Comparative Study On Deep Dewatering Process And Mechanism Of Papermaking Sludge And Oily Sludge

A large quantity of wastewater containing high concentration of pollutants will be produced in the production process of papermaking industry.This kind of wastewater is usually treated by means of physical chemistry combined with biochemistry,and a large amount of sludge will be produced in this process.It is difficult to reduce the water content of the sludge and there are problems such as secondary pollution.This has a negative impact on the clean production of paper industry.More stringent requirements for sludge treatment and disposal have been proposed in new laws and regulations,and the sludge treatment and disposal are premised on dehydration reduction.The sludge from biochemical treatment of mineral oil-containing wastewater and papermaking wastewater have a common problem of dehydration difficulty because of the characteristics of wastewater pollutants,but there are great differences in the influencing factors of sludge dehydration difficulty.These two types of sludge are representative of industrial sludge in dewatering performance,biological structure and water beam mechanism.In this paper,papermaking sludge is selected as the research object,oily sludge is introduced as a comparison,flocculation and oxidation are adopted to condition the sludge.The relationship between sludge dewatering performance,the content and composition of extracellular polymeric substance was investigated,and the mechanism of dewatering was analyzed.Based on the idea and method of papermaking sludge treatment,the treatment of oily sludge is helpful to explore the common law of dewatering treatment of papermaking sludge and other types of industrial sludge.The understanding of the dewatering reduction of papermaking sludge can be deepened and the sludge dewatering theory and provide reference for engineering practice can be enriched.The results of dewatering performance,physicochemical properties and microbial population structure of the two types of sludge showed that the content of Ca and Si was the highest.The content of Al in papermaking sludge was higher,and the content of Cl and S in oily sludge was higher.The dehydration performance of the two types of sludge was similar,with Specific resistance to filtration（SRF）reaching 1×10¹²m·kg^-1,and the water content of the two types of sludge was more than 70 wt%.The Zeta potential of the papermaking sludge was lower,its particle size and size distribution span was larger.The content of extracellular polymeric substance（EPS）of papermaking sludge was lower and concentrated in soluble extracellular polymeric substance（S-EPS）.The protein in EPS of oily sludge is high and distributed relatively evenly.The properties of the two types of sludge were different,and the common problems of dehydration difficulties were probably related to the differences of EPS and microbial population structure.After flocculation,the SRF of papermaking sludge and oily sludge was significantly reduced,and the water content was reduced to 57.28 wt%and 57.84 wt%,respectively.Flocculation conditioning can neutralize the negative charge on the surface of sludge floc,promote the aggregation of sludge particles and remove the bound water in the sludge to varying degrees.For papermaking sludge with low protein content,aluminum flocculants had stronger removal effect on S-EPS,while for oily sludge with high protein content,iron flocculants had stronger removal effect on S-EPS and loosely bound extracellular polymeric substance（LB-EPS）.The effect of flocculation on sludge dewatering performance is related to the removal ability of S-EPS and LB-EPS by flocculant.The mechanism of improving the dewatering performance of sludge by flocculation conditioning is,on the one hand,the combined action of charge neutralization and particle size distribution is to promote the flocculation of sludge;on the other hand,the dynamic balance of mutual migration and transformation of EPS at different levels is broken,and the binding strength between EPS and water of sludge is reduced,resulting in the reduction of the content of bound water.There may be competition between these two mechanisms.The flocculant has a selective effect on protein,and the iron flocculant is more suitable for deep dehydration of sludge with high protein content.The treatment of Fenton oxidation combined with calcium oxide can greatly improve the dewatering performance of papermaking sludge and oily sludge.The SRF were decreased by95.95%and 95.06%,respectively,and the water content of sludge cake after pressure filtration were reduced to 44.39 wt%and 42.65 wt%,respectively.Acid treatment and Fenton oxidation treatment are the key factors affecting the dehydration performance.The mechanism of Fenton oxidation combined with calcium oxide conditioning can be divided into three stages:Firstly,the electrostatic repulsion between sludge floc was reduced by acid treatment,and some EPS and bound water were removed.Then,Fenton oxidation treatment had a stronger synchronous removal effect on EPS and bound water,and the hydrophilic ability of the remaining EPS was weakened.After the addition of calcium oxide,the pH of the system was increased,the precipitation of ferric hydroxide and calcium sulfate was promoted,the rigid skeleton inside the sludge was reshaped,and the compressibility of the sludge was improved.Fenton oxidation combined with calcium oxide conditioning has a stronger removal effect on EPS of different sludge and a more significant improvement on dehydration performance,which has a wider applicability.