Experimental Study On The Promotion Of Anaerobic Sludge Granulation By Different Additives

Anaerobic technology has many advantages,but the start-up time of anaerobic reactor is longer and the cultivation time of anaerobic granular sludge is longer.In this paper,anaerobic granular sludge was cultured by dewatering aerobic sludge which was made into particles with the same particle size as mature granular sludge.The granules can be used as crystal nucleus,and the microorganisms continuously grow on the surface to form granular sludge.On the basis of this,the effect of adding different additives before dewatering to the granulation of sludge was studied.The conclusions are as follows:Firstly,the effect of lignin fiber on the granulation of anaerobic sludge was studied.The granular sludge content with particle size greater than 0.6mm added with 1g/3g MLSS lignin fiber reached 57 m L,while the reactor without lignin fiber has only 35 m L,it can improve the gas production capacity,COD removal rate and the mechanical strength of granular sludge.The integrity coefficient of anaerobic granular sludge without and with 1g/3g MLSS lignin fibers was 90.1% and 97.4%,respectively.The lignin fiber has a large specific surface area,after dewatering and granulation,a part of the lignin fiber is fixed in the dehydrated granular sludge,and the rest of the fiber is exposed to the outside of the particle,and the flocculent sludge is attached to the dehydrated granular sludge.The granular sludge with lignin fiber is not easy to crush,has stronger shear resistance,and the granules are denser.Secondly,the effect of xanthan gum on the granulation of anaerobic sludge was studied.The granular sludge formed by adding xanthan gum has good mechanical strength,the surface of the granular sludge is smooth and compact without large cracks,while the surface of granular sludge without xanthan gum has obvious cracks.Moreover,xanthan gum has obvious effect on improving the activity of granular sludge in the reactor.When the influent COD concentration was 6000mg/L,the COD removal rate of the reactor with 60mg/3g MLSS xanthan gum was 93.4%,while that of the reactor without xanthan gum was 83.4%.The addition of xanthan gum could affect the content of EPS but not the type of protein in EPS,the EPS in reactor with 60mg/3g MLSS xanthan gum increased from about 64.5mg/g VSS-1 to about 99.3mg/g VSS-1,while the EPS in reactor without xanthan gum only increased to 83.6mg/g VSS-1.As an extracellular polysaccharide,xanthan gum can bridge the biological population to form a cross-network structure which is beneficial to the adhesion of microorganisms.At the same time,xanthan gum molecules are adsorbed on the surface of particles,which can play a cementing role between the particles,which is conducive to the compactness of particles.Meanwhile,the granulation time was shortened.Then,the effect of microbial flocculant on anaerobic sludge granulation was studied.The extracellular substances with flocculation in aerobic sludge are extracted and added into sludge with good biocompatibility.The acid-extracted microbial flocculant was used to promote the granulation of sludge,the granular sludge with large particle was significantly more than that without adding the microbial flocculant,when the amount of addition was 30 m L/3g MLSS,the granular sludge content with particle size greater than 0.6mm reached 66 m L,which was 26 m L more than the reactor not added,and the gas production,methane concentration and COD removal rate of the reactor added with the microbial flocculant were higher than those of the unadded reactor.The addition of microbial flocculant can increase the EPS content of the sludge.As an additional EPS,the microbial flocculant acts together with the EPS secreted by the anaerobic sludge itself to promote the accumulation of anaerobic microorganisms through the bridging action on the surface of the anaerobic sludge.At the same time,protein and polysaccharide in microbial flocculant can promote the adhesion of bacteria and accelerate the granulation process of anaerobic sludge.Finally,it was found that xanthan gum and microbial flocculant had better catalytic effect by comparing the three additives on the granulation of anaerobic sludge.Each of the three substances has its own advantages and disadvantages and can be selected according to the actual situation.The sludge granulation process after the addition of the three substances is similar,mainly including the domestication stage,the rapid growth stage and the mature stage.