MetFloc Process Compared to Other Processes for Metal Removal from Wastewater

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MetFloc™ Process Compared to Other Processes for Metal Removal from Wastewater

Assessment of Chemical Processes
for Metal Removal from Wastewater

Sample Type	Process	Suitability
Highly acidic multi-metal waste solution with As, Cr(VI), Ni, Cd, Zn, Pb, Se, V, Fe, Al.	MetFloc process	Excellent. Not pH sensitive. Maximum removal of all metals in ONE pH treatment cycle. No intermediate step to reduce Cr(VI) to Cr(III).
	Hydroxide precipitation (caustic soda / lime)	Precision multiple pH adjustments required. Maximum removal not possible for all the metals in solution. Intermediate step to reduce Cr(VI) to Cr(III) can produce noxious gases. Amphoteric (dual solubility curves) property of Zn can also affect removal rates.
	Iron / Alum absorption / coprecipitation	Precision multiple pH adjustments required. Maximum removal not possible for all the metals in solution. Intermediate step to reduce Vr(VI) to Cr(III). Amphoteric (dual solubility curves) property of Zn can also affect removal rates.
	Sulfate precipitation	Precision multiple pH adjustments required. Maximum removal not possible for all the metals in solution.
	Thiocarbamates	Effective, but process depends on pre- and post-treatment. pH-sensitive steps.
	Electrochemical cells	Presences of free native Fe and Al ions interferes with the electro-chemical generation of free Fe and Al ions, a critical step in the process.
	Resin beds	Competition for adsorption sites by the various metals will drastically reduce resin beds of adsorption capacity/ Cr(VI) is poorly released fro the anion resin bed. Presence of Fe can also be a problem.
Spent plating bath chelated / complexed with ammonia sulfates; Cr(VI); Zn.	MetFloc process	ONE cycle maximum removal off all metals even in the presence of interfering agents.
	Hydroxide precipitation	Not effective in the presence of interfering agents.
	Iron / Alum absorption / coprecipitation	Not effective in the presence of interfering agents.
	Sulfate precipitation	Can be effective in the presence of interfering agents, but hazardous fumes of hydrogen sulfide gas can be a safety problem.
	Thiocarbamates	Can be effective in the presence of interfering agents.
	Electrochemical cells	Not effective in the presence of interfering agents.
	Resin beds	Interfering agents will render the beds inoperable.
Spent plating bath complexed with surfactants and ethylene diamine tetra acetic acid (EDTA); sequestering agents; Cu; Sn, Pb.	MetFloc process	ONE cycle maximum removal off all metals even in the presence of interfering agents.
	Hydroxide precipitation	Not effective in the presence of EDTA.
	Iron / Alum absorption / coprecipitation	Not effective in the presence of EDTA.
	Sulfate precipitation	Effective, but hydrogen sulfide gas emission can be a safety issue.
	Thiocarbamates	Can be effective in the presence of interfering agents.
	Electrochemical cells	Not effective.
	Resin beds	Not effective.
Mining metal-laden wastewater high in Biochemical Oxygen Demands (BODs); Cu; Fe.	MetFloc process	Maximum removal of metals and reduction of BODs.
	Hydroxide precipitation	Not effective.
	Iron / Alum absorption / coprecipitation	Not effective.
	Sulfate precipitation	Not effective.
	Thiocarbamates	Not effective.
	Electrochemical cells	Not effective.
	Resin beds	Not effective.
Aircraft maintenance strip shop; Phenols; Cd; Ni; Zn; Fe; Cr(VI); Cu; low levels of organics, oil & grease.	MetFloc process	Maximum removal of metals; reduction of Phenols and other organics.
	Hydroxide precipitation	Not effective.
	Iron / Alum absorption / coprecipitation	Not effective.
	Sulfate precipitation	Not effective.
	Thiocarbamates	Not effective.
	Electrochemical cells	Not effective.
	Resin beds	Not effective.

Sensitivity to Process Control Variables
in Metal Removal from Wastewater

Sample Type	Process	Suitability
Effect of Ph variations	MetFloc process	Process is not pH min sensitive. Metals precipitated out of solution will not dissolve back into solution with a shift away from their pH min.
	Hydroxide precipitation (caustic solda / lime)	There is a pH min for every metal to precipitate out of solution. Precipitated metals will dissolve back into solution when there is a shift away from their pH min.
	Iron / Alum absorption / coprecipitation	Metals in solution are riding on individual solubility curves. Precipitated metals will dissolve back into solution when there is a shift away from their pH min.
	Sulfate precipitation	There is a pH min for every metal to precipitate out of solution. Precipitated metals will dissolve back into solution when there is a shift away from their pH min.
	Thiocarbamates	Depends on pH-sensitive reactants for pre- and post-treatment reactions.
	Electrochemical cells	Depends on pH-sensitive Fe/Al free ions to achieve performance results. Runaway soluble excess ferrous ions need to be oxidized to the insoluble ferric form for precipitation to occur. Need an oxidizer.
	Resin beds	Optimal performance of cationic and anionic resin beds is pH dependent.
Secondary pH adjustment	MetFloc process	Not required.
	Hydroxide precipitation	Required.
	Iron / Alum absorption / coprecipitation	Required.
	Sulfate precipitation	Required.
	Thiocarbamates	Required.
	Electrochemical cells	Required.
	Resin beds	pH adjustment required for regeneration of resin beds.
Presence of chelated / complexing / sequestering agents and surfactants.	MetFloc process	Process is still highly efficient even in their presence.
	Hydroxide precipitation	Process is not effective in their presence.
	Iron / Alum absorption / coprecipitation	Process is not effective in their presence.
	Sulfate precipitation	Effective in their presence, but emission of hazardous hydrogen sulfide gas in highly acidic or alkaline waste solutions is a safety problem.
	Thiocarbamates	Can handle only if pre-treatment stage is effective.
	Electrochemical cells	Free Fe/Al ions are not effective in the presence of chelating / complexing agents and surfactants.
	Resin beds	Their presence will render resin beds inoperable.
Clarifier retention time.	MetFloc process	Very fast. Less than 1 minute.
	Hydroxide precipitation	5 to 30 minutes.
	Iron / Alum absorption / coprecipitation	5 to 30 minutes.
	Sulfate precipitation	5 to 30 minutes.
	Thiocarbamates	5 to 30 minutes.
	Electrochemical cells	5 to 30 minutes.
	Resin beds	Not applicable.
Sludge volume and profile.	MetFloc process	Low volume of sludge, highly dewaterable.
	Hydroxide precipitation	Excess lime can lead to the precipitation of gypsum. Sludge can be slimy, dense, and hard to dewater.
	Iron / Alum absorption / coprecipitation	High sludge blanked can become thickening limited for the clarifier.
	Sulfate precipitation	Metal sulfide sludge can be hazardous.
	Thiocarbamates	Low sludge, but can increase due to pre-treatment step.
	Electrochemical cells	Low volume.
	Resin beds	Large volume of water needed to regenerate resin beds.