An oxidation pond, also known as a stabilisation pond or lagoon, is a man-made water treatment system designed to purify wastewater through biological processes naturally. The primary purpose of an oxidation pond is to treat and eliminate contaminants in wastewater, rendering it safe for discharge into the environment. This treatment mechanism of oxidation pond relies on the principles of microbial degradation and oxidation to break down organic matter and remove pollutants, offering an environmentally friendly and cost-effective solution for wastewater treatment.

An oxidation pond is a natural and cost-effective method used for treating domestic and industrial wastewater. This process involves a sequence of biological activities governed by the design criteria of oxidation pond and various types of oxidation ponds like aerobic, anaerobic, and facultative. Understanding the process involved in oxidation pond is essential for optimizing treatment efficiency. While it offers several advantages, there are also notable disadvantages of oxidation pond and certain limitations of oxidation pond that must be considered. This method plays a significant role in environmental engineering and sustainable wastewater management.

This article shall unravel all about Oxidation ponds. This topic is important for all the upcoming civil engineering examinations, including SSC JE CE and RRB JE Civil.

What is an Oxidation Pond?

Oxidation ponds, also known as lagoons or stabilisation ponds, are expansive, shallow bodies of water specifically engineered for wastewater treatment, harnessing the interplay of sunlight, bacteria, and algae. Within these ponds, algae thrive by utilising solar energy, carbon dioxide, and inorganic compounds generated by waterborne bacteria. Through the process of photosynthesis, algae release essential oxygen, supporting the activities of aerobic bacteria. 

Fig 1: Oxidation Pond Diagram

In some cases, mechanical aerators are introduced to augment the oxygen supply, subsequently reducing the necessary pond dimensions. Over time, accumulated sludge within the pond necessitates removal through dredging. Any residual algae in the effluent can be eliminated through filtration or a combination of chemical treatment and settling processes.

Understanding the functioning of an oxidation pond involves a straightforward breakdown of the following steps:

• Initially, the bacteria present within the oxidation pond undertake the oxidation of organic waste from both domestic and industrial sewage, resulting in the release of carbon dioxide, water, and ammonia.
• Simultaneously, algal growth is fostered by sunlight, as it utilises the inorganic byproducts generated through the decomposition of organic matter, liberating oxygen.
• In this mutual partnership, bacteria and algae complement each other's needs. Bacteria rely on the oxygen produced by algae to oxidize biodegradable organics, yielding carbon dioxide. Subsequently, algae harness this carbon dioxide to mitigate inorganic waste components such as nitrogen and phosphorus compounds.
• Given this concurrent process of oxidation and reduction, oxidation ponds are occasionally referred to as "Redox ponds." The sludge obtained from the oxidation pond can also serve as valuable manure for irrigation purposes.

Steps Involved in Wastewater Treatment in Oxidation Pond

• Wastewater influents from industrial or domestic sources enter the oxidation pond through the inlet system.
• Bacteria play a pivotal role by converting biodegradable organics into inorganic compounds, releasing carbon dioxide. Prominent genera of bacteria, including Achromobacter, Proteus, Alcaligenes, Pseudomonas, Thiospirillum, and Rhodothecae, dominate the stabilisation pond.
• Algal biomass in the oxidation pond utilises inorganic compounds, along with sunlight and carbon dioxide produced during the oxidation of organic waste. Common genera of algae such as Chlorella, Euglena, Scenedesmus, and Microcystis thrive in the stabilisation pond.
• Non-biodegradable or solid organic waste settles at the pond's bottom as sludge. During nighttime and in the absence of oxygen, anaerobic bacteria convert these solids. Initially, the anaerobic bacteria transform insoluble organic waste into soluble organic acids like ethanol. Further decomposition by anaerobic bacteria results in the release of \(H_2S, NH_3, CH_4, CO_2\) and other byproducts.
• The treated water is discharged through the outlet system of the stabilisation pond. Separating sludge deposits from the pond can be achieved through dredging, while algal and bacterial biomass can be separated using filtration or a combination of chemical treatment and settling processes.

Favourable Conditions for Oxidation Ponds

To achieve secondary treatment of wastewater in an oxidation pond, specific environmental factors come into play:

• Sunlight: Essential for fostering algal growth, which harnesses inorganic waste products from bacteria. Algae release oxygen in the presence of sunlight, which bacteria utilise for the oxidation of organic matter.
• Microorganisms: A diverse array of microorganisms within the stabilisation pond plays a vital role in transforming organic waste into simpler forms. This includes bacteria, algae, fungi, protozoans, insects, larvae, crustaceans, viruses, rotifers, nematodes, and more. Bacteria and algae, in particular, lead the way, employing reduction-oxidation reactions for organic matter conversion. Some microorganisms compete, while others collaborate symbiotically to transform influent wastewater into reclaimed effluent.
• Oxygen: Adequate oxygen is a critical factor for the oxidation of biodegradable organic waste. Bacteria require oxygen to convert organics into simple inorganic compounds. Heterotrophic bacteria satisfy their oxygen needs using oxygen released by algae and atmospheric oxygen.
• Wastewater Quality: The initial quality of the wastewater dictates the choice of the treatment method to be applied. Stabilisation ponds are suitable for treating strong industrial organic waste, while domestic wastewater may require tertiary treatment.
• Pollutant Load: The efficiency of the entire stabilisation pond community can be impacted by higher pollutant levels in wastewater. Some contaminants in the wastewater might be toxic, leading to shock loads and the release of poor-quality effluent.

Advantages of Oxidation Pond

The advantages of an Oxidation pond are:

• Natural and energy-efficient wastewater treatment.
• Low operational and maintenance costs.
• Reduction in pathogens and organic pollutants.
• Minimal use of chemicals.

Disadvantages of Oxidation Pond

The major limitations of Oxidation ponds are:

• Land and space requirements.
• Limited effectiveness in cold climates.
• Odour and aesthetic concerns.
• Potential habitat for disease vectors.

This blog encompassed all about Oxidation ponds and their working. This topic is important for your upcoming exams. If you are preparing for State and Central level Civil examinations and other diploma-level exams, get enrolled in AE/JE Civil Coaching on the Testbook App.

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