Pretreatment Of Yeast Production Wastewater And Hydrogen Production Based On MF-CSTR Process

Wastewater produced during the yeast production has high COD concentration,Chroma and turbidity and it is difficult to dissolve the water via biological process. In china, the processed wastewater can hardly reach the request of environmental standard and the cost of the present process is usually unaffordable, which has constrained the development of yeast industry. This thesis researched the process of pretreatment of wastewater from yeast production. As high content of yeast exist in the wastewater, the massive multiplication of yeast will inhibit the hydrogen production process which require an anaerobic condition, therefore, membrane filtering pretreatment of the wastewater is introduced. The leachate is sent to produce hydrogen in anaerobic environment, while the residue is sent to extract protein. In this way, the wastewater acts as a form of an energy and resource.The filtering process utilized the PVDF membrane with an aperture of 0.2μm and the water supply and drainage speed are kept same in the process. The yeast content is checked with microscope before and after filtering to evaluate the filtering effectiveness and the results show that the yeast cannot pass the membrane. This indicates that the membrane is reliable to filter the yeast and thus facilities the hydrogen production in anaerobic reactors.In the filtering process, the influence of Aeration on the pressure difference of the membrane is studied with the flux maintained at 45.86L·m-2·h-1 by adjusting the rotating speed of Peristaltic pump to get the optimal aeration. The results show that an aeration of 0.15m3·h-1 can effectively reduce the contamination of the membrane to prolong the membrane lifespan. At the same time, it is suggested to clean the membrane regularly by backwash and chemical detergent.The Suspended solids(SS) concentration and its components are analyzed and the cost as well as the profit of the extraction of protein from the residue is compared. The results show that the protein content is around 8.5g·L-1 and for a yeast factory which has a daily wastewater production of 1 000m3, the profit can be as high as 1 090 yuan·d-1,which highlights the economic feasibility of extraction of protein from wastewater.Intermittent shake flask tests were conducted to study the difference of hydrogen production between direct anaerobic digestion and anaerobic digestion after filtration and the performance of the two kinds of wastewater under different influent p H conditions. Results showed that, biohydrogen production rate of filtered group was higher than the group without filtration. When influent p H was 5.00, the hydrogen percentage of filtered group was 49.69%, which exceeded the group without filtration by 20.34%, while with the most highest biohydrogen rate 5.20 m L·mg-1COD, which was1.71 m L·mg-1COD higher than direct anaerobic digestion.The study used CSTR(Continuous Stirred Tank Reactor) for hydrogen production through anaerobic digestion of the filtered yeast industry wastewater and realized the highest benefits of hydrogen production by adjusting HRT and OLR. Results showed that, when HRT was 8h and OLR was 24 kg COD·m-3·d-1, the system can get the highest biohydrogen production rate at 13.2L·d-1.This test suggested that MF-CSTR pretreatment process can simultaneously treat yeast industry wastewater effectively and realize resource recovery from yeast protein and energy recovery and utilization from hydrogen, which provides the theoretical foundation for the treatment and resource utilization from yeast industry wastewater.