Oxidation ditch

The process of nitrification—denitrification can be practiced in one of two ways. In the oxidation ditch, nitrification occurs in the vicinity of the aerators. When the dissolved oxygen is depleted as the sludge—wastewater mixture passes from the aerator, denitrification occurs. 

The oxidation ditch process is usually considered when nitrogen removal is required. 

FIG. 25-54 Schematic diagrams of various modifications of the activated-sludge process, a) Conventional activated sludge. (h) Step aeration, (c) Contact stabilization, (d) Complete mixing, (e) Pure o gen. (f ) Activated hiofiltration (ABF), (g) Oxidation ditch. 

There is no standard aeration-tank shape or size. Aeration tanks can be round, square, or rectangular. Shallow aeration tanks are more difficult to mix than deeper tanks. Yet aeration-tank depths have ranged from 0.6 m (2 ft) to 18 m (60 ft). The oxidation-ditch systems tend to be shallow, while some high-rate diffused-aeration systems have used veiy deep tanks to provide more efficient oxygen transfer. 

This southern Colorado town uses about 32.5 ha (80 ac) of grass on a private ranch for application of biosolids slurry from its oxidation ditch. Application is approximately 56 dry Mg/yr (62 dry tons/yr) through a sprinkler gun. Other dry land parcels on ranches have also been used. 

Development work has been carried out on processes to produce feed from starch effluents in non-aseptic waste treatment systems (such as oxidation ditches and aeration ponds) using amylolytic filamentous fungi. These often belonging to the genera Aspergillus and Rhizopus. In such processes, the levels of contaminating bacteria are depressed by operating the systems at low pH. 

In a study of the removal of 16 FMs from wastewater, Simonich et al. [11] conducted their studies at 17 wastewater treatment plants with plant flows of 1.4x106-1.0x108 L day-1. Twelve of the plants were located in different states and regions of the U.S. and five plants were located in Europe. In addition, five of the 17 plants were activated sludge plants, two were carousel plants, two were oxidation ditch plants, five were trickling filter plants, one was a rotating bio-... 

Oxidation catalysis, molybdenum compounds in, 7 7 38 Oxidation chemistry daytime, 77 791-792 in fiber optic fabrication, 77 138-139 nightime, 77 792-793 Oxidation ditch process, in biological waste treatment, 25 905... 

Leu, H.G., C. E Ouyang, and T. Y. Pai (1997). Effects of flow velocity and depth on the rates of reaeration and BOD removal in a shallow open channel. Water Science Technol. Proc. 1995 5th lAWQ Asian Regional Conf. on Water Quality and Pollut. Control, Feb. 7-9 1995, Manila, Philippines, 35, 8, 57-67. Elsevier Science Ltd. Oxford. England. Mandt, M. G. and B. A. Bell (1982). Oxidation Ditches in Wastewater Treatment. Ann Arbor Science Publishers, Ann Arbor, Ml, 48. 

Two possible calculations can be used to determine the volume of the denitrification reactor calculation in which denitrification is allowed to occur in the same tank where nitrification is also occurring and calculation in which denitrification is done in a separate tank or in a separate portion of the same tank as in the oxidation ditch reactor. Where denitrification and nitrification occurs in the same tank, the process is a batch process, an example of which is the sequencing batch reactor (SBR). 

Separate reactors. Where denitrification and nitrification are done in separate tanks or in a separate portion of the same tank, as in the oxidation ditch process, each will require its own reactor volume. The volume of the reactor for denitrification will be given by Equation (15.101) and that for nitrification will be given by Equation (15.100). 

Furukawa, S., et al. (1998). New operational support system for high nitrogen removal in oxidation ditch process. Water Science Technol., Proc. 7th Int. Workshop on Instrumentation, Control and Automation of Water and Wastewater Treatment and Transport Syst., July 6-9, 1997, Brighton, England, 37,12, 63-68. Elsevier Science Ltd., Exeter, England. 

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