MBR systems increasingly are used in locations where water resources are scarce, reusable quality effluent is desirable, space availability is limited, and/or 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 headworks, conservative and efficient aeration design, biological foam spray system, hollow fibre membranes with incorporated aeration. Effluent from the system will discharge into evaporation/percolation ponds, and a portion of the water will eventually be used for irrigation.

The new water recycling facility is designed to produce an effluent that meets or exceeds all current environmental wastewater quality standards mandated by the U.S. 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 5 milligrams per litre (mg/L), total nitrogen less than 8 mg/L and turbidity less than 0.2 Nephelometric Turbidity Units.

MBR design

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.

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 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, PERC Water's vice president of design and engineering: “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 an energy-efficient air production and usage system, Koch Membrane Systems' PURON membranes. In total, 24 PSH-1500 modules were installed, making it one of the largest MBR installations in North America.”

PURON modules are energy-efficient. The system is claimed to be 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 fibres to reduce the risk of fibre 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 outside-to-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 large-scale 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% 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 and RO System. As flows increase, it is expected that the power consumption per thousand gallons will further decrease.