Donohue is much more than an engineering firm. We generate ideas, solve problems, and make things work. It’s innovation at its finest, and it’s something to which our clients have become accustomed.
You can always count on our team of experts to think about problems in new ways—to step back from conventional solutions and find a different path from point A to point B. Our solutions save clients money, contribute to environmental sustainability, and make processes run more efficiently. Browse the examples below to learn more about our innovative approach to projects.
Energy Independence Through High Strength Waste Recovery
Fourteen years of improvements paved the way for Wisconsin’s first wastewater treatment facility to produce all of its electrical energy using a renewable fuel. The City of Sheboygan’s 18-mgd (56 mgd peak) wastewater treatment facility serves seven communities. Working with Donohue, the City has been working toward their goal of becoming a net zero energy user by completing a series of projects focused on energy efficiency, production, and recovery.
Improvements over the years have included implementing a high-strength industrial waste program, replacing aging digester gas boilers, and modifying piping and controls to provide “free heat” to the building system. Microturbines were added, and linear motion digester mixers were installed in their primary digesters—a technology that consumes 50% less power than traditional draft tubes. With these improvements, the facility now regularly produces more than 85% of its required electrical energy and 90% of its required heat energy, often producing enough to sell energy back to the grid.
Increasing Energy Production with High Strength Waste
Partnerships with national leaders led to the Milwaukee Metropolitan Sewerage District (MMSD) becoming an early adopter of High Strength Waste (HSW) programs in the Midwest. Donohue was originally retained to develop pilot testing of a HSW program after a WERF report concluded that co-digestion of aircraft deicing fluid and other high-strength waste was more effective than separate digestion of waste alone. Following the lead of East Bay Municipal Utility District and the City of Sheboygan, MMSD decided to use the budget for the pilot program to instead fund the design of a permanent facility.
Donohue designed the facility by making use of existing, underused spaces, keeping capital costs low. With the addition of these HSW receiving facilities, MMSD now has the potential to produce enough methane gas to power their entire South Shore Facility, and the fast-tracked schedule will allow them to meet these goals much earlier than otherwise anticipated. This program benefits the regional waste generators by offering a low-cost outlet for their waste streams, as well as ratepayers and the local community by providing a sustainable, renewable resource for energy production.
Achieving 100 mgd through Hydraulic, Process, and SCADA Improvements
A series of evaluations and designs completed by Donohue will enable the City of Fort Wayne’s water pollution control plant (WPCP) to increase the rated maximum peak flow from 60 mgd up to 100 mgd by 2016. A plant-wide hydraulic model illustrated the drastic difference between theoretical and actual head losses in the primary effluent conduits, which were caused by years of accumulated debris. Improvements to these conduits will allow the plant to reach its full hydraulic capacity. Donohue assisted the City with the design of four new primary clarifiers, modifications to the secondary clarifiers, primary effluent conduits, and SCADA system improvements.
Process capacity was also a limiting factor, though, and Donohue used process modeling to identify target operational mixed liquor suspended solids for the WPCP under a range of operating conditions. A probabilistic evaluation of treatment performance helped to identify other process constraints for achieving 100 mgd of flow capacity. Instrumentation and control improvements were developed based on these identified process limitations.
Increasing Wet Weather Capacity to 330 mgd
Improvements at MMSD’s Jones Island Water Reclamation Facility increased peak wet weather flow capacity to 330 mgd. Actual operating experience has shown the improvements implemented as part of this project have added as much as 100 mgd of peak flow capacity. Donohue’s solutions to deficiencies at the facility were extremely economical compared to conventional means.
Aeration basin and control system modifications allow storing of a portion of the activated sludge solids in control-system- and/or operator-designated basins during peak flow conditions. This effectively lowers clarifier solids loading rates and increases peak flow hydraulic capacity. Additionally, secondary clarifier modifications increased hydraulic throughput. This is the largest purely plug flow facility in the country to incorporate off-line activated sludge storage without adding basins or changing the flow configuration.
Using Antecedent Moisture Modeling to Save Communities Millions
The communities that are served by Heart of the Valley Metropolitan Sewerage District had been charged with removing at least 30% of infiltration and inflow (I/I) within a 10-year period, a mandate that would have cost each community millions. Donohue applied antecedent moisture modeling technology (AMM) to gauge the actual effectiveness of previous I/I projects already completed and to identify and prioritize future projects. The team also used AMM and hydraulic modeling as risk assessment tools to predict future system performance.
This analysis determined that the original removal requirement based upon conventional modeling was too conservative, and that the projects already completed would protect the health and welfare of the Fox River and surrounding communities. Based on model results, HOVMSD submitted—and received approval for—a Facility Plan Amendment to replace the 30% reduction requirement. This was the first time a Wisconsin entity and one of only a handful in the Midwest that have used this risk assessment approach as a basis for plan approval.
Using Biological Filters to Maximize Energy Generation
The use of biological filters at Bush Brothers’ wastewater treatment facility allowed the famous baked beans company to produce and clean enough biogas to power 500 homes. This energy recovery project took advantage of the waste products on site by grinding waste beans and mixing them into the waste stream rather then using them as cattle feed. The flow sent to the anaerobic reactor now produces biogas at a rate of 20-50% more than the previous configuration.
To clean the biogas, which had extremely high concentrations of hydrogen sulfide (H2S) of up to 10,000ppm, Donohue selected a hybrid system consisting of a biofilter followed by a replaceable media scrubber. The biofilter provides efficient H2S removal at low operating costs, but the replaceable media was also sized to provide complete treatment if necessary. This efficient solution allows the facility to take advantage of lost cost operations while providing redundancy for year-round production. At the time of installation, the facility was the first in the Midwest and the second of its kind in the U.S.
Saving $1,000/day with Varying Setpoints at 182 mgd Facility
The Trinity River Authority (TRA) has been evaluating low DO operation using full-scale pilot testing for energy savings and nutrient removal. TRA conventionally operated at an average DO setpoint of 2 mg/L, but reduced that setpoint to between 0.75 and 1.0 mg/L for low-level operation. When the full facility is operated under low DO conditions, airflows were consistently reduced by 25%. This has enabled the facility to operate with three-1,000 horsepower blowers, rather than the four-1,000 horsepower blowers required at conventional DO setpoints. This energy savings equals up to $1,000 per day in savings for the facility.
Membranes Eliminate UV Disinfection Requirement
Membrane technology implemented at the City of Hutchinson’s wastewater treatment facility expanded plant capacity but also eliminated the need for a separate disinfection process. The existing facility was operating at or near capacity; a conventional approach would have been to add a new oxidation ditch and another clarifier. Instead, Donohue suggested adding an MBR system to operate in parallel with the existing oxidation ditches and clarifiers.
Now, two-thirds of the flow is sent to the existing oxidation ditches/final clarifiers and one-third is sent to the new MBR process. Donohue conducted a study to demonstrate that a separate disinfection step is not necessary, and the results have been exceptional: the count for fecal coliform and E. coli from the MBR process is 0; the permitted limit for fecal coliform is 200 per 100 mL. The parallel train solution developed by Donohue is the first in the Midwest and one of just a handful built across the U.S.
Zero Operational Downtime during Construction
Donohue designed a new a new North Pump Building and Electrical Building at the City of Fort Wayne’s Three Rivers Filtration Plant (TRFP). To maintain water treatment and distribution during the construction period, extensive construction sequences and constraints were developed by Donohue and included in the bid documents. The carefully planned design allowed construction and commissioning of the improvements while maintaining sufficient pressures throughout the system, keeping the facility continuously treating and distributing water.
Prior to this project, less than one-half of the 20 MG reservoir capacity could be used due to hydraulic limitations of the existing high service pumping systems. The design significantly increased the effective capacity of finished water storage by more than doubling the usable volume of the existing reservoirs, from 8 MG to 17 MG. This 9 MG increase allowed the City to avoid construction of a much more costly additional reservoir.
Hidden Structures Improve River Quality
Donohue designed a 3-million-gallon underground storage and primary treatment structure along the White River in Indianapolis. Located in a high profile downtown area, the cast-in-place concrete structure was constructed completely below grade in the floodplain and covered with topsoil and grass. Cleverly tucked into the embankment, the structure's electrical and automated control building provides an overlook for individuals enjoying the scenic river walk.
The project was built to significantly reduce combined sewage overflows into the White River. The aesthetically-pleasing facilities capture, treat, and store wastewater and storm water until flows can be sent to the wastewater treatment facility. Innovative engineering practices were utilized to meet the challenging and unique needs of this project, including automated flushing gates to clean out the structure and minimize odors, and thickened and heavily reinforced floor slab to prevent the structure from rising during flooding.
Permit Negotiations Save City $28 Million
The City of Superior’s permit renewal included an implementation schedule to meet new winter (November-April) acute and summer (May-October) chronic toxicity based effluent ammonia limits. Donohue developed an innovative side stream treatment alternative that could fully nitrify digested sludge filtrate while providing nitrifying seed organisms to the existing activated sludge system, saving approximately $28 million over a conventional facility. Modeling showed that this solution could meet permit limits except for during the months of May and June, when the raw wastewater was still quite cold.
Donohue recommended negotiations be conducted with the WDNR to relax the limits for certain months. During these negotiations it was found that generic, default receiving water data had been used in calculating the proposed ammonia limits, which were not representative of Superior Bay or Lake Superior. The project team was able to collect and document actual conditions in these receiving waters and other nearby tributary streams; the WDNR then used this data to revise its calculation and revise its limits. The City implemented this cost-saving, environmentally safe solution to realize these immense savings.
Innovative Construction Strategies
Milwaukee Metropolitan’s Sewerage District’s South Shore Water Reclamation Facility is one of the largest in the Midwest. Wastewater enters the plant through a 150-inch (12.5-foot) diameter sewer pipe at flow rates that exceed 200,000 gallons per minute. Prior to this project, the District was experiencing severe maintenance problems with the existing system, such as equipment plugging and failing. It also did not provide adequate grit and debris removal during high flows, which limited treatment effectiveness.
Donohue developed a design solution that could be constructed without interrupting flow into the plant. Given the plant’s size, the magnitude of the facilities, and the need to maintain flow and treatment at all times during construction, this project was extremely complex to design and construct. The preliminary treatment facilities were completed 415 days ahead of schedule and within 0.8 percent of the $21.6 million budgeted for engineering and construction.