Explore The Influencing Factors On "Ethanol-methane Dual-fermentation Coupled" System And The Process Optimization

Based on fermentation ecological engineering theory,“ethanol-methanedual-fermentation coupled” process has been built in our laboratory, which provides a newidea and method to the further emission reduction and realizes “Zero Energy Consumptionand Wastewater” in fuel ethanol production process. The “dual-fermentation coupled” systemhas been the first one who achieved industrialized run in fuel ethanol production. The systemwill not only provide a template for submerged fermentation industry, such as Citric acidfermentation industry, but also promote green and waste-free be realized in all the submergedfermentation industry.Compared with the control (tap water as cooking water), the ethanol productiondecreased3.47%while mesophilic anaerobic effluent was used as the cooking water forethanol fermentation both in laboratory scale (ethanol fermentation volume of8L) and pilotscale (ethanol fermentation volume of1.0m3). Under the early researches, the sulfide, aceticacid, propionic acid et al have a potentially inhibitory effect on ethanol fermentation, but theirconcentration in the mesophilic anaerobic effluent were lower than the critical inhibitoryconcentration. In order to industrialize the process successfully, the paper aims to find out theinhibitor in mesophilic anaerobic effluent and set up a optimized method to relieve theinhibitions. The main results are as follows:(1) The ammonia nitrogen in anaerobic effluent is the main inhibition for ethanolfermentation, which is confirmed through the stripping experiments, the ammonia nitrogenadded experiments and GC-MS detection. The critical inhibitory concentrations were500mg/L and300mg/L while the concentration of urea addition were0.05%(w/v) and0respectively. There are two reasons for the ethanol production decline:①The presence ofammonia nitrogen provided inorganic nitrogen source for the growth of yeast, promoting thecell growth and glycerol production.②Ammonia nitrogen in the cooking water could causethe Maillard reaction in the liquefaction and sterilization process, resulting in the loss ofreducing sugar and the decrease of the ethanol production.(2)The sludge, microorganisms and other substances in anaerobic effluent have negativeimpacts on ethanol fermentation. The critical inhibitory concentration of sludge is0.7g/L(dry weight). The effect of microorganisms and other substances is complex and needsfurther study. When anaerobic effluent were used as the cooking water for ethanolfermentation, the mesophilic anaerobic effluent shows a stronger inhibition on fermentationthan thermophilic anaerobic effluent. The reasons, in addition to the ammonia nitrogenconcentration in mesophilic anaerobic effluent is higher than thermophilic anaerobic effluent,may also exist other influencing factors, the specific cause needs further study. (3)The paper studied the impact factors of the ammonia nitrogen removal process bystripping,which divided into two stages of decarburization and deamination in pilot scale.Decarburization efficiency was positively correlated with the temperature of the mesophilicanaerobic effluent and the time of stripping, while negatively correlated with the gas-liquidratio; and deamination efficiency was positively correlated with the temperature and pH ofthe mesophilic anaerobic effluent and was negatively correlated with the flow rate indeamination tower. The specific optimal conditions in actual production still should bedetermined after further economic balance.(4) During the operation of “ethanol-methane dual-fermentation coupled” process inpilot scale, the result of continuous38recycles which using mesophilic anaerobic effluentafter resource reuse treatment as the cooking water for ethanol fermentation was confirmedthe feasibility of the process. The results about this circulation process were basically thesame as the tap water fermentation both in pure tapioca, corn, or mix ingredients.(5)Study the feasibility of adjusting the pH of mesophilic anaerobic effluent withdistillery waste. The results showed that the ethanol yield would descended with theincreasing of recycles when recycling proportion is above30%. The accumulation ofmetabolic non-volatile by-products such as glycerin, acetic acid, lactic acid, citric acid,succinic acid et al is the main reason for the ethanol yield reduction. In “ethanol-methanedual-fermentation coupled” process, using10%distillery waste to adjust the pH of mesophilicanaerobic effluent can reduce the usage of sulfuric acid by8.07%with guaranteeing theethanol yield.