Wastewater Treatment: Present Challenges, Future Horizons
The importance of freshwater supply and safely treated wastewater return cannot be overemphasized. No matter how hard we try, we are still a long way from the most efficient, economic and reliable ways to ensure our cities are properly equipped and ready for the challenge. As a civilization, we have achieved isolated instances of superb efficiency in water treatment and reuse. Our space shuttles and space stations that must rely on the almost perfect utilization and transformation of the water cycle are good examples. But back on Earth, the global ecology dictates the need to be most attentive to the entire scope of nature.
Can wastewater be treated in other ways? Currently, most plants use a combination of biological and chemical waste stabilization. Increasingly, the U.S. Environmental Protection Agency (EPA) is presenting the idea of making wastewater effluents cleaner in terms of nutrients. This forces most plants to add more chemicals to polish their effluents. The other unintended effect is that multiple systems now need more maintenance. Wastewater plants are having trouble maintaining complicated systems and keeping costs down. Eventually, a lot more chemical stabilization is going to displace more of the biological stabilization.
One big problem area is biological phosphorus removal followed by anaerobic digestion. The unfortunate consequence of this procedure is the release of phosphorus back into the plant, whereas chemical phosphorus removal permanently ties up the phosphorus until it leaves the system via landfill or incineration. Lesson learned: Very complex systems are not only hard to run but expensive to maintain.
Protecting pump primary, secondary and tertiary treatment from incoming grit found in water is an important step in extending equipment life.
Water pumping methods must change as well. Traditional end-suction pumps have steadily given way to wet submersible units, and now even to “dry” submersibles, where they are mounted into a dry pit and connected to a wet pit. This allows easy access to the pumps for repair or maintenance.
Combined sewers present challenges as well. It is expensive to separate the streams and, in practice, the more readily accessible piping is being handled first, leaving the more difficult accesses for future work. With the complexities that sewer separation creates and the disruption to business, many communities are turning to tunnel collection systems when upgrades (forced by capacity issues or government regulation) are required. Increasingly, drop shafts will become common in downtown urban areas. Many communities will find the added benefit of cleaning up storm water to be a much-needed amenity to growing urban cores.
The repair process should be simpler and faster. Presently, maintenance departments do basic repairs in house, leaving large and more sophisticated equipment to outside contractors. Systems have gotten more complex, and more computers are used to control them. Computer specialists are more commonplace at waste treatment plants—and although they have a good understanding of computers, they may lack the knowledge of the equipment. Likewise, maintenance personnel may be experienced with the equipment but lack proficiency in computers. Thus, a disconnect between the equipment handling and the systems that drive such handling exists in many places. More training is required to bridge this gap, and more interaction between the departments and groups would be beneficial.
New materials are available today that were novel or nonexistent years ago. For example, duplex stainless steel performs better for centrifuge applications compared to regular stainless steel. Composites are becoming more common and have the advantages of light weight, cavitation resistance and corrosion resistance.
A Look at the Future
How will our plants look 20 years from now? It is hoped that higher efficiencies in and effectiveness of the systems would allow less waste and better recycling of the resources. We may see various technologies applied and new trends. Perhaps water and waste treatment plants will combine, and less wastewater will be discharged to the rivers. Perhaps more facilities will utilize closed-cycle systems, making rivers safer and environmentally friendlier.
Plant space, especially in cities, would have to be utilized better, and some regions would likely apply new methods for individual communities with closed-cycle water technology to be more self-sustained and less polluting. Another example that is reality today—islands that get roughly 20% of their water from desalination projects.
Today’s common problems (cracks in pipes, infiltration, plugging, etc.) would go away if our homes could become equipped with self-sustained water modules. Less water discharged into the rivers would mean less piping, repairs and groundwater disruptions and therefore a better preserved infrastructure. This may mean less storm water runoff via infiltration collection devices. Perhaps one day, water supply issues will be reversed with better water treatment and delivery systems. The public is increasingly concerned about whether we remove all of the harmful pathogens in drinking water in urban areas downstream of major river systems. In the future, solar energy will be utilized better. Special bacteria growing methods will advance even further to make us less energy dependent and more efficient.
It is hard to tell, of course, how the world will look 20 years from now. But if we do not try imagining it today, the alternative may find us unprepared in the future. The time to plan, or at least talk about it, is now. We would like to hear the input from our readers and welcome any additional ideas, challenges or thoughts.