At first, it may seem odd to put a lid on a pond, but in reality, storage tanks, cisterns, and other facilities usually appear with covers in place. An underground septic tank is essentially a covered wastewater vault. There are plenty of important reasons to cover wastewater impoundments. Still, even when it's not explicitly required, failure to do so on sensitive water features could result in both environmental penalties and product losses.
It's possible to eliminate many challenges associated with storing wastewater by adding a flexible geomembrane floating cover. Consider the demands and expenses related to all of these factors when you evaluate your choices.
- Heat retention to support biological activity and treatment capacity
- Odor management
- Control or eliminate algae growth
- Promote TSS settling
- Promote nitrification
Evaporation
Open wastewater containers, ponds, and pits are subject to significant evaporation daily. Warm, dry weather, direct exposure to the sun, and regional wind patterns will ultimately determine the exact volume of water loss. Still, it can be in the neighborhood of a few to several inches every day, which translates into tens or even thousands of gallons in sites with a large, combined surface area. Anaerobic treatment systems work slowly and often hold water for multiple months to completely process unsafe levels of bacteria and other contaminants. Still, most states restrict water loss in these lagoons to no more than 1/8th of an inch of water per day.
While "dewatering" is a required step in some operations, many kinds of wastewater contain organic compounds and other elements which can be too dangerous or offensive to release through evaporation. The process of organic decomposition produces methane and other greenhouse gases and a host of sulfur compounds characterized by their foul odor. Moreover, sulfur compounds that escape into the atmosphere lead to acid rain and can be toxic or deadly to animals and people in high concentrations.
Many other volatile chemicals in wastewater contribute to the purification process, including ammonia, chlorine, chlorine dioxide, and various petrochemical solvents. When inhaled in high enough concentrations, these chemicals are deadly and are confirmed to cause significant environmental damage if released into the local environment. The only reliable method for preventing the escape of these volatile compounds is to cover and seal the wastewater impoundment completely.
Whether you're concerned about the dispersion of toxic chemicals and organic compounds for health reasons or you're facing a host of odor complaints from nearby residents, a floating cover for your wastewater ponds will go a long way toward containing the problem.
Rain
Rain is a concern for any type of open storage. Relatively clean precipitation that could be quickly made safe for human consumption becomes contaminated as soon as it touches wastewater. This contamination represents a potentially permanent loss of valuable drinking water and increases treatment costs due to ever-increasing wastewater volumes. More concerning is the possibility that containment facilities may fail or overflow during significant rainfall events. Whether above or underground, fixed storage facilities of concrete, fiberglass, or steel, for example, can contain only a strictly limited volume. Excessive rainfall, especially over a relatively short period, can add to that load until the structure fails or the wastewater overflows the impoundment altogether.
Catastrophic failure of a holding structure may be shocking, but more common are incidents of leaks, floods, and dam collapse in the case of in-ground wastewater ponds where animal waste is collected and treated. In 2016, Hurricane Matthew passed through eastern North Carolina, producing record-setting rainfall, which overwhelmed many waste lagoons employed by local farmers. The toxic flow from flooded ponds and collapsed dams triggered a series of algae blooms and fish kills in nearby estuaries. Two years later, Hurricane Florence hit the same area, and at least 30 pig-manure lagoons flooded, releasing dangerous animal waste directly into the community. The escaped slurry presented the community with a toxic soup that included contaminants like salmonella, giardia, and E. coli that flowed through their streets. Across the country, public reaction to hog waste processing has become contentious, and farmers are facing potentially ruinous costs to satisfy a host of newly instated regulations and restrictions.
Impermeable covers are a straightforward solution to problems stemming from flooding and dam collapse. Rain falling on a well-designed cover simply flows off the cover and continues into the ecosystem as clean precipitation. Since the total contained load doesn't increase, wastewater in above-ground tanks or in-ground lagoons won't overflow or cause containment structures to collapse. It's a surprisingly reasonable expense compared to the economic, environmental, and political damage of repeated lagoon failures like those seen in eastern North Carolina.
Temperature
Biological (and some chemical) treatment processes are directly affected by temperature. When wastewater maintains an ideal temperature range, microbial populations thrive, digestive processes are optimized, and waste degrades rapidly. This efficient progression through treatment reduces total holding time and lowers operational costs.
If wastewater is allowed to fall below 77 degrees F, microbial activity slows rapidly until it essentially ceases around 35 degrees F. With no microbial activity, organic compounds don't break down, other progress halts, meaning that the treatment process is virtually dormant. When inadequate temperatures trigger a protracted period of inactivity, operators have to devote significantly more storage space until temperatures rise and dormant processes resume.
Temperature variations can spell trouble in other wastewater treatment regimens as well. Temperatures at the upper extremes can kill microbial populations, rendering expensive disinfecting solutions virtually useless. At either end of the spectrum, poor temperature control results in inadequate processing and a final product that fails to meet federal, state, and local standards.
Storing wastewater in in-ground ponds that extend below local frost lines may mitigate excessively cold or warm environmental conditions. The soil both warms and cools the stored water and may be successful in keeping it within an operational range for biological activity. Wastewater managed in this fashion will undoubtedly benefit from some of the ground's insulating qualities, but exposed surfaces don't enjoy that advantage.
In the oil industry, fracking water is heated to about 70°F before being injected down the wellhead. Tanks that hold these warm waters are heated all winter long to keep the water from freezing and maintain the desired temperature. Maintaining fracking water above the ambient temperature represents a significant expense, particularly in northern oilfields where winters are long and cold.
Above-ground storage tanks are significantly more vulnerable to temperature variations even if their design includes insulation on the sides and floor. An exposed surface loses (or gains) so much heat that any amount of side insulation is virtually useless. Covering your storage tank provides significant insulating properties, even by simply shielding the water from ambient air movement (or direct sun exposure). Flexible covers fabricated with specific insulating materials provide even more benefit, whether in the depths of winter or the peak of summer.
No waste processor is seeking ways to spend money for little benefit. The cost of improvements like insulated floating covers may appear to be poorly justified. Still, carefully optimized temperatures throughout annual weather cycles and adjusting for climate changes can significantly improve operational efficiency. Isn't it time to conduct a realistic and detailed comparison of the immediate equipment and material costs versus the long-term savings potential of insulated floating covers?
