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Anaerobic Biological Treatment

Anaerobic digestion occurs naturally in the sediment in streams and lagoons that are not adequately aerated, converting carbon compounds to methane, nitrogen and hydrogen sulfide gasses (the ingredients of marsh and sewer gas) instead of the carbon dioxide and water produced by aerobic digestion.
Methane gas is liberated, in an anaerobic environment, from acetic acid by Methanosarcina, Methanococcus, Methanobacterium, and Methanobacillus. Methyloccoccus will degrade methane in an aerobic environment, so it is important to prevent its growth by excluding all free oxygen from any process that is designed to produce methane.
Anaerobic digesters are widely used to stabilize concentrated organic solids (sludge), with BOD greater than 10,000 mg/l., removed from settling tanks, biological filters, and activated sludge plants. A few plants employ an anaerobic digester as the first stage to remove excess nitrogen from the waste stream prior to aerobic treatment.
A few modern anaerobic digesters are used in conjunction with a lagoon system as a complete waste treatment system. When this system is working properly, 90% of the degradable organics should be converted to methane gas, thus minimizing the volume of excess sludge that must be discarded. The cost of operation is again reduced when the captured methane gas is used for heating or gas engine generation of electricity.
Prior to the introduction of specialized bacterial formulas, such as Alken Clear-Flo® 7020, the waste stream had to be heated to around 95 deg. F during the process in which oxygen was removed, and a large volume of natural bacteria had to be added by pump. In addition, the systems became easily upset by varying volume or concentration of the waste stream, the digesters demanded a long time to become operational, because the extremely slow rate of bacterial reproduction made it difficult to achieve the required bio-mass of correct bacterial strains to fulfill their design intent.

A three step treatment process converts organic waste to methane gas, water, and new bacterial cell mass.

  1. Simplify carbohydrates and starches into soluble organics in a process called hydrolysis. Facultative anaerobes are the most successful in this step.

  2. Change simple starches and carbohydrates into formic and acetic acid. Facultative anaerobes that can use electron acceptors from sulfates and nitrates work best in this step.

  3. Convert volatile fatty acids (organic acids from step 2) into methane gas. Strict anaerobes work best in this application.
After digestion, the excess sludge is discharged to a dewatering system, which separates the sludge into dried fertilizer pellets and water suitable for irrigation and agricultural watering.
By introducing a relatively small amount of Alken Clear-Flo® 7020 to augment the natural population of bacteria in the digester, increased rates of waste degradation with lower temperatures, and more efficient production of methane are possible.
The specialized bacterial strains in Alken Clear-Flo® 7020 are selected for their improved ability to use complex organic substrates for faster growth and reproduction rates. With the application of CF 7020, an anaerobic system flow of up to 3,000 gpm, can be started up in 90 days or less.


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