sewage treatment

what is pollution

the release of substances into the enviroment that damage it

what 2 things are measured regularly in the analysis of wastewater effluent

bod and cod

define bod

biological oxygen demand , dissolved oxygen consumed by biological action

disadvantages of a high bod

large amount of o2 removed from water , death of microorganisms and animals

eutrophication

the enrichment of water with nutrients

what causes eutophication

nitrates and phosphate ions

what happens when eutrophication occurs

algae and plants have excess growth , blocks sun , death and decomp of plants , animals die

what are natural causes of eutrophication

natural increase of nitrogen or phsphate from build up of sediment

what are the artifical causes of eutrophication

fertilizers or silage affluent or untreated sewage dumped

properties of heavy metla s

high atomic mass, dangerous when consumed , toxic

what can you find heavy metals

polluted water when batteris not disposed of

how to remove heavy metals

precipitation

name the 3 stages of sewage treatment

primary , secondary and tertiary

primary treatment

physical , screening and sedimentation

secondary treatment

biological , dissolved organic pollutants removed , passed over stone with bacteria that oxidises organic pollutants to h2o

where does the secondary take place

large aeration tanks

tertiary treatment

nitrates + phosphates removed by precipitation ,nitrates removed by bacteria , heavy metals removed , expensive and not always done