Integrating biodegradation and ozone-catalysed oxidation for treatment and reuse of biomass gasification wastewater

Syngas purification via wet-scrubbing processes generates a relevant amount of wastewater, which requires proper treatments before its disposal or reuse. Integrating chemical with cost-saving biological approaches represent a valuable alternative to traditional chemical-physical treatments. This study investigated the effectiveness of the BIO&CHEM treatment scheme for the treatment and reuse of wastewater collected from a wet-scrubber unit (chemical oxygen demand, COD = 2600 mg/L) containing several hazardous pollutants such as phenol (110 mg/L) and xylene (64 mg/L). The BIO&CHEM system included a sequencing batch biofilter granular reactor (SBBGR) and an ozonation unit that were operated at different hydraulic retention times (HRTs, from 5 to 1 day) and transferred ozone doses (TODs, 400, 280 and 250 mg/L), respectively. When a 4 d-HRT was selected, biologically treated wastewater was characterized by a COD of 140 mg/L and its toxicity on Daphnia magna was decreased from 100% to 5%. The integration between the biological SBBGR-based treatment (HRT = 1.5 d) and the ozonation (TOD = 280 mg/L) lowered effluent COD to 33 mg/L and erased toxicity on Daphnia magna. This operating condition resulted the most sustainable enabling multiple wastewater reuse and a significant reduction of plant size comparing with the biological treatment. Furthermore, the investigated aromatic and polyaromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs; including benzene, toluene, xylene and phenol) were completely removed. The analysis of the reactor biomass, performed at the end of the experimental trial, excluded also their mere accumulation within the reactor due to absorption or adsorption on the sludge.