Effects of Different Additives and Ambient Conditions on Acceleration of Sludge Stabilization: Laboratory-Scale Simulated Landfill Study

Abstract

Fresh cow dung and iron scraps were added to municipal sewage sludge under laboratory-simulated anaerobic landfill conditions. Simulated anaerobic and semiaerobic landfilling of sludge without any additives were conducted in parallel. Differently treated sludge in landfill columns and leachates from these columns were collected regularly during a 360-day period and analyzed to assess the sludge stabilization rate. The results showed that throughout the study period the water content of anaerobic sludge + iron scraps treatment decreased the most quickly, followed by the semiaerobic sludge treatment. In contrast, the addition of cow dung under anaerobic conditions conspicuously increased the water content of this sludge mixture, with no effects on reducing water content. The final water content of anaerobic sludge + cow dung treatment was approximately 1.1 times higher than that of anaerobic sludge treatment. After 360 days, the total organic carbon (TOC) content of anaerobic sludge + iron scraps treatment and semiaerobic sludge treatment was reduced by about 28%, and the volatile matter (VM) content of these two treatments was reduced by about 25%, while the TOC and VM contents of anaerobic sludge treatment was reduced by only 4.3% and 6.3%, respectively. The total nitrogen (TN) content of anaerobic sludge + iron scraps treatment and semiaerobic sludge treatment was reduced by about 20% at the end of the study period, while the final TN content of anaerobic sludge treatment and anaerobic sludge + cow dung treatment was reduced by 11% and 13%, respectively. In addition, anaerobic landfilling with iron scraps and semiaerobic landfilling approaches increased cumulative leachate production (CLP) and facilitated the discharge of heavy metals (e.g., Zn and Cu) in the sludge compared with the anaerobic sludge treatment. The largest CLP and highest contents of heavy metals in leachate were observed in the anaerobic sludge + iron scraps treatment. In general, the NH4+−N and TN contents in leachates from the four landfill columns exhibited an increasing trend with landfill time, while the TOC content in these leachates was decreased with landfill time. After 360 days, compared with the leachate from anaerobic sludge treatment, the NH4+−N, TN, and TOC contents in the leachate from anerobic sludge + iron scraps treatment were reduced by 38.6%, 32.8%, and 23.7%, respectively. The contents of these three properties in the leachate from semiaerobic sludge treatment were reduced by 40.4%, 20.7%, and 51.8%, respectively. The addition of iron scraps under anaerobic conditions and utilization of semiaerobic conditions were effective for improving the digestion performance of sludge. However, the addition of fresh cow dung did not accelerate sludge stabilization.