The ammonium mix process is sustainable because it converts municipal solids into a product that fertilizes crops.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/key-ingredient-breakthrough-commercial-grade-fertilizer-municipal-wastewater
[2] http://admin.indiaenvironmentportal.org.in/category/author/john-f-donovan
[3] http://admin.indiaenvironmentportal.org.in/category/journal/everything-about-water
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/industrial-waste-treatment
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/fertiliser-industry
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/waste-recycling