What is Oxidation Pond?

• Oxidation ponds, also known as lagoons or stabilisation ponds, are huge, shallow ponds meant to remediate wastewater by allowing sunshine, bacteria, and algae to interact.
• Algae utilise solar energy, carbon dioxide, and inorganic substances produced by bacteria in water to grow.
• During photosynthesis, algae release the oxygen required by aerobic microorganisms.
• Occasionally, mechanical aerators are built to provide even more oxygen, hence reducing the required pond size.
• Eventually, pond sludge must be cleaned through dredging. Remaining algae in the pond effluent can be eliminated using filtration, chemical treatment, or a combination of chemical treatment and settling.
• San Antonio Pond was the first oxidation pond utilised for land-based wastewater disposal. In this context, we shall explain the oxidation pond’s definition, mechanism, procedure, advantages, and downsides.

Mechanism of Waste Treatment

Understanding the following processes will facilitate comprehension of the oxidation pond’s mechanism or operation.

• First, the bacteria present in the oxidation pond will oxidise the home and industrial sewage’s organic waste. This results in the release of carbon dioxide, water, and ammonia by bacteria.
• The algal development occurs when sunshine is present. It utilises the inorganic wastes produced by the breakdown of organic matter and releases oxygen.

Based on the two mechanisms described above, it is evident that algae and bacteria fulfil one other’s needs. The bacteria oxidise the biodegradable organics with the oxygen generated by the algae. The bacterial oxidation of organic waste produces carbon dioxide. Eventually, algae use carbon dioxide to reduce inorganic wastes such as nitrogen, phosphorus, etc.

As oxidation and reduction reactions occur simultaneously, an oxidation pond is also referred to as a “Redox pond.” The oxidation pond’s sludge can be used as fertiliser in irrigation processes.

Process Involved in Oxidation Pond

The conversion of industrial and domestic wastewater to a basic form involves the following steps:

1. The industrial or domestic wastewater influents initially reach the oxidation pond via the input system.
2. The bacteria then transform the biodegradable organics into inorganic molecules while emitting carbon dioxide. The predominant genera of bacteria in the stabilisation pond include Achromobacter, Proteus, Alcaligenes, Pseudomonas, Thiospirillum, Rhodothecae, etc.
3. In the presence of sunlight and carbon dioxide generated by the oxidation of organic waste, the algal biomass in the oxidation pond consumes the inorganic components. The algal genera Chlorella, Euglena, Scenedermus, and Microcystis are the most prevalent in the stabilising pond.
4. The remaining non-degradable or solid organic wastes sink as sludge to the bottom of the stabilisation pond. They are converted by anaerobic bacteria overnight and in the absence of oxygen. Anaerobic bacteria transform insoluble organic waste into soluble organic acids, such as ethanol. Anaerobic bacteria decompose organic acids further, releasing H2S, NH3, CH4, CO2, etc.
5. The treated water is discharged through the stabilising pond’s output system. Using the dredging technique, the sludge deposits can be separated from the stabilisation pond. The algal and bacterial biomass are separated using filtering, chemical treatment, or a combination of the two.

Favorable Conditions

The following environmental conditions are required for secondary wastewater treatment in an oxidation pond:

1. Sunlight

• It is required for algal development that consumes the inorganic wastes that bacteria create.
• Only in the presence of sunshine do algae release oxygen, and bacteria use this oxygen to oxidise additional organic matter.

2. Microorganisms

• In the stabilisation pond, microorganisms play a crucial role in reducing organic wastes into simple forms.
• In the stabilising pond, bacteria, algae, fungi, protozoa, insects, larvae, crustaceans, viruses, rotifers, nematodes, etc. are frequent microorganisms.
• Bacteria and algae predominate among these microorganisms and transform organic materials through reduction-oxidation processes.
• In a stabilisation pond, certain species compete while others live symbiotically to transform the wastewater influent into reclaimed effluent.

3. Oxygen

• For the oxidation of biodegradable organic waste, oxygen demand must be substantial.
• The bacteria require oxygen in order to transform organic substances into simple inorganic chemicals.
• The heterotrophic bacteria satisfy their oxygen needs with the oxygen supplied by algae and the oxygen in the atmosphere.

4. Wastewater quality

• The treatment procedure that must be applied is determined by the quality of the wastewater.
• Initially, the stabilisation pond processes the robust organic industrial waste. Tertiary treatment can be applied to domestic wastewater.

5. Pollutant load

• The efficacy of the overall stabilisation pond community may be impacted by the presence of more contaminants in the wastewater.
• Sometimes, contaminants in wastewater can be hazardous, leading to shock loads and the production of low-quality effluent.

Advantages of Oxidation Pond

• The stabilisation pond naturally reduces the biological oxygen demand by as much as 90 percent.
• It is a straightforward procedure or requires no complicated equipment.
• In tropical regions, oxidation ponds are a viable and efficient way for treating home and commercial wastewater.
• The maintenance of a stabilising pond does not need a great deal of labour.
• It is a cost-effective technology for treating wastewater from small, isolated facilities.

Disadvantages of Oxidation Pond

• The creation of a stabilisation pond necessitates additional land space.
• The upkeep is fairly complicated.
• If not properly maintained, it might emit an offensive odour and attract mosquitoes during the procedure.
• There is a possibility of effluent seepage into the ground water, which can lead to ground water contamination.

References

• N, Oyati & Olotu, Yahaya & I.N, Gimba & Ibrahim, Rasheed. (2020). Design of a Wastewater Treatment Oxidation Pond. Asian Review of Environmental and Earth Sciences. 7. 55-60. 10.20448/journal.506.2020.71.55.60. 
• N, Oyati & Olotu, Yahaya & I.N, Gimba & Ibrahim, Rasheed. (2020). Design of a Wastewater Treatment Oxidation Pond. Asian Review of Environmental and Earth Sciences. 7. 55-60. 10.20448/journal.506.2020.71.55.60. 
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