Growing communities face many challenges in providing adequate wastewater treatment services for new development. Residential, industrial, or recreational construction on non-sewered land frequently raises many questions about the most reliable and cost-effective strategy for managing the future wastewater stream.
Projects are often delayed or even canceled if a community does not have the means to link a new development to the central wastewater treatment plant (WWTP), or to expand the existing conventional plant to accommodate the projected flow. But an expansion of the existing municipal WWTP may not provide the best solution. The existing plant processes may not be able to handle the variable flow rate or harsh composition of the new wastewater stream and the resultant effluent stream may endanger the environment or area residents with poor quality discharge.
As effluent discharge requirements become increasingly stringent, and many communities consider advanced wastewater treatment technologies to ensure regulatory compliance, there is a growing necessity to conserve dwindling potable water supplies with progressive water reuse programs. By restoring wastewater to reuse standards, communities and industry can produce high quality reuse water for non-potable applications such as irrigation, industrial process water or groundwater recharge.
On-site wastewater treatment with membrane bioreactor (MBR) technology is rapidly becoming the preferred method for meeting or exceeding the wastewater treatment requirements for discharge or reuse at non-sewered land development projects. MBR systems provide compact, cost-effective and easy-to-operate solutions for development projects in small communities with average daily flow of less than 1,000 GPD to over 1 MGD. Modular MBR systems are rapidly replacing aging conventional treatment systems in small communities and are also increasingly installed to service land development projects such as growing residential developments, hotels, resorts, shopping centers, office buildings, airports and campgrounds.
Heart of the system
Reinforced, hollow-fiber ultrafiltration membranes are at the heart of today’s most advanced and cost-effective MBR systems, providing many benefits to municipalities and industry. Systems such as the ZENON ZeeWeed MBR solution combine ultrafiltration (UF) membranes with biological wastewater treatment processes to eliminate the need for primary and secondary clarifiers, in providing solids separation by filtration rather than settling. This means that MBRs can produce high quality effluent at all times, regardless of the settling
characteristics of the sludge. Because sludge settling is not required, MBRs can operate at much higher mixed liquor
suspended solids concentrations, typically in the range of 8,000 to 15,000 mg/l. This enables the system to function with a relatively small bioreactor volume, and considerably reduces capital and operating costs because less land, fewer components and a smaller physical plant is required.
Hollow-fiber membranes are immersed directly into the mixed liquor and draw treated effluent into the fiber using a gentle suction. The membrane acts as a physical barrier, preventing suspended solids and pathogens from entering into the final effluent. MBR treatment works produce tertiary quality effluent that has very low levels of BOD, nitrogen, phosphorus and suspended solids (See Table 1). The ultrafiltered effluent may then be safely discharged into the environment or reused for any non-potable application.
The simple design of an MBR system enables complete wastewater treatment to be carried out in one or two steps and significantly reduces the operational equipment that the plant requires. A typical MBR wastewater treatment plant includes pretreatment for trash removal, membrane cassettes, bioreactor, permeate pumps, blowers for process and membrane scouring and clean-in-place equipment for membrane maintenance.
New MBR facilities can be constructed in virtually any location and can occupy as little as one-fifth of the space that a conventional WWTP requires, offering significant savings in land acquisition and construction costs. Moreover, the small space requirements and modular construction provides a great deal of flexibility in design. Often the entire WWTP can be enclosed within a portion of the building that the MBR services, or within a small, separate building. Buildings can also be architecturally crafted to blend in with the surrounding area. When completed, the discreet design, low odor and quiet operation of MBR plants makes them barely noticeable to passersby.
The operation of an MBR system is highly automated, and most small systems do not require full-time operators, as system performance can be monitored remotely. Fibers can be easily cleaned with a clean-in-place method or using an optional backpulsing process that delivers permeate water back through the membranes. This dislodges any particles that may adhere to the membranes. Intermittent aeration of the membranes is also used to scour debris from the fibers and provides mixing within the process tank to maintain solids in suspension. In-situ membrane cleaning can also be automatically performed if membrane permeability falls below a specified level.
Current applications
Hundreds of small MBR systems are currently providing localized wastewater treatment to communities, industries and recreational facilities in the U.S. and throughout the world.
The following summaries provide a brief overview of various MBR applications in the U.S. that have enabled advanced wastewater treatment in land development projects.
New York City
The Solaire is a 293-unit environmentally sustainable, green building on the bank of the Hudson River in New York City. It is the first multi-family residential building in the U.S. to incorporate an urban water reuse system as part of its environmentally responsible features. In the building’s basement, a 25,000 GPD ZENON ZeeWeed MBR recycles all of the wastewater produced by the residents of the building. The treated effluent is reused as flush water in the toilets, make up water for the building’s cooling tower and for irrigation in a neighboring park. By reusing wastewater, the building’s residents dramatically reduce their demand on New York’s potable water supply and also minimize their impact on the city’s municipal wastewater treatment plant.
Mill Run, Pa.
In November 2003, Fallingwater, Frank Lloyd Wright’s architectural masterpiece, replaced an aging septic system with a ZeeWeed MBR. Concerns had been raised that the septic system might soon fail and discharge sewage into Bear Run Creek––an environmentally sensitive stream that tumbles over the waterfall beneath the home’s cantilevered floors. The 8,840 GPD system is housed in a separate 1,800 sq ft building discreetly located away from the facility. The system recycles 100% of the wastewater that is produced by the facility’s 140,000 annual visitors and reuses it as flush water in the Visitor’s Pavilion. Any excess treated wastewater is used for irrigating the surrounding gardens.
Lincoln, Calif.
Each day about 8,000 visitors walk through the doors of this 200,000-sq ft Las Vegas-style casino in northern California’s Sierra Foothills, about an hour west of Reno, Nev.
Developed on an unserviced parcel of land in the United Auburn Indian Community, the casino uses a 350,000 GPD ZeeWeed MBR to treat wastewater produced within the complex. The effluent produced by the MBR is reused for toilet flush water throughout the building.
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