Бурение грунтовых зондов, установка энергетических колодцев

Municipal solid waste (MSW) disposal is a major issue in all parts of the world. Even though there are currently many examples of sorting and recycling of selected fractions of MSW on a global scale, most of the solid waste goes into landfills. Municipal solid waste needs to be presorted to biodegradable and non-biodegrad­able fractions before being used as a cellulosic ethanol feedstock. Lignocellulosic-rich urban waste streams are abundant and eco­nomical feedstocks for the production of fuel ethanol. Similar to other feedstock materials, MSW can be converted to bioethanol via the saccharification-fermentation route or gasification route.

This class of cellulosic ethanol feedstock can be broadly divided into three subgroups:

1. Cellulosic municipal solid waste (MSW)

2. Low-grade mixed waste paper (MWP)

3. Organic yard waste (YW)

In comparison to other cellulosic ethanol feedstock, there are relatively few techno-economic studies on the use of MSW for cel- lulosic ethanol production [252, 253]. In one study carried out in the state of California, Chester and Martin suggested that by means of cellulosic ethanol technologies advances, states could use the organic content of municipal solid waste as a transportation fuel feedstock and simultaneously reduce externalities associated with waste disposal. In this study they examined the major processes required to support a municipal solid waste-to-ethanol infrastruc­ture employing enzymatic hydrolysis route, computing cost, energy, and greenhouse gas effects for the state of California in the United States. According to this study, assuming 60-90% practical yields for ethanol production, California could produce 1.0-1.5 billion gal­lons of ethanol per year from 55% of the 40 million metric tonnes of waste currently sent to landfills annually. The separation of organic wastes from the non-organic waste and ethanol plant operation represents almost the entire system cost. Furthermore, they noted that the net greenhouse gas impacts are ultimately dependent on how well landfills control their emissions of decomposing organ­ics. Additionally they found that, based on the current landfill mix in the state of California, the cellulosic infrastructure would experience a slight gain in greenhouse gas emissions. However, net emissions can rise if organics diversion releases carbon that would otherwise be flared and sequestered. Additionally, they estimated the break-even price for lignocellulosic ethanol between $2.90 and $3.47/gal (p = $3.13/gal) [253].

The waste collected in urban areas is a complex mixture and in general approximately half is lignocellulosic material. There are several studies in the United States and in Europe, analyzing the composition of waste in large cities, states or regions. One study carried out in the state of Washington is presented as an example. According to this report, in the state of Washington alone, over four million tons per year of lignocellulosic-rich municipal solid waste is available for use as a biofuel feedstock. More than half (55.3%) of the total waste surveyed within the state in 2009 was composed of lignocellulosic material. In fact, nearly one-third of the MSW was composed of: food waste (18.3%), leaves and grass (4.1%), mixed waste paper (6.7%) and cardboard (3.7%). Composition and charac­terization of municipal solid waste in the state of Washington in the year 2009 is shown in Table 3.23. [254].

In this state of Washington study on cellulosic waste, samples were divided into three categories: cellulosic municipal solid waste (MSW), low-grade mixed waste paper (MWP), and organic yard waste (YW). Lignin and ash contents of the samples were deter­mined before the saccharification. The three types of waste samples were subjected to sulfur-dioxide-catalyzed steam explosion pre­treatment before the hydrolysis. Then, solids were enzymatically hydrolyzed using cellulase (Spezyme-CP, 26 FPU/mL, 20 FPU/g) and were supplemented with в-glucosidase (Novozym 188, 492 CBU/mL, 40 CBU/g). The chemical composition of three types of waste samples and the hydrolysis results are shown in Table 3.24.

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a Numbers without the bracket correspond to concentration of monomeric sugars in WSFs after acid hydrolysis; numbers in the bracket correspond to concentration of total sugars (monomers and oligomers).

b Relative ethanol yield for the liquid fractions obtained after pretreatment. c Relative ethanol yield for the liquid fractions obtained after enzymatic hydrolysis.

Water soluble fractions obtained from each of the pretreatment and enzymatic hydrolysis steps were assessed for their efficiency dur­ing fermentation to ethanol by Rhodotorula mucilaginosa, without employing any detoxification steps, and the ethanol yields are also shown in Table 3.24.

As shown in Table 3.24, the total polysaccharides content for MSW, MWP, and YW proved to be very high, 79%, 88%, and 62%, respec­tively, making these lignocellulosic-rich urban wastes attractive materials for saccharification and fermentation processes. Glucose, followed by mannose and xylose were shown to be the most abun­dant components as determined by secondary acid hydrolysis of constituent polysaccharides. The ash content was determined to be highest for MWP, 6.9%, and the lowest for MSW, 3.1%.

In another study, a lignocellulosic concentrate from MSW obtained after an autoclave separation process has been investi­gated for its potential as a feedstock to produce fermentable sug­ars for ethanol production [255]. In this study, Li et al. reported a maximum enzymatic hydrolysis conversion of 53% of cellulose and hemicellulose, where lignocellulosic MSW with particle size in the range of 150-300 pm was hydrolyzed with cellulases. Their find­ings indicate that about 152 L of ethanol could be obtained from a ton of lignocellulosic MSW [255].

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