Fed-batch processing of algae hydrothermal carbonization process water improves anaerobic digestion and digestate nutrient content

Abstract

The effects of the fed-batch process on anaerobic digestion (AD) of algae hydrothermal carbonization (HTC) process water were evaluated. The results showed that the methane (CH4) yields during ten rounds of the fed-batch process were relatively stable, ranging from 177 to 210 mL CH4·g CODadded−1. Interestingly, the fed-batch process could promote sludge granulation and significantly shorten the AD period, namely from 14 d of the initial group to 4 d of round 7. The nutrient concentrations of digestate accumulated gradually with the increasing rounds of the fed-batch process, producing the easy storable, and transportable concentrated digestate. Moreover, the concentrated digestate from round 10 induced seed germination index 61% higher than that of the initial group, showing great potential in improving soil fertility. This study provided an efficient and water-saving technology to treat algae HTC process water for CH4 production and concentrated liquid fertilizer recovery.