Study On Biofilm Characteristics Of Carriers With Different Space Scale For Biofilm Formation

Biocarrier is the core of biofilm technology,which directly influences the effect of wastewater treatment.At present,most of researches focus on the innovation and improvement of wastewater treatment process or the analysis of characteristics of single carrier.Due to the lack of comparative study on different carriers,it is difficult to select carrier rationally.In order to explore the law of biofilm growth and then provide the theoretical basis for carrier selection,the treatment experiments with artificial wastewater and actual sewage were carried out by sequencing batch biofilm process,and the biofilm characteristics of carriers with different space scale(multi-surface hollow ball,K3 suspended filler,stub tube fillers and ceramsite)for biofilm formation were studied.The physical properties,chemical composition,activity of biofilm and microfauna community structure of carriers were analyzed,and the multi-surface hollow ball which has advantage over other carriers was chosen to study effects of biofilm detachment on attaching biofilm characteristics to explore the dynamic change of biofilm.The main results are as follows:1.Effects of carriers with different space structures on the physical characteristics of attached biofilm1)The bigger space scale for biofilm formation of carrier was,the larger biomass and biofilm thickness the carriers had.There were a certain fluctuation similarities of biomass on the 4 carriers.In the stage of simulated wastewater,the biomass attached to carriers decreased with the decrease of influent concentration,the biofilm thickness of hollow ball and K3 suspended filler decreased,too.In the actual domestic sewage,the biomasses were lower,and the thicknesses of biofilm were relatively stable.2)The larger space scale of carrier had,the better dehydration of biofilm and mixed liquor carriers had.When simulated wastewater were treated,dehydrations of K3 suspended fillers,multi-surface hollow ball and stub tube fillers changed from good to bad;nevertheless,so did when domestic sewage were treated,the dehydrating rates of mixed liquid were multi-surface hollow ball> K3 suspended fillers> stub tube fillers> ceramsite,and the dehydrating rates showed a downward tend with the running time in 4 systems.2.Effects of carriers with different space structures on the chemical composition of EPS(extracellular polymeric substances)1)The amount of biofilm EPS increased with the space scale of different carrierswhen treating simulated wastewater,while that of 4 kinds of carriers were similar when treating domestic sewage.The protein contents were close to or even more than the polysaccharide contents in biofilm EPS,and the microbial species and their growth status were different,causing different EPS components of microbial degradation of organic matter in different stages.2)The contents of slime EPS(S-EPS)and loosely bound EPS(LB-EPS)of biofilm were similar on different carriers;The differences of EPS contents were mainly caused by tightly bound EPS(TB-EPS),and the TB-EPS quantity of biofilm attached to multi-surface hollow ball was highest.The protein of EPS was tightly bound to the cell;The polysaccharide contents of different layers were different: TB layer> S layer> LB layer,and the polysaccharide was the main component of the S-EPS,LB-EPS.3.Effects of carriers with different space structures on biofilm activityThe larger space scale of carrier for biofilm formation,the activities of biofilm were higher and microorganism and organic matter were more,which was due to the difference of carrier structure related to biological activity difference.Different water quality caused the activities of biofilm were higher when treating simulated wastewater.4.Effects of carriers with different space structures on the microfauna community structure1)In total,133 species of microfauna were identified on the biofilm of 4 kinds of carriers,including 13 species of flagellate,15 species of sarcodina,84 species of ciliate and 3 kinds of metazoan.Dominant species of microfauna mainly included Bodo sp.,Vorticella sp.,Epistylis sp.,Paramecium sp.,Nematode,etc.The abundances of microfauna ranged from 28 ~14359 ind·g-1 carriers,and the high porosity of carriers were conducive to more abundant microfauna.The influences of carrier structure on the species of microfauna were less with adequate nutrition and easy degradation of organic matter,while more obvious when the influent concentration was low and the pollutants were difficult to be decomposed.2)The composition of microfauna community structure on carriers dynamically changed with the time variation;When treating simulated wastewater,the microfauna abundances showed the first fluctuation and then became stable on K3 suspension filler,stub tube fillers and ceramsite.The changes of influent conditions had a certain impact on the structure of microfauna community.3)The species richness,evenness,dominance,diversity and stability indexes of microfauna on carriers dynamically changed with the time variation,and the species biodiversity level of microfauna on multi-surface hollow balls was high and stable fluctuation.The carriers with lager space scale for biofilm formation and the simulated wastewater was conducive to the stability of microfauna community.5.Biofilm detachment characteristics and its effect on biofilm attached1)The biomass of biofilm detached was more when the organic loading was heavier.The pH value of the system decreased over time,the activity of biofilm was inhibited gradually,and led the increase of the biomass of biofilm detached.The biomass of biofilm loss was less if the polysaccharide content of EPS was higher.The results of factor analysis showed that factors closely related to biofilm detachment were factor of composition and activity of biofilm,biological factor,and load factor etc.,successively.Effluent2)The detached biofilm and biofilm attached on carriers interacted and affected each other,the detached biofilm had an inhibitory effect on biofilm attached,the increase of biomass of detached biofilm led to the decrease of biofilm activity on carriers,which affected effluent quality.With biofilm falling off,species number and abundance of microfauna on biofilm decreased,and the species diversity of microfauna community decreased;in the high organic loading system,the level of microfauna species biodiversity was high,the species stability(WS)was high,the stability of species diversity(WH)was low.The removal rate of CODCr decreased with the increase of biofilm detachment.