Boosting VFAs production during the anaerobic acidification of lignocellulose waste pulp and paper mill excess sludge: Ultrasonic pretreatment and inoculating rumen microorganisms

Ultrasonic pretreatment combined rumen microorganisms (RM) anaerobic hydrolysis was used as a novel method to boost volatile fatty acids (VFAs) production from lignocellulose waste pulp and paper mill excess sludge (PPES). To investigate the effect of ultrasonic on PPES degradation, various ultrasonic power levels and treatment time were used to treat PPES. The findings showed that ultrasonic pretreatment breaks the structure of PPES distinctly and significantly contributes to promoting PPES degradation. Under ultrasonic power level of 540 W and treatment time of 50 min conditions, the production of soluble chemical oxygen demand (SCOD), ammonia nitrogen (NH4+-N), reducing sugar, and soluble protein was 36.9, 16.9, 29.2, and 26.8 times of control-1, respectively. In the following RM anaerobic acidification experiment, VFAs production of PPES after ultrasonic treatment increased by 92 % compared to that of PPES without ultrasonic treatment and were much higher than that of the control-2 group without inoculating RM. During the fermentation stage, the degradation yield of cellulose, hemicellulose and lignin were 40.35 %, 58.35 % and 16.49 %, respectively. These results demonstrated that ultrasonic-RM treatment could improve the efficiency of the anaerobic acidification process and VFAs production and RM had a strong effect on degradation of hemicellulose and cellulose. In addition, Illumina MiSeq sequencing showed that the number of microbial species decreased, and the dominant flora changed.