COST MODELING OF COMETABOLIC SBRs FOR THE TREATMENT OF CHLORINATED VOCs
|S.G. Meganatha and B.I. Dvorak, Civil Engineering, University of Nebraska-Lincoln; Lincoln, NE 68588||
Chlorinated volatile organic contaminants are common ground water pollutants for which inexpensive treatment methods, such as biological oxidation are needed. Economical strategies for applying biological oxidation (reactor types and methods for increasing growth and degradation rates) to achieve cometabolism have not yet been identified. The goal of this research is to evaluate the cost of treating aqueous CVOCs by cometabolic biological oxidation in sequencing biological reactor (SBR).
Process performance and cost models were used to identify the least-cost design for cometabolic sequencing biological reactor for a given set of conditions; the treatment was modeled for waters with a range of flow rates, influent and effluent concentrations, and different CVOCs, and different substrates(phenol, and methane). Process performance for the cometabolic SBR was modeled using a biokinetic model. The cost of the cometabolic SBR was modeled by considering both capital and operating costs using system component quotes from equipment vendors and chemical suppliers.
The capital costs were amortized over the system's design life to estimate an annual capital cost. The amortized capital cost was added to the annual operation and maintenance cost to estimate the total annual cost. The cost required to treat a unit volume of water was determined by dividing the total annual cost by the volume of water treated in a year. The reaction time, substrate requirement, and oxygen requirement for each cycle from the SBR process model were the primary input, along with the cost information input parameters to the SBR cost model. The cost model provided the number of reactors, volume of each reactor, the capital cost, operation and maintenance cost, and total system cost for treating a unit volume of water.
From this modeling, strategies that result in the least-cost cometabolic SBR designs have been identified. A range of primary substrate concentrations were examined for each of the three TCE influent concentrations. In each case, there was minimum primary substrate addition rate (and biomass concentration) below which a steady-state condition could not exist. It was found that the use of methane as a primary substrate level that resulted in a less costly system than phenol. Further research is focusing on identifying the biodegradation rates required to reduce the cost of the cometabolic system.
Key words: cost modeling, chlorinated VOCs, cometabolism, SBR.
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