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h Technical Description L Activated sludge is generated by aerating a biologically degradable waste until a large mass of settleable solids forms. These settleable solids are active masses of living organisms, redesignated as activated sludge.Activated sludge is not formed by special floc-forming bacteria,but rather is a natural phenomenon of all bacteria at a definite'energy level. The aeration, mixing, and oxidation offresh wastes with sludge that is recycled in the treatment process takes place in the aeration chamber. Microorganisms aerobically stabilize incoming organic matter which is stored as activated sludge in the aeration chamber until enough volume is available for transfer to a clarifier tank as a batch. This storing process takes the conventional activated sludge process one step farther. The activated."sludge, while in the aeration tank, enters into an advanced aerobic stabilization mode which is comparable to the aerobic digestion process. This mode,called reaction,gives rise to the process term"batch reactor."The advantage ofthe reactor process is found in the enhanced reduction of volatile suspended solids without affecting the development of those organism types required for the basic process. Reactor sludges, unlike typical flowthrough-type processes, produce no odor and, combined with the multiple batch-return cycles, produce very little sludge in the secondary discharge. As a result, sludge-wasting is dramatically minirnized. 64 Sedimentation, or clarification, follows the aeration process. This stage allows the activated sludge ',- to flocculate and settle out, producing a-'clear effluent of low organic content. After transfer of the clarified supernatant,the settled sludge is returned to the aeration tank as seed for incoming waste and to provide the carbon source for the denitrification process. MICROORGANISMS Activated sludge is made up of essentially four kinds of organisms(bugs)which do most of the eating in an activated-sludge process. The bugs are bacteria which eat dissolved organic compounds; the ciliates(protozoa),both free-swimming and stalked,which eat the bacteria and thus are heavy enough to settle by gravity;and the suctoria,which feed on the ciliates and assist with the settling process.This chain of bug-eating-bug is known as contact stabilization. There are other lessor, more natural strains and groups of microorganisms in the process, but these four are the primary workers. The exception would be treatment plants artificially seeded with known strains of organisms, a process known as bioaugmentation (seeding). (NOTE: AquaClear does not recommend bioaugmentation of its Bio- Pure plants, as stabilization time is normally less than ten days after startup.) The bacteria are the most important group of microorganisms,as they are responsible for stabilization of the organic matter and early floc formation.Although all types ofbacteria make up activated sludge, the nature of organic compounds in the wastes being stabilized will determine which bacterial genera predominate. Protozoa do not contribute directly to stabilization of organic matter in the wastes being treated, because organic concentration is too low to support animal growth;however,the protozoa feed from the bacteria which utilize the organic matter and thus assist greatly in the settling stage in the clarifier. 2