Reuse and recycling of wastes for plant nutrition products as outlined above mainly involves biotransformation to usable soil amendments or use of incineration, pyrolysis, and gasification. These technologies are suitable for municipal solid waste treatment. Incineration, pyrolysis, gasification, and gasification coupled with ash melting are widely used for energy and nutrient recovery from solid wastes. Incineration is the combustion of waste to produce heat and electricity. The remaining products are nutrient-rich ashes that can be used as a part of fertilizer feedstock. Sewage sludge ashes are rich in phosphorus. Ashes from biomass rich in potassium, calcium and magnesium are also useful for fertilizing purposes. Pyrolysis is the heating of waste under a limited supply of oxygen; it is an important method for the processing of livestock waste. Biomass pyrolysis produces bio-oil and biochar or charcoal. Biochar quality and its saturation with nutrients depends on the used feedstocks such as biomass crops, agricultural residues, agroforestry, and sewage sludges. For instance, biochar produced from sewage sludges at 450 ⁰C contains all possible forms of phosphorus nutrients and a variety of N-based nutrients. Biochar can be also prepared by gasification. Gasification is a form of pyrolysis which applies to higher temperatures producing mainly gases and a small amount of biochar. Gasification of organic waste in supercritical water at 600 ⁰C yielded both energy and biochar containing nitrogen nutrients like ammonium salts. The narrower search of patents and journals focusing on nitrogen and phosphorus recovery from wastes and wastewaters revealed documents associated where the term "charcoal" has been emphasized (Fig. ), charcoal in this context is referring to biochar. A clear increasing trend in the patents and journals through 2021 in visualized this figure. Many of the documents found involve either processes to make biochar or describe its use as a soil amendment, as an adsorbent or carrier for nutrients or agrochemicals, or as a sorbent for pollutants. The variety of ways in which biochar is used may explain the increase in interest in biochar. If trends are compared in this set using numbers of combined journals and patents each containing a CAS term for "ashes", "wastewater treatment sludge" or "sewage sludge fertilizers" (Fig. ), an increasing number of documents concerning recovery of nutrients from wastewater treatment sludge, biochar (charcoal) and ashes (including sludge incinerator ash, fly ash, bone ash) is seen, while the number concerned with "sewage sludge fertilizers" has remained low. The term "sewage sludge fertilizers" would be indexed in documents focused more on sewage sludge formulated into a fertilizer product. Numbers indicate that sewage sludge fertilizer products, at least explicitly stating so, remain very low in the data set, while biochar, many forms incorporating use of sewage sludge as feed stock, are increasing. The use of sewage sludge is constrained by regulations to limit the transfer of organic contaminants, heavy metals, and pathogens to agricultural products and other soils. Regulations require the monitoring of biosolids and the products (such as biochar) derived from them, set limits on specific contaminants of concern, and determine when derived products can be used on soil used for fruits, vegetables, and grazing animals. These rules increase the costs of biosolids in fertilizer and so may reduce commercial interest in them. There are some pollutant and nutrient-release complications due to feedstock sources and pyrolysis processes used to form the biochar as we mentioned for sludges. However, other bio-sourced feedstocks for biochar are rising in use. A variety of feedstocks and methods have been used to prepare biochar-based fertilizer. Biochar and engineered biochar (biochar can be engineered through composition of feedstock, pyrolysis temperatures or other chemical additives) can be used as an adsorbent for ammonium, nitrate, and phosphate from wastewaters. Release of adsorbed nutrients requires a desorption process such as acid/base solutions, ion exchange, or biodegradation to release nutrients. Nutrient-adsorbed biochar can be directly applied to soil as a slow-release fertilizer to be biodegraded naturally. Similarly, in another study, varying the pyrolysis temperature of sewage sludge used as feedstock affected the availability of nutrients in the resulting biochar. The authors determined that changes in total and available contents of Ca, K, Mg, P, and S during the optimal pyrolysis of anaerobically stabilized sewage sludge was 320 °C. This lower temperature is less energetically demanding when compared to higher temperatures, and the resulting material showed the highest content of available P whereas available contents of other studied nutrients were reduced only slightly.