Pumping Your Septic Tank
Pumps are typically either vacuum or centrifugal. Vacuum pumps, the most common system used by septage haulers, have the following advantages: Iiquid does not flow through the pump, which reduces wear; the pump is less likely to freeze; and the tank contents can be discharged under pressure. Vacuum pumps should be equipped with a water trap to prevent dispersion of aerosols. Because liq-uid moves through the pump, centrifugal pumps are more likely to clog and wear more readily from grit and debris. Centrifugal pumps are typically open-impeller or recessed-impeller for handling solids. Both types of centrifugal pumps have a maximum suction lift of about 27 ft (8 m). Some truck-mounted tanks are equipped with high-level automatic shutoff controls to prevent overfilling. Pump capacities are typically at least 400 gal/min (1,500 Umin). Hoses should be of high-vacuum black rubber or synthetic material, with a minimum diameter of 3 in. (8 cm). Hoses should also be capable of being drained and capped to minimize spillage. Haulers typically carry at least 100 ft (30 m) of hose. Discharge valves on the hauler trucks should be drip tight, and a discharge nipple should accommodate a quick-disconnect coupling. Other equipment includes a device for breaking up the scum layer (e.g., a long-handled fork), shovel, soil probe for locating the septic tank, and other tools to either measure accumulations or perform other tasks in the field. A squeegee and suction wand attachments should be carried ‘“The Pumper,” a monthly publication aimed at the liquid waste hauler industry, produces an annual directory of equipment suppliers that is free with a subscription to “The Pumper.” to help clean up any spills. Lime should also be available to apply to areas where septage has been spilled.
Mobile septage dewatering systems, originally developed in Europe, are now available in the United States. Withthese systems, septage is pulled from the septic tank into one compartment on the truck; filtrate is returned to the septic tank. Polymer or lime is added to the septage during transfer to a dewatering tank, where solids are concentrated. A sludge solids content of 15 to 20 percent is reportedly achievable for polymer and lime systems, respectively Mobile dewatering systems offer: Lower transportation costs due to fewer trips to the disposal site, greater truck capacity, lower volumes of material requiring further treatment and disposal. These advantages are best suited to areas with many septic tanks and long travel distances to the discharge site. Disadvantages include more complex operational requirements and high equipment investment costs.
After the septic tank has been located and the access hatches exposed, the inlet and outlet baffles or tees are examined for such problems as damage, loose connections, and plugging. Broken pipes or baffles should be replaced or repaired. If the liquid level in the tank is higher than the outlet pipe, this may indicate clogging in the outlet pipe or in the drainfield. Next, the scum mat is manually broken up to facilitate pumping. Before this is done, the liquid level in the septic tank first is lowered below the invert of the outlet, which prevents grease and scum from being washed into the drainfield. After the scum mat is broken up, the contents of the tank are removed. Normally, the vacuum/suction hose draws air at a point where 1 to 2 in. (2.5 to 5 cm) of sludge remains over the tank bottom; this materialshould be left in the tank. Washing down the inside of the tank is unnecessary unless leakage is suspected and the inside must be inspected for cracks, If internal inspection is warranted, fresh air should be continuously blown into the tank for at least 10 min.
Displace toxic gases or oxygen-deficient air. The interior can then be inspected from the surface with a flashlight. A septic tank should never be entered without first testing the air for oxygen content, lower explosive limit, and hydrogen sulfide. This is accomplished using electronic “triple gas detectors,” available from suppliers of industrial safety equipment. Septic tanks are considered confined spaces and are subject to confined-space entry regulations published by the Occupational Safety
and Health Administration (OSHA Standard 1910.146). Anyone entering a septic tank should wear a safety harness connected to an aboveground hoist. Two additional workers should be topside to assist the inspector in the event of problems. Your state or local agency responsible for occupational health and safety should be contacted regarding any additional regulations regarding confined-space entry in their jurisdiction. In the event of a spill, septage should be immediately cleaned up. Hydrated lime should be sprinkled over the area of the spill, and a squeegee and a suction wand attached to the end of the vacuum hose are useful tools for cleanup. For large spills, a second pumper truck may be necessary; companies with one truck should reach an agreement with another company to assist in emergency spill cleanup.
Addition of any chemical or biochemical agents to the septic tank, such as disinfectants, microorganisms, and enzymes, is discouraged. Such formulations offer little or no benefit and may even be detrimental to the operation of the septic tank and drainfield. For instance, agents that emulsify grease allow its discharge to the soil absorption system, where the emulsion may break at the soil infiltrative surface and cause increased rates of clogging or pass through the soil to ground water. Other
agents are formulated of strong alkaline compounds that can pass through a tank and destroy soil structure. The most detrimental formulations contain chlorinated hydrocarbons, which can pass through the tank and soil to contaminate ground water. Fortunately, many commercial products do little to affect performance of either tanks or soil systems. Although no known benefits have been demonstrated to date, the possibility of an effective formulation in the future cannot be ruled out.
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