| Bioethanol is one of the most important bulk fermentation products in the fermentationindustry. Its production process faces problems of massive energy and water consumption andhigh cost for wastewater treatment, which are very representative in the fermentation industry.The integrated ethanol and methane fermentation ecosystem developed based on thefermentation ecological engineering theory is expected to resolve these problems and provideguidance for the cleaner production of the whole fermentation industry. Based on the presentresearch, this paper aimed to promote industrial application of the integrated ethanol andmethane fermentation ecosystem, thereby achieving the sustainable development in thebioethanol industry, in addition enrich the fermentation ecological engineering theory andconstruct the methodology for its wide application to the fermentation industry. An integratedcorn ethanol and methane fermentation ecosystem was established and assessed. And themicrobial community structure of the anaerobic digestion in the ecosystem was analyzed. Inaddition, effects of key ecological factors on the integrated ecosystem were studied andcorresponding optimization methods were proposed. Finally, the integrated ecosystem wasinvestigated at pilot scale. The main research contents and results were shown as follows:1. An integrated corn ethanol-methane fermentation ecosystem was developed andevaluated in terms of anaerobic digestion and ethanol fermentation performances, materialbalance, quality of dried distillers' grains (DDG) and energy evaluation. In the recyclingprocess, anaerobic digestion treatment of thin stillage performed with high efficiency andstability. Ethanol fermentation of each batch was not influenced and the ecosystem reachedconstant state after the seventh batch. Compared with dried distillers' grains with solubles(DDGS) produced in conventional dry-grind process, DDG exhibited higher quality. Crude fatcontent and odor of the DDG from the recycling batch showed some different with the firstbatch of DDG. In addition, net energy balance ratio of the integrated system was1.76, whichis significant higher compared to conventional process (1.26).2.454pyrosequencing and real-time PCR were used to reveal the microbial communitystructure of the anaerobic digestion in the integrated corn ethanol and methane fermentationecosystem. Thermophilic (TS) and mesophilic (MS) anaerobic sludge showed highly diverseand different microbial community structure. Abundance ratios of bacteria, archaea and fungiin TS and MS were1005:74:1and523:77:1, respectively.90bacterial genera were detected inthe TS, which mainly belonged to Nitrospirae, Chloroflexi, Thermotogae, Proteobacteria,Firmicutes and Bacteroidetes. In addition,106bacterial genera were detected in the MS,which mainly belonged to Chloroflexi, Bacteroidetes, Firmicutes, Proteobacteria andNitrospirae.52genera were shared by two sludges. As for the archaeal community,Euryarchaeota absolutely dominated both in the TS and MS. The detected10genera allbelonged to Euryarchaeota, and9and7genera were detected in the TS and MS, respectively.And the obligately acetoclastic Methanosaeta was the most abundant archaeal genus. As foreukaryotes, fungi accounted for99%of all detected genera, and protozoa and metazoanrepresented only1%in the TS. While in the MS, protozoa and metazoan had the largest abundance. Investigating the existence of pathogenic bacteria that need to be detected in theanimal feed in the TS and MS found that only Shigella existed in the TS (abundance=0.05%)while others were not detected.3. Effects of ammonium nitrogen and other key ecological factors on the integratedethanol and methane fermentation ecosystem were studied. Results indicated that highconcentration of ammonium nitrogen reduced the ethanol yield by converting more sugar foryeast growth and glycerol production, rather than reducing the total sugar in the ethanolfermentation culture medium through Maillard reaction between reducing sugar andammonium nitrogen during mashing and sterilization processes. Components exceptammonium in the anaerobic digestion effluent (ADE) could promote growth of yeast, butcause no influence to the ethanol yield. Therefore, it is necessary to control the ammoniumnitrogen concentration of the ADE in the recycling process of the system. Besides, the controlstandards were different depending on the feedstock used for ethanol fermentation. For cornand cassava, the concentration needed to be controlled below300and400mg·L-1,respectively. When the ammonium nitrogen concentration in the ADE was well controlled, thenitrogen source, urea, can be replaced, thereby reducing the cost of added nitrogen source.4. For the key ecological factors that affect the integrated ecosystem, correspondingoptimization methods for the ecosystem were proposed and tested. Firstly, a new ammoniumremoval technology suitable for the ADE was proposed. The two factors (temperature andair-liquid ratio) were confirmed in the carbon dioxide removal process. The central compositedesign (CCD) and response surface methodology (RSM) were applied to develop a model ofammonium stripping from the ADE. Secondly, a double circular ecosystem was establishedand the recycling ratio of thin stillage (40%) was confirmed in the recycling process. In thiscondition, usage of sulfate acid was eliminated, thereby avoiding the effect caused by sulfate.Besides, the ethanol yield was enhanced. Finally, to reduce the investment and operation cost,an integrated ethanol-methane (one-stage thermophilic anaerobic digestion) fermentationecosystem was proposed. In the recycling process of this system, the fermentation rate andethanol yield in the recycling batch were higher than the control in which tap water was usedas process water. This result was caused by the relatively high concentration of VFAs andamino acids in the thermophilic ADE. However, suspended solid (SS) content in thethermophilic ADE was very high which was difficult to remove in the actual productionprocess. Therefore, economical and effective method for SS removal is required to achievethe application of this system.5. The integrated corn ethanol and methane fermentation ecosystem and double circularecosystem were studied at the pilot-scale to support the lab-scale experiments and lay afoundation for the industrial application. In the recycling process of the former system,two-stage anaerobic digesters performed well and average ethanol concentration of therecycling batches in the fermenter was equal to the first batch. And the system showed highstability and self-healing capacity. In addition, DDG as a feed additive did not affect growthof pigs. Results of ethanol fermentation in sync with the fermenter showed that ethanolproduction was closely related with the ammonium nitrogen concentration in the ADE, furtherindicating the importance of controlling the ammonium nitrogen concentration. In the recycling process of the latter system, sulfate acid was not required and degree of ammoniumnitrogen removal for the ADE was reduced. Beisdes, average ethanol production of ethanolfermentation in sync with the fermenter was higher than that of the control. The anaerobicdigestion process was not influenced as well. Finally, the achievement in this pilot scale studyhas passed the technical evaluation hosted by the National Light Industry Federation and theintegrated technical indicators were identified as reaching international advanced level. |
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