Thermophilic anaerobic fermentation of waste biomass for producing acetic acid.

摘要

The purpose of this research is to generate acetic acid from the biodegradable fraction of municipal solid wastes (MSW)/municipal sewage sludge (MSS) and corn stover/swine manure by using a thermophilic (55°C), anaerobic, high-solid fermentation. One of the advantages of using thermophilic, as opposed to mesophilic, fermentation is higher selectivity for acetic acid, which has a larger market than other carboxylic acids. Another goal is to maximize substrate conversion and product concentration. A variation of the MixAlco process allows this goal to be achieved.; A series of four countercurrent fermentors were used with a high solids content to achieve high product concentration and high substrate conversion. The substrates used were energy and nutrient combinations of 80% MSW/20% MSS and 40% corn stover/60% swine manure. MSW and corn stover were the energy sources with high carbohydrate contents, and MSS and swine manure provided good sources of minerals, metals, and vitamins. The fermentation terrestrial inocula were mixed cultures obtained from rumen fluid, lake sediment, and compost piles. Marine inocula were collected from different saline swamps at Galveston, Texas. To enhance hydrolysis, MSW and corn stover were pretreated with lime before feeding to the fermentors. The highest total carboxylic acid concentrations achieved from this research were 25.1 g/L and 20.5 g/L for corn stover/swine manure and MSW/MSS, respectively. The highest conversion obtained for corn stover/swine manure was 73%, and for MSW/MSS was 69%. The acetic acid selectivity reached as high as 70.6% for corn stover/swine manure, and 86.4% for MSW/MSS. In conclusion, MSW/MSS has higher acetic acid selectivity, but lower total acid concentration than corn stover/swine manure. Marine inocula produce higher product concentrations and higher conversions than terrestrial inocula.; Continuum Particle Distribution Modeling (CPDM) was used to predict the final acid product concentrations and substrate conversions at a wide range of liquid residence times (LRT) and volatile solid loading rates (VSLR). Product concentration and conversion “maps” were generated from CPDM and the predictions were compared to the experimental results. Acid production between the experimental and predicted values had an average of 11% and 13% differences for corn stover/swine manure and MSW/MSS, respectively.