R.A. Gibbs

The role of indigenous microorganisms in suppression of Salmonella regrowth in composted biosolids.

Composting is commonly used as an effective means of stabilizing wastewater biosolids and reducing pathogens to very low concentrations. However, it has been shown that under certain conditions Salmonella can regrow in previously composted biosolids. Growth of seeded Salmonella typhimurium in composted biosolids ranging from two weeks to two years maturity was monitored. Results from sterile and non-sterile composted biosolids were compared. Seeded S. typhimurium colonized rapidly in sterilized biosolids reaching a maximum population density of more than 10(8) g(-1). Growth of seeded S. typhimurium was suppressed in non-sterilized compost with a maximum population density of less than 10(3) g(-1). There was a significant decline in the growth rate of seeded Salmonella in sterilized compost when the compost was stored, suggesting that bio-available nutrients declined with storage. However, in non-sterilized compost this was not the case. This suggests that the indigenous microflora play a significant role in suppression of Salmonella regrowth in composted biosolids. There was a strong negative correlation (-0.85) between the Salmonella inactivation rate and the maturity of compost in non-sterilized compost. The Salmonella inactivation rate was seven times higher in biosolids composting for two weeks as compared to compost stored for two years. This suggests that the antagonistic effect of indigenous microorganisms towards Salmonella declined with compost storage. It was concluded that all composted biosolids had a Salmonella regrowth potential. However, the indigenous microflora significantly reduced this regrowth potential. Long-term storage of compost is not recommended as this may increase the pathogen regrowth potential.

Selection of Salmonella typhimurium as an indicator for pathogen regrowth potential in composted biosolids.

In order to select a suitable indicator for monitoring the pathogen regrowth potential of composted biosolids, the growth kinetics of selected bacteria were investigated. Growth parameters of six serovars of Salmonella and three strains of Escherichia coli in sterilized compost were compared. Seeded Salmonella and E. coli grew rapidly, reaching population densities of more than 108 g−1 after 30 h of incubation. The specific growth rates of Salmonella serovars and E. coli strains were similar and varied from 0·49 to 0·55 h−1. The specific growth rate of the Salm. Typhimurium isolates was significantly higher than the other bacterial strains. It was concluded that an antibiotic‐resistant strain of Salm. Typhimurium can be used as an indicator for a pathogen regrowth potential test.

Molecular characterisation of Cryptosporidium outbreaks in Western and South Australia.

Molecular typing at the 18S rRNA and Gp60 loci was conducted on Cryptosporidium-positive stool samples from cases collected during 2007 Western Australian and South Australian outbreaks of cryptosporidiosis. Analysis of 48 Western Australian samples identified that all isolates were C. hominis and were from five different Gp60C. hominis subtype families. The IbA10G2 subtype was most common across all age groups (37/48). In South Australia, analysis of 24 outbreak samples, identified 21 C. hominis isolates, two C. parvum isolates and one sample with both C. hominis and C. parvum. All C. hominis isolates were identified as the IbA10G2 subtype.

Nitrogen and phosphorus removal from sewage effluent in amended sand columns

Column experiments were conducted to examine the removal of phosphorus and nitrogen from sewage effluent by passage through sand amended with bauxite refining residue (red mud). Red mud was neutralized with 5% gypsum. The study was conducted in two parts. In Part 1 the removal of nitrogen and phosphorus in mixtures of 30, 20 and 10% red mud in sand was compared. Cycles of 10 days flooding with secondary effluent and 18 days drying were used. An average of 24% nitrogen removal was obtained with 30% red mud, 9% removal with 20% red mud and very little removal with 10% red mud. An average of 91% phosphorus removal was obtained with 30% red mud, 63% removal with 20% red mud and 50% removal with 10% red mud. The decrease in phosphorus and nitrogen removal with decreasing red mud content was caused by a decrease in the adsorption capacity of the soil and an increase in the infiltration rate. In Part 2 the use of primary and secondary effluents was compared. Phosphorus removal was excellent using both primary and secondary effluents in columns packed with 30% red mud. Nitrogen removal continued to be poor using secondary effluent (16%) but was significantly greater using primary effluent (74%).

An outbreak of Salmonella enterica serotype Litchfield infection in Australia linked to consumption of contaminated papaya.

An outbreak of 26 cases of Salmonella Litchfield infection occurred in the states of Western Australia and Queensland between October 2006 and January 2007. A case-control study was conducted with 12 cases and 24 controls, and a significant association was found between illness and consumption of papaya (odds ratio, 32.8; 95% confidence interval, 2.71 to 883.5). Papaya samples were collected from 26 stores in Western Australia, and 9 of 38 samples were contaminated with Salmonella Litchfield. These samples had pulsed-field gel electrophoresis patterns and multilocus variable-number tandem-repeat analysis profiles indistinguishable from the outbreak strain. Three farms in Western Australia supplied the contaminated papaya, and two of these farms were inspected. Salmonella Litchfield was not detected in papaya samples, fungal sprays, or water samples from the farms; however, at one farm other serotypes of Salmonella were detected in untreated river water that was used for washing papaya. Only treated potable water should be used for washing fresh produce that is to be eaten raw.

Groundwater recharge of sewage effluent through amended sand

Abstract The performance of a groundwater recharge basin at the Kwinana Groundwater Recharge Site in Western Australia was monitored between 1983 and 1986. A primary aim of the monitoring programme was to study the improvement in the removal of faecal coliforms and nutrients (nitrogen and phosphorus) by amending the sand of the recharge basin with gypsum-neutralized red mud (fine bauxite refining residue). The study consisted of five operating stages. Stage 1 was a baseline study using unamended sand. Stages 2–5 were after sand amendment with red mud. Continuous flooding and flooding/drying regimes were studied with primary effluent or a mixture of primary and secondary effluents. Phosphorus removal was maintained at a high level (over 80%) in all of the stages after the sand amendment. Faecal coliform removal was generally excellent, except at the beginning of each stage when primary effluent was used, and only a thousand-fold reduction was achieved. Removal improved with time and most monitored bore samples contained no faecal coliforms/100 ml. With one exception the groundwater met water quality criteria for irrigation. Nitrogen removal of approx. 45% was obtained with primary effluent using a cycle of flooding and drying (stage 3). Continuous flooding with primary effluent (stage 5) did not improve denitrification. No nitrogen removal was observed with a mixture of two-thirds secondary effluent and one-third primary effluent.

H2S paper strip method – a bacteriological test for faecal coliforms in drinking water at various temperatures

Epidemics arising from waterborne diseases are a global health problem. Faecal contamination of drinking water is the main cause of these outbreaks. According to WHO (1996) for drinking water to be safe, a 100 ml sample should not contain any coliform bacteria. The standard methods currently used for routine testing have many limitations especially when applied in remote areas. The H2S method has been developed as an on-site, inexpensive and easy to use method to test drinking water for remote and rural areas. The present work analyses the reliability of the H2S method for detecting faecal contamination in drinking water. The minimum level of faecal coliforms that could be detected and the incubation period required at various levels of contamination were studied. The range of temperatures at which the method was effective and the incubation period required at various temperatures were also determined. The H2S method was found to be able to detect contamination down to a level of 1 CFU/100 ml of coliform bacteria. Although the H2S method could be used at a temperature range of 20 to 44oC, temperatures between 28 to 37oC gave faster results. An incubation period of only 24 hours was required at 37oC, which was found to be the most suitable incubation temperature. The incubation period increased with a decrease or increase in temperature.

A novel method for detection of viable Giardia cysts in water samples

Assessment of Giardia viability is a major requirement for public health purveyors and the water industry. Several indicators of viability such as stains, excystation and animal infectivity have been used to enumerate cysts with varying degrees of success. A combined detection-viability method for use in water samples would be useful for detecting and determining the viability of cysts in raw and drinking waters and the efficacy of disinfection at treatment plants. Distilled water samples were seeded with purified Giardia cysts and incubated with fluorescein diacetate (FDA) initially to stain viable cysts followed by tetramethyl red labelled anti- Giardia monoclonal antibodies (TMR) for confirmation of identity. As a result of FDA staining, green fluorescence of intact viable cysts was observed microscopically using a 450-490 nm exciter filter while nonviable cysts were not stained. Giardia cysts reacted positively with TMR and glowed red using a triple band microscope filter with excitations of 400/450/570 nm. At this wavelength a combination of FDA and TMR stained viable cysts green internally with a red wall while nonviable cysts only stained red. This simple, reliable and quick method allowed differentiation of Giardia cysts in water samples while simultaneously determining their viability.

Evaluation of culture media for detection of salmonellae in composted biosolids

Abstract Although US EPA sewage sludge regulations include monitoring for salmonellae, the relative efficiency of various culture methods for detecting salmonellae in composted biosolids is not well established. In this study, four enrichment and three plating media were compared in terms of their ability to detect salmonellae from composted biosolids. Rappaport-Vassiliadis broth was more efficient than strontium chloride B, tetrathionate and mannitol selenite enrichment broths. There were no statistical differences between the salmonellae isolation rates on xylose lysine deoxycholate, bismuth sulphite and lysine mannitol glycerol agars. Attempts were also made to improve the performance of selenite enrichment broth by altering its composition. Optimal isolation media identified in this research represent a significant departure from the media recommended by the US EPA.

Giardia Die Off in Anaerobically Digested Wastewater Sludge During Composting

In the Perth metropolitan area, sludge from primary and secondary treatment is anaerobically digested in a two phase, mesophilic process, before being dewatered by belt press or centrifugation. Currently, all of the sludge produced is either stored on site, or composted by contractors and sold as a soil amendment. The composting processes and the quality of the marketed product are currently not subject to regulation. However, sludge use guidelines are expected to be released, which will specify a range of requirements for sludge based products intended for land application.