Modeling VOC Reduction in High Purity Oxygen Activated Sludge Wastewater Treatment Process: Toxchem? Based Fate Modeling Case Study

摘要

In the last decade, stringent regulations have been imposed on the permissible level of Volatile Organic Compound (VOC) emissions that can be emitted at industrial facilities. The clean air act amendments of 1990 and related regulatory extensions since then (e.g., National Emissions Standards for Hazardous Air Pollutants, NESHAPs) have significantly impacted the acceptable level of Volatile Organic Compound (VOC) emissions from industrial facilities (Woodward & Curran, 2006). A total of 188 organic compounds have been designated as Hazardous Air Pollutants (HAPs), and facilities which generate or handle these air toxics have been subjected to permitting, monitoring and reporting requirements. Although extensive emissions control efforts have been integrated into the production process at many industrial facilities, a significant amount of VOCs can still end up in the wastewater, where these VOCs can be stripped into the air during conveyance through collection systems or during biological treatment. Fate and Transport models are used for a variety of tasks including design, emissions analysis and regulatory reporting. The development of fate & transport models in wastewater collection and treatment systems were spurred by regulatory drivers like the Clean Air Act (Melcer, 1994). A variety of computer based fate & transport models such as BASTE, EPA Water Models (versions 7, 8 and 9), CORAL, PAVE, SIMS, TORONTO, INTERCEPTOR and Toxchem? have been applied for addressing the fate of volatile contaminants in collection systems, drop structures, weirs, quiescent surfaces, and wastewater treatment processes (Quigley et al, 2006; Melcer, 1994). EPA Water Models (7, 8 & 9) and Toxchem? are the most commonly utilized fate and emissions transport modeling platforms in the wastewater industry. The default aeration options in both of the commonly utilized fate & transport modeling platforms (EPA Water 7, 8, 9 & ToxChem) exclusively model the mass transfer behavior of diffused air processes or surface aeration style mechanical mixers. Attempts at modeling the performance of High Purity Oxygen (HPO) based devices have typically required finding the most appropriate approximation to the mass transfer and VOC stripping behavior of HPO aeration systems by modifying default parameters in the diffused air or surface aeration modules in fate and transport models (NYSERDA, 2000; Levine et al, 2010; Rodieck et al, 2001).Hydromantis recently released Toxchem? 4.1 (Hydromantis, 2012), which extends the simulation capabilities of the platform to include the modeling HPO and Sequencing Batch Reactor (SBR) process systems. This paper discusses results for VOC emissions modeling obtained by applying Toxchem? 4.1 to VOC reduction projects that utilize SBR and HPO systems. We provide a methodology for establishing the modifications that need to be made to the default parameters in diffuser and mechanical surface aeration modules in fate and transport models in order to enable VOC emissions characteristics associated with HPO systems to be modeled, and provide comparative analyses on the effect of the approach adopted on simulation results.