Oxidation Pond

Oxidation pond or lagoon or water stabilization pond is a secondary wastewater treatment that treats waste or sewage coming from industries, residential areas, etc.

It uses microorganisms like bacteria, algae and light energy (sunlight) to stabilize the wastewater. The oxidation pond is constructed 1-1.5 m deep inside the soil and provided with inlet and outlet systems.

Earlier, symbiotic algae and bacterial growth were used to treat the wastewater under the act of sunlight. Later on, it was found that not only the algae-bacterial association but also the fungal growth can purify the industrial effluents or raw sewage.

San Antonio Pond was the first oxidation pond used for the land disposal of wastewater. In this context, we will discuss the definition, mechanism, process, advantages and disadvantages of the oxidation pond.

Content: Oxidation Pond

1. Definition
2. Mechanism
3. Process
4. Advantages
5. Disadvantages
6. Conclusion

Definition of Oxidation Pond

Oxidation pond refers to the stabilization pond stabilizing the domestic, trade, industrial wastes etc., by the microbial interaction (primarily bacteria and algae). It seems like a large shallow pond with 2-6 feet height of water body. Oxidation pond requires the presence of sunlight and oxygen for the secondary treatment of domestic and trade wastes.

The secondary treatment of the organic and inorganic waste coming from raw sewage and industrial effluents is necessary. The direct disposal of the wastewater to the aquatic system can affect the life of water bodies and the quality of water as well.

Mechanism of Waste Treatment

The mechanism or working of the oxidation pond can be made simple by understanding the following steps:

1. First, the bacteria present in the oxidation pond will oxidize the organic waste of the domestic as well as industrial sewage. By doing this, bacteria release carbon dioxide, water and ammonia.
2. The algal growth occurs in the presence of sunlight. It utilizes the inorganic wastes formed by the organic matter decomposition and releases oxygen.

From the above two mechanisms, it is clear that the algae and bacteria work mutually to fulfil each other’s requirement. The bacteria use oxygen released by the algae to oxidize the biodegradable organics. The oxidation of organic waste by the bacteria releases carbon dioxide. Later, algae harness carbon dioxide to reduce inorganic wastes like nitrogen, phosphorus compounds etc.

As the oxidation and reduction reaction co-occurs, an oxidation pond is sometimes called “Redox pond”. The sludge of the oxidation pond can be utilized as manure for the irrigation processes.

Process Involved in Oxidation Pond

The process involved in the conversion of industrial and domestic wastewater into simple form includes:

1. Firstly, the industrial or domestic wastewater influents enter the oxidation pond through the inlet system.
2. Then, the bacteria utilize the biodegradable organics and convert them into inorganic compounds by releasing carbon dioxide. Achromobacter, Proteus, Alcaligenes, Pseudomonas, Thiospirillum, Rhodothecae etc., are the following genera of the bacteria that predominate in the stabilization pond.
3. The algal biomass in the oxidation pond utilizes the inorganic compounds in the presence of sunlight and carbon dioxide released during the oxidation of organic waste. Chlorella, Euglena, Scenedermus and Microcystis are the most common genera of algae predominating in the stabilization pond.
4. The remaining non-biodegradable or solid organic wastes settle down in the bottom of the stabilization pond as sludge. The anaerobic bacteria convert them during the night and in the absence of oxygen. The anaerobic bacteria first convert the insoluble organic waste into soluble organic acids like ethanol. Further decomposition of organic acids by the anaerobic bacteria release H₂S, NH₃, CH₄, CO₂ etc.
5. The treated water releases out through the outlet system of a stabilization pond. By employing the dredging method, one can separate the sludge deposits from the stabilization pond. The filtration method or the combination of chemical treatment and settling process separates the algal and bacterial biomass.

Favourable Conditions

Secondary treatment of wastewater in an oxidation pond requires the following environmental factors:

Sunlight: It is necessary for algal growth that utilizes the inorganic wastes produced by the bacteria. Algae release oxygen only in the presence of sunlight, and the bacteria use this oxygen to oxidize more organic matter.

Microorganisms: The microorganisms in the stabilization pond perform a fundamental role in converting organic wastes into simple forms. Bacteria, algae, fungi, protozoans, insects, larvae, crustaceans, viruses, rotifers, nematodes etc., are the common microorganisms in the stabilization pond.

Among these microorganisms, bacteria and algae dominate and convert organic matter by reduction-oxidation reactions. Some organisms compete in a stabilisation pond, and some live symbiotically to convert the wastewater influent into reclaimed effluent.

Oxygen: For the oxidation of biodegradable organic waste, there must be considerable demand for oxygen. The bacteria need oxygen to convert the organics into simple inorganic compounds. The heterotrophic bacteria fulfil their oxygen requirement through the oxygen released by the algae and the atmospheric oxygen.

Wastewater quality: The quality of wastewater is a factor that decides the type of treatment method that has to be employed. Initially, the stabilization pond treats the strong industrial organic wastes. Domestic wastewater can be subjected to tertiary treatment.

Pollutant load: More pollutants in the wastewater may affect the efficiency of the entire stabilization pond community. Contaminants in the wastewater can sometimes be toxic and may cause shock load and release effluent of poor quality.

Advantages

• The stabilization pond reduces the biological oxygen demand up to 90% naturally.
• It is a simple method to operate or does not require sophisticated equipment.
• Oxidation pond is a practical and effective method for the wastewater treatment of domestic and trade wastes in tropical areas.
• The operation of a stabilization pond does not require much labour-power.
• It is an economical method for the treatment of wastewater from small and isolated units.

Disadvantages

• The construction of a stabilization pond requires more land area.
• The maintenance is quite intricate.
• Sometimes, it gives a foul smell and mosquito menace during the process if not appropriately maintained.
• There may get a chance of effluent seepage into the ground water, which can ultimately cause ground water pollution.

Conclusion

Therefore, we can conclude that the oxidation pond is a biological system that takes about 10-40days of detention time. This method load organic matter up to 300-150Kg/hectare/day and have a length of 50-100m, a width of 30-50m and a depth of 0.9-1.5m.

Usually, an oxidation pond can hold water up to 0.3m  and settled sludge up to 0.02m. The decomposition of bio-organics produces a foul smell, due to which the stabilization pond is kept away from the residential areas. The use of sodium nitrate avoids foul odour during wastewater decomposition.