P at 43%, with an average algal growth rate of 418 mgL^-1d^-1. These findings prove that PMDCs are suitable and effective integrated desalination and wastewater treatment options.