The application of an absorbent-amended microalgal-bacterial system for enhancing hydrothermal liquefaction wastewater treatment and resource recovery

Enhancing pollutant removal and biomass production from hydrothermal liquification wastewater (HTLWW) through microalgal-bacterial systems are two crucial steps to guarantee high operation efficiency in the Environment-Enhancing Energy paradigm, which can realize energy production and environmental protection. However, the toxicity of HTLWW limits microalgal-bacterial growth. In this work, zeolite and granular-activated carbon (GAC) were used to reduce the toxicity of HTLWW. The results showed that adding adsorbents to a microalgal-bacterial system efficiently improved pollutant removal and biomass accumulation. GAC and zeolite improved microalgal growth and total suspended biomass (TSB) accumulation, respectively. The combination of zeolite and GAC can maximize the wastewater treatment efficiency while ensuring biomass yield. In adsorption experiments, the soluble chemical oxygen demand (SCOD) and ammonium (NH 4 + ) removal reached 90.0 and 85.0% with the addition of 5 g L −1 GAC and 100 g L −1 zeolite, respectively. In sequencing batch tests, both SCOD and NH 4 + removal was higher in all adsorbent addition groups. The highest TSB was 1218 ± 304 mg L −1 in the zeolite addition group, which was 35.9% higher than that in the control group. In continuous tests, the combination of adsorbents greatly improved pollutants removal. SCOD removal, NH 4 + removal, and TSB of the GAC + zeolite group were 18.1, 121.5, and 29.9% higher than the control group, respectively. In addition, component analysis showed that most of the nitrogenous organic compounds and benzene derivatives in HTLWW were removed by GAC, reducing the amount of toxic substances and consequently enhancing the biodegradability of HTLWW.