PHUnewcastle

Information about PHUnewcastle

Published on December 31, 2007

Author: Xavier

Source: authorstream.com

Content

Rainwater tanks revisited: New opportunities for Urban Water Cycle Management:  Rainwater tanks revisited: New opportunities for Urban Water Cycle Management Peter Coombes, George Kuczera, Hugh Dunstan and Jetse Kalma Urban Water Cycle Group University of Newcastle www.eng.newcastle.edu.au/~cegak/Coombes Slide2:  The Humble Rainwater Tank Rainwater tanks harvest water during droughts and reduce demand on water supply reservoirs Rainwater tanks are underutilised if water is only used for irrigation Maximum utilisation occurs when used for hot water, laundry, toilet and irrigation! Rainwater tanks complement mains water supply Regional Impacts of Rainwater Tanks:  Regional Impacts of Rainwater Tanks Reduce mains water demand resulting in delays in requirement to construct new dams: By up to 28 years in the Hunter Region By up to 100 years in the Central Coast Region By up to 41 years in the Sydney region Reduce mains water peak demands by up to 40% (CSIRO; University of Newcastle) Improve stormwater quality by reducing frequent stormwater discharges to the environment by up to 80% (3 month ARI events) Reduce the requirement for “end of pipe” infrastructure by decreasing stormwater discharges by up to 30% (10 year ARI events) Improve flood risk by reducing stormwater discharges by up to 15% (100 year ARI events) Water Quality:  Water Quality Over 3 million Australians drink rainwater with no widespread adverse health effects Many authors have found that the quality of tank water can be suitable for potable uses In a small number of cases health concerns have resulted from poor maintenance of tanks Greater number of health concerns have resulted from mains water systems The processes of flocculation, settlement and biofilms in tanks act to improve the quality of rainwater Rainwater used in hot water systems has been found to be compliant with drinking water guidelines Slide5:  The Figtree Place Site Slide6:  Layout and Main Features Slide7:  RAINWATER TANK Soil and leaves enter damaged stormwater tank when ever it rains Dual water supply system:  Dual water supply system Mains supply to units Mains or tank supply to HWS and toilet RPZD Solenoid Pump Pressure tank Rainwater tank Float switch Incorrect design! This configuration is not recommended! Roof Water Quality Results:  Roof Water Quality Results Treatment Chain! Observations:  Observations Rain water used in hot water systems set at >50°C is compliant with Australia drinking water standards Hot water systems pasteurize water removing bacteria Although roof water quality exceeded guidelines for ammonia, ph, lead and iron chemical tank water quality is compliant with guidelines Bacteria, organics and chemicals occupy the surface layer of water stored in tanks. Some of the bacteria, organics and chemicals form flocs that become biofilms on surfaces or settle to the bottom of the tanks to the sludge Contaminants such as metals and coliforms settle to the bottom of water tanks Biofilms in tanks capture microbial contamination Separation of the first flush will improve tank water quality Use of rainwater for toilet flushing and in hot water systems results in a mains water savings of up to 60% No stormwater discharge from the site in five years The Maryville House:  The Maryville House A 9,060 Litre rainwater tank was installed at an old house in Maryville an inner city suburb of Newcastle Allotment area is 245 m2 and roof area is 135 m2 Rainwater is used to supply hot water, toilet and outdoor uses Instantaneous hot water system set at 55°C The house is adjacent to Newcastle’s heavy industry and industrial highway Average of three occupants Rusty roof Slide13:  Design of the Rainwater Tank for Dual Water Supply Slide14:  Design of the Dual Water Supply System Water Quality in the tank:  Water Quality in the tank The majority of parameters complied with the Australian Drinking Water Guidelines Average values of Total Coliforms, pH and Zinc exceeded the guidelines pH of rainwater about 5.5, no health effects Corrosion of plumbing? Zinc can cause “hard’ taste in water. No health concerns with the level of exceedance. Caused by rusty roof. Coliforms occur naturally in soil and water environments One exceedance of Fecal Coliforms and Ammonia following roof maintenance work Quality of roof water improved in the tank Hot Water Quality:  Hot Water Quality Majority of parameters complied with the Australian Drinking Water Guidelines Average values for pH and Zinc exceed the guidelines Bacteria eliminated from rainwater by the instantaneous hot water system HPC <= 10 CFU/ml: Japanese and USA health guideline for HPC is 100 CFU/ml Heat kills bacteria readily at low population numbers, in water, acid conditions and rapid changes of temperature High pressures in pump may also eliminate bacteria Maryville Results:  Maryville Results Rainwater tank reduced stormwater volumetric discharges by 39% and peak discharges by 86% Reduced mains water demand by 54%, one year ARI peak demand by 80% Cost of rainwater varied from $0.3 kL to a benefit of $0.39 kL (considerably less than mains water) The quality of rainwater was acceptable for hot water, toilet, laundry and outdoor uses Quality of rainwater used in hot water systems was always compliant with drinking water guidelines (except pH and Zinc) Extensive analysis of literature and research revealed that health concerns about rainwater tanks was significantly overstated. Policy Issues:  Policy Issues Mixed messages from Government and Utility staff on permitted uses of rainwater: A number of authorities claim that DoH do not permit utilisation of rainwater for uses other than toilet and outdoor purposes Water authorities control approval of backflow prevention methods Lengthy and varied approval process ( Heritage Mews, Figtree Place) Constantly changing rules No consideration of treatment chain or methods for rainwater Roof to end use treatment chain, Filters, UV and so on Appropriate end uses for a given treatment method “Under grounding” of rainwater use Many people use rainwater tanks for drinking purposes They do not seek approval or advice due to a perceived lack of process Acceptable rainwater uses versus monopoly control of water supply Need for DoH to work with key research groups (such as University of Newcastle) to define adequate backflow prevention methods and acceptable rainwater uses. An agreed set of solutions based on research rather than assumptions and ongoing research needs should be defined Slide19:  Pathogens 1:50,000 No pathogens Mains break 1:5,000 No mains break Large storm event 1:100 No large storm event Failure of tank valve 1:1,000 No failure of tank valve Failure of check valve 1:1,000 No failure of check valve No chlorine residual 1:50 Chlorine residual Infection concentration 1:1,000 No infection concentration Risk pathway for backflow from the Maryville solution Risk of infection from backflow = 1: 1.25 x 1021

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