Search

This review analyses the relevant studies which focused on hydrogen synthesis by dark fermentation of galactose from macroalgal biomass by discussing the inoculum-related pretreatments, batch fermentation and inhibition, continuous fermentation systems, bioreactor designs for continuous operation and ionic liquid-assisted catalysis. The potential for process development is also revisited and the challenges towards suppressing glucose dominance over a galactose-based hydrogen production system are presented. The key challenges in the pretreatment process aiming to achieve a maximum recovery of upgradable (fermentable) sugars from the hydrolysates and promoting the concomitant detoxification of the hydrolysates have also been highlighted. The research avenues for bioprocess intensification connected to enhance selective sugar recovery and effective detoxification constitute the critical steps to develop future red macroalgae-derived galactose-based robust biohydrogen production system.

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350 W) were applied in a first set of runs for 15 min. The second set consisted of 20, 25 and 30 min irradiation at 350 W. Based on ANOVA analysis (α = 0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700 ml for 36 days HRT for 350 W/25 min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271 L/g VSremoved at a 350 W microwave irradiation for 30 min.

The aim of the study was to investigate the effects of carton in the composting process of mixed vegetable wastes using an experimental composter of capacity 80L. Three different mixes were set-up (Mixes 1, 2 and 3) which consisted of vegetable wastes, 2.0kg paper and bulking agents, vegetable wastes, 1.5kg carton and bulking agents, vegetable wastes, 4.5kg carton and bulking agents, respectively. Temperature evolution, pH trends, moisture levels, respiration rates, percentage volatile solids and electrical conductivity were monitored for a period of 50days. The system remained under thermophilic conditions for a very short period due to the small size of the reactor. The three mixes did not exceed a temperature of 55°C, where sanitization takes place by the destruction of pathogens. The highest peak of CO2 evolution was observed in Mix 2 indicating that maximum microbial degradation took place in that mix.

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.