Liquefaction of pineapple peel: Pretreatment and process optimization

This study explored the optimization of pretreatment of pineapple peel for biogas generation. Pre-treatments were carried out sulfuric acid and alkaline hydrogen peroxide prior to anaerobic digestionwhile the response surface methodology (RSM) was used for optimization of the pretreatment pro-cedures. The physical, chemical, proximate and structural compositions of the peels were determinedprior to and at the end of the pretreatment procedures. The dynamics of microorganisms in the reactorswere also evaluated by rapid molecular methods while the Fourier Transform Infra-red (FTIR) spec-troscopy was employed in the identification of the chemical changes as a result of pretreatments. The useof H2O2pretreatment caused enormous lignin solubilization in the pineapple peel. In comparison, biogasproduction was 67% more in the alkaline pretreated pineapple peel than the biomass treated with acidand also 51% over the untreated samples. The total biogas volume produced from the acidic pretreated,alkaline pretreated, not sifted untreated and sifted untreated samples are 194.2±3.0, 587.5±5.2,287.8±2.1 and 245.4±3.1 respectively. Thus, the alkaline pretreated experiment used lower retentiontime to achieve maximum gas production in this study. The use of alkaline H2O2on lignocelluloses hasremained unpopular prior to this study. However, its usage in this study yielded better result than all theconventional treatments in terms of lignin solubilization and improvement in methane yield. Econom-ically, the use of H2O2for pretreatment is adjudged feasible because the 1504 kWh t�1TS thermal energygain obtained from the biogas produced by the alkaline treated peel exceeded the 921 kWh t�1TS used inthe pretreatment. This gives a net thermal energy of 583 kWh t�1TS. Whereas, the investment into acidicpretreatment of pineapple peel may not be economically justified because the total thermal energy gainof�200 kWh t�1TS was far lower than the 1236 kWh t�1TS thermal energy that was consumed duringthe pretreatment giving a net thermal energy of�1436 kWh t�1TS. Therefore, the use of mild alkalinepretreatment is advocated in biogas generation from pineapple peel and also for biofertilizer productionmostly in localities of mass production