Anaerobic Acidification Effect On Dehydrated Sludge Utilization And Impact On Sludge Ability

In southern China, especially in the city of Shanghai and Shenzhen, the sewage treatment plant faces the situation of the shortcomings of carbon source of biological nitrogen removal process. While the anaerobic acidification of sludge from city sewage can produce a high concentration of dissolved organic matter (called dissolved Chemical Oxygen Demand, SCOD). It not only can provide carbon source for biological denitrification system but also improve the nitrogen removal efficiency. More and more concern is given to sludge anaerobic acidification not only for its producing more SCOD but also for its reduction of sludge volume.In recent years, many publications have been found on waste activated sludge (WAS) and primary sludge (PS) anaerobic acidification for SCOD production under pH or temperature control. But, few investigations have been made on dehydrated sludge anaerobic acidification, so the conclusion from WAS or PS is still suitable for dehydrated sludge is still to be confirmed. Secondly, although the sludge anaerobic acidification can produce large amounts of SCOD, it also produce large amounts of NH3-N and PO43-,which will weaken the treatment effect of nitrogen removal process. Last but not least although the sludge anaerobic acidification can realize sludge reduction but still there is a certain amount of the need for final disposal.In order to study the effect of sludge utilization and sludge ability during the anaerobic acidification, in the present experiment was firstly carried out at20℃to investigate the effects of different pHs on dehydrated sludge acidification for SCOD production, and the optimum pH were determined. And on this basis, effects of temperature, sludge concentration and different sludge source on the hydrolysis and acidification of dehydrated sludge were studied. Secondly, the experiment focused on the optimum conditions of chemical/coagulation sedimentation method to remove the nitrogen and phosphorus from anaerobic acidification liquid.Thirdly, the paper also studied the optimum conditions for the ammonia stripping process to solve the problem that the removal of ammonia nitrogen is not well during the chemical/coagulation sedimentation method.Finally, the paper investigated the effect of sludge ability for the anaerobic acidification from different points. All of above can provide quantities of reference for the establishment of sludge disposal technology and engineering demonstration. The experimental results showed that in the condition of20℃, dehydrated sludge anaerobic acidification, pH could promote the SOCD leaching. In alkaline conditions (pH9.0-13.0) SCOD yielded significantly higher than other conditions (neutral and acidic). The optimum conditions of dewatered sludge anaerobic acidification produced SCOD was pH10.0and6th day of acidification, when the SCOD concentration was8000mg/L and was4.82times at pH3.0and3.65times at pH7.0. Further investigation found that under the condition of pH10.0, the index of SCOD/N and SCOD/P reached the maximum of34and186on the6th day, which meet the demand for nitrogen and phosphorus removal of A/A/O process (C:N>7, C:P>28).At pH10.0, when the temperature ranged between15-50℃,not only the elution of SCOD but also the index of SCOD/N and SOCD/P at20℃was significantly higher than that of other conditions. The maximum index of SCOD/N and SOCD/P occurred at6th day. At pH10.0, the investigation about the effect of sludge concentration on dehydrate sludge anaerobic acidification showed that50g/L sludge can produce more SCOD, while It also yielded higher concentration of ammonia nitrogen and dissolved phosphorus than the20g/L sludge. The study of the alkalined pH regulation to promote20g/L sludge of different sources to acidification showed that:the optimum process conditions are still pH10.0and6th day. As the index of SCOD/N, the sludge from BINHE plant reached the highest value as34in6th day, while sludge of YANTIAN plant the maximum rate was19in6th day. The ratio of SCOD/P, the BINHE sludge reached the highest value was186in6th day, maximum value YANTIAN sludge was65in6th days.Research on chemical/coagulation sedimentation method to remove the nitrogen and phosphorus from anaerobic acidification liquid indicated that best methods were precipitation method and calcium oxide combined with Polymerization ferric chloride method. For the precipitation method with83%residual SCOD, the optimum condition was at pH9.5and the ratio of Mg/P was1.7. The optimum processing conditions of calcium oxide combined with Polymerization ferric chloride method was1000mg/L dosage of calcium oxide and80mg/L dosage of Polymerization ferric chloride, which retained80%SCOD.The results of investigation on the optimum conditions for the ammonia stripping process to removal of ammonia nitrogen as followed:using sodium hydroxide solution adapted liquid at pH11.0, gas-liquid ration was4000m3/m3, stripping time was120min. Under the optimum conditions, the SCOD residual content of acidizing fluid was4320mg/L, ammonia nitrogen removal rate was96%and the ratio of C:N and C:P were214and120which met the demand for nitrogen and phosphorus removal of A/A/o process.The effect of anaerobic acidification on the ability of dehydrated sludge from YANTIAN and BINHE plant as followed:With the sludge acidification, the ratio of VSS/SS declined, while the calorific value and volatile content decreased slightly. In the whole process of acidification, little change in element content, two kinds of sludge can be respectively denoted as CH2.03O0.38N0.10S0.01, CH1.g6O0.50N0.10S0.01-After anaerobic acidification BINHE sludge still contained a high heat value, so the sludge after acidification can deal with incineration. But as the YANTIAN sludge, the heat value is so low that to be incineration. What’s more, the heavy metal content of sludge decreased during the acidification, and the content of heavy metals met the national standard limits in china. So the acidified sludge can be deal with landfill. Acidification process made the sludge specific resistance filtration deterioration, which the specific resistance filtration (SRF) highest rose from1.50×1015m/kg to3.73±1015m/kg. The value of Extracelluler Polymer Substances (EPS) first increased and then decreased, the protein was the main component, accounting for more than60%of the total EPS. There was a certain correlation between EPS content and sludge dewatering ability:the EPS of L layer had a correlation (0.57) with SRF, the correlation coefficient between the protein of L layer and sludge specific resistance filtration was0.58.