Application of flow cytometry to monitor assimilable organic carbon (AOC) and microbial community changes in water.

Flow cytometry is an efficient monitoring tool for rapid cell counting, and can be applied to research on water quality and treatment. In this study, a method that employs flow cytometry and a natural microbial inoculum to determine assimilable organic carbon (AOC) was adapted for use with challenging surface waters that have a high organic and particle content, and subsequently applied in a long term river water study. AOC method optimization showed that river water bacteria could pass through a 0.2µm membrane filter, and therefore membrane filtration combined with heat treatment was required for sample sterilization. Preparation of the natural river inoculum with an acceptable yield value could only be achieved when grown using the natural water source, since growth was limited on different types of inorganic minimal media and in natural spring water. The resulting flow cytometry AOC method was reliable and reproducible, and results were comparable to the standard plate count AOC method. Size exclusion chromatography showed that both high and low molecular weight organic matter fractions were utilized by the natural AOC inoculum. Flow cytometry was used to measure both AOC levels and total cell counts in a long term study to monitor the water quality of a river which was used as a drinking water source. The method could distinguish between high nucleic acid (HNA) and low nucleic acid (LNA) groups of bacteria, and HNA bacteria were found to respond faster than LNA bacteria to seasonal changes in nutrients and water temperature.

Kinetics of natural organic matter (NOM) removal during drinking water biofiltration using different NOM characterization approaches.

To better understand biofiltration, concentration profiles of various natural organic matter (NOM) components throughout a pilot-scale drinking water biofilter were investigated using liquid chromatography - organic carbon detection (LC-OCD) and fluorescence excitation and emission matrices (FEEM). Over a 2 month period, water samples were collected from six ports at different biofilter media depths. Results showed substantial removal of biopolymers (i.e. high molecular weight (MW) NOM components as characterized by LC-OCD) and FEEM protein-like materials, but low removal of humic substances, building blocks and low MW neutrals and low MW acids. For the first time, relative biodegradability of different NOM components characterized by LC-OCD and FEEM approaches were investigated across the entire MW range and for different fluorophore compositions, in addition to establishing the biodegradation kinetics. The removal kinetics for FEEM protein-like materials were different than for the LC-OCD-based biopolymers, illustrating the complementary nature of the LC-OCD and FEEM approaches. LC-OCD biopolymers (both organic carbon and organic nitrogen) and FEEM protein-like materials were shown to follow either first or second order biodegradation kinetics. Due to the low percent removal and small number of data points, the performance of three kinetic models was not distinguishable for humic substances. Pre-filtration of samples for FEEM analyses affected the removal behaviours and/or kinetics especially of protein-like materials which was attributed to the removal of the colloidal/particulate materials.

Effect of hydraulically reversible and hydraulically irreversible fouling on the removal of MS2 and φX174 bacteriophage by an ultrafiltration membrane.

The effect of membrane fouling on the removal of enteric virus surrogates MS2 and φX174 bacteriophage by an ultrafiltration membrane was assessed under simulated full-scale drinking water treatment operating conditions. Filtration experiments of up to 8 days using either river or lake water ascertained how the membrane fouling layer affected virus removal. Organic carbon fractionation techniques identified potential foulants, including biopolymers, in the feed water and in the permeate. Hydraulically irreversible fouling could greatly improve the removal of both viruses at moderate and severe fouling conditions by up to 2.5 logs. Hydraulically reversible fouling increased virus removal only slightly, and increased removal of >0.5 log for both phage were only obtained under severe fouling conditions. The increase in virus removal due to irreversible and reversible fouling differed between the two water sources. As the degree of fouling increased, differences between the removal of the two phage decreased. Maintenance cleaning partially removed membrane foulants, however virus removal following maintenance cleaning was lower than that of the fouled membrane, it remained higher than that of the clean membrane.