| Diosgenin of yellow ginger is the coarse material for the steroid hormone drug production. It is estimated that two thirds of steroid hormone drugs in the world are made from diosgenin. China is the largest producer of diosgenin with an annual production more than 4000 tons, which accounts for about 90% of global production. This industry produces highly-polluted pharmaceutical wastewater, which is difficult to be treated by using conventional biological process. Bio-electrochemical system(BES) is a promising new wastewater treatment approach, with which the microorganisms degrade the organic contaminants and produce electricity simultaneously under the anaerobic or anoxic conditions. The main challenge for application of BES to treat yellow ginger wastewater is the complexity and variation of the wastewater composition, high sulfate concentration and persistent organic substance. This study focuses on the investigation of the factors affecting the treatment of the yellow ginger-derived wastewater by BES. The results can provide insights to microbial understandings and technical basis for the treatment of yellow ginger-derived wastewater.Due to complexity of the composition of the yellow ginger-derived wastewater, the anodic electrochemically active bacteria(EAB) may have difficulty to adapt it, resulting in negative effect on the selection of active electrogens. In this c hapter, the research addressed on how to efficiently enrich the electricity-generating bacteria by comparing two different inocula, i.e., aerobic versus anaerobic sludge. The effect of different sludges on startup duration, operating efficiency and anodic microbial community were investigated. The results showed that aerobic sludge-inoculated BESs started up within 170 h and reached 0.28 V with a maximum power density of 5.79W/m3; while the start-up of anaerobic sludge-inoculated BES lasted about 400 h to achieve 0.21 V with 3.66W/m3. Microbial analysis by DGGE profiling and high-throughput sequencing indicated that aerobic sludge contained more diversified bacterial populations than anaerobic sludge. Microbial community structure and composition of anodic biofilms developed respectively from a erobic and anaerobic sludge eventually become similar. Exoelectrogenic Geobacter and Anaeromusa species, biofilm-forming Zoogloea and Acinetobacter species were abundant in the anodic biofilms developed from both inocula. This study indicated that aerobic sludge performed better for BESs startup and would be favorite source to start up BES.Yellow ginger-derived wastewater contains high concentration of sulfate. Sulfate reduction reaction competes substantial electrons with electricity generation by transfering electrons from anode to cathode. Thus the electricity production efficiency would decrease due to electron consumption. Accordingly, in this c hapter, the experiments were designed to investigate the effect of influent sulfate on performance of electricity generation and wastewater treatment performace. The microbial community structure on the surface of BES anodes was also tested with the inhibition of SRB by the molybdate. Results showed that a low level of influent sulfate(<1200mg/L) enhanced power density and voltage but decreased the Coulombic efficiency from 31.5% to 8.5%. Molybdate inhibited the activity of SRB and also decreased BES voltage and power density. This suggested that some SRB might be involved in the electricity generation. Microbial community analysis indicated that Desulfovibrio desulfuricans contributed to the electricity production and stability of BES. In this study, the sulfate concentration in yellow ginger-derived wastewater was about 2400mg/L. If recycle of effluent were applied, the negative impact of high sulfate concentration of the raw wastewater would significantly decrease.The dynamics of organic compostion as well as concentration in the yellow ginger-derived wastewater could influence the operation performance and electricity production of BES. The impact of change of organic composition was investigated to characterize the BES performance and response of microbial community. Results showed that the change of organic substrates influencing the performance of BES depended on the types of substrates. BES performance recovered rapidly when the lactate was replaced by its inter mediate product, acetate. The composition and structure of anodic microbial community responded well to the substrate switch. New substrate- or its intermediate product-depended microbial populations were enriched. Acetate is the primary product during ana erobic fermentation, so the acetate-depended exoelectrogens, Geobacter spp., would be enriched with different substrates. The composition of yellow ginger-derived wastewater fluctuated greatly but the major components are polysaccharide. Acetate is a main intermediate product when polysaccharide is anaerobically degraded and thus exoelectrogens can be consequently enriched. Hence, the fluctuation of compostion of yellow ginger-derived wastewater would not influence the function of BES significantly.Yellow ginger-derived wastewater contains high concentration of COD and some active ingredients, which inhibit electricity production. The feasibility of treatment of the wastewater was tested by using BES with analysis of the microbial community relative to the organic matter degradation. The results indicated that the maximum COD removal efficiency reached 82%. The removal of total nitrogen also presented a high rate at 62.5%, while sulfate removal efficiency was still 26.5%. The maximum power density and the Coulomb efficiency reached to 18.1W/m3 and 30% respectively. Using dilution by five times, the BES achieved the effluent of treated yellow ginger-derived wastewater at COD less than 400mg/L, which meets the requirement of standard of yellow ginger-derived wastewater(GB20425-2006). By using PCR-denaturing gradient gel electrophoresis techniques we observed continuous change in microbial structure of community when the BES was fed with increasing fraction of the wastewater. We also detected some unique bacterial sequences in anodic biofilm with different wastewater. The organic matters were degraded to acetate by anaerobic fermenters, Acidovorax delafieldii and Holophaga foetida, and then acetate and other products were oxidized to CO 2 by some members in genera Dysgonomonas, Pseudomonas, and Desulfovibrio.This study provided fundamental understandings for the treatment of yellow ginger-derived wastewater by BES including the selection of inoculum for the startup, the effect of sulfate, and substrate variation as well as tested results with real wastewater. The research results can be used as reference and case data to design BES for the treatment of yellow ginger-derived wastewater and electricity production. |
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