6. What is the cost-benefit
relationship regarding sewage
treatment as a strategy to
fight water pollution?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
To treat sewage is cheaper for
society. The treated sewage
pollutes rivers, and the sea, being
cause of diseases transmitted
water. For the society costs of these
diseases much higher than the
of the sewage treatment.

the most economical systems
treat sewage is the treatment
system, reservoirs kept
oxygenated for aerobic bacteria
decompose organic material.