The U.S. Environmental Protection Agency (EPA) describe excessive nutrients (phosphorus and nitrogen) in our waters as one of America’s most pervasive, costly and challenging problems. An overabundance of nutrients leads to severe problems ranging from toxic algal blooms to complete eutrophication. These problems negatively impact the quality of water used for consumption, recreational waters and aquatic life.
A range of human activities including runoff from agriculture, stormwater, wastewater treatment plant discharges and other nutrient sources into waterbodies are often to blame. But, responses to Black & Veatch’s 2020 Strategic Directions: Water Report survey — an annual survey of qualified utility, municipal, commercial and community stakeholders — show that wastewater utilities are actively working to improve effluent quality and meet regulatory requirements.
2020 Strategic Directions: Water Report
With its survey of nearly 300 water industry stakeholders as its backbone, Black & Veatch’s 2020 Strategic Directions: Water Report comprehensively analyzes the sector’s complex landscape of challenges and opportunities. The leveraging of data in driving decision-making and optimizing efficiencies in water and wastewater systems is widening even as infrastructure continues to age, climate change strains assets, and the COVID-19 pandemic’s financial havoc pressures the bottom lines of many utilities through lost revenues. We look at all of that and more.
Nutrient regulation has been a “hot topic” for the past 30 years. Historically, the issue was relegated to specific regions around the United States, such as in the Great Lakes, Long Island Sound, Chesapeake Bay and Florida. But today, nutrient management affects more than two-thirds of the country. Activity only continues to grow, ramping up in the Midwest due to the drive to reduce hypoxia caused by the discharge of nutrients in the Mississippi River into the Gulf of Mexico and in the West as California looks at nutrient management in the San Francisco Bay area.
Survey data shows that the number of wastewater utilities whose facilities are permitted for phosphorus, total nitrogen, or both, has increased 6 percent over last year, to 56 percent of respondents. Meanwhile, the number of utilities who are not currently permitted, and have no plans for future permits, dropped 10 percent to 19 percent in this year’s survey.
When it comes to planning for future permitting, the data shows that wastewater utilities are planning to act sooner than originally planned, with 16 percent shortening their timelines expecting nutrient limits in their permits within the next five years — double the number of respondents from last year. And 9 percent are planning beyond the five-year mark, down from 14 percent last year. More and more, nutrient removal of some kind is becoming abundant in the United States.
More wastewater utilities also are implementing anaerobic digestion, with 62 percent of respondents responding affirmatively, versus 55 percent last year. There are several drivers for this shift, including pressure on landfills accepting unstabilized solids, as well as regulatory and social pressures on chemical stabilization and thermal conversion processes. Anaerobic digestion reduces the mass of biosolids and the odor potential, which contribute to greater flexibility with biosolids management options. In addition, the process generates biogas that can be recovered for energy production. Anaerobic digestion also is compatible with or necessary for other advanced stabilization processes that will create an even higher quality biosolids product.
The process has long been the mainstay of medium to large utilities because of the benefits of mass reduction, energy recovery, and the ability to use the product as a fertilizer and soil amendment. Numerous small utilities also have benefited from incorporating the process. In addition to the drivers previously noted, more utilities now are looking at their digesters as assets that can be exploited for revenue and energy generation using co-digestion with high strength wastes.
Utilities can receive revenues from waste haulers in the form of tip fees and use these organics to create additional biogas that can be used for electric power production or as a renewable fuel for powering vehicles. New regulations at the state level limiting landfill disposal of organics, such as the proposed California Rule SB 1383, also are contributing to the increased interest in using anaerobic digesters to treat a broader range of organic wastes. All these drivers have led utilities to bring back into service mothballed digesters, expand existing digestion capacities or replace stressed processes with new digestion systems.
Nitrogen and Phosphorous
As the use of anaerobic digestion increases, expect to see the use of sidestream treatment rise. Survey data shows that wastewater utilities are increasingly using sidestream treatment to remove ammonia, with 27 percent of utilities stating that they conduct sidestream treatment, up from 20 percent in 2019. A combined 42 percent are either actively planning for or considering integrating the technology.
Dewatering of anaerobically digested biosolids results in a concentrated return flow that can be mitigated using sidestream treatment, which can be a stable, cost-effective way to remove ammonia, helping utilities adhere to ammonia and total nitrogen limits. Deammonification is the most efficient way to remove ammonia-nitrogen for many facilities.
Phosphorous recovery also is increasing. Today, 22 percent report performing phosphorous recovery of some kind, up from 18 percent in 2019. A combined 44 percent either are actively planning for or considering the technology. This reflects a growing interest in recovering phosphorous, and as a result, the increasing adoption of proprietary technologies such as struvite harvesting systems. The number of responding wastewater utilities not conducting phosphorous removal also dropped 5 percent to 34 percent today.
The top operational driver behind phosphorous recovery is the need to reduce struvite buildup in the anaerobic digestor and on the pipes and equipment, helping to prevent damage to equipment and reduction in system capacity. Phosphorous removal also plays a critical role in total nutrient management for the beneficial use of biosolids. When looking at the beneficial use of biosolids in agriculture, the ratio of nitrogen to phosphorous is not favorable and can result in the overapplication of phosphorous. Removing the phosphorous broadens the potential application of biosolids in agricultural areas. Both technologies — sidestream treatment to remove ammonia and phosphorous recovery — will continue to improve, mature and come of age, leading to increased adoption.
New Technologies Offer New Opportunity
Like others in the water utility space, wastewater utilities increasingly are embracing advanced control, using sensors and automation technology as they search for new solutions in nutrient management. The survey found that 63 percent of wastewater utilities either are using or planning to use controls, sensors and/or automation to optimize nutrient removal.
This has not always been the case, with utilities previously hesitant to install online analyzers or sensors in their plants. Back in 2002, a Water Environment Research Foundation (WERF) study found that “the dependability and accuracy of the primary sensors is still cited … as the single largest impediment to wide-scale, successful implementation of automation. Participants … confirmed that sensor accuracy and reliability continue to be a problem area.”
Today, the technology has improved, the knowledge base has grown and modern sensors are far more robust, allowing for comprehensive nutrient monitoring that continuously observes and analyzes flows and nutrient data. As a result, utilities are turning to technology as they pursue improved process stability, better effluent quality, increased energy efficiency and improved capacity. These technologies are even driving new approaches such as the ABAC (ammonia-based air flow control) strategy, an advanced air flow control strategy that has grown in popularity over the last few years.
Trends in Nutrient Removal
Nutrient removal will continue to advance as regulations tighten, encouraging heightened focus on total nutrient management. Enabled by more sophisticated technology and advanced treatment processes, utilities can now exert a smarter, more targeted approach, backed by better control and automation.
This approach also is offering new, synergistic ways to reduce energy use — always a major cost driver in wastewater treatment — and increase energy recovery. For example, new treatment methods that involve less aeration can remove more nutrients using less energy and less carbon. This enables improved primary treatment to divert more carbon over to anaerobic digestors also in order to create methane gas that can be used for energy recovery.
Another trend that will continue is the increased use of biological phosphorous removal over older chemical removal processes. New approaches to enhanced biological phosphorus removal (EBPR) are being explored and adopted, enabling biological phosphorous removal on projects where it was not previously feasible. Sidestream enhanced biological phosphorus removal (S2EBPR) is a different way of implementing biological phosphorous removal and offers two key advantages: The first is that S2EPBR makes phosphorus removal reliable for plants without enough influent carbon — or influent carbon with the right characteristics — to perform traditional biological phosphorus removal. The second advantage is that S2EBPR offers capital cost savings in retrofits.
For example, a facility may have had capacity constraints where a retrofit for enhanced phosphorous removal and the corresponding process redesign would have been far too expensive. To remedy this, the S2EBPR process can repurpose other tanks on-site, mitigating the issue and allowing a capital efficient upgrade. A current Water Research Foundation project (Project 4975) is being led by Black & Veatch to develop design guidelines, operational tools, and modeling best practices for S2EPBR configurations.
There’s no doubt that wastewater utilities are actively working to advance nutrient recovery, improve effluent quality and meet tightening regulatory requirements, as demonstrated by the industry data collected in Black & Veatch’s survey.
Enabled by new approaches, utilities are investigating advanced treatment options and more sophisticated technologies. Ultimately, this will allow them to exert a smarter, more targeted approach, expanding nutrient removal and recovery across the United States.
About the Authors
Scott Carr is a global practice and technology leader for biosolids and residuals management within Black & Veatch’s water business. He has focused his 35-year career on biosolids and residuals management, including processing and beneficial use of biosolids.
Leon Downing is a principal process engineer and innovation leader for Black & Veatch’s Water Technology Group, where he provides technology leadership and client-focused support. A senior process engineer, Downing has guided and assisted in major resource recovery projects across the United States, United Kingdom, Australia, and Denmark. He is an expert in wastewater treatment and resource recovery.
Patrick Dunlap is a wastewater process engineer within Black & Veatch’s water business, specializing in phosphorus removal, wastewater aeration systems, and advanced process control. He has 10 years of experience on wastewater projects across all regions of the United
States and in the Asia-Pacific Region.
Andrew Shaw is a global practice and technology leader in sustainability and wastewater for Black & Veatch. He has more than 25 years of experience in wastewater treatment design projects in the United Kingdom, Australia, Asia and North America. His expertise includes nutrient removal, computer modeling, instrumentation, process optimization and life cycle assessments.