Effects Of Mg(Ⅱ)/Al(Ⅲ) On Biofilm And Its Extracellular Polymeric Substances (EPS)

Biofilm was the aggregate of microorganisms and it was a complex ecosystem, of which the special structure makes itself a have stronger resistance to adverse environment and impact resistance. Therefore, based on biological membrane biofilm method in the application of water biochemical treatment was becoming more common. As the main component of biofilm, extracellular polymeric substance could maintain function of biofilm microstructure and integrity plays an important role, was the key factors which influenced the stability of the biofilm. Magnesium ions was ubiquitous in the environment, and was the main factors which influencing the water hardness, the content of magnesium ions in the karst water and groundwater was higher, and magnesium ions was also used as chemical precipitation to remove nitrogen and phosphorus in wastewater, and aluminum salt as flocculants was commonly used, more widely used in water treatment, which makes the magnesium ions and aluminum ions in natural water and industrial wastewater were widespread. The magnesium ions and aluminum ion have a significant impact on a variety of physiological activity of the microorganisms, they had a potential impact on biofilm and its EPS, but because they were not water pollutants, which influence on the wastewater biochemical treatment was often ignored. At present, the effect of magnesium ions and aluminum ions on wastewater biochemical treatment system of microbial research was mainly concentrated in the sludge system, there have been many scholars do the researches, and obtained many achievements, in contrast to the researches for biofilm system was inadequate.In this paper, magnesium ions and aluminum ions were used as the researched object, the effects of magnesium ions and aluminum ions on the biofilm micromorphology and activity as well as the EPS composition and characteristics in biofilm were investigated in self-designed sequencing batch biofilm reactors (SBBRs). The mechanism of action of magnesium ions and aluminum ions with biofilm and EPS was further explored by applying scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The following conclusions could be drawn from the results:(1)The measurement of CODcr,NH3-H degradation and the biomass, as well as the SEM experiments of biofilm results showed that Mg(Ⅱ) (0-24 mg/L) led to the increase of filaments, dry weight(DW) and volatile dry weight(VDW) of biofilm and could promote biofilm’s biodegradability, while high concentrated Mg(Ⅱ) (36mg/L) would be invalid.(2) The result of the EPS composition suggested the Mg(Ⅱ) (0-24 mg/L) could increase the polysaccharide of tightly bound EPS (TB-EPS) which contributed to the adhesion between the microbial cells, however when the Mg(Ⅱ) content was over a critical concentration (36 mg/L), the promotion effect was suppressed. And FT-IR and XPS spectra demonstrated that that Mg(Ⅱ) exerted a significant influence on the functional groups in TB-EPS, especially the C=O groups from proteins and the O-C-O groups from polysaccharides. Furthermore, Mg(Ⅱ) might bridge with the carbon and oxygen atom in the functional groups of TB-EPS in biofilm.(3) The results of the CODcr degradation, biomass and SEM study of biofilm elucidated that Al(Ⅲ) led to reduction of the filaments, promotion of the EPS secretion, and affected biofilm development adversely at the beginning of biofilm growth, however Al(Ⅲ) could promote microorganisms form larger colonies, and promoted the biofilm mass and improved the biofilm activity as the biofilm growing.(4) The analysis results of EPS contents and components suggested that Al(Ⅲ) could increased the protein(PN) of tightly bound EPS (TB-EPS) which alleviated the metal toxicity inhibitation at the initial phases of biofilm growth, as the biofilm mature, the biofilm could gradually adapt the inhibition caused by Al(Ⅲ). And it was found that the Al(Ⅲ) exerted a significant influence on the functional groups in TB-EPS, especially N-O, C=O groups of proteins, the O-H, O-C-O groups of polysaccharides and the phosphate groups of nucleic acids in TB-EPS through the FT-IR analysis. And Al(Ⅲ) might bridge with the oxygen atom in the functional groups of TB-EPS in biofilm. The XPS spectra demonstrated, under the influence of Al(Ⅲ), the C-(C, H) and C-(O, N) in the TB-EPS to from the C=O, O-C-O for the growing biofilm, and the C-(C, H) in the TB-EPS to break down C-(C,H), C=O and O-C-O for mature biofilm period.