Бурение грунтовых зондов, установка энергетических колодцев

Wheat (Triticum spp.) is a cereal grain, originally from the Levant region of the Near East and Ethiopian Highlands, which is now cul­tivated worldwide. In 2009 world production of wheat was 682 mil­lion tons, making it the third most produced cereal after corn and rice. Wheat is second only to rice as a main human food crop. The whole grain can be milled to leave just the endosperm for white flour. The products of this are bran and germ. Wheat is planted to a limited extent as a forage crop for livestock, and its straw can be used as a construction material for roofing thatch. According to UN food and agricultural organization data, China was the leading wheat producer in 2009, with 112 million tons, and the other major producers were India, the USA, and Russia [45].

Wheat is the principal food grain crop produced in the USA. Wheat straw is the aboveground, non-grain portion of the wheat plant (stems, leaves, and chaff). While small quantities of wheat grain are currently used to produce ethanol and organic chemicals, most of the straw produced might be left on the field, plowed back into the soil, burned or even removed from the land depending on the decision made by the farmer. Disposal of wheat straw by burning has been practiced since the domestication of wheat. In recent years however, this practice has been challenged due to increased concern over the health effects of smoke from burning fields [46], because burning of wheat straw results in large amounts of air pollutants including carbon monoxide and nitrogen oxides [47]. In one of the most notable recent studies, molecular compositions and size distributions of water soluble organic com­pounds (WSOC, i. e., sugars, sugar alcohols and carboxylic acids) in particles from urban air of Nanjing, China, were studied during a severe haze event caused by field burning of wheat straw. In this air quality study they characterized and compared air in wheat burn­ing season with that of the summer and autumn non-haze peri­ods. During the haze event, levoglucosan was the most abundant compound among the measured WSOC, which accounts for 4030 ngm-3. This was followed by succinic acid, malic acid, glycerol, and arabitol; glucose was different from those in the non-haze samples in which sucrose or azelaic acid showed highest concentrations. Molecular compositions of organic compounds in fresh smoke particles from wheat straw burning demonstrate a sharp increase in the concentrations of glycerol, succinic and malic acids. These organic acids and volatile compounds in the atmosphere can have detrimental effects on the health of large segments of the popula­tion. Therefore, finding an alternative method to dispose of surplus wheat straw is of high interest and an immediate requirement in many parts of the world.

The quantities of wheat straw available for cellulosic ethanol production depend on the quantities produced, minus the quan­tities that must remain on the field. Crop residues play a vital role in maintaining soil characteristics such as soil organic matter and soil moisture, controlling erosion and chemical runoff, and ensuring the long-term productivity of the soil. Sufficient residue quantities must be left to maintain these functions. The quanti­ties of residues that must remain on the field to maintain soil characteristics depend on several factors. These include whether wheat is produced in a continuous cropping system or in rotation with other crops, the timing and type of management practices used (particularly tillage operations), the physical characteristics of the soil such as soil type, erodibility, field characteristics like slope, and climate. Currently, about 25% of wheat is produced in a continuous cropping system, while about 22% of wheat acres are produced in a wheat fallow rotation (particularly in areas where rainfall is a limiting constraint), and the remaining acres are produced in rotation with another crop such as soybeans, other small grains, and corn. The quantities of wheat straw pro­duced per acre are typically estimated by multiplying the grain yield by a residue-to-grain ratio. Most studies assume a residue — to-grain ratio of 1.7:1.0 for winter wheat and 1.3:1.0 for spring wheat. There are slight variations in wheat straw compositions of different wheat varieties, and the compositions of two com­mon varieties, durum wheat and Canada Prairie Spring (CPS) are shown in Table 3.6.

Practically all the common pretreatment methods have been tested on wheat straw, and there are number of thorough labora­tory-scale studies on this subject. These include dilute acid [48, 49], non-ionic surfactant assisted dilute acid [50], alkaline and alkaline peroxide [51-54], steam explosion [55-57], hot liquid water [58], wet oxidation [59, 60], gamma irradiation [61], ozonolysis [62], aqueous glycerol [63], super-critical carbon dioxide [64], and ionic liquid [65], [66] pretreatments of wheat straw.

Dilute acid and steam explosion are probably the most widely studied pretreatment methods for wheat straw. Table 3.7 presents

some of the most promising methods and corresponding con­ditions recently used for pretreatment of wheat straw. Diverse advantages and drawbacks are associated with each pretreatment method. The shorter reaction times are generally accompanied with higher temperatures. The choice of appropriate pretreat­ment method for wheat straw relies on some technological factors including energy balance, higher solid loading, and minimum use of chemicals, as well as some environmental factors such as wastewater treatment, catalyst recovery and solvent recycling. Steam explosion is probably the most suitable method for pre­treatment of wheat straw in terms of lower reaction time, higher solid loading and minimum use of chemicals (Table 3.7). In the non-gasification route, pretreatment has an enormous influence on the efficiency as well as economy of the subsequent stages, and the final decision must be made in the framework of the entire process. However, the majority of laboratory studies have been done on a very small scale, and it is difficult to extrapolate the results to industrial-scale cost calculations.

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