Water Management: Applications of Geosynthetics in Water and Wastewater treatment
When water is easily available from the tap, people rarely think about the role of geosynthetics in getting it there.
There is a wide range of applications in which geosynthetics are being used successfully to improve the process of storing and treating water and wastewater. Geosynthetics have lower penetrable properties and generally are less expensive which has therefore resulted in many different applications such as decorative ponds, potable water storage and wastewater treatment lagoons.
The need to contain animal waste product is on a steep rise with the amount of livestock being concentrated in large agricultural farms. These livestock are normally raised in larger barns with concrete floors that are gently sloped so jets of water can spray the waste into waste lagoons. Geosynthetics are therefore used to line these waste holding lagoons, treatment ponds, floating covers and evaporation ponds.
GOLF AND DECORATIVE PONDS
One of the common reasons for a golf course pond is for course irrigation, which is normally non-hazardous freshwater. The second most common reason is that these ponds are often included in the course layout as a water hazard for golfers. These water hazards are normally made to fit the overall design of the golf course which means that they are usually backfilled and landscaped to blend with the surrounding natural environment.
Dating back to the 80’s, the most common liner for golf and other decorative type ponds used to be a compacted clay liner, but thanks to the evolving use of geosynthetics, there are now inexpensive and effective geosynthetics options such as geomembranes.
Geosynthetics are used in various applications in wastewater facilities. These types of applications primarily are found in industrial and municipal treatment facilities which in include treatment lagoons, sedimentation basins and digestion ponds. The most straight forward example incorporates a geomembrane as a low absorption barrier between the water or wastewater being contained and the subgrade. However more complex systems can include:
- Anaerobic lagoons with covers
When wastewater with a reasonably high organic load is kept in a lagoon for several days an active anaerobic sludge accumulates at the bottom of the lagoon. In an uncovered lagoon the anaerobic digestion activity takes place at the base of the lagoon and the activity near the surface tends to be more aerobic.
These lagoons can be covered with a geomembrane floating cover to enhance the anaerobic digestion activity by the exclusion of air or enable the harvesting of gas (especially methane) which can be used as a fuel or to reduce the effect of odour from the anaerobic activity.
- Aerobic (aerated) lagoons
Aerated systems use either surface aerators or diffuser systems to introduce air into the wastewater and this results in consumption of the organic content of the wastewater which is mostly released as carbon dioxide.
- Geosynthetics for combined anaerobic and aerobic lagoons
Many wastewater plants make use of anaerobic and aerobic systems as a combined or two-part process. This can be readily achieved in one lagoon using a specially designed geomembrane baffle and floating cover.
- Enhanced evaporation
A typical dark geomembrane with shallow wastewater over it will see the wastewater temperature rise with solar radiation creating an enhanced capacity for evaporation. This is used in wastewater disposal and for salt and mineral extraction processes. A floating cover over the wastewater will prevent growth of waste volume in the wet season as well as enabling fresh water to be gathered from the cover.
- Sludge dewatering
Geotubes were initially developed as a construction tool enabling the user of dredged sands to build groynes and the like. These filtration properties can also be used to take sludge with high water content and rapidly dry them to a solid state which allows truck transport without dripping.
Geosynthetics also are used to line holding ponds for shrimp and fish in large aquaculture farms. The lined ponds have many advantages over standard soil or clay-lined ponds including decreased permeability and ease of cleaning and harvesting. The low permeability membranes ensure that more water stays in the ponds. It can also assure that diseases can’t migrate through the subsurface soils and contaminate other ponds.
Whatever the reason for lining a pond, the use of geosynthetics in these types of applications is growing. Geomembranes create an essentially impermeable barrier that prevents any liquid that is in the pond from migrating to the subsurface. Geonets, geocomposites, geotextiles and geogrids may be used to vent gases, cushion against uneven subgrade or provide reinforcement as needed.
SADLIER, M.A. “Geosynthetics in Wastewater Treatment” International Geosynthetics Society Education Committee