Measuring Bacterial Growth Potential of Ultra-Low Nutrient Drinking Water Produced by Reverse Osmosis: Effect of Sample Pre-treatment and Bacterial Inoculum

Abstract

Measuring bacterial growth potential (BGP) involves sample pre-treatment and inoculation, both of which may introduce contaminants in ultra-low nutrient water (e.g., remineralized RO permeate). Pasteurization pre-treatment may lead to denaturing of nutrients, and membrane filtration may leach/remove nutrients into/from water samples. Inoculating remineralized RO permeate samples with natural bacteria from conventional drinking water leads to undesired nutrient addition, which could be avoided by using the remineralized RO permeate itself as inoculum. Therefore, this study examined the effect of pasteurization and membrane filtration on the BGP of remineralized RO permeate. In addition, the possibility of using bacteria from remineralized RO permeate as inoculum was investigated by evaluating their ability to utilize organic carbon that is readily available (acetate, glucose) or complex (laminarin, gelatin, and natural dissolved organic carbon), as compared with bacteria from conventional drinking water. The results showed that membrane filtration pre-treatment increased (140-320%) the BGP of remineralized RO permeate despite the extensive soaking and flushing of filters (>350 h), whereas no effect was observed on the BGP of conventional drinking water owing to its high nutrient content. Pasteurization pre-treatment had insignificant effects on the BGP of both water types. Remineralized RO permeate bacteria showed limitations in utilizing complex organic carbon compared with bacteria from conventional drinking water. In conclusion, the BGP bioassay for ultra-low nutrient water (e.g., remineralized RO permeate) should consider pasteurization pre-treatment. However, an inoculum comprising bacteria from remineralized RO permeate is not recommended as the bacterial consortium was shown to be limited in terms of the compounds they could utilize for growth.

Evaluation of DNA extraction yield from a chlorinated drinking water distribution system

“…The same author reported that the result of 16s rRNA qPCR from those samples was below the negative control (< 10 2 copies genes/mL) and thus prevented further sequencing analysis (i.e., metagenomics and metatranscriptomics) [ 38 ]. Our study confirms a vast biomass reduction in the drinking water produced by RO, as previously reported [ 39 – 41 ]. The presence of residual chlorine further suppresses the bacterial content (i.e., lower cell density) in the water.…”

Safeguarding the microbial water quality from source to tap

“…When producing biostable water, microbial growth is controlled by one or more disinfection strategies such as membrane filtration (e.g., reverse osmosis (RO) 30 ), UV irradiation, ozone or AOP. The latter is often applied in combination with extensive biological treatment such as sand filters or biological active carbon (BAC) filtration.…”

Assessing biological stability of drinking water produced by reverse osmosis and remineralisation : method development and application

“…The observations might be different for surface water systems subjected to significant seasonal variations, for which a sampling program including different seasons is Multi-parametric assessment of biological stability of drinking water produced from groundwater: reverse osmosis vs. conventional treatment high recommended. Though the effect of seasonal variations on the analysed parameters was beyond the focus of this study, negative influences of post-treatment were previously demonstrated throughout the year (Sousi et al, 2020b).…”

“…The carbon limitation has been commonly found in many types of water (Huck, 1990;Hu et al, 1999;van der Kooij, 2000;Liu et al, 2015;Prest et al, 2016a), as observed also for water types tested in this study even when the phosphate concentration was very low (<1 μg/L PO4-P). Moreover, the carbon limitation in all samples was confirmed with the canonical correspondence analysis (CCA) without identifying which carbon fraction was the most relevant for growth, where a previous study showed that these bacteria could grow on carbon with different molecular characteristics ranging from readily available to more complex organic carbon (Sousi et al, 2020b). Similarly, the link between the presence of different OTUs and carbon fractions needs to be further explored.…”

“…The bacterial growth potential (BGP) of water was measured according to . In short, samples of Tap-water and RO-water were collected in AOC-free glassware that is treated at 550 °C for 6 h. Thereafter, samples were pre-treated at the laboratory by pasteurisation (70 °C for 30 min) to inactivate indigenous bacteria before inoculating with ~10 4 ICC/mL (ICC: intact cell count) of a natural bacteria consortium originating from Tapwater, where using RO permeate bacteria as an inoculum is not recommended due to their limited ability to consume complex organic carbon (Sousi et al, 2020b). Pre-treated samples were distributed between three individual AOC-free vials (i.e., triplicate measurements per sample), incubated in the dark at 30 °C, and lastly measured for intact cell count (ICC) or ATP over a growth period of 20 days.…”