THE SPECIFIC OXYGEN
UPTAKE RATE
Ed Stentiford
The University of Leeds
EU Biowaste Workshop – Brussels April 2002
Stability and Maturity
• Stability
§ Relates to microbial activity
§ More relevant during the early stages of
composting
• Maturity
§ Relates more to the beneficial effects of the
compost from a plant viewpoint
• Area of overlap
§ ‘grey’ area at the end of the high rate biooxidative phase
EU Biowaste Workshop – Brussels April 2002
Tests for stability
• No single parameter widely accepted
• Combination of tests likely to be
needed
• Respirometric tests seem most useful
§ Based on well-understood principles
§ Relatively high degree of reliability and
repeatability
§ Fairly simple and inexpensive
EU Biowaste Workshop – Brussels April 2002
Development of SOUR
• Originally as a research tool to monitor
composting progress
§ Since been used on a wide range of processes
and materials
• Based on the BOD test which is
§ Used routinely in wastewater treatment
§ Has been adapted to be used as a
respirometric test
• SOUR further adaptation of the BOD
EU Biowaste Workshop – Brussels April 2002
Thinking behind SOUR
• Reproducubility
§ Solid state results are dependent on material
structure and moisture
§ Liquid suspension removes limitations related to
structure, moisture content and oxygen
availability
• Ease of use
§ Uses standard pieces of laboratory equipment –
requiring no specialist training
• Low cost
§ Operates at 30oC – uses DO monitors (no need
for sealed respirometers)
EU Biowaste Workshop – Brussels April 2002
Apparatus
Interface (A/D)
& controller
DO meters
O2 probe
Fish tank
pumps
Compost
suspension
Water bath, 30 oC
EU Biowaste Workshop – Brussels April 2002
Methodology
•
•
•
•
Screen material through 10 mm
Break up large solids
Use 3-8 gm of solids (or more)
Add to 500ml of distilled water
•
•
•
•
Blend for 30s
Set in water bath at 30oC
Alternate aeration and DO measurement
Measure the max rate of DO consumption
§ The mass and liquid amount are matched
according to the projected O2 consumption rate
EU Biowaste Workshop – Brussels April 2002
Typical DO rate response – Figure 2
DO (mg O2/l)
8
6
4
2
0
0
5
10
15
Time (hours)
EU Biowaste Workshop – Brussels April 2002
20
Typical SOUR profile – Figure 3
mg O2/ g VS/ hr
25
SOUR
20
15
OD20
10
5
0
0
10
20
30
40
Time (hours)
EU Biowaste Workshop – Brussels April 2002
50
Use of SOUR
• Used in Leeds since early 90s
• SOUR v OD20 (Figure 3)
§ Correlation over a wide range of feedstocks
has been good
§ Peak value used as it is easier
• Figure 4 (in paper) shows a typical set of
results
§ Figure presented for MSW and sewage
sludge mixtures being windrowed
EU Biowaste Workshop – Brussels April 2002
Typical SOUR results - windrow
Pile 1
Pile 2
Pile 3
mg O2/ g VS/ hr
20
15
10
5
0
0
20
40
60
80
Age (days)
EU Biowaste Workshop – Brussels April 2002
Self-heating
Tmax - Ta (oC)
60
MSW1
MSW2
40
20
0
0
20
40
60
80
Age (days)
EU Biowaste Workshop – Brussels April 2002
SOUR and self-heating
Self heating - good
Tmax - Ta (oC)
60
SOUR - good
50
40
30
20
10
0
0
5
10
15
20
25
SOUR (mg O2/g VS/hr)
EU Biowaste Workshop – Brussels April 2002
Germination index
MSW1
MSW2
% of control
100
80
60
40
20
0
0
20
40
60
Age (days)
EU Biowaste Workshop – Brussels April 2002
80
SOUR and Solvita with green waste
Time (days)
Solvita
SOUR
0
3
5.9
7
3
3.1
10
4
15
4
0.8
21
4
0.9
28
5 Small change
0.5
35
5
0.4
Large change
-
EU Biowaste Workshop – Brussels April 2002
Working at different temperatures
• Temperature originally set to be above
ambient (in UK) hence 30oC
• Higher temperature more rapid result
§ Italian results from work at 35oC
• If baseline is needed relationship of the
form
SOURT = SOUR30 Θ(T – 30)
EU Biowaste Workshop – Brussels April 2002
Results from SOUR at 35oC
Refining – removed plastic
20
80
70
60
50
15
40
10
30
20
5
10
0
0
20
40
60
80
0
100
Giorni di proce s s o
SOUR
CO2
Temperatura
EU Biowaste Workshop – Brussels April 2002
Temperatura (C°)
SOUR (mgO2 · gSV-1 · h-1) & CO2 (%)
25
Conclusions
• Relatively inexpensive and simple to
operate
• Good signal response without O2 transfer
limitations with solid matrix
• Robust indicator used successfully with a
wide range of waste types
• Good indicator of stability but NOT for
following maturity
EU Biowaste Workshop – Brussels April 2002
Dilbert puts it in perspective!
EU Biowaste Workshop – Brussels April 2002