Production of Methane Biogas as Fuel Through Anaerobic Digestion - Sustainable Biotechnology: Sources of Renewable Energy - page 124

can achieve microbe-based continuous online monitoring. Such real-time monitor-
ing can directly link to automated digester controls, such as loading and mixing.
Advanced understanding of the microbial community structure, population dynam-
ics, metabolic kinetics, and online monitoring in digesters will also improve the
modeling of AD processes [6, 35].
5.3 Better Knowledge on the Microbial Communities in Digesters
The microbial community residing in digesters largely remains a black box [65].
This is largely attributed to the difficulties and inability to grow these microbes
in laboratory media. The use of cultivation-independent DNA-based molecular
biology and metagenomic techniques makes it possible to define the membership
and functionality of this complex microbial community (e.g., reviewed in [41]).
As indicated by the more than 5,265 bacterial and 839 archaeal 16S rRNA gene
sequences of anaerobic digester origin archived in the Ribosomal Database Project
(RDP) (as of this writing, unpublished data), our knowledge on this microbial
community has expanded tremendously [61, 65]. These sequences represent approx-
imately 2,500 species of bacteria (based on 97% 16S rRNA gene sequence identity)
and 160 species of archaea (unpublished data). Our statistical prediction suggests
that AD reactors can have at least 3,500 species of bacteria and 170 species of
archaea. The continued studies using both molecular biology and metagenomic
techniques should provide a better knowledge on the microbial community struc-
ture, population dynamics, adaptation, granulogenesis, and metabolic kinetics in
digesters. Eventually, this knowledge will help develop more efficient and stable
AD technologies.
5.4 Strengthening the Drivers and Eliminating the Barriers
Several barriers exist that make many industries and farmers reluctant to imple-
ment AD to convert their biomass wastes to methane biogas. Improvements in
AD technologies with respect to efficiency, reliability, and cost-effectiveness will
overcome some of the barriers related to the technologies. Other barriers can only
be debased from policy and public supports. While it is broadly realized that the
building of a sustainable society requires both renewable energy and protection of
the environment, the valuation of such is incomplete. AD is one of the few tech-
nologies that help achieve both goals. Even the bioethanol and biodiesel industries
generate biomass wastes, which need AD to extract otherwise wasted energy and
to reduce environmental pollution. Therefore, AD should be regarded as a unique,
indispensable, renewable energy-producing biotechnology that protects the environ-
ment. With continued improvement of AD technologies and supports from both the
public and the government, AD will become more cost-effective, energy-efficient,
reliable, and widely implemented. AD will evolve into one of the most environment-
friendly biotechnologies that produce cost-effective bioenergy in the next five to ten
years.