Rapid infiltration basins waste water that has undergone some level of treatment. Lined reject ponds that store water for retreatment are a sound alternative.
It seems we are regularly bombarded with news about regional droughts around the country and the planet. These droughts have made the need for water conservation even more clear.
One drought that has gained particular attention over the last decade is the one that has plagued the American Southwest, and Southern California in particular. It has become necessary for some state and local governments to place water consumption restrictions on residents and businesses, and to pass laws incorporating mandatory low-flow devices on new construction and remodel projects.
Anyone who has stayed in a hotel in recent years has probably noticed the conservation cards asking guests to help reduce water consumption by reusing towels. These efforts are not without justification. Surface and groundwater levels are decreasing across the U.S. Water plants are being required to draw their water from deeper and more problematic wells, thus increasing the necessary levels of treatment and associated costs.
Operators of wastewater treatment or reclamation facilities are typically familiar with rapid infiltration basins (RIBs). These barren plots of land are necessary in several instances. For instance, facilities that lack redundant fail-safes may need an RIB in case a piece of monitoring equipment unexpectedly fails.
At other times, toxic loads can cause microorganism upsets that degrade effluent quality to the point where it is no longer permissible to deliver the water to a reclaim system. Under these circumstances, TSS, BOD or nutrients may be at levels considered inadequate for reclaimed standards. It would therefore be necessary to divert the flow to an RIB until the effluent quality was restored to meet the reclaim standards.
Over a year, these diversions can add up to substantial percentages of wasted water at a time when water conservation is imperative for many communities. Depending on the reason for the diversion, the quality of the effluent going into the ground should also be of concern.
Improperly treated wastewater deemed unfit for reclaimed purposes is likely to contain higher levels of pathogenic bacteria and nutrients. While wastewater treatment facilities are required to maintain a certain level of treatment pursuant to their permit when diverting to an RIB, the eventual goal for the industry should be for facilities to have zero water loss and release zero pollutants. This is perhaps a lofty goal, but if we judge how far wastewater treatment has advanced in the last century, it would seem appropriate to aim for that next leap.
A simple twist
This is where the case for lined reject ponds or holding tanks can be made. In the most basic form, an RIB is converted to a lined reject holding pond by installing a water-impermeable liner. An attached lift station can then reintroduce the reject water to the treatment process.
From the lift station, a trunk line can go out to the plant with a network of valves and branch lines to control where in the process the reject water is introduced. The point of reintroduction will depend on the retreatment level required to meet reclaim standards and minimize cost.
For facilities limited in space or where odors are a concern, enclosed holding tanks can be used instead of ponds. If planned with enough foresight, reject holding tanks can serve multiple purposes. Aside from acting as a diversion tank for poor-quality effluent, they can be piped to act as emergency surge tanks during storm events.
Wastewater facilities designed and permitted to produce reclaimed water have an environmental obligation to ensure best practices at all times in their process control procedures. From a financial standpoint however, it would be in every utility’s best interest to produce the maximum output based on incoming flows.
As with many entities whose budgets are funded by taxes, wastewater treatment facilities are increasingly expected to do more with less. Sending water that has been treated to any degree to an RIB for non-beneficial uses is a waste of resources.
Typically, water that has not met reclaim standards and must be directed to an RIB has already undergone primary, secondary and tertiary, and potentially disinfection as well. Each level represents a cost per gallon. It is worth noting that lining an RIB also reduces preventive maintenance costs by eliminating the vegetative growth controls typically outlined in a permit to ensure the fastest percolation.
It is in the best interest of utility leaders — and it is also their responsibility — to research and advocate for the best and most efficient treatment technologies. For wastewater treatment facilities able to produce and dispatch reclaimed water, a justifiable and fiscally wise capital improvement suggestion would be a reject water-holding system.
As communities further restrict personal water consumption and utility customers become more aware of water shortages, utility leaders are better positioned to secure financing for water conservation improvements. As has happened with trickling filters, it may be time to start phasing out RIBs as newer options prove to be more viable.
About the author
Kirk Boulerice is chief operator for the City of Apopka, Florida.