H.J. Fallowfield

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.

The adsorption of cyanobacterial hepatotoxins from water onto soil during batch experiments

Public health concerns associated with cyanobacteria, both chronic and acute, arise from their ability to produce toxins. Rural communities within Australia and those in developing countries require an inexpensive and low-cost method for removing toxins from drinking water. A candidate technology is bank filtration. Adsorption of cyanobacterial hepatotoxins was measured in batch studies to determine the applicability of bank filtration as an efficient removal strategy. Five soils with different physicochemical properties were collected from regions around South Australia. The soils were mixed with either nodularin or microcystin-LR in distilled water and buffered solutions (pH 4.8, 6.9 and 9.1). Additionally, nodularin was mixed in unbuffered solutions (pH 4.8 and 8.9). The three soils with the high clay and/or organic carbon contents (Paringa A, McLaren Flat and Lakes Plains) had the higher nodularin adsorption coefficients, ranging from 0.2 to 16.59 L kg-1. Soil suspensions in acetate buffer (pH 4.8) generally produced significantly higher nodularin adsorption coefficients, when compared to the other buffer systems. The background interference from the ionic strength of the buffers, however, made interpretation of the effect of pH on toxin sorption difficult. Increases in solution ionic strength, from freshwater to seawater, resulted in corresponding increases in the nodularin adsorption coefficients for all sites, except the sandy Hallett Cove site. The implications for bank filtration are that higher water pH values and lower salinities will enhance the in situ mobility of the toxins, resulting in an increased distance of filtration through the river bank before toxin free water could be abstracted for human consumption.

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.

The potential of riverbank filtration for drinking water supplies in relation to microsystin removal in brackish aquifers

In semi-arid areas, pumping town water supplies from alluvium adjacent a stream rather than the stream itself has been used to reduce turbidity and has potential to remove blue-green algal toxins, such as microsystin. However for some rivers, such as the River Murray in South Eastern Australia, the ambient groundwater of unconfined aquifers skirting some reaches of the river is saline. This paper examines the compatibility of two constraints on the quality of water recovered from bank filtration schemes; that (1) removal of cyanobacterial toxins is adequate and (2) salinity is acceptable for drinking water supplies. Adsorption and biodegradation characteristics of a cyanobacterial hepatotoxin, microsystin, in porous media were quantified and these results are summarised in the current analysis. It was found that riverbank filtration schemes could meet both criteria in a limited range of conditions, excluding locations where saline groundwater discharges to a river. However, on a river meander that had been flushed due to a hydraulic gradient induced by a lock, several feasible positions for bank filtration wells were compared and a best location meeting salinity and microsystin criteria with least-energy pumping cost was identified. The simple approach developed is intended to be used to assess feasibility of alternative designs for bank filtration schemes in semi-arid areas before commencing field studies.

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).

Effect of irradiance, temperature and salinity on growth and toxin production by Nodularia spumigena

The object of this work was to determine, using a full-factorial experiment, the influence of temperature, irradiance and salinity on growth and hepatotoxin production by Nodularia spumigena, isolated from Lake Alexandrina in the south-east of South Australia. Higher levels of biomass (determined as particulate organic carbon, POC), toxin production and intracellular toxin concentration per mg POC were produced under light limited conditions (30 μmol m−2 s−1) and at salinities equal to or greater than those experienced in Lake Alexandrina. Both highest biomass and total toxin production rates were recorded at temperatures equal to or greater than those of the lake (20 and 30 °C). The temperature at which maximum biomass and toxin production was recorded decreased from 30 °C for cultures grown at 30 μmol m−2 s−1 to 20 °C when grown at 80 μmol m−2 s−1. In contrast, intracellular toxin per mg POC was highest at the lowest growth temperature, 10 °C, at both 30 and 80 μmol m−2 s−1. It appears that the optimum temperature for biosynthetic pathways used in the production of toxin is lower than the optimum temperature for those pathways associated with growth. Intracellular toxin levels were higher in cells cultured at 10 °C/30 μmol m−2 s−1 whereas the majority of the toxin was extracellular in cells grown at 30 °C/30 μmol m−2 s−1. This implies that the highest concentration of toxin in lake water would occur under high temperature and high irradiance conditions. Individual environmental parameters of salinity, irradiance and temperature were all shown to influence growth and toxin production. Notwithstanding, the overall influence of these three parameters on toxin production was mediated through their effect upon growth rate.

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).

Modelling microalgal productivity in a High Rate Algal Pond based on wavelength dependent optical properties

A model is presented to predict algal biomass concentration and productivity in a High Rate Algal Pond (HRAP) at all possible combinations of incident photon flux density (PFD), pond depth and hydraulic retention time (HRT). The total extinction coefficientkt and the absorption coefficient ka of algal biomass were measured at 1 nm intervals. Thekt values were used to calculate the underwater light climate, which included the spectral narrowing of the photon flux density with increasing depth. The number of quanta absorbed (QA) from the photosynthetic available radiation (PAR) was calculated using theka/kt ratio and incident PFD at 1 nm intervals. Algal oxygen production is related to QA by the quantum requirement (QR), which was determined fromka,and the slope of the photosynthesis versus irradiance curve (α). Based on this calculation we propose a new concept: the compensating absorption rate (CAR), which represents the rate of photon absorption necessary to balance oxygen consuming processes. The model calculated productivities using literature data on HRT, pond depth and incident PFD, that compared well with the actual measured productivities. To achieve optimal HRAP productivities under fluctuating climatological conditions, we propose a pond management strategy based on model simulations.

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.