Enhancement of microalgae anaerobic digestion by thermo-alkaline pretreatment with lime (CaO)

The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25 °C), 55 and 72 °C). The exposure time was 4 days for pretreatments at 25 °C, and 24 h for pretreatments at 55 and 72 °C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72 °C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14 day- 1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72 °C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.Peer ReviewedPostprint (author's final draft

Improving biomass production and saccharification in Brachypodium distachyon through overexpression of a sucrose-phosphate synthase from sugarcane

The substitution of fossil by renewable energy sources is a major strategy in reducing CO2 emission and mitigating climate change. In the transport sector, which is still mainly dependent on liquid fuels, the production of second generation ethanol from lignocellulosic feedstock is a promising strategy to substitute fossil fuels. The main prerequisites on designated crops for increased biomass production are high biomass yield and optimized saccharification for subsequent use in fermentation processes. We tried to address these traits by the overexpression of a sucrose-phosphate synthase gene (SoSPS) from sugarcane (Saccharum officinarum) in the model grass Brachypodium distachyon. The resulting transgenic B. distachyon lines not only revealed increased plant height at early growth stages but also higher biomass yield from fully senesced plants, which was increased up to 52 % compared to wild-type. Additionally, we determined higher sucrose content in senesced leaf biomass from the transgenic lines, which correlated with improved biomass saccharification after conventional thermo-chemical pretreatment and enzymatic hydrolysis. Combining increased biomass production and saccharification efficiency in the generated B. distachyon SoSPS overexpression lines, we obtained a maximum of 74 % increase in glucose release per plant compared to wild-type. Therefore, we consider SoSPS overexpression as a promising approach in molecular breeding of energy crops for optimizing yields of biomass and its utilization in second generation biofuel production

Integrated storage and pretreatment of lignocelluloses for bio-fuel production

The process for the production of lignocellulosic biofuel includes various sequential energy intensive stages like storage of biomass, thermochemical pretreatment, hydrolysis and fermentation. In the current study, an integrated storage and pretreatment method is investigated to get maximum ethanol yield in a single step process. A special 100 ml bioreactor was designed in which the thermochemical pretreatment (TCP) of wheat straw and simultaneous saccharification and fermentation (SSF) were performed. The ethanol production process was developed for wheat straw that was stored for one month at two different low temperatures with two different fungal species (Pichia anomala and Pichia stipitis) and a co-culture of both. Pichia stipitis inoculated wheat straw at low temperature gave 40.30% higher ethanol as compared to dry wheat straw after 96 hours SSF while a mixed culture of both species gave second highest value as compared to control. 30 minute TCP enabled higher ethanol yield (g/g)than it was obtained after 120 minute TCP, indicating less production of inhibitors during shorter TCP

Anaerobic co-digestion of microalgal biomass and wheat straw with and without thermo-alkaline pretreatment

This study aimed at analyzing the anaerobic co-digestion of microalgal biomass grown in wastewater and wheat straw. To this end, Biochemical Methane Potential (BMP) tests were carried out testing different substrate proportions (20–80, 50–50 and 80–20%, on a volatile solid basis). In order to improve their biodegradability, the co-digestion of both substrates was also evaluated after applying a thermo-alkaline pretreatment (10% CaO at 75 °C for 24 h). The highest synergies in degradation rates were observed by adding at least 50% of wheat straw. Therefore, the co-digestion of 50% microalgae – 50% wheat straw was investigated in mesophilic lab-scale reactors. The results showed that the methane yield was increased by 77% with the co-digestion as compared to microalgae mono-digestion, while the pretreatment only increased the methane yield by 15% compared to the untreated mixture. Thus, the anaerobic co-digestion of microalgae and wheat straw was successful even without applying a thermo-alkaline pretreatment.Peer ReviewedPostprint (author's final draft

Enhancement of biogas potential of primary sludge by co-digestion with cow manure and brewery sludge

Anaerobic digestion (AD) has long been used to treat different types of organic wastes especially in the developed world. However, organic wastes are still more often considered as a waste instead of a resource in the developing world, which contributes to environmental pollution arising from their disposal. This study has been conducted at Bugolobi Sewage Treatment Plant (BSTP), where two organic wastes, cow manure and brewery sludge were co-digested with primary sludge in different proportions. This study was done in lab-scale reactors at mesophilic temperature and sludge retention time of 20 d. The main objective was to evaluate the biodegradability of primary sludge generated at BSTP, Kampala, Uganda and enhance its ability of biogas production. When the brewery sludge was added to primary STP sludge at all proportions, the biogas production rate increased by a factor of 3. This was significantly (p<0.001) higher than observed gas yield (337 +/- 18 mL/(L.d)) in the control treatment containing (only STP sludge). Co-digesting STP sludge with cow manure did not show different results compared to the control treatment. In conclusion, Bugolobi STP sludge is poorly anaerobically degradable with low biogas production but co-digestion with brewery sludge enhanced the biogas production rate, while co-digestion with cow manure was not beneficial

Evaluation of ultrasonic pretreatment on anaerobic digestion of biomass for methane production

This thesis evaluated the effectiveness of ultrasonic pretreatment on biochemical methane potential (BMP) of corn-ethanol by-products (dried distiller grain with solubles (DDGs), centrifuge-solids, thin stillage, and corn-syrup) and four types of animal manure (swine slurry, beef feedlot manure, dairy manure slurry, and solids separated dairy manure effluent) and energy efficiency of ultrasonic pretreatment. Ultrasonic pretreatment was applied with various amplitude and treatment time settings. Biogas production was measured and analyzed for methane content and methane yield. Ultrasonic pretreatment of DDGs, centrifuge-solids, swine slurry, beef feedlot manure, dairy manure slurry, and solids separated dairy manure effluent increased methane production by 25, 12, 14, 55, 37 and 8%, respectively. An increase in ultrasonic amplitude and treatment time resulted in an overall increase in methane production, but with a reduction of energy efficiency. The greatest energy efficiency was obtained with the lowest ultrasonic amplitude combined with the shortest treatment time used

Integrated storage and pretreatment of wheat straw with different fungi : impact on ethanol production and storage microflora

Production of ethanol using cellulosic material as feedstock is crucial for sustainable fuel ethanol production.However a production process based on cellulosic biomass involves several energy and cost intensive steps like storage of biomass, pretreatment, hydrolysis and fermentation, where pretreatment is the energy intensive and troublesome step. This project aimed for an integration of storage and pretreatment step, to get more energy efficiency and more ethanol yield. In the present investigation wheat strawwas used as a model and was stored in moist conditions with different fungal species (Pichia anomala, Pichia stipitis, and Anthracophyllum discolor) inoculated separately in mini-silos for 1 month at 15°C and 4°C. Simultaneous saccharification and fermentation was carried out afterthe storage period and ethanol yields were compared with dry wheat straw as a control.A7.52 % higher ethanol yield (compared to the dry wheat straw) was obtained from wheat straw incubated by P. anomala at 15°C, and 6.87 % higher ethanol yield from P.stipitis inoculated wheat straw incubated at 4°C showed ISP can result in increasing the ethanol yield. Also it was obvious from the study that, the release of sugar from integrated storage and pretreatment (ISP) sample was faster than from the traditional sample. The higher concentration of non-fermentable sugars (eg: xylose, arabinose, mannose etc.) left during fermentation of ISP samples indicate that the ISP process causes more structural damage to the cellulosic substances and produces more sugar release than the control. Moreover P. anomala and P.stipitis showed a biocontrol activity during moist storageby preventing growth of other fungi and enterobacteria in the wheat straw during the one month incubation. In conclusion, ISP acted as an efficient method of storage and resulted in higher ethanol yield