The Influence of Microfibres in Municipal Sludge on Biogas Production

Abstract

Wastewater treatment plants (WWTPs) contribute to the release of microplastics into the environment. While the removal efficiency of MPs in WWTPs can reach up to 99.9 %, the highest amount of microplastics is retained in the sludge. Anaerobic digestion, one of the most promising and common processes, can help reduce sludge volume and odour, and due to the formation of biogas, mainly consisting of methane (CH4) and carbon dioxide (CO2), can help decrease the operating costs of WWTPs. A test measuring the inhibition of biogas production using the OxiTop® measuring system was employed to determine the effect of added microfibres (MFs) on biogas production. Particles less than 1 mm in size of polyester, polyamide, and polyacrylic, were added to anaerobic sludge at concentrations ranging from 0.05 to 0.10 g l−1 to simulate their effect on biogas production. The yields of CH4 and CO2 produced during anaerobic digestion of the MFs-contaminated sludge were determined. The addition of MFs to sewage sludge affects methane production. The results indicated that the lowest added concentrations of 0.05 g l−1 of MFs promoted methane production, while the presence of 0.1 g l−1 decreased methane production for all types of MFs used. Polyacrylic at 0.1 g l−1 had the most negative effect on methane production (up to 27 %), while polyamide at 0.05 g l−1 reached the highest methane production (up to 25 %).

Keywords

• anaerobic digestion
• methane production
• polyester
• polyamide
• polyacrylic