Biological wastewater management Flashcards
What is the biggest organic constitute of domestic wasteand thier %?
- 30% carbohydrates
- 28% other fats, grease and micropollutants
What microorganisms cause intestinal disease?
- Salmonella spp
- Listeria spp
How much of sewage is water?
99.9%
What is the pollution control objective in terms of health?
Minimise risk of disease transmission by water-borne route
What is the pollution control objective in terms of ecology?
Minimise risk to the natural ecological balance of receiving water (eutrophication)
What is the pollution control objective in terms of aesthetic?
Maintain value of water for recreational activities/tourism
What is the pollution control objective in terms of economics?
Provide an appropriate level of treatment to achieve environmental protection at reasonable cost, GDP will suffer
What steps are involved in waste water treatment?
- Barscreening
- Grit removal
- Primary clarifier
- Aeration
- Secondary clarifier
- Chlorination
What does the secondary clarifier do?
- Separates biological floc from the treated liquid waste stream.
- Reduces organic matter content
What does the primary clarifier do?
- The major function of the primary clarifier is the removal of all settleable and floating solid waste that has a high oxygen demand – BOD.
- Water is stilled so tiny particles are suspended
What does preliminary screening do?
- Removes solid matter
What does the primary clarifier typically remove?
- 40% of BOD
- 60% of suspended solids
- 17% of nitrogen
- 20% of phosphorus
What des the secondary biological treatment typically remove?
- 95% of BOD
- 95% of suspended solids
- 29% of nitrogen
- 35% of phosphorus
What is effluent?
Effluent is sewage that has been treated in a septic tank or sewage treatment plant.
What does the tertiary treatment do?
- Reduce the load of micro-organisms and nutrients in the effluent
What does the tertiary treatment usually remove?
- 100% BOD
- 100% of suspended solids
- 33% of nitrogen
- 38% of phosphorus
What is biological oxygen demand?
BOD, also called biological oxygen demand, is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time.
What microorganisms are involved in wastewater treatment?
Bacteria, algae, and fungi
What are attached growth processes?
Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to the media in the reactor.
What are some attached growth processes?
Trickling/percolating biological filter
What are some suspended growth processes?
- Activated sludge process
- Main process employed at major wastewater treatment plant
What are suspended growth processes?
Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are suspended in the wastewater.
What’s good about biological filters?
- Very successful wastewater treatment system
- Widespread use for >120 years
- Less energy required than activated process (30-50% less)
What’s the negatives for biological filters?
- Superseded by activated sludge process at larger treatment facilities
- Larger footprint
How is the settled sewage supplied?
Through a distributor
What are the shapes of the aggregate beds usually?
Circular or rectangular aggregate bed
Why does the beds need to be a specific depth?
- Need to be 1.5-2.0m deep otherwise, you will introduce an anaerobic community
What happens in the attached growth process, biofilm development and purification process?
- Soluble organics and O2 diffuse into biofilm
- Direct ingestion by metazoa and protozoa
- Nitrification
What is nitrification?
- The process in which bacteria in the soil use oxygen to change compounds of nitrogen in dead plant material into nitrates which plants can then absorb as food.
What’s some advantages of attached growth processes?
- Simple operation
- Low maintenance
- Low energy use (30-50%
less than activated sludge) - Reliable
- Treat industrial WW
What are some negative of attached growth processes?
- Filter clogging due to excessive microbial growth
- Potential odors
- Fly nuisance
- Difficult to control
- Poorer operation in cold conditions
What is involved in activated sludge process?
- Continuous aerated reactor with feedback of biomass providing inoculum source and sites of biological activity → continuously stirred
- Excess sludge washed away to treatment - digester
What is a floc?
A large number of cells glued together
What is mixed liquor?
biomass + wastewater
How is mixed liquor suspensions maintained?
Turbulence
What achieves maximum rate of decomposition?
High microbial population
What is supernatant?
- The relatively clear water layer between the sludge on the bottom and the scum on the surface of an anaerobic digester, septic tank
- Discharged effluent
What are the purification mechanisms?
- Rapid stage
- Oxidation stage
What is involved in the rapid stage?
- Due to properties of floc
- Rapid adsorption + flocculation of soluble & colloidal matter
- Capture of particulate solid matter
- Rapid reduction in BOD
What is involved in the oxidation stage?
- Respiration at the inlet increased as organic matter oxidized
- Rapid oxidation of readily degradable organics
- Respiration < 1/10 initial rate at end of the tank
What are advantages of suspended growth processes?
- Increased process control
– Flexible as different redox environments created by
reactor design
– Reduced odor and fly problems
– Smaller footprint (10%) than attached growth systems
What are disadvantages of suspended growth processes?
– Susceptible to shock loads and contaminants
– Susceptible to biomass wash-out
– A more complex operation
