Determining optimum nutrient management strategies for “bubble” permits – a case history based on the hampton roads sanitation district james river discharge
The Hampton Roads Sanitation District (HRSD) in Southeastern Virginia must comply with a “bubble” annual nutrient discharge limitation for its seven wastewater treatment plants (WWTPs) which discharge to the James River. Most critical is a limitation of annual total nitrogen (TN) discharges to no more than 2,720,000 kg/yr (6,000,000 lb/yr). Multi-criteria analysis and risk analysis allowed the HRSD to develop a flexible and robust plan to comply with these nutrient discharge limitations. Multi-criteria analysis allowed HRSD to define the characteristics of ideal nutrient removal options and to prioritize a variety of options relative to these characteristics and to determine which of the available options are the most desirable. Risk analysis then allowed a diverse portfolio of options to be assembled to accommodate a variety of operating scenarios and to meet a variety of objectives. The portfolio of options accommodated both typical operating conditions and also unusual operating conditions such as plant construction, facilities being removed from operation for maintenance, and plant upsets. A concept was developed concerning how the portfolio of options would be used, although this concept will be further refined through use.
For HRSD, the plan involved the addition of bioaugmentation and carbon addition facilities to the Nansemond (NP) WWTP and the staged addition of the integrated fixed film activated sludge (IFAS) process to the James River (JR) WWTP. The VIP WWTP will also continue to be operated to maximize nutrient removal. Chemically enhanced primary treatment (CEPT) at the Boat Harbor (BH) WWTP, flow diversions from the Chesapeake Elizabeth (CE) and NP WWTPs to the Atlantic (AT) WWTP which does not discharge to the James River, and carbon addition and CEPT at the NP and VIP WWTPs provide contingent options that will be “turned on and turned off”, as necessary, to achieve compliance. These options will allow compliance with James River nutrient discharge limitations by the January 1, 2011 deadline, along with the treatment of flows diverted from the York River (YR) WWTP to accommodate construction at this plant. These options, along with upgrades of the Army Base (AB) and YR WWTPs to limit of treatment (LOT) nutrient removal capabilities, will provide sufficient capability to meet HRSD’s James River nutrient river discharge limitations through the planning period (2026). The cost of unique facilities required to comply with James River discharge limitations by 2011 is estimated at about $20 M in 2006 for plants with a combined design treatment capacity of 679,400 m3/day (179.5 mg). These results demonstrate the benefit of multi-criteria and risk analysis to develop a robust and cost-effective portfolio of options.