# Chemical and Enzymatic Treatment of Hemp Biomass for Bioethanol Production
## 1 Introduction  
The increase in consumption of fossil fuels, the environmental pollution and the threat of greenhouse effect have forced a dynamic development of alternative fuel markets. A promising lignocellulosic raw material for bioethanol (second generation biofuel) is hemp (_Cannabis sativa L_.) biomass. In recent years, there has been a dynamic increase in the area of hemp cultivation in Poland (over 1000 ha). The cultivation of hemp for seed purposes is currently intensively developed, therefore hemp biomass remains unused in the field, which can be a suitable raw material for the production of second generation bioethanol. The hemp dry matter yield is 10-15 t ha-1. It is an environmentally friendly plant, with a short vegetation period of 3-4 months and a rapid growth of up to 4 m in height, which improves soil quality and is useful for the reclamation of degraded areas (post-mining heaps). Based on data from 2016, it is estimated that in Poland, the area of devastated and degraded land requiring remediation, constituting a potential area for growing hemp for energy purposes, is about 65,000 ha. Hemp is also extremely resistant, perfectly adapt to different climatic conditions. They grow on almost any soil and can improve its quality, are not susceptible to various pests and do not require the use of plant protection products, and 1 ha of hemp binds around 2.5 t CO2 [1; 2]. Hemp biomass contains in its structure a polymeric complex called lignocellulosic, which is relatively difficult to degrade. The lignocellulosic complex found in cell walls of hemp is composedof the cellulose, hemicellulose and lignin. Cellulose and hemicellulose, after efficient deconstruction, can become productive substrates in the fermentation process. Lignin, consisting of phenolic alcohol derivates, is an effective obstacle in bioethanol production from plant biomass. The production of biofuel from lignocellulosic material requires deconstruction of the cell wall into individual polymers and the hydrolysis of carbohydrates into monomeric sugars [3; 4; 5]. Bioethanol production from lignocellulosic material can be divided into three steps: physical treatment, followed by chemical pretreatment, enzymatic hydrolysis and ethanol fermentation. In order to disintegrate the biomass and remove lignin, several pretreatment methods often used including - physical, chemical and biological methods [6]. The physical methods of the pretreatment of lignocellulosic biomass, whose aim is to reduce the size of the substrate as well as to facilitate the access of bioactive substances to the surface, reduction of polymerization and crystallization degree of lignocellulosic, include: milling, an extrusion method, and an ultrasound pretreatment. The chemical processes include treatment with acid (typically sulfuric or hydrochloric acid), alkali (sodium hydroxide, calcium carbonate, ammonia) or neutral (ionic liquids, liquid hot water LHW), the organosolv process, steam explosion, SO\({}_{2}\) or ammonia (AFEX), the ammonia recycle percolation (ARP), ozonolysis [6; 7; 8]. Depending on the method used, different changes occur within the lignocellulosic complex. The alkali pretreatment's function is mainly delignification, while the acid pretreatment process degrades most hemicellulose. A neutral solvent mainly depolymerises lignin, while the application of hot liquid or steam induce the degradation of hemicellulose and a small quantity of lignin. The non-specificity of the acidic treatment leads to the formation of complex sugars and compounds inhibitory to the functioning of microorganisms utilized for ethanol production [9]. An effective pretreatment process should solves the following issues: decrystallize the cellulose without causing its hydrolysis; depolymerize hemicellulose; restrict the formation of inhibitors which impede the hydrolysis of carbohydrates; require low energy input; allow the value added products such as lignin to recover; and, finally, it should be cost-effective [10].