WATER ISSUES:

Improving energy efficiency of water

and wastewater utilities

 

 

In general, it is easy to leave the tap running without caring about the real cost of having drinking water at home. The energy-intensive effort that implied delivering water to households and then treated urban wastewater in United States is estimated around 3-4 percent of national electricity consumption annually by United States Environmental Protection Agency (EPA). That means that the emissions to the atmosphere per year are more than 45 million tons of Greenhouse gases (GHGs).

 

The cycle is simple, the water is treated to drinking water standards at the Water Treatment Plants (WTP), pumped to our homes and businesses, and then the pumped urban wastewater receives treatment at the Wastewater Treatment Plans (WWTP) before it is discharged to the environment.

 

Considering a more global approach, an average energy consumption per cubic meter of wastewater treated in developed country, the rate doesn’t differ much across these countries as seen in the table below.

 

 

 

 

Bearing in mind that pumps, motors, and other equipment operating 24 hours a day, seven days a week, water and wastewater facilities often accounting for 30-40 percent of total energy consumed in municipalities and thus among the largest contributors to the community’s total GHG emissions. Indeed, the situation is going to be worse, because it is expected to increase 20 percent in the next 15 years due to population growth. Consequently, pursuing energy efficiency at our water sector system can significantly reduce operating costs, while is mitigated the effects of climate change and it is reached a sustainable world.

 

The EPA estimates that if a 10 percent of energy use is decreased through cost-effective investments in energy efficiency, it would save about $400 million and 5 billion kWh annually in the United States. Consequently, the following question would be, how can we improve energy efficiency at utilities? What strategies can be adopted?

 

Considering the overall water use cycle, approximately 80 percent of energy consumption goes to pumping and distributing water and wastewater with the remaining for treatment. Indeed, energy usage and costs for water utilities are increasing as a result of many factors associated with regulations, treatment technology complexity, aging infrastructure, supply challenges, and growth.

 

The good news? Studies estimate potential savings of 15-30 percent that are "readily achievable" in water and wastewater plants. Indeed, many of these practices do not require expensive or extensive capital investments—simply optimizing a utility’s current equipment and operations practices can lead to significant reductions in energy consumption.

 

 

1. What kind of tools would be good to reduce the economic and environmental cost?

 

The following figure depicts each stage within the water use cycle, along with the energy opportunities to reduce the economic and environmental cost of the system. The processes of pumping and treatment are the largest consumers of energy in the water use cycle. For wastewater, where energy-intensive technologies such as mechanical aerators, blowers, and diffusers are used to keep solids suspended and to provide oxygen for biological decomposition, treatment accounts for the largest share of energy use. Facility managers can perform energy audits or install monitoring devices that feed into their Supervisory Control and Data Acquisition (SCADA) system to learn where energy is being used in their facility and identify opportunities for energy efficiency improvements.

 

Figure 1: Each stage within the water use cycle, along with the energy opportunities to reduce the economic and environmental cost of the system.

 

Sources: California Energy Commission, 2005; U.S. EPA, 2010a; U.S. EPA, 2010b; Energy Centre of Wisconsin, 2003.

 

Based upon the foregoing, opportunities for efficiency might be split up in several categories:

 

A. Optimizing system processes, such as modifying pumping and aeration operations and implementing monitoring and control systems through SCADA systems to increase the energy efficiency of equipment.

 

B. Upgrading to more efficient equipment and right-sizing equipment for the capacity of the facility (plants and pipes often are oversized, to accommodate future peak load). Pumps and other equipment used beyond their expected life operate well below optimal efficiency. In addition, energy is embedded through pipe systems, since leaking drinking water pipes require more energy to deliver water to the end user. Leaky sewer lines allow groundwater to infiltrate and increase the flow of water into the wastewater treatment plant. All water systems have losses, which are cumulative along segments of the water-use cycle.

 

C. Generation energy on-site to offset purchased electricity. Beyond efficiency measures, other option is reducing the energy costs by recovering energy from municipal waste and using the resulting biogas to generate electricity, heat the plant, and in some cases sell electricity back to the grid.

 

In brief, improvements in energy efficiency allow the same work to be done with less energy; improvements in water use efficiency reduce demand for water, which in turn reduces the amount of energy required to treat and distribute water. Capturing the energy in wastewater by burning biogas from anaerobic digesters in a combined heat and power system allows wastewater facilities to produce some or all of their own electricity and space heating, turning them into “net zero” consumers of energy.

 

It should be noted, though, that several barriers to improved energy efficiency by water and wastewater utilities are apparent. Many of them derive from the culture of water utilities and outside constraints placed on them. For example, municipalities that own and operate water utilities generally are risk-averse, reluctant to implement new technologies. The tendency is to wait until equipment fails rather than be pro-active.

 

 

2. What environmental implications do we have by reducing energy consumption? What are the benefits associated with?

 

Reducing energy consumption has a direct impact on reducing greenhouse gas emissions. This can help utilities and municipalities meet aggressive carbon reduction goals helping the environment. Investment in renewable/alternative energy can provide long-term “clean” energy for water utility operations.

 

In summary, the benefits resulting from the implementation of the tools described above are:

 

  • Reduce air pollution and GHG emissions by decreasing consumption of fossil fuel-based energy;
  • Reduce energy costs by increasing the efficiency of the pumps and aeration equipment, or well, generating their own electricity and heat from biogas;
  • Improve energy and water security. Reducing electricity demand allows to avoid the risk of brownouts or blackouts during high energy demand periods. Water efficiency strategies reduce the risk of water shortages;
  • Extend the life of infrastructure/equipment;
  • Protect public health. Reducing air and water pollution from the power plants.

 

In conclusion, building on these efforts, managing energy effectively will insure the goal of maintaining clean, safe and available water while keeping the financial and environmental cost of energy use to a minimum.

 

 

 

By Ruth García

PhD Chemical Engineer

 


Published on 2015-11-03 22:06:32

 
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