Organic Waste Recycling

Biofuels production 195

Organic matter used for CH 4 production

= Organic matter stabilized - Organic matter used for cell production (4.6)

= (BODL stabilized – BODL for cell production) (4.7)

A relationship between BODL and CH 4 production is considered as follows:

C 6 H 12 O 6 3 CH 4 + 3 CO 2 (4.8)

3 CH 4 + 6 O 2 3 CO 2 + 6 H 2 O (4.9)

180 kg glucose produces 48 kg CH 4
180 kg glucose is equivalent to 192 kg BODL
i.e. 1 kg BODL produces

= (48/180)x(180/192) kg CH 4

= 0.25 kg CH 4

= 0.25 kg x (10^3 mol/16 kg)

x (22.4 L/1 mol) x (1 m^3 /10^3 L)

= 0.35 m^3 CH 4 at STP (standard temperature & pressure)

Volume of CH 4 produced, m^3 /day

= 0.35 (BODL stabilized – BODL for cell production) (4.10)

To solve Equation 4.10, the terms "BODL stabilized" and "BODL for cell
production" need to be determined.

BODL stabilized = EQSo(10^3 g/kg)-1 kg/day (4.11)

Where: E = Efficiency of waste stabilization, fraction

Q = Influent flow rate, m^3 /day, and

So = Ultimate influent BOD, g/m^3

From Equation 2.5,

kg O 2 = 160

kg Cells 113