Specialist Group on ANAEROBIC DIGESTION Newsletter - IWA

Improving stability of anaerobic digesters for animal waste treatment
by Marcelo Loureiro Garcia (mlgarcia@rc.unesp.br)
New PhD Contact:
Assistant Professor
Universidade Estadual Paulista (UNESP)
Instituto de Geociências e Ciências Exatas de Rio Claro
Departamento de Petrologia e Metalogenia
Av. 24/A, 1515. Bela Vista
Rio Claro, SP 13506-900, Brasil
Tel: +55 (19) 3526 2833
mlgarcia@rc.unesp.br
Supervisor:
Largus (Lars) Angenent, PhD
Associate Professor
Biological and Environmental Engineering
Cornell University
214 Riley-Robb Hall
Ithaca, NY 14853, USA
Tel: +1-607-255-2480 Fax: +1-607-255-4080
la249@cornell.edu
Abstract:
In countries where concentrated animal feeding operations (CAFOs) are used, implementation of animal waste
treatment is desired for both environmental protection and energy recovery. The capability of anaerobic systems
to produce large quantities of biogas from animal wastes has been demonstrated, however, a lack of knowledge
on the microbial community structure exits. Four 5-liter anaerobic sequencing batch reactors (ASBRs) were
operated over a period of 988 days to treat swine waste. Over the course of three distinct operating periods, the
performance of the bioreactors was assessed with conventional environmental engineering techniques, while
archaeal and bacterial microbial communities were unraveled with molecular biology techniques. The bacterial
community analyses did not show a significant difference between low- and high-ammonia reactors for different
temperatures at the phyla level, with Firmicutes and Bacteroidetes as the predominant bacterial phyla. Members
of the family Methanosarcinaceae and of the order Methanomicrobiales predominated as acetoclastic and
hydrogenotrophic methanogens, respectively. The performance of the anaerobic digesters was clearly affected
by varying total ammonium concentrations and mesophilic temperatures, however, this did not result in a
considerable microbial community shift. Carbon and energy sources outplayed toxicity effects of ammonia and
temperature constraints of kinetics and thermodynamics in determining the microbial bioreactor communities.
However, some changes in the community were found. For instance, a gene sequencing survey from a sample
enriched with 13 C-acetate indicated an enhancement of sequences from the genus Pseudomonas (among other
uncultured phyla), explaining the 25% methane that was generated via an alternative pathway: syntrophic
acetate oxidation (with GC-MS). This pathway only occurred at very high ammonia concentrations (5,200 total
ammonium-N (mg/L)), which prevented unstable conditions in the bioreactors with high ammonia levels. We
showed that powerful molecular biology techniques are needed to monitor incremental changes in the
community structure that can have large effects on reactor stability.
IWA <strong>Specialist</strong> <strong>Group</strong> on Anaerobic Digestion
22 June 2009 Newsletter