sewage treatment - secondary treatment Flashcards
is this treatment more physical or biological?
this treatment is mainly biological
where does the water go once it has passed onto secondary sewage treatment?
The liquid is passed into large aeration tanks that continuously churn the water around
The liquid is passed into large aeration tanks that continuously churn the water around. What is broken down in the water in these tanks?
Micro-organisms in the tank break down the organic and suspended particles to harmless substances.
what are the organic and suspended particles broken down into?
into harmless substances
Why is the liquid churned continuously in the aeration tanks?
The churning increases the dissolved oxygen content of the water
What increases the dissolved oxygen content when the liquid is in the aeration tanks?
the liquid is continuously churned to increase the dissolved oxygen content
Where does the water move to after the aeration tanks?
The water then passes into a settlement tank and some of the sludge is removed and can be used as a fertiliser or anaerobically oxidised by bacteria to produce methane (fuel)
Why is some of the sludge removed from the settlement tank?
some of the sludge is removed and can be used as a fertiliser or anaerobically oxidised by bacteria to produce methane (fuel)
How is the sludge from the settlement tank used to produce methane (fuel)
it is anaerobically oxidised by bacteria to produce methane (fuel)
After the settlement stage, how much of the sewage has been removed from the water?
After this stage, about 95% of the original sewage is removed and so can be let into rivers or lakes.
After this settlement stage, about 95% of the original sewage is removed and so can be let into rivers or lakes.
But what may still remain?
However, it may contain dissolved chemicals containing nitrogen and phosphorus. these can be removed by tertiary treatment
how can dissolved chemicals like nitrogen and phosphorus be removed from the water?
by tertiary treatment
define secondary treatment
secondary treatment is a biological oxidation process in which the levels of suspended and dissolved organic materials are reduced, i.e. the sewage is decomposed by means of bacteria which use the nutrients from the sewage together with oxygen from the air to break down the sewage
