Agroindustrial and forestry residues, which are by-products of key industrial and economical activities, stand out as potential raw materials for the production of renewable fuels, chemicals and energy. The use of wastes is advantageous as their availability is not hindered by a requirement for arable land for the production of food and feed. In addition, waste utilization prevents its accumulation, which is of great environmental concern due to its potential for contamination of rivers and underground water. In Brazil, the agroindustry of corn (13767400 ha), sugarcane (7080920 ha), rice (2890930 ha), cassava (1894460 ha), wheat (1853220 ha), citrus (930591 ha), coconut (283205 ha), and grass (140000 ha) collectively occupies an area of 28840726 ha (FAOSTAT, http://www.faostat.fao.org/site/567/default.aspx#ancor) and generates 597 million tons of residue per year. By itself, this scale of operation calls for new solutions aiming for the appropriate utilization of these valuable resources. However, innovative dealings must be environmentally and economically acceptable and, most importantly, have social meaning. Indeed, great social benefits could draw from novel year-round activities as alternatives for the typical seasonal jobs in agroindustry. Considering the production of biomass ethanol, the abundance of feedstock near the site of processing must be taken into account, as low-density biomass involves significant handling and transportation costs. Within this context, the crushed stalk of sugar cane (bagasse) and straw are obvious choices, although bagasse is often burned for the production of steam (heat) and power/electricity in sugar-ethanol mills and important amounts of straw are needed to keep the soil nutrients balance. Other agricultural by-products of importance in Brazil, such as corn straw, wheat straw, rice straw and rice hulls, grass and forestry materials and residues from citrus, coconut and cassava processing, also deserve attention as local feedstock for the development of new and profitable activities. As each type of feedstock demands the development of tailor-made technology, the diversity of the aforementioned raw materials could allow for new solutions for the production of chemicals, fuels and energy in accordance with the local availability of these materials.

Biomass Residues in Brazil: Availability and Potential Uses

Global climate issues and a looming energy crisis put agriculture under pressure in Sub-Saharan Africa. Climate adaptation measures must entail sustainable development benefits, and growing crops for food as well as energy may be a solution, removing people from hunger and poverty without compromising the environment. The present study investigated the feasibility of using non-food parts of cassava for energy production and the promising results revealed that at least 28% of peels and stems comprise dry matter, and 10 g feedstock yields >8.5 g sugar, which in turn produced >60% ethanol, with pH ≈ 2.85, 74–84% light transmittance and a conductivity of 368 mV, indicating a potential use of cassava feedstock for ethanol production. Thus, harnessing cassava for food as well as ethanol production is deemed feasible. Such a system would, however, require supportive policies to acquire a balance between food security and fuel.

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Bio-Ethanol Production from Non-Food Parts of Cassava (Manihot esculenta Crantz)

The potential use of cassava pulp hydrolysate for fermentative hydrogen production by anaerobic mixed cultures was investigated in laboratory batch fermentation. Cassava was hydrolyzed in autoclave at 121 °C using H2SO4 at different concentrations and reaction times. The optimal conditions obtained were 0.5% H2SO4 at the ratio of 1:15 (dry wt.: volume) for 30 min, which gave the maximum yield of 27.4 g L−1 of total sugar. A series of batch fermentation were investigated for the effects of (1) sources of mixed culture, (2) initial pH, (3) initial substrate concentrations and (4) initial biomass concentrations. The tests were carried out in 100 ml serum bottles to determine the optimal operating conditions for hydrogen production using acid- hydrolyzed cassava pulp as raw material. The results indicated that the UASB granules from the local brewery company yielded the highest bio-hydrogen production at the optimal initial total sugar concentration of 25 g COD L−1 with a biomass concentration of 3.0 g L−1 and the initial medium pH of 5.5 with the peak values of hydrogen yield (HY) of 342 ml H2 g-1CODreduced and the hydrogen production rate (HPR) of 3381 ml H2 L−1 d−1. The optimum substrate/biomass ratio (S0/X0) maximizing the hydrogen yield and formation rate was determined to be 8.33. The results revealed the possibility of using cassava pulp hydrolysate as a fermentation substrate for hydrogen production by the selected mixed culture.

Hydrogen production from cassava pulp hydrolysate by mixed seed cultures: effects of initial pH, substrate and biomass concentrations.

Utilization of food wastes for sustainable development.

In Nigeria, about 70% of harvested cassava tubers are processed into gari, a toasted granule. Gari production in Nigeria is dominated by smallholders who use simple implements for cassava processing. Nigeria is the largest cassava producing nation in the world. It is suspected that significant amounts of wastes are generated during cassava processing. Hence, the study was designed to assess the amount of cassava processing wastes generated during the traditional processing of cassava to gari. Field study was embarked upon in December 2010. Triplicate samples were measured in eleven cassava processing centres in Wilberforce Island. Results show that for a given unit of raw cassava, gari yield is about 34% while generating 30%, 19.8% and 16.2% of solid, gaseous and liquid wastes respectively. The environmental impacts of cassava processing wastes were discussed. We therefore conclude that the traditional processing of cassava to gari generates several waste streams that could be converted to other useful products to prevent environmental impacts.

Biowastes Generation by Small Scale Cassava Processing Centres in Wilberforce Island, Bayelsa State, Nigeria

Investigations were conducted into the potential use of enzyme hydrolysed cassava whey for ethanol production by Saccharomyces cerevisiae Aspergillus niger grown on whct bran was used as crude enzyme source to saccharify the whey starch. The whey with an initial HCN concentration of 54.0μg/ml was fermented at pH 4.5 and 30°C in a one-step process to produce ethanol. A maximum ethanol concentration of 4.5% (v/v) was obtained in 120 h with a decrease in HCN level to 4.0 μg/ml. In a two-stage fermentation, in which the raw whey was pre-hydrolysed and under the same fermentation conditions, the unsterilized hydrolysate yielded alcohol content of 5.5% (v/v), while the sterilized hydrolysate gave higher alcohol yield, 7.5% (v/v), in 48 h. No HCN was detected in the fermented liquour at the end of the two-stage process.

C. O. Obuekwe

Papers

Production of ethanol from cassava whey