sewage waste treatment Flashcards
what is sewage?
waste water from communities, industries and commercial institutions which contain human solid and liquid excretion as well as waste water from various sources
what is sullage?
waste water that does not contain any human excreta, and is generally derived from domestic activities
what are environmental problems due to sewage?
1- contamination of food
2- nuisance
3- unpleasant odor
4-breeding of flies and mosquitoes
5-pollution of soil
6- pollution of water supply
7- increase in incidence of disease
what are disease that are transmitted through soil called?
helminthic disease
what is a disease caused due to contamination of food?
typhoid fever/ enteric fever
what are the constituents of waste water
99.9% water
0.1% inorganic and organic solids in solution or suspended
what type of solid in waste water causes odor?
organic solids
outline the recycling of water
grey water- used water without toxic chemicals/excrement and can be re-used
blackwater- contaminated water with toxic chemicals/excrement
what are the goals of waste water treatment?
produce effluent
produce sludge
discharge or reuse effluent
what are the stages of water treatment and outline them?
1-primary
- solids are separated
2-secondary
-dissolved matter is converted into solid mass via use of bacteria
3-tertiary
-biological solid are neutralized and disposed
- treated water disinfected chemically or physically
what are the types of treatments?
1-mechanical treatments
2-biological treatment
3-chemical treatment
what are the types of mechanical treatment?
1- remove of large object
2-removal of sand and grit
3- primary sedimentation
4-influent:waste water flowing into reservoir, treatment plant
what are the types of biological treatment?
1- trickling bed filter
2- activated sludge
what are the types of chemical treatment?
disinfection
what are the preliminary treatment
1- removing any waste water constituent which could clog up equipment
2- raked screen: screens the water
3-remove large objects
what are the types of primary treatment stage?
1-sand catcher
2- sedimentation tank
what are the advantages and disadvantages of sand catcher?
advantages
- remove sand and grit
- controls wastewater velocity
* suspended organic matter kept in water
*sand grit and stone settle
disadvantages
-landfills
-damage equipment’s in the remaining treatment stage
describe sedimentation tank
1-remove grease and oils
2-settles fecal matter to the bottom, where it is pumped to sludge treatment plant
3-produces homologues liquid for later biological treatment
type of material removed during primary treatment stages
1- fats,oil,grease
2- sand,gravels and rocks
3-floating materials
4- large solid able to settle
what is secondary treatment?
process on dissolved organic matter
what are the types of secondary treatment?
1- fixed film system
2-lagoon system
3- suspended film system
what is fixed film system?
growing microorganism on substrate medium such as rocks, plastic and gel which forms a thick slime layer, and waste water is spread over the substrate
what are examples of fixed film system?
1-trickling filter
2- rotating biological contactors
explain how a trickling filter works
waste water is poured onto a medium having slime like layer of microorganism, this medium is contained in a coke/limestone material
what is a lagoon system?
holds the waste water for several months, allowing natural degradation of sewage and contains reed, a particular type of grass plant
what is a suspended film system?
stir and suspend microorganism in waste water, and settle out as sludge
what is activated sludge?
mixed community of microorganism, both anerobic and aerobic may exist, forming a biological floc which is a large mass of bacteria in a mesh like structure
what is a feature of primary and secondary sludge?
primary sludge: strong odor
secondary: high concentration of microorganism
what are the goals of sludge treatment?
1- reduce odor 2-remove water 3-decompose organic matter
how much water does untreated sludge contain?
97% water
how much water does the treated sludge contain?
water reduced by 97-96% and the dried sludge is known as sludge cake
what are the components of activated sludge process?
1- aeration tank
2- aeration source
3-secondary clarifiers
4- activated sludge outflow line
5- effluent outflow line
what is aeration tank?
oxygen introduced into system
what is aeration source?
provides pure oxygen or compressed air and makes sure an adequate amount of oxygen is delivered
what is secondary clarifiers?
activated sludge solid separated from surrounding waste water
what is activated sludge outflow line?
activated sludge pumped into aeration tank again
what is effluent outflow line?
discharge effluent into sea/river or tertiary treatment plant
what are the types of sludge treatment?
aerobic digestion
anaerobic digestion
composting
what does aerobic digestion produce?
CO2
what does anaerobic digestion produce?
biogas used in electricity production
outline composting
type of aerobic process, where carbon, nitrogen, oxygen, water and sludge are mixed and produces a lot of heat
what occurs in sludge disposal?
1- sludge cake is spread out in fields
2-sludge is heated and converted into small granules rich in N2, which act as fertilizer
*all this saves landfill space
what are the types of tertiary treatment?
chlorination
uv light radiation
ozonation
advantages and disadvantages of chlorination
advantages
- low cost
-effective
advantages
- chlorine residue could be harmful to the environment
advantages and disadvantages of UV light radiation
advantages
- damages genetic structure of microorganism
- water taste more natural
- no chemicals used
disadvantages
-high maintenance of UV light
advantages and disadvantages of ozonation
advantages
- safer than chlorination
- fewer by products of disinfection
disadvantages
- expensive
what is the use of effluent?
1- discharged into rivers, lagoon and bay
2- irrigation of parks, golf course,etc
3- ground water recharged: surface water moves underground
what are the advanced treatments?
1- nitrogen removal
2- phosphorus removal
describe nitrogen removal
ammonia—nitrite—nitrate
describe phosphorus removal
precipitation with iron or aluminum salt
what do the advanced treatments cause?
eutrophication and algae blooms
