Air Permitting Strategies for Biogas Renewable Fuel Energy Projects at Wastewater Treatment Facilities

摘要

Wastewater treatment facilities (WWTFs) with anaerobic digestion capabilities have increasing economic opportunities for implementing biogas utilization projects to reclaim the energy in the biogas (digester gas). These include renewable energy credits (RECs) and grant funding for combined heat and power (CHP) projects, and Renewable Identification Numbers (RINs) for renewable natural gas production. These projects have environmental and economic benefits over traditional biogas boiler and heat exchanger projects, but can have air emissions and air permitting challenges that can affect project design and schedule, and may delay critical grant funding. For example, CHP engines can be significant emitters of carbon monoxide, sulfur oxides, nitrogen oxides and formaldehyde. This presents challenges in avoiding major source air permitting thresholds and complying with state toxic air pollutant requirements. Cleaning of biogas to meet "pipeline quality" criteria produces tail gas exhaust emissions from the cleaning equipment, including methane slip and concentrated hydrogen sulfide. Both types of projects include back-up biogas flares that can have high potential air pollutant emission rates. Both types of projects employ new and innovative technologies that have limited reliable emissions data and control device performance data. These air emissions and air permitting challenges become particularly important, because the states with the most advanced incentives and mature credit trading markets also tend to be those with the most stringent air quality regulations (e.g., California, the Northeast, and Mid-Atlantic states).This paper will discuss these two biogas utilization project types - CHP projects and renewable transportation fuel production - from an air regulatory and permitting perspective. The paper will identify the air emissions sources from representative equipment; provide air pollutant emission rates and ranges; and present the most recent available information on biogas treatment and air pollution control technologies, including current estimated capital and operational costs for these technologies. The paper will discuss the air permit thresholds, regulatory complexity and permitting challenges for each of these two project types in California and in the Northeast. Recommendations will also be included on air permit strategies that can be applied for each project type to expedite air permit approval in support of meeting state grant funding deadlines.