Near where the morning shadows of the World Trade Center used to fall is the 27-story Solaire, America's first “green” high-rise residential building. This 293-unit rental building in New York City has received a LEED Gold Certification from the U.S. Green Building Council.
A significant green component in the Solaire is a membrane bioreactor-based wastewater treatment and recycling system installed in the basement, which provides reclaimed water for use as fixture flushwater and cooling tower makeup. This is the first urban, residential treated wastewater reuse application permitted in the United States. The wastewater system, with a capacity of 25,000 gallons per day, also supplies reclaimed water to an adjacent apartment building currently under construction. With further treatment, the water is used for subsurface irrigation in the adjacent Teardrop Park. The wastewater system and its associated equipment was designed and furnished by Hillsborough, N.J.-based Applied Water Management, and began operation in January 2004.
The use of multiple features enabled the Solaire to capture all of the LEED Water Efficiency Credits and to qualify for the financial incentives offered under the New York City Department of Environmental Protection Comprehensive Water Reuse Program, which offers a 25% reduction in water and sewer charges for buildings with reuse systems that reduce potable water consumption by at least 25%. Also, implementation of the reuse system and other water conservation measures, along with compliance with other parts of Battery Park City Authority's Green Guidelines, enabled the Solaire to qualify for New York State Green Building tax credits.
The designers set up the wastewater treatment system to provide flushwater for all the toilets in the Solaire and the adjacent building at site 18B, to provide a portion of the cooling tower makeup for both buildings, and to provide water for subsurface irrigation in nearby Teardrop Park. The wastewater and recycling system at the Solaire was designed with a nominal capacity of 25,000 gallons per day with an influent waste stream of typical domestic wastewater: biochemical oxygen demand (BOD) concentrations in the range of 250 to 280 mg/L, total suspended solids (TSS) of 220 to 250 mg/L, and total nitrogen of 40 to 50 mg/L.
The building's operating engineers established a testing protocol that included initial operation of the system for two weeks with effluent going to drain. During this two-week demonstration period, the effluent was sampled three times per week for the several parameters and, after demonstrating successful compliance, was introduced into the treated effluent storage tanks. This began the initial operation period with a three-month duration during which the effluent was sampled weekly. The system was granted final approval by the Health Department when it met quality standards of less than 10 mg/L BOD and TSS, fecal coliform less than 100 colonies/100 mL, and turbidity less than 0.5 nephelometric turbidity units.
Treatment tanks consist of a series of common wall, cast-in-place concrete tanks partially recessed below the basement floor level to provide sufficient headroom over the tops of the tanks. Treated effluent is stored in two fiberglass tanks.
Tanks and Pumps
The building sewer is routed to a 6000-gallon-capacity interceptor or feed tank, which is located adjacent to the trash trap tank but at greater height above the basement floor. This tank is aerated using coarse-bubble diffusers to keep the tank mixed and to avoid septic conditions. Duplex solids-handling centrifugal pumps are mounted on top of the adjacent trash trap, with suction lines passing through the wall of the feed tank. The discharge line from these pumps rises to an elevation above the invert of the overflow from this tank, which connects with the sewer mains in the street.
An air/vacuum relief valve is installed at the high point in the pump discharge line to prevent siphoning when the pumps are not operating. The pumps are controlled by levels in the water storage and treatment tanks to provide sufficient influent to the treatment system to meet the recycled water demand. The volume of the building's wastewater not needed to meet reuse water demands flows through this feed tank to the public sewers. Valves are installed on the building sewer lines so that the treatment system can be bypassed.
Wastewater from the feed tank is pumped into a 9890-gallon, cast-in-place concrete tank termed the “trash trap” for removal of non-biodegradable solids. Effluent from the trash trap flows by gravity into the subsequent treatment tanks. This tank is vented through the odor control system to the building roof.
The biological system combines both aerobic and anoxic biological processes. Wastewater from the trash trap tank is transferred directly into the anoxic reactor section of the treatment tank. The incoming wastewater provides a carbon source for denitrifying bacteria that reduce nitrate and nitrite in nitrified mixed liquor. The anoxic reactor is mixed via periodic injections of air. A coarse-bubble diffuser system is provided to distribute air within the anoxic tank. Even though there is no nitrate limit for this system, an anoxic zone was incorporated in the process in order to recover some of the alkalinity consumed by nitrification.