Resource Recovery from Wastewater: What, Why, and Where?

InfoMetricsFiguresRef. Environmental Science & TechnologyVol 58/Issue 32Article This publication is free to access through this site. Learn More CiteCitationCitation and abstractCitation and referencesMore citation options ShareShare onFacebookX (Twitter)WeChatLinkedInRedditEmailJump toExpandCollapse ViewpointJuly 31, 2024Resource Recovery from Wastewater: What, Why, and Where?Click to copy article linkArticle link copied!Xiaodi Hao*Xiaodi HaoSino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. China*+86-131 61347675, +86-10-68322123, [email protected]More by Xiaodi HaoView Biographyhttps://orcid.org/0000-0001-6414-9566Ji LiJi LiSino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. ChinaDepartment of Biotechnology, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The NetherlandsMore by Ji Lihttps://orcid.org/0000-0001-6477-2892Ranbin LiuRanbin LiuSino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. ChinaMore by Ranbin LiuMark C. M. van LoosdrechtMark C. M. van LoosdrechtSino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. ChinaDepartment of Biotechnology, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The NetherlandsMore by Mark C. M. van Loosdrechthttps://orcid.org/0000-0003-0658-4775Open PDFEnvironmental Science & TechnologyCite this: Environ. Sci. Technol. 2024, 58, 32, 14065–14067Click to copy citationCitation copied!https://pubs.acs.org/doi/10.1021/acs.est.4c05903https://doi.org/10.1021/acs.est.4c05903Published July 31, 2024 Publication History Received 12 June 2024Published online 31 July 2024Published in issue 13 August 2024article-commentaryCopyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsThis publication is licensed for personal use by The American Chemical Society. ACS PublicationsCopyright © 2024 American Chemical SocietySubjectswhat are subjectsArticle subjects are automatically applied from the ACS Subject Taxonomy and describe the scientific concepts and themes of the article.SludgesSolar energyThermal energyWastewaterWater treatmentExistential threats from climate change and environmental degradation, coupled with increasing awareness of the depletion of natural resources, have increased the importance of sustainable development and climate neutrality. Although they protect human health, wastewater production and treatment processes contribute to increasing "material entropy", inducing environmental deterioration. Resource recovery from wastewater, instead of destroying or removing resources, can significantly minimize entropy production. (1,2) Therefore, there is a pressing need for an improved resource recovery framework to manage and reduce the climate risks associated with wastewater treatment, which is in accordance with global climate ambitions such as the EU Green Deal and the China carbon-neutral goal.Resource recovery from wastewater is frequently portrayed as a process that converts seemingly worthless resources into valuable products, such as organic matter, nutrients, energy, and water. In practice, a lack of clarity concerning exactly what should be appropriately recovered, where, and why persists, so it is important that the what, why, and where (W3) of potential resources from wastewater should be better defined.First, organics (COD) contain exergy and carbonaceous materials. Traditionally, COD is oxidized into carbon dioxide (CO2) in biological treatment processes, with excess sludge anaerobically digested for the harvesting of biogas. However, biogas production is often viewed favorably and may even receive subsidies, but its efficiency and sustainability (entropy production!) are disputed. Furthermore, the efficiency of conversion from chemical (COD) energy into electricity and heat is <15%. (3) In fact, COD can offer an opportunity for conversion into valuable organic products, like extracellular polymeric substances (EPS), polyhydroxyalkanoates (PHA), and hydrocolloids. (4) Such an approach not only generates substantial benefits for resource recovery and sustainability but also contributes to the replacement of oil-based chemicals in society. (2)Second, phosphorus recovery is a critical necessity due to the imminent depletion of accessible phosphate rock reserves, a scenario anticipated within roughly 40 years. Therefore, recovering phosphorus from wastewater is more preferred than removing it. Although struvite (MgNH4PO4·6H2O) and vivianite [Fe3(PO4)2·8H2O] can be recovered at wastewater treatment plants (WWTPs), phosphate in incinerated sludge ash is high in phosphate content (≥90% of influent P load) and technically easy to recover. (5) Along with these processes, some rare metals and elements can be additionally recovered from the ash.With regard to nitrogen recovery, the positive environmental impacts of recovering nitrogen are only outcompeted with inaccessible resources. However, nitrogen is different from phosphorus as it is not a limiting element for society. In addition to environmental considerations, nitrogen recovery should also focus on addressing the energy deficits involved in producing ammonium from nitrogen gas and the recovery of ammonium from wastewater. The Haber–Bosch process is a well-established and cost-effective method for producing synthetic ammonia such as carbamide/urea. The recovery of nitrogen from wastewater is often more energy-intensive and logistically complex. Efficient ammonium recovery is only feasible with concentrated liquids like urine, but the implementation demands a more complicated and resource-intensive collection system.Third, to offset the energy deficits and achieve a carbon-neutral operation of WWTPs, solar energy seems to be attractive, but the areas of WWTPs allow the production of only ∼10% of the required energy. Anaerobic digestion of excess sludge has been met with skepticism in the broader context of energy recovery. Sludge drying followed by incineration has been proposed to be more efficient in the context of energy recovery. (5) The efficiency of conversion of chemical energy based on influent COD can reach 32% via incineration, (5) surpassing that of anaerobic digestion (<15%). Furthermore, decarbonized hydrogen production based on wastewater effluent has also been promoted in recent years. However, it necessitates integration with excess green (wind/solar) energy and/or off-peak fossil-based electricity. Otherwise, a situation in which the loss outweighs the gain might arise, with ∼20% energy loss during energy conversion.The thermal energy in effluent offers a significantly greater potential for recovery compared to chemical and solar energy. In essence, the recoverable amount of thermal energy is 6–8 times greater than the amount of chemical energy present in the influent COD of 400 mg/L. The calculated net recoverable electrical energy equivalent is 1.77 kWh/m3 (ΔT = 4 °C; COP = 3.5) for heating purposes exchanged by water source heat pumps and 1.18 kWh/m3 (ΔT = 4 °C; COP = 4.8) for cooling. (3) Thermal energy can be harnessed for district heating/cooling, agricultural greenhouses, and even drying of dewatered sludge. Therefore, it would be highly beneficial for water and energy utilities to collaborate in jointly planning the utilization of this thermal energy. Of course, it is important to emphasize that thermal energy exchange should be performed on the effluent of WWTPs rather than in sewers, as the latter would decrease the temperature in WWTPs and thereby impact the biological treatment efficiency of the plant.A resource-based wastewater treatment within the context of the circular/blue economy is presented in Figure 1. This road map involves four critical steps: (i) producing and extracting highly valuable chemicals from organics found in wastewater and/or excess activated sludge whenever possible (examples of the chemicals being PHA and hydrocolloids), (ii) maximizing the recovery of chemical energy (COD) from excess sludge by direct incineration to generate power, rather than relying on anaerobic digestion to produce biogas, (iii) collecting and recycling phosphorus from ash produced by sludge incineration, and (iv) extracting thermal energy from the effluent for various applications, such as drying excess sludge or heating buildings or agricultural greenhouses, with the aim of indirectly offsetting electrical energy demands for wastewater treatment.Figure 1Figure 1. Steps and cruxes of the recovery of resources and energy from wastewater: (i) producing and extracting highly valuable chemicals from organics, (ii) maximizing energy recovery by direct incineration to generate power, (iii) recovering phosphorus from ash, and (iv) extracting thermal energy from the effluent.High Resolution ImageDownload MS PowerPoint SlideAuthor InformationClick to copy section linkSection link copied!Corresponding AuthorXiaodi Hao - Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. China; https://orcid.org/0000-0001-6414-9566; Email: [email protected]AuthorsJi Li - Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. China; Department of Biotechnology, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands; https://orcid.org/0000-0001-6477-2892Ranbin Liu - Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. ChinaMark C. M. van Loosdrecht - Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies/Beijing Advanced Innovation Centre of Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing 100044, P. R. China; Department of Biotechnology, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands; https://orcid.org/0000-0003-0658-4775NotesThe authors declare no competing financial interest.BiographyClick to copy section linkSection link copied!Xiaodi HaoHigh Resolution ImageDownload MS PowerPoint SlideDr. Xiaodi Hao is now a full professor at Beijing University of Civil Engineering and Architecture, China. He is an editor of Water Research, appointed July 2009. He earned his B.S. at Taiyuan University of Technology, China, his M.S. at the Harbin Institute of Technology, China, and his Ph.D. at Delft University of Technology, The Netherlands. He worked in The Netherlands (TU Delft and TNO), France (CEMAGREF), Hong Kong (Poly-U and UST), United States (Auburn University), and Japan (Gifu University) for eight years. His research interests focus on sustainable biological wastewater treatment and resource recovery (especially recovery of phosphate and energy). He has written and published six books in Chinese and two books in English as well as more than 120 international and 210 domestic papers.AcknowledgmentsClick to copy section linkSection link copied!The study was financially supported by the National Natural Science Foundation of China (52170018).ReferencesClick to copy section linkSection link copied! This article references 5 other publications. 1Schrödinger, E. In What Is Life? The Physical Aspect of the Living Cell; Cambridge University Press, 1944. DOI: 10.1086/281292 Google ScholarThere is no corresponding record for this reference.2Hao, X.; Wu, D.; Li, J.; Liu, R.; van Loosdrecht, M. Making Waves: A Sea Change in Treating Wastewater – Why Thermodynamics Supports Resource Recovery and Recycling. Water Res. 2022, 218, 118516 DOI: 10.1016/j.watres.2022.118516 Google ScholarThere is no corresponding record for this reference.3Hao, X.; Li, J.; van Loosdrecht, M. C. M.; Jiang, H.; Liu, R. Energy Recovery from Wastewater: Heat over Organics. Water Res. 2019, 161, 74– 77, DOI: 10.1016/j.watres.2019.05.106 Google Scholar3Energy recovery from wastewater: Heat over organicsHao, Xiaodi; Li, Ji; van Loosdrecht, Mark C. M.; Jiang, Han; Liu, RanbinWater Research (2019), 161 (), 74-77CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.) In dealing with wastewater, chem. energy has traditionally been perceived as the only source of recoverable energy in moving towards the carbon-neutral operation of wastewater treatment plants. Based on an estn. of practically recoverable energy embedded in municipal wastewater, however, the potential for thermal energy (90% recovery from wastewater) is much higher than for chem. energy (COD, 10% recovery). The carrier of chem. energy (COD) has a high exergy value which should, from a sustainability point of view, be utilized to the greatest extent possible. Rather than being converted into methane (and subsequently into carbon dioxide), carbon (COD) contained in wastewater should be converted into highly valuable org. products. Thermal energy could be utilized for district heating/cooling, agricultural greenhouses, and even for drying dewatered sludge. In this way, thermal energy can indirectly offset the energy demand for wastewater treatment. The limitations in utilizing thermal energy are not generally based on tech. difficulties; in fact, they can be mainly attributed to supply distances and governmental policies. It would, therefore, be greatly beneficial if municipal authorities would work together to jointly plan utilization of this thermal energy. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFalu7fO&md5=5c9c0c62dc476d6d053bdc666d1e5fbe4van Loosdrecht, M. C. M.; Brdjanovic, D. Anticipating the next Century of Wastewater Treatment. Science 2014, 344 (6191), 1452– 1453, DOI: 10.1126/science.1255183 Google Scholar4Anticipating the next century of wastewater treatmentvan Loosdrecht, Mark C. M.; Brdjanovic, DamirScience (Washington, DC, United States) (2014), 344 (6191), 1452-1453CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science) There is no expanded citation for this reference. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFanur7M&md5=c38e28a48ef50be695834d0e7987475c5Hao, X.; Chen, Q.; van Loosdrecht, M. C. M.; Li, J.; Jiang, H. Sustainable Disposal of Excess Sludge: Incineration without Anaerobic Digestion. Water Res. 2020, 170, 115298, DOI: 10.1016/j.watres.2019.115298 Google Scholar5Sustainable disposal of excess sludge: Incineration without anaerobic digestionHao, Xiaodi; Chen, Qi; van Loosdrecht, Mark C. M.; Li, Ji; Jiang, HanWater Research (2020), 170 (), 115298CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.) A review. Handling excess sludge produced by wastewater treatment is a common problem worldwide. Due to limited space available in landfills, as well as difficulties involved in using excess sludge in agriculture, there is a need for alternative disposal methods. Although anaerobic digestion (AD) is widely used in processing sludge, only partial energy recovery from methane and sludge vol. redn. can be achieved, resulting in a substantial amt. of sludge remaining, which needs to be disposed of. Direct incineration after sludge drying is one possible option, a practice that is already in place in some cities in China. A comparison between direct incineration and conventional AD (with or without pretreatment by thermal hydrolysis) has to be made with respect to the energy balance and investment & operational (I & O) costs. This comparison reveals direct incineration to have the lowest energy deficit and I & O costs. Therefore, it is expected that direct incineration without AD will become the preferred sustainable approach to handling sludge. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFOksrfK&md5=bd5c964c48c84da32a2b80dd67f571ddCited By Click to copy section linkSection link copied!This article has not yet been cited by other publications.Download PDFFiguresReferencesOpen PDF Get e-AlertsGet e-AlertsEnvironmental Science & TechnologyCite this: Environ. Sci. Technol. 2024, 58, 32, 14065–14067Click to copy citationCitation copied!https://doi.org/10.1021/acs.est.4c05903Published July 31, 2024 Publication History Received 12 June 2024Published online 31 July 2024Published in issue 13 August 2024Copyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsArticle Views2461Altmetric-Citations-Learn about these metrics closeArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.Recommended Articles FiguresReferencesAbstractHigh Resolution ImageDownload MS PowerPoint SlideFigure 1Figure 1. Steps and cruxes of the recovery of resources and energy from wastewater: (i) producing and extracting highly valuable chemicals from organics, (ii) maximizing energy recovery by direct incineration to generate power, (iii) recovering phosphorus from ash, and (iv) extracting thermal energy from the effluent.High Resolution ImageDownload MS PowerPoint SlideXiaodi HaoHigh Resolution ImageDownload MS PowerPoint SlideDr. Xiaodi Hao is now a full professor at Beijing University of Civil Engineering and Architecture, China. He is an editor of Water Research, appointed July 2009. He earned his B.S. at Taiyuan University of Technology, China, his M.S. at the Harbin Institute of Technology, China, and his Ph.D. at Delft University of Technology, The Netherlands. He worked in The Netherlands (TU Delft and TNO), France (CEMAGREF), Hong Kong (Poly-U and UST), United States (Auburn University), and Japan (Gifu University) for eight years. His research interests focus on sustainable biological wastewater treatment and resource recovery (especially recovery of phosphate and energy). He has written and published six books in Chinese and two books in English as well as more than 120 international and 210 domestic papers.References This article references 5 other publications. 1Schrödinger, E. In What Is Life? The Physical Aspect of the Living Cell; Cambridge University Press, 1944. DOI: 10.1086/281292 There is no corresponding record for this reference.2Hao, X.; Wu, D.; Li, J.; Liu, R.; van Loosdrecht, M. Making Waves: A Sea Change in Treating Wastewater – Why Thermodynamics Supports Resource Recovery and Recycling. Water Res. 2022, 218, 118516 DOI: 10.1016/j.watres.2022.118516 There is no corresponding record for this reference.3Hao, X.; Li, J.; van Loosdrecht, M. C. M.; Jiang, H.; Liu, R. Energy Recovery from Wastewater: Heat over Organics. Water Res. 2019, 161, 74– 77, DOI: 10.1016/j.watres.2019.05.106 3Energy recovery from wastewater: Heat over organicsHao, Xiaodi; Li, Ji; van Loosdrecht, Mark C. M.; Jiang, Han; Liu, RanbinWater Research (2019), 161 (), 74-77CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.) In dealing with wastewater, chem. energy has traditionally been perceived as the only source of recoverable energy in moving towards the carbon-neutral operation of wastewater treatment plants. Based on an estn. of practically recoverable energy embedded in municipal wastewater, however, the potential for thermal energy (90% recovery from wastewater) is much higher than for chem. energy (COD, 10% recovery). The carrier of chem. energy (COD) has a high exergy value which should, from a sustainability point of view, be utilized to the greatest extent possible. Rather than being converted into methane (and subsequently into carbon dioxide), carbon (COD) contained in wastewater should be converted into highly valuable org. products. Thermal energy could be utilized for district heating/cooling, agricultural greenhouses, and even for drying dewatered sludge. In this way, thermal energy can indirectly offset the energy demand for wastewater treatment. The limitations in utilizing thermal energy are not generally based on tech. difficulties; in fact, they can be mainly attributed to supply distances and governmental policies. It would, therefore, be greatly beneficial if municipal authorities would work together to jointly plan utilization of this thermal energy. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFalu7fO&md5=5c9c0c62dc476d6d053bdc666d1e5fbe4van Loosdrecht, M. C. M.; Brdjanovic, D. Anticipating the next Century of Wastewater Treatment. Science 2014, 344 (6191), 1452– 1453, DOI: 10.1126/science.1255183 4Anticipating the next century of wastewater treatmentvan Loosdrecht, Mark C. M.; Brdjanovic, DamirScience (Washington, DC, United States) (2014), 344 (6191), 1452-1453CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science) There is no expanded citation for this reference. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFanur7M&md5=c38e28a48ef50be695834d0e7987475c5Hao, X.; Chen, Q.; van Loosdrecht, M. C. M.; Li, J.; Jiang, H. Sustainable Disposal of Excess Sludge: Incineration without Anaerobic Digestion. Water Res. 2020, 170, 115298, DOI: 10.1016/j.watres.2019.115298 5Sustainable disposal of excess sludge: Incineration without anaerobic digestionHao, Xiaodi; Chen, Qi; van Loosdrecht, Mark C. M.; Li, Ji; Jiang, HanWater Research (2020), 170 (), 115298CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.) A review. Handling excess sludge produced by wastewater treatment is a common problem worldwide. Due to limited space available in landfills, as well as difficulties involved in using excess sludge in agriculture, there is a need for alternative disposal methods. Although anaerobic digestion (AD) is widely used in processing sludge, only partial energy recovery from methane and sludge vol. redn. can be achieved, resulting in a substantial amt. of sludge remaining, which needs to be disposed of. Direct incineration after sludge drying is one possible option, a practice that is already in place in some cities in China. A comparison between direct incineration and conventional AD (with or without pretreatment by thermal hydrolysis) has to be made with respect to the energy balance and investment & operational (I & O) costs. This comparison reveals direct incineration to have the lowest energy deficit and I & O costs. Therefore, it is expected that direct incineration without AD will become the preferred sustainable approach to handling sludge. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFOksrfK&md5=bd5c964c48c84da32a2b80dd67f571dd