Downloaded By: [Mississippi State University] At: 17:28 17 August 2007 Journal of Environmental Science and Health Part B (2007) 42, 393–401 Copyright C  Taylor & Francis Group, LLC ISSN: 0360-1234 (Print); 1532-4109 (Online) DOI: 10.1080/03601230701312779 Biohydrogen production through fermentation using liquid swine manure as substrate JUN ZHU 1 , XIAO WU 1 , CURTIS MILLER 1 , FEI YU 2 , PAUL CHEN 2 and ROGER RUAN 2 1 Southern Research and Outreach Center, University of Minnesota, Waseca, MN, USA 2 Bioproducts and Biosystems Engineering Department, University of Minnesota, St. Paul, MN, USA In this paper, continuous production of hydrogen through fermentation with liquid swine manure as substrate was researched using a semi-continuously fed fermenter (8 L in total volume and 4 L in working volume). The pH and temperature for the fermenter were controlled at 5.3 ± 0.1 and 35 ± 1 ◦ C, respectively, throughout the experiment. Three hydraulic retention times (16, 20, and 24 h) were investigated for their impact on the efficiency and performance of the fermenter in terms of hydrogen yields. The results indicate that hydraulic retention time (HRT) has a strong influence on the fermenter performance. An increasing HRT would increase the variation in hydrogen concentration in the offgas. To produce hydrogen with a fairly consistent concentration, the HRT of the fermenter should not exceed 16 h, which, however, did not appear to be short enough to control methanogenesis because the offgas still contained about 5% methane. When methane content in the offgas exceeded 2%, an inverse linear relationship between hydrogen and methane was observed with a correlation coefficient of 0.9699. To increase hydrogen content in the offgas, methane production has to be limited to below 2%. Also, keeping oxygen content in the fermenter below 1.5% would increase the hydrogen concentration to over 15%. The product to substrate ratio was found to be around 50% for the fermenter system studied, evidenced by the observation that for every 6 liters of manure fermented, 3 liters of pure hydrogen were produced, which was significant and encouraging. Keywords: Hydrogen production; fermentation; swine manure; bioenergy. Introduction Methane has been commonly considered for many years an energy product through anaerobic digestion and the asso- ciated technology for its production has been studied ex- tensively and well developed around the world. However, from the perspective of reducing global warming, relying on methane as an alternative energy source to fossil fuel will not accomplish the goal because methane and its combus- tion product, carbon dioxide, are both greenhouse gases. This situation has prompted a research interest in explor- ing cleaner energy sources, among which hydrogen is be- coming a promising candidate. [1] As compared to methane, hydrogen offers tremendous potential as a clean, renewable energy currency because it has the highest energy density of any known fuel and is compatible with electrochemical and combustion processes for energy conversion without producing carbon-based emissions. Many years of scientific and engineering advances have resulted in two major processes to produce hydrogen, i.e., Address correspondence to Jun Zhu, Southern Research and Outreach Center, University of Minnesota, Waseca, MN, USA; E-mail: zhuxx034@umn.edu Received December 11, 2006. electrolysis of water and thermo-catalytic reformation of hydrogen-rich organic compounds. Approximately 95% of the commercially produced hydrogen comes from carbon- containing raw materials, primarily fossil in origin. [2] The nature of these processes has, however, ultimately defined that they cannot fulfill the dual goals of waste reduction and hydrogen production. Furthermore, these methods re- quire electricity derived from fossil fuel combustion, thus by no means lessening our reliance on the consumption of petroleum-based energy sources. Given these perspectives, researchers around the world have turned to biological pro- cesses (e.g., fermentation), which is becoming an exciting new area of technology development. In contrast to elec- trical and thermo-chemical methods, biological processes are carried out largely at ambient temperatures and pres- sures, and hence are less energy-intensive. Numerous lab- scale studies using batch fermenters in the last few years have revealed that biologically producing usable hydrogen from a variety of renewable resources through fermentation is technically feasible and the possibility of promoting this technology for large-scale production isn’t beyond reach. [3] Reviewing literature indicates that there is plenty of research that has been done recently in biohydrogen pro- duction from various substrate materials, such as syn- thetic media, [4] food processing wastes, [5−7] and industrial