Composting post-anaerobic digestion for emerging contaminant biodegradation: Impacts of operating conditions

Sustainable manure management technologies are needed, and combining anaerobic digestion (AD) for energy generation and aerobic composting (AC) to stabilize digestate and remove emerging contaminants (ECs), including veterinary pharmaceuticals and steroid hormones, is promising. This study identified post-AD, AC operating conditions that maximized degradation of study ECs, expected to be present in cattle manure digested using treated municipal wastewater as the water source. Study ECs included sulfamethoxazole (SMX), chlortetracycline (CTC), oxytetracycline (OTC), estrone (E1), and naproxen (NPX). Composting conditions were simulated in bench-scale reactors, with microorganisms from digestate produced in an AD system (25L scale), by varying temperatures, pH, and carbon source compositions (representing food waste/manure co-digestion with different residence times). Results indicate maximum SMX biodegradation occurred at 35 degrees C, pH 7, and with high levels of easily degradable carbon (>= 99%, 99%, and 98%), and maximum E1 biodegradation occurred at 35 degrees C, and with low levels of easily degradable carbon (>= 97% and 99%). Abiotic degradation was responsible for the nearly complete removal of tetracyclines under all conditions and for partial degradation of NPX (between 20% and 48%). Microorganisms originating from the AD system putatively capable of SMX and E1 biodegradation, or of contributing to biodegradation during the AC phase, were identified, including phylotypes previously shown to biodegrade SMX (Brevundimonas and Alcaligenes). Sulfamethoxazole biodegradation is optimal at 35 degrees C, pH7, and carbon-rich conditions.Estrone biodegradation is optimal at 35 degrees C and under carbon-poor conditions.Chlortetracycline and oxytetracycline removal increased with temperature.Novel taxa were linked with SMX and E1 biodegradation.Five known polycyclic hydrocarbon degrader taxa are linked with SMX biodegradation.

Automated summary

This study aims to identify optimal operating conditions for the degradation of emerging contaminants, including veterinary pharmaceuticals and steroid hormones, in manure treatment. The results showed that under specific temperature, pH, and carbon source conditions, efficient degradation of certain pollutants can be achieved. Additionally, potential microorganisms that may contribute to the degradation process during the aerobic composting phase were identified from the microbial strains in the anaerobic digestion system.