biomoc(1) U.S. Geological Survey (wrdapp) biomoc(1) NAME biomoc - A multispecies solute-transport model with biodegradation ABSTRACT BIOMOC is a two-dimensional model that can simulate the transport and biotransformation of multiple reacting solutes. The program is general and flexible, allowing for any combination of biodegradation processes. A number of expressions for biological transformation rates have been included as options in the code. These include single, multiple, and minimum Monod kinetics and competitive, noncompetitive, and Haldane inhibition. The kinetic parameters can be formulated to simulate zero-order or first-order approximations of biodegradation rates. The growth and decay of several microbial populations performing the transformations is also accounted for. The microbial growth can be disabled, limited by biomass inhibition, or limited by the availability of a specified nutrient. METHOD BIOMOC is an extension of the U.S. Geological Survey's Method of Characteristics (MOC) flow and transport model (Konikow and Bredehoeft, 1978; Goode and Konikow, 1989). The two-dimensional transport equation is solved for each solute species and a biodegradation reaction term is included. The flow and transport equations are discretized using a rectangular, uniformly spaced, block-centered, finite-difference grid. Implicit finite-difference equations are used to solve the flow equation. The average linear flow velocities are then calculated and used to solve the transport equation using the method of characteristics and particle tracking. Macroscopic fluid substrate, electron acceptor, and cellular nutrient concentrations are used to calculate uptake and growth. Monod kinetics is used to represent biodegradation uptake that depends on a single solute concentration. For biodegradation processes that involve several solutes, two alternate modified Monod formulations are included in BIOMOC. The multiple Monod formulation assumes that the biodegradation reaction is limited by the concentration of each solute involved in the reaction. The alternative minimum Monod formulation assumes that a single solute is limiting the process. In addition, the Monod parameters can be specified to approximate zero-order or first-order biodegradation rates. All degradation kinetics formulations include competitive, noncompetitive, and Haldane inhibition. Competitive inhibition is used to represent the inhibition of uptake of a secondary substrate when the primary substrate is still present. The noncompetitive inhibition formulation is useful for modeling the transition between redox zones within contaminant plumes; an example of noncompetitive inhibition is the inhibition of an anaerobic biodegradation process by the presence of oxygen. Haldane inhibition is used to model toxicity. The biomass growth rate is proportional to the degradation rate. However, growth may be either turned off or limited by a biomass inhibition formulation. 25 March 1999 1 biomoc(1) U.S. Geological Survey (wrdapp) biomoc(1) BIOMOC does not include pore-scale processes and does not account for the effect of diffusion into and out of the biophase. It has also been assumed in BIOMOC that the biomass remains attached to the sediments. Pore clogging by biomass growth is not accounted for. HISTORY Version 1.0 1999/03/10 - Initial release DATA REQUIREMENTS Input data consist of initial conditions, boundary conditions, aquifer properties, and biodegradation parameters. See documentation for details. OUTPUT OPTIONS See documentation. SYSTEM REQUIREMENTS BIOMOC is written in Fortran 77 with the following extensions: use of variable names longer than 6 characters and use of include files. The code has been used on UNIX-based computers and on DOS-based 386 or greater computers having a math coprocessor. DOCUMENTATION Essaid, H.I., and Bekins, B.A., 1997, BIOMOC, A multispecies solute- transport model with biodegradation: U.S. Geological Survey Water-Resources Investigations Report 97-4022, 68 p. REFERENCES Goode, D.J., and Konikow, L.F., 1989, Modification of a method-of- characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange: U.S. Geological Survey Water-Resources Investigations Report 89-4030, 65 p. Konikow, L.F., and Bredehoeft, J.D., 1978, Computer model of two- dimensional solute transport and dispersion in ground water: U.S. Geological Survey Techniques of Water-Resources Investigations, book 7, chap. C2, 90 p. CONTACTS Operation and Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: 25 March 1999 2 biomoc(1) U.S. Geological Survey (wrdapp) biomoc(1) water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the BIOMOC software can be retrieved are, respectively: http://water.usgs.gov/software/biomoc.html --and-- /pub/software/ground_water/biomoc If you would like to obtain the price of and (or) order paper copies of USGS reports, contact the USGS Branch of Information Services at: USGS Information Services Box 25286 Denver Federal Center Denver CO 80225 To inquire about Open-File Reports or Water-Resources Investigations Reports: Tel: 303-202-4200; Fax 303-202-4695 To inquire about other USGS reports: Tel: 303-202-4700; Fax 303-202-4693 SEE ALSO moc(1) - Two-dimensional method-of-characteristics ground-water flow and transport model moc3d(1) - Three-dimensional method-of-characteristics ground-water flow and transport model 25 March 1999 3