GEN PUBLISHING INC., A MARY ANN LIEBERT INC. COMPANY • VOL. 1 NO. 2 • SUMMER 2005 INDUSTRIAL BIOTECHNOLOGY 119 Manfred Ringpfeil*, Matthias Gerhardt, Mark Zittwitz, Axel Blokesch, Vincent Pelenc, Wolfgang Speter, and Monika Wolf Biopract GmbH Rudower Chaussee 29 Entrance Kekuléstrasse 7 12489 Berlin, Germany Phone +49 30 6392-6205 Fax +49 30 6392-6206 Web www.biopract.de *Corresponding author: ringpfeil@biopract.de ne of the basic achievements of mankind in the 20th cen- tury is clean water supply and distribution 1 . Since the turn of the 19th to the 20th century, the systematic appli- cation of microbiological processes in waste water purifi- cation has enabled today's purity of rivers, lakes, and other surface waters. Now, on its way to the sea, water can safely be used repeat- edly, through purification. Yet, the common and widespread micro- bial process of cleaning sewage of municipal, agricultural, or indus- trial origin does not tap into the enormous energy potential of its organic ingredients (Figure 1A). Considerable amounts of organic substance, dissolved or suspended in water, are converted daily to gases (methane and carbon dioxide), solids (microbial biomass), and water itself. In the US, for example, this amount might come to seven million tons of organic substance, calculated as biological oxygen demand (BOD) 2 . Use of this energy remains second-priority, and there is no doubt that purity of water is the first aim of sewage purification; however, the latter needn’t be excluded at expense of the former. Furthermore, not all environmen- tal threat is eliminated by removal of organic ingredients from the sewage water: all nonsequestered carbonaceous substance within will contribute ultimately to the greenhouse effect, with the inevitable for- mation of carbon dioxide as the end product of both aerobic and anaerobic metabolism, and formation of methane, as the end product of anaerobic metabolism. Moreover, methane increases the green- house effect by a factor of about 20, per molecule, compared to car- bon dioxide 3 . Thus, channeling produced methane to controlled oxi- dation not only frees more available green energy but also lessens greenhouse effect. Decentralized energy-provision practices, such as those being adopted in Germany, will therefore facilitate the use of such energy and contribute to a decreased greenhouse effect 4 . Methane from biological processes is identical with methane from natural gas. In waste water treatment, the use of anaerobic microbial digestion offers several advantages: yield of high-caloric-value prod- uct (methane) from a very large variety of starting molecules, con- servation of virtually the entire energy potential of the starting mol- ecules, and, importantly, voluntary separation of the product from the liquid reaction phase. A further contribution to energy recovery in sewage purification comes from the biomass that inherently results during aerobic and anaerobic metabolism of the sewage con- stituents, further conserving energy content. Thus, current sewage purification technology (Figure 1B) is domi- nated by two basic reactions: Anaerobic (Process 1) COM —> CH 4 + CO 2 + MBM + (COM) R Aerobic (Process 2) COM + O 2 —> H 2 O + CO 2 + MBM + (COM) R COM - Contaminating organic matter MBM - Microbial biomass (COM) R - Residual COM Both processes convert the contaminating organic matter (dis- solved or suspended organic substance) into gaseous and solid sub- stances, allowing their separation from the liquid (water) phase. Recovering energy from organic residues during sewage purification METHODS O