38 March 2017 • Florida Water Resources Journal

Often referred to as the water-energynexus, water and energy are inextrica-bly linked in the overarching goal of

public works to provide clean water. They arealso key to the successful development of sus-tainable economic projects on local, regional,state, and national levels. Globally, 6 to 7 per-cent of the energy consumed every year is forthe production and delivery of water. Ironically,in order to meet the future demand for electri-cal power in the United States, new power facil-ities may result in the consumption of vastquantities of water.

The competition for water resources hasresulted in reduced water allocations, alongwith delay, and in some cases, cancellation ofnew power projects across the U.S. Advancedtreatments for potable water production re-quired for the processing of lower-quality wa-ters, while meeting higher environmentalstandards for a growing family of water chem-istry parameters and chemicals of concern, re-quire greater demands for energy. Ozonedisinfection, which requires a significant inputof electrical energy, is one such emerging dis-infection technology.

Integrated utility systems may grow inpotential value as the average cost of electric-ity in the U.S., which is currently around 10cents per kilowatt-hour (kWh), is expected toincrease as the drive for clean and renewableenergy continues to gain momentum. Whilethere have been successful implementations ofsolid waste management campuses for opti-mized treatment of municipal waste, a largerutility network that includes water, waste-water, solid waste, and recycling remains fer-tile ground for energy efficiency. Finding a sitethat may be suitable for this marriage of tech-nologies may not be a challenge, as there are asurprising number of “brownfield” sites inurban areas that may be ideally suited for in-tegrated public work projects. Brownfields,along with wastewater treatment facilities,may provide excellent sites to locate an inte-grated water utility campus in close proximityof urban wastes.

Modern Energy-From-Waste Technology

Currently, energy-from-waste (EfW) facili-ties process approximately 13 percent of the totalmunicipal solid waste (MSW) in the U.S. As a re-sult, there is an immense untapped resource thatcan be converted to green energy in variousforms. While some of this waste is currentlybeing converted into methane in landfills, thereare potentially more than 16,000 megawatts ofelectric power that are not currently being uti-lized because municipal wastes are not convertedinto energy. Much of this potential renewableenergy can be developed within the areas in closeproximity to the source of the waste. Renewableenergy production from wastes can provide sig-nificant economic development to localeconomies. In addition to the immediate impactof local employment during construction andthe dollars spent within the local community,there is a long-term benefit throughout the op-eration and maintenance phase of the EfW proj-ects with a 45- to 50-year service life, includinghigh-quality and well-paying jobs, along with thepurchase of local goods and services.

Federal and State Legislation

Federal Renewable Portfolio StandardsThere is a long history of MSW being rec-

ognized as a renewable fuel, including Section203 of the Energy Policy Act of 2005, PresidentBush’s Executive Order 13423, Federal PowerAct, Public Utility Regulatory Policy Act, Bio-mass Research and Development Act of 2000,Regulations of the Federal Energy RegulatoryCommission, and American Clean Energy andSecurity Act (ACESA) of 2010.

The integration of EfW and water treat-ment processes as part of a municipal utilitycampus would qualify as renewable green en-ergy, or low-carbon energy for many of the fed-eral incentives, and would be well-suited toattract future incentives in the form of federally-supported grants and/or loan guarantee pro-grams. Successfully integrated municipal utilityprojects could become role models for numer-

ous urban communities across the U.S. In fact,the development of an integrated municipalutility campus dovetails nicely with the “micro-grid” concept, which is currently being pro-moted as a way to provide resiliency andreliability for essential power and water utilities.

State Renewable Portfolio StandardsIn the absence of federal renewable portfo-

lio standards (RPS), more than half of the stateshave enacted legislation in one form or anotherthat requires electric power utilities to generateor purchase from other renewable energy gen-erators a certain percentage of electricity pro-duced from renewable fuels. Florida, however,does not currently have a mandate for RPS thatprovides a legislative and/or financial incentivefor development of EfW facilities. Most of the11 operating EfW facilities in the state currentlysell electricity to local electric suppliers under awide range of power purchase agreements(PPA). The absence of an RPS in Florida actuallyprovides an incentive for municipally ownedEfW facilities to use their green renewable elec-tricity internally for the treatment of water re-sources and other public works.

Electricity From Municipal Wastes

The average waste generation of poundsper capita per day (PCD) in the U.S. has stabi-lized over the past decade at approximately 4.5PCD. The availability of EfW facilities has in-creased over the past decade due to advance-ments in the industry. The current annualavailability of 90 to 92 percent is relatively highcompared to modern fossil power plant indus-try standards. For the purpose of the followinganalysis, the use of 4 PCD is conservative andallows local recycling programs to continue toincrease in the future. The average net electricalpower generation of EfW facilities has also in-creased over the past decade to approximately

Sustainable Solutions for the 21st Century:Integration of Water Treatment Systems

With Energy From Municipal WastesP.L. Hauck

P. L. Hauck, P.E., is senior environmentalengineer with CDM Smith in Tampa.

F W R J

Florida Water Resources Journal • March 2017 39

550 kWh per ton (kWh/ton) of waste processed.The amount of electrical energy that can be pro-duced from an EfW facility serving a given pop-ulation is shown in Figure 1.

Water Treatment Electrical Demand

Energy is expended in each of a water treat-ment facility’s process steps, including extrac-tion, transport, treatment, disinfection, anddistribution. Urban areas are fast becoming thelargest centers of population that concentrate thedemand for water supply into a dense area. Theestimated demand for potable water in a com-munity varies widely, ranging from a low of 75gal per person per day, to a high of 150 gal. Theestimated water demand for a population of upto 3 million people is illustrated in Figure 2.

Potable Water TreatmentElectrical Demand

Using water resources wisely will be ofgrowing importance in the future, and fortu-nately there are a number of advanced technolo-gies that may help meet the demands of agrowing population for production of high-qual-ity potable water, efficient wastewater treatment,and the distinct possibility for recycling reclaimedwater for both indirect and direct potable reuse.

Energy input for water treatment plants(WTPs) varies widely with the quality of thesupply water and type of treatment process re-quired to meet potable water standards.Groundwater can be energy-intensive, with en-ergy demands significantly impacted by thedepth at which water is withdrawn from theaquifer. Energy inputs may range from 250kWh/mil gal (MG) at a depth of 75 ft to 2,500kWh/MG at a depth of 2,500 ft.

Conventional water treatment processeshave many steps that require the input of energy,with pumping (raw water supply, in-plant, andfinished water distribution) being the majoruser of energy. Desalting of marginal waters, in-cluding surface water, brackish groundwater,and seawater, can range from 5,000 to 15,000kWh/MG. Recent demonstration tests using in-novative treatments for affordable desalinationhave set a goal for production of desalinatedwater at approximately 7,000 kWh/MG.

Looking to the future era of indirect reuseof reclaimed water, energy inputs for these typesof multibarrier processes with advanced disin-fection can range from 10,000 to 15,000kWh/MG, and wastewater treatment processestypically range from 2,000 to 5,000 kWh/MG.The typical range of energy input for various

Table 1. Energy required for various water treatment technologies.

Figure 1. Typical energy from waste net electrical output as a function of population.

Figure 2. Typical water demand as a function of population and use.

Continued on page 40

40 March 2017 • Florida Water Resources Journal

water treatment processes, including raw waterwithdrawal and transfer, treatment, disinfection,and distribution, is summarized in Table 1.

Energy From Waste With PotableWater Production

Matching the electrical output from amodern EfW facility with water treatmentprocesses can vary significantly, dependingupon the source water and type of treatment.Assuming a system wide input of 1,500kWh/MG for the water treatment process, Fig-ure 3 illustrates the relationship between the sizeof the EfW facility and the potential productionof potable water if all the electricity were usedfor water production. As shown, an EfW facilitycan literally provide six to eight times morepotable water than demanded.

Figure 4 is a similar graph to figure 3, de-veloped for a smaller range of EfW facilitiesscaled for smaller communities in the range of50,000 to 150,000 people.

For communities in need of securing addi-tional water supplies from alternate watersources, such as lower-quality surface water,brackish water, or seawater, the compatibility ofEfW and WTP processes improves due to thegreater demand for energy. Figure 5 shows therange of water production that can be producedif 100 percent of electricity from the EfW facil-ity is used for a range of higher-energy-demandtreatment processes. A process that uses 5,000kWh/MG may be typical for a membrane treat-ment process, whereas a process such as seawa-ter reverse osmosis may be in the range of10,000 to 20,000 kWh/MG.

An ever-growing percentage of the U.S.population currently lives in coastal states. Muchof this population resides in large- and medium-sized coastal communities, where the demandfor additional water supply may require seawaterdesalination technologies. The use of reverse os-mosis (RO), multistage flash (MSF) evaporation,and multiple effect distillation (MED) processesmay be ideally suited to use 100 percent of theEfW electricity. In many cases, the size of theEfW plant may be selected to produce the re-quired amount of potable water that is neededfor serving an expanding population. Figure 6 il-lustrates the relationship between EfW facilitysize and the potential production of potablewater from seawater desalination.

Energy From Waste With Wastewater Treatment

The average per-capita demand for water hasdeclined over the years due to a variety of conser-

Figure 3. Water treatment capacity if powered by 100 percent of electricity from a large energy-from-waste facility.

Figure 4. Water treatment capacity if powered by 100 percent of electricity from a small energy-from-waste facility.

Figure 5. Water treatment capacity for advanced technologies that demand higher inputs of energy.

Continued from page 39

Florida Water Resources Journal • March 2017 41

vation measures. For estimating purposes in thisarticle, a value of 100 gal per capita per day is used.The generally accepted demand rate for waste-water service is 90 percent of the potable water de-mand, or in this case, 90 gal per person per day.

Wastewater treatment plants (WWTPs)make perfect companions for EfW facilities. Inaddition to accepting the process wastewater (in-cluding cooling tower blowdown) from the EfWfacility, the WWTP may also provide reclaimedwater for use as process water, such as ash quenchwater and process makeup water. In some com-munities with existing EfW facilities, biosolidsfrom their WWTPs are also processed in the EfWfacility. The generally accepted rule of thumb isthat WWTP biosolids provide a positive energybalance when dried to greater than 45 percentmoisture content. Below this condition, they donot provide energy, but they may still be disposedof at a reasonable cost in the EfW facility.

The energy required for WWTPs vary as afunction of capacity, type, and level of treat-ment, disinfection, recycling, and disposal. TheWWTPs are often the single largest electricityusers in local municipal operations, with thesecondary wastewater treatment process as themost energy-intensive. The ultraviolet disinfec-tion process, which is also energy-intensive, isbeing used at an increasing number of munici-pal WWTPs due to its many advantages. Figure7 shows the estimated capacity of WWTPs thatcould be powered by 100 percent of the elec-tricity from EfW over a wide range of energy in-puts for EfW facilities up to 3,000 tons per day(TPD), which is capable of serving a populationof approximately 1.4 to 1.5 million.

Figure 7 shows promise for major urbanareas that currently do not employ EfW or haveexcess MSW that could be used by an EfW facil-ity to power existing WWTP facilities. In this case,the capacity of WWTPs that could be powered byan EfW can be significant, in the range of 200 milgal per day (mgd) to more than 1 bil gal per day.A similar graph for the smaller range of EfW fa-cilities that would serve a population in the rangeof 50,000 to 250,000 is provided in Figure 8.

As seen in Figures 7 and 8, WWTPs that arelarger than needed by a community’s populationcan be operated, in most cases, on 100 percentof the electricity from EfW. In this case, a com-munity will need to find additional internal usesfor the remaining electricity (including potablewater treatment), or sell it to the local grid.

Summary of Water Treatment Opportunities

Based on the screening analysis, a compar-ison of the sizes of water treatment processingcapacities that can be powered by a commu-

Figure 6. Water treatment capacity for seawater desalination if powered by 100 percent of elec-tricity from an energy-from-waste facility.

Figure 7. Typical wastewater treatment plant capacity if powered by 100 percent of electricity froma large energy-from-waste facility.

Figure 8. Typical wastewater treatment plant capacity if powered by 100 percent of electricity froma small energy-from-waste facility.Continued on page 42

nity’s solid waste is graphically displayed in Fig-ure 9. From a greenfield perspective, conven-tional WTPs and WWTPs may not be ideallymatched to use 100 percent of the electricityfrom a community’s EfW facility, assuming thatthe EfW plant has been sized to process 100 per-cent of the available MSW; however, most exist-ing EfW facilities are not always sized for 100percent of the local MSW stream due to a vari-ety of reasons.

In the case of large urban areas with con-centrated population centers, a new EfW facilitymay be sized to provide 100 percent of its elec-tricity for operation of the existing WTP and/orWWTP facilities. When properly sized for localwater resource demands, the project can be de-signed for optimal performance in providing

cost-effective services to both the solid waste andwater resources departments. The integration ofboth WTP and WWTP facilities will increase theuse of electricity from an EfW facility to ap-proximately 38 percent when all facilities aresized to serve the same local population base.

Future water management may include: re-claimed water distribution systems for local res-idential, commercial, and agriculturalirrigation; reservoir storage for reclaimed waterand excess stormwater during wet seasons; andstormwater treatment systems for removal ofexcess nutrients and pollutants. In such anarrangement, the demand for energy in theform of electricity or steam will increase signif-icantly and provide an opportunity for a well-matched size of an EfW facility to provide all ofthe integrated campus needs.

As noted in Figure 9, with the addition of awater reclamation facility (WRF) that is de-signed to treat and disinfect reclaimed waterand/or lower quality stormwater, the energy de-mand increases significantly to the point wherea good fit can be developed to use 100 percent ofthe EfW electricity for treatment and distribu-tion of the various water systems. Figure 10 il-lustrates diagrammatically how such a futurewater resource system and EfW facility could beintegrated into a single utility campus.

Seawater and brackish water sources mayalso be included in the discussion of advancedwater treatment, especially for coastal and low-lying inland communities. The removal of saltsand other impurities from brackish and seawa-ter requires significantly higher inputs of energy,either in the form of electricity or steam.

Proven technology exists to generate re-newable electrical energy from municipal solidwastes, along with recovery of biomethane fromlandfills and anaerobic digesters. Looking to thefuture, renewable energy systems, such as solar,wind, anaerobic digestion, codigestion, andother emerging waste treatment technologiescould help satisfy the need for backup powersupply to cover the infrequent periods when theEfW facility is offline for planned and un-planned maintenance outages.

The majority of urban communities in theU.S. do not employ EfW and have large MSWstreams that are currently being disposed of inlandfills. As local and state goals for landfill di-version gain momentum as part of a drive forsustainability, the development of regional EfWfacilities may also become viable when com-bined with regional water supply and distribu-tion projects. In these cases, there is likelysufficient MSW available that could allow anEfW facility to be sized to match the demand ofthe community’s existing and future water re-source needs.

The scoping analysis is encouraging for anumber of reasons, the most important of whichis financial. The shared electrical savings that willresult from the internal use of electricity maywarrant an evaluation of the various options anda full feasibility study for those options mostsuitable for each community. These synergisticopportunities often require that the variousprocesses be owned by a single entity (munici-pality) and also be colocated on a contiguousproperty if electricity is to be used internally.

Currently, there are rules that prevent thesale of electricity by anyone other than regu-lated electric utilities in the U.S. Alternately, thetransfer and sale of steam, hot water, bio-methane, and syngas via a pipeline may be bothtechnically and economically feasible for re-

Figure 9. Range of sizes of water treatment processes that can be powered by a community’s mu-nicipal solid waste.

Figure 10. Future integration of energy from waste and water. Continued on page 44

42 March 2017 • Florida Water Resources Journal

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motely located municipal and private facilities.Each of these opportunities should be exploredto fully evaluate the vital municipal services thatcould be synergistically integrated.

Hillsborough County Case Study

One such recent example of the internaluse of renewable energy is in HillsboroughCounty (Figure 11). In 2009, approximately 2megawatts of electricity from the county’s EfWfacility was delivered to its adjacent 12-mgd ad-vanced wastewater treatment plant (AWTP). In

this arrangement, the solid waste departmentgenerates greater revenues than if it sold renew-able energy to the local electric utility, while thewater resources department saves by avoidingthe purchase of electricity at the full commer-cial rate. This win-win arrangement has savedlocal rate payers millions of dollars over the pasteight years. In order to avoid “demand charges”imposed by the local utility if the AWTP facilityremained connected to the local electric grid, abackup diesel electric power system was pro-vided to ensure uninterrupted electric service atthe AWTP. The AWTP has 100 percent backupdiesel generation to ensure that the facility will

operate when the EfW facility is temporarily off-line for planned or unplanned maintenance.

Figure 12 illustrates the potential savings topublic works for a variety of EfW facility sizesbased upon the percentage of electricity that isused for the treatment of water resources. Asshown, the savings can be significant—poten-tially tens of millions of dollars per year basedupon a three-cent differential between the ratesat which the EfW would sell power to the localgrid versus the rate at which water resourceswould purchase electricity from the local grid.

Conclusion

A synergistic approach to managing severalmunicipal processes on a single water utilitycampus is compatible with the goals of sustain-ability, waste reduction, and development of al-ternate water supplies, while answering thechallenge of the water-energy nexus. In additionto this successful Florida project, there are nu-merous opportunities to integrate energy fromwaste with water treatment processes for vari-ous alternate water sources, including surfacewater, wastewater, reclaimed water, stormwater,brackish water, and seawater as viable optionsfor the future era of sustainable public works.

Acknowledgments

The author wishes to acknowledge assistancefrom the public utilities department and solidwaste management division of HillsboroughCounty in the preparation of this article. SSFigure 11. Potential benefits for use of renewable electrical energy from energy-from-waste facilities.

Figure 12. Hillsborough County energy-from-waste facility powers an adjacent advanced wastewater treatment plant with approximately 2 megawatts of electricity.

44 March 2017 • Florida Water Resources Journal

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