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Settling by pH
NPHarvest kalvomoduuli

4th post: Membrane reactor!

It’s finally here! With a rather long searching process we found a collaborator who agreed to design and build the reactor we needed. The membrane tube selection was another time consuming task as we wanted to find the best (and cheapest) possible choice. Practically we decided to continue using the familiar membranes from previous phases, as the other options were not robust enough to withstand the conditions of our process (pH difference of 10+ over the membrane).

The membrane reactor was built by Teollisuuden Vesi oy. After the initial contact with their engineers, the process has been smooth as the design dialogue was easygoing and both parties understood what the main objective was. Now the reactor is much improved over the old one:


volume: 2 l -> 300 l
membrane surface area: 0,15 m2 -> 18 m2
surface area / volume ratio: 15 -> 60

Now we can start testing it, and there are tests planned with WWTP digester reject water, a biogas plant reject water and separately collected urine.


3rd post: Reactor acquisition

It has been a while since the last post. Things have moved forward with the project: we have moved from our University’s lab to a wastewater treatment plant for our piloting needs. The equipment for pretreating the reject water has been constructed and optimized so that the influent for the membrane reactor contains around 200 mg/l suspended solids.

Membrane reactor has been a tad problematic though. Currently available commercial membrane reactors dictate more or less the same design philosophy; the membrane is packed tightly in small space with high pressure capacity. The downside of this is that any solids in the influent flow clog or harm the membranes and it is rather expensive to remove all the solids.

With our design choice, this is not a problem. However, acquiring such a reactor is challenging. In our lab sized pilot the reactor was easy enough to manufacture ourselves but building a reactor with 150-fold up scaled volume and even larger membrane surface area suits better for a contractor. The process of finding such as contractor takes a longer time than expected.  

We also have tested the process with one of these commercial reactors. It worked relatively well under a very short test run but it is unclear how long the reactor can perform well under a longer stress test. We’ll see after this week.

2nd post: Nitrogen flows

First post with actual content! This is about the literary review part of my thesis (which will be published soon, promise!) which focuses on nitrogen flows. It came to me as a surprise how much nitrogen flows have changed during the industrial age. Let me show this with few Sankey chart illustrations (modified from Galloway 2004):

This is from 1860. The blue arrow coming from the top is reactive nitrogen formed from atmospheric inert nitrogen by nitrogen fixation (cultivation induced and natural). Most interesting part is that the Continents box. It accounts for the nitrogen in soil and fresh water environment. In pre-industrial era there was practically no accumulation and the flows between different atmospheric compounds and continents are quite narrow.

Nitrogen cycle in 1860

Moving on to modern time, 1990. The difference compared to the previous timeframe, the Haber-Bosch process steps in as the green part of the largest arrow. This reflects to the accumulation in the Continents box and the other flows. Keep in mind that Haber-Bosch process is what we use to feed the human population so it is relatively critical for our survival. As the human population grows, the more we need fertilizers (assuming that the current method of agriculture stays the same).

Nitrogen cycle in 1990

Galloway et al. also predicted the future. 2050 chart shows us even more increased flows overall. Scary stuff, right?

Nitrogen cycle in 2050

Well, maybe not scary. Increased nitrogen availability is not the end of the world, it just changes the environment as we know it: eutrophication, ozone layer depletion and ocean acidification are all related to nitrogen compounds. Things moving on like this, the Earth system is bound to change permanently. The scary thing could be that I don’t really know what happens when the Earth system changes (not my area of expertise). I guess the question is multidisciplinary by nature anyway.

Coming back to the purpose of this post, I find it surprising that things have developed up to this point without anyone talking about it publicly. It’s always CO2 this, CO2 that. We tend to forget (or we never knew to begin with) that Earth system consist multiple different aspects and they all are affected by human activities. Should I be shouting “Wake up people!”?

1st post: About the author of this blog

The honor of maintaining this site and updating the blog has fallen on me, previously a thesis worked, now a doctoral student, Juho. I guess it’s about time to make the first post, right? After all, the website was founded a year ago. Now that the master’s thesis is more or less completed, I have should have more time and content to write about as well…

My interests are in the sustainability of the world. As such, the word sustainability means a lot of things and I’m by any means an expert in every sense of that word. As an engineer my focus is in the technical and environmental sustainability. Ending up working with nutrient recovery to reduce the energy consumption of one of the most important processes in the words sure is fitting.

I have completed my Batchelor’s degree in Aalto Uni’s School of Chemical Engineering for Environmental management. Practically that meant industrial scale treatment methods and processes, and understanding what an ‘ecological solution’ actually means. Such a poorly defined term, ecological, too. It was natural to continue working with wastewaters for my master’s.

Apart from professional life, I’m fond of martial arts and sailing, especially with tall ships. Community driven video games are also included in my spare time activities. I guess I’m your average Finnish guy with an academic direction of life?

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