THE MANURE HEAP AND SEWAGE. 1 2/ 



The first is due to the aerobic bacteria which act upon the or- 

 ganic matter in the presence of oxygen, giving rise to an ammo- 

 niacal fermentation and a considerable oxidation of the carbo- 

 naceous matter, and producing large amounts of ammonium 

 carbonate. This ceases after all the oxygen in the water has 

 been used up, and then the bacteria which grow without oxygen 

 begin to work. The decomposition which they produce is of a 

 different nature and results in the production of vile-smelling 

 gases of carbon, sulphur and phosphorus, inasmuch as the 

 destruction of the compounds without the access of oxygen 

 is less complete. These* gases partly pass off into the air, 

 or are partly oxidized by aerobic bacteria growing at the sur- 

 face, or elsewhere that oxygen may be obtained. Both of 

 these types of fermentation go on extensively, in the contact 

 beds and in the septic tank, and both seem to be necessary for 

 the thorough decomposition of the organic matter. 



As a result of these two types of decomposition the various 

 organic bodies in the sewage are very largely destroyed. The 

 same processes of decomposition that occur in the manure heap 

 take place "here. Various gases are liberated (NH 3 , N, CO 2 , 

 CH 4 , H 2 S, etc.), and the total amount of solid matter is thus 

 greatly reduced. Later in the process, especially in the con- 

 tact beds where oxygen is abundant, a vigorous oxidation of 

 the nitrogen compounds begins (nitrification) which results in 

 the formation of large amounts of nitrates. These nitrates 

 are, however, thoroughly soluble and become at once dis- 

 solved in the water of the sewage, which consequently clears 

 up. In this way nearly all of the nitrogen which was held in 

 high compounds in the original sewage, has either become dis- 

 sipated into the air as ammonia or free nitrogen, or has become 

 converted into nitrates and has dissolved in the water to form 

 a clear solution which is not objectionable when discharged 

 into streams. Such effluent water would be highly useful for 

 irrigating soil, inasmuch as it contains so much nitrate material ; 



