Effectiveness of a Membrane Bioreactor on Weak Domestic Wastewater Containing Polychlorinated Biphenyls

CDM is working with a confidential industrial client to replace/upgrade one of its older wastewater treatment plants. After an initial screening, CDM recommended that a membrane bioreactor (MBR) be evaluated as a replacement for their existing 65,000-gallon-per-day (gpd) wastewater treatment plant (WWTP). The evaluation began with a 5-month pilot (40-gpd) study, the results of which will be reported in this paper.The influent to the existing WWTP is unique because it has: a low biological oxygen demand (BOD) concentration - less than 100 milligrams per liter (mg/l); an ammonia concentration that varied from 5 mg/l to 30 mg/l; a polychlorinated biphenyls (PCB) concentration that ranged from 2.69 μg/l to 33.79 μg/l during the pilot period; and detectable concentrations of polycyclic aromatic hydrocarbons (PAHs), phenols, oil and grease (O&G), and total cyanide.The specific purpose of the pilot study was:to determine if the MBR;amp;#x0027;s treatment could be as effective as the existing WWTP;to develop the design criteria required for the full-scale MBR system, i.e. flux rate, peak flux rate, and hydraulic retention time;to determine the requirements to maintain the nitrification process; andto determine if the liquid/solid separation component of the MBR was adequate for PCB removal.The pilot apparatus used was a ZW-10 demonstration unit manufactured by Zenon Environmental, Inc. In addition to this unit, a granular activated carbon (GAC) column filter was added after the MBR, in anticipation of PCBs and/or PAHs passing through the MBR.To evaluate the performance of the MBR with respect to PCB removal, PCB Aroclors were analyzed for the influent, effluent, and mixed liquor suspended solids (MLSS).The results of the pilot study showed that:The particle size distribution of MBR effluent that passed through the MBR was larger than the absolute pore size of 0.1 μm of the MBR.The MBR removed BOD, total Kjeldahl nitrogen (TKN), O&G, total cyanide, total PAHS, and phenols below the concentrations that had been achieved by the existing WWTP.The MBR reduced the fecal coliform to below 200 cfu/100 ml.The MBR was unable to remove PCBs (based on Aroclors) to below the detection limit; therefore, tertiary treatment (carbon absorption) would be required for full scale.