Enhance primary sludge acidogenic fermentation with CaO2 addition: Investigation on soluble substrate generation, sludge dewaterability, and molecular biological characteristics

Abstract

NaOH could promote volatile fatty acids (VFAs) with the deterioration of sludge dewaterability and high concentrations of ammonia nitrogen (NH4+-N) and soluble phosphorus (SP) in sludge fermentation system. Whether calcium peroxide (CaO2), as a solid base, could improve the status quo is unknown. Therefore it is necessary to study the effect of CaO2 on primary sludge (PS) fermentation. Five experimental groups were conducted with different gradient doses of CaO2 and high-throughput sequencing was conducted to reveal the mechanisms. The results showed that CaO2 contributed to enhancing the yield of organic matter, but also reduced SP and improved the sludge dewaterability. The optimal CaO2 dosage was 0.10g/g VSS, and the yields of VFAs elevated from 872 to 2794 mg COD L−1, respectively. The concentration of SP in fermentation liquor declined from 23.74 to 3.23 mg L−1. The sludge dewaterability was improved with decreasing capillary suction time (CST) from 365 to 227 s. NH4+-N in fermentation was also controlled and the concentration declined from 581 to 276 mg L−1. For revealing the mechanism, high-throughput sequencing results demonstrated that CaO2 enhanced the bacterial richness and diversity, and Alkaliphilus, Acinetobacter, Macellibacteroides, Arobacter and Zoogloea significant increased with CaO2 adding. Meanwhile, metabolic pathway abundance results demonstrated that CaO2 promoted the microbial metabolism, and amino acid and lipid metabolisms led to VFAs and SCOD concentration increasing. As a whole CaO2 changed the microbial composition and metabolisms, and then effected soluble substrate generation.