2 Wastewater Treatment Utilizes a variety of strategies: Physical (mechanical)BiologicalChemicalThe federal government requires the monitoring of sewage discharge and sets limits on pollutant levels:Clean Water Act (‘72, ‘77, ‘87)
3 Primary treatment Pollutants Large objects: rocks, gravel, twigs, litter, female hygiene products, big food scraps, condoms, etc.Smaller: sand, grit, human or animal fecal materialEven smaller (& water insoluble): fats and greaseRemoval methodsFiltration, screening, sieving, netsInflow is slowed in a settling tank. Solids settle to the bottom and are collected (sludge).Allowed to float to surface in settling tank and are then skimmed off (sludge).
4 Secondary treatment Pollutants Dissolved/suspended organics substances (eg fecal matter, soaps, detergents, food particles)Removal methodsEffluent is pumped into aeration tanks where aerobic microorganisms break down the organic matterThere is secondary settling and filtration.This sludge is pumped into an enclosed tank with anaerobic decomposers.
5 Advanced secondary treatment (sometimes called tertiary) PollutantsPhosphateNitrates/ammoniaRemoval methodsbiological removal, chemical bindersDenitrifying bacteria in anaerobic tank
6 Final step: Disinfection Usually done with chlorine which kills pathogens (eg E. coli and other coliform bacteria, Giardia, Cholera, viruses)What is the negative effect of this?Sometimes done with UV radiation or ozone
7 Sewage treatment summary Multi-staged approach to cleaning up waste waterUtilizes mechanical, biological, and chemical strategiesProducts areClean(er) waterSludgeSolid waste (from primary treatment filters)A last step includes disinfection with chlorine (for fecal coliform and other harmful bacteria)START HERE THURSDAY
8 The solid waste of the waste Sent to already overtaxed landfillsMay contain toxins, heavy metals, POPs, etc that could potentially contaminate groundwater through leachingContributes to the production of methane during decomposition
9 The sludge waste Often used as fertilizer If not properly disinfected, could contaminate soils with bacteriaMay contain toxins, heavy metals, POPs that could contaminate groundwater, soil, and plantsThis could lead to an accumulation of heavy metals in food chainsField runoff could result in surface water contamination, leading to our old friend eutrophication if high in nitrates or phosphates.
10 Sewage sludge as fertilizer OdorsOdors may cause illness or indicate presence of harmful gasesDust ParticlesParticles of dried sludge carry viruses and harmful bacteria that can be inhaled, infect cuts or enter homes.ExposureChildren may walk or play in fertilized fields.Livestock PoisoningCows may die after grazing on sludge-treated fields.SludgeGroundwaterContaminationHarmful chemicals and pathogens may leach into groundwater and shallow wells.Surface RunoffHarmful chemicals and pathogens may pollute nearby streams, lakes, ponds, and wetlands.
11 Constructing Wetlands to Treat Sewage (1) Raw sewage drains bygravity into the first pooland flows through a longperforated PVC pipe intoa bed of limestone gravel.(3) Wastewater flows throughanother perforated pipeinto a second pool, wherethe same process is repeated.SewageTreatedwaterWetland typeplantsWetland typeplants45 centimeterlayer of limestonegravel coated withdecomposing bacteriaFirst concrete poolSecond concrete pool(2) Microbes in the limestone gravelbreak down the sewage intochemicals that can be absorbedby the plant roots, and the gravelabsorbs phosphorus.(4) Treated water flowing from thesecond pool is nearly free ofbacteria and plant nutrients.Treated water can be recycledfor irrigation and flushing toilets.