control options for pig waste practised by the farmers
in the study area were biogas and organic fertilizer
plants. The results of the financial and economic
analyses showed that both options were viable and that
the commercial biogas system yielded the highest
NPV. The use of biogas and pelletised organic
fertilizer was shown to generate high economic
returns. However, many of the farmers were resistant
to proposals to give up traditional practices, such as the
production of organic fertilizer, and adopt the new
biogas technology which was dependent on there
being government subsidies for investment costs. They
preferred to make organic fertilizer, which was easily
marketable, rather than convert the slurry into biogas.
Moreover, although surplus electrical energy produced
by biogas-driven generators could be sold to the
national electricity boards in developed countries, such
is not the case in developing countries. An option
recommended by the researchers was subsidizing the
investment costs of control options (i.e., the biogas and
organic fertilizer plants) through more affordable
credit schemes or through the donation or lease of
unused, disposable public land on which to build
biogas or fertilizer systems.
A study on pig slurries conducted in Vietnam by
Pain, Misselbrook and Crarkson (1990) concluded
that biogas digestion reduced odor emission by between
70-74 percent. The average manure DM
(decimetre) percentage was 25 percent and the loading
rates ranged from 0.1 to 1.2 kg/DM3 digester
liquid volume. Biogas digestion decreased chemical
oxygen demand (COD) from 35,610 mg/litre in the
inlet stage to 13,470 mg/litre in the effluent stage
indicating a process efficiency of 62 percent (COD
removal rate). The volume of gas per capita per day
required to cook three meals is about 200 litres.
Research by Intarangsi (2002) in Thailand showed
that the inefficiency of biogas digesters and the
general failure of the technology could be blamed
on the design of the digester. The study found that a
scum layer of manure and water in the digester
prevented gas generation and leakage of the gas was
due to the poor quality of the materials used in the
construction. In general, knowledge about the
biogas generation process using anaerobic microorganisms
was at a low level among pig farmers.
5. Research methodology
5.1. Approaches to evaluating pig waste management
options. In evaluating pig waste management
options, there are basically two approaches that
can be taken:
1. View the waste as a nuisance that has to be
eliminated. This approach focuses on finding the
(best) option that minimizes the net cost of getting
rid of the waste