Removing Hydrogen Sulfide from Digester Gas Using Aerobic and Anoxic Biotrickling Filters

Abstract

The Sanitation Districts of Los Angeles County (Districts) have been using ferrous chloride (FeCl 2 ) to control the hydrogen sulfide (H 2 S) concentration in digester gas at the Joint Water Pollution Control Plant (JWPCP) for over 30 years. Although FeCl 2 has been very effective in controlling digester H 2 S levels, the cost of this chemical has increased significantly in the last few years. Consequently, the Districts initiated a study to investigate the use of biotrickling filters (BTFs) to control digester gas H 2 S. Two pilot-scale biotrickling filters were tested under slightly aerobic and anoxic conditions. Two types of filter media, lava rock and plastic rings, were tested in the aerobic filter, and lava rock was tested in the anoxic filter. Concentrated H 2 S was spiked into the digester gas to simulate elevated H 2 S levels characteristic of lower FeCl 2 doses. For H 2 S levels between 200 and 400 ppm, the aerobic BTF with a plastic ring media was able to reduce H 2 S to below the regulatory limit of 40 ppm at empty bed retention times (EBRT) of 20 to 37 seconds. The aerobic lava rock BTF experienced a clogging problem, and the anoxic lava rock BTF was not able to reduce 200 ppm of H 2 S to below the regulatory limit at an EBRT of 50 seconds.

Full-Scale Implementation of a Novel Digester Gas Conditioning System Using Biological Scrubbing and Molecular Sponge Siloxane Removal

“…At the BBWWTP, H 2 S removal performance is typically established within 12 to 24 hours after recirculation and aeration commences. To date, the BBWWTP biological H 2 S scrubbers support pilot test data (Soroushian et al 2006;and Lee et al 2011) and have demonstrated good H 2 S removals from the digester gas. In November 2011, as part of the Source Emission Survey (Maxxam, 2011) gas samples were taken at the inlet and outlet of the H 2 S scrubber at three separate sampling times about one hour apart.…”