The Study On Modifications Of Microbial Flocculant And Treatment Of Printing And Dyeing Wastewater

In recent years,China has produced a large amount of sludge in need of innocuous treatment.If the sludge is not properly disposed of,it will cause serious secondary pollution to the environment.Extracellular polymeric substance?EPS?occupies a large proportion in sludge,and possesses unique physical,chemical and biological properties,and is the key component of microbial flocculant.Through adjusting the external conditions properly,the experiment directionally changes the content and composition of EPS.Then microbial flocculant is extracted from sludge,and further enhances its flocculation performance by chemical modification.The ultimate purpose of this experiment is to realize the resource utilization of sludge as much as possible.Firstly,the influence of carbon source types and organic load on EPS secretion and sludge characterization was studied.The carbon sources involved include sodium acetate,starch and phenol.If sodium acetate is used as the sole carbon source,the total amount of EPS only small increases,and the hydrophobicity of EPS remains basically unchanged.If starch is used as the sole carbon source,part of the starch is degraded into an intermediate product that attaches to microbial surface,and it benefits a large increase in the total amount of EPS,but the ratio of extracellular protein and extracellular polysaccharide?PN/PS?declines significantly.If phenol is used as the sole carbon source,the mass mortality of microorganism happened,and the intracellular substance was released out of the cell,and the total amount of EPS and PN/PS increased at the early stage of the test.At the later stage of the test,the part of the EPS was degraded,and the total amount of EPS and PN/PS small declined,but they are still better than other reactors.Afterwards,the influence of Fe²⁺/Fe³⁺on EPS secretion and sludge characterization was studied.Moderate Fe²⁺/Fe³⁺has a promoting role on the microbial activity,organic matter degradation,sludge granulation,EPS secretion and so on.Excessive accumulation of Fe²⁺/Fe³⁺can cause that microbial metabolism is suppressed and dehydrogenase activity and degradation efficiency of chemical oxygen demand?COD?reduce.The experimental research shows that Moderate Fe²⁺/Fe³⁺can help the increase of EPS content and the proportion of hydrophobic component-extracellular protein?PN?.When dosages of Fe²⁺and Fe³⁺are not more than 12 mg/L,EPS content will increase and the proportion of tightly bound extracellular polymeric substance?TB-EPS?will reduce.When dosages of Fe²⁺and Fe³⁺are excessive?18mg/L?,microorganisms are stimulated to secrete more EPS and PN that can effectively hinder the ability of metal ions to approach microorganisms through diffusion or biochemistry.Fe²⁺and Fe³⁺can be complex with the carboxyl group of extracellular polysaccharide?PS?,which cause the reduce of the proportion of PS and the rise of PN/PS.Compared to Fe²⁺,Fe³⁺is more beneficial to promote sludge to secrete more EPS,because Fe³⁺hold stronger promoting effect on microbial activity and more positive charges.Furthermore,the addition of Fe³⁺direct affects the structure and content of protein in EPS.Phenolic protein increases and complex amino acid protein replaces tryptophan protein.Finally,hydrophobic modification of microbial flocculant and its decoloration to printing and dyeing wastewater are studied.When silane coupling agent KH-560 is used as the sole modifier,flocculation rate and decolourization rate show a tendency of rising first and then decreasing.When the dosage is 0.5 ml,flocculation rate reaches a maximum 98.55%.When the dosage is 1.5 ml,decolourization rate reaches a maximum 97.25%.When silane coupling agent KH-550 is used as the sole modifier,decolorization efficiency of microbial flocculant for disposed printing and dyeing wastewater is enhanced,but it makes against flocculation of kaolin suspension.With the increase of stearic acid dosage,the flocculation rate increases first and then decreases,and the decolourization rate is rising first and then basically unchanged.When sodium stearate is used as the sole modifier,the flocculation rate gets effective improvement,but it has no effect on decolorization efficiency of microbial flocculant for disposed printing and dyeing wastewater.When silane coupling agent KH-560 is used as the sole modifier,modification time has more influence on flocculation rate.The best modification time is 40min⁵0min.The modification temperature has an important effect on the increase of flocculation rate,but the improvement of decolorization rate is not obvious.The flocculation rate increased first and then decreased with the increase of modified temperature.The maximum flocculation rate is 99.34%at 70?.The microbial flocculant extracted from the sludge domesticated by Fe²⁺or Fe³⁺is only suitable for decolorization of simulated printing and dyeing wastewater,but makes inorganic flocculants difficult to flocculate.