Study On Biofilm Formation And Its Activity In Wastewater Treatment Systems

Biofilm process has several advantages such as high organic load,high removal rate of organics,low yield of residual sludge,and convenient operation and management,and is bound to get more application under the demand of standard-raising,efficiency-improving,energy-saving and cost-reducing,upon wastewater treatment in the future.Based on the current situation of insufficient research on microcosmic mechanism of biofilm formation and biotic response to biofilm activity,this study focused on typical wastewater treatment systems and engineered biocarriers(i.e.fixed and suspended biocarriers),and conducted an intensive exploration on the mechanism of biofilm formation and characteristics of responses to biofilm activity by macromolecules,biotic population and bacterial communities.This study is believed to provide theoretical guidance for the stable and highly efficient operation of biofilm wastewater treatment process and can be a technical support for the realization of efficient regulation of biofilm-related processes.Three real wastewater samples containing municipal wastewater,fine chemical wastewater and chemical industrial park wastewater,and twelve corresponding synthetic wastewater samples with different configurations of organics,ion strength and calcium ion(Ca2+),were both employed.Typical biocarriers of polystyrene and polyamide were selected.The comprehensive effect of biocarrier wettability and water quality characteristics on adlayer formation on the surface of biocarriers,was systematically studied,by using Quartz crystal microbalance with dissipation monitoring(QCM-D).On this basis,biofilm formation on engineered fixed and suspended biocarriers and their activities in typical wastewater treatment systems,were investigated.Distribution of biofilm in molecular and biocoenotic levels were analyzed through phospholipid fatty acid(PLFA)analysis,and quantitative relationships between biomarkers/biotic communities and biofilm activity,were established.16S rRNA high-throughput sequencing technology was further adopted to identify bacterial communities and their distributions in biofilm,and the response of bacterial communities to biofilm activity was studied.The overall conclusions of the study were as follows:1.Conclusions on biofilm formation(1)Wettability of biocarriers has a significant influence on biofilm formation.The hydrophilic surface is more conducive to the deposition of water soluble pollutants and adlayer formation and thereby accelerates the formation of biofilm.(2)Water quality exhibits important and complex influences on the formations of adlayer and the biofilm.The higher the organic concentration,the easier the formation of adlayer,with a greater effect than that of the ion and its strength.The effect of Ca2+on adlayer formation is related to the ionic strength,i.e.promoting at a low ionic strength and inhibiting at a high ionic strength,respectively.A high salinity is favorable to the rapid formation of biofilm,for the same type of wastewater,a high concentration of suspended sludge can also significantly improve biofilm retention.(3)The mechanism of adlayer formation on biocarrier surfaces showed that the deposition of macromolecules is not only controlled by the effect of double layer compression,but also by the non DLVO processes.(4)The method that monitoring microcosmic deposition of water soluble contaminants on organic biocarrier surfaces through QCM-D,provides a rapid determination of bioaffinity of biocarriers and has a widespread application prospect.2.Conclusions on biofilm activity(1)Highly significant positive correlations are found among four biofilm activity indexes of STOUR,SHOUR,ATP/VS and AEC.It's proposed in this study that aging biofilm occurs when AEC is less than 0.6 and further activation is needed.(2)The type of biocarriers has an important influence on biofilm activity.Biofilms on soft and integrated biocarriers are more likely to become "slime" and the aging time is about 60 days.Under the same condition of water quality,STOUR,SHOUR,ATP/VS and AEC of biofilm on suspended biocarrier are higher than those on soft and integrated biocarriers,with a longer aging time of more than 70 days in general.(3)The activity of biofilm is greatly influenced by organic concentration,and secondly the nitrogen and phosphorus,and is closely related to the activity of suspended sludge in the system.Aging process of biofilm can be accelerated by high salinity and organic contents,and the concentration of suspended sludge,under tested conditions.(4)PLFA analysis showed that C16:00,C18:00,C16:1,w7c,C18:I,w7c,C12:00 and C18:1 w9c are the top six biomarkers with highest relative abundance among different sources of samples.Bacteria possesses the highest relative abundance in biotic population,among which a significantly greater amount of Gram-negative bacteria than that of Gram-positive bacteria is observed.The content of fungi is generally greater than that of actinomycetes and protozoa.C16:00 achieves the optimal quantitative response to STOUR,with the best model of compound,growth or exponential curves.Fungi gets the optimal quantitative response to AEC,with the best model of cubic curve.PLFA composition changes in aging biofilm,with the appearance of more microeucaryotes including fungi.The content of microeucaryotes is relatively lower in biofilm living in high organic wastewater.More Gram-positive bacteria and actinomycetes occur in aging biofilm on integrated biocarrier.(5)16S rRNA high-throughput sequencing results showed that the main bacteria with relatively high abundance in biofilm are Proteobacteria,Bacteroidetes,Actinobacteria,Acidobacteria and Firmicutes.Influent quality has a greater impact on bacterial community than that of the type of biocarrier,with enrichment of Alphaproteobacteria in biofilm living in high organic and saline wastewater and Gammaproteobacteria in biofilm living in high dissolved oxygen and concentration of suspended sludge,respectively.Biofilm activity can be promoted by the following bacteria in genus level:Zoogloea,Acinetobacter,Dechloromonas and Nitrospira,and is negatively related to the bacteria mainly including Coldilinea,Haliscomenobacter,Marmoricola,Thauera and Truepera.The content of Caldilinea is relatively high in aging biofilm on soft and integrated biocarriers,while Acin.etobacter is also higher in content in addition to Caldilinea,in aging biofilm on suspended biocarrier.