With increased knowledge of the constituents found in wastewater, the limits for discharge of effluents containing certain compounds are becoming increasingly more strict. Permit requirements for the discharge of an effluent may include the removal of suspended solids, organic matter, nutrients and specific toxic substances in levels that are not achieved by conventional primary and secondary treatments. The poor water resources available in some areas created the need of reusing treated wastewater, turning the limits for the presence of certain compounds more restrict.
This page presents three
treatment processes.
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Adsorption is usually used on the removal of refractory organics, present in many industrial effluents. These organics are difficult or impossible to remove by conventional biological treatment processes. It is also usual the removal of heavy metals by adsorption. The most commonly used adsorbent is activated carbon.
A solid surface in contact with a solution tends to accumulate a surface layer of solute molecules because of the unbalance of surface forces.
Activated carbons are made of a variety of materials. The most common are bituminous coal and lignite. Granular carbons obtained from these materials have been most widely applied to the wastewater treatment. Activated carbon can also be produced by roasting organic material to transform it in granular carbon. Activated carbons have specific properties depending on the material source and the mode of activation. Property standards are helpful in specifying carbons for a specific application.
Adsorptive capacity is the effectiveness of the carbon removing desired constituents such as COD, colour, phenol, etc., from the wastewater. Depending on the characteristics of the wastewater, one type of carbon may be superior to another since the capacity is greater at equilibrium effluent concentrations.
It is generally feasible to regenerate spent carbon for economic reasons. In the regeneration process, the object is to remove from the carbon pore structure the previously adsorbed materials. The modes of regeneration are thermal, steam, solvent extraction, acid or base treatment, and chemical oxidation.
Filtration is a mechanical method for separation. Its main goal in wastewater treatmente is the removal of suspended solids or flocs resulting of coagulation/floculation operations.
This method consists in forcing the flow on to a porous structure, the filter, which will retain the particles bigger than the porous dimension. One of the most important aspect about filtration us that the removed solids become the filtering surface. The removal of particles from water by an operation of filtration depends greatly on the size of the particles. For the bigger particles, its easier to apply, bat for the smaller ones, using filtration can become very expensive.
There are several filtration equipments, but not all of them are viable for effluent treatment. Sand and rotary filters are some of the filtering systems commonly used in wastewater treatment.
Besides wastewater treatment, filtration can also be used in the dehydration of sludges resulting of other treatment processes.