Biofiltration Flashcards
What is a biofilm in drinking water systems?
A microbe city where many micro-organisms live together on a surface
Describe the 5 step process of how a biofilm is formed?
Step 1: One planktonic organism attaches itself to the surface
Step 2: With the help of EPS (Extra Polymetric Substances) the bacteria glue together and form a monolayer
Step 3: The bacteria can now co-exit and begin form a multilayer where they compete with each other.
Step 4: The biofilm is now matured which resemble a ‘mushroom’ formed polysaccharide
Step 5: At a certain point planktonic organisms will detach from the film and restart the cycle
What is EPS and mention 4 reasons why EPS is important for Biofilm growth?
Extracellular Polymeric Substances:
- Aids in attachment of micro-organisms to a surface
- Natural Polymers of high molecular weight
- Excreted by mico-organisms
- Estimated 50-90% of organic matter in a biofilm is EPS
What is a biological filter?
A flow-through porous media where conversion by micro-organisms is utilised to remove specific contaminants
What does flow-through mean in relation to a Biofilter?
A continuous flow through the media aka not a batch or in-line process
What is a conversion by micro-organisms?
The removal or inactivation by bacteria or other micro-organisms
What are the fundamental differences between a submerged and a trickling filter?
Submerged filters:
- Contain Supernatant water
- Pores of filter media are filled with water
- Va = Vd/porosity (saturated)
Trickling Filter:
- No Supernatant water
- Filter Media pores contain water and air
- Va = Vd/pore moisture (unsaturated zones)
What is the difference between diffusion and mechanical dispersion within a biofilter?
Both diffusion and dispersion occur at the same time in a biofilter
Diffusion: the net movement of ions/molecules from a high concentration to a lower concentration
Mechanical Diffusion: the enhanced spreading of a solute due to changes in velocity caused by micro-scale differences in permeability and porosity of the porous media
Key difference is diffusion is driven by pressure differences and dispersion by velocity differences.
How do short-circuiting and stagnant zones occur in a biofilter?
Short-Circuiting: filter pores tend to not be homogeneously distributed therefore uneven distribution flow velocity will occur and some molecules will not pass through/ arrive at the same time
Stagnant Zones: Diffusionat the interface of the pores which are not contributing equally
What is Biodegradation?
When a solute contaminate interacts with a biofilm and is converted, broken down or inactivated
Sketch a typical retardation/breakthrough curve for the Conservative Tracer vs a Contaminant in Adsorption, Biodegradation and a combination of them both and ion exchange
Adsorption: Curve moves to the right
Biodegradation: Curve moves below
Both: Curve moves to the right and down
Why in biofiltration would you use a submerged filter or a trickling filter?
If ammonium is present in your water then a trickling filter is preferred because of the air present in the pore’s will allow O2 to be present throughout the filter however a submerged filter will limit the oxygen and therefore there will not be enough O2 present for the conversion of Ammoniu
Give two examples of stratification in filters?
Give two examples of stratification in filters?
Slow Sand Filters: The shmekdeka causes cake filtration where heterotrophic bacteria consume organic carbon present in the water. Below this layer, there could be grazing by protozoa which is responsible for the removal of pathogenic microorganisms.
Groundwater filter: the layering of processes is redox driven, first layer is the oxidation of Iron, then oxidation of Ammonumn and the oxidation of nitrite and lastly at the bottom of the filter manganese deposits are seen due to oxidation of Manganese.
Why should we remove iron during drinking water treatment?
- Athsethics: Drinking water should be clear and not brown
- Law: The drinkwaterbesluit requires it
- Costs: Cleaning the distribution network is expensive
- Operation: Iron fouling can cause problems in treatment plants
