Study On Properties Of Excess Sludge As A Carbon Source In Low-carbon System

The removal efficiency of nitrogen and phosphorus in low-carbonsewagedisposalsystem usually is low. In order to achieve discharge standards, addingexternal carbon source to improve biological nitrogen removal and post chemicalphosphorus removal have become the most common emergency measures of lowcarbon source sewage treatment plant. The macro shows that running cost is generallyhigher in low carbon source sewage plant. Therefore，it is of positive significance forimproving the effect of nitrogen and phosphorus in the low carbon source sewagetreatment system to transform sludgebio organic into carbon source of biologicalnitrogen and phosphorus removal. A large number of studies show that, the efficiency ofsludge being transformed into carbon source by direct hydrolysis acidification is usuallylow because of the influence of cell wall. Therefore, excess sludge was pretreated bythree physical and chemical methods of alkali, heat and ultrasonic in this paper. Excesssludge transformation effect of hydrolysis acidification after different disintegrationmethods was studied to provide the experimental basis for sludge carbon sourcetransformation.Results showed that:①The effect of sludge disintegration was obvious and the pH value decreasedsignificantly in the first4hours of alkaline treatment. The concentration of SCOD, TN,ammonia nitrogen and TP increased obviously. Each index tended to be stable after4hours of alkaline treatment. Five kinds of alkaline dose between0.02and0.8gNaOH/gTS were chosen in the experiment. The sludge disintegration effectincreased with the increase of alkaline dose. When sludge SCOD tended to be stable,the concentration of SCOD corresponding alkaline dose from small to large was682,1590,2292,5126,5312mg/L respectively. For alkaline dose was0.1,0.25and0.8gNaOH/gTS, the C/N ratio was greater than11and the C/P ratio was about50aftersludge disintegration. The required value for nitrogen and phosphorus removal in thesewage treatment system could be met, so the effect of carbon source was well in theory.While for alkaline dose was0.02and0.04gNaOH/gTS, the C/N ratio was about6andthe the C/P ratio was about25, so the effect of sludge disintegration was not very well.②Five heating temperatures between80and120℃were selected for sludgedisintegration. Under the heating temperature of100,110and120℃, the concentrationsof SCOD，TN, ammonia nitrogen and TP in sludge supernatant were increased obviously, then the increase rate decreased gradually. Under the heating temperature of80and90℃, sludge disintegration effect was poor. The concentrations of varioussubstances increased obviously after30min. Sludge disintegration effect increasedgradually with the increasing of heating temperature. The concentrations of SCODcorresponding the temperature from small to large were72,135,487,1876and2498mg/L respectively. Under the five heating temperatures used in the experiment, theC/N ratio was from9to14and the C/P ratio was more than40when sludgedisintegration tended to be stable. The required value for nitrogen and phosphorusremoval could be met in theory and the disintegration effect was well.③Excess sludge pH value decreased under ultrasonic treatment, but there werefew changes of the overall. The concentrations of SCOD，TN, ammonia nitrogen and TPin sludge supernatant were increased obviously in the first60min, then the increase ratedecreased gradually. Five energy densities between0.025and0.125W/mL were used inthe test. Sludge disintegration effect increased gradually with the increasing of energydensity. The concentrations of SCOD corresponding the energy density from small tolarge were2376,2417,2807,3204and3556mg/L respectively when sludge SCODtended to stable. Under the five energy densities used in the experiment, the C/N ratiowas from15to19and the C/P ratio was more than50. The disintegration effect waswell in theory.④Three methods of sludge disintegration all had a certain degree of improvementto the efficiency of hydrolytic acidification. The degree of improvement: alkalinetreatment> thermal treatment> ultrasonic treatment. The sludge disintegrationtechnologies could shorten sludge fermentation stable time. The concentrations of VFAsin the sludge fermentation liquid when all groups of sludge acid output tended to bestable were459mg/L under alkaline treatment,353mg/L under thermal treatment,259mg/L under ultrasonic treatment and234mg/L without being treated.