Water Treatment Technologies

Author: Paul Bratti
Bio: Paul Bratti has been with Clean Harbors Environmental Services for 25 years. As the Vice President of the North American Remediation Group he has managed many aspects of the Company’s core business lines including Field Services, Emergency Response, Project and Remediation Technologies. Based at the Company’s corporate headquarters in Norwell, MA, Paul manages more than 120 employees throughout the U.S. and Canada.
Summary: The plant previously had a number of discharge issues with predominant discharge contaminates of Cadmium (Cd), Chromium (Cr), and Zinc (Zn). Levels of 0.24, 5.80, and 1.20 mg/l respectively, were recorded at the last pre-system sampling event. After the system was installed the tested levels were less than 0.05, 0.29, and 0.07 mg/l respectively. This allowed the plant to meet its discharge limits, thereby avoiding costly fines and penalties.

The remediation process itself consists of a number of pre-filtration steps that could include chemical clarifier treatment, sand filters and/or bag filters to remove most of the contaminants before activated carbon cleansing. This minimizes the amount of carbon consumed by the process, reduces the replacement frequency and saves money while delivering more consistent results. The treatment facilities are sized to the process or project with treatment systems ranging from 150 lb systems to 150,000 lb systems.

In a typical water filtration application resulting from dewatered solids, the water is drawn from equalization (EQ) tanks and pumped through a sedimentation clarifier. The clarifier process typically uses a multiple-tank array. In a multiple-tank array the first tank is a coagulation tank where a coagulant, such as ferric chloride (FeCl3) is added. The ferric chloride starts the pin floc process.

The material is then pumped to the second tank – the flocculation tank, where a polyacrylamide polymer is added to complete the floc formation and speed sedimentation. The clarified water goes through a set of lamella plates to keep turbulence down as the clean water spills over to a clear well and gravitates to the next stage of the treatment process. The solids are pulled from the bottom of the clarifier tank with sand pumps and returned to sediment processing.

The clarified water is moved to a surge tank where it is stored until it is pumped through MultiMedia Filters (MMF) to remove any solids carried over from sedimentation.

Next, the water is moved through bag filters utilizing different micron-sized bags – typically 1 to 25 microns, to complete the solids removal treatment. Filtration efficiency of the bags is determined based on water quality to maximize the protection to the media filters.

After the bag filters, the water is processed through the activated carbon filtering process. Following the final carbon stage the water passes through a discharge flow meter and an inline turbidity meter that alerts the operators in real time if the water quality is below specification. The finished water is normally sent to the discharge. However, the finished water can also be diverted to storage tanks for use in backwashing and as a clean water supply to sediment processing. The entire process is controlled by Programmable Logic Control (PLC) modules and Variable Frequency Drives (VFD).

Categories: Custom Built Remediation Systems, Water Treatment Equipment