Baffles within wastewater reservoirs increase the overall retention time, or HRT, by creating a longer path for the water to travel. This is done through flow diversion or by forcing the water to travel through alternating windows or gaps formed by the baffles within the reservoir or tank. A longer HRT maximizes the treatment/contact time of the contained water. Baffles controlling the flow of water prevents dead zones where water may escape the current and remain stagnant. Dead zones can cause improper treatment times, imbalances in oxygen levels, and uneven levels of sedimentation. Floating baffles used in wastewater treatment improve settling and retention time, eliminate dead zones, and increase chlorine contact time.
The Safe Drinking Water Act has specific requirements that wastewater treatment designs are held to. This includes how long water undergoes treatment or is exposed to disinfectants. This is typically measured by the “CT” calculation, or C x T, where C is equal to the concentration of disinfectants in the water, and T is the total contact time in minutes. This is directly related to HRT and is therefore, typically guaranteed by the addition of baffles in order to redirect flow and assure proper retention time in each step.
Mixing is also an essential step when it comes to biological processing; more movement means more contact between microorganisms and the organic matter/waste that they’re looking for. Baffles interrupting water flow already assists in mixing the contents, and other additions can be made to improve mixing even further. This can be done via aeration and bubbling, mechanical mixers, or by using perforated or porous baffles that increase friction when water passes by.
TSS and BOD are two of the most important measurements when it comes to wastewater treatment. TSS refers to total suspended solids, or the measure of particles and sediment suspended within the water. BOD is biochemical or biological oxygen demand and refers to the amount of oxygen being required by decaying organic matter or waste from the water. Suspended solids can contain chemicals, toxins, and hard metals trapped within the material. These floating debris and sediment can also cause serious damage to pipes, tanks, and other equipment throughout the water transportation system. Too much demand for oxygen within water can kill off necessary microbes, and any larger critters within the water.
TSS and BOD levels within treated water are carefully regulated, and can be directly controlled by aeration, filtration, proper HRT, and frequent maintenance.
Clear well treatment for potable water.
Clear well tanks are reservoirs within a water treatment system, usually within the final stages of treatment. This is where chlorine is applied to incoming water and is used to retain water long enough in order to ensure proper treatment time.
A clear well curtain or baffle is used to extend water circuits. Like in the earlier stages of wastewater treatment, this longer path increases the water’s contact time with chlorine and other disinfectants in order to be safe for consumption and human use. Potable water is protected and regulated underneath the Safe Drinking Water Act, which has specific requirements that clearwater chambers will need to meet. This is typically measured by the “CT” calculation, or C x T, where C is equal to the concentration of disinfectants in the water, and T is the total contact time in minutes. The required CT for chlorine will change depending on the temperature of the water, and its pH level.
Turbidity control
The measurement of the dissolved solids and particles within water is known as the Total Suspended Solids (TSS). As the TSS in a natural body of water increases, less sunlight can permeate the water, and more sediment is picked up with erosion. This can suffocate or smother fish and plants, as well as carry chemicals trapped within sediment further downstream. In and around construction sites, and some industrial or agricultural areas, waterways are carefully checked for levels of turbidity due to runoff from upstream. Local regulations will specify acceptable levels of turbidity in your particular area. In some places, there may be fees associated with sediment and runoff which breach these levels.
Baffles, in the form of turbidity or silt curtains, can majorly reduce the amount of suspended sediment in a body of water. These are unique in that they aren’t typically meant to do much in the way of water flow diversion; however, solids are trapped and chemicals and metals therein and trapped in turn.
DOT Turbidity Curtain Classifications
Type I
You’ll most often see Type 1 turbidity curtains in places with milder conditions. Ponds, small lakes, and marshes are less likely to have the strong winds or currents that necessitate a higher-level curtain. These can be entirely made of PVC, or may include a filtering, permeable window for water to pass through. These skirts can extend up to 100 ft, depending on the needs of your particular project.
Type II
Type 2 turbidity curtains are most often found in larger lakes, intercoastal areas, and other waterways with mild waves, currents, or wind. Like their other counterparts, these curtains can be completely PVC, completely impermeable to water and solids or, can include a filtering window that allows some water to pass through. These curtains are more durable than Type 1 curtains but aren't quite as heavy-duty as Type 3.
Type III
Type 3 curtains, the heaviest duty version of the DOT turbidity curtains, are meant to withstand stronger winds, waves, and faster currents. You'll most often find these curtains in or around shorelines or fast, deep rivers. These curtains are built with the thickest fabric and have the highest load-bearing capacity as well as breaking point. They'll often involve a secondary steel cable that runs throughout the top and bottom of the curtain, providing extra structure.
Dredging Projects
Placing turbidity or baffle curtains around your dredging project will allow you to control particles and sediment picked up from the bottom of the lake or waterway. Sludge can be caught in submerged curtains on the bottom of the floor or caught in the form of scum on the top of the water. Afterwards, you can either allow the sediment to settle with time or pull out the excess sediment yourself. In most cases, sediment can be removed by using a debris pump to pull it from within the containment area and deposit it in dewatering bags. These bags serve as filters, trapping sediment within and allowing clean water to flow out. These work best in a place where the clean water flows into the original body of water.
