Elsevier

Water Research

Volume 209, 1 February 2022, 117898
Water Research

The significance of the biomass subfraction of high-MW organic carbon for the microbial growth and maintenance potential of disinfectant-free drinking water produced from surface water

https://doi.org/10.1016/j.watres.2021.117898Get rights and content
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Highlights

  • High-MW OC governs the microbial growth potential (MGP) of treated surface water.

  • MGP and high-MW OC concentration have opposite seasonal patterns in treated water.

  • MGP is mostly attributable to the high-MW OC's microbial biomass subfraction.

  • This results in seasonally variable ratios of the MGP – high-MW OC concentration.

  • High-MW OC consumed for biomass maintenance is important in biostability assessment.

Concise abstract

Drinking water must be sufficiently biostable to avoid excessive microbial and invertebrate growth in disinfectant-free distribution systems. The production of biologically stable drinking water is challenging for conventional surface water treatment plants using reservoirs as feed water due to the presence of slowly biodegradable particulate and high-molecular weight biopolymeric organic carbon (high-MW OC) which increases the Microbial Growth Potential (MGP) in the feed water and produced drinking water. The study presented here provides new insights in the relationship between high-MW OC and MGP for a full-scale surface water treatment plant. Controlled-conditions addition series experiments showed that MGP increases linearly with the high-MW OC concentration with a seasonally variable ratio. Laboratory filtration indicated that MGP is mainly attributable to the high-MW OC subfraction of >  0.12 µm particle size coinciding with microbial biomass. Intensive field monitoring revealed clear seasonal patterns in the plant's feed water and treated water levels of high-MW OC, biomass and MGP. These parameters reach maximum levels in the periods of high water temperature with the notable exception of the treated water's high-MW OC concentration which exhibits an opposite seasonal pattern (reflecting seasonally variable removal in the treatment). Moreover, the field monitoring showed that MGP correlates well with the concentrations of biodegradable biopolymeric OC and with microbial biomass measured as ATP (adenosine triphosphate) and cell counts, but not with the total high-MW OC concentration in the treated water. Theoretical estimations showed that the OC quantities present in and consumed by the microbial biomass are in the same order of magnitude as slowly biodegradable biopolymers. From these results it is concluded that specifically the microbial biomass-associated and biodegradable biopolymeric OC subfraction of the totally present high-MW OC is important for MGP. Finally, the MGP-assay results and theoretical calculations showed for the high-MW OC matrix that the microbial biomass’ OC consumption for maintenance is significant vis-á-vis that for growth, and that stable and high levels of biomass are sustained in the treated water which may adversely affect biological stability in the distribution network.

Keywords

biological stability, microbial growth potential, microbial biomass, biopolymers, biomass maintenance, surface water treatment

Abbreviations

AOC
Assimilable Organic Carbon
AOC-A3
slowly biodegradable biopolymeric AOC (bioassay) (µg biopolymer mix-C/L)
AOC-P17/NOX
low molecular weight, easily biodegradable AOC (bioassay) (µg acetate-C/L)
ATP
Adenosine tri phosphate
ATP0, ATPmin, ATPmax
initial, minimum and maximum ATP concentration observed during the BPP-incubation (ng/L)
BACF
Biological Activated Carbon Filtration
BPC14
Cumulative Biomass Production in the 14-day BPP-incubation (ng.d/L)
BPP
Biomass Production Potential (bioassay)
Cg
OC consumption by microbial biomass growth during BPP-incubation (µg/L)
Cm
OC consumption by microbial biomass maintenance during BPP-incubation (µg/L)
kDa
kilo Dalton = 1000 Da (g/mol)
LC-OCD
Liquid Chromatography – Organic Carbon Detection
mD
biomass specific daily OC consumption for maintenance (µg nutrient-C/(d.µg biomass-C))
MGP
Microbial Growth Potential
OC
Organic Carbon
R2
Coefficient of determination (–)
RP
Pearson correlation coefficient (–)
RS
Spearman-rho correlation coefficient (–)
S…
Supplementary Information (Figure or Table followed by number)
TOC
Total Organic Carbon (mg/L)

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