초록 ▼

An aerobic treatment process is operated to reduce overall oxygen requirements, to maintain general pH balance and to produce a low-coliform solids effluent. From the system's clarifier a slurry of concentrated solids is moved to a premix basin, where the slurry is vigorously aerated for a sufficien

An aerobic treatment process is operated to reduce overall oxygen requirements, to maintain general pH balance and to produce a low-coliform solids effluent. From the system's clarifier a slurry of concentrated solids is moved to a premix basin, where the slurry is vigorously aerated for a sufficient time to raise microbial activity and dissolved oxygen content. The aerated, microbially active sludge is then moved to a gravity thickener basin, in which solids are allowed to settle to the bottom without aeration, to establish a quiescent state in the settled sludge and also an anoxic stage. This causes the sludge to be denitrified by microbial action, raising and stabilizing the pH of the sludge. Separated supernatant liquid is decanted and removed from the gravity thickener. The sludge is moved into an aerobic digester, where the sludge is aerated and nitrification occurs but using less aeration than normally required in a digester, due to the effect of anoxic/aerobic phases. A portion of the slurry in the aerobic digester basin is recycled back to the premix basin. Another important aspect is the use of two digesters, only one in loop with the premix and thickener at any one time, with each digester being taken out of the loop and isolated when a solids content of about 25,000 to 35,000 mg/L (21/2% to 3.5%) is achieved in that digester. The isolation results in a significantly lowered coliform content in the effluent sludge.

대표청구항 ▼

[ I claim:] [1.] In a sewage treatment process which includes a main activated sludge process and/or at least one clarifier basin and an aerobic digester basin, and in which sludge from the main activated sludge process or clarifier is prethickened in a thickener prior to delivery into the digester,

[ I claim:] [1.] In a sewage treatment process which includes a main activated sludge process and/or at least one clarifier basin and an aerobic digester basin, and in which sludge from the main activated sludge process or clarifier is prethickened in a thickener prior to delivery into the digester, a method for operating the process so as to reduce overall aeration requirements, substantially eliminate addition of alkaline agents, and reduce tankage requirements, comprising:transferring waste sludge from the main activated sludge process or clarifier basin first to a premix basin,mixing the sludge in the premix basin,moving the mixed sludge to a gravity thickener basin,in the gravity thickener basin, allowing solids to settle to the bottom of the basin as a sludge, without aeration of the sludge in the thickener basin, thus establishing a quiescent state and an anoxic stage within the settled sludge, and maintaining the anoxic stage long enough to cause the sludge to be denitrified by microbial action, releasing nitrogen and raising and stabilizing the pH of the sludge,decanting supernatant liquid resulting from separation in the gravity thickener, out of the gravity thickener basin,moving the thickened sludge from the bottom of the thickener basin into the aerobic digester,aerating the sludge in the aerobic digester basin,cycling back a portion of the sludge in the aerobic digester basin to the premix basin to mix with waste sludge from the main activated sludge process or clarifier basin,maintaining the anoxic stage at such volume, as compared to the digester, and at such detention time and recycle rate as to maintain pH in the thickener and digester essentially within a range of 6.8 to 8.0, andrepeating the above steps, thus continuing to recycle sludge in a premix/thickener/digester loop, until a preselected solids content level is achieved in the digester basin.