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.

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.

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.