Sewage sludge
Sewage sludge is usually treated by one or several of the following treatment steps: lime stabilization, thickening, dewatering, drying, anaerobic digestion or composting.
Following treatment, sewage sludge is either landfilled, dumped in the ocean, incinerated, applied on agricultural land or, in some cases, retailed or given away for free to the general public.
[24] The findings of a 20-year field study of air, land, and water in Arizona, concluded that use of biosolids is sustainable and improves the soil and crops.
[25] Other studies report that plants uptake large quantities of heavy metals and toxic pollutants that are retained by produce, which is then consumed by humans.
[29] Studies have indicated that pharmaceuticals and personal care products, which often adsorb to sludge during wastewater treatment, can persist in agricultural soils following biosolid application.
[30] Some of these chemicals, including potential endocrine disruptor triclosan, can also travel through the soil column and leach into agricultural tile drainage at detectable levels.
The impact of this persistence in soils is unknown, but the link to human and land animal health is likely tied to the capacity for plants to absorb and accumulate these chemicals in their consumed tissues.
Studies of this kind are in early stages, but evidence of root uptake and translocation to leaves did occur for both triclosan and triclocarban in soybeans.
[35][36] In 2007 the Northeast Regional Multi-State Research Committee (NEC 1001) issued conservative guidelines tailored to the soils and conditions typical of the northeastern US.
[48] These can include using sludge to produce energy, create carbon-based components, extract phosphorus and nitrogen, or make bricks or other construction materials.
[49] Phosphate can be recovered with minimal capital expenditure as technology currently exists, but municipalities have little political will to attempt nutrient extraction, instead opting for a "take all the other stuff" mentality.
[57] Some highlights include: Micro-pollutants are compounds which are normally found at concentrations up to microgram per liter and milligram per kilogram in the aquatic and terrestrial environment, respectively, and they are considered to be potential threats to environmental ecosystems.
[57] Sewage treatment plants receive various forms of hazardous waste from hospitals, nursing homes, industry and households.
SCDHEC issued emergency regulatory order banning all PCB laden sewage sludge from being land applied on farm fields or deposited into landfills in South Carolina.
[63][64] Also in 2013, after DHEC request, the city of Charlotte decided to stop land applying sewage sludge in South Carolina while authorities investigated the source of PCB contamination.
[66] Contaminants of concern in sewage sludge are plasticizers, PDBEs, PFASs ("forever chemicals"),[67] and others generated by human activities, including personal care products and medicines.
Synthetic fibers from fabrics persist in treated sewage sludge as well as in biosolids-treated soils and may thus serve as an indicator of past biosolids application.
[71] The NRC noted that further research is needed and made about 60 recommendations for addressing public health concerns, scientific uncertainties, and data gaps in the science underlying the sewage sludge standards.
The findings suggest an increased risk for certain respiratory, gastrointestinal, and other diseases among residents living near farm fields on which the use of biosolids was permitted."
[77] The chain of sewage sledge to biosolids to fertilizers has resulted in PFASs ("forever chemicals") contamination of farm produce in Maine in 2021[78] and beef raised in Michigan in 2022.
[83] The EU has directives in place to encourage the use of sewage sludge in agriculture, in a way that the soil, humans, and the environment are not harmed.
[89] The directive explicitly regulates the allowable levels of seven heavy metals (cadmium, copper, nickel, lead, zinc, mercury, and chromium) in soil and sludge, and regulates any application of sewage sludge that would cause levels of these heavy metals in soil to exceed those limits.
[87][89] EU member states are tasked with implementing and enforcing the Directive within their borders, as well as monitoring and reporting on sludge production, treatment, characteristics, and use.
[93] Each of Austria's federal states has its own regulations for the use of sewage sludge in agriculture, including different limits for heavy metals.
[96][97] The Sewage Sludge Directive has been evaluated several times under EU proposals to build a circular economy through the reduction and reuse of wastes.
[104][105] After the 1991 Congressional ban on ocean dumping, the U.S. Environmental Protection Agency (EPA) instituted a policy of digested sludge reuse on agricultural land.
[106] According to the EPA, biosolids that meet treatment and pollutant content criteria of Part 503.13 "can be safely recycled and applied as fertilizer to sustainably improve and maintain productive soils and stimulate plant growth."
PFRPs include pasteurization, heat drying, thermophilic composting (aerobic digestion, most common method), and beta or gamma ray irradiation.
[108][109] Biosolids that meet the Class B pathogen treatment and pollutant criteria, in accordance with the EPA "Standards for the use or disposal of sewage sludge" (40 CFR Part 503), can be land applied with formal site restrictions and strict record keeping.
The follow-up report in 2002 documented that "the EPA cannot assure the public that current land application practices are protective of human health and the environment."
