Methane potential and biodegradability of rice straw, rice husk and rice residues from the drying process.

Agricultural solid residues are a potential renewable energy source. Rice harvesting and production in Sancti Spíritus province, Cuba, currently generates residues without an environmentally sustainable disposal route. Rice residues (rice straw, rice husk and rice residues from the drying process) are potentially an important carbon source for anaerobic digestion. For this paper, rice residues were placed for 36 days retention time in anaerobic batch reactor environments at both mesophilic (37 °C) and thermophilic (55 °C) conditions. Biogas and methane yield were determined as well as biogas composition. The results showed that rice straw as well as rice residues from the drying process had the highest biogas and methane yield. Temperature played an important role in determining both biogas yield and kinetics. In all cases, rice straw produced the highest yields; under mesophilic conditions the biogas yield was 0.43 m(3) kg(VS)(-1), under thermophilic conditions biogas yield reached 0.52 m(3) kg(VS)(-1). In the case of the rice husk, the biodegradability was very low. Methane content in all batches was kept above 55% vol. All digested material had a high carbon:nitrogen (C:N) ratio, even though significant biodegradation was recorded with the exception of rice husk. A first-order model can be used to describe the rice crop residues fermentation effectively.

Solid mining residues from ni extraction applied as nutrients supplier to anaerobic process: optimal dose approach through Taguchi's methodology.

The use of solid mining residues (Cola) which contain a certain amount of Ni, Fe and Co, to stimulate anaerobic processes was evaluated. The effect over methane production and chemical oxygen demand (COD) removal efficiency was analysed. The studies were carried out in discontinuous reactors at lab scale under mesophilic conditions until exhausted. 0, 3, 5 and 7 mg Cola l(-1) doses were applied to synthetic wastewater. Volatile fatty acids (VFA) and sucrose were used as substrate, sulphur and nitrogen concentration, being the noise variable. Cola addition at dose around 5 mg I(-1), turned out to be stimulating for the anaerobic process. It was the factor that most influenced on methane production rate together with VFA and high content of volatile suspended solids. In the case of methane yield, pH was the control factor of strongest influence. Higher values of COD removal efficiency were obtained when the reactors were operated with sucrose at relatively low pH and at the smallest concentration of nitrogen and sulphur. Solid residues dose and the type of substrate were the factors that had most influence on COD removal efficiency.