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Expanded Summary Urban water-cycle energy use and greenhouse gas emissions JOAN O PPENHEIME R, M O H A M M A D B A D RU ZZAMAN , R O BY N MC G U C K I N , AN D J O S EP H G . J AC AN G EL O http://dx.doi.org/10.5942/jawwa.2014.106.0017 The water–energy nexus has motivated water industry professionals to maintain water performance goals with less energy input and fewer greenhouse gas (GHG) emissions. This article investigates protocols and methodologies, as well as tools for energy and GHG emissions control and tracking, that are adaptable to or specifically developed for use within the urban water cycle. Although there are many operational energy-minimizing strategies available, real-time or near-real-time tools for monitoring and reporting energy use and GHG emissions are not yet widely developed for the water sector. Additional study is warranted to obtain a better understanding of process-specific emission factors and real-time measurement and control of activity levels associated with emissions. It may also be beneficial for the water industry to consider a continually updated compendium of GHG emission estimation methodologies. The urban water cycle represents the movement of water into, within, and out of defined urban boundaries that contain the engineered systems for potable water production, wastewater processing, and stormwater management. GHG emissions occur indirectly from energy use and also occur directly from certain processes within the urban water cycle. A key feature of sustainable urban development is minimization of the carbon footprint of the urban water cycle in order to curtail global changes in climate. Water quality criteria and reporting requirements are established for urban water cycle segments through use of codified regulations, guidelines, industry standards, and uniform practices. Corresponding requirements for energy and GHG emission minimization are lacking because reporting is largely voluntary. Thus the objective of this article is to assess the availability of relevant and appropriate tools for managing segments of the urban water cycle for energy minimization and GHG emissions accounting. aspects within the urban water cycle. Also, because emission reporting usually is not mandated, utilities frequently lack the monitoring tools for accurate isolation and assessment of the activity data. Six GHGs are required for monitoring on a national scale by the signatory countries to the Kyoto Protocol. Within the urban water cycle, only carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are considered relevant. The global warming potential of CH4 and N2O are higher than CO2 and demonstrate the importance of monitoring for these gases even when these emissions occur at much lower levels than CO2. Emission ownership (direct or indirect) is also tracked to prevent double accounting. Within the urban water cycle, emissions associated with power for pumping or treatment processes are considered scope 1 (direct ownership) when onsite fuel combustion is used for its generation; processes are considered scope 2 (indirect ownership) when grid electricity is used. Scope 1 direct-process emissions of CH4 and N2O occur in wastewater treatment facilities and to a lesser degree from water treatment processes using activated carbon or ozone generated from air. Scope 3 emissions (indirect ownership) include emissions associated with product life-cycle activities before and after use onsite, and outsourced activities. Facility-owned vehicles are direct ownership (scope 1) and contractorowned vehicles and employee business travel emissions are indirect ownership (scope 3). GHG REPORTING FRAMEWORK FOR THE URBAN WATER CYCLE GHG emissions reporting for any sector derives from a protocol that provides an organizational framework for the emissions sources and a methodology that defines the quantification process. Tools provide software-driven algorithms that translate input parameters to the output variables needed to report in accordance with a prescribed methodology. Most rely on calculating an emission rate in accordance with the following equation: Emission Rate = Emission Factor × Activity Data (1) The difficulty comes in how the emission factor is characterized for use with site estimations of the activity level. High-level approaches showing greatest global harmonization rely on gross averages that lack the detail needed for application to many design and operational URBAN WATER CYCLE ENERGY-DEMAND MINIMIZATION STRATEGIES The greatest opportunity for energy minimization in the potable water sector lies in selecting source waters with lower embedded energy. This embedded energy results from requirements for pumping, treatment, and distribution before a given quantity of water can be used at a specific location. Energy intensities of 380–2,800 O P P ENH EIM ER ET A L | 106: 2 • JO U R NA L AWWA | FEB R U A R Y 2014 2014 © American Water Works Association 43 kW·h/mil gal have been reported for potable water, with 85% attributed to pumping in systems that are not gravity fed and values as high as 9,200 kW·h/mil gal for pumping over 2,000-ft mountains in California. Typical energy intensities of 670–4,600 kW·h/mil gal have been reported for wastewater treatment process facilities, and 6,000 kW·h/mil gal when membrane bioreactors are used in place of activated sludge or extended aeration. Low-impact development technologies that reduce urban stormwater runoff and pollution loads contribute to urban water-cycle energy minimization by augmenting local water supplies with use of less energy for treatment and distribution. Energy inefficiency in pumping system design can be curtailed by reducing oversizing for performance unknowns and by less restriction of operational expenditure improvements because of capital expenditure costs. On an individual facility basis, potable water systems can achieve additional energy-demand reduction through four key strategies: • implementing water-use efficiency programs • selecting water sources with lower embedded energy • optimizing distribution system energy efficiency • increased reliance on energy obtained from renew able fuel sources The wastewater industry, on an individual facility basis, can achieve additional energy-demand reduction through five key strategies: • minimizing collection system infiltration and inflow • modifying activated sludge aeration systems • optimizing ultraviolet disinfection systems • capitalizing on combined heat and power installation opportunities • capturing additional latent energy in digested biosolids TOOLS FOR GHG EMISSION MANAGEMENT BY CONTROL OF ENERGY USE OR DIRECT PROCESS EMISSIONS Several energy-fficiency tools are applicable for use in the urban water cycle. Energy-use survey data have been statistically assessed and benchmarking tools have been used for evaluating energy performance at water and wastewater facilities. Examples are the US Environmental Protection Agency’s Energy Star®, the Water Research Foundation’s energy benchmarking, the New York State Energy Research and Development Authority, and the Canadian National Water and Wastewater Benchmarking Initiative. There are pump- and motor-efficiency evaluation tools (e.g., the US Department of Energy’s pump-system assessment tool and MotorMaster) as well as GHG emission-activity factor spreadsheets for different energy mix alternatives (such as the Pacific Institute’s Water to Air Model). There are also commercial energy management tools that provide automated or near real-time control for improved energy efficiency of water facility operations. Such systems use de mand forecasting and hydraulic modeling to reduce distribution system water pumping, improve pumping system efficiencies, or provide real-time relative energy-use 44 data through system submetering. Although the energy reductions achieved simultaneously reduce carbon emissions, these tools do not use carbon emissions as a control parameter and often focus more on energy cost savings through the use of lower electricity-tariff periods. Two processes at water facilities generate direct GHG emissions. N2O is produced when air (not oxygen) is used to generate ozone for oxidation/disinfection with a reported emission factor of 0.00011 kg/m3 N2O (UKWIR, 2005). CO2, CH4, and N2O are produced from the fuel combusted to heat the furnace for the granular activated carbon (GAC) regeneration process when GAC is used for treatment. These GHG emissions can be assessed from direct measurement of the consumed fuel or estimated (Huxley et al, 2009). Direct emissions of CH4 and N2O are a larger concern for wastewater facilities, and models have been developed and are being further refined to better estimate or depict these emission factors. Processes that are not at steady-state require mechanistic process models with dynamic simulators to capture real-time rather than average process emissions. Scope 3 emissions occurring outside the boundary of the utility are less emphasized in government enterprise reporting than in commercial product-level reporting. For this reason, many urban water cycle agencies that voluntarily report carbon emissions focus on scope 1 and 2 categories (McGuckin et al, 2013). Scope 3 accounting can be difficult to assess because of a dearth of appropriate emissions factors for water facility construction or the manufacturing of water utility supplies. CONCLUSIONS Comprehensive GHG emissions accounting and control methodologies for the urban water cycle are not fully developed. This overview presents a snapshot of available tools for energy and GHG emissions management. Tackling GHG reductions through energy minimization can be difficult because of the need to congruently optimize for water quality, operational needs, and asset management. Achieving reduction of direct-process GHG emissions requires enhanced process-modeling tools that provide more accurate GHG emissions factor estimates. REFERENCES McGuckin, R.; Oppenheimer, J.; Badruzzaman, M.; Contrerras, A.; & Jacangelo, J., 2013. Toolbox for Water Utility Energy and Greenhosuse Gas Emission Management. Water Research Foundation, Denver. UKWIR (UK Water Industry Research), 2005. Workbook for Quantifying Greenhouse Gas Emissions, 05/CL/01/3. Superseded by UKWIR, 2007/2008. Carbon Accounting in the UK Water Industry: Methodology for Estimating Operational Emissions, 08/CL/01/5. Corresponding author: Joan Oppenheimer is principal scientist for MWH, 618 Michillinda Ave., Ste. 200, Arcadia, CA 91107 USA; joan.oppenheimer@ mwhglobal.com. F E BRUARY 2 0 1 4 | J O U R N A L AW WA • 1 0 6 :2 | O P P E N H E I M ER ET A L 2014 © American Water Works Association