Experimental Study On Metal Ion-driven EPS Membrane Separation/purification Of Sludge

Sludge recycling is the trend of excess sludge treatment in the future.Bacterial cell’s Extracellular polymers substances（EPS）in excess sludge content is high（about 10⁴0%of dry weight of sludge）.EPS is widely used,can be economically and efficiently separated and recycled.However,the traditional method of drying EPS solution is power-hungry,consumed a lot of chemicals,and secondary pollution.Membrane separation technology can avoid these disadvantages.Literatures show that metal ions,such as Ca²⁺and Fe³⁺,can be combined with EPS to reduce membrane fouling and increase the recovery rate of EPS.Therefore,in this paper,simulation and actual EPS solution were studied for the first time.The effects of the pressure drive membrane separation under metal ions were investigated.Due to the interaction between metal ions and carboxylic acid groups in sodium alginate,the high price metal ions reduced the sodium alginate membrane fouling.The filtering resistances is reduced by Mg²⁺<Ca²⁺<Fe³⁺<Al³⁺.Trivalent metal ions can change the pH,produce hydroxide and other reasons,so the effect of membrane pollution is more obvious.The microfiltration membrane can isolate sodium alginate and bovine serum protein with the addition of Ca²⁺,and the filtration resistances decreased with the increase of membrane pore.The filtration surface shear can not reduce membrane fouling and reduce the separation efficiency.As long as the Ca²⁺concentration is appropriate,the separation efficiency does not depend on the concentration ratio of the both.All kinds of EPS extraction methods have a similar ratio of polysaccharide,and the protein ratio is quite different.In the complex compound with calcium of various EPS,cationic exchange resin method is the closest approach to sodium alginate.Due to the existence of Ca²⁺and other divalent ions,the cooperative mode of polysaccharide carboxylic acid and metal ions in various EPS is the bridge type.The addition of Ca²⁺can reduce the filtration resistances of The EPS recovery of ultrafiltration membrane is much higher than microfiltration membrane（⁹0%）.The ability of Fe³⁺to reduce membrane fouling is much better than Ca²⁺,but it can lessen the adsorption capacity of EPS on heavy metals.The Pb²⁺theoretical absorption of EPS and their complex compound with Ca²⁺is significantly higher than other common adsorption materials,which can reach up to 833.33 mg/g.Extracting a certain amount of EPS can reduce the filtration resistences of the sludge.