Enviroquip Inc.

Hallsten Corporation

Elena Bailey

Robert H Shurtleff

Jeffrey A Hallsten

A clarifier in a sewage treatment process includes efficient scum removal within the influent well, with discharge of the scum and other floatables as a dedicated waste stream separate from return activated sludge and biological scum collected in the clarifier. In one embodiment the scum removal system has an inclined scum ramp at the leading edge of each of two scum removal troughs, with a forward edge below the liquid surface. The scum troughs pass through an arc of rotation, building up scum, which accumulates and is pushed forward by the scum ramp. At least once per revolution, the moving scum ramp approaches a stationary scum surface blade that extends partially under the liquid surface and provides a barrier to the forwardly pushed scum. This blade contacts and slides up the ramp, sweeping the scum up the ramp and into the scum trough. The described arrangement greatly reduces the amount of free water with the collected effluent scum as compared to the typical designs and permits scum and gross floatables from the influent well to be trapped and contained and discharged and treated separately.

Clarifier with influent well scum removal

A clarifier in a sewage treatment process includes efficient scum removal within the influent well, with discharge of the scum and other floatables as a dedicated waste stream separate from return activated sludge and biological scum collected in the clarifier. Foam contained within the influent well may be treated with bacteria-killing agents or with anti-foaming agents. In one embodiment the scum removal system has an inclined scum ramp at the leading edge of each of two scum removal troughs, with a forward edge below the liquid surface. The scum troughs pass through an arc of rotation, building up scum, which accumulates and is pushed forward by the scum ramp. At least once per revolution, the moving scum ramp approaches a stationary scum surface blade that extends partially under the liquid surface and provides a barrier to the forwardly pushed scum. This blade contacts and slides up the ramp, sweeping the is scum up the ramp and into the scum trough. The described arrangement greatly reduces the amount of free water with the collected effluent scum as compared to the typical designs and permits scum and gross floatables from the influent well to be trapped and contained and discharged and treated separately.

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.

Pre-thickened aerobic digester system

Improved gas distribution and mixing is achieved in a gas/liquid mixing basin particularly for aerobic or anaerobic sewage digesters. In addition to a draft tube positioned generally centrally in the aeration or anaerobic basin and served by one or more gas-releasing diffusers, the system of the invention includes peripheral draft tubes surrounding the central draft tube, each tube having at least one gas diffuser within. The circulation of liquid and gas bubbles from the larger, central draft tube is supplemented by circulation from the peripheral draft tubes. In particular, 'dead areas' or less active areas of the liquid, which are not sufficiently reached by gas-mixing from a single draft tube in many basin configurations, are reached by circulation from the peripheral draft tubes and such dead areas are virtually eliminated. As a result, power requirements can be reduced when compared to double throw or single drop systems, thus increasing overall system efficiency while achieving the desired level of liquid aeration or gas dispersion. In addition, the inclusion of the peripheral draft tubes allows versatility in achieving the desired degree of mixing in a wide range of different basin configurations.

Multi-eductor system

A substantially gas tight tank cover is designed such that the structural beams of the cover serve also as an air distribution system for bubbling air through a liquid in the tank. Vertically oriented gas bubbler and orifice devices include hardware enabling easy access to the orifice and bubbler from the top of the tank cover. The design is such that all necessary maintenance including major repairs can be performed from the cover without draining the basin or removing the cover. The system is particularly adaptable to sewage treatment plants, but is advantageous for other applications as well, wherein gases are to be bubbled through liquids at multiple locations.

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Austin, TX, United States of America

Elena Bailey