| dc.description.abstract | Schizophyllan glucan (SPG) could be used as biodegradable bioflocculant proved by Ferretti et al.(2003). But, SPG has failed in some areas of application to supplant conventional chemical flocculants due to its relatively high production costs. Thus, using low-cost substrate for SPG production would be economical attractive. The objective of this study was to develop a fermentation process for the bioflocculant SPG production from agricultural waste such as rice hulls.
Results indicated that biomass from the untreated rice hulls reached only 0.54 g/L which was relatively poor as compared to those using glucose, currently the primary source for SPG, as carbon sources. Similar observation was reported that the corn fiber without suitable pretreatment could not be utilized by S. commune (Leathers et al.，2006). The results imply that effective pretreatment of rice hulls is crucial to successfully convert its carbohydrates for SPG production. In our study, an optimal pretreatment conditions was found to be 10% solids content with addition of 1% sulfuric acid and treatment time of 60 min at 121℃, in which 28g/L monosaccharide was released. And, xylose was the major sugar present in the hydrolysate. Although, both cell yield (YX/S) and product yield (YP/S) increased slightly as glucose was replaced by xylose, poor fermentation performance from crude hemicellulosic hydrolysate, when compared to those from synthetic medium. These results imply that some inhibitory components were present in rice hull hydrolysate and accounted for the poor fermentation performance of S. commune.
Iin order to utilize rice hull hydrolysate more effectively for SPG production, this research carries on the discussion with the inhibitor tolerance ability of S.commune, both the effects of detoxification methods on the inhibitors remove ability and fermentation, and the flocculation activity of SPG.
The experimental result shows, S. commune has a low tolerance to furfural as compared with HMF and acetic acid. No apparent cell growth was observed while 2.0g/L of furfural was added. Although HMF had a little influence on cellular biomass formation, it had a significant influence on SPG fermentation. When HMF was added to 2.0g/L, the relative SPG formation decreased to 43％ of the control run. Acetic acid had a less inhibitory influence on SPG fermentation by S.commune, as compared with furfural and HMF. Moreover, the medium supplemented with 0.5g/L acetic acid, both xylose utilization and product yield were enhanced. Additionally, among all salt ions tested, sodium ions showed the maximum inhibitory effect toward SPG production, but calcium ions showed the minimum inhibitory influence. Based on the results of inhibitor supplementation, detoxification of rice hull hydrolysate using Ca(OH)2 to adjust pH and powered activated charcoal to remove furfural and HMF were adopted. The SPG product yield (YP/S) from the detoxificated hydrolysate was two folds of that of the hydrolysate without detoxification.
We further demonstrated that acetic acid inhibition could be alleviated to some extend by pH adjustment to pH=6.5.
| en_US |