Two-temperature membrane filter method for enumerating fecal coliform bacteria from chlorinated effluents

Area of Science:

• Environmental microbiology
• Water quality assessment
• Sanitation science

Background:

• Standard membrane filter (MF) techniques show limitations in recovering fecal coliform bacteria from chlorinated sewage effluents.
• The multiple-tube (most-probable-number [MPN]) procedure is often considered more effective but is more complex.
• Accurate enumeration of fecal coliforms is crucial for assessing the effectiveness of wastewater treatment and disinfection.

Purpose of the Study:

• To develop and evaluate a modified membrane filter (MF) method for improved recovery of fecal coliform bacteria.
• To compare the efficacy of the modified MF technique against the standard MF method and the MPN procedure.
• To determine the suitability of the modified MF method for analyzing chlorinated primary and secondary sewage effluents.

Main Methods:

• A modified MF method was developed incorporating a specific preincubation schedule: 5 hours at 35°C followed by 18±1 hours at 44.5°C.
• The modified MF technique and the standard MF technique were evaluated using both laboratory- and plant-chlorinated primary and secondary effluents.
• Results from the MF methods were compared with those obtained using the multiple-tube (MPN) procedure.

Main Results:

• The modified MF method demonstrated significantly improved recovery of fecal coliforms compared to the standard MF technique.
• Average fecal coliform recovery with the standard MF procedure was only 14% of MPN counts, while the modified technique achieved 68% of MPN counts.
• Agreement between the modified MF method and the MPN technique was highest for samples from secondary treatment plants.

Conclusions:

• The modified membrane filter (MF) technique, with its adjusted incubation schedule, substantially enhances fecal coliform recovery from chlorinated sewage effluents.
• This improved MF method provides a more reliable and valuable tool for enumerating fecal coliforms, complementing the MPN technique.
• The findings support the adoption of the modified MF procedure for more accurate water quality monitoring in wastewater treatment.