Treatment of Odors and Emissions using an In-Situ Floating Reactive Barrier Technology

Anaerobic digestion ponds are widely implemented in the agriculture and meat processing industry as a secondary treatment system for the removal of chemical oxygen demand (COD) and biological oxygen demand (BOD). To maintain anaerobic conditions, these digestion ponds typically implement a naturally occurring cover consisting of fats, oils, and greases (FOG) that accumulate on the pond surface as a solid layer. However, even with the FOG cap, many anaerobic digestion ponds continuously suffer from odor (e.g., volatile fatty acids, ammonia, H2S and other reduced sulfur compounds, RSCs) and greenhouse gas (GHG) emission issues, resulting from anaerobic biological activity [1]-[3]. Geomembrane covers have been implemented for odor reduction and biogas collection but are often impractical for large anaerobic ponds or those that produce uneconomic levels of biogas to warrant gas capture. Further, these systems act primarily as a physical barrier without any reactive properties to treat the emissions compounds intercepted by the cover, necessitating separate biogas processing systems. To this end H2nanO has developed SolarPass, a passive floating reactive barrier (FRB) technology consisting of a system of buoyant photocatalyst beads that provide a physical barrier to odor compound and GHG emissions, while simultaneously providing sunlight-driven oxidative treatment of the emissions compounds, as well as treatment of aqueous contaminants (Figure 1). Additionally, the FRB can be implemented as a 2-way barrier by limiting both odor emissions out of the pond and oxygen transport into the aqueous phase, therefore promoting anaerobic digestion. Further, SolarPass can photocatalytically degrade anaerobic inhibitors and co-oxidize organics to render them more biodegradable. The SolarPass system can be deployed and recovered in-situ for pond coverage, or to tanks for off-grid, for high strength oxidative treatment of odor compounds without the need for chemical or electrical inputs (Figure 2). Further, SolarPass can be continuously operated without gas handling or adsorbent regeneration/disposal (i.e., the catalyst beads are not consumed during treatment). Previously, the SolarPass floating reactive barrier was demonstrated as an effective solution to mitigate reduced sulfur compound and volatile organic compound (VOC) emissions [4]. Continuing to develop new FRB applications, H2nanO recently validated its SolarPass technology at the bench-scale (2 L) for the passive treatment of odor compounds from an industry sample of water from a meat processing plant anaerobic treatment pond. Volatile fatty acids (VFAs) emissions with the SolarPass barrier were compared to a bare surface control using a bench-scale reactor (designed to simulate an outdoor open pond deployment, while allowing for capture and quantification of gas fluxes). The headspace of the reactor was continuously flushed for 4 hours through a caustic scrubber to collect any VFA odor emissions and the captured VFAs were subsequently quantified via titration [5]. Additionally, the 2-way barrier properties of SolarPass were evaluated for reducing oxygen transport into the pond and promoting anaerobic treatment conditions. Anaerobic digestion of the organic content was monitored using chemical oxygen demand (COD) measurements and anaerobic indicator strips. Anaerobic digestion rates for the COD were compared to a bare water surface as well as synthetic FOG layer controls. Comparing the cumulative VFA emissions with SolarPass to the bare surface control, it was found that the anaerobic pond effluent produced 6x fewer odor emissions when covered by SolarPass compared to the bare surface alone, demonstrating the effectiveness of the floating reactive barrier to reduce odor issues (Figure 3). Further, when investigating the anaerobic capabilities of SolarPass in an open vessel, the FOG and bare controls had 92% greater volatilization of odour compounds and limited anaerobic digestion compared to SolarPass. Following an initial lag phase prior to anaerobic activity, the organics in the SolarPass vessel exhibited 160% faster anerobic degradation of COD compared to the controls at a rate of 86.7 mg/L/d (Table 1). These results further demonstrate the bi-directional barrier properties of SolarPass and highlight its capability to effectively reduce odor emissions while concurrently stimulating anaerobic treatment of bulk COD. As a standalone process or part of a larger treatment system, SolarPass is a promising low-cost platform for the passive treatment and capture of odor emissions from aqueous sources. Under lab-scale simulated solar conditions, SolarPass effectively reduced odor emissions while simultaneously promoting anerobic digestion of residual organics in a meat processing effluent. Prior to implementation of SolarPass at the pilot-scale, these results demonstrate the scalability of the technology and its readiness for further deployment. SolarPass has now been demonstrated an effective solution for passive odor management of volatile fatty acids, sulfur, and organic compound emissions while providing simultaneous passive aqueous treatment.