Optimization of biohydrogen production by dark fermentation of African food-processing waste streams.

In the challenge of mitigating greenhouse gases produced mainly by fossil fuels, the recovery of agricultural and food waste to produce biohydrogen by dark fermentation is considered a promising source for the future. However, industrial-scale production remains challenging and several parameters significantly influencing the application of the technology need to be finely tuned. In the present study, an evaluation of the production of biohydrogen from cassava and pineapple waste, widely available in many African countries, was carried out using different microbial consortia originating from industrial biogas plants in Italy. The production of biohydrogen was defined both by screening the most appropriate inoculum and by using a "centered composite design" to optimize the inoculum pretreatment time and the pH. From cassava waste, which is abundant of starch (43%), the highest hydrogen levels (62.32 mL H 2 /gVS) were obtained at pH 7.72 adopting a 4-h heat treated inoculum originating from an anaerobic digester fed with corn and barley silage. Higher hydrogen yields (75.50 mL H 2 /gVS) were achieved at pH 6 once pineapple, which has a high content of hemicellulose, was converted by another selected inoculum, isolated from an olive pomace treating plant, where hemicellulose is one of the most common polysaccharide. The correlation coefficients R2 and adjusted R2 are close to unity, proving the model to be appropriate to express the concentration of hydrogen produced. This combined approach performed successfully and represents a strong strategy to optimize the production of biohydrogen from agricultural residues even in African contexts. [Display omitted] • African residues are good candidates for biohydrogen production. • Response surface methodology optimized bio-H 2 yields. • The selection of proper inoculum is decisive for bio-H 2 production. • Inoculum treatment and pH are major factors for bio-H 2 production. • Cassava and pineapple were converted up to 62 and 75 mL H 2 /gVS, respectively. [ABSTRACT FROM AUTHOR]