Organic Waste Recycling

216 Organic waste recycling: technology and management

loading rate of the bag digester and HRT recommended by the producer are,

respectively, 1.5 kg VS/m^3 -day and 30 days for pig wastes diluted with

water. Other data are available in Table 2.7. Determine the number of bag

digesters that should be installed to treat the pig wastes and the amount of

biogas to be produced if the biogas production rate is 0.3 m^3 /kg VS added. If

the density of the pig wastes is 1.1 kg/L, what is the volume of dilution

water required?

4.5 Differentiate the hydraulic patterns and treatment mechanisms occurring in
an anaerobic filter and an upflow sludge blanket reactor.

4.6 A farmer in a rural area in northern Thailand plans to use cattle manure to
produce about 5 m^3 /day of biogas for domestic use.

a) Determine the size of the biogas digester, the amount of cattle manure

to be added to the biogas digester and the amount of water dilution (if

necessary), in order to produce the required amount of biogas.

b) If the biogas contains 30% CO 2 (by volume), determine the amount of

Ca(OH) 2 needed to completely remove CO 2 from the biogas. How

much sludge is produced from this CO 2 removal operation and how

should this sludge be handled by the farmer?

Given: Ca(OH) 2 + CO 2 ĺ CaCO 3 + H 2 O

c) If the farmer wants to produce ethanol from his cattle manure, based on

theoretical knowledge given in section 4.7, explain how it can be done.

Draw schematic diagram.

d) If you are to advise this farmer on the production of biofuel from cattle

manure, would you advise that he produce biogas or ethanol? Give

reasons.

The following information are given:

For cattle manure:

VS content = 300 kg/m^3 of manure (wet weight)

For biogas digester:

Organic loading rate = 3 kg VS/(m^3 -day)

Hydraulic retention time = 30 days

Biogas production = 0.3 m^3 /kg VS added