Cleaner energy through liquefaction of Cocoa (Theobroma cacao) pod husk: Pretreatment and process optimization

Abstract

This study explored the production of biogas from the mono-fermentation of pretreated Cocoa pod husk. The pretreatment was carried out with sulfuric acid (H2SO4) and alkaline hydrogen peroxide (H2O2) prepared by adjusting the pH of H2O2 to 11.5 by the addition of 5 M NaOH solution. Prior to and after the pretreatments, physicochemical, structural and microbial analyses were carried on the husk using a standard method in each case. In order to determine the changes to the biomass structures after pretreatments, the Fourier Transform Infra-red (FTIR) spectroscopy were used. Average total biogas volume from all the experiments i.e. the acidic pretreated (AcP), alkaline pretreated (AlP), not sifted untreated (NsU) and sifted untreated (SU) was 162.8 ± 5.0, 564.8 ± 5.1, 243.3 ± 4.1 and 220.8 ± 3.3 respectively. This shows that the AlP Cocoa pod husk yielded the highest biogas volume and was followed by the NsU and the SU husk while the lowest was obtained from the AcP biomass. Overall, the AlP biomass produced 71% more total biogas than the AcP one and also produced 57% more biogas than the NsU Cocoa pod husk. The AlP Cocoa pod husk did not only produce the highest biogas volume but also achieved peak of production faster than all the other experimental setups. Total biogas generation was achieved in just 12 days out of the 30-day retention period used in the study in which biogas production started on the 3rd day and climaxed on the 15th experimental day whereas, biogas generation did not commence until after the 5th and 6th days in other experiments and climax was not reached until between the 18th and 21st days. The result of this study has revealed that use of the low cost mild alkali is more efficient in lignin (L) solubilization and subsequent biogas yield improvement. Also, Cocoa pod husk has been shown in this study to be a profound biofuel substrate. Therefore, further use of AlP Cocoa pod husk for biogas and biofertilizer production is hereby advocated especially in major Cocoa producing regions of the world.