Study On Efficient Recovery And Technology Of Suspended Organic Carbon In Primary Sludge

In the wastewater treatment process, vast amounts of suspended solids and part oforganic carbon were removed in the primary sedimentation tank, resulting in effluentC/N, C/P value decreased, and carbon source of the subsequent biological treatment unitwas inadequate. If the primary sedimentation tank was canceled, loading and aerationenergy consumption of biological treatment unit would be increased, thus the cost ofsewage treatment would be increasd. The carbon source in the primary sludge would beharvested efficiently by modification of the primary sedimentation tank, mitigating thecarbon source inadequate issues, while improving the carbon structure andbiodegradability of influent, thereby improving efficiency of the subsequent biologicaltreatment unit.In this study, carbon source in the primary sludge was harvested through effientcarbon harvest process. Primary sludge was elutriated under mechanical shearing forcegenerated by the impeller rotation, hydrolyzed and fermented by sludge reflux. Therefor,the carbon source in the primary sludge had been harvested.(1)The influent and effluentqualities were investigated under different rotating speeds and different reflux ratios.The results showed that: stirring intensity had little effect on it. Soluble ChemicalOxygen Demand (SCOD) and VolatileFatty Acid (VFA) in effluent were increased butthe increasing trend was not obvious when the rotating speeds were increased from20rpm to80rpm. However, sludge reflux had greater impact on the effluent．SCOD, VFA,SCOD/TN, SCOD/TP in effluent were increased substantially when the reflux ratioswere changed from10%to30%. SCOD, VFA, SCOD/TN, SCOD/TP, VFA/TP ineffluent increased respectively by34.87%,26.42%,66.34%,58.86%,48.11%withrotation rate60rpm，sludge return ratio20%.(2) The carbon structure and effiency of effluent with different rotating speeds and different sludge reflux ratios had beenanalyzed. The results showed that: With the increase of speeds and reflux ratios, theproportion of acetic acid was increased; propionic acid and other types of acid weredecreased. And sludge reflux ratios had greater effect on the proportion of acetic acid.When the rotating speed were20rpm,40rpm,60rpm,80rpm, phosphorus release rateincreased by13.39%,15.73%,16.85%,15.21%, respectively. Denitrification rates wereincreased by29.44%,30.97%,32.36%,31.67%, respectively. When sludge return ratiowas10%,20%,30%, phosphorus release rates increased by16.85%,49.79%,51.24%,respectively. Denitrification rates increased32.36%,45.56%,49.58%, respectively.(3)Carbon balance of the system was analyzed, the results showed that the reduction ratesof carbon source and VSS/SS in primary sludge of effient carbon harvest process werebasically concordant with the increasing rates of carbon source in effluent, and theeffient carbon harvest process also could reduce primary sludge production.Efficient harvest of the suspended organic carbon process was formed throughabove researches. Vast amounts of available carbon sources which can be biodegradedthrough elutriation, hydrolysis and fermentation by this process, thereby suspendedorganic carbon were harvested. These carbon sources could enhance nitrogen andphosphorus removal process which used as a substitute for methanol or ethanol. Thus,the dual purpose of improving wastewater nutrient removal and utilization of waste hadbeen achieved.