Home Running Small-scale


Volatile Solids

COD

Temp (°C)

C

(m3kgVS-1)

k

(d-1)

C

(m3kgCOD-1)

k

(d-1)

34

0.895

0.0129 to 0.0033

0.513

0.0188 to 0.0054

25

0.829

0.0068 to 0.0023

0.525

0.0090 to 0.0031

16



0.514

0.0038

Table 1. First order rate constants for cattle dung in a batch plant.

There are two rate constants, the higher one up to about 35 days, the lower one after that time.

Tests at the University of Reading, detailed in “Running a biogas programme” gave the following results:


Volatile Solids

COD

Temp (°C)

C

(m3kgVS-1)

k

(d-1)

C

(m3kgCOD-1)

k

(d-1)

34

0.402

0.083

0.347

0.081

25

0.289

0.069

0.237

0.078

16

0.178

0.033

0.164

0.026

Table 2. First order rate constants for dung for semi-continuous plant.

The data derived for semi-continuous tests gave rather different values from those derived from batch tests. This suggests that data from batch tests does not properly predict the behaviour of semi-continuous plants.

Published data (Banks and Heaven, 2013) from Southampton University provides values for food waste:


Volatile Solids

Temp (°C)

C

(m3kgVS-1)

k

(d-1)

34

0.47

0.73, 1.02 to 0.06

Table 3. First order rate constants for food waste in a batch plant.

This data also suggests two rate constants, one at shorter retention times, the other at longer; the first value is an average.

Food wastes have higher rate constant values than cattle dung.    

More tests need to be done.