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'MBR Technology' Santa Paula's Answer to Wastewater Treatment Needs
The City of Santa Paula, California, opted to pursue a design-build-operate-finance strategy to construct a new state-of-the-art water recycling facility designed to meet the city’s current and future wastewater treatment needs. This new Membrane Bioreactor (MBR) technology combines biological wastewater treatment and membrane filtration into one unit process, producing a consistently high quality effluent in an extremely compact footprint and are energy efficient and provide significantly lower lifecycle costs than other alternatives.

The City of Santa Paula, California, recently completed construction of the first water recycling facility built under California government code 5956 to encourage private investment aiding in solving public infrastructure needs. The city selected the PERC Water and Alinda Capital team to design, build, operate and finance a 7.2 MGD peak day flow (10.4 MGD peak hour) membrane bioreactor facility that will allow Santa Paula to meet current and future wastewater treatment needs while complying with environmental standards. The city also expects the new facility to enable the use of recycled wastewater for irrigation.

Santa Paula chose Membrane Bioreactor (MBR) technology because it combines biological wastewater treatment and membrane filtration into one unit process, producing a consistently high quality effluent in an extremely compact footprint.

PERC Water selected the single header PURONTM membrane filtration modules from Koch Membrane Systems (KMS) to incorporate into the MBR design, because they are energy efficient and provide significantly lower lifecycle costs than other alternatives. The Santa Paula project is the first large MBR installation in North America to use the KMS PURON membrane filtration modules.

Aging Infrastructure Needed to Be Replaced
Santa Paula is a city 65 miles northwest of Los Angeles and in the rich agricultural Santa Clara River Valley. Surrounded by rolling hills, rugged mountain peaks, and orange, lemon and avocado groves, Santa Paula is sometimes called the 'Citrus Capital of the World'.

Santa Paula's wastewater treatment facility was constructed in 1939 and today serves about 30,000 residents. Hindered by failing infrastructure and dated technology, the facility was in violation of several discharge requirements issued by the Los Angeles Regional Water Quality Control Board (RWQCB), and had received more than 3,000 violations and fines in excess of USD 8 million. To comply with the increasingly stringent regulations, the city made several plant modifications, but ultimately failed to achieve the operating requirements.

A consent judgment with the state issued in 2007 allowed the city to apply the fines toward a new wastewater treatment plant, if the facility was completed and in compliant operation by December 15, 2010. Santa Paula opted to pursue a designbuild- operate-finance strategy to construct a new state-of-the-art water recycling facility designed to meet the city’s current and future wastewater treatment needs. The project was awarded to Santa Paula Water, a partnership of PERC Water and Alinda Capital, in May, 2008. The new facility is designed for 7.2 MGD peak day flow (10.4 MGD peak hour) and 3.4 MGD average day flow capacity with the ability to expand to 4.2 MGD. The system was completed and in full operation in May 2010, seven months ahead of the December 15, 2010 deadline.

MBR Technology Chosen for Energy Effi cient and Space Saving Features
After a thorough assessment of the facility needs, Santa Paula Water chose MBR technology to provide advanced treatment process, increase plant capacity and reuse water for irrigation. MBR systems are increasingly used in locations where water resources are scarce; reusable quality effluent is desirable; space availability is limited; and stringent discharge standards are in effect. These locations may include small communities, housing developments, commercial developments, resorts, hotels, malls, schools and golf courses. The MBR is also employed for industrial applications to recycle process water, reducing wastewater disposal costs and reducing water footprints.

The Santa Paula MBR facility has a compact design, with fully redundant headwork, conservative and efficient aeration design, biological foam spray system, hollow fibre membranes with incorporated aeration. Effluent from the system will discharge into evaporation or percolation ponds, and a portion of the water will eventually be used for irrigation. Figure 1 provides a general illustration of the overall system.

The new water recycling facility is designed to produce an effluent that meets or exceeds all current environmental wastewater quality standards mandated by the US EPA and the RWQCB. The MBR is designed to produce a finished effluent with biochemical oxygen demand and total suspended solids concentrations of less than five milligrams per litre, total nitrogen less than 8 mg/ L and turbidity less than 0.2 Nephelometric Turbidity Units. Table 1 shows the facility’s water quality results for October 2010.

MBR Requires Careful Design to Meet Water Quality Objectives An MBR is a biological process that combines secondary and tertiary treatment using a membrane filtration process. Because membranes are used to provide the necessary solids-liquid separation, MBR effluent is consistently high quality with low turbidity, low bacterial counts, and low TSS and NTU. The filtrate quality, in many instances, is suitable for feeding directly into a reverse osmosis (RO) process, if required in the future. An additional advantage of an MBR system is its compact footprint. This is achieved by replacing the secondary clarification process with membrane separation and by operating the biological process with higher mixed liquor suspended solids than conventional activated sludge systems.

Despite its advantages, using membranes for solids-liquid separation requires careful assessment of several critical design elements. Table 2 shows these design requirements along with a brief overview of how they were handled in the Santa Paula Water project.

PURON Membrane Filtration Modules Selected for Energy Effi ciency and Ease of Operations
PERC Water turned to Koch Membrane Systems’ PURON membrane modules as a cost-effective and energy-efficient solution to meet the RWQCB’s stringent discharge requirements. PURON membrane modules produce high-quality effluent that meets stringent water reuse and recycling requirements, while significantly reducing the treatment system footprint, installation cost, and manpower commitment, all key requirements for the Santa Paula site.

According to Juergen Nick, Vice President (design and engineering), PERC Water, “The water recycling technology we are employing in the Santa Paula facility sets the industry bar to help control and minimise operational energy costs within the smallest environmental footprint possible. As membrane scouring and biological aeration account for nearly half of the facility’s power consumption, PERC Water chose to employ the most energy-efficient air production and usage systems on the market. In total, 24 PSH-1500 modules were installed, making it one of the largest MBR installations in North America."

PURON modules are energyefficient, with the lowest energy demand of all commercially available MBR modules. The system is easy-to-operate, with features that are designed to provide significantly lower lifecycle costs, including a single header design that provides better solids management in the module, braided fibers to reduce the risk of fiber breakage, and highly effective air scouring that virtually eliminates sludging.

An important advantage of the patented PURON module is the use of a single header with reinforced hollow fibres that are fixed only at the bottom. The sealed upper end of the fibre is allowed to float freely. The free floating tip design eliminates the build-up of hair and fibrous materials that typically clog the upper ends of membrane fibres in MBR module designs that employ both top and bottom headers.

Solids and particulates, including bacteria, are retained by the membrane and remain on the outside, while permeate is drawn through the membrane to the inside of the fibres. The outsideto- inside flow pattern provides optimal solids management and a high flow-rate. Figure 2 illustrates the single header design of the PURON module’s fibre bundles.

The Santa Paula facility includes the larger 1,500 m2 PURON module, which simplifies design, operation and retrofit of large-scale MBR plants. The improved submerged membrane module features greater packing density, lower energy costs for aeration, and simplified installation, while providing even greater compatibility with other commercially available systems. The 1,500 m2 module is particularly significant because it was specifically designed for largescale MBR projects.

Features such as an optimised permeate extraction manifold and air supply lines reduce the number of piping connections during installation. For additional flexibility, the new product line enables users to easily retrofit the advanced PURON technology into systems with comparably sized modules. Figure 3 shows how the module works.

In addition, to simplify membrane cleaning and maintenance, the central aeration system and the bottom header have been redesigned. The new aeration system reduces the flow rate during air scouring, resulting in a decrease in air usage by up to 20 per cent over the original design. PERC Water’s innovative design uses five acres less land than would be required by a conventional wastewater treatment facility. The plan includes a recycling education centre, where local students can learn how water recycling facilities function. In its first few months of operation, the power consumption of the plant was only 4.4 kWh/1000 gallons treated. The consumption is based on power used by all processes throughout the facility including digestion, building power, MBR Process, UV System, RO System etc. As flows increase, it is expected that the power consumption per thousand gallons will further decrease. With the equipment selected for this facility, Santa Paula’s MBR promises to be one of the most energy-efficient MBR installations in the world.