242 Microbes and You 



1. Overloading the tank because of inadequate tank capacity. 



2. Insufficient or improperly prepared drainage field to accom- 

 modate the effluent from the septic tank. 



3. Lack of a grease trap between the kitchen and the tank. It is 

 just as undesirable to have a grease trap that is not regularly 

 cleaned as it is to have no grease trap at all. 



4. Introducing materials into the sewage which are unable to 

 undergo biological digestion. 



While persons engaged in building their own home naturally 

 are interested in keeping costs to a minimum, economizing by pur- 

 chasing and installing a septic tank of insufficient capacity is, in 

 the main, false economy. They should anticipate any eventuality 

 and provide a tank large enough to allow for future increased 

 volumes of sewage. If precautions are taken to obviate the dif- 

 ficulties listed above, septic tanks will generally provide an efficient 

 and reliable means of disposing of sewage on a relatively small 

 scale. 



IMHOFF TANKS 



For capacities up to 300,000 gallons of sewage per day, a two- 

 story septic tank called an Imhoff Tank is frequently employed. 



As the sewage passes through a v-shaped trough, the solids 

 drop to the bottom of the tank where anaerobic action occurs. 

 Since undigested material accumulates in time, a sludge-removal 

 vent is provided. Gas being liberated in the process is sometimes 

 collected and used to burn garbage, or it may be used to warm 

 the building in which the Imhoff tanks are kept. Thus a more 

 favorable temperature can be maintained to encourage sewage 

 decomposition. 



CONTACT BEDS 



Disposal of the effluent from large sewage digestion tanks is 

 handled in a number of ways. The contact bed, while not as 

 popular today as it once was, may be employed in this process. A 

 contact bed is prepared by filling water-tight basins with stones, 

 slate, slag, broken crockery, etc. The basin is filled with sewage 



