The trend towards infrastructure decentralization is well understood with respect to energy production. Since humanity’s collective energy requirements will double in the next generation – even with extraordinary improvements in energy efficiency – thousands of new utility scale energy developments will compete with, for example, millions of solar arrays deployed on rooftops.
Another example of infrastructure decentralization is in the many waste-to-energy technologies under development. These solutions have utility scale applications, but also onsite applications, as reported in our recent post “Onsite Waste-to-Energy.” In both of these areas, energy production, and disposal of municipal solid waste, there is a great deal of overlap where centralized solutions vs. decentralized solutions display remarkable parity when considering overall costs to implement.
Treating wastewater, however, is not only another area where decentralized solutions are rapidly evolving, but appears to offer a broader range of situations where decentralized wastewater solutions are already clearly more more cost effective than utility scale solutions. In recent years these decentralized sewage treatment applications have become not only much cheaper to implement, but deliver better solutions for aquifer health and overall watershed management.
According to the American Society of Civil Engineers, in the United States there are 16,000 major wastewater treatment facilities. All of these large plants collect sewage from urbanized areas through large, usually gravity fed pipes, discharging the treated water well downstream from the source. Because these plants are so big, and the collection pipes so old, and because maintenance on many of these thousands of systems has been deferred for years if not decades, it is often no longer cost-effective to tap into these legacy systems to accomodate new construction.
Meanwhile, small-scale wastewater treatment systems that have traditionally been installed are not representative of technologies available today. Many communities rely on wells for drinking water and ideally wish to recycle this water back into the aquifers onsite. Their onsite water treatment systems are inadequate to meet today’s water standards, however, so while they are properly replenishing their aquifers with localized systems, often the percolating wastewater is not sufficiently cleaned and is degrading the overall quality of the aquifer. But the cost of upgrading these systems and deploying modern decentralized systems to accomodate new construction in rural areas and outlying suburbs is far cheaper than the cost to extend sewers upstream to service every remote home or community.
|AquaTech’s patented trickling filter
uses gravity to increase efficiency
(Diagram: AquaTech Systems)
One company addressing this burgeoning market for cost effective onsite wastewater treatment is AquaTech Systems, based in Fayetteville, Arkansas, with installed systems all over the world. The array of solutions they offer provide a compelling illustration of just how much money a developer or a municipality can save by going off-grid with their waste water treatment infrastructure.
For example, the cost to extend “big pipe” gravity fed sewers into small communities can cost as much as $40 per linear foot, even without rock excavation. A typical bill to an individual homesite – whether they are upgrading or for new construction – can be over $20,000 per connection. By using smaller diameter pressure sewer pipe, the cost can be reduced to under $5.00 per linear foot. In turn, these collection pipes can feed into small scale treatment plants located within the local community, reducing the diameter and length of total pipe required by orders of magnitude.
Similarly, the cost per household to finance a small scale wastewater treatment plant can be significantly lower than tying into a large urban water treatment plant. These small scale facilities now can treat wastewater to standards comparable to the larger facilities, while releasing the treated water into the aquifers onsite upstream, instead of conveying raw sewage through often leaking pipes to be treated at a central facility well downstream.
Some of the technologies that have made cost effective quality onsite water treatment a reality include fixed film treatment processes that have been systematically improved over the past 20 years. AquaTech Systems offers the “BioTank” treatment reactor, a container-sized module utilizing microorganisms that adhere to a high surface area media submerged in the wastewater. Much of this process borrows from large scale water treatment plants, but now that the microbial process is better understood, and with advances in materials such as high surface area media, today it is possible to offer high quality wastewater treatment at the scale of a neighborhood or small community.
Aquatech Systems offers a number of innovative solutions, such as a “trickling filter” that recirculates effluent through a tower shaped bioreactor. This configuration allows the treatment process to be accelerated by taking advantage of gravity to move the effluent through the microbial digesters. All of AquaTech System’s solutions are modular and can be scaled to address the needs of anywhere from 10 to 10,000 households.
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|The container-sized AquaTech bioreactor is available in
modules and can accomodate from 10 to 10,000 households.
(Diagram: AquaTech Systems)
The promise of off-grid solutions is not only of immense value to developed nations such as the United States, where the crippling cost of inefficient public sector bureaucracies nearly precludes necessary infrastructure upgrades, but equally throughout the world. In nations without legacy investments in grids for communications, energy, and treatment of solid waste and wastewater, advanced decentralized solutions will offer emerging nations dramatically more cost effective opportunities to build a 21st century infrastructure.