2010 Issue

20 Wastewater Utility Energy Conservation In the initial phases, benchmarking andmetrics are important, thus the first step is to assess the current performance. A comprehensive energy audit that includes an energy balance is important as a means of determining the best place to begin and the most return on investment. The following list, adapted from EPA Energy Efficiency and Renewable EnergyOpportunities atWater andWastewater Facilities (Rogers, Turgeon, 2009), indicates how and where energy can be conserved at a wastewater facility: • Include energy efficiency and renewable energy in the design phase • Aeration can be as high as 60 percent of the electric load at wastewater facilities • Pumping—in drinking water plants, pumping is often 90 percent or more of the electric load. In wastewater plants, it is typically 20 to 30 percent • Heating, ventilation, and air–conditioning (HVAC) controls are very important, especially where codes mandate frequent air changes • Lighting can be a significant energy user Renewable Energy Overview Renewable energy systems that could be employed at wastewater facilities include bioenergy, solar, wind, hydro, and geothermal resources. Waste- water facilities make up a significant portion of overall municipal power demand, present the opportunity for bioenergy generation, and typically have open land near themor even within the existing fence-line; therefore, they are logical places to employ renewable energy projects. It is important that tThe wastewater facility should employ consulting teams that include individuals with in-depth understanding of the technical requirements associatedwith renewable power generation. Understanding the ever-changing local, state, and federal incentivemoney and regulatory permitting is important. At a wastewater facility, one obvious choice for renewable energy creation is utilizing using the biogas from anaerobic digestion. Biogas can provide roughly 50 percent of the power demand and nearly all of the process and building heat at most wastewater facilities. The combination of primary treatment and primary solids digestion is one of the most energy-efficient and economic means of wastewater treatment. Biogas is a proven fuel for producing renewable energy by generation of heat, power, combined heat and power (CHP), and a natural-gas-grade fuel that can be exported from the wastewater facility. • Approaches to augmenting biogas production include the following: • Modifications for enhanced solids destruction efficiency in anaerobic digestion • Pretreatment of wastewater residual solids • Advanced anaerobic digestion • Codigestion of industrial or commercial wastes with wastewater residuals • Established codigestion processes Biogas Energy Recovery Technologies The various systems used to convert biogas to energy include: • Combined heat and power systems (such as reciprocating gas engines, gas turbines, and fuel cells) • Heating only for steam or hydronic boiler Choosing the appropriate technology for converting biogas to energy is often a cost-based decision as one of the primary objectives in increasing anaerobic digester efficiency is to increasemonetary gains from the biogas produced and the energy associated with it while avoiding costs of solids disposal. Hence, the capital and operation and maintenance costs of the energy-recovery-technology systems should be offset by the monetary gains recovered from the biogas-derived energy. Further, in estimating the monetary gains from the bioenergy produced, the variable inefficien- cies of the recovery systems should be considered. It should be noted that carbon cap and trade programs that are expected to be federally mandated by 2012 could make the economics of these systems more at- tractive to wastewater facilities. Also, some leaders at the municipal level have implemented programs now to reduce the carbon footprint. Because of this principle, many wastewater facilities have invested in CHP because it is consistent with the goal of reducing GHG emissions. Efficient conversion of biogas to energy is also largely dependent on the pretreatment of the biogas. It is imperative that water vapors be removed for the energy recovery systems to effectively convert the biogas to energy. Further, the health, air emissions, and odor concerns associatedwithH2S in the biogas havemade it of primary concern for removal frombiogas before it is combusted. Likewise, the fouling of the energy recovery system is likely unless siloxanes are extracted. With the appropriate measures taken to scrub the gas, digester biogas is an excellent source of renewable energy for the wastewater treatment industry and thereby alleviates a portion of the economy’s consumption of nonrenewable energy sources. Conclusions There are decided advantages for the wastewater treatment industry SUSTAINABLE ENERGY — continued from page 19 A R W 1594 Park Circle, Ogden, Utah 84404 ph. 801.782.6008 www.arwengineers.com A Commi tment to Qual i ty, A Four -Decade Legacy of Serv i ce structural consultant s ENGINEERS