Reduction of Excess Sludge Production in SBR Using Integrated Ozonation Process

Sludge production is an unavoidable outcome of biological wastewater treatment processes, presenting a significant challenge, especially in aerobic systems used in both urban and industrial wastewater facilities. The generation of excess sludge is critical due to its large volume and high moisture content, which cause environmental pollution and incur substantial disposal costs. To manage the excess sludge produced in wastewater treatment plants effectively, various treatment methods have been developed and implemented. Prominent among these are aerobic and anaerobic stabilization techniques, which aim to reduce the sludge mass and improve its handle ability. Additionally, thermal processing methods, involving the application of heat to dewater and stabilize the sludge, are often utilized. Advanced oxidation processes (AOPs) are also vital, employing powerful oxidants to decompose complex organic materials within the sludge. Furthermore, a combination of physical and chemical approaches is used to enhance sludge dewatering and minimize harmful components. An integrated strategy that combines thermal and chemical processes can further optimize sludge treatment, improving both efficiency and sustainability in managing excess sludge in wastewater treatment facilities. In this regard, the use of ozone is an effective and efficient method for breaking down microorganisms. Ozone, as a strong oxidant, can penetrate the cell walls of various organisms, causing the destruction of the cell membrane and disrupting their cellular structure. However, there are challenges to scaling up this process. Overcoming these issues could make ozone treatment more preferable than other methods. The purpose of this research is to reduce activated sludge production in a Sequencing Batch Reactor (SBR) with the application of the ozonation process. The study was performed on two identical laboratory-scale SBRs with a net volume of 4.5 L, fed with artificial domestic sewage. A fraction (30% of the working volume) of the activated sludge from one reactor (Experiment SBR) was periodically transferred to ozonation cylinder and subjected to ozone as a cell-lysing agent with dosages of 3, 7, 11, 15, 19 and 23(mg O_3)/(g MLSS); the other reactor was used as a control and managed at the same condition. During the experiments (120 cycles for each ozone dosage), regular sampling was done. The impact of recirculation of the ozonated sludge on parameters such as biomass production yield, Chemical Oxygen Demand (COD), Total Nitrogen (TN) and Total Phosphorous (TP) removal efficiency, Sludge Volume Index (SVI), Turbidity, Electrical Conductivity (EC) and Specific Oxygen Uptake Rate (SOUR) was evaluated. Based on the results, at a dosage of 19(mg O_3)/(g MLSS) , the sludge yield coefficient was reduced from 0.71 in the control reactor to 0.32 (mg MLSS)/(mg COD) in the experiment reactor. The effluent quality of the Experimental SBR deteriorated in comparison with the Control one. In Experimental SBR with 19 (mg O_3)/(g MLSS) ozonation, the removal efficiencies of the COD, TN and TP parameters were 80, 70 and 70 which was reduced 15,19 and 13%, respectively and SVI reduced by 48% (compared to a reference system running in the same condition), which shows the improvement of sludge settling characteristics.