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| Sewage Treatment Plants & Grey Water Treatment Plants |
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| The basic technology generally used for the treatment of Sewage is activated sludge process. This applies to both small and large processing plants and the difference lies in the arrangement and enhancement of the various sections of the process.
The activated sludge process is a natural process and nature offers us a unique solution to treat sewage. Nature has provided a special balance in this process in that the micro organisms present when the food levels are high, will also consume the largest amount. This allows the quick breakdown of the BOD levels to more reasonable levels.
Once these levels are reached, other microorganisms, which are heavier and less mobile, will reduce the BOD levels further, until the final acceptable standards are obtained
The fact that the last organisms are large and heavy, allows us in practical terms to settle these organisms out very efficiently, producing a clear liquor.
To balance the process, we can identify four major sections in a activated sewage plant system: |
- Collection and anaerobic storage
- Aeration of the Sludge
- Setting of the sludge removing all solids
- Chlorination and phosphor removal to bring the final effluent up to the required standard.
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| These sections are repeated in the different systems available. Only the anaerobic stage is not always required, depending on the solids removal systems proposed. |
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| QUESTIONS |
| What is Biochemical Oxygen Demand (BOD)? |
| The BOD is an important measure of water quality. It is a measure of the amount of oxygen needed (in milligrams per liter or parts per million) by bacteria and other microorganisms to oxidize the organic matter present in a water sample over a period of 5 days. The BOD of drinking water should be less than 1. That of raw sewage may run to several hundred. It is also called the biological oxygen demand.
What is Primary Treatment? The simplest, and least effective, method of treatment is to allow the un dissolved solids in raw sewage to settle out of suspension forming sludge. Such primary treatment removes only one-third of the BOD and virtually none of the dissolved minerals.
Attempts to use digested sludge as a fertilizer have been hampered by its frequent contamination by toxic chemicals derived from industrial wastes. |
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| What is Secondary Treatment? |
Many treatment plants pass the effluent from primary treatment to secondary treatment. Here the effluent is brought in contact with oxygen and aerobic microorganisms. They break down much of the organic matter to harmless substances such as carbon dioxide.
Primary and secondary treatment together can remove up 90% of the BOD. After chlorination to remove its content of bacteria, the effluent from secondary treatment is discharged to surface water. |
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| ADVANCED WASTE TREATMENT |
| The combination of primary and secondary treatment removes most of the organic matter in sewage and thus lowers the BOD. However, most of the nitrogen and phosphorus in sewage remains in the effluent from secondary treatment. These inorganic nutrients can cause eutrophication of surface water receiving the effluent causing blooms of algae. To avoid this, a few add a third stage of treatment called tertiary treatment. |
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| BIOLOGICAL TREATMENT |
| Biological treatment is the process of utilizing naturally occurring living organisms to degrade, stabilize and destroy organic contaminants. These microorganisms use the waste as their source of energy and carbon. Biological treatment technologies are restricted to organic wastes, and therefore have limited application. It is appropriate at this point to review some principles of biological process.
All living organisms require a source of energy and carbon to be able to develop and reproduce. Many organisms (autographic) get their carbon from inorganic compounds (such as CO2), while other organisms (heterotrophic) use organic compounds to get their carbon. Aerobic and anaerobic metabolic
pathways are used by microorganisms to degrade organic waste. During aerobic respiration, the organism utilizes oxygen to break down complex organic compounds into simple in organic salts, carbon dioxide and water. These microorganisms require an electron acceptor (oxygen in the case of aerobic), nutrients such as nitrogen (N) and phosphorous (P), and other trace elements.
One of the most important characteristics of the waste is its biodegradability. Microorganisms can either directly use the contaminated waste and gain energy and carbon from it; or, with the help of another substance they can co-metabolically break down the contaminated waste. The biodegradability of a waste can be measured in the laboratory through BOD (5) / COD tests. BOD (biological oxygen demand) is a test through which contaminants can be categorized according to their biodegradability. COD (chemical oxygen demand) is a measure of the oxygen required to oxidize all compounds in water, both organic and inorganic. |
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| CHEMICAL TREATMENT |
| The technologies described in this section are chemical treatment technologies that are used for the cleanup of uncontrolled hazardous waste sites. In general, chemical treatments alter the structure of the waste constitutions to render them less hazardous than their original form. The objectives in using chemicals and chemical reaction are to either immobilize, mobilize for extraction, or detoxify the contaminants. A chemical technology may achieve one or all of the above tasks. Before describing any of the treatments in detail, a few points must be emphasized. |
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- The feasibility of chemical treatment is dependent on site and waste characteristics. Therefore, a careful study of site hydrology and geology must be performed before choosing teleology.
- Many chemical treatments involve delivery of a fluid to the subsurface. Care must be taken to avoid the migration of treatment reagents since they can be toxic themselves.
- Chemical treatment can be applied to both organic and inorganic wastes. However, a detailed study of the waste must be done, so that the wrong reagents are not mixed with the waster resulting in increased toxicity.
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| SEQUENTIAL BATH REACTOR FOR INTENSIVE BIOLOGICAL TREATMENT TO CRUD SEWAGE |
- The Sequential Batch Reactor combines
- The efficiency of activated sludge aeration with batch
- Treatment to provide exceptional efficient quality even
- Under extreme loadings.
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| BENEFITS AND FEATURES |
- Reduces main pollutants including ammonia by 95%.
- Reduces phosphates by 99% .
- Batching system eliminates peak surges.
- Fully recyclable.
- All components easily accessible.
- The SBR uses an aeration process known as activated sludge but operates on a storage and batch treatment cycle.
- Which ensures full treatment of all the effluent even under pack flow conditions.
- Circle sewage enters the primary Settlement Tank where gross solids settle out and the supernatant liquor.
- Remaining near the surface can be drawn off. Substantial buffer storage volume is provided to cope with even the most extreme peak flow loadings and aerated by a powerful air bubble diffusers for a period of 4 to 6 hours.
- During this aeration cycle efficient Oxygen transfer cultures of bacteria (the active sludge) which feeds on the sewage liquor thereby removing most of the organic pollutants. After carnation, the bubble diffuser is switched off and three is a setting period of two hours
- During which the dense activated sludge sinks to the bottom leaving behind the clarified
- Effluent, which is then discharged in to the drain.
- The SBR is an advanced biological aeration type treatment plant designed to produce a very high quality of final effluent in addition to overcoming several of the common problems
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| COMMON PROBLEMS, WHICH NORMALLY OCCUR, IN OTHER TREATMENT PLANTS |
- Peak surges flow (i.e. Mornings and evenings) can force effluent through the plant before it has had sufficient treatment time.
- Fixed film, types, which have a media matrix, can suffer from media blockage because of excessive bacteria growth. Replacement / maintenance of the media material may be required at regular intervals.
- Mechanical / electrical components within the tanks are difficult to maintain and can be a safety risk.
- The liquor is not spread evenly over the available bacteria preventing an adequate Oxygen supply.
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| The SBR overcomes these problems by Operating on a storage and batching system – storing the effluent at peak times in the primary settlement tank and treating in a small batches throughout rest of the day – thereby ensuring that each batch receives the full treatment time
There is no fixed media within the SBR to become blocked up it operates on the activated sludge, principal where by the bacteria float in suspension in the reactor and form an active mixed liquor.
There are no moving parts or electrical components hence.
The bacteria receives a high quality are supply and is completely mixed and aerated by the high volume. |
