Encyclopedia of Renewable Energy. James G. Speight. Читать онлайн. Newlib. NEWLIB.NET

Автор: James G. Speight
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Физика
Год издания: 0
isbn: 9781119364092
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soil and thereby reduces environmental pollution caused by leaching of inorganic fertilizer. It also plays a vital role in increasing crop productivity. Apart from improving soil quality, biochar provides various other benefits such as (i) mitigation of greenhouse gases (such as methane, CH4, nitrous oxide, N2O, and carbon dioxide, CO2), (ii) a decrease in the dissipation rate of herbicide in soil, and (iii) wastewater treatment. Due to large availability of biomass resources, biochar can be a prime product in many countries.

      See also: Pyrolysis.

      Biochemical Conversion

      Ethanol is the principal product of the fermentation processes appropriate to biomass conversion, although other alcohols, as well as organic acids, ketones, and aldehydes, may be produced either as main products or as by-products. Anaerobic digestion is the decomposition of any organic material by the metabolic action of bacteria without the participation of atmospheric oxygen. Methane and carbon dioxide are the main products of the decomposition. The source of the oxygen in the carbon dioxide is the combined oxygen in the organic molecules and in the water.

Process Biomass feedstock Scale* Product
Combustion Wood, municipal solid waste, grasses, crop residue Small, large Heat, steam, electricity
Gasification Wood, municipal solid waste (grasses, crop residue) Large Low-heat content gas, synthesis gas ethanol
Pyrolysis Wood, sewage sludge Large Medium-heat content gas tar
Fermentation Grain and sugar crops Small, large Ethanol
*Small implies domestic or farm application; large is industrial-scale processing of up to 1,000 t/d of biomass.

      Biomass fermentation to produce ethanol is similar to glycolysis (the fermentation that occurs in muscle tissue and converts glucose to lactic acid with the release of energy), but the use of different enzymes results in different end products.

      See also: Aerobic Digestion, Anaerobic Digestion, Bioconversion, Fermentation.

      Biochemical Oxygen Demand

      Biochemical oxygen demand (BOD) is a chemical procedure for determining the rate of uptake of dissolved oxygen by the rate biological organisms in a body of water use up oxygen. It is a chemical measure of the power of an effluent to deoxygenate water. The test is widely used as an indication of the quality of water. The biochemical oxygen demand can be used as a gauge of the effectiveness of wastewater treatment plants. There are two recognized methods for the measurement of biochemical oxygen demand which are (i) the dilution method and (ii) the manometric method.

      In the dilution method, a small amount of microorganism seed is added to each sample being tested. This seed is typically generated by diluting activated sludge with de-ionized water. The test is carried out by diluting the sample with oxygen saturated de-ionized water, inoculating it with a fixed aliquot of seed, measuring the dissolved oxygen, and then sealing the sample to prevent further oxygen dissolving in. The sample is kept at 20°C in the dark to prevent photosynthesis (and thereby the addition of oxygen) for five days, and the dissolved oxygen is measured again. The difference between the final dissolved oxygen and initial dissolved oxygen is the biochemical oxygen demand. The apparent biochemical oxygen demand for the control is subtracted from the control result to provide the corrected value.

      In the manometric method, the sample is kept in a sealed container fitted with a pressure sensor. A substance that absorbs carbon dioxide (typically lithium hydroxide) is added in the container above the sample level. The sample is stored in conditions identical to the dilution method. Oxygen is consumed, and dioxide is released. The total amount of gas, and thus the pressure, decreases because carbon dioxide is absorbed. From the drop of pressure, the sensor electronics computes and displays the consumed quantity of oxygen.

      Biochemicals

      Biochemicals, as opposed to petrochemicals, are in the context of this encyclopedia, chemicals produced from biomass.

      The production of chemicals from biomass, a renewable feedstock, is highly desirable in replacing petrochemicals to make biorefineries more economical. The best approach to compete with fossil-based refineries is the upgradation of biomass in integrated biorefineries. The integrated biorefineries employed various biomass feedstocks and conversion technologies to produce biofuels and bio-based chemicals. Bio-based chemicals can help to replace a large fraction of industrial chemicals and materials from fossil resources. Biomass-derived chemicals, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid, furfurals, sugar alcohols, lactic acid, succinic acid, and phenols, are considered platform chemicals. These platform chemicals can be further used for the production of a variety of important chemicals on an industrial scale. However, current industrial production relies on relatively old and inefficient strategies and low production yields, which have decreased their competitiveness with fossil-based alternatives.