Floating covers are used to secure wastewater held in tanks, lagoons, and similar impoundments. The covers are attached firmly to the container material, and together they create an enclosed space that can prevent leaks and spills, control gas production, block sunlight, and more. Floating covers rest on the water's surface, but they are aided by equipment designed to maintain tension and keep the cover in position. Most ponds call for the floating cover to rest as close to the surface of the water as possible to limit gas build-up and evaporation, but some designs require a small air gap for gas capture. Whichever format you're using, wastewater will be piped in between the liner and cover to create a wholly contained body of water.
Scum Submergence
The floating material that gathers in settling tanks is a particularly troublesome type of scum to eliminate. Suspended at the surface of the water, the components of scum don't benefit from the digestion activities of aquatic bacteria and may persist indefinitely, increasing in size with each batch of incoming waste. In some cases, scum layers can be several feet thick and may reduce usable storage volume by as much as 30%. Scum also causes operational problems in treatment plants, ranging from clogged pipes and intakes to blocking overflow channels. In cases where a scum problem has been allowed to persist over time, it can directly lead to severe structural damage.
Fortunately, geomembrane floating covers are exceptionally well qualified to maintain the proper submergence of runaway scum layers. The same floats and weights that work together to keep a floating geomembrane cover right at the water's surface as it rises and falls help push the scum layer just below the water's surface. Bacteria quickly digest the fully submerged scum, an essential outcome in wastewater treatment and manure digestion for biogas production.
Solid, single-piece tanks and rigid covers do not move with changing water levels and can't help with scum submergence. Disconnected devices like balls or plates adjust to floating water levels but separate and drift around any floating scum. Not only do they not keep scum submerged, but they can also actually impede efforts to collect and remove it.
Changes in Water Level
Water levels in containment and treatment ponds rise and drop periodically, perhaps as portions of sewage are added or pumped out, maybe due to evaporation or other factors. Since rigid and flexible suspended covers do not have direct contact with the water, they cannot adjust to changes in level. Their ability to restrict oxygen exchange, minimize wind effects and water movement, and control loss through evaporation is minimal. Even insulating properties are limited since efforts to heat or cool the water must also manage the temperature of the air mass in contact with it.
Floating covers, which have direct contact with the water in all cases except where gases are diverted for use or disposal, automatically adjust to the water levels. They're able to continue submerging scum, blocking light, and insulating wastewater regardless of if the lagoon is at 25% or 100% capacity.
Because floating covers adjust to the water level, they're uniquely able to curb the effects of wind and rain. The edges of the cover are weighted, so they remain in direct contact with the water's surface, no matter how full or empty the container. The wind is unable to slip under the cover's edge and lift it away. Since a floating cover will remain reliably in place even during extreme weather, it can be depended on to divert and discharge excess rainfall and prevent it from overtopping holding tanks and lagoons, triggering a catastrophic failure.
Floating covers offer still more essential benefits like:
- Odor and harmful gas containment -- floating covers can be configured to collect gases in a small space between the water's surface and the liner, where it is diverted to an appropriate collection setup. Since the gas cannot accumulate, the cover does not billow up, become dislodged, or tear out of place in windy conditions.
- Improved security and access control -- Floating covers not only disguise ponds and make them unappealing to wildlife, but they can also be sealed off entirely and eliminate access for everything from frogs to curious humans.
- Meet stricter emissions requirements -- Floating covers are ideal for closely limiting the release of methane and CO2 produced by wastewater ponds and lagoons.
- Precise control of evaporation rate -- Floating covers rest directly on the surface of the water, eliminating contact with air and physically impeding evaporation.
- Prevention of environmental contamination -- Sealed covers prevent the incursion of runoff water into lagoons and containers, and the dampening effect of the floating cover itself retards splashes that could spread chemical or bacteria-rich wastewater.
- Improve temperature regulation by eliminating the need to warm and cool large air pockets over the water's surface. Eliminating these air pockets saves energy and improves the efficiency and effectiveness of water treatment or storage processes.
- Limit the volume and sources of incoming water. Floating covers seal the container or the pond from water influx, diverting it around or beyond the storage facility and limiting the risk of overflow or flooding.
