page_title: Sewage sludge treatment
section_title: Emerging technologies
hierarchical_section_title: Sewage sludge treatment / Treatment processes / Emerging technologies
caption_attribution_description: English: View of sludge thermal hydrolysis reactors at the Blue Plains Advanced Wastewater Treatment Plant, Washington, D.C. This is the largest thermal hydrolysis plant in the world as of 2016. The system began operation in 2015 and generates high quality sludge that is used as soil amendments (200,000 tons/year). It also generates 10 MW of electricity that is used elsewhere at the treatment plant.
context_page_description: Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors.
  Sludge treatment is focused on reducing sludge weight and volume to reduce disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options.
context_section_description: Phosphorus recovery from sewage sludge or from sludge dewatering streams is receiving increased attention particularly in Sweden, Germany and Canada, as phosphorus is a limited resource (a concept also known as "peak phosphorus") and is needed as fertilizer to feed a growing world population. Phosphorus recovery methods from wastewater or sludge can be categorized by the origin of the used matter (wastewater, sludge liquor, digested or non-digested sludge, ash) or by the type of recovery processes (precipitation, wet-chemical extraction and precipitation, thermal treatment). Research on phosphorus recovery methods from sewage sludge has been carried out in Sweden and Germany since around 2003, but the technologies currently under development are not yet cost effective, given the current price of phosphorus on the world market.
  The Omni Processor is a process that is currently under development that treats sewage sludge and can generate a surplus of electrical energy if the input materials have the right level of dryness.
  Thermal depolymerization produces light hydrocarbons from sludge heated to 250 °C and compressed to 40 MPa.
  Thermal hydrolysis is a two-stage process combining high-pressure boiling of sludge, followed by a rapid decompression. This combined action sterilizes the sludge and makes it more biodegradable, which improves digestion performance. Sterilization destroys pathogens in the sludge resulting in it exceeding the stringent requirements for land application (agriculture). Thermal hydrolysis systems are operating at sewage treatment plants in Europe, China and North America, and can generate electricity as well as high quality sludge.
caption: The thermal hydrolysis system at the Blue Plains treatment plant in Washington, D.C. is the largest in the world as of 2016.
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