Lecture 5: Wastewater treatment outline Flashcards
What is the history of waste water treatment?
- Mesopotamians (~4000BCE)
Dev storm water drainage systems (babylon, iraq)
Larger homes had below ground cesspools
Origin of the earliest known clay work - Minoans pioneers of sewers (~3000BCE)
Royal palace at Knossos (crete, greece) had a latrine on the ground floor - Further developed by romans (~800 BCE)
Latrines were essential infrastructure even in remote settlements - Sewers (1830)
Originally used to carry away rain water. Sewage was acc collected by nigh-soil men - Water closet in affluent london houses (early 1800s)
No sewage systems in place though. This became a problem in from the industrial revolution, where cities became densely packed, leading to prevalence of water-Bourne diseases (eg typhoid, TB, cholera) - Sewers designed for rain water now carried raw sewage (1850s)
This was extracted and used for drinking water. The Thames basically became a cess pit
Who demonstrated that cholera was a water-bourne disease?
John Snow (1854)
Who was Joseph Bazalgette and what did he do?
Chief engineer to the metropolitan board works (1865)
Construction of main sewage collectors along the river Thames in 1865. Completed in 1875, separating waste from drinking water
How was the treatment of wastewater developed
Germ theory (Pasteur 1870s, Koch 1880s) and infection awareness - pollution and disease link
Trickling filter - 1890; rotating biological contractors early 1900s
1914 Arden & Lockett developed activated sludge process
What is the composition of wastewater?
Domestic wastewater: human & animal faeces/urine, gray water from washing, cooking, bathing etc
What are the objectives of wastewater treatment?
“reduce inorganic and organic materials in wastewater to a level that no longer supports microbial growth and eliminates other potentially toxic materials”
What are the 5 goals of wastewater treatments
- reduction of organic content
- removal/reduction of trace organics recalcitrant to biodegeneration that may be toxic
- removal/reduction of toxic metals
- removal/reduction of nutrients to reduce pollution of receiving waters
- removal/inactivation of pathogens
How is wastewater treated (from a process pov)
water water must be characterised (location, components)
treatment process must be monitored
treated water and sludge must be safely disposed of
What needs to be monitored in wastewater?
- organic carbon - req oxidation, measured as BOD or COD
- Inorganics - nutrients such as N, P, S. Toxic metals mainly from industrial and mining activates
- Special organics - volatiles, petroleum hydrocarbons. Non volatile polychlorinated biphenyls (PCBs), pesticides
- Microbiology - pathogens (not routinely monitored). “indicator” organisms
What does treatment need to achieve?
Typical concentrations of wastewater and effluent guidelines:
(mg/L)
BOD: 240 -> 25
COD: 500 -> 124
Suspended solids: 280 -> 35
pH: 7.2 -> 6.9
Phosphorus total: 11 -> 1-2
Nitrogen total: 40 -> 10-15
What is routinely analysed in wastewater?
- BOD (biochemical oxygen demand)
- NOD (nitrogenous oxygen demand)
- COD (chemical oxygen demand)
- Total organic carbon
- Suspended solids (SS)
What is BOD?
Biological oxygen demand - amount of dissolved oxygen (DO) consumed by microorganism for the biochemical oxidation of organic (carbonaceous BOD) and inorganic NOD
CBOD or BOD - 5 day measurement of the amount of O2 req to oxidise organic matter in sample
Organic compounds + O2 (microbes ->) CO2 + H2O + NH4 + biomass
How is BOD measured?
- Aliquot of wastewater placed in bottle, diluted, may be seeded with culture, saturated with oxygen and left in the dark
- DO is measured at start and after 5 days of incubation at 5C
- As carbon substrate is consumed a plateu is reached
What is NOD?
Nitrogenous oxygen demand - amount of DO req for biological oxidation of organic nitrogen in wastewater
Due to nitrifying bacteria that oxidise NH4 to NO3
Usually occurs after BOD due to slower growth of nitrifyers
Addition of nitrification inhibitor enable distinction between CBOD and NDO
What is COD?
Chemical oxygen demand - amount of O2 to oxidise organic carbon COMPLETELY to CO2, H2O and NH4 (independent of microbes)
Orgnanic compounds are oxidsed to CO2 by adding strong oxidisng agent (eg potassium dichromate) unfer acidic conditions
