Oxidation Ditch

CEBU TECHNOLOGICAL UNIVERSITY Main Campus M.J. Cuenco Ave., R. Palma St., Cebu City  A.Y. 2018 - 2019 2019

CE 422

TECHNICAL ELECTIVE ELECTIVE II SANITARY ENGINEERING

OXIDATION DITCH

Paquera, Robert P. Saplad, Daryll M. Tan, Lyka Isabel V. BSCE IV - D1

Engr. Evalinda C. Pelimer Instructor 

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

I. INTRODUCTION

 An oxidation ditch is a modified modified activated activated sludge biological biological treatment treatment process that utilizes long solids retention times (SRTs) to remove biodegradable organics. Oxidation ditches are typically complete mix systems, but they can be modified to approach plug flow conditions. (Note: as conditions approach plug flow, diffused air must be used to provide enough mixing. The system will also no longer operate as an oxidation ditch). Typical oxidation ditch treatment systems consist of a single or multichannel configuration within a ring, oval, or horseshoe-shaped basin. As a result, oxidation ditches are called “racetrack type” reactors. Horizontally or vertically mounted aerators provide circulation, oxygen transfer, and aeration in the ditch.  An oxidation oxidation ditch is a large large circular circular basin equipped with with aerators that is used used to remove organic matter and pollutants from sewage through the processes of adsorption, oxidation, and decomposition. decomposition. 

Ensures stable, continuous dissolved oxygen measurement



Reduces operating costs



Eliminates the need for manual cleaning

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

II. PROCESS

The ditch is built on the surface of the ground and is lined with an impermeable lining. This allows the waste water to have plenty of exposure to the open air for the diffusion of oxygen. Mounted aerators provide circulation of the wastewater and mixed liquor in the channel as well as oxygen transfer to the biomass in the ditch and the shallow liquid depth (0.9 to 1.5 m) helps to prevent anaerobic conditions from occurring at the bottom of the ditch. The circulation process entrains oxygen into the mixed liquor to foster microbial growth, maintains the solids in suspension and ensures the contact of microorganisms with the incoming wastewater. After treatment, the wastewater is pumped to a clarifier where the sludge and the water are allowed to separate. It should be noted that the configuration can be adapted to provide biological nutrients removal by including anoxic zones. The liquid depth in the ditches is very shallow, 0.9 to 1.5 m, which helps to prevent anaerobic conditions from occurring at the bottom of the ditch. The oxidation ditch effluent is clarified in a secondary clarifier and the settled sludge is returned to maintain a desirable MLSS concentration. The MLSS concentration in the oxidation ditch generally ranges from 3,000 mg/ L to 5,000 mg/ L; however, this is dependent upon the surface area provided for sedimentation, the rate of sludge return, and the aeration process. III. APPLICABILITY

The oxidation ditch process is a fully demonstrated secondary wastewater treatment technology, applicable in any situation where activated sludge treatment (conventional or extended aeration) is appropriate. Oxidation ditches are applicable in plants that require nitrification because the basins can be sized using an appropriate SRT to achieve nitrification at the mixed liquor minimum temperature. This technology is very effective in small installations, small communities, and isolated institutions, because it requires more land than conventional treatment plants. IV. ADVANTAGES

The main advantage of the oxidation ditch is the ability to achieve removal performance objectives with low operational requirements and operation and maintenance costs. Some specific advantages of oxidation ditches include:

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

which lowers the weir overflow rate and eliminates the periodic effluent surge common to other biological processes, such as SBRs. 

Long hydraulic hydraulic retention time and complete complete mixing minimize the impact impact of a shock load or hydraulic surge.



Produces less sludge than other biological treatment processes owing to extended biological activity during the activated sludge process.



Energy efficient operations result in reduced energy costs compared with other biological treatment processes.

V. DISADVANTAGES 

Effluent suspended solids concentrations concentratio ns are relatively high compared to other modifications of the activated sludge process.



Requires a larger land area than other activated sludge treatment options. This can prove costly, limiting the feasibility of oxidation ditches in urban, suburban, or other areas where land acquisition costs are relatively high.

VI. DESIGN CRITERIA

The design criteria are affected by the influent wastewater parameters and the required effluent characteristics, including the decision or requirement to achieve nitrification, denitrification, and/or biological phosphorus removal. Specific design parameters for oxidation ditches include: 

Solids Retention Time (SRT): Oxidation ditch volume is sized based on the required SRT to meet effluent quality requirements. The SRT is selected as a function of nitrification requirements and the minimum mixed liquor temperature. Design SRT values vary from 4 to 48 or more days. Typical SRTs required for nitrification range from 12 to 24 days.



BOD Loading: BOD loading rates vary from less than 160,000 mg/1000 liters (10 lb./1000 ft3 ) to more than 4x107 mg/1000 liters (50 lb./1000 ft3 ). A BOD loading rate of 240,000 mg/1000 liters per day (15 lb./1000 ft3 /day) is commonly used as a design loading rate. However, the BOD loading rate is not typically used to determine whether or not nitrification

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.



Hydraulic Retention Time: While rarely used as a basis basis for oxidation ditch ditch design, hydraulic Retention Times (HRTs) within the oxidation ditch range from 6 to 30 hours for most municipal wastewater treatment plants.

VII. PERFORMANCE

 As all conventional conventional aerobic biological systems, oxidation ditches are very efficient at removing organic matter from wastewater, and, depending on the configuration, they can also be adapted to remove nutrients and in particular nitrogen (nitrification/denitrification with aerobic and anoxic zones in the channel). However, phosphorus removal may be limited due to a low biodegradable COD to phosphorus ratio in the incoming wastewater. An average pollutant removal efficiency of 17 oxidation ditch plants and a wastewater treatment plant in the USA is presented in Table 1. Table 1. Pollutant removal rates of 17 oxidation ditch plants and a wastewater treatment plant. (Source: Shammas et al., 2009)

Pollutant

Biological oxygen demand (BOD)

Removal Rate [%]

96

Total suspended solids (TSS)

97

Total Nitrogen (TN)

94

Pollutant

Biological oxygen demand (BOD)

Source

Removal Rate [%]

Pollutant removal rates of 17 oxidation ditch plants in the City of Casa Grande, Arizona, USA (1999)

Source

99

Total suspended solids (TSS)

97

Total Nitrogen (TN)

90

Wastewater treatment plant in the Town of Edgartown, Massachusetts, USA (1999)

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Table 2. Design and Operational Parameters of Oxidation Ditches (Source: Shammas et al., 2009)

Design and Operational Parameters of Oxidation Ditches Circulation

0.20  – 0.35 0.20 –  0.35 m/s

RAS recycle ratio

75 – 75  – 150%  150%

MLSS

1500 – 5000 1500 –  5000 mg/L

SRT

4-48 days

SRT for nitrification nitrification

12-24 days

BOD loading

160 g/1000L - 4x10 4 g/1000L

Typical design BOD loading rate

240 g/1000L per day

HRT

6-30 hours

Sludge production

0.2-0.85 kg TSS / kg BOD

Oxygen requirements

•1.1-1.5 •1.1-1.5 kg O2 / kg BOD •4.57 kg O2 / kg TKN

VIII. OPERATION AND MAINTENANCE

Oxidation ditches require relatively little maintenance compared to other secondary treatment processes. No chemicals are required in most applications, but metal salts can be added to enhance phosphorus removal. removal. 

Residuals Generated

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

Trusted by over 1 million members

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.

kg of BOD (0.65 lb TSS per lb. of BOD). This is less than conventional activated sludge facilities because of long SRTs. 

Operating Parameters The oxygen coefficient for BOD removal varies with temperature and SRT. Typical oxygen requirements range from 1.1 to 1.5 kg of O2 per kg of BOD removed (1.1 to 1.5 lbs of O2 per lb. of BOD removed) and 4.57 kg of O2 per kilogram of TKN oxidized (4.57 lbs of O2 per lb. of TKN oxidized) (EPA, 1991; Baker Process, 1999). Oxygen transfer efficiency ranges from2.5 to 3.5 lb./Hphour (Baker Process, 1999).

IX. COSTS

The basin volume and footprint required for oxidation ditch plants have traditionally been very large compared with other secondary treatment processes. Larger footprints result in higher capital costs, especially in urbanized locations where available land is very expensive. Vertical reactors, in which process flow travels downward through the reactor, are generally more expensive than traditional horizontal reactors. However, because they require less land than more conventional horizontal reactors, they can significantly reduce overall capital costs where land costs are high. The cost of an oxidation ditch plant varies depending on treatment capacity size, design effluent limitations, land cost, local construction costs, and other site specific factors. Oxidation ditches offer significantly lower operation and maintenance costs than other secondary treatment processes. Compared to other treatment technologies, energy requirements are low, operator attention is minimal, and chemical addition is not usually required. The oxidation ditch has also eliminated