Production of combustible biogas using tomato crop residues

We study the anaerobic decomposition of tomato crop residues to produce combustible biogas (with at least 45% methane). Testing was done considering: a) adding cow or pig manure, b) 20 or 50% manure c) with or without pH adjust to 7.5 and d) C/N ratios to 12/1 or 20/1.

We use batch anaerobic digesters of 3 liters, at 30°C, during 75 days. Analyzes were according to NMX-AA-034-SCFI-2001: total solids, volatile solids and pH. The methane content in biogas and volatile fatty acids were determined by GC.

Considering the digesters using tomato crop residues mixed with cow manure, the highest methane (almost 50%), was produced in digesters adjusting C/N to 20/1, adding 50% manure and could be with or without adjusting pH to 7.5, there was no difference; the biogas produced considering this conditions could be used as an alternative energy source.

In other hand digesters using tomato crop residues and pig manure produced nearby 30% methane, it does not matter if the pH was adjusted to 7.5 or not, the C/N to 20/1 or using 20 or 50% manure, in all cases the methane produced was statistically equal. This mixture is not recommended to be used as a source of alternative energy source because methane content is low.