Ultrasonic cavitation for wastewater treatment. A Review
Article Sidebar
Main Article Content
This review focuses on the technique known by the name of cavitation for wastewater treatment. There are several ways to make a fluid cavitate, the focus of this document is hydrodynamic cavitation and acoustic cavitation. Cavitation occurs when a fluid abruptly changes phase due to a variation in its pressure, the cavities have a considerable amount of energy that favors reactions inside and at the interface of each bubble or cavity that forms within the liquid, as well as in a fluid. This treatment technique is favorable since by itself it does not imply the use or dosage of chemical inputs to reduce the concentration of contaminants in the water. The sources consulted indicate that to achieve greater effectiveness of the cavitation process, it is necessary to intensify the process by the simultaneous implementation of other treatment techniques, including advanced oxidation processes, electrochemical processes, and water clarification. The combinations of cavitation with other wastewater treatment techniques have been studied for different recalcitrant pollutants, achieving very favorable results. This work emphasized mainly as a case study, the wastewater of tanneries.
Rafael N. Agudelo Valencia, Universidad Libre, Facultad de Ingeniería, Bogotá, Colombia
https://orcid.org/0000-0002-6646-7725
Gabriel de J. Camargo Vargas, Universidad Libre, Facultad de Ingeniería, Bogotá, Colombia
https://orcid.org/0000-0003-3721-0936
Héctor F. Rojas Molano, Universidad Libre, Facultad de Ingeniería, Bogotá, Colombia
https://orcid.org/0000-0001-8725-3008
Siby Garcés Polo, Universidad Libre Seccional Barranquilla, Facultad de Ingeniería, Barranquilla, Colombia
https://orcid.org/0000-0001-5892-8205
Santiago Arias Sierra, Universidad Libre, Facultad de Ingeniería, Bogotá, Colombia
https://orcid.org/0000-0003-2844-5805
Isabel C. Agudelo Carrascal, Universidad Libre, Facultad de Ingeniería, Bogotá, Colombia
https://orcid.org/0000-0002-4881-8704
Gogate PR, Thanekar PD, Oke AP. Strategies to improve biological oxidation of real wastewater using cavitation based pre-treatment approaches. Ultrason Sonochem [Internet]. 2020;64(February):105016. Available from: https://doi.org/10.1016/j.ultsonch.2020.105016
Cristóvão RO, Botelho CM, Martins RJE, Loureiro JM, Boaventura RAR. Primary treatment optimization of a fish canning wastewater from a Portuguese plant. Water Resour Ind [Internet]. 2014;6:51–63. Available from: http://dx.doi.org/10.1016/j.wri.2014.07.002
Alfonso-Muniozguren P, Hazzwan Bohari M, Sicilia A, Avignone-Rossa C, Bussemaker M, Saroj D, et al. Tertiary treatment of real abattoir wastewater using combined acoustic cavitation and ozonation. Ultrason Sonochem [Internet]. 2020;64(June 2019):104986. Available from: https://doi.org/10.1016/j.ultsonch.2020.104986
Garcia-Segura S, Eiband MMSG, de Melo JV, Martínez-Huitle CA. Electrocoagulation and advanced electrocoagulation processes: A general review about the fundamentals, emerging applications and its association with other technologies. J Electroanal Chem [Internet]. 2017;801(July):267–99. Available from: http://dx.doi.org/10.1016/j.jelechem.2017.07.047
Liang Y, Zhu H, Bañuelos G, Yan B, Zhou Q, Yu X, et al. Constructed wetlands for saline wastewater treatment: A review. Ecol Eng. 2017;98:275–85.
Fababuj-Roger M, Mendoza-Roca JA, Galiana-Aleixandre M V., Bes-Piá A, Cuartas-Uribe B, Iborra-Clar A. Reuse of tannery wastewaters by combination of ultrafiltration and reverse osmosis after a conventional physical-chemical treatment. Desalination. 2007;204(1-3 SPEC. ISS.):219–26.
Thalmann B, von Gunten U, Kaegi R. Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: Kinetics and mechanisms. Water Res [Internet]. 2018;134:170–80. Available from: https://doi.org/10.1016/j.watres.2018.01.042
Sivagami K, Sakthivel KP, Nambi IM. Advanced oxidation processes for the treatment of tannery wastewater. J Environ Chem Eng [Internet]. 2016;(October 2016):0–1. Available from: http://dx.doi.org/10.1016/j.jece.2017.06.004
Wang Z, Srivastava V, Ambat I, Safaei Z, Sillanpää M. Degradation of Ibuprofen by UV-LED/catalytic advanced oxidation process. J Water Process Eng [Internet]. 2019;31(October 2018):100808. Available from: https://doi.org/10.1016/j.jwpe.2019.100808
Thanekar P, Panda M, Gogate PR. Degradation of carbamazepine using hydrodynamic cavitation combined with advanced oxidation processes. Ultrason Sonochem [Internet]. 2018;40(May 2017):567–76. Available from: https://doi.org/10.1016/j.ultsonch.2017.08.001
Gujar SK, Gogate PR, Kanthale P, Pandey R, Thakre S, Agrawal M. Combined oxidation processes based on ultrasound, hydrodynamic cavitation and chemical oxidants for treatment of real industrial wastewater from cellulosic fiber manufacturing sector. Sep Purif Technol [Internet]. 2021;257(October 2020):117888. Available from: https://doi.org/10.1016/j.seppur.2020.117888
Gągol M, Przyjazny A, Boczkaj G. Wastewater treatment by means of advanced oxidation processes based on cavitation – A review. Chem Eng J. 2018;338(January):599–627.
Wu P, Bai L, Lin W, Wang X. Mechanism and dynamics of hydrodynamic-acoustic cavitation (HAC). Ultrason Sonochem [Internet]. 2018;49(July):89–96. Available from: https://doi.org/10.1016/j.ultsonch.2018.07.021
Yi C, Lu Q, Wang Y, Wang Y, Yang B. Degradation of organic wastewater by hydrodynamic cavitation combined with acoustic cavitation. Ultrason Sonochem [Internet]. 2018;43(28):156–65. Available from: https://doi.org/10.1016/j.ultsonch.2018.01.013
Dular M, Griessler-Bulc T, Gutierrez-Aguirre I, Heath E, Kosjek T, Krivograd Klemenčič A, et al. Use of hydrodynamic cavitation in (waste)water treatment. Ultrason Sonochem. 2016;29:577–88.
Pozsgai E, Galambos I, Dóka G, Csóka L. Use of hydrodynamic cavitation with additional high purity water for thermal water treatment. Chem Eng Process - Process Intensif [Internet]. 2018;128(December 2017):77–9. Available from: https://doi.org/10.1016/j.cep.2018.04.016
Gogate PR, Pandit AB. A review and assessment of hydrodynamic cavitation as a technology for the future. Ultrason Sonochem. 2005;12(1-2 SPEC. ISS.):21–7.
Gore MM, Saharan VK, Pinjari D V., Chavan P V., Pandit AB. Degradation of reactive orange 4 dye using hydrodynamic cavitation based hybrid techniques. Ultrason Sonochem [Internet]. 2014;21(3):1075–82. Available from: http://dx.doi.org/10.1016/j.ultsonch.2013.11.015
Arrojo S, Benito Y, Martínez Tarifa A. A parametrical study of disinfection with hydrodynamic cavitation. Ultrason Sonochem. 2008;15(5):903–8.
Ozonek J. Application of hydrodynamic cavitation in environmental engineering. CRC Press; 2012. 122 p.
Badve M, Gogate P, Pandit A, Csoka L. Hydrodynamic cavitation as a novel approach for wastewater treatment in wood finishing industry. Sep Purif Technol [Internet]. 2013;106:15–21. Available from: http://dx.doi.org/10.1016/j.seppur.2012.12.029
Thanekar P, Murugesan P, Gogate PR. Improvement in biological oxidation process for the removal of dichlorvos from aqueous solutions using pretreatment based on Hydrodynamic Cavitation. J Water Process Eng [Internet]. 2018;23(March):20–6. Available from: https://doi.org/10.1016/j.jwpe.2018.03.004
Wang X, Jia J, Wang Y. Combination of photocatalysis with hydrodynamic cavitation for degradation of tetracycline. Chem Eng J [Internet]. 2017;315:274–82. Available from: http://dx.doi.org/10.1016/j.cej.2017.01.011
Huang Y, Wu Y, Huang W, Yang F, Ren XE. Degradation of chitosan by hydrodynamic cavitation. Polym Degrad Stab. 2013;98(1):37–43.
Malade L V., Deshannavar UB. Decolorisation of Reactive Red 120 by hydrodynamic cavitation. Mater Today Proc [Internet]. 2018;5(9):18400–9. Available from: https://doi.org/10.1016/j.matpr.2018.06.180
Prajapat AL, Gogate PR. Depolymerization of carboxymethyl cellulose using hydrodynamic cavitation combined with ultraviolet irradiation and potassium persulfate. Ultrason Sonochem [Internet]. 2019;51(August 2018):258–63. Available from: https://doi.org/10.1016/j.ultsonch.2018.10.009
Choi J, Cui M, Lee Y, Kim J, Son Y, Khim J. Hydrodynamic cavitation and activated persulfate oxidation for degradation of bisphenol A: Kinetics and mechanism. Chem Eng J [Internet]. 2018;338(January):323–32. Available from: https://doi.org/10.1016/j.cej.2018.01.018
Bagal M V., Gogate PR. Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis. Ultrason Sonochem [Internet]. 2014;21(3):1035–43. Available from: http://dx.doi.org/10.1016/j.ultsonch.2013.10.020
Doltade SB, Dastane GG, Jadhav NL, Pandit AB, Pinjari D V., Somkuwar N, et al. Hydrodynamic cavitation as an imperative technology for the treatment of petroleum refinery effluent. J Water Process Eng [Internet]. 2019;29(January):100768. Available from: https://doi.org/10.1016/j.jwpe.2019.02.008
Barik AJ, Gogate PR. Degradation of 4-chloro 2-aminophenol using a novel combined process based on hydrodynamic cavitation, UV photolysis and ozone. Ultrason Sonochem [Internet]. 2016;30:70–8. Available from: http://dx.doi.org/10.1016/j.ultsonch.2015.11.007
Panda D, Manickam S. Hydrodynamic cavitation assisted degradation of persistent endocrine-disrupting organochlorine pesticide Dicofol: Optimization of operating parameters and investigations on the mechanism of intensification. Ultrason Sonochem [Internet]. 2019;51(May 2018):526–32. Available from: https://doi.org/10.1016/j.ultsonch.2018.04.003
Capocelli M, Prisciandaro M, Lancia A, Musmarra D. Hydrodynamic cavitation of p-nitrophenol: A theoretical and experimental insight. Chem Eng J [Internet]. 2014;254:1–8. Available from: http://dx.doi.org/10.1016/j.cej.2014.05.102
Timothy Mason. Dietmar Peters. Practical sonochemistry. Power ultrasound uses and aplications. Philadelphia: Woodhead Publishing Limited; 2002. 155 p.
Ghafarzadeh M, Abedini R, Rajabi R. Optimization of ultrasonic waves application in municipal wastewater sludge treatment using response surface method. J Clean Prod [Internet]. 2017;150:361–70. Available from: http://dx.doi.org/10.1016/j.jclepro.2017.02.159
Luo X, Gong H, He Z, Zhang P, He L. Recent advances in applications of power ultrasound for petroleum industry. Ultrason Sonochem [Internet]. 2021;70(August 2020):105337. Available from: https://doi.org/10.1016/j.ultsonch.2020.105337
Bai L, Yan J, Zeng Z, Ma Y. Cavitation in thin liquid layer: A review. Ultrason Sonochem. 2020;66(March).
Mohanty P, Mahapatra R, Padhi P, Ramana CHVV, Mishra DK. Ultrasonic cavitation: An approach to synthesize uniformly dispersed metal matrix nanocomposites—A review. Nano-Structures and Nano-Objects [Internet]. 2020;23:100475. Available from: https://doi.org/10.1016/j.nanoso.2020.100475
Lippert T, Bandelin J, Schlederer F, Drewes JE, Koch K. Effects of ultrasonic reactor design on sewage sludge disintegration. Ultrason Sonochem [Internet]. 2020;68(June):105223. Available from: https://doi.org/10.1016/j.ultsonch.2020.105223
Rodríguez-Calvo A, Gonzalez-Lopez J, Ruiz LM, Gómez-Nieto MÁ, Muñoz-Palazon B. Effect of ultrasonic frequency on the bacterial community structure during biofouling formation in microfiltration membrane bioreactors for wastewater treatment. Int Biodeterior Biodegrad. 2020;155(April).
Jyoti KK, Pandit AB. Water disinfection by acoustic and hydrodynamic cavitation. Biochem Eng J. 2001;7(3):201–12.
Saxena S, Rajoriya S, Saharan VK, George S. An advanced pretreatment strategy involving hydrodynamic and acoustic cavitation along with alum coagulation for the mineralization and biodegradability enhancement of tannery waste effluent. Ultrason Sonochem [Internet]. 2018;44(February):299–309. Available from: https://doi.org/10.1016/j.ultsonch.2018.02.035
Korpe S, Bethi B, Sonawane SH, Jayakumar K V. Tannery wastewater treatment by cavitation combined with advanced oxidation process (AOP). Ultrason Sonochem [Internet]. 2019;59(March):104723. Available from: https://doi.org/10.1016/j.ultsonch.2019.104723
Gogate PR, Bhosale GS. Comparison of effectiveness of acoustic and hydrodynamic cavitation in combined treatment schemes for degradation of dye wastewaters. Chem Eng Process Process Intensif [Internet]. 2013;71:59–69. Available from: http://dx.doi.org/10.1016/j.cep.2013.03.001
Chandak S, Ghosh PK, Gogate PR. Treatment of real pharmaceutical wastewater using different processes based on ultrasound in combination with oxidants. Process Saf Environ Prot [Internet]. 2020;137:149–57. Available from: https://doi.org/10.1016/j.psep.2020.02.025
Bagal M V., Gogate PR. Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: A review. Ultrason Sonochem [Internet]. 2014;21(1):1–14. Available from: http://dx.doi.org/10.1016/j.ultsonch.2013.07.009
Hilares RT, Atoche-Garay DF, Pagaza DAP, Ahmed MA, Andrade GJC, Santos JC. Promising physicochemical technologies for poultry slaughterhouse wastewater treatment: A critical review. J Environ Chem Eng. 2021;9(2).
Ifelebuegu AO, Onubogu J, Joyce E, Mason T. Sonochemical degradation of endocrine disrupting chemicals 17β-estradiol and 17α-ethinylestradiol in water and wastewater. Int J Environ Sci Technol. 2014;11(1):1–8.
Zhang M, Zhang Z, Liu S, Peng Y, Chen J, Yoo Ki S. Ultrasound-assisted electrochemical treatment for phenolic wastewater. Ultrason Sonochem [Internet]. 2020;65(February):105058. Available from: https://doi.org/10.1016/j.ultsonch.2020.105058
Jaafarzadeh N, Takdastan A, Jorfi S, Ghanbari F, Ahmadi M, Barzegar G. The performance study on ultrasonic/Fe3O4/H2O2 for degradation of azo dye and real textile wastewater treatment. J Mol Liq. 2018;256:462–70.
Patil V V., Gogate PR, Bhat AP, Ghosh PK. Treatment of laundry wastewater containing residual surfactants using combined approaches based on ozone, catalyst and cavitation. Sep Purif Technol [Internet]. 2020;239(January):116594. Available from: https://doi.org/10.1016/j.seppur.2020.116594
Pulicharla R, Das RK, Kaur Brar S, Drogui P, Surampalli RY. Degradation kinetics of chlortetracycline in wastewater using ultrasonication assisted laccase. Chem Eng J [Internet]. 2018;347(April):828–35. Available from: https://doi.org/10.1016/j.cej.2018.04.162
Ayare SD, Gogate PR. Sonophotocatalytic oxidation based treatment of phthalocyanine pigment containing industrial wastewater intensified using oxidising agents. Sep Purif Technol [Internet]. 2020;233(July 2019):115979. Available from: https://doi.org/10.1016/j.seppur.2019.115979
Tan WK, Cheah SC, Parthasarathy S, Rajesh RP, Pang CH, Manickam S. Fish pond water treatment using ultrasonic cavitation and advanced oxidation processes. Chemosphere [Internet]. 2021;274:129702. Available from: https://doi.org/10.1016/j.chemosphere.2021.129702
Farhadi N, Tabatabaie T, Ramavandi B, Amiri F. Ibuprofen elimination from water and wastewater using sonication/ultraviolet/hydrogen peroxide/zeolite-titanate photocatalyst system. Environ Res [Internet]. 2021;198(April):111260. Available from: https://doi.org/10.1016/j.envres.2021.111260
Patil PB, Raut-Jadhav S, Pandit AB. Effect of intensifying additives on the degradation of thiamethoxam using ultrasound cavitation. Ultrason Sonochem [Internet]. 2021;70(August 2020):105310. Available from: https://doi.org/10.1016/j.ultsonch.2020.105310
Ren Q, Kong C, Chen Z, Zhou J, Li W, Li D, et al. Ultrasonic assisted electrochemical degradation of malachite green in wastewater. Microchem J [Internet]. 2021;164(November 2020):106059. Available from: https://doi.org/10.1016/j.microc.2021.106059
Alibardi L, Cossu R. Pre-treatment of tannery sludge for sustainable landfilling. Waste Manag [Internet]. 2016;52:202–11. Available from: http://dx.doi.org/10.1016/j.wasman.2016.04.008
Selvaraj H, Aravind P, George HS, Sundaram M. Removal of sulfide and recycling of recovered product from tannery lime wastewater using photoassisted-electrochemical oxidation process. J Ind Eng Chem [Internet]. 2020;83:164–72. Available from: https://doi.org/10.1016/j.jiec.2019.11.024
Saxena S, Saharan VK, George S. Enhanced synergistic degradation efficiency using hybrid hydrodynamic cavitation for treatment of tannery waste effluent. J Clean Prod [Internet]. 2018;198:1406–21. Available from: https://doi.org/10.1016/j.jclepro.2018.07.135
Haydar S, Aziz JA. Coagulation-flocculation studies of tannery wastewater using combination of alum with cationic and anionic polymers. J Hazard Mater. 2009;168(2–3):1035–40.
Aber S, Salari D, Parsa MR. Employing the Taguchi method to obtain the optimum conditions of coagulation-flocculation process in tannery wastewater treatment. Chem Eng J [Internet]. 2010;162(1):127–34. Available from: http://dx.doi.org/10.1016/j.cej.2010.05.012
Azizi M, Biard PF, Couvert A, Ben Amor M. Competitive kinetics study of sulfide oxidation by chlorine using sulfite as reference compound. Chem Eng Res Des. 2015;94(August):141–52.
El-Sheikh MA, Saleh HI, Flora JR, AbdEl-Ghany MR. Biological tannery wastewater treatment using two stage UASB reactors. Desalination [Internet]. 2011;276(1–3):253–9. Available from: http://dx.doi.org/10.1016/j.desal.2011.03.060
De Gisi S, Galasso M, De Feo G. Treatment of tannery wastewater through the combination of a conventional activated sludge process and reverse osmosis with a plane membrane. Desalination [Internet]. 2009;249(1):337–42. Available from: http://dx.doi.org/10.1016/j.desal.2009.03.014
Tammaro M, Salluzzo A, Perfetto R, Lancia A. A comparative evaluation of biological activated carbon and activated sludge processes for the treatment of tannery wastewater. J Environ Chem Eng [Internet]. 2014;2(3):1445–55. Available from: http://dx.doi.org/10.1016/j.jece.2014.07.004
Sundarapandiyan S, Chandrasekar R, Ramanaiah B, Krishnan S, Saravanan P. Electrochemical oxidation and reuse of tannery saline wastewater. J Hazard Mater [Internet]. 2010;180(1–3):197–203. Available from: http://dx.doi.org/10.1016/j.jhazmat.2010.04.013
Elabbas S, Ouazzani N, Mandi L, Berrekhis F, Perdicakis M, Pontvianne S, et al. Treatment of highly concentrated tannery wastewater using electrocoagulation: Influence of the quality of aluminium used for the electrode. J Hazard Mater [Internet]. 2016;319:69–77. Available from: http://dx.doi.org/10.1016/j.jhazmat.2015.12.067
Sivagami K, Sakthivel KP, Nambi IM. Advanced oxidation processes for the treatment of tannery wastewater. J Environ Chem Eng [Internet]. 2016;6(3):3656–63. Available from: https://doi.org/10.1016/j.jece.2017.06.004
Sauer TP, Casaril L, Oberziner ALB, José HJ, Moreira R de FPM. Advanced oxidation processes applied to tannery wastewater containing Direct Black 38-Elimination and degradation kinetics. J Hazard Mater. 2006;135(1–3):274–9.
Dotro G, Castro S, Tujchneider O, Piovano N, Paris M, Faggi A, et al. Performance of pilot-scale constructed wetlands for secondary treatment of chromium-bearing tannery wastewaters. J Hazard Mater [Internet]. 2012;239–240:142–51. Available from: http://dx.doi.org/10.1016/j.jhazmat.2012.08.050
Di Iaconi C, Ramadori R, Lopez A. The effect of ozone on tannery wastewater biological treatment at demonstrative scale. Bioresour Technol [Internet]. 2009;100(23):6121–4. Available from: http://dx.doi.org/10.1016/j.biortech.2009.06.022
Hashem MA, Nur-A-Tomal MS, Bushra SA. Oxidation-coagulation-filtration processes for the reduction of sulfide from the hair burning liming wastewater in tannery. J Clean Prod [Internet]. 2016;127:339–42. Available from: http://dx.doi.org/10.1016/j.jclepro.2016.03.159
Pérez JF, Llanos J, Sáez C, López C, Cañizares P, Rodrigo MA. The pressurized jet aerator: A new aeration system for high-performance H2O2electrolyzers. Electrochem commun [Internet]. 2018;89(February):19–22. Available from: https://doi.org/10.1016/j.elecom.2018.02.012
Kandasamy K, Tharmalingam K, Velusamy S. Treatment of tannery effluent using sono catalytic reactor. J Water Process Eng [Internet]. 2017;15:72–7. Available from: http://dx.doi.org/10.1016/j.jwpe.2016.09.001
Korpe S, Bethi B, Sonawane SH, Jayakumar K V. Tannery wastewater treatment by cavitation combined with advanced oxidation process (AOP). Ultrason Sonochem [Internet]. 2019;59(August):104723. Available from: https://doi.org/10.1016/j.ultsonch.2019.104723
Jeganathan S, Kandasamy K, Velusamy S, Sankaran P. Comparative studies on ultrasound assisted treatment of tannery effluent using multiple oxy-catalysts using response surface methodology. Arab J Chem [Internet]. 2020;13(9):7066–77. Available from: https://doi.org/10.1016/j.arabjc.2020.07.012
Saxena S, Saharan VK, George S. Enhanced synergistic degradation efficiency using hybrid hydrodynamic cavitation for treatment of tannery waste effluent. J Clean Prod [Internet]. 2018;198:1406–21. Available from: https://doi.org/10.1016/j.jclepro.2018.07.135
Gogate PR, Mujumdar S, Pandit AB. Sonochemical reactors for waste water treatment: comparison using formic acid degradation as a model reaction. Adv Environ Res. 2003 Jan 1;7(2):283–99.
Mason TJ, Joyce E, Phull SS, Lorimer JP. Potential uses of ultrasound in the biological decontamination of water. Ultrason Sonochem. 2003 Oct 1;10(6):319–23.
Gilpavas E, Arbeláez-Castaño PE, Medina-Arroyave JD, Gómez-Atehortua CM, Gilpavas E, Arbeláez-Castaño PE, et al. TRATAMIENTO DE AGUAS RESIDUALES DE LA INDUSTRIA TEXTIL MEDIANTE COAGULACIÓN QUÍMICA ACOPLADA A PROCESOS FENTON INTENSIFICADOS CON ULTRASONIDO DE BAJA FRECUENCIA. Rev Int Contam Ambient [Internet]. 2018 [cited 2021 Oct 15];34(1):157–67. Available from: http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0188-49992018000100157&lng=es&nrm=iso&tlng=es
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Authors grant the journal and Universidad del Valle the economic rights over accepted manuscripts, but may make any reuse they deem appropriate for professional, educational, academic or scientific reasons, in accordance with the terms of the license granted by the journal to all its articles.
Articles will be published under the Creative Commons 4.0 BY-NC-SA licence (Attribution-NonCommercial-ShareAlike).