Lecture 10: Water Efficiency Flashcards
What is a case study for the water crisis?
Lake Oroville, California
2011- valley filled
2014 - river 1/3 of the width
How much water is fresh?
2.5% (but only 0.5% not frozen)
Explain the concept of water being a local resource?
While some populations are larger, geographical conditions mean they may not have a corresponding proportion of freshwater resources.
Eg. Asia is over 1/2 of world population but only has just over 1/3 of freshwater resources
Over 2.8 billion people face water scarcity
Why is water a seasonal resource?
- Water supply is considered at river basin level (area of land that river and tributaries flow into)
- Flux of water in a basin varies seasonally, usually lowest when human demand is highest eg. In summer
What industry is the largest consumer of freshwater?
Agriculture
What is abstraction in regards to water and what are the problems with it?
- Volume of water taken from natural or modified resources over a given period, usually a year
- Reservoirs provide a constant supply despite fluctuation in rainfall etc.
- Water transfer is moving water between basins (can have losses up to 50%, can move ecosystems etc.)
How can drawing from groundwater help the water scarcity problem?
- Underground water stored in porous or fractured rock, referred to as an AQUIFER which can be pumped in during wet periods and drawn out when needed
- Shallow groundwater can be exploited sustainably as it is in dynamic exchange with surface water
- Over-exploitation can cause land sinkage, contamination and infiltration of saltwater
- Less visible than surface water so effects of human activity can often be missed
Describe the process of desalinisation and the drawbacks?
Multi-Stage Flash:
Saltwater is heated in a boiler then the vapour enters a chamber with a cooling pipe which allows the condensation to drip into a funnel which goes into the next chamber and repeats until water is fresh.
Reverse Osmosis:
Water is pressurised in a chamber with a semi-permeable membrane which allows only the fresh water to pass through.
Drawbacks:
- 1m3 of seawater takes about 4kWh - enough to light a home for a day
- Produces highly concentrated brine that is often discharged back into the sea (could affect bottom dwelling organisms as it sinks to sea bed)
How to reduce consumption of freshwater?
- Social and behavioural (awareness campaigns, water pricing and metering)
- Reduce loss through leaks and evaporation in distribution
- Water saving devices (low flush toilets, aerated showers, sensor taps)
- Reuse of Greywater (all household water that isn’t from toilets - can be used for toilet flushing, watering gardens)
- Rainwater harvesting
- Industry (water efficient process, onsite water recycling, alternative cooling methods)
- Agriculture (efficient irrigation, recycling treated wastewater, crop management, soil management)
What is the ecological impact of water use?
- Rivers require sufficient flow to maintain a healthy ecosystem (flow is reduced by over-abstraction)
- Lower flow rivers struggle to dilute pollutants, have reduced wetlands and reduced river biodiversity
- Building dams and reservoirs can cause buildup of toxic substances
Compare blue, green, and grey water.
Blue - from freshwater/underground source
Green - from soil or rain water
Grey - from household use to dilute wastewater to be fit for discharge
Compare direct to indirect water.
Direct - real water used in actual product’s processing (irrigation)
Indirect - invisible water in the supply chain (transport, energy)
How much water per annum per capita is used in the UK?
54m3
What is the Energy-Water Nexus?
- The link between water and energy (most of the water footprint of industrial processes is traceable to the water footprint of the energy required)
Eg. In coal mining, water used for coal washing, dust suppression, machine cooling. In oil extraction, water used for water injection
What are the two main parameters used to measure sewage strength?
- Density of Suspended Solids (SS) - any particle in suspension in the water, they carry pathogens which are a health risk. Turbidity (cloudiness) caused can affect photosynthesis and oxygen generation of aquatic plants.
-Biological Oxygen Demand (BOD) - organic matter is broken down by micro-organisms which consume oxygen in the process, too much organic matter means depletion of oxygen, causing fish to die. BOD measures potential of sewage to deplete in oxygen.
