Contamination of ground waters has occurred at many locations due to factors such as leaking underground storage tanks LUST Sites) and improper chemical disposal practices. Often, the major contaminants are petroleum hydrocarbons such as gasoline, jet fuel, or VOC’s (volatile organic compounds) such as BTEX (BTEX is an acronym for benzene, toluene, ethylbenzene, and xylene. This group of volatile organic compounds (VOCs) is found in petroleum hydrocarbons, such as gasoline, and other common environmental contaminants).
The ground water remediation process is designed to prevent the further spread of the contamination and to remove the volatile contaminants. Extraction wells are drilled around the perimeter of the contamination zone and the water is pumped out for pressing through an air stripper.
After remediation, the purified water may be pumped back into the ground utilizing injection wells. These wells are located such that the injected water forces the contaminated water toward the extraction wells.
The typical method to reduce and remove soluble electroplating metals from wastewater is as follows:
Stage 1– Precipitation and Coagulation:
pH is raised from ~3 to 8.5 with the pH controller using caustic while adding a coagulant such as ferric chloride. Testing of the wastewater may confirm that a coagulant is not needed. A “pin floc” is developed indicating the metal is insoluble. Some applications have plating enhancing chemicals present, emulsifiers and such that may require more sophisticated high performance coagulants to break the bonds and allow the metal to precipitate.
Stage 2 - Flash Mix:
The wastewater with it’s precipitated pin floc is introduced to the flash mix zone where a polymer flocculent is added. This stage maximizes flocculent dispersion throughout the coagulated wastewater.
Stage 3 - Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate the pin floc into larger rapid settling particles.
Clarifier, Inclined Plate:
The flocculated wastewater is introduced into the clarifier where the settling particles land on the inclined plates and are directed downward and into the sludge chamber. The clarified treated water then exits the top of the clarifier and flows downstream to sewer or further treatment if necessary.
Clarifier Sludge Handling:
The resulting clarifier waste sludge is periodically removed from the clarifier at a slow rate and sent to the sludge holding tank where it further thickens and accumulates a batch for disposal or processing in a filter press.
The thickened clarifier sludge is allowed to accumulate sufficiently to provide a full batch for the Filter Press. The filter press is pumped full of the sludge until it is full. The filter press is then emptied of the “cake” which is a semi solid of approximately 20-35 % solids. Sludge cake is high in phosphate and should be disposed of according to environmental regulations.
Air stripping is used for removal of VOC’s and petroleum hydrocarbons on small packaged systems. To prevent fouling of the air stripping column, iron in solution must be removed prior to the stripper.
Iron may be removed by converting the soluble iron to the hydroxide form or by oxidizing to ferric oxide. Although the sludge produced in either case can be dewatered in a filter press, the oxide form is easier to dewater than the hydroxide form. A small amount of bodyfeed or other conditioning chemicals may be required to produce acceptable filter cakes.
Ground Water Remediation Sites