Industrial Waste Treatment Handbook, Second Edition

Physical Methods of Wastewater Treatment

Physical methods of wastewater treatment accomplish removal of substances by use of naturally occurring forces, such as gravity, electrical attraction, and van der Waal forces, as well as by use of physical barriers. In general, the mechanisms involved in physical treatment do not result in changes in chemical structure of the target substances. In some cases, physical state is changed, as in vaporization, and often dispersed substances are caused to agglomerate, as happens during filtration.

Physical methods of wastewater treatment include sedimentation, flotation, and adsorption, as well as barriers such as bar racks, screens, deep bed filters, and membranes.

Separation Using Physical Barriers

There are many separation processes that make use of a physical barrier through which the target pollutants cannot pass, simply because of their size. These physical barriers are classified according to the size of the passageways through which all but the target pollutants (and larger) can pass, and they range from bar racks to reverse osmosis. Bar racks, screens, and sieves are considered to be either part of the headworks or part of primary treatment, while filters, microscreens, dialysis processes, and reverse osmosis are normally considered either secondary or tertiary treatment, depending on specific use.

In the cases of the physical barriers with smaller pores (filters and microscreens, for instance), particles are often caught on the barrier bridge cross the openings and form a filter themselves. For some substances, this surface filter is very effective with respect to degree of...

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