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Sludge-To-Energy Energy And Resource Recovery: Generating Resources, Not Waste Streams "Sludge-to-energy" is trending in wastewater treatment, but what technologies have the most potential? wateronline.com ■ Water Online The Magazine 20 I ncreasing populations and urbanization are putting cumulative pressures on the Earth's energy, water, and nutrient resources. As wastewater contains these valuable resources, it can potentially help address these issues. Several factors are driving energy and resource recovery, including tightening regulations related to the land application of sludge, sludge incineration, and sludge disposal at landfills, as well as rising sludge treatment and disposal costs. Given that sludge treatment and disposal can account for up to 50 percent of operational spending at a wastewater treatment plant (WWTP), a strong economic driver exists for finding efficient technologies and inexpensive, long-term disposal routes to reduce sludge management costs. The increased emphasis on energy and resource recovery has become a primary focus for BlueTech Research, a market intelligence firm specializing in innovative water technologies. Areas of coverage, analyzed in a recent BlueTech Research Insight Report entitled Sludge to Energy – Biogas Generation and Utilization: Technology Trends and Market Potential, include biogas generation via anaerobic digestion (AD), biogas contaminants removal, biogas utilization via combined heat and power (CHP) technologies, and energy generation optimization practices such as pretreatment technologies and co-digestion. More efficient CHP technologies, sludge pretreatment, and co-digestion with high-energy fats, oil, and grease (FOG) can increase energy generation, reduce sludge volumes, reduce sludge management and operational costs, and provide a viable waste management solution for food wastes. According to the most recent WEF Biogas Survey (2012), sewage sludge is anaerobically digested at approximately 1,238 WWTPs in the U.S., most of which are more than 1 MGD in capacity. Approximately 270 of these 1,238 facilities (22 percent) utilize the pro- duced biogas through CHP, which equates to approxi- mately 231 megawatt (MW). The remaining 968 plants (78 percent) use the biogas for digester heating and potentially space heating; the surplus is wasted or flared. Considering the pretreatment market in the U.S., in particular for the Cambi thermal hydrolysis pre- treatment (THP) technology, there is potential to increase market share considerably in the plants with AD. Cambi has installed its first THP plant in the U.S. at the Blue Plains facility in Washington, D.C., with an installed capacity of 149,000 tons of dry solids (TDS)/year. If the initial focus were primarily on the 270 AD plants, which utilize their biogas in their CHP units, the total installed Cambi capacity would be approxi- mately 1.7 million TDS/year (assum- ing a two-thirds uptake rate). This would represent an 11-fold increase in installed capacity within the U.S. market for Cambi. BlueTech's comprehensive analysis of "sludge-to-energy" technologies provides several key takeaways: • Anaerobic Digestion Is The Principal Sludge-To-Energy Technology The predominant sludge-to-energy technology on the market is AD, which has a dual purpose: It stabilizes the sludge and generates a biogas. AD is advantageous for use in WWTPs, as it is a well-established and robust sludge-stabilization technology. Also, AD does not require a dewatered sludge feedstock prior to digestion, unlike gasification or pyrolysis. This reduces the energy consumption and operation costs associated with dewatering. • Internal Combustion Engines (ICE) Currently Dominate The CHP Market Various energy-generation CHP technologies that were assessed include fuel cells, microturbines, ICE, and the Stirling engine. While ICE currently dominates the CHP market, underutilization of biogas at smaller WWTPs and tightening air regulations could alter this. Small-capacity (30kW-1MW), low-air-emissions microturbines offer an opportunity for the smaller WWTPs to start consuming their presently untapped biogas. Currently, these smaller plants do not utilize the biogas due to perceived and actual barriers, such as inadequate payback and economics. Non- combustion fuel cells, although still relatively expensive, offer the cleanest and most efficient CHP option. They By Aoife Moloney Anaerobic digestion is advantageous for use in WWTPs, as it is a well- established and robust sludge-stabilization technology . 2 0 _ V E R T _ 0 2 1 4 E Z i n e _ B l u e T e c h _ D G . i n d d 1 20_VERT_0214 EZine_Blue Tech_DG.indd 1 2 / 3 / 2 0 1 4 4 : 2 0 : 4 0 P M 2/3/2014 4:20:40 PM