Kalan Braun

Reduced Efficiency of Chlorine Disinfection of Naegleria fowleri in a Drinking Water Distribution Biofilm

Naegleria fowleri associated with biofilm and biological demand water (organic matter suspended in water that consumes disinfectants) sourced from operational drinking water distribution systems (DWDSs) had significantly increased resistance to chlorine disinfection. N. fowleri survived intermittent chlorine dosing of 0.6 mg/L for 7 days in a mixed biofilm from field and laboratory-cultured Escherichia coli strains. However, N. fowleri associated with an attached drinking water distribution biofilm survived more than 30 times (20 mg/L for 3 h) the recommended concentration of chlorine for drinking water. N. fowleri showed considerably more resistance to chlorine when associated with a real field biofilm compared to the mixed laboratory biofilm. This increased resistance is likely due to not only the consumption of disinfectants by the biofilm and the reduced disinfectant penetration into the biofilm but also the composition and microbial community of the biofilm itself. The increased diversity of the field biofilm community likely increased N. fowleris resistance to chlorine disinfection compared to that of the laboratory-cultured biofilm. Previous research has been conducted in only laboratory scale models of DWDSs and laboratory-cultured biofilms. To the best of our knowledge, this is the first study demonstrating how N. fowleri can persist in a field drinking water distribution biofilm despite chlorination.

Characterization of a Drinking Water Distribution Pipeline Terminally Colonized by Naegleria fowleri

Free-living amoebae, such as Naegleria fowleri, Acanthamoeba spp., and Vermamoeba spp., have been identified as organisms of concern due to their role as hosts for pathogenic bacteria and as agents of human disease. In particular, N. fowleri is known to cause the disease primary amoebic meningoencephalitis (PAM) and can be found in drinking water systems in many countries. Understanding the temporal dynamics in relation to environmental and biological factors is vital for developing management tools for mitigating the risks of PAM. Characterizing drinking water systems in Western Australia with a combination of physical, chemical and biological measurements over the course of a year showed a close association of N. fowleri with free chlorine and distance from treatment over the course of a year. This information can be used to help design optimal management strategies for the control of N. fowleri in drinking-water-distribution systems.

Comparison of biofilm ecology supporting growth of individual Naegleria species in a drinking water distribution system

Free-living amoebae (FLA) are common components of microbial communities in drinking water distribution systems (DWDS). FLA are of clinical importance both as pathogens and as reservoirs for bacterial pathogens, so identifying the conditions promoting amoebae colonisation of DWDSs is an important public health concern for water utilities. We used high-throughput amplicon sequencing to compare eukaryotic and bacterial communities associated with DWDS biofilms supporting distinct FLA species (Naegleria fowleri, N. lovaniensis or Vermamoeba sp.) at sites with similar physical/chemical conditions. Eukaryote and bacterial communities were characteristics of different FLA species presence, and biofilms supporting Naegleria growth had higher bacterial richness and higher abundance of Proteobacteria, Bacteroidetes (bacteria), Nematoda and Rotifera (eukaryota). The eukaryotic community in the biofilms had the greatest difference in relation to the presence of N. fowleri, while the bacterial community identified individual bacterial families associated with the presence of different Naegleria species. Our results demonstrate that ecogenomics data provide a powerful tool for studying the microbial and meiobiotal content of biofilms, and, in these samples can effectively discriminate biofilm communities supporting pathogenic N. fowleri. The identification of microbial species associated with N. fowleri could further be used in the management and control of N. fowleri in DWDS.

Drought to flood: A comparative assessment of four parallel surface water treatments during the 2010–2012 inflows to the Murray–Darling Basin, South Australia

Four treatment processes; conventional coagulation, magnetic ion exchange (MIEX)/coagulation, with and without granular activated carbon (GAC), and membrane treatment combining microfiltration (MF) and nanofiltration (NF), were operated in parallel using the same source water from the Murray-Darling basin in South Australia. During the two year study, high levels of natural organic matter and turbidity arising from floods affecting the Murray-Darling basin in 2010-2012 challenged the four processes. The comparative study indicated that all four processes could effectively meet basic water quality guidelines of turbidity and colour despite challenging source water quality but that the more advanced treatments improved overall organic and bacterial removal. Interestingly, the high organics and turbidity arising from the floods resulted in improved treatment efficiency for all treatments incorporating coagulation to the extent that, despite flood conditions, treated water quality could remain comparatively constant provided that the process was operated and optimised effectively.

Comparison of coagulation and MIEX pre-treatment processes for bacterial and turbidity removal, utilizing real-time optical monitoring techniques

Jar testing and flow cytometry were used in conjunction with photometric dispersion analysis (PDA) to assess conventional alum coagulation with and without magnetic ion exchange (MIEX) pre-treatment for turbidity and bacterial removal capacity. Treatment assessment included powdered activated carbon (PAC) and pre-chlorination of the MIEX-treated raw water. Floc particles were subjected to shear forces after settling and re-suspended to gauge bacterial release potential, floc breakage and re-aggregation. MIEX in conjunction with alum coagulation achieved improved coagulation as measured by PDA but did not increase bacterial log removal value (LRV) in comparison with conventional coagulation. Pre-chlorination and PAC addition were seen to improve bacterial removal and coagulation, respectively, but were less effective for bacterial LRVs when they were used in conjunction during coagulation.

Surface analysis of pilot distribution system pipe autopsies: The relationship of organic and inorganic deposits to input water quality

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) surface analysis was conducted to characterise deposits in polyethylene pipes used in a novel pilot water distribution system (PDS). The system consisted of four (4) parallel distribution systems receiving water from different treatment processes, ranging from conventional coagulation through to an advanced membrane filtration system. After two years of operation, the distribution system was shut down and samples of pipe were collected for autopsy analysis. Inlet and outlet samples from each PDS were collected for purpose of comparison. ToF-SIMS was used to assess chemical differences in surface biofilm accumulation and particulate deposition, which resulted as a consequence of the treatment method and operational mode of each system. These data supplemented previously collected bacteriological and chemical water quality data. Results from the inorganic analysis of the pipes were consistent with corrosion and contamination events that occurred upstream in the corresponding treatment systems. Principal component analysis of data on organic constituents showed oxygen and nitrogen containing fragments were associated with the treatment inlet and outlet samples. These types of signals can often be ascribed to biofilm polysaccharides and proteins. A trend was observed when comparing samples from the same PDS, showing an association of lower molecular weight (MW) organic fragments with the inlet and higher MW organic fragments with the outlet samples.