Stormwater Treatment Technology
Industrial storm water discharge results can vary depending on the size of a facility, the materials that are stored on the facility, the transportation activity on the facility and the mentality and attitude of all of the employees working in a facility. Because of this wide variance there is not one treatment technology designed to handle everything. Below are the different types of mechanical and enhanced treatments available from Storm Water Systems.
Clarifiers are designed to be installed below grade to allow the storm water to flow via gravity and are designed to reduce heavy solids and O&G. Gravity flow is important as the free oils need to be kept separate from the storm water so separation may take place in the clarifier. If the storm water is pumped into the clarifier, the free oils may become emulsified and not separate inside the clarifier. Also, it is important to have an “Off Line” clarifier to keep a large storm event from scouring the clarifier and washing out all of the contaminants previously trapped inside. The clarifier can also be used as a pump basin if downstream treatment is needed.
Flocculants are an environmentally safe and economical treatment option. Storm Water Systems offers them in both solid and liquid forms and should be installed up stream of a clarifier or mechanical filter. Flocculants are substances which cause small particles to stick together thereby forming larger particles which both settle and filter more easily.
Additionally, flocculants can encapsulate oils and greases, also allowing these materials to be settled and filtered. Solid flocculants typically come in a sock to be placed on the ground where the storm water will be forced to flow through it. Liquid flocculants should be injected into a clarifier or mixing tank and allow ample time for the coagulation to take place.
Sand filters are pressure vessels filled with sand and are designed to remove solids down to 75 – 100 micron in size. The filters have an automated backwash sequence that can be determined by time or pressure and the backwash water should be filtered as well to keep the solids from re-entering the treatment system. The sand filter protects the downstream enhanced treatment technology that can be harmed by a large volume of solids. This technology is a very good first step BMP for sites with heavy solids.
Bag Filters are designed to remove very small solids and can come in many sizes. Bag filters are the last mechanical filtration before the storm water is treated with enhanced medias. These enhanced media vessels can plug if too high of a level of solids is introduced to them and some contaminants can actually damage enhanced medias so it is very important to remove as much of the solids as possible up stream. Storm Water Systems typically installs both a 25 micron and 10 micron bag filter prior to enhanced media treatment.
Enhanced medias are designed to remove organics, nutrients, and dissolved metals. Certain medias are designed to remove certain contaminants and there is no one media that can remove everything. Also, enhanced medias need time to work so the larger the media vessel is the better removal rates will be achieved. Storm water effluent data should be evaluated carefully to determine how much and what type of medias should be used and in what order they should be installed. This is critical to achieve benchmarks.
(last updated March 13, 2013)