Quantitative microbial risk assessment models for consumption of raw vegetables irrigated with reclaimed water

Quantitative microbial risk assessment models for estimating the annual risk of enteric virus infection associated with consuming raw vegetables that have been overhead irrigated with nondisinfected secondary treated reclaimed water were constructed. We ran models for several different scenarios of crop type, viral concentration in effluent, and time since last irrigation event. The mean annual risk of infection was always less for cucumber than for broccoli, cabbage, or lettuce. Across the various crops, effluent qualities, and viral decay rates considered, the annual risk of infection ranged from 10–3 to 10–1 when reclaimed-water irrigation ceased 1 day before harvest and from 10–9 to 10–3 when it ceased 2 weeks before harvest. Two previously published decay coefficients were used to describe the die-off of viruses in the environment. For all combinations of crop type and effluent quality, application of the more aggressive decay coefficient led to annual risks of infection that satisfied the commonly propounded benchmark of ≤10–4, i.e., one infection or less per 10,000 people per year, providing that 14 days had elapsed since irrigation with reclaimed water. Conversely, this benchmark was not attained for any combination of crop and water quality when this withholding period was 1 day. The lower decay rate conferred markedly less protection, with broccoli and cucumber being the only crops satisfying the 10–4 standard for all water qualities after a 14-day withholding period. Sensitivity analyses on the models revealed that in nearly all cases, variation in the amount of produce consumed had the most significant effect on the total uncertainty surrounding the estimate of annual infection risk. The models presented cover what would generally be considered to be worst-case scenarios: overhead irrigation and consumption of vegetables raw. Practices such as subsurface, furrow, or drip irrigation and postharvest washing/disinfection and food preparation could substantially lower risks and need to be considered in future models, particularly for developed nations where these extra risk reduction measures are more common.

Domestic drinking water in rural areas : are water tanks on farms a health hazard?

The aim of the research was to gain a better understanding of the relationship between drinking water quality, householders' knowledge and maintenance practices of private water supplies and drinking water-related public health risk on farms. Samples of drinking water were taken from 100 farming households. The Colilert-18 method was used for the detection of total coliforms and Escherichia coli (E. coli) as indicators of water quality. Each household completed a questionnaire about their knowledge and practices relating to a safe water supply. Coliforms were present in 52 water samples and E. coli was present in 38. Seven households reported minor illnesses in the previous three months and two households reported gastroenteritis. Some tank maintenance occurred in 86 households, but tank maintenance activities varied considerably. Four of the households had published guidelines on water quality. None of the participating households had their drinking water tested regularly. There was no obvious relationship between drinking water quality, householder knowledge, maintenance practices and drinking water-related health risk on farms.

Human Health Impacts of Contaminants Found in Local Drinking Water Supply

Many contaminants are currently unregulated by the government and do not have a set limit, known as the Maximum Contaminant Level, which is dictated by cost and the best available treatment technology. The Maximum Contaminant Level Goal, on the other hand, is based solely upon health considerations and is non-enforceable. In addition to being naturally occurring, contaminants may enter drinking water supplies through industrial sources, agricultural practices, urban pollution, sprawl, and water treatment byproducts. Exposure to these contaminants is not limited to ingestion and can also occur through dermal absorption and inhalation in the shower. Health risks for the general public include skin damage, increased risk of cancer, circulatory problems, and multiple toxicities. At low levels, these contaminants generally are not harmful in our drinking water. However, children, pregnant women, and people with compromised immune systems are more vulnerable to the health risks associated with these contaminants. Vulnerable peoples should take additional precautions with drinking water. This research project was conducted in order to learn more about our local drinking water and to characterize our exposure to contaminants. We hope to increase public awareness of water quality issues by educating the local residents about their drinking water in order to promote public health and minimize exposure to some of the contaminants contained within public water supplies.

The use of artificial biofilms to strip nutrients from an industrial smelters waste water under conditions of low temperature and high pH

The Victorian Environment Protection Authority (EPA) has identified Alcoa’s Point Henry aluminium smelter as being a major source of recognized pollutant input due to its disposal of effluent into Corio Bay. Historically, the water quality parameters that have most often exceeded Point Henry’s EPA limits have been pH and suspended solids from the smelter’s discharge points. These waste water discharges also experience high nitrogen and phosphorus concentrations which result in algal blooms that occur at the onset of warm weather. The main hypothesis of this study was that “prevention of algal blooming with the onset of warm weather by removal of nutrients during the cooler months, and continued removal thereafter, is better than curing the problems chemically”. Biofilms have been used to remove nutrients from waste waters, but not under the conditions experienced at Point Henry. The aim of this study, therefore, was to determine if significant biofilm growth would be observed on floating structures suspended in the Point Henry waste water stream during the cooler, winter months of the year. Statistically significant biofilm growth occurred on all suspended structures in all discharge ponds during the winter and early spring of 2000. The use of suspended structures, such as AquaMatTM, as an artificial substrate to attract and support periphyton and bacterial communities (biofilms), which are then able to out-compete phytoplankton communities for available nutrients, is therefore a viable option for the Point Henry smelter. However, further research on the competitive performance of biofilms in the Point Henry ponds during the summer months is required before adequate biofilm management strategies can be developed.

Performance evaluation and improved risk control philosophies for drinking water systems

World-wide, water is the single most used substance by humans every day. Water is also the major cause of illness and death in many countries including the affluent nations. Through this research, new risk control philosophies from catchment to consumers are highlighted. This thesis is about identifying the hazards, evaluating the risks and implementing controls to protect public health from drinking water.

Influence of land cover on water resources

The influence of land cover on water quality and quantity was examined using a multidisciplinary approach that integrated land use maps, historical databases, and statistical modelling. Systematic changes in the Glenelg Hopkins landscape were identified, in addition to a relationship between greater proportions of vegetation and better water quality.

Wood to water : short-term effects of the re-introduction of wood to streams in agricultural environments

Rehabilitation of streams on agricultural properties has become a priority for landholders and managers in recent years in Australia. Fencing and re-vegetation of riparian zones are first priorities to improve riparian habitat values and biodiversity, however changes to in-stream habitat complexity are unlikely to result in the short term. Little evidence exists to guide subsequent rehabilitation actions to address this issue. Artificially re-introducing wood to such streams may be a useful strategy to increase habitat complexity more rapidly, thereby improving in-stream biodiversity values. To test this hypothesis, as a part of the larger Productive Grazing, Healthy Rivers project, small pieces of wood were introduced to eight sites on beef and dairy properties across southern Victoria, monitoring aquatic macroinvertebrates, water quality, hydrology and habitat quality. Comparing macroinvertebrate communities before and after treatment, and between experimental and control sites, changes in community composition and colonisation are explored.

Chlorine decay and biofilm growth in tropical drinking water distribution systems - a case study for Townsville

Water quality modelling is becoming increasingly popular in the water industry due to its applications in drinking water and treated wastewater reuse. Microbial growth and disinfectant decay are the two most important factors to be considered in drinking water if they are to comply with stringent guidelines imposed by relevant water regulatory authorities. In the case of drinking water, an optimum level of disinfectant is an important criterion to have pathogen free water with minimal disinfectant by products (DBPs) below the acceptable levels.

Reclaiming spent liquor from cotton reactive dyebaths using nanofiltration membrane for possible reuse of water and salt

During dyeing, salts are placed in a dyebath to aid the fixation of various dyes on to the fabric while bases are added to raise the pH from around neutral to pH 11. Afterwards, the used dyebath solution, called dyebath spent liquor, is discharged with almost all the salts and bases added as well as unfixed dyes. Consequently, a lot of raw materials are lost in the waste stream ending up in the environment as pollutants. In this study, possibilities of reusing water and salts of dyebathes were investigated, using a nanofiltration membrane. When the salt concentration in the spent liquor was increased from 10 to 80 g/L, the salt rejection by membrane was found to decrease initially; however, the salt rejection increased over the time, which was not expected. The aggregation of dye was also studied and found to decrease in the concentrate when the salt concentration was increased. This may be due to the aggregation of salt in the concentrate, which explains the increase in salt rejection. This information is useful for the textile industry in evaluating the treated water quality for the purpose of reuse.

Sustainable aquaculture through water recycling

The discharge of nutrient rich effluent from aquaculture systems into coastal waters is cause for concern. Direct filtration of aquaculture wastewater, using floating medium and sand with in line flocculation, and biological filtration using activated carbon, has the potential to improve water quality for recycling within aquaculture systems. This study looked at the performance of laboratory scale dual media and activated carbon filters in suspended solids and nutrient removal in the treatment of aquaculture wastewater. The dual media filter, with flocculant FeCl3 of 9mg/L, functioned best at a velocity of 7mJh with low headloss, and good turbidity and phosphorus removal (80% and 53% respectively). The activated carbon filter removed ammonia (84%) and nitrite (71 %) in the process of nitrification with a five-hour hydraulic retention time. This paper reports preliminary results from a longer term sustainable aquaculture project.

Nanofiltration for the possible reuse of water and recovery of sodium chloride salt from textile effluent

During the reactive dyeing of cotton, salts such as sodium chloride (NaCI) are placed in a dyebath to aid the exhaustion of various dyes onto the fabric while bases are added to raise the pH from around neutral to pH 11 to achieve fixation. Afterwards, the used dyebath solution, called dyebath spent liquor, is discharged with almost all the salts and bases added as well as unfixed dyes. Consequently, many raw materials are lost in the waste stream ending up in the environment as pollutants. In this study possibilities of reusing the water and salts of dyebaths were investigated using a nanofiltration membrane. When the NaCI concentration in the spent liquor was increased from 10 to 80 g/L, the NaC1 rejection by the membrane was found to decrease initially; however, the NaC1 rejection increased over time, which was not expected. The aggregation of dye was also studied and found to decrease in the concentrate when the salt concentration was increased. This information is useful for the textile industry in evaluating the treated water quality for the purpose of reuse.

Evaluation of chlorine decay kinetics expressions for drinking water distribution systems modelling

The decay of chlorine in drinking water involves a complex set of reactions that is usually simplified to first order kinetics in models of water quality in distribution systems. However, to be useful in optimising chlorine dosing regimes, the kinetics expression should accurately describe the shape of the chlorine decay curve for different chlorine doses and be able to simulate re-chlorination. After considering the nature of the reactions involved in chlorine decay, five simplified reaction schemes were evaluated for their suitability to describe chlorine concentration in bulk water. Each scheme was fitted to a sample of experimental data of chlorine decay in raw water obtained from Warragamba Dam (the major source of water supplied to Sydney, Australia). A scheme involving two parallel reactions of organic carbon compounds with chlorine is both necessary and sufficient to satisfy the requirements of modelling chlorine decay accurately.

Modelling biofilm growth and disinfectant decay in drinking water

A simple biofilm model was developed to describe the growth of bacteria in drinking water biofilms and the subsequent interactions with disinfectant residuals incorporating the important processes, such as attachment of free bacteria to the biofilm on a wall surface, detachment of bacteria from the biofilm, growth of biofilm bacteria with chloramine inhibition, chloramine decay in the bulk water phase, and chloramine decay due to biofilm bacteria and wall surfaces. The model is useful in evaluating the biological stability of different waters, as it can predict concentration of organic substances in water. In addition, the model can be used to predict the bacterial growth and biofilm decay in distribution systems. A model of this kind is a useful tool in developing system management strategies to ultimately improve drinking water quality.

Suitability of chlorine bulk decay models for planning and management of water distribution systems

Effective disinfection planning and management in large, complex water distribution systems requires an accurate network water quality model. This model should be based on reaction kinetics, which describes disinfectant loss from bulk water over time, within experimental error. Models in the literature were reviewed for their ability to meet this requirement in real networks. Essential features were identified as accuracy, simplicity, computational efficiency, and ability to describe consistently the effects of initial chlorine dose, temperature variation, and successive rechlorinations. A reaction scheme of two organic constituents reacting with free chlorine was found to be necessary and sufficient to provide the required features. Recent release of the multispecies extension (MSX) to EPANET and MWH Soft's H2OMap Water MSX network software enables users to implement this and other multiple-reactant bulk decay models in real system simulations.