Duluth, MN (Source: The New York Times)

By Sally Brown, University of Washington

Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.

  1. A changing framework for urban water systems

  2. Impact of soil filtration on metals, nutrients, and estrogenic activity of reclaimed water

  3. Impact of reclaimed water irrigation on soil health in urban green areas

  4. Nutrient, metal, and organics removal from stormwater using a range of bioretention soil mixtures

  5. Single house on-site grey water treatment using a submerged membrane bioreactor for toilet flushing

You can still get lake front property in Duluth, MN for a reasonable price but you may want to act fast.  A recent article in the New York Times (Duluth photo from article) said that Duluth would be a great place to live with the onset of climate change.  Not too hot, likely not as cold in the winter as it has been in the past, safe from sea level rise, and with an ample source of fresh water.  The article notes that with climate change, access to a secure water supply will be critical.  If that isn’t enough to get you looking at real estate in Minnesota, it might be enough to get you to rethink how we treat water in most urban areas.  That is the topic of this month’s library.  

To get you in the right frame of mind the library starts with an overview of challenges and opportunities in urban water management.  This overview includes discussions of the end of life of much of our existing water infrastructure.  As I was reading this I saw an article in the Washington Post that provides a case in point.  The water infrastructure has failed in a section of Kentucky.

The authors note that water managers tend to prefer tried and true solutions over more innovative ones. This is due to critical role of water systems to protect both public and environmental health.  Plus these systems tend to cost a fortune to build.  The article talks about conservation reaching a limiting point for further reductions in water use.  Improved sensors can reduce leakage and loss of treated waters (up to 14% of treated water in the US and up to 40% in developing countries).  Other sources of water include desalination and effluent reuse.  Storm water capture is also a potential source of water in urban areas.  While desalinization is much less energy intensive, reclaimed water reuse is still less costly to produce.  In Southern California, recycled water will run you 1.8-2.6 kWh/m3 while desalinization costs 3-4 kWh/m3 and bringing water in from elsewhere comes in right in the middle (2-3.2 kWh/m3).  The authors also talk about decentralized treatment systems on a household or neighborhood scale.  While once beyond our comprehension, improved sensors may provide a means to monitor these systems.  They also talk about using a range of systems, many based on natural processes.  These include wetlands and storm water bioretention systems.  Water they note, now comes in a range of flavors.  Potable, industrial, and irrigation waters will have different treatment requirements and should be treated to end use and not for best use.  

reclaimed waterReclaimed water - what a wonderful concept!  The 2nd paper in the library comes from work sponsored by King County and the NW Biosolids.  Rebecca Singer, then a MS student, tested two kinds of reclaimed water to see what would happen to the water as it passed through two different kinds of soil.  In the first paragraph I mentioned the recognition that not all water needs to be treated to potable standards.  Part of that recognition suggests that not all water in the environment needs to be held to the highest standards either.  At the time that research was conducted, the standards for groundwater in WA state were stricter in many ways than the standards for drinking water.  Reclaimed water, treated to meet the requirements for unrestricted irrigation was not clean enough to be used for subsurface recharge.  In many cases soils will provide additional filtration when water passes through them.  We tested that concept.  The soils removed all of the estrogenicity of the water - a very good thing.  They also appeared to add nitrogen to the water, not so good but likely to happen to rainwater as well as reclaimed water. General conclusion of the paper was that soil filtration had a mixed impact on water quality.  Depending on where you expect that water to go and how the water budget is in your community - irrigation in excess of plant requirements might be a way to get subsurface recharge and save on infrastructure.

The next paper talks about what irrigating with reclaimed water does to the soil.  The authors used reclaimed water to irrigate parks in Beijing.  They monitored a range of soil conditions in order to evaluate impacts of this practice on soil health.  They observed increases in soil organic matter, available nutrients, and microbial activity.  No increases in soil heavy metals or soil salinity.  There was a slight increase in alkalinity- which is not a bad thing.  Both studies- just a small subset of what is out there- suggest that properly treated reclaimed water can provide a critical tool for assuring a steady water supply in urban areas.  

Harvesting stormwater is another area that is discussed in the first paper.  Next article in the library addresses the soils that go into green stormwater infrastructure.  This is another one brought to you by UW via NW Biosolids, DC Water and King County.  We tested a range of bioretention stormwater soil blends by filtering actual stormwater collected from under a highway bridge through them.  We measured nutrients, metals, turbidity and PAHs in the effluent from columns filled with the different stormwater mixtures.  For the PAHs we used a biosolids compost +/- water treatment residuals and a food/ yard compost. The biosolids columns removed all of the PAHs and the other compost removed the majority.  All mixtures did a good job removing metals as well.  Nutrients was a bit of a different story.  The biosolids based materials leached more N and P than the food/ yard composts.  Adding sawdust to increase the C:N ratio just about eliminated N leaching.  Adding WTR to biosolids composts or Fe during wastewater treatment was able to reduce P movement.  Retention time in the columns was pretty much a poor indicator of effluent quality.  Lesson here is that a range of residuals based composts can be used for green stormwater systems.  Another tool for a new urban water infrastructure.

The final paper in the library takes things a step further.  It reports on a test of a membrane bioreactor system (MBR) for treating greywater (shower, sink and washing machine) in a single family home in Crete.  The system treated about 37 L per day per inhabitant or 73 L total.  The system did a good job reducing COD (see below) but was less efficient at nutrient removal.  The system was 100% efficient at pathogen removal with data presented on both total coliforms and E coli.

COD findings

On the island where it was tested, the authors calculated a payback time of less than 13 years.  Longer payback times were calculated for a similar system located on the Greek Mainland in part due to lower traditional sewer fees and a higher cost for annual operation.  Not quite there yet but on the horizon. Maybe something to look into when you renovate that house in Duluth.

Big changes are coming, both as a result of our crumbling infrastructure and our changing climate. Understanding how to best harvest water in urban areas and how to use the water that we treat can be a part of the solution.