Thermochemical valorization of greenhouse cucumber, tomato and pepper as biofuel.

Agricultural residues adequate managing contributes to reduce CO emissions and easy the circular economy. In this paper, cucumber, tomato and pepper greenhouse crop residues were characterized both chemically and energetically to potential of waste as a biofuel. When compared to other herbaceous and woody biomass, the data show higher moisture, ash and chlorine contents. The gross calorific values of these residues are in the same range as the herbaceous biomass (14.92 MJ/kg), with net values of 13.71, 14.58 and 15.73 MJ/kg for cucumber, tomato and pepper, respectively. The study also included other not common elements, finding the highest values for calcium (13-25 mg/kg) and potassium (23-30 mg/kg). To date, empirical correlations have been defined to predict the CV as a function of total C content (expressed as % in dry weight) for these residues individually. The empirical correlations obtained had maximum absolute errors (MAE) of 0.11, 0.32 and 0.58 % for cucumber, tomato and pepper whereas the marginal mean bias errors (MBE) were 0.016, 0.002 and 0.004 %, respectively, which confirms the value of using this method to determinate the gross calorific value of these residues. The correlations shown provide a useful tool for developing energy production processes based on crop residues, that would appear to be an interesting source of renewable energy to produce heat.