By Katya Bilyk, Senior Principal Engineer Joe Rohrbacher, Senior Principal EngineerTheresa Bruton, Principal Engineer

Water Environment Solutions

Winter 2012

InsidePage 2

Page 4

Page 8

Page 10

Nitrosamines: Understand Your Risk

Wastewater as Energy Resource: F. Wayne Hill WRC

Extreme Weather Impacts on the Water Sector

Rooftop Stormwater Management Systems

oing More with LessD

Two recent projects funded through the American Reinvestment and Recovery Act have dramatically cut operating costs at the F. Wayne Hill Water Resources Center.

2

N�itrosamines are an emerging class of drinking water

contaminants of potential concern to many utilities,

particularly those employing or considering chloramines

for residual disinfection. Hazen and Sawyer is currently

examining low-cost strategies that target the chemistry of

nitrosamine formation as means of mitigating risk.

Typically associated with the chlorination of wastewaters or the chloramination of surface waters under the influence of wastewater, nitrosamines can be formed as a disinfection byproduct or sometimes found as an industrial degradation product in groundwater source wells. As carcinogens, nitrosamines are associated with a 1 in 1,000,000 lifetime drinking water cancer risk from levels ranging between 0.2 and 20 ng/L. However, it is not clear even that drinking water is a major exposure route for humans, as most human

exposure to nitrosamines actually comes from processed food and beverage items, including meats (e.g., hot dogs, salami, bacon, sausages) and beer, where it is present at much higher concentrations than those typically found in drinking water.

Regulatory StatusWhile no federal maximum contaminant level has been

established to date, there have been regulatory rumblings within the USEPA regarding nitrosamines, which have been identified for potential near-term regulatory development within the new “group regulation” strategy focus of the Safe Drinking Water Act. Currently, only two states, California and Massachusetts, have set notification or guidance levels for NDMA, each at 0.01 mg/L. Recently, five nitrosamines were included on the USEPA’s Criteria Contaminant List 2 and

Nitrosamines: Understand Your RiskBy Erik Rosenfeldt, Ph.D., P.E.

SD

Highest rate34.5%

NJ

MDDE

CTRI

MA

TX

OK

LA

ARNM

AZ

MSAL GA

FL

SC

NCTN

KY VAWV

OHINIL

MOKS

COUT

NVNE IA

WI

MI

MN

WY NY

MEVT

NH

PA

NDMT

ID

OR

WA

NDMA Occurence Rate by State

AK

HI

Under 5%

5-9.9%

10-14.9%

15-19.9%

20%+

NDMA Occurrence rate of collected samples

10.3%

Samplescollected1,375

Samplescollected4,188 11%

CA

Samplescollected1,479

1.4%

Less than 50 samplestaken within state

Source: US Environmental Protection Agency,Unregulated Contaminant Monitoring Rule 2 Occurrence Database as of April 11, 2010http://water.epa.gov/lawsregs/rulesregs/sdwa/ucmr/data.cfm

National AverageOccurrence Rate

NDMA Occurrence Rate By State

Horizons Winter 2012 3

many drinking water utilities were required to collect finished water samples for nitrosamines analysis as part of the second Unregulated Contaminant Monitoring Rule (UCMR2), which has yielded an extensive nitrosamine occurrence dataset.

A recent examination of the UCMR2 data revealed several interesting findings. First, one nitrosamine, N-Nitrosodimethylamine (NDMA), accounted for 94.5% of all detected nitrosamine occurrences and is likely the nitrosamine of concern for most utilities. A state-by-state summary of NDMA occurrence rates is shown in the figure at left, and reveals that NDMA occurrence rates are generally highest in the Central states. The UCMR2 data also indicate that NDMA is more prevalent in systems utilizing chloramines than in those relying only on free chlorine for residual disinfection, with a 34.4% occurrence rate in chloraminated systems, compared to only 2.7% in systems utilizing chlorine only. This presents a potentially difficult situation for many utilities struggling to comply with the Stage 2 Disinfectant/Disinfection Byproduct Rule, as the use of chloramines is a viable and proven technique for limiting levels of currently regulated DBPs.

Limiting Your RiskThe good news is that techniques are currently being

researched for dealing with potential risks associated with nitrosamines. Potential “best available technologies” identified by the USEPA for reducing formation of nitrosamines include modifying the disinfection process by adding oxidants (e.g., free chlorine, ozone, or others) prior to chloramine application, managing polymer addition, using TTHM/THAA

precursor removal treatment in lieu of chloramines, and considering source water protection.

Hazen and Sawyer’s Applied Research group is currently examining a nitrosamine-mitigation approach that targets nitrosamine formation chemistry. The generally-accepted chemical mechanism of NDMA formation identifies dichloramine and nitrogen-containing organic compounds as NDMA precursors. This mechanism helps explain many of the general observations surrounding NDMA formation in drinking water, particularly elevated levels found in finished waters from sources impacted by wastewater, and elevated levels in finished waters treated under conditions that favor dichloramine formation (e.g., high Cl2:N ratios). Targeting this formation mechanism, we are using modeling techniques to evaluate and optimize control of the ammonification process to minimize formation of dichloramine. This approach is informing our chloramines design strategies, and may prove to be invaluable for clients facing a potential regulatory catch 22: trying to best comply with current EPA DBP regulations, while at the same time concerned about the risk of nitrosamines to their customers.

See related linkswww.hazenandsawyer.com

æ Nitrosamines: Economics of the Unknown

æ Hydraulic Models Shed Light on Water Age

@

May 25, 2011

June 6, 2011

No Dedicated Mixing

Static Mixing

0

peak nitrosamine formation

10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0

Detail

A

BAmmonia injection point

Comparison of Mixing Alternatives to Reduce Nitrosamine Formation Computational Fluid Dynamics (CFD) modeling evaluations of a closed conduit pipe system

4

T�he Gwinnett County (GA) Department of Water

Resources, recognizing the energy resource that

wastewater represents, recently completed construction of

Gas-to-Energy and Fats, Oils, and Grease/High-Strength

Waste Receiving Facilities that will reduce energy costs as

much as 40% at the F. Wayne Hill Water Resources Center.

The F. Wayne Hill Water Resources Center (FWHWRC) is a highly-advanced wastewater treatment facility located in Gwinnett County, Georgia, with a design capacity of 60 million gallons per day. The treatment facility includes both primary and secondary treatment unit processes that generate residuals that are anaerobically digested and dewatered. Additional liquid train treatment processes include advanced membrane filtration facilities that produce a very high-quality effluent, which is returned to Lake Sydney Lanier, a major recreational and water supply source for Metro Atlanta.

Optimizing for Energy RecoveryLong committed to sustainability, Gwinnett County

explored the economic feasibility of utilizing digester gas in a combined heat and power (CHP) system as a means of decreasing operational costs. A CHP system captures the energy potential in the digester gas and converts it to both electrical power and thermal energy. The electrical power offsets current usage at the facility; thermal energy is utilized to heat the digesters.

After securing $5M in funding through the American Recovery and Reinvestment Act (ARRA), Gwinnett County competitively bid and selected the design/build team of Hazen and Sawyer and Crowder Construction Company to design and construct the CHP system.

The engine-generator is sized to operate in a “peak cycling” mode (operating the generator during peak electricity rate periods) or continuously on a blend of digester gas and natural gas to provide more constant

Wastewater as Energy Resource: The F. Wayne Hill Water Resources CenterBy Scott Hardy, P.E.

The FOG/HSW facility injects waste rich in readily-digestible volatile solids directly into the existing egg-shaped anaerobic digesters, increasing gas production.

Continued on page 6

Horizons Winter 2012 5

Contours of Velocity Magnitude (ft/s)

Before: Without Canopy Baffle

FWHWRC’s primary clarifiers historically experienced TSS removal efficiencies in the 10 to 20 percent range. Hazen and Sawyer evaluated the performance and capabilities of the primary clarifiers to remove solids and increase primary sludge loading to the anaerobic digesters to boost digester gas production. Hazen and Sawyer modeled the primary clarifiers using computation fluid dynamics

(CFD), which revealed scouring of the sludge hopper greatly hindering percent removal performance.

To remedy this, Hazen and Sawyer assisted plant operations with optimization of the clarifier’s pumping rates, influent flow distribution, and general standard operating procedures, which increased primary sludge production more than 200 percent and

subsequent digester gas production by more than 50%.

In addition, Hazen and Sawyer designed a low-cost, horizontal canopy baffle that plant staff installed in one of the clarifiers. Side-by-side field testing revealed a 20 percent increase in removal efficiency in the clarifier with the baffle plate as opposed to adjacent clarifiers with no modifications.

May 25, 2011

June 6, 2011

No Mixing

Inline Mixing

Modeled Chloramine Mixing Alternative to Reduce Nitrosamine FormationComputational fluid dynamics (CFD) evaluations of a closed conduit pipe system

Mass ratio of HOCL to NH4

0

peak nitrosamine formation

10.09.08.07.06.05.04.03.02.01.0

Detail

Detail

After: With Canopy Baffle

Canopy baffle prevents scouring

Influent scouring hopper, re-suspending sludge

Primary Clarifier Optimization Increases Digester Gas Production

100% TSS Removal

0

-100

-200

-300

July 52009 2010

Aug. 4 Sept. 3 Oct. 3 Nov. 2 Dec. 2 Jan. 1 Jan. 31 Mar. 2

Changes in operating procedures and a low-cost physical modification improved both clarifier performance and digester gas production

6

electrical and heat generation. In either operating condition, the engine and exhaust heat recovery systems are tied into the digester hot-water loop to transfer heat to the existing anaerobic digesters. Since the engine generator started operation in August 2011, Gwinnett County realized a savings of over $1,000 per day and used the engine to offset real-time peak power costs as high as $0.75/kWh. Recovered heat more than meets the demand of the digester process.

To more fully utilize the CHP system, Gwinnett County selected the design/build team of Hazen and Sawyer and Crowder Construction Company to design and construct a Fats, Oils, and Grease (FOG) and High Strength Waste (HSW) Receiving Station. The FOG/HSW facility will inject waste streams rich in readily-digestible volatile solids directly into the anaerobic digesters, increasing gas production.

The receiving facility consists of transfer pumping, storage tanks, heating systems, and conveyance facilities.

The FOG/HSW project was funded by a $3.5 million U.S. Department of Energy grant through the ARRA. The construction of the receiving facility is complete and Gwinnett County is currently evaluating potential FOG and HSW suppliers.

Design of the receiving station was a collaborative effort with plant staff to maximize the system’s storage capacity and flexibility. Existing facilities were repurposed to the extent possible to reduce construction costs. For example, several hose pumps are reused from the existing treatment facility to provide unloading and digester feed capabilities.

The receiving facility is designed with a hot water washdown system utilizing an in-line hot water heater tank. Other features include a grinder with integral rock trap, glass-lined ductile iron piping, duty and standby piping to the anaerobic digesters, ability to heat the FOG/HSW facilities to 43oC (110oF) in one day using recovered heat from the CHP system, and a bioscrubber system for controlling odors.

The $5-million Gas-to-Energy and $3.5-million FOG/HSW projects are funded through the American Reinvestment and Recovery Act.

Horizons Winter 2012 7

Maximizing Return on InvestmentIn an effort to maximize return on investment,

Gwinnett County and Hazen and Sawyer teamed with Dr. Spyros Pavlostathis, a professor at Georgia Institute of Technology, to characterize and evaluate the digester gas production capacity of potential external FOG/HSW streams through bench-scale digestibility studies.

The studies identified volatile solids destruction, dewaterability, and supernatant nutrient concentrations of food processing dissolved air floatation (DAF) skimmings, poultry processing DAF skimmings, restaurant grease trap waste, and chewing gum waste, to quantify the potential increase in digester gas production per unit volume of digester space taken. The studies also identified any negative impacts of accepting the waste stream, such as toxicity to digesters, nutrient loadings in recycle streams, and decrease in dewatered solids concentration.

These two projects combine to dramatically reduce plant electricity expenditures and add revenue in the form of tipping fees, providing the facility and the County with a buffer against volatility in the price of energy

over time. Hazen and Sawyer is currently designing additional projects that will add to the facility’s energy self-sufficiency and create new revenue streams, further establishing the F. Wayne Hill Water Resources Center as a leader in sustainable treatment plant technology.

See related linkswww.hazenandsawyer.com

æ Gwinnett County Gas-to-Energy Program to Produce Cost Savings

æ Biogas Upgrades Cut Energy Costs in South Africa

@

Since the engine generator started operation in August 2011, Gwinnett County has realized a savings of more than $1,000 per day.

8

T�he water sector is sensitive to extreme weather-related

events. Our research team is addressing a growing

concern within the industry raised by recent weather

volatility, assessing the risks posed by different extreme

weather events and helping utilities manage those risks.

The primary goal of this Water Research Foundation project (co-sponsored by the Water Services Association of Australia and the Water Environment Research Foundation) is to develop an understanding of the relationship between water quality and extreme weather-related events to assist utilities in preparing for those extreme events. Our research team is collecting information on extreme event impacts – along with utility preparation and response procedures in both the U.S. and Australia – and synthesizing that data into a tool that can be accessed by utilities to help inform future planning and decision-making.

In the last few decades there has been anecdotal evidence

that low-probability weather events (floods, droughts, heat waves, etc.) are recurring more frequently, and are affecting different regions than in the past. Climate change is one possible explanation for this, as supported by trends in global weather drivers such as arctic ice decline and sea surface temperature increases. Regardless of the underlying mechanism, however, the fact is that more people are reliant on large-scale infrastructure systems (water and wastewater treatment, transportation networks, energy and food production, etc.) than ever before, and are thus are more susceptible to negative impacts to those systems.

More than most essential infrastructure systems, weather is integral to the water sector. Weather supplies a valuable resource while also influencing quality, demand, and infrastructure performance. Extreme weather-related events are of primary concern to drinking water utilities, since they may potentially affect both the supply and quality of drinking water, service reliability, regulatory compliance, consumer

Extreme Weather Impacts on the Water Sector By Ben Stanford, Ph.D., Director of Applied Research

Extreme weather-related events (x-axis) can bring about a variety of water quality, water quantity, and infrastructure impacts (y-axis) which utilities should consider in their planning. This data is based on initial introductory questionnaire responses from utilities across the U.S. (including Alaska and Hawaii) and Australia.

*Extended changes in normal seasonal temperatures; may be associated with

prolonged hot or cold periods or shifts towards longer/shorter seasons.

Change in Treatment

Service Disruption

Disinfection Byproducts

Disease Outbreaks

Regulated Contaminants

Emerging Contaminants

Algae/Taste & Odor

Water Quantity

Wastewater Influence

Turbidity Spike

Loss of Disinfectant

Water Age

HurricaneFlood Heat WaveExtended Temperature*

July

PrecipitationChanges

Drought

Utility-Reported Impacts

Horizons Winter 2012 9

perception, and costs. This could result in severe issues such as having to announce boil notices for tap water, or more minor concerns such as aesthetic impacts (e.g., taste and odor). Water utility infrastructure and operations procedures are generally designed to enable utilities to reduce the risks from typical, region-specific extreme weather events to an acceptable level, but a thorough understanding of the potential risks is necessary to limit current and future vulnerabilities.

To address these issues and to provide both small and large utilities and other utility support entities with new insights and guidelines necessary to adapt to extreme weather-related events, we have assembled a team of experts in water quality, water resources, and climate change to analyze extreme weather events, associated trends (historical data and anecdotal evidence), and recorded changes/disruptions to source water quantity/quality and treatment. The on-going approach to the project is addressing several key questions of importance to utility managers, planners, and operators including:

• What are the most recent occurrences and patterns of extreme weather events potentially affecting drinking water utilities across the U.S. and Australia?

• What are the experiences and observed effects of extreme weather events on source and finished water quantity and quality over short and long term durations?

• What impacts do extreme weather-related events have on the concentration of regulated and emerging and indicator contaminants in source and finished waters?

• What impacts do extreme weather-related events have on the functioning of existing drinking water treatment processes (i.e., change in filter backwash intervals; changes in amount of chemicals used during treatment; disruption of treatment processes, overloading of residual handling systems, etc.)?

• What detection, prevention, and recovery/remediation actions are being implemented at case study sites experiencing extreme weather-related events and what are the related costs?

• How can the combined project findings be assimilated into valuable guidance useful for all utilities responding to extreme weather events?

The result of this research will be an integrated, searchable, Water Quality Impacts of Extreme Weather-Related Events software-based tool (Water QIEWE), database, and guide to assist utilities and support agencies in preparing for and adapting to extreme weather-related events, and tracking/monitoring impact trends on an ongoing basis. Findings of this project will also be combined into widely useful general recommendations for utility use in preparing for and adapting to extreme weather events. This project will be completed in 2012, with updates posted at www.hazenandsawyer.com.

Change in Treatment

Service Disruption

Disinfection Byproducts

Disease Outbreaks

Regulated Contaminants

Emerging Contaminants

Algae/Taste & Odor

Water Quantity

Wastewater Influence

Turbidity Spike

Loss of Disinfectant

Water Age

Tornado/High Winds

LightningIce StormsSnow MeltWater Temperature

Wildfires

Utility-Reported Impacts

Salt Water Intrusion

10

Low Impact Development (LID) is an approach to land

development (or re-development) that works with

nature to manage stormwater where it falls. Rooftop systems

– particularly important in dense, urban areas – relieve

strain on sewers and deliver a host of additional benefits.

One of the primary objectives of LID site design is to minimize, detain, and retain post-development runoff uniformly throughout a site so as to mimic the site’s predevelopment hydrologic functions. The environmental, economic, and social benefits of employing LID strategies are many. The most important include:

Improved human health – LID detains and treats stormwater that often picks up pollutants as it runs across impermeable surfaces such as roads and sidewalks. These pollutants might otherwise be delivered directly to surrounding water bodies used for recreation or as drinking water sources.

Decreased infrastructure costs – Rain gardens and permeable pavement cost only a fraction of sewer

replacement and/or wastewater treatment plant expansion or enhancement costs, in terms of both initial capital investment and ongoing maintenance.

Improved quality of life – Detention ponds, rain gardens, and even green and blue roofs can quickly become recreation spaces where people gather, exercise, and relax. They improve the appearance of a community, reduce operating costs of a facility, and enhance property value.

Rooftop systemsRooftop systems detain stormwater on roof

surfaces, most often either releasing it gradually to the sewer system or allowing for vegetative uptake and evapotranspiration. Selection of the appropriate rooftop system depends on siting, design, and construction considerations specific to each development. Rooftop systems may also be incorporated into rainwater recycling systems, where flows routed from rooftop systems to cisterns or other harvesting features are captured and used for onsite purposes such as site irrigation, toilet flushing, or vehicle washing.

Rooftop Stormwater Management SystemsBy Dahlia Thompson, P.E., LEED AP

Hazen and Sawyer recently designed a combination green and blue roof system for a building in New York City. Concern about the additional loading on the existing structure led us to select a tray system for both blue roof and green roof elements, in order to easily distribute the additional roof loading in the locations that have the greatest load-bearing capacity.

With proper maintenance, the useful life of the rooftop system is expected to outlast the life of the roof membrane, in excess of 30 years. Another advantage of the tray system is that it can be moved to accommodate repairs to the roof as needed, and individual trays can be replaced if problems arise, without a wholesale replacement of the overall system.

Green Roof TrayThe Blue Roof -Green Roof Combination Blue Roof Tray

Horizons Winter 2012 11

M:\Corporate Communications\Horizons\2011 winter\Graphics

Filter FabricPrevents soil

erosion

Growing Media

Vegetation

Reservoir SheetAssists drainage

Root Barrier

Aluminum TrayMobility and

minimal maintenance

GravelOptional alternative

for securing roof

GeotextileModerate�ow rate

Corrugated PlasticCreates �at surface

Roof DeckInsulation

Roof Membrane

Roof Deck

Insulation

Roof Membrane

M:\Corporate Communications\Horizons\2011 winter\Graphics

Filter FabricPrevents soil

erosion

Growing Media

Vegetation

Reservoir SheetAssists drainage

Root Barrier

Aluminum TrayMobility and

minimal maintenance

GravelOptional alternative

for securing roof

GeotextileModerate�ow rate

Corrugated PlasticCreates �at surface

Roof DeckInsulation

Roof Membrane

Roof Deck

Insulation

Roof Membrane

• Makes beneficial use of stormwater, creating a natural habitat for local flora and fauna.

• Better insulates buildings, lowering heating and cooling costs, while sometimes actually reversing the urban heat island effect.

• Absorbs carbon dioxide and airborne pollutants, improving air quality and reducing the incidence of diseases such as asthma.

• Along with light-colored materials, reduces the urban heat island effect and provides rooftop cooling, lowering a facility’s operating costs.

• Represents a better rooftop option where a roof cannot handle the additional weight of a green roof.

• Provides equivalent stormwater detention to a green roof at a fraction of the cost.

The Blue RoofBlue roofs are non-vegetated source controls that detain stormwater, either releasing it more gradually to the sewer system or storing it for beneficial reuse.

The Green RoofA green roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. Most often, green roofs are designed to require only a minimum of maintenance.

Cutting-edge wastewater treatmentOptimizing clarifier operation with computational fluid dynamics modeling

By Alonso Griborio, Ph.D., P.E., and Paul Pitt, Ph.D., P.E.

PROGRESSIVE ENGINEERING

Full-plant simulators are limited in their ability to simulate accurately the performance of clarifiers, which play a significant role in the wastewater treatment process.

October 2010www.cenews.com

f o r t h e b u s i n e s s o f c i v i l e n g i n e e r i n gce NEWS

Visit www.hazenandsawyer.comæ Abstracts from ACE, WEFTEC,

and other conferences from coast-to-coast.

æ Articles reprinted from industry-leading publications WE&T, the AWWA Journal, and many more.

æ Write-ups of our award-winning work.

www.hazenandsawyer.com

For the latest research news