31    EFFICACY OF BIOAUGMENTATION PRODUCTS AS
PREDICTED BY A MODEL OF STEADY-STATE
FLOCCULENT CULTURES
Susan J. Hull, Graduate Student
Richard B. Kapuscinski, Assistant Professor
Department of Civil Engineering
University of Michigan
Ann Arbor, MI 48109
INTRODUCTION
Bioaugmentation refers to attempts to increase the rate or extent of biological transformations by
an intentional introduction of whole cells and/or enzymes into contaminated water or soil or into
systems for wastewater treatment. The focus of this paper is bioaugmentation for enhancing the
transformation of specific, potentially hazardous organic compounds (PHOCs) in industrial and
municipal wastewater treatment. Commercial bioaugmentation products which have claims for rapid
transformation of specific, priority organic compounds are available for use in industrial and municipal wastewater treatment. Unfortunately, reports of properly controlled experimental investigations
on the efficacy of these products in suspended-growth, reactor-systems are practically non-existent.1-5
Given the substantial interest in the effectiveness of bioaugmentation products that has been
expressed within the waste treatment community and the dearth of pertinent experimental data, it
seemed appropriate and timely to analyze bioaugmentation through mathematical modeling and
numerical simulation.
Manufacturer's recommendations typically prescribe higher initial doses of product, to hasten the
development of an active microflora, and lower subsequent doses to maintain the active populations.
We have developed a rational mathematical model to analyze the efficacy of these maintenance doses
in steady-state, continuous-flow, suspended-growth reactor-systems with recycle of flocculent bio-
mass.
MAINTENANCE DOSES
Commercial bioaugmentation products are available as freeze-dried or air-dried solids, which
require wetting for activation, or as stabilized microbial suspensions in liquid form.1'6 Most commercial products consist of mixtures of microbial populations. As many as twenty microbial species,
representing autotrophs, as well as heterotrophs, and facultative anaerobes, as well as aerobes, can be
found in some products that are intended to serve a broad range of purposes.6 Levels of viable
heterotrophic cells, as assessed by plate counting techniques, can vary widely among the available
products. Representative data on the abundance of aerobic heterotrophs in bioaugmentating preparations are reported in Table I. Influent concentrations of viable, capable biomass were calculated from
the observed levels of heterotrophic, colony-forming units in bioaugmentation products and are also
presented in Table I for a product dose of 10 mg/L (which corresponds to approximately 10 uL/L for
liquid products). These calculated influent concentrations indicate: 1) that aerobic plate counts varied
over six orders of magnitude among the seventeen products that were tested; 2) dry products tended to
exhibit higher levels of colony-forming units than liquid products; and 3) most importantly for our
analysis, the maximum influent concentration of viable heterotrophic biomass that is likely to be
provided by typically recommended doses of representative products is approximately 5 /ig/L (0.005
mg/L). This maximum value of 0.005 mg-cells/L is low relative to the dose of 10 mg-product/L,
because viable biomass constitutes but a small mass fraction of bioaugmentation products. For liquid
products, the majority of the mass is occupied by liquid. For dry products, the majority of the
product mass is a carrier material rather than microbial biomass. In our simulations, the influent
concentration of viable, augmenting biomass is designated as Xdai. Values for Xdai ranging from zero
to 5 mg-cells/L were employed; hence, the simulations considered doses of bioaugmentation products
297