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Anaerobic digestion is an efficient and renewable energy technology that can produce biogas from a variety of biomasses such as animal manure, food waste and plant residues. In developing countries this technology is widely used for the production of biogas using local biomasses, but there is little information about the value of these biomasses for energy production. This study was therefore carried out with the objective of estimating the biogas production potential of typical Vietnamese biomasses such as animal manure, slaughterhouse waste and plant residues, and developing a model that relates methane (CH4) production to the chemical characteristics of the biomass. The biochemical methane potential (BMP) and biomass characteristics were measured. Results showed that piglet manure produced the highest CH4 yield of 443 normal litter (NL) CH4 kg−1 volatile solids (VS) compared to 222 from cows, 177 from sows, 172 from rabbits, 169 from goats and 153 from buffaloes. Methane production from duckweed (Spirodela polyrrhiza) was higher than from lawn grass and water spinach at 340, 220, and 110.6 NL CH4 kg−1 VS, respectively. The BMP experiment also demonstrated that the CH4 production was inhibited with chicken manure, slaughterhouse waste, cassava residue and shoe-making waste. Statistical analysis showed that lipid and lignin are the most significant predictors of BMP. The model was developed from knowledge that the BMP was related to biomass content of lipid, lignin and protein from manure and plant residues as a percentage of VS with coefficient of determination (R-square) at 0.95. This model was applied to calculate the CH4 yield for a household with 17 fattening pigs in the highlands and lowlands of northern Vietnam.

In developing countries, biogas energy production is seen as a technology that can provide clean energy in poor regions and reduce pollution caused by animal manure. Laboratories in these countries have little access to advanced gas measuring equipment, which may limit research aimed at improving local adapted biogas production. They may also be unable to produce valid estimates of an international standard that can be used for articles published in international peer-reviewed science journals. This study tested and validated methods for measuring total biogas and methane (CH4) production using batch fermentation and for characterizing the biomass. The biochemical methane potential (BMP) (CH4 NL kg−1 VS) of pig manure, cow manure and cellulose determined with the Moller and VDI methods was not significantly different in this test (p>0.05). The biodegradability using a ratio of BMP and theoretical BMP (TBMP) was slightly higher using the Hansen method, but differences were not significant. Degradation rate assessed by methane formation rate showed wide variation within the batch method tested. The first-order kinetics constant k for the cumulative methane production curve was highest when two animal manures were fermented using the VDI 4630 method, indicating that this method was able to reach steady conditions in a shorter time, reducing fermentation duration. In precision tests, the repeatability of the relative standard deviation (RSDr) for all batch methods was very low (4.8 to 8.1%), while the reproducibility of the relative standard deviation (RSDR) varied widely, from 7.3 to 19.8%. In determination of biomethane concentration, the values obtained using the liquid replacement method (LRM) were comparable to those obtained using gas chromatography (GC). This indicates that the LRM method could be used to determine biomethane concentration in biogas in laboratories with limited access to GC.

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The utility of low‐frequency ultrasonics in evaluating the viscoelastic properties of dough from different biscuit wheat flour qualities was studied. No distinct correlation was found between the ultrasonic characteristic (ultrasound velocity, v) and the rheological characteristics storage modulus, G' (r=0.43), or loss modulus, G″ (r=0.61), when a constant amount of water was added to the dough. Fairly high correlations were obtained between the ultrasound velocity, v, and the rheological measurements G' (r=0.93), G″ (r=0.92) and the phase angle G′ (r=0.81) with variable addition of water, corresponding to the water absorption capacity of the dough. It was not possible to distinguish between hard and soft endosperm biscuit wheat varieties using ultrasonic measurements, whether with a constant or a variable amount of water added. A high negative correlation was obtained between ultrasonic measurements and the amount of water added to the dough (r = ‐0.94), indicating that the amount of water added affected the ultrasonic measurements more significantly than differences in dough structure and rheological properties. The effect of ageing on the ultrasonic characteristics of dough samples was also studied. The ultrasound velocity, v, and storage modulus, G', increased during 40 min ageing. A high correlation obtained between ultrasound velocity, v, and the storage modulus, G' (r=0.97), indicates that ultrasonics may be a valid method of process control of rheological properties during the manufacture of dough.