Co-Hydrothermal Liquefaction of Sewage Sludge and Beverage Waste for High-Quality Bio-energy Production

Abstract

The environment continues to experience pollution from a variety of industries including the beverage and wastewater treatment industries. These industries produce organic wastes; hence, they are costly to manage. As a result, they are largely incinerated or sent to landfills, respectively causing environmental pollution, and shrinking landfill space. To prevent these occurrences and better manage these wastes, thermochemical conversion processes have been touted as a possible solution. One such process is hydrothermal liquefaction (HTL). HTL is a process that converts wet waste biomass feedstocks at high temperature and pressure into biocrude oil, a solid residue (i.e., biochar), an aqueous co-product (i.e., wastewater, ACP), and vented gas. This study assessed the co-HTL of beverage waste with sewage sludge. Two beverage wastes: brewery trub (BT) and winery rose lees (RL) were co-liquefied with primary sludge (PS) and return activated sludge (RAS) at 300 °C, 90% water content, 30-min residence time, and co-HTL ratios (100/0, 75/25, 50/50, 25/75, and 0/100). The individual maximum yields of biocrude were PS (14.8%), BT (10.37%), RL (5.4%), and RAS (4.29%). In all cases, biocrude and biochar produced a higher heating value (HHV) greater than those of the original feedstocks. During the co-HTL experiments, a positive synergistic effect in terms of crude yield was observed between co-HTL of BT and PS; BT and RAS; and RL and PS while there was no appreciable effect in RL and RAS. Maximum yields of 15.45% and 15.14% were observed in the biocrude of co-liquefied BT and PS at 75/25 and 50/50 respectively. Co-HTL led to an increase in the HHV of the biocrude and biochar, and total organic carbon of ACP. The results of this study represent a favorable method for the simultaneous valorization of both sewage sludge and beverage waste into bioenergy products.