Editing Sewage sludge (section)

== Quantities produced ==
The amount of sewage sludge produced is proportional to the amount and concentration of wastewater treated, and it also depends on the type of wastewater treatment process used. It can be expressed as kg dry solids per cubic metre of wastewater treated. The total sludge production from a wastewater treatment process is the sum of sludge from primary settling tanks (if they are part of the process configuration) plus excess sludge from the biological treatment step. For example, primary sedimentation produces about 110–170&nbsp;kg/ML of so-called primary sludge, with a value of 150&nbsp;kg/ML regarded as being typical for municipal wastewater in the U.S. or Europe.<ref name="Tchobanoglous-2003" /> The sludge production is expressed as kg of dry solids produced per ML of wastewater treated; one mega litre (ML) is 10<sup>3</sup> m<sup>3</sup>. Of the biological treatment processes, the [[activated sludge]] process produces about 70–100&nbsp;kg/ML of waste activated sludge, and a [[trickling filter]] process produces slightly less sludge from the biological part of the process: 60–100&nbsp;kg/ML.<ref name="Tchobanoglous-2003" /> This means that the total sludge production of an activated sludge process that uses primary sedimentation tanks is in the range of 180–270&nbsp;kg/ML, being the sum of primary sludge and waste activated sludge.

United States municipal wastewater treatment plants in 1997 produced about 7.7 million dry tons of sewage sludge, and about 6.8 million dry tons in 1998 according to [[United States Environmental Protection Agency|EPA]] estimates.<ref name="EPA530R99009">{{cite report |url=https://www.epa.gov/sites/production/files/2015-07/documents/biosolids_generation_use_disposal_in_u.s_1999.pdf |title=Biosolids Generation, Use, and Disposal in The United States |date=September 1999 |publisher=[[United States Environmental Protection Agency|EPA]] |page=2 |id=EPA530-R-99-009 |access-date=30 May 2017}}</ref> As of 2004, about 60% of all sewage sludge was applied to land as a [[soil amendment]] and [[fertilizer]] for growing crops.<ref name="Lu2012">{{cite journal |last1=Lu |first1=Qin |last2=He |first2=Zhenli H. |last3=Stoffella |first3=Peter J. |year=2012 |editor-last=Torri |editor-first=Silvana I. |title=Land Application of Biosolids in the USA: A Review |journal=Applied and Environmental Soil Science |volume=2012 |page=4 |doi=10.1155/2012/201462 |id=201462 |doi-access=free}}</ref> In a review article published in 2012, it was reported that a total amount of 10.1 million tn DS/year were produced in EU-27 countries.<ref>Kelessidis and Stasinakis, 2012. COMPARATIVE STUDY OF THE METHODS USED FOR TREATMENT AND FINAL DISPOSAL OF SEWAGE SLUDGE IN EUROPEAN COUNTRIES. Waste Management, vol.32, June 2012, p. 1186-1195. [https://www.sciencedirect.com/science/article/pii/S0956053X12000268?via%3Dihub Kelessidis and Stasinakis, 2012]</ref> As of 2023, the EU produced 2 to 3 million tons of sludge each year.<ref name=":212">{{Citation |title=COMMISSION STAFF WORKING DOCUMENT EXECUTIVE SUMMARY OF THE EVALUATION Council Directive 86/278/EEC of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture |date=2023 |url=https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=SWD:2023:158:FIN&qid=1684830815132 |access-date=2024-10-18 |language=en}}</ref> Worldwide it is estimated that as much as 75 Million Mg of dry sewage sludge per year.<ref>{{Cite journal |last1=Kominko |first1=Halyna |last2=Gorazda |first2=Katarzyna |last3=Wzorek |first3=Zbigniew |date=2024-06-01 |title=Sewage sludge: A review of its risks and circular raw material potential |url=https://www.sciencedirect.com/science/article/pii/S2214714424007542 |journal=Journal of Water Process Engineering |volume=63 |pages=105522 |doi=10.1016/j.jwpe.2024.105522 |bibcode=2024JWPE...6305522K |issn=2214-7144}}</ref>

Production of sewage sludge can be reduced by conversion from [[flush toilet]]s to [[dry toilets]] such as [[urine-diverting dry toilet]]s and [[composting toilet]]s.<ref name="Rieck-2012">{{cite web |last1=Rieck |first1=Christian |last2=von Münch |first2=Elisabeth |last3=Hoffmann |first3=Heike |date=December 2012 |title=Technology Review of Urine-diverting dry toilets (UDDTs) |url=http://www.susana.org/_resources/documents/default/2-874-technology-review-of-uddts-18-june-2013.pdf |access-date=5 June 2017 |website=[[Sustainable Sanitation Alliance|Susana]] |publisher=[[Deutsche Gesellschaft für Internationale Zusammenarbeit|GIZ]]}}</ref>