Effect of heat pre-treatment on biohydrogen production by starch-degrading bacteria

Abstract

The combustion of fossil fuels emits majority parts of greenhouse gases thus contributing to global warming. In addition, global economic development leads to the increasing demand for fossil fuels as a major source of energy which causes this non-renewable resource to become depleted. Therefore, hydrogen was discovered as an alternative source of energy with carbon-neutral and renewable energy because it only produces water vapour and heat upon combustion and can be generated from waste materials. The low hydrogen yield is major challenges in biohydrogen production by the mixed culture via dark fermentation approach. Hence, this study was conducted to study the effect of heat pre-treatments on biohydrogen production of pre-treated cassava sludge at 80oC, 90oC and 100oC for 60 minutes. The sludge was pre-treated to select spore-forming hydrogen-producing bacteria and at the same time inhibit non-spore hydrogen-consuming bacteria. Batch tests were conducted to investigate and compare biohydrogen formation of untreated and pre-treated sludge at 80oC, 90oC and 100oC over 96 hours utilising cassava starch wastewater as substrate with an initial pH 5.5 at 30oC. Based on the experimental results, only hydrogen and carbon dioxide was detected throughout the experiment without the presence of methane. No biohydrogen was recorded for untreated sludge, 80oC and 100oC pre-treated sludge but biohydrogen was detected only by 90oC pre-treated sludge with 0.0883 mL of cumulative hydrogen formation. The biohydrogen production had the maximum biohydrogen production, maximum biohydrogen production rate, starch utilisation, the yield of biohydrogen per substrate and yield of biohydrogen per cell were 0.0012 mol H2, 0.0002 mol H2/h, 13.9%, 0.0050 mol H2/g and 0.0002 mol H2/g respectively. In conclusion, heat pre-treatment by boiling at 90oC was suitable for enriching biohydrogen-producing bacteria from cassava-processing sludge.