140 MISC. PUBLICATION 5 4 ; U. S. DEPT. OF AGRICULTURE 



When all the dissolved oxygen has been used up, the remaining (un- 

 oxidized) organic materials will begin to decompose anaerobically 

 (ferment), and odoriferous and unsightly conditions will result. If 

 the wastes are dumped into a sewer which flows into a sewage-treat- 

 ment plant, trouble can again be expected. Most treatment plants are 

 designed to handle only a limited loading of organic matter, and 

 if this amount is exceeded the entire operating balance of the plant 

 will be upset and objectionable conditions will exist. It is usually 

 desirable to separate the dehydration plant-food wastes from toilet 

 wastes. The relatively small volume of the latter can be treated 

 separately by approved methods, which involve little difficulty. 



If a dehydration plant is located in sandy terrain and there is suf- 

 ficient area available, the waste water can be drained into the soil. 

 It may be necessary to remove all suspended solids prior to the final 

 disposal of the waste. This may be accomplished by first running 

 the wastes from the plant through mechanical screens having a mesh 

 of from 40 to 60 per inch. After this, the effluent is treated with a 

 chemical agent which will change the pH of the product. Lime is 

 one of the agents most commonly used for this purpose. By the ad- 

 dition of sufficient lime so that the pH is approximately 9.0, the waste 

 material is rendered alkaline. Iron sulfate is another agent that can 

 be used. These chemicals will facilitate the precipitation of finely 

 suspended materials so that the waste water can be run into a settling 

 tank, and the suspended solids removed by gravity. Even after 

 such treatment, further treatment may be necessary when the rela- 

 tively clear water is removed from the upper levels of the tank. This 

 may involve the utilization of trickling filters or spray devices which 

 permit an aeration of the wastes. 



In some instances, the waste material can be run directly into shal- 

 low lagoons or closed areas of land diked on the edges, from which 

 the liquids drain into the soil. The addition of small amounts of 

 sodium nitrate has been found beneficial in controlling bacterial 

 changes at this stage of waste treatment. 



The best solution of the waste-disposal problem for any particular 

 plant is a complicated one, and will generally require the services of 

 a competent sanitary engineer. Careful consideration must be given 

 to the possible means of final disposal, the degree of treatment re- 

 quired by each, and the funds available for building and operating 

 treatment works. Possibly the most satisfactory scheme of disposal 

 for general use is that comprising primary treatment by settling, with 

 the effluent from the settling tank disposed of on irrigation beds, the 

 liquid percolating into the ground. This scheme of disposal avoids 

 any use of public sewerage systems and is therefore recommended 

 whenever suitable irrigation beds are available. 



Operating Personnel 



No matter how good the plant, the equipment, and the water supply, 

 if the employees have sanitary habits that are open to question, the 

 products which they handle may be contaminated. If workers happen 

 to have disease organisms on their hands, there will be disease organ- 

 isms on the products. 



Employees cannot be expected to keep clean unless proper facilities 

 are available, Dirty wash rooms and dirty latrines, with no towels 



