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

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 fedbatch process were relatively stable, ranging from 177 to 210 mL CH4 center dot 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.