| The treatment of livestock wastewater by microalgae-bacteria symbionts shows high efficiency.And the further combination of microalgae-bacteria symbionts and membrane technology can realize the advanced treatment of wastewater and the efficient recycling of resources.However,membrane fouling is still an important factor limiting the development of microalgae-bacteria symbiotic membrane bioreactor technology.The interaction of common metal ions in livestock wastewater with organic matter and extracellular polymeric substance(EPS)is one of the key factors affecting membrane fouling.In this paper,starting from the common metal ion aluminum ion in the wastewater,the effects of different concentrations of aluminum ions on the growth and EPS secretion of microalgae-bacteria symbionts were investigated,and the effect of aluminum ions on the membrane fouling of microalgae-bacteria symbiotic membrane bioreactor was studied.In this study,the effects of different concentrations of aluminum ions(0 mmol/L,0.2 mmol/L,1.0 mmol/L,1.2 mmol/L,2.0 mmol/L)combined with EPS on membrane fouling were investigated,and the effects of aluminum ions on the growth and secretion of EPS and subsequent membrane fouling in the presence of aluminum ions were investigated.The effects of aluminum ions on membrane fouling were further analyzed by combining various characterization methods,such as dissolved organic carbon content determination,three-dimensional fluorescence,Fourier transform infrared spectroscopy,and contact angle.Through the study of the interaction between aluminum ions and EPS components and its effect on membrane fouling,it was found that in the membrane fouling phenomenon formed by the interaction between aluminum ions and soluble microbial products(SMP),loosely bound EPS(LB-EPS)and microbial floc residue(MFR),the normalized membrane flux increased first and then decreased with the increase of aluminum ion concentration,but the addition of aluminum ions reduced membrane fouling as a whole.Moreover,aluminum ions were easy to complex with substances in EPS to form macromolecular substances,which were deposited on the membrane surface causing cake layer blockage.The results of characterization analysis proved that the main contributor for membrane fouling were protein-like substances in the EPS,which were mainly tyrosine-like substances.The effects of aluminum ions on the physicochemical properties and membrane fouling of microalgae-bacteria symbionts in simulated wastewater were studied.It was found that aluminum ions within certain concentration range promoted the growth of microalgae-bacteria symbionts,and the promotion effect increased with the increase of aluminum ion concentration.High concentration of aluminum ion led to the decrease of COD removal rate,but had little effect on total nitrogen removal,and has a promoting effect on total phosphorus removal.In addition,aluminum ions had an effect on the contents of proteins,humic acids and polysaccharides in EPS of microalgae-bacteria symbionts.At low aluminum ion concentrations,the contents of humic acids and polysaccharides decreased,indicating that aluminum ions might inhibit the decomposition and metabolism of organic matter in microalgae-bacteria symbionts.Furthermore,the effect of aluminum ions on the membrane fouling of EPS secreted by microalgae-bacteria symbionts was further explored.The results showed that with the increase of aluminum ion concentration in SMP,TB-EPS and MFR,the variations of membrane flux gradually decreased with the increase of aluminum ion concentration,and the membrane fouling conditions gradually mitigated.The addition of aluminum ions mainly changed the membrane fouling model of TB-EPS(tightly bound EPS,TB-EPS)components,from intermediate blockage to cake layer blockage.Meanwhile,proteins were still the main components contributing to membrane fouling. |
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