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Comment by aragonite | Hacker News Reader

I wonder how much more expensive this process is than the conventional approach.

Apparently 'five times as expensive' according to Vaclav Smil (who is very pessimistic about rapid decarbonization) in How the World Works (2022):

> In terms of the second category, as I will detail in the next chapter, synthesis of the ammonia needed to produce nitrogenous fertilizers now depends heavily on natural gas as the source of hydrogen. Hydrogen could be produced by the decomposition (electrolysis) of water instead, but this route remains nearly five times as expensive as when the element is derived from abundant and inexpensive methane — and we have yet to create a mass-scale hydrogen industry.

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Also how many years of fertilizer and storage could be purchased for the price of all that manufactured equipment? And what are the carbon dioxide emissions from its production and transport? How does all this compare to the carbon footprint and effectiveness of something like regenerative organic farming, which does not typically require inputs of synthetic fertilizers? For the cost of one of these plants, how much equipment could a farmer purchase to aid in a transition to regenerative organic practices. What are the relative effects on waterways between the two approaches, over the subsequent 10 year period?

The phrasing is odd - is methane more abundant and less expensive than water? I get the subtext that there’s something else in the process that drives cost, but at least in that out of context quote it isn’t obvious what it is. I would assume it’s electricity, however using solar which has a lifespan of 25+ years seems like it obviates that.

the absurdity is, there would be enough nitrogen in waste water, but bacteria in the sewage plants release it into air

Milorganite is exactly that, it's composed of heat-dried microbes that have digested the organic material in wastewater. It's manufactured by the Milwaukee Metropolitan Sewerage District, which captures waste water from the metropolitan Milwaukee area and uses naturally occurring microbes to digest the nutrients. After the organic matter has been consumed, the cleaned water is returned to Lake Michigan and the resulting material is dried and marketed as Milorganite®.

The problem with human waste is the concentration of heavy metals as I understand it. We are the very top of the food chain and we accumulate all of the heavy metals from below which then gets further concentrated in our dried waste.

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