The Boundaries of Biosolids

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Have you ever considered doing something completely out of bounds? How about eating a strange animal while visiting another country? What is taboo in the U.S. may be perfectly acceptable in another country, and vice versa. Personal boundaries not only vary from person to person, they are often different in other parts of the world.

Last month I took part in the Wetskills student competition at the Milwaukee Water Summit co-sponsored by UW Whitewater and the Kingdom of the Netherlands. The event encouraged students to develop innovative solutions for water challenges posed by case sponsors. It featured a number of Dutch students and wastewater professionals and provided a great opportunity to connect people of different backgrounds. Today people are more connected than ever via the Internet and social media, so knowledge sharing between peoples of different cultures transcends geopolitical boundaries. Today I’d like to discuss a boundary in the environmental realm most rarely consider.


Wetskills Water Challenge – Alisa Doornhof, Michael Keleman, Nould Kuilder, Paul Proios

Many people are unaware of what happens to our waste after we flush, and take it for granted that it will disappear and never return. But the remaining byproduct of wastewater treatment – biosolids – must be managed. In the U.S. over half of all biosolids generated by water resource recovery facilities are beneficially reused, such as being used for land application as fertilizer. Most end up on corn and soy bean fields. In the Netherlands, however, land application of biosolids is not practiced and is considered unacceptable, largely because of the fear of pathogens (disease-causing organisms). In the United States, to meet Class A pathogen reduction requirements, biosolids must contain less than 1000 fecal coliforms/gram of solids. Class B requirements are much higher – 2,000,000 fecal coliforms/gram of solids.

Biosolids are the byproduct of the wastewater treatment plant but are explicitly processed to reduce pathogens so that they are much different than “humanure.” Biosolids are basically comprised of the remaining cell walls of microorganisms left over from the treatment process as well as whatever organic biomass remains after digestion. Much of the organic material has been degraded, in many cases by as much as 40-50% (measured as volatile solids destruction). For comparison, biosolids are very similar to soil on an elemental level. The main difference is that biosolids have more Carbon and less Silicon, as well as more Nitrogen and Phosphorus. The next post will show this in graphical form.

Pathogens have been significantly reduced in the treatment process; much more than manure from hogs, poultry and cattle in the agricultural sector, which has been used for centuries around the globe. Yet there is so much fuss across boundaries regarding the beneficial reuse of biosolids. Isn’t it just a superior fertilizer?




Pay as You Throw

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Pay-As-You-Throw (PAYT) is a fee based garbage management program designed to encourage recycling and landfill diversion by proportionally charging users for the amount of trash they generate.  In the case of Fall River, MA, citizens can only dispose of their trash using official purple trash bags they purchase at local stores; $2.00 for the large, $1.25 for the medium and $0.75 for the small. On trash day, even when the bag is only partially filled, a homeowner is motivated to throw that bag out if there is food in it rather than endure the nuisance of rotting food for another week. But if the putrescible waste is eliminated, by using a food waste disposer for instance, the user can make that bag last a little longer.

On the other side of the country, Tacoma’s method of trash disposal is different but the incentive is the same. Residents can get a 90-gallon roller cart for $57.90/month, a 60-gallon cart for $38.59/month, a 45-gallon cart for $28.95/month, and a 30-gallon cart for $19.30/month. This means residents can save over $100 a year by dropping down from a 45-gallon cart to a 30-gallon one, and over $230 a year for dropping down to a 60-gallon cart from a 90-gallon one.

Regular readers of this blog understand that a wastewater treatment plant is capable of managing what goes through a disposer.  A disposer doesn’t use a lot of water or electricity and it won’t clog sewers or overload the treatment plant.  But it also helps households in PAYT communities reduce their garbage bill.  Not bad for an appliance that’s been around for over 75 years.

Fall River, MA Zero Waste

City of Tacoma Trash Rates


Coho and Climate Change

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The Wisconsin weather is finally getting warmer and so begins the best time to enjoy my favorite outdoor activities ‒ golf and fishing. This past week I had the pleasure of both, including a successful expedition on Lake Michigan to catch Coho salmon.


Lake Michigan in Racine, WI May 23, 2015

Just as we were planning another trip for the weekend, we were reminded of how volatile spring weather can be. High winds are in the forecast, making it hazardous to fish Lake Michigan. The volatility of spring weather was even more evident this week in Texas when severe rains led to devastating flooding. Obviously, spring is the most unpredictable weather of the year but one has to wonder if climate change is making things worse.

Discussing climate change is a challenge for me because as a scientist I rely on facts and a strong technical foundation to form my position. On the one hand, the CO2 level in the atmosphere is the highest in centuries. At 400 ppm, it is about double the level of a couple hundred years ago.

On the other hand, consider what fraction the CO2 of the atmosphere represents.


Composition of Earth’s Atmosphere

The controversy about climate change usually revolves around one of three things – whether this small component of the atmosphere is to blame for extreme weather (drought, floods and warmer temperatures), whether the increase in carbon dioxide is anthropogenic (man-made), and if we should do anything about it.

I feel pretty confident making the following statement: our infrastructure should be designed for resilience against nature’s impacts, whether it’s rising sea levels or flooding from heavy rains. Engineers must model future weather events to properly design for such incidents and it is prudent to consider how climate change may impact the models. However, modeling uncertainty makes it difficult to design resilient infrastructure that is also fiscally responsible. And so debates ensue whether climate change is real or imagined and whether we should do anything about it.

To me, the best approach consists of simple steps that make good sense for additional reasons beyond climate change. An example is the diversion of organics from landfills and promoting the use of biogas instead of fossil fuels. This practice not only reduces greenhouse gas emissions but also provides economic benefits at the same time. Along that line of thinking – the Coho were outstanding made on the grill; the secondary benefit of a fun day on the lake.