Nitrogen removal from wastewater using a hybrid membrane-biofilm process: pilot-scale studies.

The hybrid membrane biofilm process (HMBP) is a new approach to achieving total nitrogen removal from wastewater. Air-filled, hollow-fiber membranes are placed into an activated sludge basin and bulk aeration is suppressed. A nitrifying biofilm develops on the membranes, exporting nitrate and nitrite to the bulk liquid. The nitrate and nitrite are reduced by suspended biomass using influent BOD as the electron donor. Previous research demonstrated the HMBP concept at the bench scale and explored process fundamentals. This research explored the HMBP at the pilot scale, with a 120-L reaction tank, real wastewater, and a potentially scalable configuration. Nitrification rates averaged 0.5 g N m(-2)/d(-1), which were lower than found at the bench scale, and lower than predicted by a mathematical model, but still allowed effluent total nitrogen concentrations below 6 mg N/L with an average influent total nitrogen concentration of 25 mg N/L and a hydraulic retention time of 12 hours. More than 75% of the produced nitrate and nitrite was reduced with an average influent sCOD of only 68 mg/L and an average C:N ratio of 3.1. Mass balances on carbon and nitrogen suggest that nitrogen removal via nitrite occurred. This research confirms that the HMBP process is effective for BOD and nitrogen removal from wastewater, and suggests that the grid configuration is viable for scale-up.

Detection of Cryptosporidium parvum in secondary effluents using a most probable number-polymerase chain reaction assay.

Polymerase chain reaction (PCR) was used to detect Cryptosporidium parvum oocysts in secondary effluent samples collected from activated-sludge facilities. Serial dilutions of the purified nucleic acid extracts from the samples were made and PCR was conducted to estimate the C. parvum oocyst concentration via a Poisson distribution-based most probable number (MPN). The degree of oocysts associated with wastewater particles was also evaluated. The sensitivity of the MPN-PCR assay was 20 oocysts/PCR unit. The detection limit of the concentration, extraction, and purification protocols in phosphate buffer saline spiked with a known concentration of oocysts ranged from 1.1 to 4.6 oocysts/L; the detection limit for the wastewater samples ranged from 11 to 4200 oocysts/L depending on the extent of inhibition in each sample. The recovery efficiency of the oocysts ranged from 48 to 59% in most samples. Oocysts were found in two out of seven samples with concentrations of 203 and 308 oocysts/L, as estimated by the MPN-PCR method. The oocysts were found only in the filtrate of the grab samples; particle-associated oocysts were not detected. Association of spiked C. parvum oocysts with particles in secondary effluent drawn from wastewater plants with varying operating conditions indicated a weak correlation between the degree of association and the mean cell residence time of the system.