Sustainability Archive » Energy Savings

An Economic Approach to Off-Line Storage: A Means of Mitigating SSOs

justin — Fri, 20 May 2011 16:47:05 +0000

This paper reports on the use of a two cell 30-million-gallon (MG) equalization basin and diesel
engine-driven pump station as a means of mitigating sanitary sewer overflows (SSOs). The
ultimate capacity of the pump station, which utilizes vertical turbine solids handling pumps
(VTSH) arranged in a self-cleaning trench-style wet well, is 68 million gallons per day (MGD).
Configuring the pump station with diesel engine-driven pumps provided a 20-year, $1 million
present worth savings in comparison to a conventional electrical motor driven pump station
arrangement. The use of diesel engine-driven pumps eliminated the peak electrical usage of 450-
horsepower (HP) electrical motors, as well as the need for variable frequency drives and
redundant power generation needs during electrical outage time periods. A supplemental 150-
kilowatt (kW) generator was installed to provide emergency power needs for SCADA, seal water
systems, influent screen, and a 50-HP maintenance pump for wetwell cleaning.

Improving Nutrient Removal While Reducing Carbon Footprint at Three Swiss WWTPs Thanks to Advanced Control

justin — Fri, 20 May 2011 16:47:05 +0000

Aeration consumes about 60% of the total energy of a WWTP and therefore makes up for a
major part of its carbon footprint. Introducing advanced process control can help plants to reduce
their carbon footprint and at the same time improve effluent quality through making available
unused capacity for denitrification, if the ammonia concentration is below a certain set-point.
Measuring and control concepts are a cost-saving alternative to the extension of reactor volume.
However, they also involve the risk of violation of the effluent limits due to measuring errors,
unsuitable control concepts or inadequate implementation of the measuring and control system.
Dynamic simulation is a suitable tool to analyze the plant and to design tailored measuring and
control systems.
During this work, extensive data collection, modeling and full-scale implementation of aeration
control algorithms were carried out at three conventional activated sludge plants with fixed predenitrification
and nitrification reactor zones. Full-scale energy savings in the range of 16-20 %
could be achieved together with an increase of total nitrogen removal of 40%.

Optimizing Energy Harvest in Wastewater Treatment Using Hydrogen Producing Biofermentor (HPB) and Microbial Fuel Cell (MFC)

justin — Fri, 20 May 2011 16:47:05 +0000

Two clean technologies, namely, “Anaerobic hydrogen production” and “Microbial fuel cells
(MFC)”, hold great potential for producing energy from wastewater, which can provide economic
and environmental benefits. Although 1 mole of glucose can theoretically produce 12 moles of
hydrogen, the experimental hydrogen yields obtained are only 0.9-2.0 moles [1, 2]. The liquid
fermentation products in the anaerobic treated wastewater cause the high chemical oxygen demand
(COD) in the effluent. It is desired to further treat these liquid products using MFCs to improve
effluent quality and harvest energy. By converting the chemical energy stored in wastewater to
electricity, MFCs can substantially reduce the operational cost in wastewater treatment plants [3].
Due to the limitation of current technologies, the operation of hydrogen bioproduction and MFC
individually in wastewater treatment is not suitable. Although hydrogen production is a good energy
resource, the COD removal efficiency remains low. On the other hand, MFC could achieve high
COD removal efficiency, but the power densities are low. In this study, the HPB and SCMFC were,
for the first time, operated in series to increase overall energy recovery from wastewater and enhance
COD removal efficiency for potential reclamation.

MAKING ENERGY FROM BIOSOLIDS, FATS, OILS AND GREASE

justin — Fri, 20 May 2011 16:24:36 +0000

The F. Wayne Hill Water Resources Center (FWHWRC), owned and operated by the Gwinnett
County, GA, Department of Water Resources (DWR), is an advanced wastewater treatment plant
which currently discharges into the Chattahoochee River and Lake Lanier. The FWHWRC
maximum month design flow is 60 million gallons per day (mgd) and currently about 30 mgd of
wastewater is received.
In light of rising energy costs and declining revenues reflective of the continuing, severe
economic downturn that began in 2007, the Gwinnett County DWR began an initiative to make
the best possible use of resources under DWR control, including renewable energy resources.
DWR retained CH2M HILL to identify and evaluate opportunities to improve resource
utilization and reduce energy costs at the FWHWRC. The results of the evaluations, procedures
for capturing stimulus funding, and technologies employed are discussed in this paper.
The energy types considered for the FWHWRC were biogas derived from anaerobic digestion,
solar, wind, and low-head hydropower. A screening analysis concluded that biogas combustion
to produce power and heat was the optimum alternative.
Next, a Business Case Evaluation (BCE) was conducted to determine if the construction and
operation of a gas-to-energy facility would be economically feasible. The BCE considered
several different scenarios for generating power from biogas, including biogas production with
and without addition of fats, oil & grease (FOG) and high strength waste (HSW) to the existing,
anaerobic sludge digesters.
The BCE concluded that a gas to energy facility based on an internal combustion engine (ICE)
was feasible. The proposed system, in addition to continuously generating electrical energy for
use at the FWHWRC, would be capable of producing sufficient heat to keep the anaerobic
digesters operating in the mesophilic temperature range of 95-100 degrees Fahrenheit (F). By
capturing the heat produced by the ICE, in addition to generating power, the system would have
a total energy-recovery efficiency approaching 80%.
The BCE recommended a gas to energy facility of approximately 2 megawatts (MW) in capacity
at the FWHWRC. The biogas requirement at a nominal 600 British Thermal Units (BTU) per
cubic foot (ft3) for an ICE of this capacity is approximately 520 standard cubic feet per minute
(scfm). However, as the FWHWRC is at only about 50% of its total design capacity, the
currently available biogas is considerably less than 520 scfm, and a purchased natural gas fuel
blend would be required to obtain full power generation and heat recovery benefits. To minimize purchase of natural gas, maximize biogas, and as a result improve the return on
investment in the cogeneration system, DWR next investigated addition of FOG and high
strength waste (HSW) to the anaerobic digesters to supplement the solids feed. The project was
made even more attractive by DWR’s successful pursuit of funding under the American
Recovery and Reinvestment Act (ARRA), as administered by the Georgia Environmental
Facility Administration (GEFA), and from the U.S. Department of Energy (DOE).
A schematic design of the system with specifications was prepared for competitive selection of a
design-build contractor. The design-build contract was awarded in October 2009. The contract
value is $5.19 million and includes the installation of a 2.1 MW engine generator along with
digester gas cleaning and drying equipment. The gas-to-energy facility is expected to reach
substantial completion by the end of 2010 with contractual completion in May 2011.
A second RFP for the design and construction of a FOG and HSW receiving facility was
advertised in February 2010. The design-build contract was awarded in June 2010 at a contract
value of $3.16 million. Its completion and startup will closely follow the completion and startup
of gas cogeneration facilities.
Once operational, the FOG/HSW handling and cogeneration facilities will have the potential to
save over one million dollars annually in power costs and generate more revenue in FOG and
HSW disposal fees. When operating at its rated capacity, the resulting power production will
offset the amount of fossil fuel used to generate over 17,000 MW-hours of electrical power
annually.

Energy Efficient Advanced Treatment Process for Microconstituents Removal

justin — Fri, 20 May 2011 16:24:35 +0000

The objective of this study was to demonstrate the effectiveness of an advanced treatment
process not utilizing reverse osmosis (RO) for removal of hormones, pharmaceuticals, and flame
retardants (collectively termed microconstituents or chemicals of emerging concern [CECs])
from municipal effluent. The advanced treatment process consisted of (in the order of use):
membrane filtration (MF), ozonation (O3), and biological activated carbon (BAC). The 15-
month, continuous flow, 10.7 gpm, MF-O3-BAC demonstration study was conducted in two
phases at the Reno-Stead Water Reclamation Facility (RSWRF): Phase 1 focused on ozone
process optimization and bromate mitigation; Phase 2 was a 10-month steady-state
demonstration of process performance. For RSWRF effluent, an ozone dosage of at least 5 mg/L
was needed for desired CEC removals. Peroxide (year-round) and ammonia (seasonal) were
added to mitigate bromate formation during ozonation. BAC removed flame retardants, and
ozonation byproducts including NDMA (N-Nitrosodimethylamine), aldehydes, and
biodegradable organic carbon. Findings of this study imply that MF-O3-BAC treatment is
equally effective as RO-based treatment for CEC removals, but with substantially less energy
utilization.

Energy Efficiency in Wastewater Treatment In North America: A WERF Compendium of Best Practices and Case Studies of Novel Approaches

justin — Fri, 20 May 2011 16:24:35 +0000

After manpower, energy is the highest operating cost item for most water and wastewater companies.
Over the last decade, energy consumption by the sector has considerably increased as a result of
implementation of new technologies to meet new effluent and potable water quality standards. High
energy consumption will affect the water industry worldwide and is inextricably linked to the issue of
Climate Change. Through its Optimization Challenge program, the Water Environment Research
Foundation (WERF) participated in the Global Water Research Coalition’s (GWRC) project titled Energy
Efficiency in the Water Industry: A Compendium of Best Practices and Case Studies. For this project,
WERF served the role of North America practice coordinator, developing a Compendium of best
practices in the energy efficient design and operation of water industry assets for this region of the world.

Getting to Zero: Sustainability Best practices to Significantly Reduce Greenhouse Gas and Energy at Your Wastewater Facility

justin — Fri, 20 May 2011 16:24:34 +0000

Public agencies are increasingly pressured to become more sustainable. Wastewater plants are
significant consumers of energy and correspondingly produce significant quantities of
greenhouse gas (GHG). Reductions in energy and GHG are challenges for wastewater facilities
as flows and loads increase and discharge requirements become more restrictive. The results
highlight some methods to reduce energy and GHG, including the concept of becoming energy
neutral. Energy (as represented by electrical energy or fuels) equate directly to GHG production.
A significant portion of the fuel source for most utilities in the United States is from
anthropogenic sources such as coal, oil, or electric. To achieve energy neutral facilities, the
wastewater plant must implement energy conservation and shift to biogenically derived energy
sources, such as biogas, or alternative energy sources, such as wind. This paper and presentation
describe how wastewater treatment plants can significantly reduce energy to the point of
becoming energy neutral.

Energy Conservation Measures for Municipal Wastewater Treatment – Innovative Technologies and Practices

justin — Fri, 20 May 2011 16:24:34 +0000

Energy consumption for municipal wastewater treatment accounts for 15% to 30% of the
operating cost at large treatment facilities and 30% to 40% at small facilities (WEF, 2009).
Energy costs are expected to continue escalating as a result of the rising price of fossil fuels used
for energy production while the energy demand for wastewater treatment is expected to grow as
the use of energy intensive treatment processes increases to meet water quality objectives that
may demand increasingly stringent wastewater discharge limits.
The United States Environmental Protection Agency (EPA) is committed to promoting energy
efficiency and implementation/use of energy conservation measures at municipal wastewater
treatment facilities. EPA, in partnership with The Cadmus Group and HDR, has undertaken a
project to identify and evaluate innovative energy conservation methods implemented at
wastewater utilities in the U.S. and report on their effectiveness in achieving reductions in energy
use and cost associated with wastewater treatment.

Employing Energy Management Planning to Achieve Net Zero Energy in Wastewater Operations

justin — Fri, 20 May 2011 16:24:34 +0000

This paper outlines how energy management planning can accomplish dual goals of
energy self-sufficiency and optimum treatment processing, and how this provides robust
performance and acceptable payback on investment, leading to net zero energy
wastewater operations. The energy content of wastewater surpasses the energy required
by treatment, reportedly be a factor of up to 10 times. Nevertheless, conventional
activated sludge plants with advanced treatment consume typically 1,800 kWh/MG of
electricity, but facilities vary from 1,000 to 3,000 kWh/MG. Energy efficiency studies
conclude that the potential for energy use reductions through efficient pumps and aerators
are on the order of 30 to 50 percent, which is a range of about 400 to 700 kWh/MG. For
plants with anaerobic digestion, a rule-of-thumb for electrical production from biogasfueled
generators is 500 kWh/MG. Supplementation of anaerobic digesters with high
strength organic waste and fats, oils and grease is possible where utilities have excess
digester capacity. The experience with supplementation is that facilities have increased
biogas by a factor of two or three times pre-existing conditions, and are able to have a
corresponding increases in electricity production, where generators have been adequately
sized. When thermal heat can be returned for plant processes, overall plant efficiencies
rise even higher. Energy planning studies have also shown that innovative technologies
that build upon anaerobic processes reduce energy usage from typical values, and,
further, energy plans have demonstrated some unexpected results, such as the economic
and environmental justification of anaerobic digestion combined with thermal processing,
such as dryers and incinerators. While local conditions, particularly energy pricing and
government subsidies, likely shape the specific planning objectives and outcomes of any
individual plant, the variety of energy efficiency and production technologies that are
becoming proven can result in a similar endpoint, and specifically net zero energy
wastewater treatment.

CHEApet: A Comprehensive Energy Analysis Tool for WWTPs

justin — Fri, 20 May 2011 16:24:34 +0000

The development of the Carbon Heat Energy Analysis Plant Evaluation Tool (CHEApet) by
the Water Environment Research Federation (WERF) was in response to the identified need
for a predictive modeling tool that unifies prior WERF research information regarding
quantifying and managing energy consumption. CHEApet was created under OWSO4R07C
of WERF’s Optimization Challenge to model performance and energy consumption of waste
water treatment plants (WWTPs). Energy consumption, along with treatment process
emissions, contributes to a facility’s carbon footprint. CHEApet can be used to create a
baseline scenario, or inventory, of a utility’s carbon footprint for informational purposes as
well as to compare with hypothetical treatment plants. This kind of comparison allows the
user to identify facilities in the utility for energy optimization and the potential for biogas
recovery which can save in costs and improve the footprint of the facility.