Technical and economic investigation of chemical scrubber and bio-filtration in removal of H2S and NH3 from wastewater treatment plant.

A detailed techno-economic comparison of a chemical scrubber (CS) and a bio-filter (BF) was conducted over a 45-day time period at a municipal wastewater treatment plant (WWTP), Yazd city. The assessment of emissions quantity indicated that odor emissions from the Yazd WWPT mainly consist of hydrogen sulfide (H2S) and ammonia (NH3). It was also found that odor gaseous loading changes corresponding to water consumption pattern in society (R2 = 0.922) for H2S and (R2 = 0.978) for NH3. The highest level of 25 and 3 ppm for H2S and NH3, respectively were detected at specific times during the day. The BF system was continuously supplied with Yazd WWPT's off-gas treatment while the CS was only examined at the times during the day when the gas emissions are at the highest level. The removal efficiency of NH3 and H2S were found to be affected by their respective loading rate. Additionally, among the various oxidants examined in the CS, the NaOCl solution showed the best results in terms of removal efficiency and compatibility. The experiment revealed almost complete removal of NH3 while the H2S removal efficiency remained above 95% for both systems regardless of the operating conditions. This study clearly demonstrates the effectiveness of both systems in treating actual waste gases containing H2S and NH3. By comparing the gas loading rate of both systems and considering limitations of the BF system, the CS seems to be more efficient applicable odor control technology from a technical viewpoint. From the economic viewpoint, comparisons revealed that chemical usage and operating expenses were costly parts of the CS and the BF, respectively. The economic indexes of 1.58 €.m-3. h-1 and 2.57 €.m-3. h-1 were obtained for the BF and CS, respectively, reflecting cost-effectiveness of the BF system.