Didn't know peak phosphate was nearly upon us! On the bright side, technologies to recover phosphate via industrial-scale composting are already mature. My home

Didn't know peak phosphate was nearly upon us! On the bright side, technologies to recover phosphate via industrial-scale composting are already mature. My home state of Wisconsin leads the way on this, at least in the United States: https://en.wikipedia.org/wiki/Milorganite https://en.wikipedia.org/wiki/Milorganite >Milorganite is a brand of biosolids fertilizer produced by treating sewage sludge by the Milwaukee Metropolitan Sewerage District. The term is a portmanteau of the term Milwaukee Organic Nitrogen. The sewer system of the District collects municipal wastewater from the Milwaukee metropolitan area. After settling, wastewater is treated with microbes to break down organic matter at the Jones Island sewage treatment plant (also called "Water Reclamation Facility") in Milwaukee, Wisconsin. >The byproduct sewage sludge is produced. This is heat-dried with hot air in the range of 900–1,200 °F (482–649 °C), which heats the sewage sludge to at least 176 °F (80 °C) to kill pathogens. The material is then pelletized and marketed throughout the United States under the name Milorganite. The result is recycling of the nitrogen and phosphorus from the waste-stream as fertilizer. >The Milwaukee Metropolitan Sewerage District's Jones Island Plant had the largest wastewater treatment capacity of any in the world when constructed in 1925. It was the first plant in the United States to succeed in using the activated sludge treatment process to produce fertilizer. Potassium is excreted by humans mainly in urine, which is easy to recover. But NPK fertilizer is just one piece of the puzzle. AFAIK, plants require 17 essential micro- and macro-nutrients to grow [0]. I'm just a lay gardener, not a chemist nor research scientist, so I'm not sure how to approach recovering calcium, magnesium, sulfur, or metals like zinc and molybdenum for nutrient solution manufacture. That's the nice thing about composting for soil-based gardening; so long as the right microbes are there to make it bioavailable, all the elements you need are in the used-up biomatter. If it was eaten and not exhaled, sweated out, nor incorporated into the body, it'll be there in the waste stream. [0] https://www.researchgate.net/figure/There-are-17-essential-plant-nutrients-required-for-plant-growth_fig25_272818140 https://www.researchgate.net/figure/There-are-17-essential-p...