Microbial culture system

Abstract

The specification discloses making a mixed fungal (yeast and yeast-like) system culture adapted to biodegradation of spent sulfite liquor (SSL) comprising the steps of exposing a mixed culture system (being a sludge from a sewage treatment plant) to increasing concentration of SSL until the fungus becomes acclimatized to SSL of the desired concentration. The resulting biotic population comprises a fungal mixture, of yeast and yeast-like cultures. It was based on an autolytic culture system: Phialophora jeanselmei, Phialophora richardsiae, Hyalodendron lignicola, Trichosporon infestans and Candida tropicalis. A method and apparatus are disclosed for biodegrading both the soluble substrates in a spent sulfite liquor and the biological solids produced therefrom by a potentially autolytic culture system. The method comprises the steps of adding a nutrient medium, adjusting the pH to mildly acid or neutral condition, feeding the mixture to a fungal culture inoculated fermentor with agitation and with aeration, resulting in foaming of the mixture, said foam carrying with it the fungi and sludge resulting from the fermentation, the suspended solids content of the foam when collapsed being generally not more than half the suspended solids content of the fermentor broth, said foam being processed so as to separate the components into a sludge and a clarified effluent, said sludge being recycled to the fermentor vessel and the clarified effluent prepared for discharge or additional processing. The recycling of sludge to the fermentor vessel is controlled where necessary to maintain the suspended solids in the fermentor vessel at not greater than 60,000 parts per million. The degree of recycling and retention time are held at a level at which autolysis of the suspended solids may be maintained. The process differs from other extended aeration processes in the high MLSS level in the reactor (.about.30,000-55,000 ppm); low sludge return rate (.about.43% of fresh feed rate); high BOD loading (1400 lb BOD/1000 cu. ft.); long mean cell residence time (up to 95 days). The system may be maintained at full sludge recycle thus obviating the need for an external sludge handling and disposal system. Under optimum operating conditions as much as 85 to 90% BOD removal from spent sulfite liquor is accomplished.