Sustainability Archive » Environmental Impact

Selection of a Solids Management Plan to Meet a Sewerage District’s Vision of Becoming a Leader in Sustainability

justin — Fri, 20 May 2011 16:47:34 +0000

The Green Bay Metropolitan Sewerage District (GBMSD) is a public utility, established in 1931,
that reclaims 38 million gallons of wastewater per day at two treatment facilities in Green Bay
and De Pere, WI. Its service area covers 285 square miles and serves more than 219,000 people.
GBMSD’s mission is to promote public health and welfare through the collection, treatment, and
reclamation of wastewater, while assessing stable, competitive rates. In conjunction with others,
the organization will encourage pollution prevention and support programs to help ensure that
water contaminated by human activity is returned clean to the environment. GBMSD conducts
its business using a sustainable approach within the social, environmental, and economical
values of our customers and stakeholders.
GBMSD initiated the development of a Solids Management Plan in 2008 to address aging solids
handling facilities and the solids loadings from recently acquired De Pere Facility. The existing
solids processing system consists of belt press dewatering followed by multiple hearth
incineration. The solids system is located at the Green Bay Facility. Solids from the De Pere
Facility are transferred by pipeline to the Green Bay Facility for processing. The solids system
was constructed in the 1970s and is reaching the end of its useful life. The multiple hearth
incineration process is now considered an outdated technology. Current incineration technology
uses fluidized beds, which consume less fuel and lower air emissions.
The solids management planning effort was undertaken to develop a long-term plan for handling,
processing, and disposing of solids. The plan included a comprehensive evaluation of numerous
solids management technologies and approaches. This paper describes the process used to
develop the plan, the alternatives that were considered, the alternatives evaluation process, and
the preferred solids management alternative.

SPOTSYLVANIA COUNTY’S EXPANDED COMPOSTING FACILITY APPLIES AERATED STATIC PILE TECHNOLOGY ADVANCES

justin — Fri, 20 May 2011 16:47:06 +0000

Spotsylvania County embarked up an aerated static pile composting program in 2002 to manage
undigested dewatered wastewater treatment plant (WWTP) residuals cake from their
Massaponax WWTP in conjunction with brush collected through a convenience center and at the
Livingston Landfill. The initial compost facility included a covered aerated static pile process
that provided intermittent positive aeration only. The quantity of dewatered residuals being
composted has increased from approximately 8,800 tons per year in 2003 to in excess of 12,600
tons per year in 2009. Even with this rapid increase in quantities, all regulatory process criteria
have been met and offsite odor impacts have been non-existent. Howeverer, residuals cake
continued to be landfilled from a second WWTP, the FMC plant, in the amount of 5,000 – 6,000
tons per year. The County embarked upon a compost facility expansion program in 2006 with
three main goals.
1. To manage the ever increasing quantities of residuals cake generated from both County
WWTP’s over the next 20 years.
2. To enhance and automate the compost process performance.
3. To accomplish this expansion with no offsite odor impacts.

Construction of the new facilities was completed in March, 2010. This paper presents data on the
process flow, process controls, and the odor management system of this successfully expanded
aerated static pile composting operation.

Integrated Approach to Biosolids Management for a Utility with Multiple Small Facilities

justin — Fri, 20 May 2011 16:47:06 +0000

To assure that Polk County Utilities (PCU) is ready for coming changes in regulations and ever
increasing solids production from ten treatment facilities geographically dispersed throughout the
County, the County wanted to develop a proactive long term biosolids management plan that
integrated residuals management approaches among the various treatment plants. Geographical
dispersion and capacity diversity combined with a desire for an integrated long-term
management plan gave rise to a number of possible alternatives to be included in the evaluation.
The landfill disposal alternative investigated met PCU’s objectives which were to identify a cost
effective method for managing current and future biosolids generated at PCU’s facilities that
would represent a viable plan for the next twenty years. An agreement developed between PCU
and Polk County’s Solid Waste Division to mutually address disposal of leachate and biosolids
resulted in significant cost savings for both these County agencies.

EPA’s Response to the Current Status of CSO Control Efforts Development of New Tools and Guidance

justin — Fri, 20 May 2011 16:47:06 +0000

EPA’s combined sewer overflow (CSO) program has reached a mature stage. Some communities
have completed their CSO controls, while others are in the process of constructing controls or
evaluating potential alternatives. With the recent emphasis on green infrastructure, some
communities are evaluating the role of natural systems and ecological processes in Long Term
Control Plans (LTCPs) for controlling CSOs. The convergence of these critical milestones and
issues for the national CSO program highlights the need for updated tools and guidance to
facilitate future CSO control efforts. In response, EPA is developing guidance on post
construction compliance monitoring for CSOs, as well as the Green LTCP-EZ, a tool that allows
small CSO communities to incorporate green infrastructure as part of their LTCP efforts. This
paper discusses these initiatives serves as outreach to CSO communities on these efforts.

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.

GREASE CO-DIGESTION AT DALLAS WATER UTILITIES SHOWS MAJOR ECONOMIC BENEFITS

justin — Fri, 20 May 2011 16:47:04 +0000

Dallas Water Utilities (DWU) has identified multiple projects within their wastewater treatment
plants (WWTPs) to support the Green Dallas Initiative for energy conservation and
sustainability. In 2010, a new co-generation facility at the Southside Wastewater Treatment Plant
(SWWTP) will be brought on-line. This facility will utilize digester gas for electricity
production. As part of the Green Dallas Initiative, and to optimize the co-generation facility, the
feasibility of adding high strength wastes to the anaerobic digesters at SWWTP to increase the
digester gas production was evaluated.

Co-digestion at Annacis Island WWTP: Metro Vancouver’s Path to Renewable Energy and Greenhouse Gas Emissions Reductions

justin — Fri, 20 May 2011 16:47:03 +0000

Annacis Island Wastewater Treatment Plant which is operated by Metro Vancouver, is leading
the way in working within a carbon based regulatory environment. British Columbia has
instituted carbon reduction legislation province wide, a leader in North America. As a result
public entities, such as Metro Vancouver, must be carbon neutral by 2012. In response the utility
is holistically investigating different approaches to achieve the required GHG reductions. One
approach now being actively pursued is the implementation of co-digestion at Annacis Island.
Having developed a the scope for a full co-digestion program at the plant, a pilot facility was
constructed to provide further process controls as well as a start at reducing emissions by codigesting
material at the plant. This project also provided Metro Vancouver a basis of handling
its own sludges from other wastewater treatment plants on an emergency or planned basis by
dual tasking the receiving facility to receive both sludges and co-digestion substrates.

Anaerobic Co-Digestion for Increased Renewable Energy

justin — Fri, 20 May 2011 16:24:37 +0000

Significant opportunities exist to increase renewable energy production using existing municipal
anaerobic digesters. Many wastes can be added to co-digest more carbon and produce more
methane. The objectives of this study were to identify and compare potential co-digestates,
determine synergistic, antagonistic and neutral co-digestion outcomes, quantify performance of
co-digestion for selected wastes and estimate economic benefits. Over 80 wastes were identified
from 54 facilities within 160 km of an existing municipal digester. The most promising wastes
(26 wastes) were characterized by biochemical methane potential (BMP) and other testing. A
simple economic comparison identified the greatest benefits for seven co-digestates.
Performance was investigated using bench-scale digesters receiving synthetic primary sludge
with and without co-digestates. Methane production rates in co-digesters were as much as 180%
greater than anticipated from the additional chemical oxygen demand (COD). Therefore,
significant synergism was observed. The VS destruction efficiencies were 49 and 33% higher
when co-digestates were present. Co-digestion is one method to increase renewable energy
production via anaerobic digestion.

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.