Recharge Regulations Drive MBR Development

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Located in Wrentham, Mass., the 144-bed, 36,000-sq-ft Maples Rehabilitation and Nursing Center was operating with a failed leach field system and subsequently was violating the discharge limits for the state-promulgated Zone 2 Aquifer Recharge Regulations. The state DEP dictates plant discharge requirements relative to the proximity of the receiving stream within several drinking water district recharge zones. The closer a plant discharge is to a district’s recharge zone, the more stringent the parameters for discharge become.

Utilizing the California Title 22 reuse standards, the state DEP required the Maples facility to seek out a best available technology (BAT) to replace its failing leach field operation. Early in 2004, the Maples management team selected Beta Engineers as their consultant of record. Beta identified the Enviroquip MBR system as the viable solution of choice after careful consideration.

Beta determined the parameters for design and felt that an overall limited footprint Enviroquip MBR BAT approach would allow the owner to realize the greatest cost savings over the system life cycle. The new facility design mandated constituent discharge loadings to meet or fall below the following levels: BOD5 < 5 parts per million (ppm), total suspended solids (TSS) < 5 ppm, NH3 < 1 ppm, TN < 10 ppm based upon a raw loading of BOD5 = 400 ppm, TSS = 203 ppm, NH3 = 44 ppm and TN = 61 ppm.

Enviroquip employed a standard MLE design approach utilizing a single anoxic basin with dual pre-aeration and MBR basins and two ES 100 units placed for duty service. A full denitrification volume was allotted in the anoxic zone, with the nitrifying pre-aeration basins segregated to allow for fine bubble equipment maintenance during plant operation. Plant influent is collected in a below grade EQ basin and directed into the facility fine screen system via lift pumps. A standard anoxic, pre-aeration MBR flow path is employed and permeate produced is directed equally into one of four leach fields.

The following data reflects the average of over two years worth of influent criteria data. BOD5 concentrations for design were set at 400 ppm and dependent on the internal facility functions, such as laundry, floor cleaning or kitchen wash-down, the loadings have exceeded design conditions on a routine basis.

BOD: 180.82
TSS: 119.54
TS: 585.13
NH3: 14.821
NO2: 0.001
NO3: 0.1695
TKN: 27.436
Total N: 27.606
O&G: 25.296
Even with the peaks in design loadings, the plant routinely discharges a high–quality, low-nutrient effluent as represented by the same two year data set average.
BOD: 1.7255
TSS: 0
TS: 375
NH3: 0.2878
NO2: 0
NO3: 1.85
TKN: 1.0414
Total N: 3.6505263

Enviroquip Kubota MBR systems trend several discharge parameters for troubleshooting operations and performance quantification. The required Title 22 reuse requirements for turbidity for a given discharge period are 5 NTU. The Maples facility over the first few years of operation has reported an average turbidity of 0.0806 NTU. The listed MLSS concentrations are reflective of years one and two; these higher operating MLSS levels function to act as a buffer against spike chemical loadings.

Turbidity: 0.0806
MLSS 1: 10692.86
MLSS 2: 11720

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