Production of Methane Biogas as Fuel Through Anaerobic Digestion - Sustainable Biotechnology: Sources of Renewable Energy - page 122

4.3 Tipping the Balance Between Drivers and Barriers
The balance between the drivers and the barriers for a potential commercial AD
project is primarily centered on the financial economics of the AD system to be
installed, which includes the capital and operating cost, the cost of the feedstock
(e.g., the cost of acquisition, transportation, preparation, or alternative disposal),
and the revenues and credits that can be realized from AD operations. To tip the
balance towards the drivers, the capital and operating cost need to be minimized
while the revenues and credits need to be maximized. More efficient, cost-effective,
reliable, and versatile AD technologies are needed to strengthen key drivers and
diminish many of the uncertainties related to AD technologies. However, a bet-
ter understanding of the microbiological underpinning of AD processes is required
to develop such AD technologies. Additionally, incentives from governments and
public support are also important to encourage AD implementation.
5 Future Perspective
Methane biogas production is rather slow [89], and large digesters are often required
to produce enough biogas to be recovered cost-effectively as energy. AD processes
are also susceptible to a host of factors, which can render AD suboptimal or some-
times lead to unpredictable upset or total failure of AD [17]. The re-startup and
recovery process after failure are often slow [17, 64, 84]. These limitations and
other barriers can severely undermine the economic viability of AD processes and
make many industries and farmers reluctant to implement this biotechnology. These
issues and the research required to improve AD for bioenergy production are briefly
discussed below.
5.1 Enhancing Biomass Conversion and Methane Production
From an economic, social and environmental perspective, lignocellulosic biomass
wastes are good feedstocks for methane production through AD. Due to the slow
hydrolysis of lignocellulose, however, methane production is slow, and a long reten-
tion time and large digester volumes are required to produce enough methane
biogas for cost-effective recovery. In the case of livestock manure, 40-50% of
the solid passes through mesophilic AD undigested [8]. Two-stage AD processes
can improve solid reduction and stability by separating the more robust hydrolysis
and acidogenesis from the less robust syntrophic acetogenesis and methanogenesis
[13]. TPAD digesters are promising two-stage designs, with the hydrolysis being
enhanced in the first digester operated at an elevated temperature (typically at 55 ◦ C)
and syntrophic acetogenesis and methanogenesis being enhanced and stabilized in
the second digester operated at a mesophilic temperature (typically 35 ◦ C) [46, 78].
Indeed, significant increases in hydrolysis, TS reduction, and methane production