Submitted to: Water Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2012
Publication Date: 5/15/2012
Citation: Francy, D.S., Stelzer, E.A., Bushon, R.N., Brady, A.M., Williston, A.G., Riddell, K.R., Borchardt, M.A., Spencer, S.K., Gellner, T.M. 2012. Comparative effectiveness of membrane bioreactors, conventional secondary treatment, and disinfection to remove microorganisms from municipal wastewaters. Water Research. 46:4164-4178. Interpretive Summary: Membrane bioreactors (MBR) are used for wastewater treatment; they use membranes with small pores (approximately 0.1 micron in diameter) to separate solids from liquids. Because the pore sizes are so small, pathogens that are larger than the pores, such as bacteria, can be separated with the solids and prevented from being released to the environment. Pathogenic viruses are much smaller than bacteria and might not be removed by the MBR technology. We tested the effectiveness of three MBR plants in three cities in Ohio for removing human pathogenic viruses. Viruses were detected in all the wastewater influent samples before the MBR process. After MBR treatment, virus concentrations were reduced by approximately 99.9%. We compared virus removal by the MBR process with removal we measured in two conventional wastewater treatment plants, also located in Ohio, and found MBR was more effective. Reducing levels of pathogens, like viruses, in treated wastewater before releasing it to a river or lake is important for preventing disease transmission. The MBR process may have future applications for treatment of other waste streams, such as animal manure.
Technical Abstract: Log removals of bacterial indicators, coliphage, and enteric viruses were studied in three membrane bioreactor activated-sludge (MBR) and two conventional secondary activated-sludge municipal wastewater treatment plants during three disinfection seasons (May–Oct.). In total, 73 regular samples were collected from key locations throughout treatment processes: post-preliminary, post-MBR, post-secondary, post-tertiary, and post-disinfection. Out of 19 post-preliminary samples, adenovirus by quantitative polymerase chain reaction (qPCR) was detected in all 19, enterovirus by quantitative reverse transcription polymerase chain reaction (qRT-PCR) was detected in 15, and norovirus GI by qRT-PCR was detected in 11. Norovirus GII and Hepatitis A virus were not detected in any samples, and rotavirus was detected in one sample but could not be quantified. Although culturable viruses were found in 12 out of 19 post-preliminary samples, they were not detected in any post-secondary, post-MBR, post-ultraviolet, or post-chlorine samples. Median log removals for all organisms were higher for MBR than for conventional secondary treatment. Ultraviolet disinfection after MBR treatment provided little additional removal of any organism except for somatic coliphage, whereas ultraviolet or chlorine disinfection after conventional secondary treatment provided significant log removals (above the analytical variability) of all bacterial indicators and somatic and F-specific coliphage. Log removals of adenovirus across disinfection were low in both MBR and conventional secondary plants, and few removals were above the analytical variability of 1.2 log genomic copies per liter. Log removals less than the analytical variability may just be due to artifacts of the analytical variability and not to actual removals. Based on qualitative examinations of plots showing reductions of organisms throughout treatment processes, somatic coliphage may best represent the removal of viruses across secondary treatment in both MBR and conventional secondary plants. F-specific coliphage and E. coli may best represent the removal of viruses across the disinfection process in MBR facilities, but none of the indicators represented the removal of viruses across disinfection in conventional secondary plants.