Oxidation ditches can be defined as modified activated sludge with addition in keeping clip to guarantee effectual remotion of biodegradable organic through biological intervention procedure. This is chiefly observed to be complex mix but in some instances the procedure can be modified into pluge flow ( USEPA, 2000 ) . Crites and Tchobanoglous, ( 1998: 471 ) revealed that oxidization was originally discovered by Dr. Pasveer in Netherlands in the twelvemonth 1950s installed in 1954 and subsequently introduced in the United State in 1963. Oxidation ditche can be designed in different forms but chiefly in signifier of ring or egg-shaped form. Crites and Tchobanoglous, ( 1998 ) indicate that the rotor may look to be horizontally or vertically designed for aeration intent. The aeration circulates at 0.25 to 0.35m/s to guarantee effectual commixture of the effluent and pollutant to maintain solids and biomass suspended in the solution ( Crites and Tchobanoglous, 1998 ) and ( Moore and Dee, n.d ) . The O transportation and ditch aeration is the map of rotor through aeration ( USEPA, 2000 ) .
Mode Of Operation
The effluent Influent in some instance may non be screen before intervention ( Smith, 2003 ) . The primary intervention may be achieved utilizing saloon screen or grit remotion ( USEPA, 2000 ) , before the effluent flows into oxidization ditche. The add-on of activated sludge encourages the microorganism consumption of the Biochemical Oxidation Demand ( BOD ) in the H2O ( Oxidation ditch, n.d ) . Wastewater aeration allows effectual dislocation of organic solid, flux within the oxidization ditch and let solid motion within the ditche ( Smith, 2003 ) . The aeration aggressively increases the dissolved O ( DO ) concentration but decreases as biomass uptake O as the assorted spirits travels through the ditch ( USEPA, 2000 ) . After the remotion of the BOD in the influent, the mix spirits mercantile establishment via the oxidization ditch while the sludge is eliminated in the clarified. Then aerator pumps are used to inspissate the sludge in the aerophilic digester and understate the volume of the sludge produced. Some of the sludge is disposed off while some are used as Return Activated Sludge ( RAS ) in the oxidization ditch ( Oxidation, ditch n.d )
Nitrification and denitrification in most instances are possible to achieved in effluent intervention if anaerobiotic zone is included in the design of the oxidization ditch likewise P ( USEPA, 2009 ) .
Advantages And Disadvantages As Follow:
Easy to run, dependable, energy efficient, sensible cost of operation and care comparison to biological intervention procedures.
Removal of Nitrogen and Less sludge produced
No weir flood and Less hydraulic rush due to long keeping clip
Power supply required
High wastewater suspended solid comparison to other biological intervention procedures
Unsuitable in urban country due to set down cost and large hectares required.
Inappropriate in cold clime
May damage the rotor if no showing and unfastened armored combat vehicle danger
Beginning: Smith, ( 2003:8.22 ) and ( USEPA, 2000 )
The cardinal consideration prior to design of oxidization ditch is the effluent feature and the aim of the oxidization ditch sing nitrification, denitrification and P remotion ( USEPA, 2000 ) . The deepness in most instances is between 1-4m to guarantee effectual intervention of effluent and to heighten rotors surface aeration speed at 70 revolutions per minute and 30-60 revolutions per minute horizontal and perpendicular severally ( Smith, 2003 ) .
Retention Time: The solid keeping clip in oxidization ditch design should be 30 yearss and 24 to 26 hours hydraulic keeping clip while the solid keeping clip for nitrification is 12 to 24 yearss ( Smith, 2003 and USEPA, 2000 ) , this is to guarantee that the period of clip allocated to activated sludge microorganism to handle effluent is sensible plenty to guarantee effectual mix of the effluent and nitrification.
BOD Loading: The needed BOD for oxidization ditch is about 160,000 mg/1000 litres ( 10 lb./1000 ft3 ) to more than 4×107 mg/1000 liters ( 50 lb./1000 ft3 ) . In the designing procedure the lading rate of 240,000 mg/1000 litres per twenty-four hours ( 15 lb./1000 ft3/day ) are most frequently considered although this may non utilize to determine the degree of nitrification in the intervention procedure ( USEPA, 2000 ) . The F/M ( Food to Micro-organism ) ration ranges from F/M & A ; gt ; 0.5 Kg BOD5/day/kg sludge which produce high degree of sludge, medium sludge at 0.2 & A ; lt ; F/M & A ; lt ; 0.5 and low sludge at 0.07 & A ; lt ; F/M & A ; lt ; 0.2 ( Smith, 2003 ) . The choice of appropriate F/M ratio is based on expected BOD degree at the terminal of the biological intervention procedure, if short clip means that the microorganisms may non be able to eat all the nutrient ensuing to high sludge burden. .
Crites and Tchobanoglous ( 1998 ) Small and Decentralized Wastewater Management System.
McGraw-Hill Companies, Inc.
Moore. Larry. W. , and Dee. P.E. , ( n.d ) Enhancing The Performance of Oxidation Ditches. The University of Memphis United States of America.
Smith, Michael ( 2003 ) Wastewater Treatment. Unpublished talk notes, WEDC, Loughborough University: UK.
United States Environmental Protection Agency ( 2000 ) Wastewater Technology Fact Sheet Oxidation Ditches. Environmental Protection Agency EPA832-F-00-013.
United States Environmental Protection Agency ( 2009 ) Nutrient Control Design Manual State of Technology Review Report. Environmental Protection Agency EPA/600/R-09/012.
Oxidation Ditch ( n.d ) available at & A ; lt ; hypertext transfer protocol: //water.me.vccs.edu/concepts/oxidation.html & A ; gt ; ( Accessed 06 January 2010 )