Flow cytometry-based evaluation of the bacterial removal efficiency of a blackwater reuse treatment plant and the microbiological changes in the associated non-potable distribution network

Abstract

The study evaluated the changes in bacterial numbers across a full-scale membrane bioreactor (MBR) blackwater reuse system. Flow cytometry was used to quantify total and intact bacterial concentrations across the treatment train and during distribution of the recycled water. Membrane passage reduced bacterial numbers by up to 5-log units resulting in coliform-free permeate. A 2-log increase in bacterial cell concentration was subsequently observed after the granular activated carbon unit followed by a reduction in intact cells after chlorination, which corresponds to an overall intact bacteria removal of 3.4-log units. In the distribution network, the proportion of intact cells greatly depended on the free chlorine residual, with decreasing residual enabling regrowth. An initial target of 0.5 mg L free chlorine ensured sufficient suppression of intact cells for up to 14 days (setting the time intervals for system flushes at times of low water usage). Bacterial regrowth was only observed when the free chlorine concentration was below 0.34 mg L. Such loss of residual chlorine mainly applied to distant points in the distribution network from the blackwater reuse treatment plant (BRTP). Flushing these network points for 5 min did not substantially reduce cell numbers. At points closer to the BRTP, on the other hand, flushing reduced cell numbers by up to 1.5-log units concomitant with a decreasing proportion of intact cells. Intact cell concentrations did not correlate with DOC, total nitrogen, or soluble reactive phosphate, but it was shown that dead biomass could be efficiently converted into new biomass within seven days.

Bacterial Species Identified in the Filtrate of Microfiltration Membranes in the Separation of Activated Sludge

“…The possible origins of the bacteria in the filtrate of small pore-size membranes can be classified into three: (1) penetration through membrane, (2) incomplete disinfection of filtrate side of the membrane, and (3) regrowth in filtrate side after penetration. The penetration through membrane, as was reported in several literatures [7][8][9][10] is reasonable because the presence of bacteria was observed in the filtrate with 9 out of 14 tested pieces in this study, although no bacteria were detected during chlorination of the apparatus before the start of the filtration with activated sludge. Fig.…”

“…Indeed, a welldesigned experiment shows that some pathogenic bacteria larger than 0.2 μm penetrated from the feed-side of a membrane to the solid nutrient medium below the membrane [7]. Recent studies have demonstrated that bacteria could penetrate microfiltration membranes, even if the pore size is significantly smaller than the bacterial cell size [8][9][10]. One probable reason for this unexpected leakage is the loss of membrane integrity [11], while the deformation of bacteria would also be responsible for the passage [12].…”

Retention of Bacteria and DNA by Microfiltration Membranes in Wastewater Reclamation

“…Bacteria is often detected in the permeate side of microfiltration (MF) processes in water and wastewater treatment facilities, even when coliform-free permeate is obtained [7]. These bacteria in the MBR permeate induce biological fouling of reverse osmosis (RO) membranes in MF-RO process [8,9].…”

Characterization of Bioaerosols in Controlled Environment Broiler Houses at Different Stages of Growth

“…Prior to fluorescent staining, the filter samples were vortexed for 2 minutes at a speed of 2 revolutions per minute followed by serial dilutions of samples by using 0.22µm filtered mineral water (Evian, Evian-les-Bains, France). Fluorescent staining and flow cytometry analysis was carried out by the method described in detail by Whitton et al (2018).…”