While all produced water requires some amount of storage, there’s a big difference in how the pits are designed if you plan to simply discharge the water rather than reusing it. Both purposes tend typically require processing to bring the water to certain parameters but discharge obviously demands much cleaner water. Reusing or injecting the water into closed wells can put it to good use while requiring minimal processing. However, you’ll definitely need to control losses to evaporation when planning to make the most of each gallon by reusing it. Make the decision on whether to discharge, reuse, or combine both methods before designing your holding ponds and pits since it will affect the final design.
Potential for Reuse
Most hydraulic fracturing facilities focus on the reuse potential for turning produced water into a fresh fracking fluid; keeping the cycle of extraction going. However, there are plenty of other potential reuse opportunities depending on the amount of treatment available. If there’s enough processing to restore the water to a relatively clean state, it’s perfectly safe to distribute the water as irrigation supplies to keep nearby fields green and healthy. Other potential uses include watering livestock, water application for dirt roads to suppress dust clouds, and drying for salt production to keep roads from icing over in winter.
Treatment Requirements
The requirements for the treatment of produced water don’t just vary depending on the final use for the liquid. Treatment is also based upon the quality of the water coming out of the drilling operation. Some produced water is nearly drinkable as it is, while other liquids can emerge as sludge so thick it’s hard to reuse as fracturing fluid. The condition of the processed water can change from day to day, or even hourly, all from the same well. This makes it tricky to guess how much treatment is needed and to plan a comprehensive pit and pond system. Some treatment methods are easily adaptable to increase as water quality drops, while other techniques are far less adaptable.
Options for Produced Water Treatment
Like with any other kind of wastewater, there are plenty of options for treating produced water. Most facilities aiming to reuse or discharge the water will need a combined approach, with more methods required for discharge than reuse in most cases. Some of the many treatment methods available today include:
- Traditional filtration: with a wide range of media to absorb chemicals, oils, dissolved solids, and other contaminants. Filter media appropriate for produced water treatment may be ground up walnut shells, anthracite coal, expanded charcoal, or standard sand.
- Microfiltration and ultrafiltration: aim to remove even more liquids and chemicals from the processed water mix through the use of ceramic membranes. Tiny openings in the material only allow water to seep through, keeping other chemicals and compounds trapped on the other side.
- Various forms of osmosis, including the familiar reverse osmosis. These treatments are good at handling salinity and dissolved minerals and metals, but they won’t necessarily help with petrochemicals and hydrocarbons mixed into the fluid.
- Evaporation: which is handled through a mixture of freeze and thaw cycles in this industry rather than wind or heat methods. Freezing the brine helps concentrate minerals and other compounds that need removal from the mixture.
- Flash distillation: in which a pressure change causes the water to evaporate suddenly without the addition of heat. This sterilizes the water in the process, making it ideal for discharge into open waterways or reuse as livestock or crop water.
- Electrical methods like electrodialysis and capacitive deionization. Low voltage currents are used to separate the compounds out of the water, encouraging other flocculation methods.
Types of Produced Water Discharge
Even after deciding on discharge as the final way to deal with excess produced water, it’s necessary to decide where to discharge the liquid. Clean water that’s been thoroughly processed is often permitted to go directly into an existing river, lake, ocean, or other open body of water. Waste that can’t be processed further is usually injected into a well, or enclosed in a buried pit, to keep it from reaching any other bodies of water. Sewer discharge is an option in some areas, but most lines can’t handle the huge amount of processed water that can come from a fracturing facility. Finally, some facilities build their own manufactured wetlands to discharge and process the water all at once.
Discharge Costs and Limitations
Discharging water is more expensive than reuse in most cases, even if it’s only due to the high costs of getting permits for this kind of wastewater release. The extensive amount of processing needed to bring the produced water to the high level of quality required for discharge, also adds to the final cost. Don’t underestimate the price of changes in local regulations on wastewater discharge in the future. You may be able to secure approval today and then find yourself building storage ponds and tanks later to keep up with changing demands in water quality.
The Importance of Lining Pits and Ponds
No matter which use you choose for your produced water supply, the ponds and pits holding the water during treatment must be lined. There’s no way to reduce or eliminate the need to line these pits just by choosing a specific method of discharge or treatment. Processed water is simply too contaminated and requires too much processing, to reach a safe and stable state, to risk exposing it to bare soil. Even if a pit will only hold the wastewater for a few days until it can be pumped and discharged somewhere else, make sure to line the pit and protect it with secondary containment.
