Biosurfactant-enhanced Degradation Of Biomass In Different Media Environment

The large quantity of waste biomass produced all over the world is a kind of organic materials which is difficult to be degraded, while it represents a renewable resource that has attracted more and more attentions. To enhance the degradation of biomass is significant for improving the resource utilization and wastes minimization. Still the waste biomass degradation is important for environmental pollution control. As the biomass degradation is mainly carried out by the microorganisms in nature, the process can be enhanced by the presence of surfactant through increasing the degradable enzymes excretion, improving the microbial growth and the reacting micro-environment. The bio surfactants are typical surfactants which have the similar characteristics in molecular structure compared with synthetic surfactants. They can reduce the surface/interface tension of air-water, oil-water or solid-water phases. In special, the biosurfactants are believe to have a good prospect as they have several advantages such as lower toxicity, easier to be degraded and higher environmental compatibility, thus they are regarded as "green chemicals" which showing high efficient during utilization.This dessertation investigated the biosurfactant-enhanced degradation of biomass in several typical media environment, and used the lignocellulosic wastes and sewage sludge in composting system as substrates. The experimental performances of biomass degradation included enzymatic hydrolysis, biodegradation and composting process. While the effects of biosurfactants in aqueous environment, in reversed micellar media, in solid-state fermentation and in composting matrix are studied. This research helps to understand the behaviors and interfacial influences of biosurfactants in different reacting media, and provides scientific data for biosurfactant application in different medium conditions. As a result, this work is significant for the development of contaminants enhanced-degradation technologies and the application of extrinsic accelerants.The first section describes the research on the effects of biosurfactants on enzymatic hydrolysis of cellulosic biomass in aqueous liquid media. The rhamnolipid biosurfactant was produced by Pseudomonas aeruginosa and was used in the following experiments. The effects of three surfactants (Tween80, saponin and monorhamnolipid) on the hydrolysis of NaOH-pretreated rice straw by low dosage of cellulase were studied, and the results indicated that at the same condition, all surfactants were able to enhance the enzymatic hydrolysis by reducing the cellulase denaturalization, while the biosurfactant monorhamnolipid was demonstrated to be more active than Tween80and saponin. In addition, a new magnetic immobilized cellulase was developed by the presence of dirhamnolipid. It was applied in the hydrolysis of cellulosic biomass and showed capable in improving the enzyme stability.The second section focuses on the feasibility of biosurfactant on enzymatic hydrolysis of cellulose in non-aqueous liquid media. For the first time, the biosurfactant was introduced into the enzyme-containing reversed micellar system. The’rhamnolipid/isooctane/n-hexanol/water’ reversed micellar system was formed, and its electrical conductivity was measured to determine the maximum water solubilization W0. The critical micelle concentrations of surfactant rhamnolipid, SDS, CTAB and Tween80in isooctane/n-hexanol (1/1, v/v) were determined by steady-state fluorescence used the rhodamine B (Rh-B) as a probe. The degradation of cellulose model substrate in reversed micelle was conducted in the condition of W0=W0, max, while the effects of different surfactants were compared. The results showed that the W0, max of anionic surfactant (rhamnolipid and SDS) reversed micellar system was higher than it was in cationic surfactant (CTAB) and in nonionic surfactant (Tween80) system. The peak conversion rates of substrate were obtained when the surfactants concentration was at1CMC of their each. The enzymatic hydrolysis efficiency in reversed micelles was higher than that in aqueous reaction media at the same conditions, independent of surfactant types. While the rhamnolipid showed more effective than the other three synthetic surfactants.The third section focuses on the effects of biosurfactant rhamnolipid on biomass degradation at solid-liquid interface. The influence of dirhamnolipid biosurfactant on biodegradation of rice straw by Phanerochaete chrysosporium was investigated. The results showed that the biodelignification of rice straw can be significantly enhanced by the presence of dirhamnolipid biosurfactant. In particular, the dirhamnolipid at the concentration of0.007%increased the peak activity of lignin peroxidase (LiP) by86%. The water-soluble organic carbon (WSOC) contents in the straw substrates as well as the microbial growth and activity were effectively improved by dirhamnolipid, while the degradation rate of lignin increased by54%with dirhamnolipid of0.007%. Variation partitioning analysis revealed that the improvement by dirhamnolipid addition is significant. To investigate the effect of biosurfactant on composting of sewage sludge, a static forced-aeration composting matrix was constructed by the presence of rhamnolipid. The physicochemical factors, microbial parameters and the biological toxicity were analysis. In addition, the influence of biosurfactant addition was compared with that of the microbial inoculants.The fourth section demonstrates the interaction between enzyme and surfactant molecules during the micelle or reversed micelle formation. The cellulase and the laccase were taken as an example, while the rhamnolipid, SDS, CTAB and Tween80were used in the analysis of their interactions with enzymes, respectively, in the aqueous media. According to the fluorescence behavior of pyrene, the characterization of interactions depends on the type of surfactant and as well as the enzyme. The changes of pyrene fluorescence intensity along with the concentration of surfactants were reduced by the presence of cellulase, while the laccase seemed to inhibit the surfactant micelle formation in aqueous. Otherwise, the rhamnolipid showed higher stability than SDS at concentrations above CMC. The ANS and Rh-B probes were employed in analysis of interactions between rhamnolipid and enzymes in reversed micellar system. The fluorescence behavior of each probe demonstrated the micro-environmental polarity changes along with the W0, and it described the combining sites of enzymes and surfactant molecules as well as their trends.