Groundwater Remediation at a Landfill
Hexavalent Chrome Waste Treatment & Chrome Reduction Systems

Remediation of Contaminated Groundwater at a Landfill

Project Condition:  Ground water at the landfill of a military base was contaminated with Arsenic (As) at a very low level of 22 ppb, Manganese (Mn) at 1.7 ppm and Iron (Fe) at 47 ppm. These metal levels were higher than the discharge limits required by the county water board. The base was looking for the best available process treatment system to meet metals discharge requirements.

Unit description:  The system is fully automated with an Allen Bradley PLC and a SCADA system running on a Wonderware software system. Two carbon bed filters are used for secondary treatment and for removal of anticipated low levels of organics. Three LMI metering pumps are used for the dosing of MetFloc™ chemicals. These are injected in-line through static mixers. Because of the very low amount of sludge produced, an automated gravity bed filter with a 25-micron filter paper is used for filtration of solids. The piping for the unit is PVC schedule 80.

Process Run:  Well water is then pumped to an equalization tank and through the treatment system. The MetFloc™ chemicals are proportionally injected in-line based on pre-determined dosage rates. The reaction is very fast. The treated water is then pumped through the gravity bed filter to remove the solids and then to an intermediate holding tank. The water is then pumped through two carbon bed filters and then to a clean water holding tank. From here the water is pumped to a 30,000-gallon storage tank. The tanks are equipped with a sprinkler, and the water is used for dust suppression and irrigation at the landfill.

Project Results:  Over a six-year project period, quarterly samples were sent to an independent US EPA certified lab for analysis before and after treatment. The results were always below regulatory agency discharge limits

Metal type	Average before treatment	Average after treatment
Arsenic (As)	22 ppb (µg/L)	9 ppb (µg/L)
Manganese (Mn)	1.7 ppm (mg/L)	0.220 ppm (mg/L)
Iron (Fe)	47 ppm (mg/L)	0.375 ppm (mg/L)

 

Hexavalent Chrome Waste Treatment
& Chrome Reduction Systems

Electroplating metals is a common way to provide corrosion resistant properties to products. After the electroplating is completed, the plated parts are rinsed with water. This rinse water will become contaminated with time and must be replaced. The rinse water will have a high concentration of toxic material including chromates, copper, or zinc that must be treated before dumping to the sewer or reusing.

MetFloc™ technology is a highly efficient and cost effective advanced treatment process for total chrome reduction that eliminates the multiple treatment steps associated with conventional processes. The residence time is very short, eliminating the need for large holding tanks. The intermediate step of reducing hexavalent chrome to trivalent chrome is eliminated. MetFloc works with the initial waste, in this case, with a pH of 3.5 and converts chromium to a stable hydroxide. All metals of concern in this case are eliminated in one treatment step to below the local discharge limits. Secondary pH adjustment is also eliminated since MetFloc raises the pH to above pH 6. The MetFloc™ treatment process also produces 20 – 50% less sludge. The flocs are dense, large and highly dewaterable. Pin flocs are eliminated. No filter aid is required for the sludge in the filter press. The sludge produced is highly stable and passes the Toxicity Characteristics Leaching Procedure (TCLP).

Some discharge authorities are now testing for total chrome and not just hexavalent or trivalent chrome (Cr +6 or Cr +3.)  The MetFloc process is uniquely capable of reducing total chrome below discharge limits. The reduction of chemicals, ease of operation, cost advantages, faster treatment times and better sludge make this revolutionary process worth evaluating. 

Analytical lab results

Metal type	Before treatment (ppm)	After treatment (ppm)	Local limits (ppm)
Hexavalent chrome (Cr)	683	0.03	1.71.
Cadmium (Cd)	366	0.02	0.26
Zinc (Zn)	32	0.001	1.38
Copper (Cu)	469	0.001	2.05
Lead (Pb)	411	0.02	0.43
Nickel (Ni)	243	0.21	2.38