Semi-continuous anaerobic digestion of different silage crops: VFAs formation, methane yield from fiber and non-fiber components and digestate composition.

This study presents the results of long-term semi-continuous experiments on anaerobic digestion at an HRT of 45d with ten silages: 2 annual and 4 perennial crops, and 4 mixtures of annual with perennial crops. The composition of substrates and digestates was determined with Van Soest's fractionation method. Removal of non-fiber materials ranged from 49.4% (Miscanthus sacchariflorus) to 89.3% (Zea mays alone and mixed with M. sacchariflorus), that of fiber materials like lignin ranged from 0.005% (Z. mays alone and mixed with grasses at VS ratio of 90:10%) to 46.5% (Sida hermaphrodita). The lowest stability of anaerobic digestion, as confirmed by normalized data concentrations of volatile fatty acids, was reported for both miscanthuses and sugar sorghum. The methane yield coefficients for non-fiber and fiber materials were 0.3666 and 0.2556L/g, respectively. All digestate residues had high fertilizing value, especially those from mixtures of crops.

Optimization of anaerobic digestion of a mixture of Zea mays and Miscanthus sacchariflorus silages with various pig manure dosages.

Digestion of crop silage (Zea mays L. and Miscanthus sacchariflorus) with 0%, 7.5%, 12.5% and 25% pig manure as co-substrate was performed in continuous stirred-tank reactors, for a constant hydraulic retention time of 45 d and organic load rate of 2.1 g L(-1)d(-1). A matrix of correlations between biogas/methane production and parameters of anaerobic digestion was created in order to estimate process stability. The values of the correlation coefficients indicated that the most stable anaerobic digestion was achieved using 7.5% and 12.5% pig manure. In contrast, the positive correlation between ammonium and volatile fatty acids (r=0.8698, p<0.001) at 25% pig manure showed process instability. Compared to crop silage alone, pig manure favored the production of biogas and methane; the highest production rates were obtained with 12.5% pig manure.

Molecular detection and diversity of medium-chain-length polyhydroxyalkanoates-producing bacteria enriched from activated sludge.

AIMS: Knowledge of the species composition of complex bacterial communities is still very limited. The main objectives of this study were to identify medium-chain-length polyhydroxyalkanoates (mcl-PHAs)-producing bacteria from activated sludge fed with methanol as well as to characterize their PHA operon. METHODS AND RESULTS: The identification was based on PCR amplification of mcl-PHA synthase gene fragments. In the analysed sample, four isolates possessing mcl-PHA synthesis systems were distinguished. The results of a 16S rDNA sequence analysis revealed that three strains belonged to Pseudomonas species and the fourth one was characterized as Comamonas testosteroni. CONCLUSIONS: The results of this study indicate that the PCR-RFLP approach is an excellent way to identify mcl-PHA-synthesizing micro-organisms. The discovery of 4 genetic variants, among the 20 analysed, demonstrates that microbial diversity of activated sludge is high and thus offers a great opportunity for the discovery of novel gene forms. SIGNIFICANCE AND IMPACT OF THE STUDY: An important discovery of this study is that C. testosteroni could harbour mcl-PHA operon. Moreover, the results obtained indicate that PHAs synthesis ability can be spread by horizontal gene transfer. The results of a comparative phylogenetic analysis revealed that mcl-PHA-synthesizing bacteria can be divided into Pseudomonas fluorescens and Pseudomonas aeruginosa groups.