Department of Infrastructure Engineering, Renewable Energy and Energy Efficiency Group

This paper presents a critical review of the physical impacts of decentralized water supply systems on existing centralized water infrastructures. This paper highlights the combination of centralized and decentralized systems, which is referred to as hybrid water supply systems. The system is hypothesized to generate more sustainable and resilient urban water systems. The basic concept is to use decentralized water supply options such as rainwater tanks, storm water harvesting and localized wastewater treatment and reuse in combination with centralized systems. Currently the impact of hybrid water supply technologies on the operational performance of the downstream infrastructure and existing treatment processes is yet to be known. The paper identifies a number of significant research gaps related to interactions between centralized and decentralized urban water services. It indicates that an improved understanding of the interaction between these systems is expected to provide a better integration of hybrid systems by improved sewerage and drainage design, as well as facilitate operation and maintenance planning. The paper also highlights the need for a framework to better understand the interaction between different components of hybrid water supply systems.

Centralized water services in many major cities are increasingly being considered to be inadequate in achieving important goals for the urban water sector. It has been argued that new approaches need to be considered in order to cater for additional demand due to increasing population, changing climate, limited resource availability and a desire to protect ecosystems and build more livable cities. It has therefore been argued that providing additional capacity by using only conventional centralized systems is not economically or environmentally the best option. The use of decentralized water supply options such as rainwater tanks; storm water harvesting and reuse; and localized wastewater treatment and reuse in combination with centralized systems can help provide a sustainable solution to address these challenges by reducing the load on fresh water and decreasing the amount of wastewater to receiving environment. It is currently unknown how such technologies impact on the operational performance of the downstream infrastructure and existing treatment processes. For instance, reuse of greywater reduces the wastewater flow and hence there will be more change of solid deposition in the sewerage system. A comprehensive literature review has identified several significant research gaps related to interactions between centralized and decentralized water supply services. One of the prominent gaps is the effects of such hybrid water supply systems (combination of centralized and decentralized systems) on changes in the quantity and quality of wastewater and storm water of the existing system. Therefore, research is necessary to assess the feasibility of their implementation in conjunction with existing centralized systems. Prior to implementing these hybrid water supply systems (WSS), the interaction of these systems with the local environment needs to be understood.
The interactions between centralized and decentralized systems are highly complex. Current practices do not consider the impacts of these systems on the existing infrastructure. Furthermore, implementation of these systems does not consider the external impacts on the rest of the water cycle. This paper proposes a comprehensive framework that focuses on the interactions between decentralized and centralized water supply systems while planning a well integrated hybrid water supply system. Such a system is expected to enhance the performance of water supply in terms of meeting increased water demand with less impact on other urban water cycle components including sewerage and drainage. In addition, it makes it possible to understand, predict and manage the various impacts on the urban water cycle components. However there is a paucity of research in the area of hybrid water supply systems. In order to fulfill this major research gap, this study presents a framework integrated with a number of analytical tools and modeling approaches to evaluate the hybrid water supply systems.
The proposed framework would evaluate the impacts from the implementation of hybrid water supply systems on the quantity and quality of wastewater and storm water in the existing centralized system. This generalized framework coupled with associated models and tools (i.e., water balance modeling, contaminant balance modeling, multi-criteria decision analysis (MCDA), and uncertainty analysis) considers the varying nature of urban areas and is sufficiently generic to analyze the impacts of hybrid water supply systems in any type of urban developments. Hybrid water supply systems can be assessed based on volume and peak flow rates of wastewater and storm water; wastewater and storm water quality; and water supply reliability.

Surface modifications of natural zeolite were performed by coating it with a chitosan layer. The chitosan coated zeolite (Ch-Z) was protonated with either sulfuric or hydrochloric acid and tested for its suitability to capture nitrate from water at 20 and 4° C. The surface ...

... Meenakshi Arora1*, Ian Snape2, Geoff W. Stevens1 1Particulate Fluids Processing Centre, Department of Chemical and Biomolecular Engineering University of Melbourne, Victoria 3010, Australia ... McGraw-Hill Hindarso, H., Ismadji, S., Wicaksana, F., Mudjijati, N., 2001. ...

Sorption characteristics of toluene on a granular activated carbon (GAC) derived from coconut shell have been investigated at 4and 20° C to facilitate the development of a permeable reactive barrier (PRB) to treat oil-contaminated surface and sub-surface waters ...

Excess fluoride in drinking water is harmful for human health, so it is necessary to be removed. In this study thepotential of a reverse osmosis (RO) membrane for defluoridation of underground water samples at different solute concentrations was studied. Because of the ...

ABSTRACT The imbalance between water demand and supply has become a significant concern of human life as demand is increasing exponentially. With growing urbanization, this imbalance has become more acute in urban areas. So implementation of alternative water supply options has become an inevitable need for urban water management. Grey water and black water recycling is one of the most reliable options to reduce urban water demand. Both centralized and decentralized recycling systems are used based on available site, economic condition and treatment system facilities. But decentralized systems should be given priority for grey water recycling to reduce burden on centralized system and save transportation cost. This paper has proposed a strategy of recycling grey water separately from black water by using decentralized approach. There are various kinds of grey water treatment systems around the world. A review of those processes has been done to identify the best suited processes at household and community level. Septic tank, constructed wetland and intermittent sand filter are identified as the most suitable processes for decentralized treatment due to the simple operation and maintenance facilities as well as cost effectiveness of these systems. Some case studies have been presented to demonstrate the successful execution and impressive performance of these systems on cluster level. Though the systems contain some disadvantages, effective uses of these systems can be made with proper management, execution of awareness program and strict monitoring practices among users.

Urban water managers around the world are adopting decentralized water supply
systems, often in combination with centralized systems. While increasing demand for water
arising from population growth is one of the primary reasons for this increased adoption of
alternative technologies, factors such as climate change, increased frequency of extreme weather
events and rapid urbanization also contribute to an increased rate of adoption of these technologies.
This combination of centralized-decentralized water systems approach is referred to as “hybrid
water supply systems” and is based on the premise that the provision of alternative water sources
at local scales can both extend the capacity of existing centralized water supply infrastructures,
and improve resilience to variable climatic conditions. It is important to understand, however,
that decentralized water production and reuse may change the flow and composition of wastewater
and stormwater, thereby potentially also having negative impacts on its effectiveness and
performance. This paper describes a framework to assess the interactions between decentralized
water supply systems and existing centralized water servicing approaches using several analytical
tools, including water balance modelling, contaminant balance modelling and multi-criteria
decision analysis. The framework enables the evaluation of impacts due to change in quantity
and quality of wastewater and stormwater on the existing centralized system arising from the
implementation of hybrid water supply systems. The framework consists of two parts: (1) Physical
system analysis for various potential scenarios and (2) Ranking of Scenarios. This paper includes the
demonstration of the first part of the framework for an area of Melbourne, Australia by comparing
centralized water supply scenario with a combination of centralized water supply and reuse of
treated waste water supply scenario.