Method for subsurface aerated treatment of wastewater

Abstract

The performance of a leach field of a septic tank type wastewater treatment system and other analogous devices is enhanced, maintained or rejuvenated by flowing air or other active gas through conduits of the system. Air is flowed serially through cesspools, leaching chambers, perforated pipes in stone filled trenches, leach pits and the like, and the adjacent soil where wastewater treatment takes place. In alternate embodiments, conduits are pressurized or evacuated; and, auxiliary pipes are buried in vicinity of the conduits. An air mover creates a differential pressure sufficient to effect a significant pressure differential with atmosphere and to effect a desired physical or biochemical change in the soil adjacent the conduits. A typical pressure will be around 7-8 cm (about 3 inch) water column. If the soil is saturated, the air pressure will push water from the soil, as well as change the gas composition in the soil. The flow of wastewater may be alternated with the flow of air. Different valve devices and piping configurations are used to manage the desired flow of air and wastewater.

I claim:  
     
         1 . A method of subsurface sewage treatment, wherein waste water is flowed from a conduit into an influence zone within soil, in which zone the biochemistry of the waste water is changed by biochemical activity, toward being environmentally benign, and wherein said waste water is then flowed within the soil away from the influence zone, which comprises creating a significant gas pressure differential within the influence zone, to thereby flow a biochemically or physically effective amount of gas comprised of air or other active gas within the influence zone.  
     
     
         2 . The method of  claim 1 , wherein the gas flow is sufficient to cause the composition of the gas within the influence zone to significantly differ from the composition of gas which is otherwise present in the influence zone, in absence of said gas flow.  
     
     
         3 . The method of  claim 2 , wherein the influence zone is changed from anaerobic to aerobic.  
     
     
         4 . The method of  claim 2 , wherein the measured oxygen in the influence zone at a point about 15 cm from the inner boundary of the influence zone is increased from less than about 20 weight percent to about 20 weight percent or more.  
     
     
         5 . The method of  claim 1  wherein said gas is flowed simultaneously with, and in the same direction as, the flow of wastewater.  
     
     
         6 . The method of  claim 1  wherein, for a unit time, the amount of air or other active gas which is flowed contains several times the calculated weight amount of oxygen which would theoretically satisfy the oxygen demand of the wastewater which is flowed into the system and then the influence zone.  
     
     
         7 . The method of  claim 1  wherein the unit time is a day and wherein the oxygen which is flowed in with the gas is at least 10 times that which would theoretically satisfy said oxygen demand.  
     
     
         8 . The method of  claim 7 , wherein the oxygen demand, measured in terms of BOD, of the wastewater is at least about 100 milligrams per liter, and wherein the flow of oxygen in the gas is at least about 2500 milligrams per liter.  
     
     
         9 . The method of  claim 1 , wherein the significant pressure differential is created by a blower.  
     
     
         10 . The method of  claim 1  wherein the gas pressure within the influence zone is at least about 0.03 mm water column above atmosphere at a point about 15 cm from the inner boundary of the influence zone.  
     
     
         11 . The method of  claim 10  wherein said gas pressure is at least about 0.08 mm.  
     
     
         12 . The method of  claim 1 , wherein at least a portion of the wastewater flows vertically downward through the influence zone from a void space thereabove, which void space is within or below said conduit, which method further comprises: 
 (a) flowing wastewater into the void space so that it flows into the influence zone for a first period of time;    (b) providing pressurized air to the void space for a second period of time, to thereby impel water through the influence zone;    (c) ceasing said providing of pressurized air for a third period of time, to enable the air pressure in the void space to naturally dissipate; and,    (d) repeating step (a) again.    
     
     
         13 . The method of  claim 12  wherein said steps (a), (b), (c), and (d) are repeated a multiplicity of times.  
     
     
         14 . The method of  claim 12  wherein said third time period of step (c) is at least two times greater than said second time period of step (b)  
     
     
         15 . The method of  claim 14 , wherein said third time period is about one hour and said first time period is less than about one quarter hour.  
     
     
         16 . The method of  claim 12  which further comprises the steps of: 
 (e) sensing the level of water within the void space, and generating a signal responsive to such;  
 (f) flowing wastewater into the void space at a rate and amount sufficient to cause water to accumulate within the void space and rise to a first liquid level, whereby a first level of water signal is generated; and,  
 (g) ceasing the flowing of wastewater and providing pressurized air in response to said first level of water signal.  
 
     
     
         17 . The method of  claim 16  wherein said steps (a) through (g) are repeated a multiplicity of times.  
     
     
         18 . A method of rejuvenating a subsurface wastewater treatment system, wherein waste water is flowed from a conduit into an influence zone in the soil, in which zone the biochemistry of the waste water is altered by biochemical activity, which comprises creating a significant gas pressure differential within the influence zone, to thereby flow a biochemically or physically effective amount of gas comprised of air or other active gas into the influence zone.