1. Recovery of precious materials from wastewater

1.1. Physical methods

1.1.1. Ion exchange

1. (https://www.tandfonline.com/doi/abs/10.1080/00032710008543224)
2. (https://www.sciencedirect.com/science/article/pii/S0304389410002785)
3. (https://www.sciencedirect.com/science/article/pii/S002197971101054X)
4. (https://link.springer.com/article/10.1007/s10967-007-1112-2)
5. (https://pubs.acs.org/doi/abs/10.1021/es061499l)
6. (http://www.freepatentsonline.com/7687663.pdf)
7. (http://www.freepatentsonline.com/6346195.pdf)

1.1.2. Ion flotation

1. (https://www.tandfonline.com/doi/abs/10.1080/03602549108021407)
2. (https://www.tandfonline.com/doi/abs/10.1081/SS-100108362)
3. (https://www.tandfonline.com/doi/abs/10.1080/01496399408006631)
4. (https://www.sciencedirect.com/science/article/abs/pii/S0043135498000657)
5. (http://scindeks.ceon.rs/article.aspx?artid=1450-59590204001M)
6. (http://www.freepatentsonline.com/4219416.pdf)

1.1.3. Adsorption

1. (https://www.tandfonline.com/doi/abs/10.1080/01496395.2013.811692)
2. (https://pubs.acs.org/doi/abs/10.1021/je2007154)
3. (https://www.mdpi.com/2075-4701/7/12/529)
4. (http://www.freepatentsonline.com/6315906.pdf)

1.2. Chemical methods

1.2.1. Precipitation

1. (https://www.sciencedirect.com/science/article/abs/pii/S0043135405001922)
2. (https://www.sciencedirect.com/science/article/pii/S0304389409017865)
3. (http://www.freepatentsonline.com/20020079269.pdf)
4. (http://www.freepatentsonline.com/7935173.pdf)

1.2.2. Cementation

1. (https://www.sciencedirect.com/science/article/abs/pii/S0304386X10003178)
2. (https://www.sciencedirect.com/science/article/abs/pii/S0301751612000865)
3. (https://www.tandfonline.com/doi/abs/10.1179/cmq.2010.49.2.147)
4. (https://patents.google.com/patent/JP2014214316A/en)
5. (http://www.freepatentsonline.com/5133873.pdf)

1.2.3. Electroextraction/Electro winning

1. (https://www.sciencedirect.com/science/article/pii/S0304386X04002142)
2. (https://link.springer.com/article/10.1007/BF02701852)
3. (http://www.freepatentsonline.com/20170002472.pdf)
4. (http://www.freepatentsonline.com/20040251199.pdf)

1.2.4. Electrocoagulation

1. (https://www.sciencedirect.com/science/article/pii/S0960148115000488)
2. (www.uest.ntua.gr/cyprus2016/proceedings/pdf/dermentzis_Marmanis_recovery_metallic_nickel_waste_sludge.pdf)
3. (https://www.sciencedirect.com/science/article/pii/S0360319910012814)

1.2.5. Photocatalysis

1. (https://pubs.acs.org/doi/abs/10.1021/acssuschemeng.6b01871)
2. (https://pubs.rsc.org/en/content/articlelanding/2014/gc/c3gc42496k/unauth#!divAbstract)
3. (https://www.sciencedirect.com/science/article/abs/pii/S036031991734291X)
4. (https://www.sciencedirect.com/science/article/abs/pii/S004313541730372X)
5. (https://link.springer.com/article/10.1007/s10832-006-9118-7)
6. (https://www.mdpi.com/2227-9717/7/4/225)

1.2.6. Struvite crystallization

1. (https://www.sciencedirect.com/science/article/pii/S0011916411003948)
2. (https://www.researchgate.net/profile/Zhi_Long_Ye/publication/261371550_Phosphorus_recovery_from_wastewater_by_struvite_crystallization_Property_of_aggregates/links/5a7c6fd00f7e9b477a02c61e/Phosphorus-recovery-from-wastewater-by-struvite-crystallization-Property-of-aggregates.pdf)
3. (https://www.nrcresearchpress.com/doi/abs/10.1139/s03-040)

1.3. Biological Methods

1.3.1. Biosorption

1. (https://www.sciencedirect.com/science/article/pii/S0960852409012620)
2.  (https://www.sciencedirect.com/science/article/pii/S0960852410019097)
3. (https://pubs.acs.org/doi/abs/10.1021/ie202584k)
4. (https://www.sciencedirect.com/science/article/abs/pii/S004313549700273X)
5. (https://www.sciencedirect.com/science/article/pii/S0960852411016294)
6. (https://www.sciencedirect.com/science/article/pii/S0304386X10000848)
7. (http://www.freepatentsonline.com/20020029957.pdf)

1.3.2. Bioremediation

1. (https://www.sciencedirect.com/science/article/abs/pii/S0167779915002437)
2. (https://link.springer.com/article/10.1007/s00253-003-1322-7)
3. (https://www.sciencedirect.com/science/article/pii/S1001074208623463)

1.4. Bio electrochemical systems

1. (https://www.sciencedirect.com/science/article/abs/pii/S0167779915002437)
2. (https://www.sciencedirect.com/science/article/pii/S1385894717312792)
3. (https://www.sciencedirect.com/science/article/pii/S1364032117304318)
4. (https://www.sciencedirect.com/science/article/pii/S0960852415008494)
5. (https://www.tandfonline.com/doi/abs/10.1080/12269328.2015.1037966)
6. (https://www.sciencedirect.com/science/article/abs/pii/S0043135408006611)
7. (https://link.springer.com/article/10.1007/s00253-012-4456-7)
8. (https://www.frontiersin.org/articles/10.3389/fenrg.2014.00019)
9. (https://www.sciencedirect.com/science/article/abs/pii/S0892687506002792)
10. (https://www.sciencedirect.com/science/article/pii/S0043135414005806)
11. Bio electrochemical platform
12. Abiotic cathodes
13. Abiotic cathodes supplemented by external power sources
14. Bio-cathodes
15. Bio-cathodes supplemented by external power sources
16. Microbial electrolysis cells

2. Soil water retention by polymer based hydrogels

• (https://www.scientific.net/AMR.96.177)
• (https://onlinelibrary.wiley.com/doi/abs/10.1002/app.41060)
• (https://www.sciencedirect.com/science/article/pii/S001670611400192X)
• (https://www.sciencedirect.com/science/article/pii/S0141391014003917)
• (http://www.freepatentsonline.com/20140113821.pdf)

3. Energy-based technologies

3.1. Electric water heaters

1. (https://ieeexplore.ieee.org/abstract/document/8472102)
2. (https://ieeexplore.ieee.org/abstract/document/8586582)
3. (https://www.sciencedirect.com/science/article/pii/S0959652618319917)
4. (https://ieeexplore.ieee.org/abstract/document/8587499)
5. (http://www.freepatentsonline.com/10302312.pdf)
6. (http://www.freepatentsonline.com/20180299165.pdf)
7. (http://www.freepatentsonline.com/20190128540.pdf)
8. (http://www.freepatentsonline.com/10151511.pdf)
9. (http://www.freepatentsonline.com/9927131.pdf)

3.2. Solar water heaters

1. (https://www.sciencedirect.com/science/article/abs/pii/S1359431117347804)
2. (https://www.sciencedirect.com/science/article/pii/S0960148117309163)
3. (https://www.sciencedirect.com/science/article/pii/S0960148117308765)
4. (https://www.sciencedirect.com/science/article/pii/S0048969717334769)
5. (https://www.sciencedirect.com/science/article/pii/S0038092X18300495)
6. (http://www.freepatentsonline.com/9890314.pdf)
7. (http://www.freepatentsonline.com/20120060829.pdf)
8. (http://www.freepatentsonline.com/8375934.pdf)

3.3. Microbial fuel cells

1. (https://www.sciencedirect.com/science/article/pii/S0048969719320145)
2. (https://www.sciencedirect.com/science/article/pii/S156753941730107X)
3. (https://biotechnologyforbiofuels.biomedcentral.com/articles/10.1186/s13068-018-1208-7)
4. (https://www.sciencedirect.com/science/article/pii/S0378775317316191)
5. (https://onlinelibrary.wiley.com/doi/abs/10.1002/wer.1183)
6. (www.freepatentsonline.com/8962165.pdf)
7. (http://www.freepatentsonline.com/10347931.pdf)
8. (http://www.freepatentsonline.com/20080220292.pdf)

3.4. Photo electrochemical cells

1. (https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201712280)
2. (https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201806514)
3. (https://www.sciencedirect.com/science/article/abs/pii/S0925838818335254)
4. (https://aip.scitation.org/doi/abs/10.1063/1.5109785)
5. (https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201705232)
6. (http://www.freepatentsonline.com/20100133111.pdf)
7. (http://www.freepatentsonline.com/20100282601.pdf)
8. (http://www.freepatentsonline.com/20100101643.pdf)
9. (http://www.freepatentsonline.com/20120080310.pdf)

3.5. Hydroelectricity

1. (https://www.sciencedirect.com/science/article/pii/S030917081730307X)
2. (www.ijmerr.com/uploadfile/2018/1025/20181025024637556.pdf)
3. (https://www.sciencedirect.com/science/article/pii/S1876610218312244)
4. (https://www.sciencedirect.com/science/article/abs/pii/S0360544218309447)
5. (http://www.freepatentsonline.com/8956103.pdf)
6. (http://www.freepatentsonline.com/7478974.pdf)
7. (www.freepatentsonline.com/7804182.pdf)

3.6. Water fuel emulsions

1. (https://www.sciencedirect.com/science/article/pii/S0017931018338936)
2. (https://www.sciencedirect.com/science/article/pii/S019689041830774X)
3. (https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.8b00502)
4. (https://www.mdpi.com/1996-1073/12/14/2689/htm)
5. (https://www.sciencedirect.com/science/article/pii/S019689041830548X)
6. (http://www.freepatentsonline.com/3490237.pdf)
7. (http://www.freepatentsonline.com/WO1998021294A1.pdf)

3.7. Seawater as fuel

1. (https://www.sciencedirect.com/science/article/pii/S0959652617332110)
2. (https://pubag.nal.usda.gov/catalog/6346882)
3. (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3266869)

4. Water/air-related systems

4.1. Dehumidifiers

1. (https://www.sciencedirect.com/science/article/pii/S0378778819314021)
2. (https://academic.oup.com/ijlct/article/13/3/240/5020711)
3. (https://www.sciencedirect.com/science/article/abs/pii/S0360544218318279)
4. (https://www.sciencedirect.com/science/article/pii/S0011916419301493)
5. (http://www.freepatentsonline.com/4193443.pdf)
6. (http://www.freepatentsonline.com/20090289461.pdf)
7. (http://www.freepatentsonline.com/20110061408.pdf)

4.2. Water generation from atmospheric air

1. (https://www.nature.com/articles/s41467-018-03162-7)
2. (https://www.sciencedirect.com/science/article/pii/S0960148100001129)
3. (http://www.freepatentsonline.com/20050103615.pdf)
4. (http://www.freepatentsonline.com/20080314058.pdf)