Engineering concerns and new developments in anaerobic waste-water treatment M. Gavrilescu Abstract A non-comprehensive review of several devel- opments in the field of anaerobic biological waste-water treatment engineering is carried out, considering the active role engineers have to play in this field. The analysis is done as a result of the fact that the general performance of anaerobic systems and the diversity of wastes that these can treat are increasing as a result of new reactor design, operating conditions, and use of specialized microorgan- isms. This paper illustrates a few examples of conventional and new applications of anaerobic treatment and several advantages, such as no energy-intensive oxygen transfer, less excess sludge, production of combustible biogas, and space saving. Such an overview of biological waste-water treatment also precedes comments on some important aspects on process microbiology as well as considerations of the application of fundamentals and kinetics to the analysis of the biological processes used most commonly for anaerobic biological waste-water treatment. Models developed for this reaction type are discussed, considering four overall steps. Also, models for a contin- uous-stirred tank bioreactor, a fluidized bed reactor, and a packed bed reactor as basic configurations are described. Major anaerobic biological treatment processes used for waste-water treatment, both suspended-growth pro- cesses and reactors (anaerobic stirred tank, anaerobic contact process, upflow anaerobic sludge-blanket process) and attached-growth processes and reactors (anaerobic filter process, expanded-bed process), are considered. It was also shown that the breakthroughs dealing with reactor design and operating conditions offer practical solutions to many of the drawbacks that were initially thought to limit the purpose of anaerobic processes. Finally, the paper includes some aspects regarding the control of anaerobic biological systems. List of symbols BC bicarbonate concentration [M L –3 ] [CO 2 ] d concentration of dissolved CO 2 [M L –3 ] CO 2 ½   d equilibrium value of dissolved CO 2 concentra- tion [M L –3 ] CTR CO 2 mass transfer rate [M L –3 T –1 ] C TOX toxin concentration [M L –3 ] c cation concentration [M L –3 ] D dilution rate [T –1 ] F influent flow rate [L 3 T –1 ] F R circulation flow rate [L 3 T –1 ] G biogass flow rate [L 3 T –1 ] [H + ] protons concentration [M L –3 ] H S non-ionized substrate [M L –3 ] [H 2 ] dissolved hydrogen concentration [M L –3 ] K 1 bicarbonate dissociation constant [–] K a acid dissociation constant [M L –3 ] K I substrate inhibition constant [M L –3 ] K H Henry constant for CO 2 [M 2 L –4 T –2 ] K H2 K S value for H 2 [M L –3 ] K NO2 K S value for nitrite [M L –3 ] K NO3 K S value for nitrate [M L –3 ] K L a mass transfer coefficient [T –1 ] K S Monod constant [M L –3 ] K t toxic death constant [T –1 ] [NH 4 + ] ammonium ion concentration [M L –3 ] [NO 3 – ] nitrate concentration [M L –3 ] [NO 2 – ] nitrite concentration [M L –3 ] P CO2 carbon dioxide production rate from biomass [M L –3 T –1 ] P CO2 ð Þ B carbon dioxide production rate from bicarbonate [M L –3 T –1 ] P CH4 methane production rate [M L –3 T –1 ] p CO2 CO 2 partial pressure [M L –1 T –2 ] Q volumetric flow rate [L 3 T –1 ] r(S) specific substrate consumption rate [M L –3 T –1 ] r max maximum specific substrate consumption rate [M L –3 T –1 ] S substrate concentration [M L –3 ] S in input substrate concentration [M L –3 ] S 1 , S 2 stoichiometric parameters [M M –1 ] T time [T] V, V R reactor volume [L 3 ] V A volume of absorption tank [L 3 ] V FB volume of fluidized bed reactor [L 3 ] V m mole volume of ideal gases [L 3 M –1 ] v max maximum reaction rate [M L –3 T –1 ] X biomass concentration [M L –3 ] Received: 1 February 2001 / Accepted: 13 September 2001 Published online: 24 January 2002 Ó Springer-Verlag 2002 M. Gavrilescu Technical University ‘‘Gh. Asachi’’ Iasi, Faculty of Industrial Chemistry, Department of Environmental Engineering, Mangeron Street 71, 6600 – Iasi, Romania E-mail: mgav@ch.tuiasi.ro Fax: 4032271311 Original paper Clean Techn Environ Policy 3 (2002) 346–362 DOI 10.1007/s10098-001-0123-x 346