Biofiltration Flashcards
What is the Empty bed residence time, EBRT equation?
EBRT (T) = Volume / Q (flowrate)
Biofilter/trickling filters/bio scrubbing comparison?
Biofilters are the best as there is no other treatment option which can treat such high concentration and high gas flow rate.
Why are trickling bed with recirculating water less attractive than biofilters for compounds with large henrys constant?
gases have lower solubility = high henry’s constant.
The efficiency of trickling beds is based on the solubility of the component so the water can capture the soluble material and remove it from the gaseous phase.
Why clay/sand ratio of the soil in a soil/bark biofilter is important?
When there is too much clay it can become very hard when not supplied enough water, which would result in bed cracking and have lasting issues within the bed.
Why biofiltration?
When is it best used?
A biology based reactor to treat gas streams for emissions and odour control
Biofiltration is best for low concentration and high air flowrates
Describe the biofiltration process?
- The contaminated air is pre-treated to remove dust and entrained oils and fats
- The air then moves through the air distribution system into the bed. The clean air comes out the top and the condensate come out the bottom.
- The containment will diffuse into the biofilm, an oxidation reaction will occur.
What are the 5 major phases of a multiphase plug flow packed bed reactor?
- air - waste stream in and out
- solid support treated as inert
- biofilm is the catalytic activity which drives the oxidation reaction
- water phase, never let it dry out or bacteria will die
- nutrients to get higher activity of biomass growth, can plug system however
Three things to monitor in the design and operation of bioreactor?
- Emission Requirements
Smelly effluent?
Emission standards from council? - Pressure drop increase
Bad if this happens.
Decreased flow rate, in turn will need an increased blower speed which costs money - Water
Too dry? Too Wet?
Need to make sure not too dry
Why would a biofilter fail? (Physically and biologically)
Physically:
- Moisture percent
- high pressure issues
Biologically
- Rare
- pH or nutrient problems
What are the four design parameters of a biofilter reactor BED?
- Pressure drop
Low as possible, expensive if high gas flows - Temperature
Wide range, fluctuations can change water percentage greatly - EBRT
Between 30-120 seconds - Bed depth
Average 1 m, impact air distribution and pressure drop.
What four things does biofilter pre-treatment invole?
- Particulates -> dust and entrained liquids
- Temperature -> May need to vary the inlet temp
- Humidity -> if the air stream in dry is <98% you will have to humidify it and add water to your bed. if hot and wet some dehumidification may be needed.
- Concentration fluctuations
Design for max Conc
Describe the flow directions for:
- Hot water saturated gas
- Humidified dry gas
- high mass loading
- H2S or NH3
- Hot water saturated gas= UP FLOW
(Ground can be heat sink, collect condensate at the bottom) - Humidified dry gas= DOWN FLOW
(drying concentration at inlet, spray extra water on top of bed) - high mass loading = DOWN FLOW
- H2S or NH3 = UP FLOW
(do not want it to acidify)
Compare the two moisture controls for
- Low containments loading/saturated air (3)
- High containments loading/unsaturated air (2)
- Low containments loading/saturated air
- Open top
- Manual water addition
- very low water demand - High containments loading/unsaturated air
- Automatic control by embedded controls or weight of entire biofilter overtime
- High rate of water addition and recycle effluent water
What are the two pH controls when pH = 7?
- Extra irrigation
- wash acid from bed
- leachate disposal an issue - Buffering
- add CaCO3
- amount should be less than 10% of the bed volume
- this leads to shorter bed life
What are the strengths of biofilters? (4)
- Low Opex and Capex
- No additional fuel or NOx emissions
- Minimal additional waste
- Familar technology
