Cyrous Gilani, P.E., Project Manager, Hamed Haddad-Zadegan, Ph.D., P.E. Assistant Project Manager, Ali Poosti, P.E., Division Manager, Adel Hagekhalil, P.E., B.C.E.E., Assistant Director
Wastewater Engineering Services Division, City of Los Angeles, LA Sanitation, 2714 Media Center Drive, Los Angeles, CA 90065
The LA Sanitation owns and maintains 6,700 miles of sewer and operates three Air Treatment Facilities (ATFs) logistically located along the sewer system for removing odor and other related constituents from the collection system. The ATFs utilize Bio-trickling Filters (BTFs) technology followed by carbon adsorbers as polishing units. The BTFs at the ATFs consist of two (2) media levels. Both media levels use the liquid from the BTF’s sump for irrigation.
In order to improve the BTFs performance, a pilot test started in September of 2015 to evaluate and improve the biological process performance in the BTFs in terms of its odor and specific compound removal efficiencies under different pH irrigation conditions. The removal efficiencies of BTFs for Hydrogen Sulfide (H2S), speciated Volatile Organic Compounds (VOC) and Total Non-Methane Hydrocarbon (TNMHC) were measured and recorded for different pH levels during this test.
The knowledge and information gained from the results of these tests will be used to optimize the BTF operational procedure followed at the City’s collection system Air Treatment Facilities (ATFs) and extend the life of the polishing carbon units installed down-stream from the BTFs by reducing the inlet VOC/TNMHC load and the potential capacity taken up by the presence of these compounds.
The BTF test units were installed on the top of Primary Battery at Hyperion Water Reclamation Plant (Figure 1). The foul air from the primary battery channel was collected by a fan and pushed to an air duct manifold where it was distributed to the BTFs.
The test units were two 3-foot diameter BTF vessels installed in series for this test to simulate the 2 levels of media in one unit at actual BTF. Each BTF vessel contained 3-feet of Matala polyurethane media with a single head distribution nozzle to irrigate the top of the media with liquid from the sump of the BTF. Each BTF also contained a 3-foot sump, make-up water, overflow drain with p-trap, re-circulation pump, nutrient tank and nutrient pump. All testing parameter including Empty Bed Residence Time (EBRT) were adjusted in the test units to also simulate the actual BTF conditions.
The foul air from the primary channel entered the 1st BTF vessel, was treated, and then was directed to the inlet of 2nd BTF. After passing through the second BTF, the treated exhaust air from the second BTF was discharged to a main duct header that returned the flow back to the headspace of the primary battery tanks.
There was also a damper installed on the inlet of each BTF to control the air flow and thereby the EBRT for each BTF.
A nutrient tank and pump was used for each BTF to supplement the water irrigation system with appropriate nutrients to keep the microorganisms healthy and active.
The inlet and outlet concentrations of H2S and TNMHC of each BTF, the pH of the drain water and the amount of make-up water applied to each BTF were measured daily. This routine monitoring was conducted throughout this test period.