Filtering out excess Nitrogen with Biochar

In many areas, you can't drink your well water, because they've been adding synthetic nitrogen fertilizers, that aren't mostly soaked up by the lack of organic material.  It goes into the water table.  This paper talks about a method to make biochar with iron to filter it out:
John S
PDX OR

https://link.springer.com/epdf/10.1007/s42773-025-00516-5?sharing_token=WgulsZOnS7w33XLPZwigqPe4RwlQNchNByi7wbcMAY6r2grbVa9pygSUhu5QRBxumO76vymTJcFJjVoj0yaVOUlRpQOYAlnlzmXk6-bjY-fu0w5ZUkzjMYgtz0E7TzbTV_GOoPTClLMvU7BR1UZ2paKHIen6NOPGN8tWPOg0U_k%3D

I'm hoping this could help folks in Eastern OR who have this problem, its bad in certain areas over there, lots of tainted wells.  

I remember going through Central California's valleys.  Forest Service people told me not to drink the tap water 35 years ago, because so much of the synthetic fertilizers and pesticides had permeated the water table. They all drank bottled water then.  Yes, there were tons of plastic bottles strewn about that county.

John S
PDX OR

Encouraging, but the process looks like it requires inputs that most of us don't have. Enhanced biochars are a fascinating topic and I have a low-tech method of making magnetic biochar by treating feedstock with rust and oxalic acid. Hopefully I can get it tested soon to see how it performs (lab work is $$).

I'm sure that straight biochar without inoculation is a pretty good filter, even if the metal enhanced and more complicated version is superior.

JohN S
PDX OR

How much of the problem is Nitrogen and how much is toxic gick along with Nitrogen?

If the problem was just Nitrogen, I would wonder if the better approach would be a hydroponics system that you put the well water through first with lots of fast growing plants, then used just a regular sand/gravel/biochar filter to get drinkable water that the plants had partially cleaned?

Then again, if it was that easy, someone else would have thought it up, so maybe I'm out to lunch?

Excess nitrogen can take different forms. Nitrate is the most common one encountered in food-growing and domestic situations, but ammonia is also an issue (think poultry litter or an overly hot compost pile). Plain biochar made from woody material is really good at mitigating ammonia and moderately good at adsorbing nitrates. The feedstock and temperature can influence nitrate mitigation potential, like using grass or crop residue instead of wood, and producing it at lower temperatures. Then there are the additives and tweaks. Iron is just one of many...clay also adds interesting qualities and enhances a lot of the filtering properties of biochar.

Without getting too far into the weeds, the main things that are happening with biochar when we try to sop up contaminants are cation exchange and functionality. Cation exchange is something that clay soils are really good at and involves negative electrical charges on the edges of the particles that attract positively charged ions when they're in solution with water. Functionality refers to the formation of organic molecule complexes (clumps) on the edges of the biochar surface structure. High functionality is something we get in lower temperature biochars, which tend to have less surface area...tradeoffs are everywhere.

Ammonium ions are positively charged, so any biochar with a decent cation exchange capacity (CEC) will soak them up. Nitrate is negative, though, so all the CEC in the world doesn't really help. But functional groups can have anion exchange potential and handle this problem. What's neat about biochar is that regardless of the material or method, after it's been in the soil for a while this property actually improves (not forever, but at least for the first several years). The other thing that's advantageous about using biochar to mitigate excess nitrogen is that it will happily give it up to plants and fungi when they need it.