Making waves: Microbe-photocatalyst hybrids may provide new opportunities for treating heavy metal polluted wastewater

Abstract

Heavy metal contamination has received increasing attention as a growing worldwide environmental problem. Traditional remediation methods are mainly based on adsorption, precipitation and oxidation–reduction, which reduce the availability or toxicity of heavy metal ions. Microbe-photocatalyst hybrids (MPH), which behave as a semi-artificial photosynthetic system, integrate microbial cells with artificial photocatalysts for solar-to-chemical conversion. A few very recent studies indicate that MPH can be applied to treat organic contamination in water. Here, we propose a novel idea that MPH may also have great potential for solving heavy metal pollution. Heavy metals in wastewater could possibly be utilized to synthesize photocatalysts for MPH by microbial mineralization. Photo-induced electrons generated by photocatalysts in MPH can be transferred into microbial cells to promote intracellular enzymatic reductions, which allows heavy metal ions such as Cr6+ and Se4+ to be reduced and detoxified. Moreover, heavy metal ions like As3+ and Sb3+ can be used as sacrificial electron donors to maintain the continuous operation of the MPH, whereby these metal ions are simultaneously oxidized and detoxified. The excellent potential of MPH in the treatment of heavy metal-polluted wastewater is explained and a solution based on MPH is put forward as well as verified experimentally in this work. This solution can realize electron transfer between different metal ions to simultaneously remediate multiple heavy metal ions in wastewater. This finding may bring new hope for treating multiple heavy metal polluted wastewater in the future.