Introduction

Cellulose is the most abundant carbohydrate polymer in wastes from forest products agriculture, fruits, and vegetables. Agricultural wastes and in fact all lignocellulosics can be converted into products that are of commercial interest such as ethanol, glucose, single cell protein (Solomon et al., 1999). In these waste products, the polysaccharides, cellulose and hemicellulose are intimately associated with lignin in the plant cell wall. The lignin component acts as a physical barrier and must be removed to make the carbohydrates available for further transformation processes (Kadam, 2000). Therefore, the pretreatment is a necessary process for utilization of lignocellulosic materials to obtain ultimately high degree of fermentable sugars. Pretreatment affects the structure of biomass by solubilizing hemicellulose, reducing crystallinity and increase the available surface area and pore volume of the substrate. There are numerous pretreatment methods or combinations of pretreatment methods available. In general, pretreatment techniques can be grouped into three categories: physical, chemical, and biological. Physical pretreatment methods include comminution, steam explosion etc. The most common chemical pretreatment methods used for cellulosic feedstocks are dilute acid, alkaline, organic solvent, ammonia, sulfur dioxide, carbon dioxide or other chemicals to make the biomass more digestible by the enzymes. Biological pretreatments are sometimes used in combination with chemical treatments to solubilize the lignin in order to make cellulose more accessible to hydrolysis and fermentation (Ayhan Demirbas, 2005). Pretreatment of cellulosic biomass in a cost-effective manner is a major challenge of cellulose-ethanol technology research and development. In the present work comparative study of chemical and biological treatments on wheat straw and rice straw are conducted.

Materials and Methods

Substrates: Wheat straw and rice straw were obtained from local fields of Davanagere district. Each raw material was powdered and sieved into a 1mm sieve and this was used as carbon source.

Isolation of fungi: Screening of fungi capable of degrading cellulose was done (Abdul et al 1999) from the soil of local paddy and wheat fields and fungi of interest were selected after proper identification through manuals and confirmation by MTTCC, Chandigarh.

Acid hydrolysis and saccharification

Alkaline hydrolysis

Culture medium

Culture conditions

Results and discussion

Initial composition of the raw materials was determined (Table 1). Pretreatment of raw materials makes it accessible for microbial treatment. So chemical treatments were conducted (table 2). Results of fungal treatments are shown in table 3.

Figure 1

Table 1 Initial composition of raw materials

Figure 2

Table 2 Results of chemical treatment

Figure 3

Table 3 Results of fungal treatment

Autoclaving for sterilization has affected and resulted in increase in sugar release. With fungal treatment still increase in the yield of sugars was observed. Treatments with A. awamori and A. niger has shown better yield of reducing sugar compared to any of the two chemical treatments. Because pretreatment of cellulosic biomass in a cost-effective manner is a major challenge of cellulose-ethanol technology research and development, with the results of present work we have shown that microbial treatment, which is less costly and with less severe physical conditions, gives better yield of sugars from cellulosic residues like wheat straw and rice straw.