Waste Water Treatment And Life Cycle Assessment

What produces large amounts of waste water?

urban lifestyles and industrial processes

What must happen to water before it is released into the environment?

water must be treated

Types of sewage treatment

screening and grit removal, sedimentation to produce sewage sludge and effluent, aerobic biological treatment of effluent & anaerobic digestion of sewage sludge

Screening and grit removal

removes large objects (twigs, carrier bag etc) and grit/sand

Sedimentation to produce sewage sludge and effluent

the heavier solids in the waste water sinks to the bottom (sedimentation) to produce sewage and the less dense effluent floats on top

Aerobic biological treatment of effluent

air is bubbled through the effluent in a separate tank & this causes aerobic bacteria to break down (digest) organic matter and other microbes

Anaerobic digestion of sewage sludge

-the solid sewage is transferred to another tank, where anaerobic digestion occurs
-this forms methane(can be used as a fuel)
-the solid digested waste can be used as fertiliser

Sources of potable water

fresh (ground) water, salt water, waste water

Advantages of fresh (ground) water

low energy

Disadvantages of fresh (ground) water

requires a ready supply of ground water - this may vary with seasons

Advantages of salt water

constant supply of sea water all year around

Disadvantages of salt water

high energy processes

Advantages of waste water

low energy than salt water

Disadvantages of waste water

higher energy process than fresh water & some people dislike the idea of drinking waste water

Life Cycle Assessments (LCA)

carried out to assess the environmental impact of products

What are the stages of the life cycle assessment?

-extracting and processing raw materials
-manufacturing and packaging
-use and operation during lifetime
-disposal at the end of its useful life including transport

What is use of water, resources, energy and waste measured using?

numbers (quantified), however the impact of pollutants (and other factors) may require a more subjective judgment

Can a company always be trusted to write an accurate LCA for their products?

no because companies are not likely to be independent and may show bias