N.J. Cromar

Use of microcosms to determine persistence of Escherichia coli in recreational coastal water and sediment and validation with in situ measurements

Aims:  To determine the persistence of the faecal indicator organism Escherichia coli in recreational coastal water and sediment using laboratory‐based microcosms and validation with in situ measurements.

Enumeration of faecal coliforms from recreational coastal sites: evaluation of techniques for the separation of bacteria from sediments

Aims: To identify the most efficient techniques for the separation of micro‐organisms from coastal sediments and, using these techniques, to determine the concentration of faecal indicator organisms in recreational coastal water and sediment. 
Methods and Results: Sediment samples were taken from a range of recreational coastal sites and subjected to various physical techniques to separate micro‐organisms from sediment particles. Techniques investigated included manual shaking, treatment by sonication bath for 6 and 10 min, respectively, and by sonication probe for 15 s and 1 min, respectively. The use of the sonication bath for 10 min was the most successful method for removing micro‐organisms from sediment particles where sediments consisted mainly of sand. When sediments contained considerable proportions of silt and clay, however, manual shaking was most successful. Faecal coliforms were then enumerated by membrane filtration in both water and sediment from three recreational coastal sites, chosen to represent different physical sediment characteristics, over a 12‐month period. Faecal coliform concentrations were generally greater in sediment compared with overlying water for all samples. This was most evident in sediment consisting of greater silt/clay and organic carbon content. 
Conclusions: This study demonstrated the importance of sediment characteristics in determining the most efficient method for the separation of micro‐organisms from coastal sediments. Sediment characteristics were also found to influence the persistence of micro‐organisms in coastal areas. 
Significance and Impact of the Study: Recreational coastal sediments can act as a reservoir for faecal coliforms; therefore, sampling only overlying water may greatly underestimate the risk of exposure to potentially pathogenic micro‐organisms in recreational waters.

Application of high rate nitrifying trickling filters for potable water treatment

The interference of ammonia with chlorination is a prevalent problem encountered by water treatment plants located throughout South East Asia. The efficacy of high rate, plastic-packed trickling filters as a pre-treatment process to remove low concentrations of ammonia from polluted surface water was investigated. This paper presents the findings from a series of pilot experiments, which were designed to investigate the effect of specific conditions-namely low ammonia feed concentrations (0.5-5.0 mg NH(4)-NL(-1)), variations in hydraulic surface load (72.5-145 m(3)m(-2)d(-1)) and high suspended solid loads (51+/-25 mgL(-1))-on filter nitrifying capacity. The distribution of nitrification activity throughout a trickling filter bed was also characterised. Results confirmed that high hydraulic rate trickling filters were able to operate successfully, under ammonia-N concentrations some 10- to 50-fold lower and at hydraulic loading rates 30-100 times greater than those of conventional wastewater applications. Mass transport limitations posed by low ammonia-N concentrations on overall filter performance were insignificant, where apparent nitrification rates (0.4-1.6 g NH(4)-Nm(-2)d(-1)), equivalent to that of wastewater filters were recorded. High inert suspended solid loadings had no adverse effect on nitrification. Results imply that implementation of high rate trickling filters at the front-end of a water treatment train would reduce the ammonia-related chlorine demand, thereby offering significant cost savings.

A review of the factors affecting sunlight inactivation of micro-organisms in waste stabilisation ponds: preliminary results for enterococci

Waste stabilisation ponds (WSP) are efficient, cost-effective methods of treating wastewater in rural and remote communities in Australia. It is recognised that sunlight plays a significant role in their disinfection, however, due to the poor penetration of light in turbid waters it has been hypothesised that other mechanisms may also contribute to disinfection in WSPs. To date, studies have reported various and conflicting results with regards to the relative contributions of UVA, UVB, PAR and environmental factors including pH, DO and photo-sensitisers on micro-organism disinfection. Initially we investigated the role of these environmental factors on the solar disinfection of enterococci in buffered distilled water to control for potential confounding factors within the wastewater. Die-off rate constants were measured, in sterile buffered distilled water at varying pH and dissolved oxygen concentrations, for enterococci irradiated with UVA and UVB. Enterococci were found to be predominantly inactivated by UVB (p<0.001), however, UVA was also observed to increase inactivation rates relative to the dark control (p<0.001). DO and pH were found to have no effect on inactivation rate when enterococci were irradiated with UVB (p>0.05), however, when irradiated with UVA, both DO and pH were observed to further increase inactivation rates (p<0.01).

Safe drinking water: Critical components of effective inter-agency relationships

The paper supports the development of evidence-based emergency management frameworks of cooperation between agencies in the area of drinking water and public health, as part of developing the overall risk management culture within water utilities. We employed a qualitative research design to understand critical gaps in inter-agency relations that aggravated past drinking water and health incidents and from these identified determinants of effective relationships. We identified six critical institutional relationship components that were deficient in past incidents, namely proactivity, communication, training, sharing expertise, trust and regulation. We then analysed how these components are addressed by reputable water utilities and public health departments to develop positive examples of inter-agency cooperation. Control of different risks (e.g. public health, business, and reputation) resulting from drinking water incidents should employ a preventive framework similar to the multiple barrier approach for management of drinking water quality.

Biofilms and microbially influenced cuprosolvency in domestic copper plumbing systems

Aims: To survey biofilm accumulation within domestic copper plumbing pipes in South Australian drinking water distribution systems and examine its role in copper solvation (cuprosolvency).

Structure of nitrifying biofilms in a high-rate trickling filter designed for potable water pre-treatment.

This study examined the composition and structure of nitrifying biofilms sampled from a high-rate nitrifying trickling filter which was designed to pre-treat raw surface water for potable supply. The filter was operated under a range of feed water ammonia and organic carbon concentrations that mimicked the raw water quality of poorly protected catchments. The biofilm structure was examined using a combination of fluorescence in situ hybridisation and scanning electron microscopy. Biopolymers (carbohydrate and protein) were also measured. When the filter was operated under low organic loads, nitrifiers were abundant, representing the majority of microorganisms present. Uniquely, the study identified not only Nitrospira but also the less common Nitrobacter. Small increases in organic carbon promoted the rapid growth of filamentous heterotrophs, as well as the production of large amounts of polysaccharide. Stratification of nitrifiers and heterotrophs, and high polysaccharide were observed at all filter bed depths, which coincided with the impediment of nitrification throughout most of the filter bed. Observations presented here specifically linked biofilm structure with filter functionality, physically validating previous empirical modelling hypotheses regarding competitive interactions between autotrophic and heterotrophic bacteria in biofilms.

Microbially influenced corrosion of galvanized steel pipes in aerobic water systems

Aims:  To investigate the role of heterotrophic bacteria in the corrosion of galvanized steel in the presence of water.

Separation of components of the biomass from high rate algal ponds using PercollR density gradient centrifugation

The biomass of a High Rate Algal Pond was separated into individual components of algae, bacteria and detritus. The two stage technique involved mechanical and chemical disaggregation of concentrated pond samples, followed by separation on preformed PercollR/sucrose density gradients. Throughout a diurnal cycle, monitored in September 1990, between 85 and 90% of the total chlorophylla was recovered in the algal fraction. The greatest loss of chlorophyll from the sample occurred during the concentration stage; no further losses were encountered during physical and chemical disaggregation. The technique enabled the direct gravimetric determination of the separated algal biomass. The potential applications of the technique are discussed.

Application of high rate nitrifying trickling filters to remove low concentrations of ammonia from reclaimed municipal wastewater.

The interference of ammonia with the chlorination process is a problem for many reclaimed water treatment plant operators. This paper presents the findings from a series of pilot experiments that investigated the efficacy of high flow rate nitrifying trickling filters (NTFs) for the removal of low concentrations of ammonia (0.5-3.0 mg N L(-1)) from reclaimed wastewater. Results showed that nitrification was impeded by a combination of high organic carbon loads and aquatic snails, which consumed much of the active biomass. With adequate snail control, nitrification rates (0.3-1.1 g NH(4)-N m(-2) d(-1)) equivalent to that of traditional wastewater NTFs were achieved, despite operating under comparably low ammonia feed concentrations and high hydraulic flow rates.