Anaerobic processes slurry reactors

Because of advanced computer control (auxostat mode) and an anaerobic culture, sterilization of the feed, aseptic techniques, and sparging of the broth are not required. Using standard equipment mills, waste paper would be shredded directly into the reactor. This avoids expensive pre-suspending of the paper in a separate tank, prevents microbial contamination of the feed stock, and circumvents difficult pumping of paper slurries. Once the acetic acid has been extracted, some of the broth could be recycled back to the reactor. If the product were mixed calcium/magnesium salts, the solution could be concentrated to form crystals and sold. While the process control is sophisticated, the overall system represents a low cost approach for the production of acetic acid mixed with small amounts of other acids. The obvious application is acetate salts for deicing of highways. 

Cell recycle fermentors consist of two main units a vessel where the biomass is allowed to grow, and a membrane separation unit (as in Figure 7.40). Vessels are usually designed to insure a uniform concentration of nutrients and pH throughout the whole volume. Due to complete mixing, process control and stability of the microbial slurry are not difficult to achieve.88 After anaerobic stabilization, when the biomass is well developed, the reactor biomass is pumped to the UF unit where solid-liquid separation occurs. The sludge is flushed back to the reactor. In most cases, the flow rate of nutrient feed is kept equal to the permeate flow rate thus keeping a constant liquid level in the anaerobic reactor. 

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