Please note that the current pandemic has negatively impacted the Academy’s finances. Please seriously consider making a donation to support AAEES Programs. All donations are tax-deductible contributions to the Environmental Engineering and Science Foundation, a closely-related charitable foundation. Every dollar is used to support Academy Programs. To donate today, go to


Leadership and Excellence in
Environmental Engineering and Science

Related Items

2016 Excellence in Environmental Engineering and Science™ Awards Competition Winner

E3S Grand Prize

Grand Prize - Design

State-of-the-Art Nitrogen Upgrade

Entrant: CH2M
Engineer in Charge: Richard Voigt, P.E.
Location: Alexandria, Virginia
Media Contact: Jodie Willson

Entrant Profile

A 9‐year partnership between Alexandria Renew Enterprises (AlexRenew) and CH2M successfully implemented the vision of the State‐of‐the‐Art Nitrogen Upgrade Program. Completed improvements will allow AlexRenew to meet stringent nutrient limits at design flows and loads and protect the Potomac River and Chesapeake Bay. The facility uses cutting‐edge deammonification technology in sidestream and mainstream processes to provide reliable treatment while optimizing operational costs.

Achieving the project goals required a multi‐disciplinary design team. CH2M was retained as the engineer for a long‐range planning effort, design, permitting, and construction services. Clark and Ulliman Schutte were a joint venture that performed as the Construction Manager at Risk (CMAR) for Package C. KCE and KTLH provided structural quality control and inspections in the field for Package C. Jacobs provided construction management and inspection services for all work.

CH2M is a global engineering and project delivery company partnering with public and private clients to tackle the world's most complex infrastructure and natural resource challenges. The firm's work is concentrated in the water, transportation, energy, environment and industrial markets. CH2M had 2014 gross revenues of $5.4 billion, has 22,000 employees and is a specialist in program, construction and operations management and design. CH2M's partnership with leading water agencies around the globe earned the firm one of the highest honors in the water industry—the 2015 Stockholm Industry Water Award, for leadership in potable reuse technology and public acceptance. The firm was also named Water Company of the Year at the 2012 Global Water Awards.

Project Description

An Environmentally Integrated Project

Since the 1950s, Alexandria Renew Enterprises, (AlexRenew) has provided water resource recovery services for the City of Alexandria and portions of Fairfax County in Virginia. AlexRenew discharges to the Chesapeake Bay, an environmentally sensitive water body and ecosystem. Driven by efforts to protect the Bay, stringent limits were enacted and took effect in 2011. A phased series of improvements was required to comply with the new limits, equivalent to 3 mg/l total nitrogen, based on waste load allocations at the permitted flow of 54 mgd. Sitting on only 30 acres, AlexRenew was already one of the most constrained water resource recovery facilities in the U.S.—at less than 0.5 acre per million gallons of treatment capacity.

The resulting project included a Long Range Planning Study through 2030 and design and construction of a treatment upgrade that is at the forefront of nutrient removal technology and engages the public like never before. Improvements on the existing Main Plant Site feature deammonification technology and provide additional biological process capacity. Acquisition of the adjacent West Plant Site presented an opportunity to transform a historic landfill into a Nutrient Management Facility (NMF) to balance diurnal loadings. A "zero" odor control strategy was needed to address the extremely close proximity of the public. Odors are collected internal to the NMF, treated using carbon systems, and then treated air is exhausted away from the field.

Quality and a Satisfied Client

The effective partnership between AlexRenew and CH2M was formed at the project outset, with chartering and sustainability workshops used to establish goals and desired outcomes. Throughout the project, focused workshops were held to discuss challenges and develop technical solutions. A custom decision matrix/model was developed and used to balance AlexRenew's goals, while employing sustainable practices. CH2M provided evaluations and facilitated the scoring by AlexRenew staff.

The project included over 800 drawings covering all engineering disciplines and was completed in five construction contracts: three design/bid/build and two using a Construction Manager at Risk (CMAR) approach. Improvements included supplemental carbon enhancements, the addition of a biological reactor basin, a Centrate Pretreatment Facility, mainstream deammonification systems, a NMF and athletic field, a new Hooffs Run Crossing, and various site work. Key deammonification equipment was evaluated, pre‐selected, and negotiated on behalf of the Owner.

The project met schedule requirements by opening the athletic field as scheduled and delivering the work before January 2016. The overall SANUP cost of $131 million compares favorably to the baseline budget of $154 million. Design error and omission‐based change orders for the design/bid/build packages were a combined 3.0% of constructed value. Work executed under a CMAR approach yielded a 10.4% reduction against the established guaranteed maximum price amounts.

Social and Economic Advancement

Acquisition and development of a historic landfill property, in the middle of a planned South Carlyle Development Area, required a unique approach. The resulting design of the NMF pushed the facility principally below grade. Process piping, equipment, and other project components were buried or kept internal to the NMF structure, with accesses limited. The facilities were designed to dovetail with adjacent development and provide a seamless connection for public access to the field, connection of biking/pedestrian paths, and a consistent aesthetic.

The finished upgrades protect the water quality in the region and reclaim resources for public recreation and use. Deammonification technology was selected to conserve chemicals and energy and enable future resource recovery enhancements. The development of the West Plant Site provided the opportunity to recover a brownfield site and develop it into a public resource.

In addition to protecting public health and the Chesapeake Bay, provision of the athletic field directly on top of process tankage and integration of a public‐private partnership with adjacent stakeholders delivers previously unheard of amenities for the community. Planned commercial, residential, and green spaces are connected together, in keeping with the City of Alexandria's revitalization of the Eisenhower Corridor.

Innovation—Game Changing Nitrogen Removal Technology

Deammonification is an emerging technology to remove nitrogen from wastewater. AlexRenew is one of the first utilities in North America to implement the deammonification process for nitrogen removal in sidestream applications, and the first to implement it for mainstream treatment. AlexRenew's Water Resource Recovery Facility is also the first in the world to adopt the technology with such stringent nutrient discharge requirements. The deammonification process selectively cultivates naturally occurring micro‐organisms (anaerobic ammonia oxidizers, or anammox) to remove nitrogen, while significantly reducing process air and supplemental carbon needs, as compared to traditional methods.

A new sidestream Centrate Pretreatment (CPT) Facility was constructed to pre‐treat the ammonia‐rich recycle stream that results from centrifuge dewatering of anaerobically digested biosolids. The process uses 60% less process air than conventional treatment, with no supplemental carbon required. Two larger reactors provide treatment, while a third smaller or "daughter" reactor can be used to optimize and demonstrate process control enhancements.

AlexRenew has also implemented upgrades that will utilize the anammox micro‐organisms in the main plant process stream. The CPT system seeds anammox into the mainstream, while also ensuring stability of the ammonia oxidizer population and overall reliability of the system.


The project was not without complexities. Because of coordination requirements with a fast track adjacent development, AlexRenew implemented a CMAR delivery for the NMF after the design was complete.

Also, a value engineering option was selected to replace the designed cast‐in‐place 18‐million‐gallon NMF structure with a precast post‐tensioned structure made up of more than 1,700 concrete panels. The design team used 3‐D modeling to coordinate process piping and other features with the precast provider to avoid panel seams and tensioning wires. Models were repeatedly merged and assessed, with re‐ engineering as needed, over the span of 6 months. This work was conducted in parallel with the construction, which was already underway. These efforts enabled capture of the $6 million credit associated with the change.

In summary, a 9‐year partnership between AlexRenew and CH2M successfully implemented the vision of the State‐of‐the‐Art Nitrogen Upgrade Program, maximizing use of available resources, utilizing cutting‐ edge technology to drive towards energy neutrality while integrating seamlessly with the community to provide long‐term aesthetic and recreational value.

Click images to enlarge in separate window.

E3S Photos

The State‐of‐the‐Art Nitrogen Upgrade Program (SANUP) for Alexandria Renew Enterprises (AlexRenew) was designed and constructed in a phased approach. Main Plant Site Improvements Packages A, B, and D were constructed using a conventional design/bid/build approach. Constructed value was $30 million, with 3.0% change orders due to design errors and omissions. Package C, along with Mainstream Anammox that was an amendment to Package C, were conducted with a Construction Management at Risk approach. Constructed value was $101 million, with a savings of 10.4% achieved against the original Guaranteed Maximum Price.

E3S Photos

A private‐public partnership was used to plan development of the South Carlyle Area, which includes AlexRenew's newly acquired West Plant Site, as well as more than 1.2 million square feet of commercial and residential developments by others immediately to the north. The South Carlyle Area is a subcomponent of the City of Alexandria's ongoing revitalization of the East Eisenhower Corridor. Stakeholders included the City of Alexandria, an adjacent developer, and AlexRenew. The entire South Carlyle area was a historic landfill with contaminated soils. As a result, AlexRenew entered their site into the Commonwealth of Virginia's Voluntary Remediation Program. The design also considered process needs, utility restrictions, resource protection areas, and aesthetics. The result was an optimized partially buried tankage configuration for the Nutrient Management Facility to store 18 million gallons of treated primary effluent for diurnal nitrogen load equalization, as well as a full‐ size athletic playing field for community use that connects to other public spaces. (Image courtesy of FXFOWLE).

E3S Photos

Because of poor soil conditions, piles were used to support all structures, including the Nutrient Management Facility (NMF), electrical duct banks, and process piping. More than 2,200 precast concrete piles were driven on the project. Concrete piles were selected as best value after conducting an evaluation of various factors, including cost, speed of installation, and noise pollution impacts to the community. A test pile program was also used to validate the concrete piles would meet engineering design requirements. Public outreach meetings and social media were used to advise the community of the work, as well as receive feedback on any issues to be resolved.

E3S Photos

Only 3.75 acres of the 10‐acre West Plant Site were available for development due to various site constraints. A Construction Management at Risk approach was implemented by the Owner at the 100% design stage to provide additional coordination and synergies with adjacent projects, as well as accelerate delivery. Package C consisted of the removal of 200,000 tons of soil and the installation of more than 60,000 yards of concrete. As no additional footprint was available for a future 128‐million‐gallon‐per‐day wet weather pumping station need, a wet weather wet well was incorporated beneath the NMF structure at the 60% design level. Provisions and allocations were also made for future pumps, electrical, and instrumentation and controls. Laydown on the site was at a premium and was primarily confined within the project's footprint. AlexRenew reimbursed public transportation costs for all workers to mitigate parking needs.

E3S Photos

The Limerick Athletic Field is a full‐size athletic field located directly on top of the Nutrient Management Facility. Operated and maintained by AlexRenew, the NMF provides diurnal storage for nitrogen loads, ensuring a consistent feed to secondary treatment processes. The field, operated and maintained by the City of Alexandria, provides green space for recreation and can be used for soccer, lacrosse, and other sporting activities.

E3S Photos

The NMF Central Operating Gallery houses process pumps, piping, valves, and instrumentation. As a result, routine access requirements into the tanks are minimized. A "home run" line was provided from the tanks to the odor control systems to provide up to 30,000 cubic feet per minute of additional air from a single tank when taken down for maintenance. Space allocations were also made in the gallery for future wet weather pumps, piping, and valves.

E3S Photos

A total of four carbon treatment vessels, each with a capacity of 15,000 cubic feet per minute, provide treatment for the odorous air in the NMF tank headspaces. Odorous air from each tank is vented using a dedicated line with an air damper and a flowmeter. The individual ducts from each tank are collected into a main header, upstream of the carbon vessels. The flowmeters, dampers, and variable frequency fan drives allow Operations staff to tune the air flowrate from each tank via the plant SCADA system, as well as vary the number of carbon units in service as needed. Treated air is discharged through a common buried line and exhausted via a 50‐foot‐tall stack.

E3S Photos

Providing an athletic field on top of the NMF, a vital treatment process for the AlexRenew facility, presented aesthetic and operational design challenges. Because there could be no access to the NMF from above, access was limited primarily to the east side of the NMF structure. Glass storefronts were used to provide equipment and personnel access, as well as complement the unfinished precast concrete structure. The odor control exhaust stack, seen in the background, ventilates treated exhaust from the carbon scrubbers away from the field. Permeable pavers instead of pavement provide environmentally friendly drainage as well as visual interest.

E3S Photos

A ribbon‐cutting ceremony was held for the opening of the Limerick Athletic field on October 23, 2015. A FamilyFieldFest Day was held by the City and AlexRenew on October 24, 2015, to introduce the field to Alexandria residents. AlexRenew and City of Alexandria staff, local vendors, and the public came out to play on the new field, conduct activities for kids, and promote local businesses. The field, which is anticipated to host a variety of sports teams and community groups, is located on Limerick Street in the Carlyle‐Eisenhower East neighborhood.

E3S Photos

The Centrate Pretreatment (CPT) Facility was designed to pre‐treat the ammonia‐rich recycle stream that results from centrifuge dewatering of anaerobically digested biosolids. The deammonification process uses 60% less process air than conventional treatment, with no supplemental carbon required. The facility can receive a maximum flow of 0.276 million gallons per day, and provides 80% removal of nitrogen prior to secondary treatment. Utilization of deammonification in the sidestream and mainstream will result in potential O&M savings of $400,000 annually. The CPT Facility at AlexRenew is one of the first full‐scale deammonification systems to be implemented in the U.S.

E3S Photos

Centrate from dewatering centrifuges, with concentrated amounts of nitrogen, are conveyed to the sidestream Centrate Pretreatment Facility. The centrate pretreatment process uses the ANaerobic AMMonia OXidizing (ANAMMOX) bacteria to achieve a "shortcut" in the metabolic pathways that transform ammonia in the water into nitrogen gas that diffuses to the atmosphere. The microbial population in each reactor must be carefully balanced to ensure that the anammox bacteria can out‐compete other microbes present in the biomass. One strategy is the use of hydrocyclones to separate the heavier anammox granules in the underflow and keep them in the reactor while the lighter biomass exits via the overflow and is removed.

E3S Photos

Anammox granules from the Centrate Pretreatment Facility are seeded into the mainstream biological process. Four launders with multiple cyclones each are used to retain the Anammox granules in AlexRenew's biological reactor basins and to improve mixed liquor settleability. Combined with improvements to the process aeration controls, the cyclones can potentially reduce AlexRenew's aeration energy use in the mainstream by 25% and the supplemental carbon use by 45%. The canopy was designed to both protect the equipment and to facilitate the future addition of solar panels on the canopy roof.

E3S Photos

Cutting‐edge deammonification technology utilizes cyclones to separate and retain the anammox bacteria population. In addition, the cyclones retain other heavier biomass and improve the settleability of the mixed liquor, which results in a more reliable and robust system operation.

E3S Photos

AlexRenew partnered with a global network of academics and utilities to participate in several high visibility research projects. This collaboration has resulted in further enhancement of the process at AlexRenew, sharing of information with partner utilities, and deriving lessons learned for the industry as a whole. Return activated sludge (RAS) influx analysis baseline data is collected to evaluate the impact of Anammox granules and hydrocyclones on the settleability of the mainstream mixed liquor. Pictured are 30‐minute settling column tests performed on RAS at different dilutions (photos taken after 30 minutes). The testing is being conducted bi‐weekly at AlexRenew's laboratory facility.

E3S Photos

Shown are active anammox granules from the sidestream reactor. Microscopic evaluation of flocs and granules in the sidestream mixed liquor helps to quantify and qualify granule formation in the mixed liquor and the impact on sludge settleability.

E3S Photos

Biological reactor basin 6 (BRB6) provides an additional 3.8 million gallons of secondary treatment capacity. The sixth basin is designed as a post‐aerobic polishing step to reliably achieve 3 mg/l total nitrogen at design flows and loads. A crossover channel was needed to connect the new basin with the existing mixed liquor channel, an integral part of the existing five reactor basins structure shown in the background to the right. Live connections to the mixed liquor channel (influent to BRB 6) and secondary settling tank influent channel (effluent from BRB 6) were needed, as the channels could not be taken out of service. Construction of the basin was significantly constrained, as it was surrounded on all sides by existing active facilities and underground galleries. The entire basin is pile supported, and 1,000 yard concrete pours were used to accelerate construction.

E3S Photos

Three‐dimensional (3‐D) design software was used for all SANUP facilities. The use of 3‐D allowed enhanced clash detection and also provided the means to "walk through" the facility with plant staff and other stakeholders during the design phase. Multiple contractors used the 3‐D files for the basis of their as‐builts, and returned 3‐D files for construction of record documentation. An electronic record 3‐D model is in progress for SANUP Package C. The 3‐D record model will yield design efficiencies and savings for the future wet weather pump station, which will be integral to the NMF.

Click here to return to the list of 2016 winners.

Back to Top

Facebook logo Instagram logo Linked logo Twitter logo YouTube logo Flickr logo