Study On The Application Of Bioflocculants In Water Treatment And Sludge-based Biochar Under The Background Of No-waste Cities

Sludge is a major solid waste pollutant of the wastewater treatment industry,and with the promotion of "no-waste cities",the resourceful disposal of sludge is a pressing issue for sustainable development in society.As a means of enhancing solid-liquid separation in wastewater treatment processes,flocculation can help to form compact flocs and promote its rapid settling.However,traditional flocculation(e.g.,polyacrylamide,PAM)have many drawbacks,such as poor biodegradability,corrosiveness and toxicity,which limit the resource utilization of sludge.In this study,a new rapidly degradable bioflocculant(RBDF)was synthesized by graft copolymerization reaction of modified starch and maltodextrin with PAM under the action of initiator.And the effects of RBDF in the application of sewage treatment and sludge-based biochar adsorption materials were evaluated experimentally.The results showed that:1.By FTIR,successful graft copolymerization of starch and PAM.In municipal wastewater flocculation experiments,RBDF exhibited better flocculation performance than PAM,with removal rates of COD,SS,and TOC at 98.79%,93.36%,and 86.93%,respectively,and a turbidity reduction of 53.2%;through the experiments on the variation of supernatant indexes with time,it was concluded that RBDF was more easily degraded by microorganisms compared with PAM and had good biochemical properties.TG-FTIR,Py-GC/MS,and SPME-GC/MS were used to detect the composition and volatile components of different sludges.The results showed that RBDF sludge was more easily pyrolyzed at 350-500℃,producing various organic gases that were beneficial to the subsequent preparation of sludge-based biochar;Compared with PAM,RBDF could better inhibit the odor of raw sludge,and the total amount and types of odor compounds produced during thermal drying of RBDF sludge were significantly lower than those of PAM sludge,accounting for less than 50% of the latter.2.Sludge-based biochar was prepared,and characterized by SEM,FTIR and zeta potential,the RBDF-BC structure is more sparse and porous,with the presence of oxygen-containing functional groups and some aromatized structure,and stronger adsorption performance;Adsorption experiments on different sludge-based biochars for Cr(VI)and Pb(II)yielded the following conclusions: RBDF-BC was suitable for adsorbing low-concentration heavy metal solutions,and its adsorption effect was better than that of PAM-BC under the optimal adsorption conditions.By modifying the sludge-based biochar,the results showed that the acid modification was more suitable for Cr(VI)adsorption and the metal modification was more suitable for Pb(II)adsorption.The adsorption process was analyzed by fitting adsorption kinetics and adsorption isotherms,and the sludge-based biochar was mainly chemisorbed,It is a monolayer adsorption on homogeneous surface.3.The leaching rate of heavy metals from sludge-based biochar was tested,and Cr,Cd,and Pb were not detected,indicating that it could be used for environmental remediation.The results of DOC detection in soil with sludge-based biochar showed that the DOC loss rate decreased significantly after soil was incorporated with sludge-based biochar under leaching conditions.The DOC loss rate was reduced by 14.72%,11.42%,and 16.81% in the soil with sludge-based biochar(PAM1,PAM2,RBDF)compared with the control group,respectively;Stabilization experiments for soil heavy metals showed that adding RBDF-BC increased the enrichment effect of the soil on Cd and Cr by 7.2% and 5.93%,respectively,indicating that it could stabilize specific heavy metals and mitigate soil heavy metal pollution.