Anaerobic system design

In considering the application of process kinetics to anaerobic system design, this paper describes (1) the kinetic model employed, (2) the microbiological and biochemical evidence used as the basis for selecting the process rate-limiting step, (3) available kinetic information for that step, and (4) an illustrative example of kinetic based process design. 

The system design is based on two upflow anaerobic bioreactors (ABRs) followed by three horizontal sub-surface flow (HSSF) wetlands cells. The water flows by gravity through the cells. Once treated, the water is stored in a holding pond and subsequently used for irrigation of a tree farm. 

Since the system design is driven by the requirement for anaerobiosis, the electrodes must fit inside a spectrophotometric cuvette whose contents have previously been made anaerobic by the procedure described in the following section. The electrodes must also be custom made to fit inside without leaking oxygen, either around the joints or through the tips. They must also be stored anaerobically between experiments (see following section). 

Careful design and control often can solve these problems, but vendors are reluctant to recommend anaerobic mobile systems. Anaerobic systems are much more susceptible to variation in waste stream characteristics and environmental parameters. Fixed anaerobic systems are widely used in industry for treatment of uniform, concentrated biodegradable waste in aqueous waste streams due to the low-cost, low-residual generation and production of usable methane gas. However, application to variable CERCLA waste streams is relatively infrequent. Anaerobic systems have the best potential as a pretreatment step for an aerobic system that would otherwise be unable to process a high-strength waste such as a leachate. 

In Situ Bioremediation. In situ bioremediation can be an aerobic or anaerobic process, or a combination of the two. In designing an in situ bioremediation system, one should consider the types of microorganisms available (naturally in place or added), the stmctural and chemical makeup of the soil matrix, types of contaminants, oxygen and nutrient addition and distribution, and temperature. These factors are discussed prior to introducing the individual techniques for in situ bioremediation. 

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