L8 - Ex-situ Microbial strategies

Question 1

How can groundwater be collected?

Answer 1

Pumping water to the surface setting up a flow towards the bore hole

Question 2

What is an aerated lagoon?

Answer 2

• Contaminated water pumped in one end
• Nutrients and O added
• Clean water removed at other end

Question 3

How do suspended growth bioreactors work?

Answer 3

• Control of temp, pH and nutrient levels

Question 4

What is a disadvantage of suspended growth bioreactors and how is this overcome?

Answer 4

• If washout rate of organisms greater than growth, only limited treatment will occur
• Dispersed or homogeneous growth reactor processes used

Question 5

What are dispersed or homogeeous growth reactors commonly referred to as?

Answer 5

Activated sludge process

Question 6

What do the microbes in activated sludge do?

Answer 6

Breakdown pollutant into biomass, CO2 and water

Question 7

What is done with the biomass from bioreactors and what is it used for?

Answer 7

Collected as sludge (floc forming bacteria)

Some re-used as inoculum

Question 8

What two types of activated sludge plants are there?

Answer 8

Batch and continuous

Question 9

What are the features of a batch reactor?

Answer 9

Tank filled, reaction carried out, sludge settles, water drawn off, sludge removed, repeat

Question 10

What are the features of continuous systems?

Answer 10

Continually added to and removed from

Question 11

What happens when a continuous system is too fast or too slow?

Answer 11

Fast - wash out

Slow - inefficient

Question 12

What are fixed film bioreactors?

Answer 12

Microbes immobilised and water is passed over

- Organisms that oxidise form a biofilm over support matrix

Question 13

What is a trickle filter / biofilter / bacteria bed / percolating filter

Answer 13

Water distributed over a media trickles down through packing material before collection underneath

Question 14

What are the features of trickle filters?

Answer 14

Air passes through spaces allowing oxygen transfer

Microbial film grows and eventually falls through as small flocs

Question 15

What are the advantages of trickle filters?

Answer 15

Simple to operate
Low running costs
Able to survive toxic loading

Question 16

What aare the disadvantages of trickle filters?

Answer 16

Use a lot of land
Limited treatment efficiency
Seasonal patterns of treatment

Question 17

What is a rotating biological contactor (RBCs) / biodisk?

Answer 17

Support matrix dipped into contaminated water using rotating supports

Question 18

What are the advantages of RBCs?

Answer 18

Easy to operate
Low land requirement
Reduced power costs
Stable against toxics

Question 19

What are the disadvantages of RBCs?

Answer 19

Lack of operational control

Problems of bearing failures and broken disks

Question 20

What are slurry reactors?

Answer 20

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

Question 21

How do soil piles work?

Answer 21

Like landfarming
Impermeable lining underneath
Soil contains perforated pipes for O, nutrients rained on
Can be kept inside

Question 22

What is the degradation rate of hydrocarbons in soil piles?

Answer 22

69% per year

Question 23

Disadvantages of soil piles?

Answer 23

Limited by permeability of soil

Land use

Question 24

What is composting?

Answer 24

Polluted material mixed with solid organic substance that is slowly degraded (straw, woodchips)
Bulking agent improves aeration and drainage
Stimulate cometabolism

Question 25

What 3 separate tasks are necessary for composting?

Answer 25

Excavation
Sizing and mixing
Biological decomposition

Question 26

What 3 ways can composting be optimised?

Answer 26

Rate of decomp
Pathogen control
Odour management

Question 27

What are the key parameters of composting?

Answer 27

C:N ratio (25:1 to 40:1)
Moisture (50%)
Oxygen
Increased temp (45-59)

Question 28

What are the features of the composting process?

Answer 28

1. Initial warming, rapidly degradable components, mesophilic bacteria and fungi
2. High microbial activity, high temp (60+), thermophilic bacteria high
3. Curing, temp falls, bacteria and fungi return

Question 29

What is windrow composting?

Answer 29

Material laid out in long rows and is turned mechanically

Question 30

What are the features of static composting piles?

Answer 30

Not mechanically agitaed

Aerated by blower and tubes

Question 31

What are the features of horizontal reactors?

Answer 31

Turn to move material through aerated tube continuously

Question 32

What changes occur to materials during composting?

Answer 32

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