Field of the Invention
The invention relates to a system for treatment of biological materials and wastewater and, more particularly, a system for the separation of microbial biomass from an aqueous liquid from which it was produced.
Description of Related Art
The biological treatment of aqueous liquids containing organic materials and nutrients has been employed in many different configurations for well over 100 years. Applications include food production, agriculture, wastewater treatment, pharmaceuticals preparation, and the like. Most of these applications involve the growth of microorganisms, principally bacteria, which bioconvert the organic materials and nutrients in the aqueous liquids into carbon dioxide, water, various other products, and microbial cell biomass. The microorganisms usually are grown in suspended growth systems or in fixed film systems. Virtually all of these processes produce a biological mass, and this biological mass is often associated with other materials such as particulate solids or other non soluble materials that are present in the aqueous liquids. Often, it is desirable to separate the biological masses, and associated particulate and non-soluble materials, from the aqueous liquids being treated. This may occur after or during the treatment process itself.
There are many different processes for performing such separations. Commonly used procedures include gravity settling or floatation, or a wide variety of mechanical procedures involving filtration, centrifugation, screening, and the like. Such processes and procedures produce a mixture of biological masses and associated particulate and non-soluble materials, which are often termed “sludge”, which must be periodically removed from the treatment or production process and utilized or disposed of in some manner. Methods of disposal of sludge that are commonly used include land application, containment in landfills, incineration with disposal or reuse of ash, or similar methods.
Prior to disposal, it is often common for biological sludge to be stabilized by one or more stabilization processes. These processes are designed to reduce the volatile content of the sludge, reduce the volume of the sludge, destroy pathogens, reduce or minimize the likelihood that bacteria can grow in the processed sludge, and to reduce or eliminate odors.
Two processes commonly used for biosolid sludge stabilization include aerobic digestion or anaerobic digestion. These two processes use microorganisms, mostly bacteria, to bioconvert organic materials in the biosolids into carbon dioxide and water, and in the case of anaerobic digestion, methane. After all or most of the biosolids material has been reacted, both processes produce a microbial biomass which is either not susceptible to further reaction, or which only reacts relatively slowly compared with the design performance of the basic stabilization processes.
This stabilized sludge or microbial biomass contains bacteria and other microorganisms which contain significant amounts of carbon and nutrients such as nitrogen, phosphorus, and the like. The carbonaceous materials and nutrients that are constituents of these organisms are generally impervious to further action by either the wastewater treatment or other process from which they were obtained, or to the anaerobic or aerobic digestion processes which may have been used to stabilized them. Hence they must be removed from the treated liquid stream and be disposed of in a suitable manner.