In current scenario to utilize the lignocellulosic material for green energy, the pre­treatment is an unavoidable step in biorefinery with the cost as high as 30 cents/gallon ethanol produced [10]. Approximately, pretreatment alone costs around 30 % to the

total processing cost in the conversion oflignocellulosics into ethanol [29]. Perfor­mance of pretreatment methods and the incurred cost on bioconversion process was comprehensively analyzed by Eggeman and Elander [72]. The ideal pretreatment process needs to be highly efficient with imposing low operational and capital cost with less pollution [10, 16, 73]. Recovery of maximum sugars after pretreatment, less chemical load, usage of by-products, faster kinetics, and less process complexity are the important criteria to determine the overall impact of pretreatment methods [11, 16, 17]. All these features determine the cost on downstream processing steps and the trade-off with operational cost, capital cost, and biomass cost [10, 68, 73]. Table 16.5 analyzes the environment and economic impact of various pretreatment

methods applied to SB/SL. Critical features like upstream and downstream process­ing cost, capital investment, chemical recycling, usage of by-products, and waste treatment systems makes the comparison and evaluation of pretreatment methods difficult [74]. Net impact of each pretreatment method concerning the economics and environmental impact shows that chemical-based pretreatment methods have strong impact on economics of overall biomass conversion along with considerable environmental pollution burden (Table 16.5).

Pure chemical based pretreatment methods require significant amount of chemi­cals for biomass destruction with the significant amount of by-products generation [14, 17]. However, these methods are highly effective toward either lignin re­moval or hemicellulose degradation from lignocelluloses in short reaction times. Physico-chemical methods (dilute acid hydrolysis, AFEX, steam explosion, etc) have considerable effect on economics and environmental concerns [14, 17]. These methods are more specific toward hemicellulose or lignin degradation leaving cel — lulignin and holocellulose together but in disorganized manner amenable for better cellulases action. In comparison to alkaline methods, physic-chemical methods need less chemical load for the hemicellulose degradation. Biological, physical and LHW pretreatment methods do not require chemicals and are generally considered as mod­erate. Biological methods are generally safe but take longer time periods for lignin removal from the substrates.

Application of lignin generated during alkaline pretreatment has been found im­portant in many products of commercial significance such as resins, adhesives and coatings. Many industries are aiming forward to commercialize the lignin derived products [73]. Pretreatment like dilute acid hydrolysis, auto-hydrolysis and LHW degrade hemicellulose fraction of cell wall into varieties of sugars (xylose, arabi- nose, glucose, mannose and galactose) are used for the production of value-added products like D-xylitol, ethanol, lactic acid, single cell protein etc [2].

A detail economic analysis of each pretreatment strategy considering all the in­volving factors will help to direct research and development efforts in the success of commercialization of bioconversion processes [72, 73]. The renewed interest in sus­tainable development and environment friendly based practices, biotransformation processes are generally preferred over the conventional chemical conversion process. Unfortunately, most pretreatment protocols involve either strong chemicals or harsh physical conditions except bio-delignification. Pretreatment methods autohydrolysis, LHW, steam explosion do not deal with corrosive chemicals however strong physical parameters (high temperature and pressure) are the matter of concern [10]. Biolog­ical pretreatment are the least environmental pollution causing methods but their slow reaction time and loss of significant amount of carbohydrates are the important concerns while selecting them as pretreatment method of choice [13,16]. Biological pretreatment methods have important benefits in a life cycle context also [68].