If you’ve ever wondered why sludge is not supposed to be used as a fertilizer on organic foods, the answer is, actually, quite clear – sludge is nothing else but solid waste from industrial wastewater and sewage treatment plants, so why should it be allowed?
Following what’s said in Urban Farming by Thomas J. Fox, we see that in order to label a product “organic,” it has to fit the following description: “agricultural product cannot be produced using excluded methods, sewage sludge or ionizing radiation.” And, once again, the definition of sludge is “solid, semi-solid or liquid residue generated during the treatment of domestic sewage in a treatment works.”
One might wonder why not use human manure when organic farmers can use animal manure, right? Well, the answer is quite clear – our sewage mostly combines residential and industrial waste, and such mixture could easily result in contamination by substances such as mercury, lead, and dioxins.
Standards for anyone who wants to sell any agricultural product as organically produced are regulated by The United States Department of Agriculture’s National Organic Program.