Hybrid Biological Treatment of Polluted Water
Hybrid biological treatment processes are designed to utilize the same breakdown mechanisms employed by nature to degrade nutrients, but may also include other physical processes as well.
Toxic chemicals that persist in nature, such as heavy metals, can survive sewage treatment systems and where they are present and must be removed, a wide variety of what are termed 'hybrid biological treatment systems' are being used.
Also those chemicals essential to life in small quantities, such as common salt, may also be damaging to the environment if they exceed certain levels.
Biological treatment has always been the most important application for water treatment worldwide.
Within the next 10 years some say that as much as one third of all the world's surface water in rivers and streams will be being used by man in some way, and they must be kept clean for these uses.
Biological treatment is still the obvious and accepted best choice to do the majority of the treatment needed.
Increasingly, higher water discharge quality is being required and additional substances must now be removed in addition to the simple biologically treatable contaminants.
Simple biological treatment by aeration in the presence of a biological sludge, alone, will no longer be adequate as population pressure on watercourses increases.
Population growth is reducing the ability of water regulators to allow the use of the old standby of relying on the ample dilution available when a small sewage works discharges its treated effluent into a large river.
In other words, it used to be acceptable to use the natural processes in our rivers to complete the job we started but only 80% (say) completed, in our sewage works, but is becoming much less so.
Municipal sewage treatment plant designers are increasingly working with the principle of hybrid biological treatment, and the traditional biological sewage works treatment by oxidation alone followed by solids removal is being augmented by nitrification and now also at times, denitrification treatment.
In addition to biological contamination always removed in sewage works, and as mentioned earlier, those substances such as common salt in sewage, which did not used to be controlled in the discharges from sewage treatment works, are now being controlled.
This is due to problems in arid climates with rising salinity in the ground, causing crop loss, and even failure.
Biological treatment is, as a result needing to be developed into something more sophisticated and include other technologies.
There are many things driving this as well as discharge quality improvement and higher environmental standards, and these include the pressing need to use less space, treat difficult waste, deal with intermittent flows, and keep costs down.
To meet this challenge, a number of different designs of hybrid treatment plants have been produced.
Such plants often combine at least two stages of the three main treatment stages into one combined stage.
In the rural areas of most nations where a large number of sewage treatment plants serve small populations, package plants are particularly important.
At these plant it is necessary to combine the complexity of a hybrid process, at a small scale, and without excessive capital cost.
So hybrid plants have been developed to combine aeration, settlement, and even at some an anoxic treatment stage.
This is done all in one tank, and these plants have become a realistic alternative to building separate dedicated structures for each process stage.
The success of these small schemes has recently lead to similar savings being achieved in much larger plants.
The best known type of system that combines secondary treatment and settlement is the Sequencing Batch Reactor (SBR).
In these, the incoming raw sewage is mixed with activated sludge and then further mixed and aerated.
The resultant mixture (mixed liquor) is then allowed to settle producing a high quality effluent.
The settled sludge tends to build-up, so it is pumped out on a regular basis and thickened and taken away for disposal.
SBR plants are now being deployed in many parts of the world including the United Kingdom, the United States, and even developing nations which seek to minimize their capital investment and benefit from hybrid technologies in water treatment used first in the developed nations.
India for example has recently adopted a policy to install SBR sewage treatment in many areas.
The following processes have been included in hybrid biological treatment plants, and no doubt there are others not mentioned here: - wet oxidation - stripping - anoxic biological treatment - membranes from micro-strainers, to Ultrafiltration to Reverse Osmosis - BAF units (Biological Aerated Filters) - DAF units (Dissolved Air Flotation) - RBCs (Rotating Biological Contactors) - Activated Carbon Absorption.
Toxic chemicals that persist in nature, such as heavy metals, can survive sewage treatment systems and where they are present and must be removed, a wide variety of what are termed 'hybrid biological treatment systems' are being used.
Also those chemicals essential to life in small quantities, such as common salt, may also be damaging to the environment if they exceed certain levels.
Biological treatment has always been the most important application for water treatment worldwide.
Within the next 10 years some say that as much as one third of all the world's surface water in rivers and streams will be being used by man in some way, and they must be kept clean for these uses.
Biological treatment is still the obvious and accepted best choice to do the majority of the treatment needed.
Increasingly, higher water discharge quality is being required and additional substances must now be removed in addition to the simple biologically treatable contaminants.
Simple biological treatment by aeration in the presence of a biological sludge, alone, will no longer be adequate as population pressure on watercourses increases.
Population growth is reducing the ability of water regulators to allow the use of the old standby of relying on the ample dilution available when a small sewage works discharges its treated effluent into a large river.
In other words, it used to be acceptable to use the natural processes in our rivers to complete the job we started but only 80% (say) completed, in our sewage works, but is becoming much less so.
Municipal sewage treatment plant designers are increasingly working with the principle of hybrid biological treatment, and the traditional biological sewage works treatment by oxidation alone followed by solids removal is being augmented by nitrification and now also at times, denitrification treatment.
In addition to biological contamination always removed in sewage works, and as mentioned earlier, those substances such as common salt in sewage, which did not used to be controlled in the discharges from sewage treatment works, are now being controlled.
This is due to problems in arid climates with rising salinity in the ground, causing crop loss, and even failure.
Biological treatment is, as a result needing to be developed into something more sophisticated and include other technologies.
There are many things driving this as well as discharge quality improvement and higher environmental standards, and these include the pressing need to use less space, treat difficult waste, deal with intermittent flows, and keep costs down.
To meet this challenge, a number of different designs of hybrid treatment plants have been produced.
Such plants often combine at least two stages of the three main treatment stages into one combined stage.
In the rural areas of most nations where a large number of sewage treatment plants serve small populations, package plants are particularly important.
At these plant it is necessary to combine the complexity of a hybrid process, at a small scale, and without excessive capital cost.
So hybrid plants have been developed to combine aeration, settlement, and even at some an anoxic treatment stage.
This is done all in one tank, and these plants have become a realistic alternative to building separate dedicated structures for each process stage.
The success of these small schemes has recently lead to similar savings being achieved in much larger plants.
The best known type of system that combines secondary treatment and settlement is the Sequencing Batch Reactor (SBR).
In these, the incoming raw sewage is mixed with activated sludge and then further mixed and aerated.
The resultant mixture (mixed liquor) is then allowed to settle producing a high quality effluent.
The settled sludge tends to build-up, so it is pumped out on a regular basis and thickened and taken away for disposal.
SBR plants are now being deployed in many parts of the world including the United Kingdom, the United States, and even developing nations which seek to minimize their capital investment and benefit from hybrid technologies in water treatment used first in the developed nations.
India for example has recently adopted a policy to install SBR sewage treatment in many areas.
The following processes have been included in hybrid biological treatment plants, and no doubt there are others not mentioned here: - wet oxidation - stripping - anoxic biological treatment - membranes from micro-strainers, to Ultrafiltration to Reverse Osmosis - BAF units (Biological Aerated Filters) - DAF units (Dissolved Air Flotation) - RBCs (Rotating Biological Contactors) - Activated Carbon Absorption.
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