Date of Award

5-2010

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

G. Peter van Walsum

Second Committee Member

Adriaan R.P. van Heiningen

Third Committee Member

Paul J. Millard

Abstract

Wood is composed of cellulose, hemicellulose and lignin. In the paper industry the cellulose fraction is the major resource used in paper production, whereas the hemicellulose and the lignin are usually burned for heat recovery. Recently, wood-derived hemicellulose extracts have received much attention for the production of valuable bioproduct fuels and chemicals. Mixed-culture microbial ecosystems are capable of converting biomass materials, such as wood extracts, into mixtures of carboxylic acids (C1-C7), which can in turn be purified and sold as products, or converted into other organic chemicals through chemical means. The relative concentrations of the acids produced in the fermentations vary depending upon the type of extracts used and also on the microbial communities employed, such as those growing at mesophilic or thermophilic temperatures or different buffered pH levels . In this study, we were looking for the maximum production of carboxylic acids at varying temperatures using mesophilic and the thermophilic microbes growing on green liquor and hot water extracts. Steps had to be taken to restrict the growth of methanogenic cultures, thereby inhibiting the production of methane and enabling higher carboxylic acid accumulation. The inhibition of methane was done by adding iodoform at low concentrations or using ammonium bicarbonate as a buffer. The buffering agents calcium carbonate and ammonium bicarbonate were tested as alternate means of maintaining neutral pH during acidogenic growth on pure sugars. Results from the pure sugar fermentations led to applying ammonium bicarbonate as the buffer of choice for wood extracts fermentations. During fermentations, samples were collected at specific time intervals and the pH, off-gas volume, off-gas composition and total sugar and carboxylic acid contents were measured Analytical methods used included GC for determining gas composition and GC and HPLC for determining acid and sugar concentrations.. Results indicated that mixed microbial cultures were capable of converting glucose and xylose sugars and hydrolyzing oligomeric hemicellulose without addition of supplemental enzymes. Conversion yields of organic acids to carbohydrate ranged from 50 to 80%, with lactic acid dominating in lower pH fermentations and acetic acid dominating in fermentations at closer to neutral pH. Methane production in all cases was detected at very low levels compared to CO2 production rates. With the benefits of autohydrolysis, high product yields and low operating costs due to the non-aseptic fermentation, conversion of aqueous wood extracts to carboxylic acids may be an economically attractive method of adding value to these extracts.

Share