The application of anaerobic digestion technology is growing worldwide because of its economic and environmental benefits. As a consequence, a number of studies and research activities dealing with the determination of the biogas potential of solid organic substrates have been carrying out in the recent years. Therefore, it is of particular importance to define a protocol for the determination of the ultimate methane potential for a given solid substrates. In fact, this parameter determines, to a certain extent, both design and economic details of a biogas plant. Furthermore, the definition of common units to be used in anaerobic assays is increasingly requested from the scientific and engineering community. This paper presents some guidelines for biomethane potential assays prepared by the Task Group for the Anaerobic Biodegradation, Activity and Inhibition Assays of the Anaerobic Digestion Specialist Group of the International Water Association. This is the first step for the definition of a standard protocol.

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To provide new insight into the dark fermentation process, a multi-lateral study was performed to study the microbiology of 20 different lab-scale bioreactors operated in four different countries (Brazil, Chile, Mexico, and Uruguay). Samples (29) were collected from bioreactors with different configurations, operation conditions, and performances. The microbial communities were analyzed using 16S rRNA genes 454 pyrosequencing. The results showed notably uneven communities with a high predominance of a particular genus. The phylum Firmicutes predominated in most of the samples, but the phyla Thermotogae or Proteobacteria dominated in a few samples. Genera from three physiological groups were detected: high-yield hydrogen producers (Clostridium, Kosmotoga, Enterobacter), fermenters with low-hydrogen yield (mostly from Veillonelaceae), and competitors (Lactobacillus). Inocula, reactor configurations, and substrates influence the microbial communities. This is the first joint effort that evaluates hydrogen-producing reactors and operational conditions from different countries and contributes to understand the dark fermentation process.

This study investigated the microbial community developed in a UASB reactor for hydrogen production and correlated it to reactor performance. The reactor was inoculated with kitchen waste compost and fed with raw cheese whey at two organic loading rates, 20 gCOD/Ld and 30 gCOD/Ld. Hydrogen production was very variable, using an OLR of 30 gCOD/Ld averaged 1.0 LH(2)/Ld with no methane produced under these conditions. The hydrogen yield was also very variable and far from the theoretical. This low yield could be explained by selection of a mixed fermentative population with presence of hydrogen producing organisms (Clostridium, Ruminococcus and Enterobacter) and other non-hydrogen producing fermenters (Lactobacillus, Dialister and Prevotella). The molecular analysis of the raw cheese whey used for feeding revealed the presence of three predominant organisms that are affiliated with the genera Buttiauxella (a low-yield hydrogen producer) and Streptococcus (a lactic acid-producing fermenter). Although these organisms did not persist in the reactor, the continuous addition of these fermenters could decrease the reactor's hydrogen yield.

Performance parameters were studied in an alternative full-scale dairy effluent treatment system comprising two anaerobic sludge-blanket reactors in parallel arrangement with upward flow, internal fat-separation by flotation, external lamella settler and floated material digester. Reactors were initially inoculated with flocculent sludge and granulated in a high-load stage. Using loading rates up to a maximum 5.5 kg COD/m(3) x d-hydraulic residence time of 17 hours- reactor efficiency was found to remain stable around 90% of COD. Average sludge digester efficiency using a loading rate of 3.5 kgVS/m(3) x d with a lipid content of 47% of COD amounted to 78% of VS (87% of lipid removal). LCFA inhibition as assayed using palmitate was found to depend not only on the palmitate concentration but also on the palmitate-to-biomass concentration ratio.

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