Applied research is both a service to our clients and a means of pushing the industry to achieve greater levels of treatment, reduce energy costs, and ultimately improve the environment. We aim to increase effectiveness while minimizing costs through innovative applications of new and emerging technologies. Our Applied Research branch serves to achieve these goals through pilot testing and participation in research foundations.
We develop effective applied research projects for our clients to investigate specific needs, maximizing existing infrastructure and minimizing capital and operating expenditures. Our experience and knowledge base allow us to develop effective, targeted testing plans to solve facility-specific problems and give clients/owners a sense of how specific technologies will work for them. These research programs demonstrate a technology’s true applicability to a certain facility, meaning our clients need not rely on manufacturer-dictated pilot results.
Donohue team members also participate in several Water Environment Research Foundation (WERF) committees, contributing our expertise and exploring the most pressing questions in our industry. Current contributions to these teams include the following:
- Project Subcommittee Members:
- Anaerobic Digester Foaming
- Energy Neutral Nitrogen Removal
- Issue Area Team Member: Nutrient Recovery Challenge
- Exploratory Team Member: Resource Recovery Challenge Statement
Explore some of our current and past research activities below.
Anaerobic Digester Foam Prevention & Control
Foaming of anaerobic digesters has been an ongoing challenge for the wastewater industry, with consequences ranging from housekeeping issues (overtopping of walls with floating cover digesters) to O&M challenges (plugged gas utilization piping) to potentially significant tank/cover damage (plugged flame arrestors/pressure vacuum relief valves). There have been many theorized causes for digester foaming, including surfactants, oil and grease content, foaming microorganisms, excessive gas production due to high strength waste addition, and digester mixing practices.
WERF commissioned a project to address the issue of anaerobic digester foaming in different water resource recovery facilities (WRRFs). The project included a comprehensive literature review, a plant survey, and findings from studies at several WRRFs experiencing digester foaming episodes. Project results included documentation of knowledge gaps related to causes and control of anaerobic digester foaming, identification of common causative factors, and assessment of foam detection, control, and mitigation methods at several full-scale WRRFs.
Donohue has had extensive experience in assisting clients with evaluating and mitigating digester foaming problems caused by a range of factors. Donohue utilized this knowledge and experience while serving on the Project Subcommittee for this WERF project. In this role one of our senior process engineers, along with fellow Project Subcommittee members, provided quality reviews throughout the project’s activities including development of the project’s final report.
Low Level Phosphorus Removal
The Wisconsin Department of Natural Resources has begun state-wide implementation of water-quality based effluent limits (WQBELs) for phosphorus. A great deal of debate has focused on the appropriate technology to achieve an effluent limit of 0.075 to 0.1 mg/L. Initial discussions focused on high energy use, high capital membrane systems, but other technologies were theoretically possible to achieve these limits. Donohue arranged for a no-rental cost testing of tertiary disc filter technology for six communities in 2013 and 2014. Testing indicated that the tertiary filters could achieve effluent levels below 0.075 mg/L at 20 to 30% of the capital and operating cost of comparable membrane filtration technologies.
Low-Energy Alternatives to Activated Sludge Treatment
Reducing energy costs for treatment processes continues to be an emergent and evolving topic within the wastewater industry. For treating activated sludge, several technologies have become options in recent years, leaving engineers and facility operators to sift through alternatives piecemeal.
Donohue’s personnel participated on a research team for a project co-funded by the Water Reuse Research Foundation and WERF to comprehensively evaluate these emerging technologies and develop a resource for those looking to implement them. A Donohue team member also served as a technical advisor on the investigation of the membrane biofilm reactor (MBfR) for energy efficient wastewater treatment.
Energy Implications of Selector Zone Mixing Technologies
The Trinity River Authority of Texas (TRA) has been completing applied research with Donohue’s assistance to investigate lowering selector zone mixing energy with the low-capital floating mixers. This initiative is aimed at reducing the facility’s annual operating costs while minimizing capital expenditure.
Four conditions were tested with two different horsepower floating mixers:
- Condition 1: 37 hp/mgal, via two 10 horsepower mixers
- Condition 2: 17.5 hp/mgal, via one 10 horsepower mixer
- Condition 3: 17.5 hp/mgal, via two 5 horsepower mixers
- Condition 4: 8.75 hp/mgal, via one 5 horsepower mixer
Online selector zone TSS and ORP were evaluated, as well as final effluent total phosphorus for the mixer energy conditions. The study looks at capital and operating costs against energy demands while maintaining effluent quality and has the potential to save the facility $40,000 per year in operating expenses.
Low Level DO Operation:
Impacts on Energy, Ecology, and Nutrients
Recently, the wastewater field has had a great deal of interest and discussion centered around the concept of shifting our industry to a resource recovery paradigm, with an emphasis on recovering nutrients, energy, and water. While these three areas are sometimes viewed independently, there can be significant overlap. For example, low DO operation has been documented to reduce aeration requirements.
This study looks at full-scale facilities that operate consistently under low DO conditions (DO setpoints less than 1 mg/L). The Trinity River Authority (TRA) Central Regional Wastewater System (CRWS) Treatment Plant began experimenting with low DO operation in October 2012, and has continued to refine the setpoints and operational strategies. Overall, the low DO setpoints have resulted in a 25% reduction in aeration energy, while maintaining low effluent ammonium (<0.1 mg/L) and low effluent phosphorus (<0.5 mg/L). Microbial ecology investigations are being conducted to examine any shift in bacterial populations that may be resulting in the ability to operate at these low DO setpoints.