Degradation kinetics of toilet paper fiber during wastewater treatment: Effects of solid retention time and microbial community

Abstract

Abstract Toilet paper (TP) fiber is a major slowly biodegradable constituent of municipal wastewater. Oftentimes, they cannot be efficiently removed during the preliminary treatment of wastewater treatment plants (WWTPs), especially for those without installation of primary clarifiers. Although fine-mesh sieves are effective in removing fibers, their applications are not common in current WWTPs. Therefore, it is critical to understand the degradation of TP fibers during the secondary wastewater treatment. In this study, the effects of solids retention time (SRT) and microbial community on the hydrolysis kinetics of TP were investigated in sequencing-batch activated sludge systems. Meanwhile, the influence of the addition of readily biodegradable organics such as glucose on fiber degradation was also studied. It was found that the overall degradation of TP linearly increased versus SRT. At 40-day SRT, approximately 83% of TP was degraded. The hydrolysis coefficient at 40-day SRT (0.116–0.137 d−1) significantly increased compared to those at SRTs smaller than 20 days (0.025–0.034 d−1), which was probably due to the stepwise hydrolysis of cellulose and hemicellulose fibers, as well as the synergistic enzymatic activities owing to the enhanced microbial diversity at larger SRTs. Actively functioning fiber-degrading Cellvibrio genus was identified as the dominant driver of fiber hydrolysis. Interestingly, it was discovered that fiber-degrading microbial communities were inefficient at consuming either glucose or acetate. Therefore, the addition of these substrates did not enhance TP degradation.