Study On The Effect And Mechanism Of Polydimethyldiallylammonium Chloride On Methane Production From Sludge Anaerobic Digestion And Hydrogen Production From Sludge Anaerobic Fermentation

Polydimethyldiallylammonium chloride(PDDA)flocculant is widely used in wastewater treatment and sludge conditioning,but its current potential impact on the subsequent treatment of sludge is unclear.In this paper,the potential effects of PDDA on the performance of sludge anaerobic fermentation for hydrogen and methane production were investigated through biochemical methane potential test and long-term operation of the reactor,and revealing the mechanism of PDDA affects anaeobic digestion and anaerobic fermentation by model substrate degradation test,key enzyme activity analysis and microbial community.The results showed that the addition of PDDA(5–40 g/kg TSS)significantly inhibited the performance of methane production from sludge anaerobic digestion,and the higher concentration to stronger inhibition effect.40 g/kg TSS PDDA caused the cumulative methane productin decreased from 227.2±9.1 m L/g TSS to 81.1±8.2m L/g TSS,a decrease of 64.3±0.2%.The mechanism explorations indicated that the inhibit effect of PDDA in sludge anaerobic fermentation was mainly attributed to its quaternary amine groups.Quaternary amine groups can form larger sludge floc and enhance the compactness of the sludge structure by neutralizing negatively charged amino groups in extracellular polymeric substances,thus hindering the release of soluable organic matter in the sludge.In addition,Quaternary amine groups can cause oxidative stress by inducing reactive oxygen species production,resulting in the decrease of cell viability.Further,it will inhibit the activities of key enzymes involved in the anaerobic digestion process,and also reduce the microbial abundance of hydrolyzing,acidifying,and methanogenic bacteria,thereby inhibiting the sludge anaerobic digestion process.Further research showed that PDDA inhibited the production of hydrogen of sludge anaerobic fermentation due to the stronger inhibition of the hydrogen production process than the hydrogen consumption process,and the degree of inhibition was positively correlated with PDDA concentration.40 g/kg TSS PDDA declined the cumulative hydrogen yield from 3.8±0.1 to 2.4±0.1 m L/g volatile suspended solids,reduced by 36.8±2.6%.PDDA induces anaerobic fermentation type transferred from propionic acid to acetic acid pathway,thereby reducing the production of hydrogen.Meanwhile,the Cl~–group of PDDA molecular structure makes Fe Fe hydrogenase inactivation by binding with H~+,diminishing the electron transport chain activity,which also constrained hydrogen production.In addition,PDDA also reduces the abundance of hydrogen producing bacteria including Firmicutes and Proteiniborus,thereby not conducive to the hydrogen production.This study reveals the negative effects of PDDA on methane production from sludge anaerobic digestion and hydrogen production from sludge anaerobic fermentation and its impact mechanism.The findings provide a new insight for In-depth understanding the potential behavior of quaternary ammonium salt cationic flocculants during anaerobic sludge fermentation,which has important theoretical guidance and practical significance for the selection of flocculants and ensuring the healthy and stable operation of sludge anaerobic digestion and anaerobic fermentation system in wasterwater treatment plants.