**4. Preservation and extraction of sugars from biomass for biorefinery**

There are numerous research results indicating sweet sorghum as one of the best crops for biofuels industry. Still, industrial exploitation of sorghum cultures as an energy carrier is inhibited by a short harvesting period in temperate regions (1–2 months in Romania) and storage challenges leading either to high costs (in either processing or storage facilities) or high losses of fermentable sugar [48, 49]. Apart from tropical climates where there is a minimum of two harvests a year of sugar cane, the production of biofuels from sugary plants in other part of the world (and in particular in Europe) does not allow processing cycles on an annual basis. This means that the entire production capacity of the plants is not exploited, with the consequent problems of scale economy that penalize these types of feedstock in Europe for bioethanol production. In North America market corn is widely used since this type of feedstock (corn grains) can be stored for long periods and the full capacity of the plant is fulfilled on annul basis. In Europe this approach is not considered environmentally friendly due to the large soil and water usage for non-food application. On the other hand, pretreatments of lignocellulose matrices have not yet exploited their full potential in order to be competitive with bioethanol produced in Brazil and North America.

The main disadvantage is the impossibility of preserving the sugar-containing sorghum crop throughout the year without losing the sugar content accumulated in sorghum stems. Having a considerable moisture content (30–35%), sugar sorghum biomass is easily colonized by microorganisms, which consume sugars and cause the degradation of biomass. Classical ensiling (by lactic bacteria) has the same effect of sugar consumption, and drying of the biomass and preservation in dried form until processing is an alternative that cannot be applied on an industrial scale due to high energy inputs and storage costs. Therefore, the main bottleneck in using sweet sorghum as feedstock in biorefinery is preservation of sugar content in the biomass to be available around the year as feedstock for biorefinery.

Without preservation of sugars, the processing of sweet sorghum biomass would resemble sugar-beet processing: high capacity processing within a short period of time to minimize loss of sugars contained in the biomass. Processing facilities have large capacity and are only operated for a short period. This classical approach makes the process expensive due to high cost of capital per outputs unit. Furthermore, current sugar extraction technologies involve pressing the sorghum stalks (sometimes hydrated by the addition of water) and the harvesting of the sugar-containing juice. This process extracts only part of the sugar content stored in the sorghum biomass; the rest of the sugars remain in the bagasse. Sugars left in the bagasse are lost shortly after pressing by microbial proliferation. Incomplete use of sugars from sugar-containing biomass results in a much lower energy balance, reflected in a low degree of sustainability, low economic efficiency and higher carbon footprint.

Laboratory studies made by BUAS team have validated analytical predictions regarding sugars preservation and extraction from sorghum biomass and sugar beet. The analysis was carried out in small scale batches preserved during periods of over 12 months and the whole biorefinery of biomass was carried out in laboratory equipment. This technology, patented by BUAS Timisoara, is registered to Romanian Office for Inventions and Marks (OSIM) under the title "*PROCESS FOR BIOREFINING OF SUGAR YIELDING PLANTS WITH CONSERVATION AND EXTRACTION OF SUGARS FOR PRODUCTION OF BIOFUELS AND OTHER BIOPRODUCTS*", Patent no. 131499/2021 [41]. Recently, at the global "Climate Launchpad" event - the world's largest green business ideas competition, the invention reached the world semifinal and won the 1st place at national Climate Launchpad final in Romania.

### **The innovation of our approach lies in:**

The use of a sorghum pre-treatment approach, proved at laboratory-scale (TRL3), consisting of preservation of sorghum biomass containing sugars for several months, more than one year, to make possible the use of sweet sorghum crops as feedstock for biofuels and biochemicals. The preservation of the main energy carrier (sugar) in the plants is the main criterion in considering a certain crop as feedstock for biorefinery. The patent developed a process of preservation of sugars in sorghum biomass by additivated ensilage, using a cost effective, recoverable, produced in situ additive. In traditional ensiling techniques, the sugars are lost by fermentation and transformed into organic acids such as lactic acid.

The invention has triple effect: (1) preservation of sugars, (2) extraction of sugars and (3) release of cellulose from lignocellulosic complex and access of cellulolytic enzymes to hydrolyse cellulose to glucose.

The advantages of the pre-treatment method can be found on three levels:

• Firstly, this method preserves sugars in the biomass for year around, improve extraction and releasing the sugars from biomass resulting in higher sugar yields and energy yields on the surface of land and the possibility to produce sweet

juice for fermentation on an ongoing basis; reducing the required pressing capacity and hence investment costs.


In order to protect patent priority, data regarding sugars extraction and preservation have not yet been published.

By chaining the three main processes: (1) alcoholic fermentation of sugars extracted from sweet sorghum (2) enzymatic hydrolysis and fermentation of bagasse results after extraction of sugars and (3) anaerobic digestion of waste resulted after hydrolysis and fermentation for biogas production, total energy production is maximized (see **Table 3**), and the digestate returns to soil as organic fertilizer.

In order to increase technology readiness level (TRL), the pre-treatment process will be tested at pilot scale, and coupled with down-stream pressing, hydrolysis and fermentation to produce amounts of bioethanol and biochemicals in sufficient amounts to prove higher TRL. More than that, modeling of environmental impact and energy balance, profitability and costs need to be assessed to support transferability of project results from research to industrial application. Equipment located in University of Life Science from Timisoara, part of the pilot scale biorefinery, will be used to fulfill these objectives. **Figure 6** summarizes the innovative processes of preservation and biorefinery of sugary plants.

Circular bioeconomy proposed here integrate several technologies such as energy crops production, extraction of sugars, biorefinery, anaerobic digestion and remediation of heavy metals polluted soil. The concept can be summarized as follows.

Sweet sorghum harvested from highly and low polluted area is sent to preservation phase. In order to make sugars available for biorefinery around the year, the innovative technology for preservation of sugar containing biomass is proposed. In the next phase of the integrated circular bioeconomy, the extracted sugars are converted to first generation biofuels & biochemicals and the resulted lignocellulosic portion of the biomass is converted to second generation biofuels & biochemicals. The by-products generated in biofuels technology (bagasse, thin stillage, vinasse etc) are converted by anaerobic digestion to biogas (for bioelectricity or bio-methane) and digestate. From this phase, the bioeconomy will follow two paths:

a.Digestate containing high concentration of pollutants (over the limits according to EU legal frame) is sent to combustion and to extraction of heavy metals. In

### *Heavy Metals – Recent Advances*


### **Table 3.**

*Energy production by several processes applied in laboratory scale for biorefinery of sweet sorghum preserved by original preservation method.*

industrial scale application, it is envisaged to deliver the heavy metals containing ash back to the smelter responsible for dispersion of pollutants in the area.

b.The digestate containing low concentration of pollutants (between the limits according to EU legal frame) is used as soil improver to remediate, improve soil characteristics and to immobilize heavy metals inside the polluted area.

According with results from previous studies carried out in experimental field from Copsa Mica [26] the addition of organic amendments enhances the formation of stable complexes with organic compounds, improving the heavy metals immobilization processes in soil and leads to a decreasing of metals available amounts in soil. By addition of organic solids such as digestate resulted from AD of biorefinery by-products, it is foreseen to immobilize important part of pollutants (heavy metals), this way allowing the cultivation of edible crops at least in the low polluted area. Previous studies [7] indicated important rates of immobilization in polluted area due to the addition of organic fertilizer (digested plants) in the ranges of 38–40% of extractable Cd, 77–83% of extractable Pb and 43–47% of extractable Zn. Addition of organic residues will have significant effects on metal accumulation in biomass

*Biorefinery for Rehabilitation of Heavy Metals Polluted Areas DOI: http://dx.doi.org/10.5772/intechopen.109626*

### **Figure 6.**

*Summary of innovative process of preservation and biorefinery of sugary plants.*

and the contents of pollutants in plants will significantly decrease. The target is to reach below the threshold for green fodder (40 mg kg−1) according with EU legislation on undesirable substances in animal feed [8]. Also, by reducing metal toxicity and improving soil fertility, the application of organic amendments, will result in the development of a permanent vegetation cover in non-arable land of polluted area. Development of a dense plant cover can halt erosion and thus prevent pollutants from spreading to other areas.

Particular outcome is envisaged in low polluted area, where application of digestate for immobilization of metals can restore the agriculture lands for food and feed production in shorter time frame, improving social attractiveness of the area and consolidating social acceptance of the biorefinery-bioenergy-remediation circular economy in polluted areas.

Summarizing, the overall methodology proposed here consists of the following main aspects to be approached:

