A Study On The Impact Of Sludge Water On Process Of Municipal Wastewater Treatment Plant And Granulation And Coagulation Treatment Technology

Sludge water is the wastewater generated in the process of sludge disposal in themunicipal wastewater treatment plant（MWWTP）, the process of sludge disposalcontains sludge thickening, sludge digestion and sludge dewatering. The flow of sludgewater is small, but the pollutants that mainly are nitrogen and phosphorus havegenerally high concentration. MWWTP that have been built or that are building bothadopt the method that back sludge water to the front of system for recycling treatment.As a result, the impact of sludge water on the MWWTP cannot be ignored.In view of the above questions, the paper selected three typical MWWTPs inXi’an city, the quantity and quality of sludge water and impact of sludge water onprocess were analyzed and investigated. The results showed that the sludge water ofthree MWWTP were mainly composed by concentrated supernatant and dewateredsupernatant, the quantity of sludge water was only account for2%to3%of influent ofMWWTP. But the concentration of nitrogen and phosphorus from sludge water is veryhigher, the concentrations of dissolved total phosphorus and total nitrogen wererespectively more than300mg/L and160mg/L. The sludge water also had thecharacteristic of high suspended solids concentration, which was up to about6000mg/L.The high load reflow phosphorus of sludge water had an enormous influence upon thesewage treatment system, so that the effluent of MWWTP was not up to standard.In combination with the characteristics of high phosphorous and suspended solidconcentration in the sludge water, the sludge water in the fifth MWWTP was treated asresearch object, delay stirring granulation technology was proposed to achieve the single treatment of sludge water, So as to achieve the purpose of cutting down thephosphorus load in the biological treatment system. Delay stirring granulationtechnology is through a mechanical stirring which has high speed and last for a longperiod of time in order to break the sludge particles and make the particles tend to beuniform, dense and have a good spherical degree, thus in the process of coagulation,according to the theory of syneresis, the porosity can be reduced in the flocs distributiongrowing process, dense flocs can be formed better,then through solid-liquid separation,the method can achieve a good effect of phosphorus removal. The results showed that,through delay stirring granulation technology, when the dosage was50mg/L of PACand，10mg/L of PAM, the size, settling velocity, fractal dimension and effective densityof flocs were larger than the conventional chemical phosphorus removal, solid-liquidwas separated rapidly and the sludge sedimentation ratio was about30%, totalphosphorus concentration can be reduced by50%. Comparing to the process ofconventional chemical phosphorus removal, delay stirring granulation technology hadthe advantages of smaller dosage, higher solid-liquid separation rate and the bettereffect of settlement and phosphorus removal. Delay stirring granulation technologyprovides a new method for treatment of sludge water which has high phosphorusconcentration and suspended solid concentration.