Recycling of treated domestic effluent from an on-site wastewater treatment system for hydroponics.

An alternative method to conserve water and produce crops in arid regions is through hydroponics. Application of treated wastewater for hydroponics will help in stripping off nutrients from wastewater, maximising reuse through reduced evaporation losses, increasing control on quality of water and reducing risk of pathogen contamination. This study focuses on the efficiency of treated wastewater from an on-site aerobic wastewater treatment unit. The experiment aimed to investigate 1) nutrient reduction 2) microbial reduction and 3) growth rate of plants fed on wastewater compared to a commercial hydroponics medium. The study revealed that the chemical and microbial quality of wastewater after hydroponics was safe and satisfactory for irrigation and plant growth rate in wastewater hydroponics was similar to those grown in a commercial medium.

Vermiculture as a tool for domestic wastewater management.

Organic waste management is a growing issue due to the unsustainable practices of its disposal. Sewage treatment plants are designed to treat wastewater to produce a safe effluent. However, one of the by-products, the sewage sludge which is disposed off in landfill or used as fertilizer in agricultural operation is high in pathogens. Sustainability can be achieved by Vermicomposting of organic matter which involves accelerated cycling of nutrients though a closed cycle whereby waste products are put to productive end use. Vermicomposting and vermifiltration are natural waste management processes relying on the use of worms to convert organic wastes to stable soil enriching compounds. Domestic wastewater management can be accommodated through these processes in a sustainable manner. A considerable reduction in pathogens has been noticed in the end product to a level that it can be safely applied to land. This paper provides an overview of the system characteristics of management systems utilising vermiculture, to manage wastewater. The process can be used in a small scale for household waste treatment to rural or urban waste management.

Influence of co-substrates on structure of microbial aggregates in long-chain fatty acid-fed anaerobic digesters.

AIMS: The purpose of this study was to investigate the influence of co-substrates, such as glucose and cysteine, on the structure of microbial aggregates in anaerobic digesters treating oleate, a long-chain fatty acid (LCFA). METHODS AND RESULTS: Transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to examine the structure of microbial aggregates. Fluorescence in situ hybridization (FISH) techniques were also used to characterize and localize the different trophic groups present in the aggregates. Oleate was found to inhibit the methanogenic activity and formation of granular biomass in digesters. The addition of co-substrates, such as glucose and cysteine either singly or in combination, increased the methanogenic activity and formation of granular biomass. Glucose was more effective than cysteine in reducing the inhibition by oleate on the methanogenic bacteria and in enhancing the formation of granules. CONCLUSIONS: The addition of nutrient substrate, such as glucose and cysteine could decrease the toxicity of LCFA on anaerobic granulation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the addition of other substrates might decrease the toxicity of LCFA on the granulation of biomass in anaerobic digesters and enhance methanogenic activity. A combination of TEM, CLSM and FISH techniques provides a better tool for visualizing microbial aggregates and for differentiating and localizing different microbial groups within these aggregates.

Suitability of the H2S method for testing untreated and chlorinated water supplies.

Rainwater, borewater and catchment water are used for domestic water supply purposes with or without treatment in remote areas around the world. These places seldom have any facilities for routine testing of their drinking water. A simple on-site testing method is highly required in such areas. The H2S method has been tested for treated drinking water and was found to have a good correlation with the standard methods. The present study was aimed at assessing the suitability of the H2S method for testing different sources of drinking water. Since these types of water may contain H2S producing bacteria not of faecal origin the occurrence of false results in this method cannot be overruled. Therefore it was worthwhile to study whether the positive results are true positive results and what percentage of false positive and false negative results could be expected while using this test for routine analysis of water samples. Results were compared with the results using standard procedures for testing total coliforms, Escherichia coli and Salmonella spp. The present experiment analysed 121 rainwater samples, 17 borewater samples, 41 catchment water samples and 74 remote Aboriginal community water samples. Rainwater, borewater and catchment water samples gave true results of 78.5%, 82.3% and 80.5% respectively while the treated and untreated community samples gave true results of 93.7 and 84.6% respectively. It was concluded that in the developing countries where the acceptable level of total coliform is <10 MPN, the H2S method would be a good test to identify microbial contamination. In other regions, the H2S method could be used as a screening test for drinking water supplies.

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.

Characterisation of waste solutions to determine optimised P recovery.

A number of waste solutions from processes operating in Western Australia (anaerobic digester supernatants, facultative lagoon treated piggery and abattoir waste effluents) were characterised chemically and by automated titration to determine acid-base characteristics. Titrations were over the pH range 2-12 or less. All waste solutions were excess molar ratios of NH3-N to PO4-P (5:1 up to 20:1). The amounts of acid or base reagent required for each waste solution type were in the sequence anaerobic digestor supernatant>>piggery effluent>abattoir effluent. The most efficient removal of N and P of the field samples considered is from piggery effluent. The results indicate conditions for optmising the removal of N and P by precipitation (predominantly struvite) as well as the way forward in determining the full scope of N and P waste streams for which recycling by precipitation (either magnesium or calcium based salts) may be feasible.

Reuse of wastewater in aboriginal communities in Western Australia.

Western Australia is a very arid area and freshwater is a precious resource. The wise and efficient use of this resource is essential for the establishment of communities in this region. Wastewater reuse in Aboriginal communities is a very recent development. Initially leach drains disposed of wastewater. Due to their failure most of the major communities now have the effluent from the septic tanks collected by a small diameter reticulated sewerage system and directed to oxidation ponds for treatment. The overflow from the oxidation ponds is allowed to flow over land or to a creek without any specific use. This paper discusses available reuse options as well as the options specific to Aboriginal communities in Western Australia. It is intended to demonstrate that in arid regions reuse wastewater can act as a water conservation and pollution control measure.

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 10(8) 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.