| Anaerobic digestion technology can be used to convert the biomass waste into renewable bioenergy through the production of biomethane. Large amount of agricultural wastes are produced annually in different parts of the world however, vastly are under-utilized. Teff is one of the largely produced cereal crops in African, United States and some European countries which have a considerable amount of straw as byproduct. Teff straw is a new lignocellulosic biomass which could be a potential source of biomethane in the process of anaerobic digestion technology. However, high content of lignocellulosic compounds in agricultural straws hinders microbial hydrolysis which leads to reduction in anaerobic digestion rate and generation of biomethane; this is due to the presence of recalcitrant lignin in compounds. Pretreatment of lignocellulosic biomass before the process of anaerobic digestion has been confirmed to be easy and efficient technique to enhance hydrolysis and biomethane conversion of straws. In this study the effects of pretreatment of teff straw with NaOH and KOH on anaerobic digestion were conducted independently. The objectives of this study were to (1) explore the anaerobic digestion and biomethane potential of teff straw pretreated with sodium hydroxide; (2) investigate the effects of three (pretreatment time, concentration of NaOH used for pretreatment and, solid loading) operating parameters of anaerobic digestion process the on NaOH pretreated teff straw sample; (3) identify the efficiency of KOH pretreated teff straw for the production of biogas in anaerobic digestion process using different concentrations of KOH and organic loading rates; (4) analyze the change in main compositions and structural variations of alkaline pretreated and unpretreated teff straw samples; and (5) analyze the fertilizer value of teff straw digestate at the end of anaerobic digestion.Biogas generation capacity and methane yield of NaOH pretreated teff straw were determined. Various dozes of NaOH such as 1,2,4 and 6% were applied for every organic loading 50 g/L,65 g/L,80 g/L and 95 g/L). According to the results,4% NaOH for pretreatment coupled with 80g/L organic loading gave 40.1% greater cumulative biogas yield and 48.2% more bio methane production than the untreated sample of teff straw. Analysis of changes in main chemical compositions and physical micro-structures showed that there were 4.2-22.3% total lignocellulosic compositions removal after three days pretreatment with NaOH. Generally, NaOH pretreated teff straw revealed better production of biogas as well as biomethane and also showed enhancement in biodegradability of the raw materials than the untreated sample.The KOH pretreatment was carried out for four days in sealed bottles and, results showed that 2% KOH pretreatment of 65 g/L organic loading produced 51.4% and 68.8% higher biogas and biomethane respectively than the unpretreated sample. Total solids and volatile solids were reduced by about 59.9-70.7 and 61.6-72.2% as compared to 52.4-62.3 and 50.4-61.4%, respectively for the untreated samples. Potassium hydroxide pretreatment led to structural and compositional changes in lignocellulosic compounds such as cellulose, hemicellulose and lignin in the teff straw, which were confirmed by Fourier transform infrared spectroscopy (FTIR). These results confirmed that KOH pretreatment technique can significantly improve biomethane production from teff straw as a result of changes in the main compositions of the substrate which subsequently have favorable effect on its biodegradability. |
PDF Full Text Request