Changes in pH and Bacterial Populations in Sewage Sludge and Mixture of Sewage Sludge With Rice Husk Silica to Remove H2S Pollution

Abstract

Background: The amount of bacterial population in the packing material of the biologic filter is very important to the treatment of air pollution. It is important to note that pH is a certain parameter in any biofiltration system application. Objectives: The main goal of this study was to investigate the changes in microbial population and pH value in the two new packing materials, namely sewage sludge (SS) and mixture of SS with rice husk silica (MSSRHS) to remove H2S pollution. Martial and Methods: The SS and MSSRHS packing materials were used into the two laboratory-scale filters (packed one litter). RHS was prepared at temperature of 800°C, after acid leaching. The SS was collected from the Putrajaya sewage treatment plant in Malaysia. The SS was mixed with RHS (50:50 volume) to be utilized as a packing material. This research was performed in two stages. In the first stage, the performance of the filters was evaluated during the start-up period at a constant empty bed residence time (EBRT) of 60 seconds and different inlet concentrations of H2S ranging from 10 to 300 ppm. In the second stage, the flow rate (L/min) was variable with different EBRTs ranging from 30 to 90 seconds and the concentration of H2S was fixed at 300 ppm. Results: In this study, after 53 days of operating time and 54 g/m3h mass loading, the pH values in the SS and MSSRHS packed filters were reduced from 6.8 to 1.8 and from 6.9 to 3.4, respectively. The MSSRHS packed filter showed more buffering capacity to resist pH changes. Therefore, in this packed filter, both sulfur bacteria, namely, Thiobacillus thioparus and Thiobacillus thiooxidans, could grow and oxidize H2S better than SS packed filter could. These are very important in maintaining microorganisms’ activity for long-term biofilter operation to remove air pollutants. Conclusions: The MSSRHS could be considered as a more suitable packing material for long-term biofilter operation to remove H2S pollution.