Sanitary Engineering Lecture 8

Water Reuse Water reuse describes the process whereby wastewater (it's include storm water which is a term used to describe water that originates during precipitation events) treated to an appropriate standard, is reused for a variety of beneficial purposes. The treated water ready to be reused is termed recycled or reclaimed water. The degree of water treatment depends on the source of the wastewater and the reused of the treated water. For example  Demotic  industrial Water is an increasingly scarce resource for much of the World’s population. Global warming, an increasing world population and generally increasing incomes mean the demand for water is likely to rise further. If current trends continue, we will use 40% more water by 2024 than we do now.

Benefits of water reuse include:  Increasing water resource availability  Making scarce potable water previously used for non potable applications available for drinking  Reduced consumption of expensively treated potable water supplies (cost saving where there is water metering)  Reduced effluent flow loads to sewers  Reduced nutrient discharge to water bodies  Flood prevention potential (storage)  A less drought sensitive water resource  Enhanced recreation and tourism opportunities and biodiversity benefits through the restoration/creation of wetlands.

Storm water Reuse Techniques There is a wide range of tried and tested storm water reuse techniques used around the world and elsewhere in the world. These include the following:  Urban lakes.  Wetlands.  Aquifer storage and recovery.  Rainwater tanks.  Water harvesting.  Industrial reuse.  Unplanned reuse.  Water sensitive urban design.

Urban lakes refer to the construction of dedicated, and typically artificial, lakes within an urban land use setting for the storage, treatment and possible reuse of storm water entering them. The water stored in these lakes is typically reused for non-potable applications such as irrigation and lawn watering, and also often supplies local area amenity benefits, such as aesthetic appreciation and habitat provision. Urban lakes are Often an essential, providing improvement in the quality of storm water before it is to be injected into underlying aquifers. 1. Urban Lakes

2. Wetlands Wetlands are similar to urban lakes; however they are configured in such a way that they contribute more in terms of local environmental value, typically via the creation of extensive areas of weed and aquatic reed beds within the wetland. Wetlands are more efficient in terms of water quality improvement of impounded waters, and are likely to be required if a particularly high quality of water is required for aquifer injection Similarly to urban lakes, water stored in wetlands can also be directly reused for irrigation and local area lawn watering.

Wetlands provide many benefits, which include wildlife and wildfowl habitat, water quality improvement, flood diminishment, and fisheries breeding grounds. For streams that have been impaired or dried from water diversion, water flow can be augmented with recycled water to sustain and improve the aquatic and wildlife habitat 3. Aquifer Storage and Recovery: Aquifer recharge refers to the collection and treatment of storm water before it is discharged or injected into suitable, available, unconfined or confined aquifers. This recharge could either be applied to supplement the natural recharge of an over utilized aquifer, or alternatively injection of water in the aquifer could allow the storage of injected waters for subsequent reuse at the site. This latter practice is referred to as Aquifer Storage and Recovery (ASR).

There are several benefits to support why aquifer recharge or ASR should be considered as a possible storm water reuse practice, as follows:  To reduce groundwater salinity.  To assist in flood mitigation.  To reduce pressures on often scarce potable surface water supplies.  To increase the potential for larger local water allocations from the aquifer.  To assist in improving the environment by reducing the quantities of possibly polluted storm water discharging from an area.

a) illustrates a typical ASR application, shows the injection of excess surface waters into the aquifer during periods of local rainfall and runoff. b) illustrates a typical ASR application, shows the recovery of injected waters, when surface usage is required.

4. Rainwater tanks: Rainwater tanks refer to storages used for the collection and possible reuse of roof water. These storages can be used on an individual Household basis or alternatively larger storages can be constructed to collect roof water runoff from several houses. There are numerous ways In which such tanks can be configured, ranging from the well recognized above ground, or under the ground, corrugated iron or concrete tanks. Uses for rainwater collected from rooftops include irrigating gardens and landscapes, cleaning tools, mixing concrete and flushing toilets.

5. Water Harvesting Water harvesting refers to the collection and storage of water during times of significant stream flow, with reuse at later times when less water is available. This harvesting usually takes the form of an off line lake or wetland to which water is pumped or routed at times of significant stream flow. The water stored by such an application is usually reused for irrigation purposes.

Collected and treated storm water may be used by industries for processes that do not require water of potable quality. Examples in this regard include the following:  evaporative cooling water  Boiler feed water and process water. 6. Industrial Reuse

Storm water Reuse Advantages  Reduction in potable water Usage  Receiving environment protection  Regulation’ of potable water usage  Profile and awareness raising Storm water Reuse Disadvantages  Cost  Extra Maintenance Load  Environmental Flow Aspect  Public Health  ‘New’ Approach  Require new standards and education practices