Frederick J. Schendel

Industrial symbiosis: Corn ethanol fermentation, hydrothermal carbonization, and anaerobic digestion

The production of dry‐grind corn ethanol results in the generation of intermediate products, thin and whole stillage, which require energy‐intensive downstream processing for conversion into commercial animal feed products. Hydrothermal carbonization of thin and whole stillage coupled with anaerobic digestion was investigated as alternative processing methods that could benefit the industry. By substantially eliminating evaporation of water, reductions in downstream energy consumption from 65% to 73% were achieved while generating hydrochar, fatty acids, treated process water, and biogas co‐products providing new opportunities for the industry. Processing whole stillage in this manner produced the four co‐products, eliminated centrifugation and evaporation, and substantially reduced drying. With thin stillage, all four co‐products were again produced, as well as a high quality animal feed. Anaerobic digestion of the aqueous product stream from the hydrothermal carbonization of thin stillage reduced chemical oxygen demand (COD) by more than 90% and converted 83% of the initial COD to methane. Internal use of this biogas could entirely fuel the HTC process and reduce overall natural gas usage. Biotechnol. Bioeng. 2013;110: 2624–2632.

Chemical characterization of phosphoribosylamine, a substrate for newly discovered trifunctional protein containing glycineamide ribonucleotide synthetase activity

PRA has been characterized for the first time using 13C-NMR spectroscopy. Incubation of [1-13C]ribose-5-phosphate with NH3 results in the production of 38:62 alpha:beta anomeric mixture of PRA, alpha,beta ribose-5-phosphate and variable amounts of dimeric materials. NMR studies at various pHs allowed determination of the pH independent Kequi = 0.95 +/- 0.14 M-1 for this reaction. In addition, using magnetization transfer NMR methodology the rate of conversion of alpha to beta PRA was determined to be 44 sec-1 at 37 degrees C (pH 8.0). The rates of formation (from ribose-5-phosphate and NH3) and degradation of PRA were also measured using E. coli GAR synthetase (recently cloned, overproduced and purified to homogeneity) as a trap. Determination of these rates allowed an independent and accurate measurement of Kequi = 2.7 M-1. In addition, in close agreement with early studies of Nierlich and Magasanik, the half life of PRA at 37 degrees C and pH 7.5 was determined to be 35 sec. Characterization of the chemical stability of PRA and Kequi for ribose-5-phosphate, NH3 with PRA will now allow detailed kinetic analysis of the newly discovered trifunctional protein containing GAR synthetase activity in addition to AIR synthetase and GAR transformylase activities. Comparison of the properties of the 110 kd GAR synthetase and an independently isolated 54 kd GAR synthetase are reported. Experiments are underway to investigate the possibility that unstable intermediates such as PRA are not released into solution, but that the transfer is mediated by specific protein-protein interactions between GAR synthetase and PRPP amidotransferase.