PROCESS DESCRIPTION

BATCH SME STORMWATER AND CONSTRUCTION WATER TREATMENT SYSTEM

 

NEAT and Keeco, in development of the Canadian Marketing and Project Servicing Alliance, are offering the SME Keeco “Silt Settlement” Stormwater and Construction Water Treatment process and treatment systems to our clients.  The following will describe the process and trial testing that has been completed to date.  Please call us for further information and project estimates.  

 

Overview

 

KEECO, in conjunction with Aero Construction Company, has developed a batch treatment system for removing turbidity and heavy metals in stormwater using the Silica Micro Encapsulation (SME) technology.    A full-scale treatment system operating on a trial basis has undergone extensive review and testing by Washington state and City of Redmond officials, including water quality monitoring and bioassay testing.   The technology is currently pending approval by the State as a Best Management Practice for treating stormwater runoff.

 

The following process description applies to the batch system that has been constructed and tested.  The batch SME treatment system has been designed to process stormwater at a minimum effective flow rate of 100 gpm.  The system, as designed, does not include polymer addition to enhance settling.   Based upon bench-scale tests, it is estimated that polymers could reduce clarification time to allow for an effective process flow rate of 150 gpm or more.  The system design can be modified to include multiple units of the same size or scaled up to increase treatment capacity.  Alternately, a continuous flow system could be designed for more permanent installations.  Although this system has been demonstrated on stormwater, it should be equally effective on the treatment of water generated from dredging operations.

 

Process Description

 

Stormwater is pumped from a holding area into the Batch Mix Tank with the Feed Pump at an approximate rate of 1,500 gpm.  At this rate, the Batch Mix Tank can be filled in about 5 minutes.  Compressed air, piped into a distribution header in the bottom of the Batch Mix Tank, is regulated using valves located on each segment of the distribution header to provide even and thorough mixing of the water and treatment chemicals.

 

Approximately 10.6 liters of a dilute 3 percent ferric sulfate solution (0.56 gal ferric sulfate per 1,000 gallons water treated) are gravity drained from the Ferric Sulfate Drum to the Ferric Sulfate Air Pressurized Delivery Pot.  A calibrated sight glass is affixed to the delivery pot to measure the dispensed volume of ferric sulfate.  The delivery pot valving is then reversed to allow compressed air

to pressurize the pot.


Page 2.0                                                Keeco/NEAT SME Silt Settlement Process                   N.E.A.T. Environment, Inc.

 

Process Description….. Continued

 

The discharge valve is then opened, thereby transferring the solution through a flexible hose to a spray nozzle header located directly above the open top of the Batch Mix Tank for even distribution.  Ferric sulfate pretreatment adds an iron seed that enhances the precipitation and clarification process.   Approximately 7.5 liters of 33 percent sulfuric acid (0.4gal acid per 1,000 gallons water treated) are then dispensed from the Sulfuric Acid Drum into the Sulfuric Acid Air Pressurized Delivery Pot and transferred to the Batch Mix Tank in the same manner as the ferric sulfate through the same distribution header.  Through bench-scale testing, it was determined that sulfuric acid, added in an amount to provide a pH of approximately 2.85 to 3.0, results in the most effective treatment in conjunction with the SME slurry.  Sulfuric acid requirements may vary depending upon the initial pH and buffering capacity of the water to be treated.  The ferric sulfate and acid are allowed to mix for a couple of minutes until fairly uniform pH values are measured in the tank using a portable handheld pH probe.

 

A dilute slurry of the SME reagent META-LOCK (approximately 6.25 lbs. to 20gallons water) is made up in the SME Slurry Mix Tank using either fresh water or treated stormwater.   This usage rate equates to approximately 1.25 pounds of META-LOCK per 1,000 gallons of water treated.  The slurry is mixed in the Slurry Mix Tank via compressed air supplied to a distribution header.  The SME slurry is then pumped into the Batch Mix Tank with the air diaphragm Slurry Transfer Pump through a spray nozzle header adjacent to the ferric sulfate/acid delivery header.  The tank is allowed to mix for several minutes until a fairly uniform pH is observed using a portable handheld pH probe.  The target pH range is 6.5 to 8.5.  Additional META-LOCK slurry may be added as a final adjustment to pH if required. Valving to the Batch Mix Tank air mix header is shut off and the coagulated particulates (floc) are allowed to settle for approximately 30 minutes. 

 

After 30 minutes, the majority of the floc is settled to the bottom of the Batch Mix Tank.  Treated clarified water is then drained from the tank to the Detention Pond via a floating suction header to within about 8 to 12 inches of the tank bottom.  The 6-inch gravity discharge line provides a high rate of flow averaging about 750 gpm, draining the tank in about 7 minutes.  The total processing time for one batch is approximately 45 minutes.

 

The Batch Mix Tank is then refilled and the process repeated.  While this takes place, the water in the Detention Pond is discharged, pumping the water with the Filter Feed Pump through one train of the 5-micron Bag Filters to the selected discharge location.  The Bag Filters serve as a backup to ensure that excess solids are not discharged.

 

The solids collected in the Batch Mix tank are allowed to remain in the tank for successive treatments as solids recycle improve the floc settling characteristics.  When the sludge height builds up to approximately 6 inches, the sludge is pumped off to within about 2 inches of the bottom via the Sludge Pump that is connected to the sludge collection manifold in the tank bottom.  The sludge can be temporarily stored in a small portable holding tank or disposed of either onsite or off site.