Study On The Mechanism Of Membrane Fouling Caused By Iron Ions And Microalgae-bacteria Symbionts In Livestock Wastewater Treatment

Microalgae-bacteria symbionts are able to achieve high removal efficiency on carbon,nitrogen and phosphorus in livestock and poultry wastewater treatment.And the combination of microalgae-bacteria symbionts and membrane technology could further enhance the treatment load and performance stability.The characteristics of high color,high turbidity and high salinity of livestock and poultry wastewater limit the continuous and stable operation of microalgae-bacteria symbionts and membrane combined process,and membrane fouling is one of the bottlenecks restricting its application.Therefore,based on the application of microalgae-bacteria symbionts and membrane combined process in livestock and poultry wastewater treatment,this paper focused on the effect of iron ions existing in livestock and poultry wastewater on microalgae-bacteria symbionts and the secretion of EPS,then further investigation on the influence of iron ions on the membrane fouling mechanism in microalgae-bacteria symbionts and membrane combined process.The influence of iron ions at different concentrations on microalgae-bacteria symbionts and EPS secretion were focused and analyzed in this study.Multiple characterization methods,such as Fourier transform infrared(FTIR)characterization and contact angle,were deployed to further investigate its impact on membrane fouling.The results would provide theoretical support for the practical application of microalgae-bacteria symbionts and membrane combined process in livestock and poultry wastewater treatment.Study on the influence of the interaction between iron ions and EPS on membrane fouling showed that there are critical points for the influence of iron ions on soluble microbial products(SMP),loosely bound EPS(LB-EPS)and microbial floc residue(MFR).When iron ions concentration was among 0-60mg/L,the membrane fouling conditions could be mitigated,while iron ions concentration at 150 mg/L would aggravate membrane fouling.Iron ions changed the fouling model type of EPS components and impacted the hydrophilicity and hydrophobicity of membrane surface.The membrane fouling caused by SMP was severely affected by iron ions.Study on the influence of iron ions on the growth of microalgae-bacteria symbionts in artificial wastewater and membrane fouling showed that iron ions can significantly affect total phosphorus removal in wastewater and promote the growth rate of microalgae-bacteria symbionts.,The chlorella growth was accelerated with iron ions at 0-60mg/L,while both Chlorella and activated sludge grew well with iron ions at 150mg/L.Higher iron ions concentration exhibited stronger inhibiton on the secretion of polysaccharide,protein and humic acid.In addition,iron ions can further combine Chlorella and activated sludge with microalgae-bacteria symbionts to form larger size of bioflocs in the mixture.The effect of iron ions on EPS composition and membrane fouling showed that iron ions affected the total amount and composition of EPS,especially for the amount of LB-EPS.Besides,the distribution of polysaccharides and proteins of EPS secreted by microalgae-bacteria symbionts was also significantly influenced.Both contributed to the explanation of how iron ions impact the membrane fouling conditions.