Microplastics decrease the toxicity of cadmium to methane production from anaerobic digestion of sewage sludge

Area of Science:

• Environmental Science
• Biotechnology
• Environmental Chemistry

Background:

• Microplastics (MPs) and cadmium (Cd) individually inhibit methane production in sewage sludge anaerobic digestion.
• Previous research primarily focused on single pollutant effects, not their co-occurrence in real-world scenarios.

Purpose of the Study:

• To investigate the combined effects of PVC-MPs and Cd on the anaerobic digestion of sewage sludge.
• To elucidate the mechanisms behind the mitigation of Cd toxicity by PVC-MPs.

Main Methods:

• Anaerobic digestion experiments with varying concentrations of PVC-MPs and Cd.
• Analysis of methane yield, organic fluxes, dissolved substances, and short-chain fatty acids.
• Investigation of Cd adsorption by PVC-MPs and sludge.

Main Results:

• Environmentally relevant PVC-MP levels reduced Cd toxicity without impacting methane yield.
• At higher PVC-MP concentrations (30 particles/g TS), methane production recovered significantly (from 58.8% to 89.7% of control) in the presence of Cd.
• Increased organic fluxes, particularly dissolved substances and short-chain fatty acids, were observed.
• PVC-MPs showed higher Cd adsorption than sludge, reducing Cd bioavailability to anaerobes.

Conclusions:

• PVC-MPs can mitigate the inhibitory effects of Cd on anaerobic digestion of sewage sludge.
• The adsorption of Cd by PVC-MPs is a key mechanism reducing its bioavailability and toxicity.
• Findings provide crucial data for evaluating the combined toxicity of MPs and metals in anaerobic environments.