Conference Agenda

Many water resource recovery facilities (WRRFs) in the Chesapeake Bay and mid-Atlantic region have completed improvements to address low effluent nutrient requirements over the last two decades. Many utilities in this region have to meet total nitrogen (TN) below 3 mg/L and total phosphorus (TP) below 0.2 mg/L.

The extensive experience in the Chesapeake Bay and mid-Atlantic regions uniquely positions utilities facing new effluent nutrient limits to learn from their peers’ experiences and adopt best practices and technology advancements for nutrient removal. This presentation will introduce key design considerations and best practices with a focus on nutrient removal experiences and introduce advances in nutrient removal technologies. Specific topics, including actual case studies, will include:

• Optimizing biological nutrient removal (BNR) Reactor Design – Providing flexibility in anaerobic, anoxic, and aerobic zones to address seasonal variations in temperature and loads allows fine-tuning of nutrient removal processes and can reduce overall volume. Providing deoxygenation zones prior to nitrified recycle pumping or unaerated zones optimizes carbon usage for nutrient removal. Proper baffle wall design to allow foam transport and surface wasting.

• Optimized Aeration System Design – Oversized aeration systems increase energy and chemical costs to meet effluent nutrient limits. Aeration systems need to be designed for flexibility over a range of variable load and environmental conditions, with a focus on maximizing turndown to avoid overaerating and allowing adoption of advanced aeration control strategies such as ammonia-based aeration control (ABAC).

• Carbon Management for Chemical Reduction – Providing flexibility in BNR reactor design and low dissolved oxygen operation improves utilization of influent carbon for nutrient removal. Many WRRFs in the region were designed to meet effluent TN limits through both BNR and denitrification filters, which require methanol addition. As WRRFs optimized their BNR processes they have become less reliant on denitrification filters, and many have discontinued methanol feed to filters.

• Next Generation Nutrient Removal – New “intensification technologies” such as aerobic granular sludge (AGS) and densified activated sludge (DAS) reduce footprints and capital costs of nutrient removal improvements. Shortcut nitrogen removal approaches such as deammonification and partial denitrification-anammox (PdNA) to lower the carbon and energy inputs required for nitrogen removal.

Many coastal waters in the US and worldwide are adversely affected by excessive nitrogen loading; however, high costs and scientific uncertainties can impede stakeholder agreement regarding the degree of nitrogen control necessary. This paper presents a case study of how regulatory agencies, utilities, and environmental groups charted a path forward for reduction of nitrogen loads to the Great Bay estuary in New Hampshire. This network of tidal rivers, bays, and harbors has experienced historical declines in seagrass. In the mid 2010s, agencies attempted to impose a nitrogen criterion that would drive stringent limits on municipal wastewater treatment facilities (WWTFs). This attempt stalled after an independent expert panel found insufficient scientific evidence that the proposed criterion would achieve the desired ecological benefits. At this impasse, utilities preferred optimization and voluntary nitrogen reductions, whereas other stakeholders continued to advocate low, enforceable nitrogen limits.

Ultimately, the parties negotiated a resolution that culminated in USEPA’s issuance of the Great Bay Total Nitrogen General Permit in 2020. This permit currently covers thirteen WWTFs, with the option for additional utilities to obtain coverage in the future. The first 5-year permit term includes enforceable nitrogen load caps, intended to limit the aggregate nitrogen loading to 100 kg/year per hectare of estuary surface area. The general permit does not include nitrogen concentration limits, and the load limits are expressed as rolling seasonal averages. This approach provides operational flexibilities to the WWTFs and allows some utilities to postpone upgrades by staying under design flow rates.

A key element of the general permit is a utility-authored adaptive management plan that charts a course for future permit terms. Under this plan, the utilities support regional water quality monitoring and scientific studies to improve our understanding of the role of nitrogen and other stressors in the Great Bay. Brown and Caldwell serves as the technical representative to the municipal alliance, advocating sound science and reasonable regulatory interpretations of the ongoing studies. This paper will describe ongoing nitrogen-seagrass studies and how those results are being considered for future general permit terms.