World Toilet Day, observed Nov. 19, calls much needed attention to global...
Sustainability is becoming a major concern for water systems, especially as a growing number of factors stress natural resources. Here Dr. James Mihelcic of the University of South Florida discusses the future of sustainability and nutrient recovery technology with WWD Associate Editor Kate Cline.
Kate Cline: What are the biggest factors affecting water sustainability today?
Dr. James Mihelcic: Population, urbanization, climate and consumption are stressors we encounter at both the local and global level that greatly affect the sustainability of our water resources and water infrastructure. We also need to think of how to provide services to the 884 million people in the world who do not have access to safe drinking water and the 2.5 billion people in the world not served by any type of sanitation technology.
Cline: What do water suppliers need to do in the coming years to increase sustainability? What are the challenges?
Mihelcic: Different challenges include the geographical and economic context that the water system is located in, and also the size of the water systems. One of the challenges we face is how technology should be deployed. That is, is it best to deploy technology in a centralized or decentralized manner? We also need to think carefully how technological solutions are linked to policy and behavioral changes, as we need more integrated approaches that are not solely based on technology. We should also think how this integrative method is impacted by the size and geographical location of the water system.
We need to have a more integrated system of how we design and manage our water, wastewater and storm water infrastructure. These sometimes separate systems need to be integrated in the minds of water managers and, importantly, local residents. This is because both groups need to see natural and engineered water features as part of a broader urban hydrological system.
Water suppliers large and small must also think of the energy and materials that are embodied in the water over the lifetime of a particular water infrastructure. What I mean is that we can no longer solve our water problems by throwing a lot of energy and materials at them. We also need to emphasize the resources that can be recovered from wastewater rather than the constituents that must be treated or removed.
Cline: What sustainable technologies will we see in the future for recovery of nutrients in wastewater?
Mihelcic: At the moment we probably do a good job of recovering solids from wastewater. These are the biosolids applied to agricultural fields or processed into soil amendments for golf courses or homeowners. They are enriched with nitrogen, phosphorus and organic matter.
However, the solids are where the energy is. We know already how to produce methane from these biosolids. You can use methane for heating or running an electrical generator. We could perhaps generate electricity and hydrogen via microbial fuel cells from this material. Also, we already know how to recover energy from burning them. The choices lie in how we recover the material and how sustainable the recovery methods are.
[People excrete] about 75% of nitrogen in urine; the percentage of phosphorus is a bit lower, perhaps 50% to 60%. These nutrients can be recovered by collecting urine (done in many parts of the world) and then applying it to crops. You can have a compost latrine and recover the solids there—I even have one in the U.S. There are urinals and toilets designed to recover urine, but there are some piping issues and behavioral issues. Sweden, for example, has implemented this on a building scale.
On a larger scale, there is talk of recovering the nitrogen and phosphorus as struvite (ammonium magnesium phosphate). You can also recover nitrogen and phosphorus in biosolids or perhaps grow algae from wastewater. Algae is also being looked at as a source of energy in terms of extracting biofuels from it.