Wastewater treatment process

DETAILED DESCRIPTION Wastewater is treated to remove pollutional factors such as biochemical oxygen demand (BOD), nitrogen, color and toxic substances, using one to four fixed media filters in combination with a powdered adsorbent.
In one form of the invention, powdered adsorbent which will remove impurities from the wastewater is added to the wastewater and the mixture is passed downward through a fixed media filter having microorganisms attached to the media.
Air is passed by natural convection or forced ventilation through the filter, either upward or downward.
In another aspect of the invention, a portion of the adsorbent-wastewater mixture or clarified wastewater which has passed through the filter may be recycled to the filter inlet.
This portion is equivalent in volume of up to 300 percent of the influent wastewater.
The adsorbent in the remaining portion of adsorbent-wastewater mixture from the fixed media filter is separated from the mixture as a concentrated slurry.
It is optionally recycled to the inlet of the fixed media filter where it is mixed with further portions of influent wastewater.
A portion may be removed intermittently or continuously for regeneration and recycle to the incoming wastewater.
Alternately, a portion occasionally may be removed for disposal, particularly if disposal is less expensive than regeneration.
Such disposal may be preferred for very small wastewater treatment plants where regeneration costs per ton of adsorbent are high.
In one aspect of this invention, operation of a single-stage (i.
e.
one fixed media filter) continuous system utilizes the steps of: (a) adding to the wastewater an adsorbent capable of adsorbing impurities from said wastewater, forming a mixture thereby; (b) continuously passing said mixture downward through a fixed media filter through which air passes by natural or forced ventilation and having microorganisms attached to the media, wherein wastewater, adsorbent, microorganisms and air are contacted; (c) returning a portion of said mixture which has passed through the fixed media filter in step (b) to the influent wastewater in step (a), in volume equivalent to up to 300 percent of said influent wastewater; and (d) passing remainder of said mixture from the fixed media filter to a quiescent settling-clarification zone where the settleable solids separate from the treated wastewater