Cassava as feedstock for ethanol production in South Africa

South Africa’s economy is primarily coal-based, but the high ash content is a contributing factor to the high per capita production of green house gases. Rising crude oil prices, lower crop prices on world markets and the realisation that coal and oil are limiting energy resources has led to the decision to substitute a minimum of 2% of the country’s transportation fuel with biomass based fuels. The biofuels industrial strategy of South Africa suggests the use of sugar based crops, but due to the tropical climate preferable for these crops, alternative crops need to be found that can be grown in the more arid and marginal parts of the country. Cassava (Manihot esculent) is rich in starch and is not a staple food in South Africa. It can be grown on marginal lands where frost is not prevalent. In this study, the production of ethanol from unpeeled Cassava roots and cassava peels were investigated. It was found that temperature; pH and biomass loading had a significant effect on glucose yield during hydrolysis. Simultaneous saccharification and fermentation (SSF) showed the highest ethanol yield and direct fermentation the lowest. A final ethanol yield of 530 L of ethanol per ton of unpeeled cassava roots or 2400 L/ha were obtained.Keywords: Cassava, bio-ethanol, yield, separate hydrolysis and fermentation, simultaneous saccharification and fermentation.African Journal of Biotechnology Vol. 12(31), pp. 4975-498

Recovery of water from cacti for use in small farming communities

In this study, an extensive investigation was conducted to determine if declared weeds could be used as a source of water for agricultural practices in dry areas. The objective of this study was to determineif declared weeds  could successfully be used as a source of water for agricultural practices in dry areas by extracting the water by means of mechanical and chemical methods. The Cereus jamacura cactus, also known as Queen of the Night, with a moisture content of 91 wt%, was selected for this study. Both mechanical and chemical extraction methods were used to determine the maximum water yield possible. Juicing, pressing with a hydraulic cold press and pressing with rollers were used as mechanical methods to extract water from the cacti and water yields of 7.0, 4.9 and 2.9 wt% were obtained respectively. The chemical extraction processes entailed the pulping of the cacti and the filtering off of the water. The effect of pectinase, cellulase and a surfactant at a fixed dosage on the amount of water extracted (mass of water per mass of cacti used) was investigated. The quality of the water was also determined. Temperature (30 to 50°C) and pH (2.5 to 6.5) were varied to find the optimum extraction conditions. The highest water yield (55 wt% of total cacti mass) was obtained using pectinase enzymes at a temperature of 40°C and a pH of 3.5 and cellulose enzymes at a temperature of 35°C and a pH of 5.5. This relates to a yield of 550 L of water per ton of cacti, making chemical water extraction a viable option if compared to the pollution created by the annual burning of the cacti. It was concluded from this study that the water that was extracted from the C. jamacaru cacti would not be suitable for either domestic or industrial application due to the high levels of potassium (up to 2,650 ppm), phosphates (up to 2,200 ppm), sulphates (up to 3,800 ppm) and nitrates (up to 670 ppm) in the water. The high concentration of phosphates and nitrates, however, makes the extracted water an excellent fertiliser for crops requiring high nitrate and phosphate dosages. Small community farmers could thus benefit by using cacti as a source of water for small scale biofuels production plants while also obtaining an excellent additional fertiliser for crop cultivation.Keywords: Cereus jamacaru, water yield, water quality.African Journal of Biotechnology Vol. 12(40), pp. 5926-593

Harvesting of Hartbeespoort Dam micro-algal biomass through sand filtration and solar drying

Renewable energy sources such as biomass are becoming more and more important as alternative to fossil fuels. One of the most exciting new sources of biomass is microalgae. One of the major obstacles in the commercial production of microalgae as feedstock for biomass-to-liquid fuels, is the development of energy efficient and cost effective harvesting methods for the separation of micro-algal biomass from its growth medium. In this study, a promising method of harvesting micro-algal biomass from the Hartbeespoort Dam through a combination of sand filtration and solar drying was investigated, which could be used to increase the energy efficiency and cost effectiveness of an integrated biomass-to-liquids process. Microalgal biomass was collected from the Hartbeespoort Dam and the wet biomass was allowed to separate from the aqueous phase for 24 h through its natural buoyancy. The bottom aqueous layer was drained and the top green layer of wet biomass was poured onto metal palettes containing buildings sand and left in the sun to dry for 24 h. An average dry weight of 7.6 g of dried micro-algal biomass from the Hartbeespoort Dam was harvested after one day of sun-drying on a patch of 0.0484 m2 or 497.7 g of building sand. An average, annualized, volumetric harvesting yield of 4.6 kg L 1 a 1 of dry weight micro-algal biomass was achieved per liter of Hartbeespoort Dam pulp and an average, annualized, aerial harvesting yield of 47.3 kg m 2 a 1 of dry weight micro-algal biomass was achieved per square meter of drying area. Micro-algal biomass from the Hartbeespoort Dam was successfully harvested by sun-drying on building sand. The building sand substrate improves the separation of water from the wet micro-algal biomass. As water is absorbed into the sand, it increases the drying area and thus increases the drying rate of the micro-algal biomass. Solar radiation provides the energy to evaporate the moisture. Thermo-chemical liquefaction is one of the preferred methods to extract bio-oils from microalgae, but is very energy-intensive. After extraction of bio-oils, micro-algal biomass rests could be sand-filtered, sun-dried and combusted to provide heating for the liquefaction section. Sand filtration and solar drying has the potential to produce 9938 GJ ha 1 a 1 of renewable energy which could be used to offset the energy requirements of an integrated biomass-to-liquids process. Harvesting costs could also be reduced from 20% to 30% of the total cost of biomass-to-liquids production to 18–19% by utilizing sand filtration and solar drying