Application of membrane bioreactors (MBR) in wastewater treatment of Kahrizak waste landfill site in Tehran

With the growth of population and industry, human demand for consumables and consequently waste production has increased. The purpose of this study is to investigate the biological, physical and chemical purification of hazardous wastewater using membrane bioreactor (MBR) method. The MBR method is a combination of an active sludge suspension system and a membrane separation process. These membrane filtration systems have been extensively tested and have been quite effective in removing organic and inorganic contaminants. In this study, 185 L leachate from a landfill with a semi-continuous flow regime and polypropylene halo fiber membrane were used. For this reactor, two polyethylene tanks with the total capacity of 200 L were considered as feed tanks. The temperature was 21° C and the pH inside the reactor was about 9. Considering the sludge age of 30 to 35 days and the hydraulic retention time of 15 days, the MLSS was about 6300 mg/L. For diffuser aeration speeds of 2 and 4 cubic meters per hour, the amount of dissolved oxygen for each was 2.3 and 3.2 mg / l, respectively.. It seems that COD above the inlet leachate would be greatly reduced if ozone, pure oxygen, high aeration rates, and hydraulic and microbial retention time were used. In the first step, after determining the sludge age and stability of the results from the reactor outputs, the results were recorded within 30 days. The amount of 1733 mg/L COD was reported as the average output. As the rate of dissolved oxygen increases, the amount of nitrite, which is known to be toxic for microorganisms, also decreases. The amount of nitrite in and out of the reactor has always been in the range of 0.5 to 1 mg/L (less than 1 mg/L). By reducing the aeration rate, the amount of active biomass present in the reactor decreases. Based on the results, the COD and BOD concentrations were about 2514 and 1247 mg/L, and the removal efficiencies were 96 and 93%, respectively, which significantly reduced the BOD removal. The nitrate concentration decreased in this state. The nitrite concentration increased significantly up to 20-times, indicating the completion of nitrification process. The turbidity reduction, measured in NTU 59, will be about 69%, which is 9% less than normal. In addition, about 98.83 and 96.14% of the input iron load can be eliminated using MBR systems with high aeration rates. At high and low aeration rates, the iron removal rates were about 96.14 and 94.4%, respectively. The reduction of zinc content using MBR system with aeration speed of 4 cubic meters per hour is 86% and with aeration speed of 2 cubic meters per hour is approximately 82.2%. While the removal of zinc in the RO system is about 85.8%. About 14% of zinc cannot be removed using the RO system. Also, about 15% of the copper present in the leachate has the particles size less than 0.001 μm and cannot be removed by RO and in this experiment it was found that about 76% of the copper is less than 0.1 μm in size and was not reducible. In order to have MBR process with an economically justified use for purification, some parameters such as the type of membrane, physical conditions and quality of membrane output and economic considerations must be considered. Comparison between the activated sludge system and the MBR shows that MBR is much more common in the MLVSS aerobic process than the activated sludge system and its purification concentration reaches to about 7 g/L, which is due to the chemical factors and ions. In MBR systems, high efficiency of BOD removal and nitrification can be jointly achieved. Based on the results of this study, about 99% of BOD was removed and the nitrification removal efficiency reached about 97%. The MBR system is well-suited for the treatment of strong wastewaters, such as leachate treatment. Due to the high concentration of COD and BOD output from MBR, the use of RO for purification due to rapid clogging cannot be justified unless there is no longer a viable solution.