Abstract: An egg-shaped anaerobic sludge digester has upper and lower draft tubes, and an optional middle draft tube. The draft tubes are arranged so that liquid can be (1) simultaneously pumped downwards through the upper (or middle) draft tube and upwards through the lower (or middle) draft tube; (2) simultaneously pumped upwards through two or more draft tubes; or (3) simultaneously pumped downwards through two or more draft tubes. When a middle draft tube is provided, it can be used in place of the upper draft tube when the liquid surface in the digester falls below the top of the upper draft tube. Alternatively, the middle draft tube can work as a coordinated relay conduit to move liquid either in the same direction as the upper draft tube or to move liquid in the same direction as the lower draft tube.

Abstract: An anaerobic sludge digester has a top, a bottom, sloped sides leading to the bottom, and a draft tube with an upper end spaced downward of the top of the digester and a lower end spaced upward of the bottom of the digester. The draft tube may have a propeller, impeller, or jets that enable liquid to be transported through the draft tube from one part of the digester to another. The digester has a discharge mouth positioned within the digester to receive heavy material that is pumped from the bottom of the digester and which flows outward across the liquid surface. One or more spray nozzles are located above the liquid surface to break up foam and emulsions. The mouth may also be used to effectively remove scum and light solids from the liquid surface. A shutoff valve on a discharge pipe extending from the discharge mouth can be closed while sludge is added to the system, causing the liquid level to rise above the mouth.

Abstract: A safety apparatus for use on a hoisting crane used to hoist cargo from cargo transport trucks that detects hoisting such trucks and renders the hoisting mechanism inoperative. The safety apparatus includes sensors responsive to an unsafe condition in such trucks to generate a safety signal. A transmitter responsive to the safety signal transmits an operational signal to the hoisting crane that upon receiving and recognizing the operational signal renders the hoisting mechanism inoperative and alerts the crane operator of the unsafe condition.

Abstract: A transmitter attached to the overhang of a hoisting crane that is movable over rails. The transmitter is operative to transmit signals to receivers also mounted on the hoisting crane. During movement of the crane, the signals may be blocked by objects that may come between the transmitter and receivers indicating a pending collision. The receivers upon detecting a blockage are operative to alert the operator of the unsafe condition and deactivate the gantry motors moving the crane.

Abstract: Sensors mounted on respective cargo transport trucks transferring cargo to a hoisting crane and responsive to an unsafe condition in such trucks to generate an electrical safety signal to be transmitted to such crane for rendering the hoisting mechanism inoperative.