Study Of Improving The Dewaterability Of Sewage Sludge By Filamentous Fungi

Dewatering is the key step of sewage sludge treatment,which can reduce the difficulty and cost of subsequent treatment and disposal of sludge.Nevertheless,the dewaterability of excess sludge of wastewater treatment plants is generally poor.Therefore,conditioning is needed to improve the dewaterablility of sludge.At present,organic and inorganic chemical flocculants are the most widely used dewatering conditioners.However,these chemical conditioners are expensive,and may cause secondary pollutions of environment.Owing to lower cost and secondary pollution risk,biological conditioning methods are attracting more and more attentions.In this study,a filamentous fungus was isolated from municipal sludge for sludge conditioning.The effects of the filamentous fungus on sludge dewaterability under different treatment conditions were investigated in lab scale.Furthermore,the improvement of sludge dewatering performance by the filamentous fungus was also evaluated on a pilot-scale plate and frame filter press.The main research contents and results are as follows:(1)Isolation and identification of the filamentous fungus,and its growth and pelletization characteristicsA filamentous fungus was isolated from the municipal sludge,and named as Talaromyces flavus S1 after identification.The pelletizing ability of the fungus was preliminary analyzed.The appropriate cultivation condition for the pelletizing of T.flavus S1 in liquid nutrient medium was rotating speed 150 rpm or 175 rpm,pH 3.0,after spore inoculation.The pelletization rate achieved 15.17%.No sludge-mycelium pellet formed when cultivation T.flavus S1 in raw sludge with spores inoculation,however,the particle size of sludge was increased under high rotating speed.While stable sludge-mycelium pellets formed when cultivation T.flavus S1 in the sterilized sludge with spores inoculation.The pelletization rate of sludge-mycelium pellets achieved 33.99%,and the average diameter of the pellets was 5.2mm under pH 6.81.(2)The performance and mechanism of sludge dewaterability improvement by inoculation of T.flavus S1 sporesThe sludge dewaterability could not be improved when the T.flavus S1 spores was inoculated into the raw sludge.While after the T.flavus S1 spores was inoculated into the sterilized sludge,the T.flavus S1 spores grew well as there is no competition from other microorganisms in the sludge.The dewaterability of the sterilized sludge was significantly improve by T.flavus S1,with the main reasons of 1)the growth of T.flavus S1 reduced the extracellular polymeric substances(EPS)in the sludge,especially the polysaccharide in slime-EPS and loosely-bound EPS(LB-EPS);2)the growth of T.Flavus S1 mycelia promoted the formation of sludge-mycelium pellets as well as increasing the particle size of non-pelletized sludge.In addition,the pH and the total COD(TCOD)of the sludge both decreased with the growth of T.flavus S1.(3)The performance and mechanism of sludge dewaterability improvement by conditioning of T.flavus S1 myceliaThe raw sludge was conditioned with pre-cultured T.flavus S1 mycelia,and thedewaterability of sludge was significantly improved.More significant improvement was found when the sludge was with a poorer initial dewaterability,or with a higher of sludge concentration.In addition,the larger mycelium dosage used,the more significant improvement of dewaterability achieved.When mycelium dosage was 50%(v/v),the capillary suction time(CST)and specific resistance of sludge(SRF)of the treated sludge were lower than that of the sludge respectively treated with 2‰(w/w)polyacrylamide(PAM)and 5%(v/v)polyaluminum ferric chloride(PAFC).The improvement of sludge dewaterability by combined treatment of PAM and mycelium was only slightly higher than that by individual conditioning with the T.flavus S1 mycelia.The dewaterability improvement by T.flavus S1 mycelia may mainly be attributed to that the fine sludge particles was wrapped into the fungal mycelia and further formed the sludge-mycelium pellets.The wrapping of fine sludge particles could alleviate the blocking of interspaces between sludge flocs and pores of filter media,which ensuring the flowing out of free water.It was noticed that the secretions of fungal mycelium were not conducive to the improvement of sludge dewaterability.(4)The pilot-scale study on sludge dewaterability improvement by T.flavus S1 mycelia conditioningThe actual dewatering performance of the mycelia conditioned sludge was investigated on a small plate and frame filter press.Firstly,the optimal operation parameters of the plate and frame filter press were determined: feed pressure 0.6 MPa,feed time 60 min,compression pressure 0.85 MPa,compression time 30 min.Dewatering results showed that the T.flavus S1 mycelia could improve the dewaterability and dewatering rate of sludge,as well as decrease the moisture content and increase the thicknees of sludge cake.Though,PAM conditioning showed a better sludge dewaterability improvement performance,the explored conditioning method with T.flavus S1 mycelia is still very helpful for the development of novel biological conditioning process for sludge dewatering,owing to it comparable performance and particular environment friendliness.