Oxidation pond is a type of wastewater treatment which also refers as lagoons or water stabilization pond. It is a secondary treatment of wastewater coming from industries, residential areas etc. It makes the use of microorganisms like bacteria, algae and light energy (sunlight) to stabilize the wastewater. Oxidation pond is constructed 1-1.5m deep inside the soil and have inlet and outlet systems.
Earlier, it was believed that the wastewater is treated by the symbiotic algae and bacterial growth in the presence of sunlight. Later, on further study, it was found that not only the algae-bacterial growth but also the fungal growth required to purify industrial effluents or raw sewage. San Antonio Pond was the first oxidation pond that was used for the land disposal of the wastewater.
Content: Oxidation Pond
Definition of Oxidation Pond
Oxidation pond can define as the stabilization pond that stabilizes the domestic, trade, industrial wastes etc. by the microbial interaction, primarily bacteria and algae. It is the large, shallow ponds having 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 of working of the oxidation can be made simple by understanding the following steps:
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. The algal growth occurs in the presence of sunlight. It utilizes the inorganic waste formed by the organic matter decomposition and releases oxygen.
From the above two mechanisms, it is clear that the algae and bacteria work corporately to fulfil each other’s requirement. The bacteria use oxygen released by the algae, to oxidize the biodegradable organics. A carbon-dioxide release as the result of organic waste oxidation by the bacteria is used by the algae to undergo a reduction of inorganic waste like nitrogen, phosphorus compounds etc. As the oxidation and reduction reaction co-occurs, an oxidation pond also refers as “Redox pond”. The sludge of oxidation pond may use as a manure for the irrigation processes.
Process Involved in Oxidation Pond
The process involved in the conversion of industrial, domestic wastewater into simple form includes:
- First, through the inlet system, the industrial, domestic wastewater influents into the oxidation pond.
- Then, the bacteria utilize the biodegradable organics and convert it into inorganic compounds by releasing carbon dioxide. Achromobacter, Proteus, Alcaligenes, Pseudomonas, Thiospirillum, Rhodothecae etc. are the following genera of the bacteria that predominates in the stabilization pond.
- 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 that predominates in the stabilization pond.
- Remaining non-biodegradable or solid organic wastes settle down in the bottom of stabilization pond as Sludge. The anaerobic bacteria convert it 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 releases H2S, NH3, CH4, CO2 etc.
- The treated water releases out through outlet system of a stabilization pond. Sludge deposits remove out from stabilization pond by the method of dredging. The algal and bacterial biomass can separate out either by filtration method or the combination of chemical treatment and settling process.
Secondary treatment of wastewater in an oxidation pond requires the following environmental factors:
Sunlight: It is necessary for the algal growth, which in turn can utilize the inorganic wastes produced by the bacteria. Algae release oxygen only in the presence of sunlight, which then harnesses by the bacteria to oxidize more organic matter.
Microorganisms: The microorganisms in the stabilization pond performs a fundamental role in the conversion of organic waste into a simple form. In the stabilization pond, organisms like bacteria, algae, fungi, protozoans, insects, larvae, crustaceans, viruses, rotifers, nematodes etc.
Among these microorganisms, bacteria and algae dominate and carry out a conversion of organic matter by reduction-oxidation reactions. In stabilization pond, some organisms compete with each other, and some live symbiotically to convert the wastewater influent into reclaimed effluent.
Oxygen: For the oxidation of biodegradable organic waste, there is a considerable demand for oxygen by the bacteria to convert it into simple inorganic compounds. The heterotrophic bacteria fulfil its oxygen requirement released by the algae and the atmospheric oxygen.
Wastewater quality: The quality of wastewater is a factor that decides which treatment method should be employed. The stabilization pond can initially treat strong industrial organic waste. Domestic wastewater can undergo tertiary treatment in the oxidation pond.
Pollutant load: It there are more pollutants in the wastewater then it can affect the efficiency of the entire stabilization pond community. Contaminants in the wastewater sometimes can also be toxic and may cause shock load and the release of effluent with poor quality.
- The stabilization pond can reduce the biological oxygen demand up to 90% naturally.
- It is a simple method to operate, does not require sophisticated equipment.
- Oxidation pond is a practical and effective method for the wastewater treatment of domestic and trade wastes in the 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.
- 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.
Therefore, we can conclude that the oxidation pond is a biological system which takes about 10-40days of detention time. This method can load organic matter up to 300-150Kg/hectare/day and having 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, that’s why the stabilization pond is kept away from the residential areas. The use of sodium nitrate can avoid foul odour during the wastewater decomposition.