Trade Ya! One Organic, Open Biofilter for One Synthetic, Modular, Closed Biofilter

Introduction Biofiltration is a term in the odor control industry used to define a vapor phase odor control technology category that focuses on the ability of microorganisms to remove nuisance odors from a foul smelling airstream. Biofiltration, biofilters, have been around for decades. It was Pomeroy in 1957 that constructed one of the first open pits filled with porous soil and perforated pipes for air distribution to treat wastewater odors. Systems evolved from those first porous soil biofilters to include bark and wood chips as support media to reduce compaction and enhance air movement in Europe in the 1970's. With rapid progression in the 1980's and 1990's in Europe, the technology began to slowly become accepted and used in North America as the previous black box approach turned more toward a science based effort. Today's biofilters include a range of medias (soil, bark, wood chips, compost, extruded wood, glass, proprietary, etc.) and styles (in ground, open, hybrid, modular, closed, etc.) that still all rely on the founding principle of biofiltration the ability of microorganisms to mitigate odors! For a plant (see Figure 1) in coastal central New Jersey, TRWRA, the application of an in ground, wood chip and compost open biofilter had been accepted years ago and treated plant odors associated with their solids processing/handling building (sludge thickening room, sludge dewatering room, and truck loading room), and two sludge storage tanks. The biofilter mitigated nuisance odors but the unit took up quite a bit of plant real estate as it was treating 19,600 cfm of odorous air, was more maintenance intensive then they envisioned, and the media was replaced every five years, which was a major event. With an upcoming plant upgrade, space was at a premium and the biofilter was evaluated to see if it could be modified, moved, or replaced. Satisfied with biofilter technology, the plant was willing to keep the technology but uncertain how to fit it and make it work. This paper will discuss the odor control evaluation conducted and how the plant got to keep the biofiltration technology but delivered in a new form. Project Statement The existing odor control system for the Solids Handling Building (SHB) and Sludge Storage Tanks (SSTs) consisted of an in-ground, constructed-in-place, wood chip media biofilter. The Two Rivers Water Reclamation Authority (TRWRA) indicated that the biofilter required increased maintenance to ensure satisfactory performance and that the media was nearing the end of its useful life and needed to be replaced prior to the evaluation. In addition, a new Main Pump Station (MPS) at the plant was in the planning phase and with no other available space, TRWRA management made the decision to use land currently occupied by the biofilter. As a result, an evaluation was conducted that focused on newer biofilter technology using a synthetic, proprietary media that significantly reduced the overall size of the biofilter and provided a guaranteed 15 year life for the media. The new standalone biofilter would treat the same odorous airflow from the SHB and SSTs. and provided a significant increase in odor treatment capabilities as compared to the existing biofilter. Based on the significantly reduced size it could be located adjacent to the existing SHB. As an added benefit the new biofilter was constructed and placed into service prior to the beginning of construction of the MPS to avoid unnecessary sunk cost for providing a temporary odor control system as well as related construction time delays. Evaluation Before considering either alternate technologies or biofilter systems, odor monitoring was conducted at the site to determine the odor characteristics of the various odor sources in order to share with the vendors. Continuous hydrogen sulfide, Hâ‚‚S, was monitored with data loggers (results presented in Table 1), grab air samples were collected and sent to an independent laboratory to analyze for reduced sulfur compounds (results presented in Table 2), differential pressure continuous monitors were placed in the SSTs to assess whether they were under negative pressure thereby containing the odors, and smoke tests were run to determine if any localized leaks were present on the SSTs. Conclusions Several biofilter vendors were contacted and provided the data collected at the plant. Simply replacing in kind was not an option for many reasons including size and the fact that organic media breaks down in the presence of the sulfuric acid byproduct, which affects media stability, air transmittance and treatment performance. The recommended odor control system consisted of two constructed-in-place concrete biofilter cells with covers containing engineered synthetic and proprietary media. The engineered synthetic media has several advantages over the original organic media it was replacing with respect to media life, treatment efficiency, pressure drop, media depth, and required footprint. These advantages led to a more sustainable system where less water, less pressure drop, less power, less maintenance, longer media life (minimally three times longer), and a stack discharge with higher velocity rather than an area-wide, low velocity, ground level discharge. Despite Covid-19 related supply chain issues with FRP duct work during construction, the system is permitted, operating, and meeting performance. TRWRA and the neighbors are happy!