L8 - Ex-situ Microbial strategies Flashcards
How can groundwater be collected?
Pumping water to the surface setting up a flow towards the bore hole
What is an aerated lagoon?
- Contaminated water pumped in one end
- Nutrients and O added
- Clean water removed at other end
How do suspended growth bioreactors work?
- Control of temp, pH and nutrient levels
What is a disadvantage of suspended growth bioreactors and how is this overcome?
- If washout rate of organisms greater than growth, only limited treatment will occur
- Dispersed or homogeneous growth reactor processes used
What are dispersed or homogeeous growth reactors commonly referred to as?
Activated sludge process
What do the microbes in activated sludge do?
Breakdown pollutant into biomass, CO2 and water
What is done with the biomass from bioreactors and what is it used for?
Collected as sludge (floc forming bacteria)
Some re-used as inoculum
What two types of activated sludge plants are there?
Batch and continuous
What are the features of a batch reactor?
Tank filled, reaction carried out, sludge settles, water drawn off, sludge removed, repeat
What are the features of continuous systems?
Continually added to and removed from
What happens when a continuous system is too fast or too slow?
Fast - wash out
Slow - inefficient
What are fixed film bioreactors?
Microbes immobilised and water is passed over
- Organisms that oxidise form a biofilm over support matrix
What is a trickle filter / biofilter / bacteria bed / percolating filter
Water distributed over a media trickles down through packing material before collection underneath
What are the features of trickle filters?
Air passes through spaces allowing oxygen transfer
Microbial film grows and eventually falls through as small flocs
What are the advantages of trickle filters?
Simple to operate
Low running costs
Able to survive toxic loading
What aare the disadvantages of trickle filters?
Use a lot of land
Limited treatment efficiency
Seasonal patterns of treatment
What is a rotating biological contactor (RBCs) / biodisk?
Support matrix dipped into contaminated water using rotating supports
What are the advantages of RBCs?
Easy to operate
Low land requirement
Reduced power costs
Stable against toxics
What are the disadvantages of RBCs?
Lack of operational control
Problems of bearing failures and broken disks
What are slurry reactors?
Similar to sludge process but with soil
Material screened to remove 60mm+ which could block pipes
30-50% Contaminated soil mixed with water
Fed into slurry reactor for decontamination then passed into settling tank - water recycled
How do soil piles work?
Like landfarming
Impermeable lining underneath
Soil contains perforated pipes for O, nutrients rained on
Can be kept inside
What is the degradation rate of hydrocarbons in soil piles?
69% per year
Disadvantages of soil piles?
Limited by permeability of soil
Land use
What is composting?
Polluted material mixed with solid organic substance that is slowly degraded (straw, woodchips)
Bulking agent improves aeration and drainage
Stimulate cometabolism
What 3 separate tasks are necessary for composting?
Excavation
Sizing and mixing
Biological decomposition
What 3 ways can composting be optimised?
Rate of decomp
Pathogen control
Odour management
What are the key parameters of composting?
C:N ratio (25:1 to 40:1)
Moisture (50%)
Oxygen
Increased temp (45-59)
What are the features of the composting process?
- Initial warming, rapidly degradable components, mesophilic bacteria and fungi
- High microbial activity, high temp (60+), thermophilic bacteria high
- Curing, temp falls, bacteria and fungi return
What is windrow composting?
Material laid out in long rows and is turned mechanically
What are the features of static composting piles?
Not mechanically agitaed
Aerated by blower and tubes
What are the features of horizontal reactors?
Turn to move material through aerated tube continuously
What changes occur to materials during composting?
Start as polysaccharides, lignin and tannin
End has low polysaccharide content, most is microbial cell wall and extracellular gums
25% of initial C present in humic substances, rest lost as CO2
30-50% organic matter, remainder minerals
