Floating covers are flexible, adaptable, and function remarkably well to improve efficiency in wastewater processing. However, floating covers don't work alone to keep a pond or tank covered when difficult conditions such as gas accumulation, wind lifting, or rain and snow weight add to the load. This is where accessories like floats, supports, rails, tensioners, and even automatic retraction mechanisms come in. Pumps and other drainage equipment are also necessary since covers made with impermeable geomembranes, by design, won't drain on their own when filled with rainwater.
Floats and Supports
Almost all floating covers need additional buoyancy because most liner materials, including relatively thin and light polymer geomembranes, are heavier than water and are likely to sink at the first minor rain. Floating covers need to 1) maintain high tension across the cover to keep the surface flat and featureless, minimizing exposure to wind. 2) maintain neutral buoyancy and keep the cover resting directly on the water's surface. The cover material should neither sink below the surface (where untreated wastewater might escape into the environment) nor lift from it (permitting infiltration of precipitation and untreated water). However, certain types of floating covers that rely on air trapped between the pond's surface and the cover to provide buoyancy are at increased risk of excessive wear and tear from wind exposure.
Large ponds generally require central floats to provide targeted buoyancy. In floating covers for wastewater treatment, lateral floats are arranged in continuous branching patterns leading out from the center. These lateral floats serve a two-fold purpose. Under the cover itself, the floats form channels that guide gases to the edge, where they can be collected. On top, those same channels encourage rain and melting snow to flow to catchments where it is pumped out.
Anchors, Tensioners, and Attachment Systems
Tension systems go beyond the simple float and weight design and include springs or other devices that pull and spread the cover's edges until it is uniformly taut, much like the springs and supporting frame of a trampoline bed. This constant tension keeps the cover from sinking below the water's surface, eliminating folds and sagging centers. Large covers, especially, benefit from this treatment, with improved drainage and lower long-term maintenance demands.
Drainage Channels and Pumps
Drainage channels are often formed simply by installing floats and weights in a specific configuration that directs collected water to sumps around the cover's perimeter. If those channels cannot provide adequate drainage, designers may add reinforcements and frames to increase drainage capacity, allowing pumps and pipes to remove water as soon as it accumulates. These are critical tools since an accumulation of water on top of a floating cover will quickly overload and sink it.
Ballast Weights
Floating covers need to rest at a precise point with relation to the surface of the contained water. Covers that sink can't do an adequate job of controlling gas, odors, or evaporation. Similarly, covers suspended well above the surface provide relatively poor thermal control and are highly vulnerable to wind damage. In some cases, ballast weights are included in the cover design to maintain a precise balance of tension and buoyancy. Sometimes, pulleys can help manage the pressure exerted by each weight.
Venting
Wastewater generates gas. There's no way around that, so the gas needs to be released or collected as it's accumulated to avoid a build-up that can rupture the cover or stretch it out of shape. Biodigesters full of sewage are particularly challenging since their design promotes the production of gas. In these structures, the goal is to route methane to storage or pressurization equipment. Whenever possible, design vents to pass through the seams rather than directly through a solid layer of geomembrane cover since it's easier to patch and seal a seam that's within relatively easy reach.
