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Abstract: Accurate and reliable predictions of sulfide production in a sewer system greatly benefit formulation of appropriate strategies for optimal sewer management. Sewer systems, rising main systems in particular, are highly dynamic in terms of both flow and wastewater composition. In order to get an insight in sulfide production as a response to the dynamic changes in sewer conditions, several measurement campaigns were conducted in two rising mains in Gold Coast, Australia. The levels of various sulfur species and volatile fatty acids (VFAs) were monitored through hourly sampling for periods ranging from 8 to 29h. The results of these field studies showed large temporal as well as spatial variations in sulfide generation. A dynamic sewer model taking into account the hydraulics and the biochemical transformation processes was formulated and calibrated and validated using the data collected during the four measurement campaigns at the two sites. The model was demonstrated to reasonably well describe the temporal and spatial variations in sulfide, sulfate and VFA concentrations. Application of the model was illustrated with a case study aimed to optimize oxygen injection to one of the two mains studied, which is being used as a means to control sulfide production on this site. The model predicted that, moving the current oxygen injection point to a location close to the end of the sewer line could achieve the same degree of sulfide control with only 50% of the current oxygen use. This study highlighted that the location at which oxygen is injected plays a major role in sulfide control and a dynamic model could be used to make a proper choice of the location. [Copyright &y& Elsevier]

The water sector needs to make efficient and prudent investment decisions by carefully considering the long-term viability of water infrastructure projects. To support the assessment and planning of residential recycled water schemes in Australia, we have sought to clarify scheme objectives and to further define the array of critical risks that can impact the long-term viability of schemes. Building on historical information, we conducted a national survey which elicited responses from 88 Australian expert practitioners, of which 64% have over 10 years of industry experience and 42% have experience with more than five residential recycled water schemes. On the basis of expert opinion, residential recycled water schemes are considered to be highly relevant for diversifying and improving water supply security, reducing wastewater effluent discharge and pollutant load to waterways and contributing to sustainable urban development. At present however, the inability to demonstrate an incontestable business case is posing a significant risk to the long-term viability of residential recycled water schemes. Political, regulatory, organisational and financial factors were also rated as critical risks, in addition to community risk perception and fall in demand. The survey results shed further light on the regulatory environment of residential recycled water schemes, with regulatory participants rating the level and impact of risk factors higher than other survey participants in most cases. The research outcomes provide a comprehensive understanding of the critical risks to the long-term viability of residential recycled water schemes, thereby enabling the specification of targeted risk management measures at the assessment and planning stage of a scheme. [ABSTRACT FROM AUTHOR]

In Australia, recycled water schemes have been implemented in residential developments to contribute to sustainable urban development, improve water supply security and reduce pollutant discharges to the environment. A proportion of these schemes, however, have been decommissioned well before the end of their design life which raises questions about the adequacy of the risk assessment and management practices adopted for recycled water schemes. Through a detailed literature review, an investigation of 21 residential recycled water schemes and in-depth interviews with nine scheme stakeholders, we identified 34 risk factors arising from six sources which have the potential to impact the long-term viability of residential recycled water schemes. Of the 34 risk factors identified, 17 were reported to have occurred during the development and implementation of the 21 schemes investigated. The overall risk rating of the 17 factors was qualitatively defined on the basis of the likelihood of occurrence and the impact of the risk factors on the scheme objectives. The outcomes of the assessment indicate that the critical risks to the long-term viability of residential recycled water schemes are 1. unanticipated operational costs, 2. legal and contractual arrangements, 3. regulatory requirements and approval process and 4. customer complaints and expectations not met. To date, public health risks associated with the provision of recycled water have been of primary concern, though the outcomes of this study indicate that the impact to public health has been low. Evidently there is a need for improved assessment and management practices which address the range of critical risk factors, in addition to the routine consideration of public health risks. [ABSTRACT FROM AUTHOR]

Abstract: Intermittent dosing of free nitrous acid (FNA), with or without the simultaneous dosing of hydrogen peroxide, is a new strategy developed recently for the control of sulfide production in sewers. Six-month field trials have been carried out in a rising main sewer in Australia (150 mm in diameter and 1080 m in length) to evaluate the performance of the strategy that was previously demonstrated in laboratory studies. In each trial, FNA was dosed at a pumping station for a period of 8 or 24 h, some with simultaneous hydrogen peroxide dosing. The sulfide control effectiveness was monitored by measuring, on-line, the dissolved sulfide concentration at a downstream location of the pipeline (828 m from the pumping station) and the gaseous H2S concentration at the discharge manhole. Effective sulfide control was achieved in all nine consecutive trials, with sulfide production reduced by more than 80% in 10 days following each dose. Later trials achieved better control efficiency than the first few trials possibly due to the disrupting effects of FNA on sewer biofilms. This suggests that an initial strong dose (more chemical consumption) followed by maintenance dosing (less chemical consumption) could be a very cost-effective way to achieve consistent control efficiency. It was also found that heavy rainfall slowed the recovery of sulfide production after dosing, likely due to the dilution effects and reduced retention time. Overall, intermittent dose of FNA or FNA in combination with H2O2 was successfully demonstrated to be a cost-effective method for sulfide control in rising main sewers. [Copyright &y& Elsevier]

Abstract: Controlling sulfide (H2S) production and emission in sewer systems is critical due to the corrosion and malodour problems that sulfide causes. Chemical dosing is one of the most commonly used measures to mitigate these problems. Many chemicals have been reported to be effective for sulfide control, but the extent of success varies between chemicals and is also dependent on how they are applied. This industry survey aims to summarise the current practice in Australia with the view to assist the water industry to further improve their practices and to identify new research questions. Results showed that dosing is mainly undertaken in pressure mains. Magnesium hydroxide, sodium hydroxide and nitrate are the most commonly used chemicals for sewers with low flows. In comparison, iron salts are preferentially used for sulfide control in large systems. The use of oxygen injection has declined dramatically in the past few years. Chemical dosing is mainly conducted at wet wells and pumping stations, except for oxygen, which is injected into the pipe. The dosing rates are normally linked to the control mechanisms of the chemicals and the dosing locations, with constant or profiled dosing rates usually applied. Finally, key opportunities for improvement are the use of mathematical models for the selection of chemicals and dosing locations, on-line dynamic control of the dosing rates and the development of more cost-effective chemicals for sulfide control. [Copyright &y& Elsevier]