Wastewater treatment

sewage or wastewater examples

• black water from toilets

• grey water from baths, showers, kitchen

• storm water from rain run off

The 7 common sources of water pollutants

• Agriculture (crops and livestock; runoff)

• Atmosphere (acid rain)

• Illegal dumping of waste

• Industry

• Mines (drainage)

• Sewage

• Urban runoff

The 8 most common pollutants

• Ammonia/Ammonium

• Nitrate/Nitrite

• Phosphorous /Phosphate

• Sulphates/sulphide minerals

• Organic matter

• Pathogens

• Crude oil

• Heavy metals

2 water pollution sources

• point sources

• diffused sources

How does agriculture affect wastewater and pollutants in argiculture and examples of causes

• farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments and saline drainage into bodies of water

• fertilisers have nitrogen and phosphorus. animal excrements have nitrate, ammonia and phosphate

• pesticide have herbicides, insecticides, fungicides and bactericides

• salts can affect the total dissolved solids or electric conductivity. contains ions of sodium, chloride, potassium, magnesium etc

• emerging pollutants have drug residue, hormones and feed additives

problems associated with agricultural pollutants

• eutrophication aka the stimulation of algal growth which reduces water clarify and released toxic metabolite sand organic carbon

• algal growth also disturbs oxygen balance where some placer are overly saturated or veery low levels

What are examples of heavy metals that pollutes water

• arsenic

• lead

• cadmium

• nickel

• mercury

• zinc

What are sources of heavy metal pollutants

• pesticide use

• waste discharge

• mining

• rock weathering

• natural geological occurrence aka arsenic

what are water quality issues that need treatment + methods

• physical: suspended solids in surface water. screening, sedimentations, filtration

• chemical: arsenic in groundwater. chemically assisted sedimentation, chlorination, aeration

• microbiological: removal of pathogens. slow sand filtration

• aesthetic: bad taste, odour or colour

why is wastewater a problem?

• poor management of wastewater can result in increased disease and environmental pollution

resources that can be found from wastewater?

• solids can be used as agricultural fertilisers

• gases can be used as fuel

what factors decide the type of treatment that is suitable for wastewater

• income levels

• community size

• population density

• water usage

• resources and skills available

what 6 things does domestic sewage contain?

• thermotolerant coliform bacteria

• patheogens

• aerobic and anaerobic bacteria

• organic matter

• inorganic matter

• water

What are some reasons for treating wastewater

• to reduce the spread of diseases by pathogens present in wasewaters

• to reduce environmental damage caused with polluting matter present i wastewater

• to protect the distribution system

What are 3 objectives of wastewater treatment

• to encourage the growth of saprophytic bacteria which is bacteria that feeds on dead and decaying organic matter

• to accelerate natural treatment processes

• to reduce environmental pollution

what are some effects on a river or stream that received untreated sewage

• there would be suspended solids which would change the appearance, smothering of stream bed

• oils therefore there would be a change the appearance and dissolve oxygen

• has nutrients that would help with food growth or be toxic to some organisms

• has pathogens where there is a risk of disease transmissions

What are the stages in conventional treatment of domestic wastewater

1. screening: remove large solids

2. grit removal: remove dense suspended solids

3. primary sedimentation: remove light organic particles e.g. food waste, faecal matter, fats and greases

4. biological treatment: encourage biological decomposition of remaining organic matter into stable end-products or to produce additional microbiological organisms

5. secondary sedimentation: remove organic particles produced during biological oxidation

describe the preliminary treatment

• screening and grit removal

• used perforated metal plates for screenings

• Screenings are compressed to remove water and then the debris is caught on the actual screen which is then disposed in landfill

• grit is buried locally or disposed in landfill after being removed

• sludge is dried and then digested anaerobically making methane + CO2 + new bacteria and then used as fertiliser

describe primary treatment

• the removal of sediments which was done in either a rectangular or circular sedimentation tank

describe secondary treatment

• the biological oxidation and secondary sedimentation treatment

• the aerobic biological treatment uses bacterial and a supply of oxygen inorder to oxidise the organic waste present and to create new bacteria

• some treatment systems use bacteria tat are attached to fixed surfaced and others use bacteria that remain in suspension within wastewater

• organic matter decomposes through aerobic or anaerobic reactions.

• Aerobic: oxygen + organic waste —→ oxidised waste + new bacteria

• anaerobic: organic waste —→ methane + carbon dioxide + new bacteria

• instead of oxidation by bacteria organic matter can be converted into bacterial cells which are removed by sedimentation