Shaw A.,Black and Veatch Corporation |
Shaw A.,Illinois Institute of Technology |
Takacs I.,Dynamita |
Pagilla K.R.,Illinois Institute of Technology |
Murthy S.,DC Water
Water Research | Year: 2013
The Monod equation is often used to describe biological treatment processes and is the foundation for many activated sludge models. The Monod equation includes a "half-saturation coefficient" to describe the effect of substrate limitations on the process rate and it is customary to consider this parameter to be a constant for a given system. The purpose of this study was to develop a methodology, and its use to show that the half-saturation coefficient for denitrification is not constant but is in fact a function of the maximum denitrification rate. A 4-step procedure is developed to investigate the dependency of half-saturation coefficients on the maximum rate and two different models are used to describe this dependency: (a) an empirical linear model and (b) a deterministic model based on Fick's law of diffusion. Both models are proved better for describing denitrification kinetics than assuming a fixed KNO3 at low nitrate concentrations. The empirical model is more utilitarian whereas the model based on Fick's law has a fundamental basis that enables the intrinsic KNO3 to be estimated. In this study data was analyzed from 56 denitrification rate tests and it was found that the extant KNO3 varied between 0.07mgN/L and 1.47mgN/L (5th and 95th percentile respectively) with an average of 0.47mgN/L. In contrast to this, the intrinsic KNO3 estimated for the diffusion model was 0.01mgN/L which indicates that the extant KNO3 is greatly influenced by, and mostly describes, diffusion limitations. © 2013 Elsevier Ltd.
Aynur S.K.,George Washington University |
Riffat R.,George Washington University |
Murthy S.,DC Water
Water Environment Research | Year: 2014
The objective of this research was to understand the influence of oxygenation at two different oxygen flow rates (0.105 and 0.210 L/L/h) on autothermal thermophilic aerobic digestion (ATAD), and on the overall performance of Dual Digestion (DD). Profile experiments on an ATAD reactor showed that a significant portion of volatile fatty acids and ammonia were produced in the first 12 h period, and both followed first order kinetics. Ammonia concentrations of ATAD effluent were 1015 mg/L and 1450 mg/L, respectively, at the two oxygenation rates. Ammonia production was not complete in the ATAD reactor at the lower oxygenation rate. However, it was sufficient to maximize volatile solids reduction in the DD process. The biological heat of oxidations were 14,300 J/g Volatile Solids (VS) removed and 15,900 J/g VS removed for the two oxygen flow rates, respectively. The ATAD step provided enhanced digestion for the DD process with higher volatile solids removal and methane yield when compared to conventional digestion.
Jolly E.,DC Water |
Atoulikian R.,MWH Americas Inc.
Strategic Planning for Energy and the Environment | Year: 2012
The operating pressures faced by today's utilities include an increased focus on fiscal responsibility and cost reductions, combined with a higher and ever-increasing level of environmental quality standards. This puts a brighter spotlight and greater pressure on improving operational efficiency and optimizing the performance and operation of their facilities, which not only saves energy but makes them more environmentally sustainable. An energy audit is a process typically used to evaluate a system for such efficiency and the associated energy savings. Energy audits also provide the factual basis needed to support the establishment of a culture that focuses on energy efficiency as a core part of its decision-making model.When energy audits are performed for water and wastewater utilities, not only can electrical energy savings be achieved, but savings in other areas such as process chemical use or parasitic water losses may also realized. The energy audit and savings plan conducted for DC Water at their Blue Plains Advanced Wastewater Treatment Plant and associated water, wastewater, and stormwater pumping stations provides a case study on how these audits should be conducted for maximum effectiveness and identification of a path forward toward realizing energy savings and carbon footprint reductions. Specific focus areas include:1. Evaluation of treatment process configuration and operation, followed by an analysis of modifications or capital additions that can be made to reduce energy consumption. This also includes an analysis of building envelopes, HVAC systems, lighting, general rotating equipment, and electrical distribution systems.2. A review of current energy use, patterns of use, and opportunities to conserve, including development of an energy baseline and benchmarking.3. Alternative energy evaluation covering the areas of biosolids, solar, wind, and small hydro, including both on-site production and procurement from third parties.Development of an implementable, prioritized energy management plan is critical. This includes identifying "quick wins" or low- to no-cost measures that can be implemented in the short term with little initial capital investment, resulting in an almost immediate decrease in energy consumption. The process continues with the identification of opportunities that are more capital intensive (but still have reasonable payback periods) and are more time consuming to implement. In addition, a successful program must go beyond implementation of audit results and include monitoring and verification, as well as continuous improvement practices. When conducted properly, our experience demonstrates that the payback period on these audits is such that the cost of the audit alone can be recovered in less than two years by implementing certain recommendations. The actual payback period on the recommended opportunities is also very short.Finally, the technical side of an energy management plan is only half of the equation. The other half is the culture change required at all levels in the organization to implement the results of the plan, both initially, and more importantly, in a sustainable fashion. Organizational change management starts with a compelling vision from the top of the organization, with an understanding of the significance and potential benefits of the change at all levels. Regular communication is essential, once the vision is set. A process for feedback from the organization and demonstrating that the organization is engaging input from its employees is also important.This article examines the benefits of energy savings for one of the nation's largest water utilities at the forefront of sustainable practices, DC Water. Included will be a brief overview of why DC Water has chosen to implement an energy and carbon reduction program, how and what has been done, and how the data will be used to implement energy reduction programs in the future, from both technical and cultural perspectives.
Maher C.,Illinois Institute of Technology |
Neethling J.B.,HDR |
Murthy S.,DC Water |
Pagilla K.,Illinois Institute of Technology
Water Research | Year: 2015
The role of adsorption and/or complexation in removal of reactive or unreactive effluent phosphorus by already formed chemical precipitates or complexes has been investigated. Potential operational efficiency gains resulting from age of chemically precipitated tertiary alum sludge and the recycle of sludge to the process stream was undertaken at the Iowa Hill Water Reclamation Facility which employs the DensaDeg® process (IDI, Richmond, VA) for tertiary chemical P removal to achieve a filtered final effluent total phosphorus concentration of <30 μg/L. The effect of sludge solids age was found to be insignificant over the solids retention time (SRT) of 2-8 days, indicating that the solids were unaffected by the aging effects of decreasing porosity and surface acidity. The bulk of solids inventory was retained in the clarifier blanket, providing no advantage in P removal from increased solids inventory at higher SRTs. When solids recycle was redirected from the traditional location of the flocculation reactor to a point just prior to chemical addition in the chemical mixing reactor, lower effluent soluble P concentrations at lower molar doses of aluminum were achieved.At laboratory scale, the "spent" or "waste" chemical alum sludge from P removal showed high capacity and rapid kinetics for P sorption from real wastewater effluents. Saturation concentrations were in the range of 8-29 mg soluble reactive P/g solids. Higher saturation concentrations were found at higher temperatures. Alum sludge produced without a coagulant aid polymer had a much higher capacity for P sorption than polymer containing alum sludge. The adsorption reaction reached equilibrium in less than 10 min with 50% or greater removal within the first minute. © 2015 Elsevier Ltd.
"They make green energy," said engineer Chris Peot of Washington's toilet-goers during a tour of the sprawling space in the southeast of the city. DC Water's Blue Plains plant treats 370 million gallons (1,400 million liters) of dirty water from more than two million households on a daily basis, purging it with micro-organisms that first ingest carbon and then transform nitrates into nitrogen gas. Once that's done, the water is clean enough to flow into the nearby Potomac River or Chesapeake Bay without disrupting the fragile ecosystems. As for the excrement, it is either recycled as compost or, in a new step implemented six months ago, used to produce 10 megawatts of electricity. The "poop power" generated is theoretically enough to supply some 8,000 households, although in practice the energy is ploughed straight back into powering the plant. To do so, plant workers collect the solid matter that slips to the bottom of the treatment pools and subject it to a Norwegian hydrolysis technique that is being used in North America for the first time. According to Peot, DC Water's director of resource recovery, the process allows the plant to extract organic material and convert it to methane. When burned, the methane generate power that is used to help run the plant. "This project embodies a shift from treating used water as waste to leveraging it as a resource," said DC Water's chief executive, George Hawkins, as he inaugurated the new $470 million facility on October 5, financed by water bills. The methane is produced through the decomposition of organic waste by bacteria in huge vats that stand 80 feet (25 meters) tall, with each capable of "digesting" 3.8 million gallons of solid matter. The biogas is then used to operate three turbines, each the size of a jet engine, to produce 13 megawatts of electricity, three of which are immediately used for the hydrolysis. The 10 remaining megawatts are used by the water treatment plant—the biggest energy consumer in Washington—reducing its carbon footprint by a third and cutting operating costs by millions of dollars a year, according to Peot. "It saves us money, avoids us having to buy power off the grid, which largely comes from coal," he said. According to Todd Foley, chief strategy officer at the American Council on Renewable Energy, it's a "way to diversify the energy mix and control our energy costs." "There will be an increased role for that kind of activity," he predicted. Wind, solar and biomass combined accounted for just six percent of the world's electricity supply in 2014, according to the International Energy Agency (IEA)—against 41 percent for coal, 22 percent for gas, 17 percent for hydro-power, 11 percent for nuclear and four percent for oil. Biogas derived from human waste provides hope for poor countries as an energy source capable of producing power for 138 million households worldwide, according to a United Nations report published in November. The process could improve hygiene in poorer countries, where a lack of sanitation accounts for 10 percent of illnesses. It can also produce valuable fertilizer for agriculture. The Washington facility produces 1,200 tons of biosolids a day—recycled organic matter used as compost in community gardens, for example. "It is making use of an asset that we have here at the plant," Peot said. "For years, we would give it away to farmers for free as fertilizer." In the short term, there are plans to operate a fourth turbine and generate an additional five megawatts of power. And further down the road, Peot hopes the plant could become fully self-sufficient—as is the case of a similar operation in Gresham, Oregon—or even produce enough power to sell to Washington residents.