Sustainability Assessment of Hospital Wastewater Treatment Techniques: A Comprehensive Review

Abstract

Hospitals discharge wastewater containing toxic pollutants that pose risks to human health and the environment if not properly treated. Therefore, effective treatment techniques are essential. Although various reviews have explored hospital wastewater treatment (HWWT) methods, few have comprehensively assessed their sustainability—including technical, environmental, economic, and social aspects. This paper reviews the literature on these dimensions and identifies critical research gaps. Technically, the combination of biological and tertiary techniques can achieve removal efficiencies between 60% and 99% for emerging contaminants. Environmentally, electricity consumption is a major concern, ranging from 0.2 to 3 kWh/m³, depending on the technique. Economically, costs rise with energy-intensive methods; ultraviolet disinfection operates at 0.016 €/m³, while Fenton treatment reaches 23.38 €/m³. No dedicated social assessments exist for HWWT; therefore, municipal wastewater studies were used as references. This paper proposes public health-related social indicators tailored for HWWT. Two key research gaps are identified: the lack of integrated sustainability and social assessments and limited comparability across studies. This review adapts the life cycle sustainability assessment framework to HWWT and offers recommendations for improved comparability and targeted future research. Addressing these gaps will support more holistic evaluations and guide effective and informed decision-making in hospital wastewater management.

1. Introduction

Hospitals serve as critical institutions that provide a wide range of medical services, from diagnostics and therapy to emergency care and surgery [1]. However, they generate wastewater due to many activities and facilities, such as laboratories, wards, and treatment departments [2]. The discharge of untreated wastewater further exacerbates water pollution, which has become a global crisis due to concerns regarding the release of harmful pollutants into natural water bodies [3]. Similar to municipal wastewater (MWW), hospital wastewater (HWW) is characterized by the biological oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), ammonia nitrogen, nitrites, nitrates, and total phosphorus (TP), but at much higher concentrations [4]. For example, typical HWW may contain BOD concentrations ranging from 80 to 250 mg/L, COD from 350 to 700 mg/L, total nitrogen between 30 and 60 mg/L, and total phosphorus between 10 and 30 mg/L. Ammonia levels are often in the range of 10 to 35 mg/L, total suspended solids range from 70 to 150 mg/L, and nitrate concentrations vary between 0.7 and 8 mg/L [4]. In addition, HWW contains heavy metals (such as zinc, lead, silver, mercury, platinum, and barium) and emerging contaminants (ECs), such as pharmaceutically active compounds (PhACs) and pharmaceutical and personal care products (PPCPs), along with some antibiotic-resistant genes (ARG) and antibiotic-resistant bacteria (ARB), such as enrofloxacin, ciprofloxacin, oxalinic, ofloxacin, norfloxacin, sulfapyridine, trimethoprim, and metronidazole [4,5]. It is worth mentioning that due to these toxic pollutants, the biodegradability index (BOD/COD) is lower in HWW than in MWW, meaning that conventional methods, such as biological treatments, are not very effective in treating HWW alone [5]. However, many physicochemical treatment methods utilized in industrial settings, such as coagulation-flocculation, membrane filtration, and advanced oxidation processes (AOPs), are also relevant to hospital wastewater treatment (HWWT) [6]. Recent advances in these methods have increased wastewater treatment efficiency in different sectors, such as hospitals. Coagulation-flocculation is commonly used in industrial and hospital wastewater treatment to remove suspended solids and organic pollutants [7]. Ultrafiltration and reverse osmosis are commonly employed to effectively remove pharmaceutical contaminants. Furthermore, advanced oxidation processes (AOPs), such as ozonation, Fenton, and electrochemical oxidation, are known for their ability to degrade persistent organic pollutants and ARGs in hospital effluents [8]. Hybrid systems that combine biological treatments, such as the activated sludge process (ASP), membrane bioreactor (MBR), moving bed bioreactor (MBBR), constructed wetlands (CWs), and fluidized bed reactor (FBR), with AOPs are also efficient solutions for removing ECs [9]. Such practices are necessary to eliminate persistent contaminants that contribute to antimicrobial resistance, chemical pollution, and potential toxicity risks, particularly in vulnerable populations such as infants, immunocompromised individuals, and pregnant women [10,11].

Few review studies have explored the technical performance of various HWW treatment techniques. The first review by M. T. Khan et al. (2021) showed that primary treatment is not very effective in eliminating ECs and that the removal efficiencies depend on the type of EC [12]. For instance, it is easier to eliminate methylparaben than trimethoprim. Secondary treatments, such as ASP, have removal efficiencies ranging between 20% and 94%. Tertiary treatment techniques such as ultrafiltration membranes, nanofiltration membranes, and reverse osmosis (RO) are also efficient in removing ECs, especially when combined with secondary treatment, achieving a removal efficiency of 99% [12]. The second review by Majumder et al. (2021) evaluated the different secondary and tertiary techniques used to treat HWW containing different PhACs [4]. The results show that ASP is capable of eliminating some PhACs, such as olanzapine and risperidone, by approximately 95%, while it is ineffective in eliminating others, such as hydrochlorothiazide and trimethoprim (21% and 11%, respectively). MBR can also effectively eliminate some PhACs; however, one drawback is that this technique is not efficient in removing X-ray contrast media. MBBR can remove ibuprofen by 90%, but it has a negative removal effect on sulfamethoxazole. Tertiary treatment techniques, conversely, are found to be effective in not only eliminating PhACs but also ARG and ARB; these techniques include photocatalytic treatment, Fenton oxidation, anodic oxidation, and the use of nanoparticles with average removal efficiencies of 95%. This review also highlights the importance of combining secondary techniques, such as CW, with tertiary techniques, such as chlorination, to reduce ARB by 93% [4]. In the third review, Parida et al. (2022) investigated the efficiency of different techniques for eliminating ECs [2]. The results show that primary treatments, such as chemical flocculation and coagulation, are efficient in removing solids and oils but are not very effective in removing ECs. Conventional biological treatments such as ASP, CW, and trickling filters have removal efficiencies of 58.5%, 41.5%, and 68.5%, respectively, while advanced secondary techniques such as FBR, MBR, and MBBR have removal efficiencies of 77.6%, 73.2%, and 54.5%. When combined with secondary techniques, tertiary or advanced treatment processes can achieve removal efficiencies of 70% to 99% [2]. The fourth review done by N. A. Khan et al. (2020) showed that biological treatments such as MBR have a removal efficiency that ranges between 34% and 90% depending on the type of PhACs [13]. This removal efficiency increases to 70–100% when MBR is combined with techniques such as ozone and ultraviolet disinfection. Similarly, the efficiency of ASP increased from 62% to 92% when combined with chlorination [13].

While existing reviews highlight the importance of combining different techniques to enhance removal efficiencies, they all shed light on a common issue, which is the need for a review containing the different economic and environmental studies conducted on this subject. This gap is significant because the combination of different techniques requires high energy and cost. Moreover, no international consensus currently exists on the most sustainable approach to HWWT, further complicating decision-making in this field [2,4,12]. Additionally, none of these reviews have addressed the critical need to evaluate HWWT techniques from a social perspective, which is an essential pillar of sustainability. Social considerations are essential for ensuring long-term and sustainable wastewater management. The lack of focus on this dimension in previous reviews further highlights the importance of conducting a more holistic sustainability assessment that encompasses the social, economic, environmental, and technical aspects. Addressing these aspects is important, especially because wastewater treatment plays a crucial role in achieving sustainability goals, particularly those related to the United Nations Sustainable Development Goals (SDG 6: Clean Water and Sanitation, SDG 12: Responsible Consumption and Production).

The primary objective of this paper is to conduct a comprehensive review of the existing literature on the sustainability assessment of various HWWT techniques. This includes evaluating their technical performance, environmental impacts, economic feasibility, and social implications. To our knowledge, no previous work has evaluated all four sustainability dimensions for any HWWT technique. Therefore, papers evaluating the environmental, economic, or social impacts separately will be identified, and their main findings will be highlighted. By analyzing these aspects, this paper offers a comparative evaluation of different HWWT methods based on well-established sustainability parameters. The second aim is to identify research gaps related to this matter and propose a framework for conducting sustainability assessments adapted to HWWT techniques. To the best of our knowledge, no such review has been conducted yet, making this paper a pioneering effort in this field.

2. Materials and Methods

The databases used for this review are Google Scholar and Scopus. Keyword search terms are used for technical, environmental, economic, and social evaluations. For the technical evaluation, the following keywords are used: “hospital wastewater”, “hospital effluent”, “wastewater from hospitals”, “treatment”, “management”, “detection”; these keywords are also used for the other evaluations. However, for the environmental evaluation the following search terms are also used: “life cycle assessment”, “LCA”, “environmental impact”, “environmental assessment”, “environmental evaluation”; for the economic evaluation, the following terms are used: “economic evaluation”, “economic assessment”, “cost effective”; and finally for the social evaluation, the following terms are used: “social evaluation”, “social assessment” and “social sustainability”. The following inclusion and exclusion criteria were applied:

• Inclusion Criteria:
  • Studies published in peer-reviewed journals.
  • Articles published in the last 21 years (2001–2022).
  • Studies that consider the technical, environmental, economic, or social aspects of HWWT.
  • Papers that include comparative assessments of different HWWT techniques.
  • Articles written in English.

• Exclusion criteria:
  • Studies that focus solely on municipal or industrial wastewater without relevance to hospital wastewater.
  • Papers with insufficient data or a lack of methodological clarity.
  • Non-English studies.

Additionally, no strict threshold was applied for the citation count or journal impact factor, as newer studies with fewer citations may provide novel insights into emerging treatment technologies. However, preference was given to highly cited papers from high-impact journals. The methodological steps followed for the review and the number of papers found are shown in Figure 1.

3. Results

As mentioned previously, no complete sustainability assessment comparing different hospital wastewater treatment (HWWT) methods has been reported in the literature. Thus, separate technical, environmental, economic, and social assessments found in the literature are presented and discussed in this section.

The main limitations of this review are as follows: (i) in the environmental assessment, only life cycle assessments (LCA) were considered, and because they are scarce for HWWTs, pharmaceutical wastewater treatment techniques were also included; (ii) no social assessment was found in the literature related to HWWT; therefore, social assessments for general wastewater treatment (WWT) facilities were used instead.

3.1. Technical Assessment of HWWT

Several studies have been conducted to demonstrate the efficiency of certain treatment techniques in managing and disinfecting hospital wastewater (HWW). All of the studies found are discussed in detail in the Supplementary Materials, technique by technique, and are summarized in Table 1. The technique evaluated process type, country, type of plant, removal efficiency, year, and reference of the study are presented in the table.

Some techniques, such as the activated sludge process (ASP) and membrane bioreactor (MBR), have good removal efficiencies for both general parameters and pharmaceutically active compounds (PhACs), while others, such as constructed wetlands (CW) and moving bed bioreactors (MBBR), are more effective in removing one than the other. For instance, ASP can eliminate 75–99% of general parameters such as chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), and total nitrogen (TN) [14,15,16] and 20–80% of PhACs [17,18,19]. MBR can also remove 80–90% of general parameters [20,21] and 70–99% of PhACs [21,22,23]. On the other hand, CW and MBBR have good removal rates of PhACs (54–90%) and COD and BOD (64–90%) but a negative removal rate of nitrites [24,25]. Tertiary techniques such as photocatalytic treatment, Fenton, photo-Fenton, catalytic wet air oxidation (CWAO), and electrochemical oxidation (EO) have good removal efficiencies for PhACs; however, it is important to combine them with secondary techniques in order to eliminate general parameters.

In summary, the most appropriate solution appears to be the combination of ASP or MBR, which have the highest efficiencies in removing COD, BOD, TSS, TN, and PhACs, with tertiary oxidation techniques (such as EO or ultraviolet (UV) for example) to further increase the removal rates, especially for PhACs. Another important finding from the literature review is that no common agreement exists on the type of PhACs that must be analyzed to measure the removal efficiency of a specific treatment. For example, while some authors measure ibuprofen (IBU) or carbamazepine (CBZ), others mention the removal rate of PhACs in general.

It is important to note that HWW composition differs significantly across hospitals due to several factors, such as hospital size, medical specialization, pharmaceutical usage, and regional regulations on wastewater disposal. Studies have reported variations in pollutant concentrations, with some hospitals showing higher levels of PhACs, ARB, and heavy metals, while others primarily showed elevated organic loads (COD, BOD, and nutrients). Although these variations may influence the performance of different treatment techniques, they are unlikely to affect the main results obtained from the technical assessment review.

Table 1. Summary of the different technical assessments of HWWT in the literature.

Treatment Techniques	Process Type	Country Considered	Type of Plant (Scale)	Outcomes		Date and References
				General Parameters	Emerging Contaminants (ECs)
Activated Sludge Process (ASP)	Anaerobic + aerobic	Greece	Full-scale	–	Removal rates of 77% for IBU, 48–62% for naproxen, 21% for diclofenac, and 7–19% for CBZ.	2010 [17]
	Aerobic	France	Full-scale	87.9% of COD, 99.6% of TSS, 97.5% of VSS, and 91.1% of TN are removed.	Removal of 62% of ketoprofen, 30% of diclofenac, and 95% of IBU.	2015 [14]
	Aerobic	Vietnam	Full-scale	–	Rural Hospital: 46% of MET, 35.2% of SUL, 80.5% of TRI, 45% of CEF, 49.8% of CIP, 54.9% of OFL, and 72.3% of SPI are removed. Urban Hospital: 59.3% of MET, 69.6% of SUL, 51.3% of TRI, 58.6% of CIP,78.7% of OFL, and 79.6% of SPI are eliminated.	2016 [18]
	Aerobic	Brazil	Full-scale	Removal rates of 75.3%, 85.7%, and 84% for COD, BOD, and ammonia are achieved.	–	2011 [15]
	Aerobic	Iran	Pilot scale	More than 90% of TSS, BOD, COD, and nitrite are removed.	–	2010 [16]
	Aerobic	Saudi Arabia	Full-scale	–	83% and 97% removal of PhACS are achieved in two hospitals.	2016 [19]
Constructed Wetlands (CWs)	Anaerobic + aerobic	Belgium	Pilot scale	Removal rates of 83% and 95% are achieved for COD and ammonia, respectively, with negative removal of nitrate.	–	2017 [24]
	Anaerobic + aerobic	India	Pilot scale	More than 90% of TSS, BOD, and COD are eliminated, resulting in the negative removal of nitrate.	54% of PhACs are removed.	2020 [26]
	Anaerobic + aerobic	Ethiopia	Pilot scale	Removal of 93.2%, 83.7%, 90.4%, and 64.3% of TSS, COD, BOD, and ammonia.	–	2019 [27]
	Anaerobic + aerobic	Nepal	Full- scale	97%, 94%, 97%, and 80% of TSS, COD, BOD, and ammonia are removed.	–	2001 [28]
	Anaerobic + aerobic	Thailand	Pilot scale	More than 80% of TSS, COD, and ammonia are eliminated. Only 22% of TN is removed.	Removal of more than 99% of paracetamol.	2019 [29]
Membrane Bioreactor (MBR)	Aerobic	Spain	Full-scale	More than 98% of COD, 99% of ammonia, and 82% of TN are removed.	78% to 82% of PhACs are eliminated.	2013 [20]
	Anaerobic + aerobic	Switzerland	Pilot scale	–	The removal rate of PhACs is more than 93%.	2012 [22]
	Aerobic	Germany	Full-scale	–	99% of PhACs are removed.	2010 [23]
	Aerobic	Luxembourg	Pilot scale	Removal of 90% of COD and 70% of TN	73% of PhACs are eliminated.	2012 [21]
Moving Bed Biofilm Reactor (MBBR)	Aerobic	Denmark	Pilot scale	More than 99% of ammonium is removed; negative removal is detected for nitrite.	–	2015 [25]
	Aerobic	Denmark	Pilot scale	–	PhACs removal rate is 50%.	2018 [30]
	Aerobic	Iran	Lab scale	Reduction of BOD and COD by more than 95%.	–	2017 [31]
Photocatalytic Treatment	N/A	Taiwan	Lab scale	–	Reduction of the number of bacteria by 1–3 log units.	2010 [32]
		Singapore and Thailand	Lab scale	–	Successful inactivation of E-coli and ARB.	2013 [33] 2009 [34]
		Taiwan	Lab scale	–	Decrease in the levels of ketamine and norketamine.	2014 [35]
Fenton Oxidation	N/A	India	Lab scale	–	99.3% of ciprofloxacin is eliminated.	2018 [36]
		Spain	Lab scale	–	Almost complete removal of atenolol and ketoprofen.	2009 [37]
		USA	Lab scale	–	Complete removal of ketoprofen.	2018 [38]
		Spain	Full-scale	Decrease of COD by 70%, and 50% of total organic carbon (TOC) is mineralized.	–	2021 [39]
Photo-Fenton Oxidation	N/A	Spain	Full-scale	Only 30% of COD and 5% of TOC are removed.	–	2021 [39]
		Greece	Pilot scale	–	Atenolol is almost completely removed.	2014 [40]
Catalytic Wet Air Oxidation (CWAO)	N/A	Spain	Full-scale	Maximum elimination of 98% of COD and 75% of TOC is achieved.		2021 [39]
		China	Lab scale	–	93% of pollutants are eliminated.	2021 [41]
Electrochemical Oxidation (EO)	N/A	China	Lab scale	–	99% of ciprofloxacin is degraded.	2016 [42]
		Canada	Lab scale	–	More than 88% of CBZ is removed.	2014 [43]
		Korea	Lab scale	–	Inactivation of E-coli.	2006 [44]
		Canada	Lab scale	–	Removal rate of the first group of PhACs is more than 80%, and that of the second group is between 50% and 80%.	2019 [45]
		Iran	Lab scale	–	More than 92% of PhACs are removed.	2020 [46]
Combination of different techniques	Aerobic + anaerobic	ASP followed by CW (Semarang)	Lab scale	COD decreases from 1225 mg/L to 28.2 mg/L, ammonia from 40.05 mg/L to 0.5 mg/L and phosphate from 5.9 mg/L to 2.475 mg/L following the ASP Ammonia content is decreased to less than 0.01 mg/L and the phosphorous content to 0.46 mg/L following the CW.	–	2021 [47]
	Aerobic	- ASP followed by UV/H2O2 - UV/H2O2 followed by ASP (Spain)	Lab scale	–	95% of PhACs are removed. The removal rate of IBU increases from 74% to 100% and that of gemfibrozil from 45% to 60%.	2021 [48]
	Aerobic	- EO followed by MBR - MBR followed by EO (Canada)	Lab scale	–	50%, 55%, 90%, and 60% of VEN, IBU, E-E, and CBZ are removed following the EO process; these rates increased following the MBR treatment. More than 90% of IBU and E-E and less than 10% of CBZ and VEN are removed when MBR is applied as pre-treatment. Following the EO treatment, complete removal of E-E, VEN, and CBZ is accomplished, and more than 92% of IBU is removed.	2018 [49]
	Aerobic	MBR + ozonation and H2O2 (Taiwan)	Lab scale	–	Two-thirds of pollutants are eliminated.	2014 [35]
	Aerobic	ASP + ozonation (France)	Pilot scale	–	Good removal characteristics are achieved.	2016 [50]

ARB: antibiotic-resistant bacteria; CBZ: carbamazepine; CEF: ceftazidime; COD: chemical oxygen demand; CIP: ciprofloxacin; E-E: estradiol; IBU: ibuprofen; MET: metronidazole; OFL: ofloxacin; PhACs: pharmaceutically active compounds; SPI: spiramycin; SUL: sulfamethoxazole; TOC: total organic carbon; TN: total nitrogen; TSS: total suspended solids; TRI: trimethoprim; VEN: venlafaxine; VSS: volatile suspended solids. Note: “Aerobic” refers to processes requiring oxygen for microbial degradation, “Anaerobic” to those occurring without oxygen or nitrate, “N/A” (Not Applicable) is used for physicochemical or advanced oxidation processes that do not rely on microbial activity and thus are not classified based on oxygen conditions.

Table 1. Summary of the different technical assessments of HWWT in the literature.

Treatment Techniques	Process Type	Country Considered	Type of Plant (Scale)	Outcomes		Date and References
				General Parameters	Emerging Contaminants (ECs)
Activated Sludge Process (ASP)	Anaerobic + aerobic	Greece	Full-scale	–	Removal rates of 77% for IBU, 48–62% for naproxen, 21% for diclofenac, and 7–19% for CBZ.	2010 [17]
	Aerobic	France	Full-scale	87.9% of COD, 99.6% of TSS, 97.5% of VSS, and 91.1% of TN are removed.	Removal of 62% of ketoprofen, 30% of diclofenac, and 95% of IBU.	2015 [14]
	Aerobic	Vietnam	Full-scale	–	Rural Hospital: 46% of MET, 35.2% of SUL, 80.5% of TRI, 45% of CEF, 49.8% of CIP, 54.9% of OFL, and 72.3% of SPI are removed. Urban Hospital: 59.3% of MET, 69.6% of SUL, 51.3% of TRI, 58.6% of CIP,78.7% of OFL, and 79.6% of SPI are eliminated.	2016 [18]
	Aerobic	Brazil	Full-scale	Removal rates of 75.3%, 85.7%, and 84% for COD, BOD, and ammonia are achieved.	–	2011 [15]
	Aerobic	Iran	Pilot scale	More than 90% of TSS, BOD, COD, and nitrite are removed.	–	2010 [16]
	Aerobic	Saudi Arabia	Full-scale	–	83% and 97% removal of PhACS are achieved in two hospitals.	2016 [19]
Constructed Wetlands (CWs)	Anaerobic + aerobic	Belgium	Pilot scale	Removal rates of 83% and 95% are achieved for COD and ammonia, respectively, with negative removal of nitrate.	–	2017 [24]
	Anaerobic + aerobic	India	Pilot scale	More than 90% of TSS, BOD, and COD are eliminated, resulting in the negative removal of nitrate.	54% of PhACs are removed.	2020 [26]
	Anaerobic + aerobic	Ethiopia	Pilot scale	Removal of 93.2%, 83.7%, 90.4%, and 64.3% of TSS, COD, BOD, and ammonia.	–	2019 [27]
	Anaerobic + aerobic	Nepal	Full- scale	97%, 94%, 97%, and 80% of TSS, COD, BOD, and ammonia are removed.	–	2001 [28]
	Anaerobic + aerobic	Thailand	Pilot scale	More than 80% of TSS, COD, and ammonia are eliminated. Only 22% of TN is removed.	Removal of more than 99% of paracetamol.	2019 [29]
Membrane Bioreactor (MBR)	Aerobic	Spain	Full-scale	More than 98% of COD, 99% of ammonia, and 82% of TN are removed.	78% to 82% of PhACs are eliminated.	2013 [20]
	Anaerobic + aerobic	Switzerland	Pilot scale	–	The removal rate of PhACs is more than 93%.	2012 [22]
	Aerobic	Germany	Full-scale	–	99% of PhACs are removed.	2010 [23]
	Aerobic	Luxembourg	Pilot scale	Removal of 90% of COD and 70% of TN	73% of PhACs are eliminated.	2012 [21]
Moving Bed Biofilm Reactor (MBBR)	Aerobic	Denmark	Pilot scale	More than 99% of ammonium is removed; negative removal is detected for nitrite.	–	2015 [25]
	Aerobic	Denmark	Pilot scale	–	PhACs removal rate is 50%.	2018 [30]
	Aerobic	Iran	Lab scale	Reduction of BOD and COD by more than 95%.	–	2017 [31]
Photocatalytic Treatment	N/A	Taiwan	Lab scale	–	Reduction of the number of bacteria by 1–3 log units.	2010 [32]
		Singapore and Thailand	Lab scale	–	Successful inactivation of E-coli and ARB.	2013 [33] 2009 [34]
		Taiwan	Lab scale	–	Decrease in the levels of ketamine and norketamine.	2014 [35]
Fenton Oxidation	N/A	India	Lab scale	–	99.3% of ciprofloxacin is eliminated.	2018 [36]
		Spain	Lab scale	–	Almost complete removal of atenolol and ketoprofen.	2009 [37]
		USA	Lab scale	–	Complete removal of ketoprofen.	2018 [38]
		Spain	Full-scale	Decrease of COD by 70%, and 50% of total organic carbon (TOC) is mineralized.	–	2021 [39]
Photo-Fenton Oxidation	N/A	Spain	Full-scale	Only 30% of COD and 5% of TOC are removed.	–	2021 [39]
		Greece	Pilot scale	–	Atenolol is almost completely removed.	2014 [40]
Catalytic Wet Air Oxidation (CWAO)	N/A	Spain	Full-scale	Maximum elimination of 98% of COD and 75% of TOC is achieved.		2021 [39]
		China	Lab scale	–	93% of pollutants are eliminated.	2021 [41]
Electrochemical Oxidation (EO)	N/A	China	Lab scale	–	99% of ciprofloxacin is degraded.	2016 [42]
		Canada	Lab scale	–	More than 88% of CBZ is removed.	2014 [43]
		Korea	Lab scale	–	Inactivation of E-coli.	2006 [44]
		Canada	Lab scale	–	Removal rate of the first group of PhACs is more than 80%, and that of the second group is between 50% and 80%.	2019 [45]
		Iran	Lab scale	–	More than 92% of PhACs are removed.	2020 [46]
Combination of different techniques	Aerobic + anaerobic	ASP followed by CW (Semarang)	Lab scale	COD decreases from 1225 mg/L to 28.2 mg/L, ammonia from 40.05 mg/L to 0.5 mg/L and phosphate from 5.9 mg/L to 2.475 mg/L following the ASP Ammonia content is decreased to less than 0.01 mg/L and the phosphorous content to 0.46 mg/L following the CW.	–	2021 [47]
	Aerobic	- ASP followed by UV/H2O2 - UV/H2O2 followed by ASP (Spain)	Lab scale	–	95% of PhACs are removed. The removal rate of IBU increases from 74% to 100% and that of gemfibrozil from 45% to 60%.	2021 [48]
	Aerobic	- EO followed by MBR - MBR followed by EO (Canada)	Lab scale	–	50%, 55%, 90%, and 60% of VEN, IBU, E-E, and CBZ are removed following the EO process; these rates increased following the MBR treatment. More than 90% of IBU and E-E and less than 10% of CBZ and VEN are removed when MBR is applied as pre-treatment. Following the EO treatment, complete removal of E-E, VEN, and CBZ is accomplished, and more than 92% of IBU is removed.	2018 [49]
	Aerobic	MBR + ozonation and H2O2 (Taiwan)	Lab scale	–	Two-thirds of pollutants are eliminated.	2014 [35]
	Aerobic	ASP + ozonation (France)	Pilot scale	–	Good removal characteristics are achieved.	2016 [50]

ARB: antibiotic-resistant bacteria; CBZ: carbamazepine; CEF: ceftazidime; COD: chemical oxygen demand; CIP: ciprofloxacin; E-E: estradiol; IBU: ibuprofen; MET: metronidazole; OFL: ofloxacin; PhACs: pharmaceutically active compounds; SPI: spiramycin; SUL: sulfamethoxazole; TOC: total organic carbon; TN: total nitrogen; TSS: total suspended solids; TRI: trimethoprim; VEN: venlafaxine; VSS: volatile suspended solids. Note: “Aerobic” refers to processes requiring oxygen for microbial degradation, “Anaerobic” to those occurring without oxygen or nitrate, “N/A” (Not Applicable) is used for physicochemical or advanced oxidation processes that do not rely on microbial activity and thus are not classified based on oxygen conditions.

3.2. Environmental Assessment of HWWT

This section discusses the different life cycle assessment (LCA) studies found in the literature for hospital wastewater treatment (HWWT) techniques. It is worth mentioning that since LCA studies regarding this subject are scarce, studies considering pharmaceutical wastewater treatment techniques are also considered since such wastewater contains pharmaceutically active compounds (PhACs) and pharmaceutical and personal care products (PPCPs), and the techniques used to treat it are also adopted for the treatment of HWW. Only nine studies were found, and they are summarized in Table 2, where the country, type of plant, techniques evaluated, system boundaries, main outcomes, year, and reference of the study are presented. Additional information on each study can be found in the Supplementary Materials.

The main findings from these studies show that they are mostly focused on tertiary treatment oxidation techniques, such as different ultraviolet (UV)-assisted oxidations, like UVV and UVC. The tertiary techniques discussed in six of the nine studies are EO, UV/TiO₂/O₃, Fenton, UV/O₃/Fe²⁺, UVV/UVC/O₃, UVC, UVV, O₃, UVC/O₃, UVV/O₃, UVV/UVC, sand filtration, granulated activated carbon (GAC), microfiltration (MF), reverse osmosis (RO), activated carbon (AC), nanofiltration (NF), solar photo-Fenton (SPF), and membrane bioreactor (MBR). For the remaining studies, Igos et al. (2012) considered centralized and decentralized options (in Luxembourg) that rely on conventional wastewater treatment processes, such as the activated sludge process (ASP) and MBR combined with some tertiary techniques mentioned above [51]. In fact, this is the only study found in the literature that considers a decentralized option where the treatment of hospital effluent is done separately using an MBR followed by ozonation (O₃), activated carbon (AC), and UV. Rahman et al. (2018) consider biological nutrient removal (BNR) combined with some tertiary techniques in the United States [52], and Lorenzo-Toja et al. (2016) consider different primary and secondary (mainly ASP) techniques in two different wastewater treatment plants (WWTPs) located in two different climatic regions in Spain [53]. All studies considered a functional unit (FU) of 1 m³, except for one study that considered 1000 m³, and the main software used to perform the environmental evaluation was Gabi 6.0 and SimaPro 8.0. The results of the different studies show that electricity is the major contributor to the impact categories; however, only four of these studies [54,55,56,57] show the percentage contribution of electricity to environmental impacts. Moreover, techniques such as constructed wetlands (CWs), moving bed biofilm (MBBR), photo-Fenton, catalytic wet air oxidation (CWAO), and photocatalytic treatments are not evaluated in these studies. Finally, the impact assessment methodologies used by the nine studies reported are different (IMPACT 2002+, EDIP 2003, CML 2001, etc.), which means that the impact categories evaluated are not always the same.

It is worth noting that only two [51,53] of the nine studies considered the environmental assessment of the entire plant; however, only one of these [53] provided a detailed and complete life cycle inventory. The remaining seven studies focused primarily on tertiary or secondary treatment techniques, with inventories limited to specific processes. Additionally, one study [57] of these seven studies did not include any inventory. Including inventory data is very important for the reproducibility of the results and for being able to update or calculate other impact categories from this inventory.

From an application perspective, the results show that it is essential to employ techniques with high efficiency and low energy demand (such as ASP, EO, or sand filtration) because electricity consumption per m³ of wastewater appears to be the most significant environmental aspect.

Table 2. Summary of the different studies on the LCA of HWWT techniques.

Studies	Type of Plant (Scale)	Treatment Techniques	System Boundaries	Outcomes	Date and References
Brazil	Laboratory scale	EO UV/TiO2/O3 Fenton UV/O3/Fe2+ UVV/UVC/O3	Operational stage (i.e., electricity and chemicals)	UVV/UVC/O3 is the highest contributor due to the use of two lamps, UVV and UVC, which require more electricity (about 60 kW/m3). EO is the lowest contributor since it consumes less electricity (about 1.5 kWh/m3) and chemicals. When replacing the Brazilian electricity grid with solar energy, the contribution of EO decreased.	2020 [58]
Luxembourg	Pilot scale	UV irradiation coupled with H2O2	Infrastructure and natural resources	The low-pressure UV lamps (LP) have a lower contribution than the medium-pressure (MP) ones because they require less energy (1 kWh/m3 versus 3 kWh/m3). A 1.11 g/L dosage of H2O2 is the optimum amount. MP UV lamps have low investment and maintenance costs. Infrastructure has a minimal impact because UV lamps have a good lifetime of about 8800 h.	2019 [21]
Brazil	Pilot scale	UVC UVV O3 UVC/O3 UVV/O3 UVV/UVC UVV/UVC/O3	-	UVC, UVV, and O3 have the lowest contribution due to their low energy consumption (27 kW/m3, 34 kW/m3, and 34.8 kW/m3, respectively) in comparison to the other configurations. UVV/UVC/O3 presents the highest contribution to all categories due to the use of the two lamps, which require more energy (about 62 kW/m3).	2017 [54]
Luxembourg	Full scale	Centralized WWTP: conventional treatment or upgraded conventional treatment involving the addition of ozonation (O3). Decentralized WWTP: MBR followed by three options: O3, activated carbon (AC) adsorption, or UV.	The operational stage and the treatment of the sludge	The upgraded conventional centralized treatment is the best option since it has a low energy consumption of about 0.06 kWh/m3.	2012 [51]
China	Not mentioned	Scenario A: O3 + sand filtration + disinfection tank Scenario B: Two-column reactors with granular activated carbon (GAC) adsorbent + sand filter + disinfection tank Scenario C: MF + reverse osmosis (RO) filter + disinfection tank	Construction and operational stages of the tertiary treatments	Scenario A: Electricity (0.579 kWh/m3) is the major contributor to acidification, global warming, ozone depletion, and smog air (4 out of 9 categories). The second contributor to the other four categories (eutrophication, ecotoxicity, human toxicity cancer, and human toxicity non-cancer) is the effluent. Scenario B: The major contributor to acidification, ozone depletion, and smog air is electricity (0.231 kWh/m3), whereas chemicals are the major contributors to ecotoxicity, human toxicity, cancer, and toxicity non-cancer. Scenario C: Electricity (1.19 kWh/m3) is the major contributor to the following 6 out of 9 categories: acidification, ecotoxicity, human toxicity cancer, human toxicity non-cancer, global warming, and smog air. Comparative results show that scenario C has the highest contribution while scenario A has the lowest since it requires less energy and chemicals.	2019 [55]
United States	Pilot scale	Tertiary treatment via AC, O3, UV-H2O2, and RO. Secondary treatment via biological nutrient removal (BNR-1 and BNR-2).	Liquid and solid streams of the treatment facilities	RO has the highest contribution, followed by UV-H2O2, while AC and ozonation have a low contribution. These results are mainly due to electricity and chemicals needed during each scenario since RO needs about 1–2 kWh/m3. In some cases, the combination of secondary and tertiary treatment decreases the environmental impacts.	2018 [52]
Spain	Full scale (size: 6250–12,000 m3/day)	Betanzos WWTP (6250 m3/day): pre-treatment, secondary treatment using biological reactors with suspended biomass and sludge de-watering. Calafell WWTP (12,000 m3/day): primary treatment, secondary treatment using AS reactors with extended aeration, a secondary settle, and a sludge line.	The operational phase (chemicals, fuel, and electricity), the transport of the chemicals and waste, management of the waste, the construction stage, and composting of the sludge and its application in agricultural activities	The contribution of the two plants to global warming potential is due to energy use and sludge management. Result of the ozone depletion potential category is due to electricity from secondary treatment and chemical consumption from primary treatment. The contribution to human toxicity potential is also due to energy use. The difference in the marine ecotoxicity potential category is mainly due to the management and final disposal of the sludge. The freshwater ecotoxicity potential category is due to the WWTP operation, especially the pre-treatment step. These two plants have close energy consumption since, for example, for the biological reactors, the energy needed is 0.476 kWh/m3 for Betanzos and 0.407 kWh/m3 for Calafell.	2016 [53]
United Kingdom	Full scale except for solar photo-Fenton (SPF), which is at pilot scale	Granular activated carbon (GAC) Nanofiltration (NF) Solar photo-Fenton (SPF) Ozonation (O3)	Construction, operation, and decommissioning	O3 and SPF are the highest contributors to 8 out of 18 categories each due to electricity generation for ozonation (0.750 kWh/m3) and the production of H2O2 and sodium hydroxide for SPF. GAC contributes to the two remaining categories: marine eutrophication because of the disposal of AC and urban land occupation because of operational requirements.	2018 [56]
Denmark	Not mentioned	Sand filtration Ozone treatment MBR	-	For sand filtration, the contribution to the induced impacts is lower than the prevented ones, whereas, for ozonation and MBR, it is the opposite. This is due to the fact that a significant amount of energy is needed for ozonation and MBR.	2008 [57]

AC: activated carbon; EO: electrochemical oxidation; Fe²⁺: ferrous ion; GAC: granular activated carbon; H₂O₂: hydrogen peroxide; MBR: membrane bioreactor; MF: microfiltration; O₃: ozonation; RO: reverse osmosis; SPF: solar photo-Fenton; TiO₂: titanium dioxide; UV: ultraviolet; UVV: ultraviolet (short); UVC: ultraviolet (long); WWTP: wastewater treatment plant. Note: Some studies report energy-related values in kW/m³, which refer to the installed or operational power per unit of flow rather than the total energy consumed. These values were retained as originally reported for consistency but should be interpreted with caution.

Table 2. Summary of the different studies on the LCA of HWWT techniques.

Studies	Type of Plant (Scale)	Treatment Techniques	System Boundaries	Outcomes	Date and References
Brazil	Laboratory scale	EO UV/TiO2/O3 Fenton UV/O3/Fe2+ UVV/UVC/O3	Operational stage (i.e., electricity and chemicals)	UVV/UVC/O3 is the highest contributor due to the use of two lamps, UVV and UVC, which require more electricity (about 60 kW/m3). EO is the lowest contributor since it consumes less electricity (about 1.5 kWh/m3) and chemicals. When replacing the Brazilian electricity grid with solar energy, the contribution of EO decreased.	2020 [58]
Luxembourg	Pilot scale	UV irradiation coupled with H2O2	Infrastructure and natural resources	The low-pressure UV lamps (LP) have a lower contribution than the medium-pressure (MP) ones because they require less energy (1 kWh/m3 versus 3 kWh/m3). A 1.11 g/L dosage of H2O2 is the optimum amount. MP UV lamps have low investment and maintenance costs. Infrastructure has a minimal impact because UV lamps have a good lifetime of about 8800 h.	2019 [21]
Brazil	Pilot scale	UVC UVV O3 UVC/O3 UVV/O3 UVV/UVC UVV/UVC/O3	-	UVC, UVV, and O3 have the lowest contribution due to their low energy consumption (27 kW/m3, 34 kW/m3, and 34.8 kW/m3, respectively) in comparison to the other configurations. UVV/UVC/O3 presents the highest contribution to all categories due to the use of the two lamps, which require more energy (about 62 kW/m3).	2017 [54]
Luxembourg	Full scale	Centralized WWTP: conventional treatment or upgraded conventional treatment involving the addition of ozonation (O3). Decentralized WWTP: MBR followed by three options: O3, activated carbon (AC) adsorption, or UV.	The operational stage and the treatment of the sludge	The upgraded conventional centralized treatment is the best option since it has a low energy consumption of about 0.06 kWh/m3.	2012 [51]
China	Not mentioned	Scenario A: O3 + sand filtration + disinfection tank Scenario B: Two-column reactors with granular activated carbon (GAC) adsorbent + sand filter + disinfection tank Scenario C: MF + reverse osmosis (RO) filter + disinfection tank	Construction and operational stages of the tertiary treatments	Scenario A: Electricity (0.579 kWh/m3) is the major contributor to acidification, global warming, ozone depletion, and smog air (4 out of 9 categories). The second contributor to the other four categories (eutrophication, ecotoxicity, human toxicity cancer, and human toxicity non-cancer) is the effluent. Scenario B: The major contributor to acidification, ozone depletion, and smog air is electricity (0.231 kWh/m3), whereas chemicals are the major contributors to ecotoxicity, human toxicity, cancer, and toxicity non-cancer. Scenario C: Electricity (1.19 kWh/m3) is the major contributor to the following 6 out of 9 categories: acidification, ecotoxicity, human toxicity cancer, human toxicity non-cancer, global warming, and smog air. Comparative results show that scenario C has the highest contribution while scenario A has the lowest since it requires less energy and chemicals.	2019 [55]
United States	Pilot scale	Tertiary treatment via AC, O3, UV-H2O2, and RO. Secondary treatment via biological nutrient removal (BNR-1 and BNR-2).	Liquid and solid streams of the treatment facilities	RO has the highest contribution, followed by UV-H2O2, while AC and ozonation have a low contribution. These results are mainly due to electricity and chemicals needed during each scenario since RO needs about 1–2 kWh/m3. In some cases, the combination of secondary and tertiary treatment decreases the environmental impacts.	2018 [52]
Spain	Full scale (size: 6250–12,000 m3/day)	Betanzos WWTP (6250 m3/day): pre-treatment, secondary treatment using biological reactors with suspended biomass and sludge de-watering. Calafell WWTP (12,000 m3/day): primary treatment, secondary treatment using AS reactors with extended aeration, a secondary settle, and a sludge line.	The operational phase (chemicals, fuel, and electricity), the transport of the chemicals and waste, management of the waste, the construction stage, and composting of the sludge and its application in agricultural activities	The contribution of the two plants to global warming potential is due to energy use and sludge management. Result of the ozone depletion potential category is due to electricity from secondary treatment and chemical consumption from primary treatment. The contribution to human toxicity potential is also due to energy use. The difference in the marine ecotoxicity potential category is mainly due to the management and final disposal of the sludge. The freshwater ecotoxicity potential category is due to the WWTP operation, especially the pre-treatment step. These two plants have close energy consumption since, for example, for the biological reactors, the energy needed is 0.476 kWh/m3 for Betanzos and 0.407 kWh/m3 for Calafell.	2016 [53]
United Kingdom	Full scale except for solar photo-Fenton (SPF), which is at pilot scale	Granular activated carbon (GAC) Nanofiltration (NF) Solar photo-Fenton (SPF) Ozonation (O3)	Construction, operation, and decommissioning	O3 and SPF are the highest contributors to 8 out of 18 categories each due to electricity generation for ozonation (0.750 kWh/m3) and the production of H2O2 and sodium hydroxide for SPF. GAC contributes to the two remaining categories: marine eutrophication because of the disposal of AC and urban land occupation because of operational requirements.	2018 [56]
Denmark	Not mentioned	Sand filtration Ozone treatment MBR	-	For sand filtration, the contribution to the induced impacts is lower than the prevented ones, whereas, for ozonation and MBR, it is the opposite. This is due to the fact that a significant amount of energy is needed for ozonation and MBR.	2008 [57]

AC: activated carbon; EO: electrochemical oxidation; Fe²⁺: ferrous ion; GAC: granular activated carbon; H₂O₂: hydrogen peroxide; MBR: membrane bioreactor; MF: microfiltration; O₃: ozonation; RO: reverse osmosis; SPF: solar photo-Fenton; TiO₂: titanium dioxide; UV: ultraviolet; UVV: ultraviolet (short); UVC: ultraviolet (long); WWTP: wastewater treatment plant. Note: Some studies report energy-related values in kW/m³, which refer to the installed or operational power per unit of flow rather than the total energy consumed. These values were retained as originally reported for consistency but should be interpreted with caution.

The main limitations of these studies are related to their geographical scope and plant size. Most studies are concentrated in specific regions, such as Europe and North America, neglecting developing countries, such as Africa and the Middle East. Given that environmental impacts can vary significantly due to differences in energy sources and regulatory frameworks, this geographical limitation may affect the global applicability of the findings. Additionally, many studies focus on pilot- or laboratory-scale plants, which may not fully capture the environmental evaluation of full-scale HWWT plants. Large-scale plants often exhibit different energy consumption patterns, material usage, and treatment efficiencies due to economies of scale. In addition, only one of the studies mentioned the actual capacity/size of the treatment. As a result, findings from small-scale studies may not be directly applicable to large-scale operations, underscoring the need for future research that includes full-scale assessments across diverse geographic regions. Additionally, future studies should explicitly report plant size or capacity, as these factors can significantly influence environmental impact results. It is also important to note that while most studies report electricity consumption in kWh/m³, some express it in kW/m³, which reflects the power demand rather than the total energy use. This difference in units can hinder direct comparisons; therefore, caution should be exercised when interpreting or aggregating such data across studies.

Environmental studies of hospital wastewater (HWW) treatment techniques are still scarce, and more efforts need to be made, especially including complete treatment, including all treatment techniques (primary, secondary, and tertiary). In addition, guidelines are needed to ensure that environmental studies are conducted in a consistent manner, allowing for comparable results. In addition to energy consumption and greenhouse gas emissions, several other environmental criteria must be considered when assessing HWWT techniques. These include the scale of environmental impact across categories such as freshwater and marine ecotoxicity, ozone depletion, eutrophication, and human toxicity. The quality of receiving water bodies is another crucial consideration, especially concerning the persistence of pharmaceutical residues and the release of antibiotic-resistant genes (ARGs) and bacteria (ARBs), which may pose ecological and health risks. Furthermore, the generation of waste byproducts, such as sludge and chemicals, can contribute to environmental burdens if not managed properly. Finally, environmental safety and damage potential must be considered, especially in settings with poor infrastructure or inadequate downstream monitoring. Future LCA studies should integrate these dimensions for a more comprehensive evaluation of environmental sustainability in hospital wastewater management.

3.3. Economic Assessment of HWWT

Similar to previous sections, this part presents the different literature studies conducted to assess the economic effectiveness of the different hospital and pharmaceutical wastewater treatment techniques. Six studies are found and are summarized in the Supplementary Materials.

Table 3. Summary of the different literature studies on the economic evaluation of HWWT techniques.

Studies	Type of Plant (Scale)	Treatment Techniques	Outcomes	References
Denmark	Not mentioned	Sand filtration Ozone treatment UV for disinfection MBR UV combined with advanced oxidation	Operational costs of UV for disinfection and ozone followed by UV are 0.016 €/m3, those of MBR are 0.086 €/m3, and those of sand filtration are 4.6 €/m3.	2008 [57]
Spain	Full scale Pilot and lab scale Full scale	PAC-ASP PAC-MBR BAC	BAC has the lowest CAPEX value, followed by PAC-ASP and finally, PAC-MBR because less equipment is needed in BAC in comparison to the other techniques. The high CAPEX of the PAC-MBR is mainly due to the membrane cost.	2021 [8]
Iran	Full scale	Extended aeration Sequencing batch reactor (SBR)	Operational costs are 0.23 €/m3 for extended aeration system and 0.16 €/m3 for SBR.	2016 [59]
Algeria	Pilot scale	Photocatalysis	Treatment costs are 0.082 €/m3.	2022 [60]
Spain	Industrial scale	Combination of Fenton/SBR Single Fenton process	Operating costs of the coupled system are 11.60 €/m3, and those of the single Fenton process are 23.38 €/m3.	2018 [61]
India	Laboratory scale	Combination of coagulation, E-beam, and ASP for low and high organic strength wastewater (Losw and Hosw, respectively)	For Losw, the cost of E-beam treatment is 0.46 €/m3, that of ASP is 2.15 €/m3, and the combined treatment is 2.61 €/m3. For Hosw, the cost of E-beam is 0.61 €/m3, that of ASP is 0.64 €/m3, and the combined treatment is 1.26 €/m3.	2020 [62]

ASP: activated sludge process; BAC: biofilm reactor; CAPEX: capital expenditure; H_osw: high organic strength wastewater; L_osw: low organic strength wastewater; MBR: membrane bioreactor; PAC-ASP: powdered activated carbon in a conventional activated sludge process; PAC-MBR: powdered activated carbon in a membrane bioreactor; SBR: sequencing batch reactor; UV: ultraviolet.

shows the country, type of plant, treatment techniques, main outcomes (costs/m³), year, and reference.

The main findings of all these studies show that economic assessments are mainly performed for secondary and tertiary treatment techniques such as sand filtration, ozonation (O₃), ultraviolet (UV), membrane bioreactor (MBR), powdered activated carbon in a conventional activated sludge reactor (PAC-ASP), powdered activated carbon in a membrane bioreactor (PAC-MBR), granular activated carbon in a biofilm reactor (BAC), extended aeration, sequencing batch reactor (SBR), photocatalysis, Fenton combined with SBR, Fenton, E-beam, and activated sludge process (ASP). The treatment techniques not involved in these studies are constructed wetlands (CWs), membrane biofilm reactors (MBBR), electrochemical oxidation (EO), and photo-Fenton. The assessment is performed using capital expenditure (CAPEX), manually from the costs provided by the wastewater treatment plant (WWTP) and suppliers, or using software such as SuperPro Designer v9.5. The results show that techniques that require more equipment and electricity have higher costs, such as MBR, PAC-MBR, and extended aeration. However, the combination of some techniques shows a decrease in operating expenses, such as the case of Fenton combined with SBR. A comparison of the economic costs for hospital and municipal wastewater treatment techniques is shown in

Table 4. Comparison of operational costs of municipal and hospital wastewater.

Technique	Municipal Wastewater	Hospital Wastewater	Reference
MBR	0.072 €/m3	0.086 €/m3	[63]
UV	0.010 €/m3	0.016 €/m3	[64]
ASP	1.32 €/m3	2.15 €/m3	[65]
Extended aeration	0.20 €/m3	0.23 €/m3	[66]
Ozone	0.012 €/m3	0.016 €/m3	[67]

ASP: activated sludge process; MBR: membrane bioreactor; UV: ultraviolet.

, where the authors compare the costs per specific technology (without mentioning the capacity of the plant). The results of this comparison show that the operational costs of a specific technique are slightly higher for the treatment of hospital wastewater than for conventional municipal wastewater.

The main limitations of the economic assessment results are related to geographic coverage and plant size, similar to those of the environmental assessment. In this case, none of the studies mentioned the size or capacity of the treatment. Another limitation is related to differences in cost calculation methodologies. Some studies assess only investment costs, while others focus solely on operational costs, making comparisons between different studies challenging.

Similar to environmental assessments, common guidelines are needed to ensure consistency in economic studies for comparison purposes. These guidelines should specify the types of economic indicators to be measured and account for both the investment and maintenance costs associated with treating a specific volume of wastewater.

3.4. Social Assessment of Wastewater Treatment

To date, no studies have been conducted on the social evaluation of hospital wastewater treatment (HWWT); therefore, in this section, this evaluation is conducted for urban and municipal wastewater treatment (WWT) facilities. Such studies offer valuable insights and indicators that can be used for hospital wastewater since social dimensions are driven more by stakeholder interactions than by chemical composition. However, it is worth mentioning that social assessment is usually based on qualitative indicators, not quantitative ones, which explains why technical, environmental, and economic evaluations are more common (as quantitative indicators can be easily evaluated). In total, six social WWT studies have been identified in the literature. These are summarized in

Table 5. Summary of the different literature studies on the social evaluation of WWT techniques.

Studies	Social Indicators Considered	Outcomes	References
Mexico	Community & society: Public participation, social acceptance, community engagement, sustainable behavior, safe and healthy living conditions, local employment, public commitments to sustainable issues, contribution to economic development; Workers: freedom of association and collective bargaining, child labor, fair salary, working hours, equal opportunities/discrimination, health and safety, training, availability of wastewater management documentation, management performance, monitoring program; Consumers & supply chain: effluent quality, demand satisfaction, health and safety, feedback mechanism, consumer satisfaction, fair competition, promoting social responsibility, and supplier relationships.	This study is only done to suggest indicators. Results showed that the mentioned indicators could be applied to assess and compare WWT processes; however, the indicators need to be quantified.	[68]
Finland	Worker stress, worker satisfaction, and attitude to achieving sustainability.	Workers recognize sustainability importance but are limited by policies, training, and workplace culture. Community awareness influences social acceptance. These social indicators are qualitative, which means that questionnaires are needed. Social indicators in wastewater treatment involve not just safety protocols but also employee engagement and internal communication, which can also be used in the case of hospital wastewater treatment.	[69]
Malaysia	Worker’s health and safety and public health and safety.	These two indicators can be evaluated qualitatively through questionnaires related to safety awareness and quantitatively through determining if proper procedures and guidelines are followed.	[70]
Bolivia	Public acceptance, aesthetics, staff requirements, employee satisfaction, awareness, and expertise.	The aim of this study was mostly to rank indicators according to priorities. Results show that local experts related to the technical field gave the following rankings in low and lower-middle-income countries: institutional, social, technical, economic and environmental; whereas local experts related to the social field gave the following rankings: institutional, economic, social, technical, and environmental.	[71]
Finland	Social capital: customer value, efficiency, subsidies; Social equity: fees, local affairs/autonomy, social compatibleness; Social peace: responsiveness, corporate environmental awareness, participative.	Results show that all the mentioned indicators can be quantified by using mathematical approaches, which allow measurement of the indicators through a set of formulas. Such an approach is necessary since it facilitates comparisons across wastewater treatment plants.	[72]
USA	Public participation in selecting the treatment technology, community size served, aesthetics, staffing required to operate the plant, level of education and open space availability.	For public participation, developed countries prefer mechanical systems, and developing ones prefer simple technologies. For the community size served, mechanical systems are preferable for a larger population. Aesthetic problems are more significant for mechanical systems. For the staffing needed, land treatment and lagoon systems provide more employment. For the level of education, land treatment, and lagoon systems only require simple degrees. For open space availability, results show that mechanical systems require less land.	[73]

, with additional details in the Supplementary Materials. None of the studies mentioned the social framework or methodology used; they mainly suggested social indicators for WWT.

The main findings show that these studies propose different social indicators, about 30 different ones, that can be used to evaluate WWT facilities (see Figure 2). Some of these indicators can be quantified, such as workers’ health and safety or public health and safety, through the determination of the potential impacts of the plant design on the public and the implementation of specific procedures and guidelines related to safety. In addition, some of these studies show that the ranking in importance of different social, technical, economic, and environmental indicators is dependent on many factors, such as the country and field of expertise of the questionnaire respondents. Therefore, obtaining a single sustainability index from separate sustainability dimensions may not be advisable. However, if necessary, the weighting of these dimensions should be adapted to each specific application to ensure its relevance and accuracy. Only one study implemented social indicators in the comparison of different WWT technologies, such as mechanical, lagoon, and land treatment systems. Figure 2 shows the different indicators discussed in the literature.

This review shows that the social evaluation of different WWT technologies still needs to be intensified, as only one study considered the implementation of social indicators to compare different treatment technologies. All other studies discuss how to measure social indicators qualitatively or quantitatively or rank the importance of technological, economic, social, and environmental indicators. From the findings of these studies, the following indicators have been identified as meaningful social indicators for the comparison of HWWT techniques: workers’ health and safety, public health and safety, effluent quality, sustainable behavior, and open space availability.

4. Discussion and Recommendations

Based on the findings of the different studies discussed above, two main research gaps are identified: (i) the lack of sustainability assessment studies of hospital wastewater treatment (HWWT) options and (ii) the difficulty in comparing assessments from different authors.

To address these gaps, this review provides recommendations in two key areas: (1) enhancing the comparability of technical, environmental, and economic assessments (Section 4.1), and (2) guiding future research on the social assessment of HWWT plants (Section 4.2).

4.1. Recommendations for More Comparable Technical, Environmental, and Economic Assessments

The technical assessment shows that a fair number of studies discuss the efficiency of the different techniques needed to treat HWW. However, an agreement is needed on which pharmaceutically active compounds (PhACs), emerging contaminants (ECs), antibiotic-resistant genes (ARG), and antibiotic-resistant bacteria (ARB) are more important to be measured and removed (i.e., carbamazepine, ibuprofen, E-coli, or others). Then, depending on this agreement, common indicators based on the % removal efficiency of those substances can be adopted in technical assessments of different technologies to help make different studies comparable. In addition to agreeing on key pollutants to monitor, there is a need to standardize the assessment of treatment performance. Strotmann et al. (1993) proposed a structured testing protocol for evaluating the anaerobic biodegradability of wastewaters [74]. Although this strategy was developed specifically for anaerobic digestion, it serves as a valuable example of how integrated test methods can improve the comparability between studies [74]. Given that HWWT involves a wide range of technologies, including aerobic biological processes, membrane filtration systems, and advanced oxidation techniques, developing tailored test protocols for each category is essential. Such protocols would allow for more consistent technical evaluations across different studies, plants, and geographic contexts, ultimately supporting more harmonized sustainability assessments.

The environmental assessment highlights the necessity for more life cycle assessment (LCA) studies on the entire life cycle of HWWT plants, not only on tertiary techniques. The same impact assessment methodology should be used in all studies (i.e., the Environmental Footprint method [75], which employs the best set of environmental impact indicators previously described). The functional unit of the LCA study should take into account the pollutant removal efficiency of each technique. Inventory data (such as chemicals and electricity consumption) should always be presented in studies, in addition to the environmental impact results. Detailed impact results should be presented, showing not only the total impact but also the contribution of different aspects to this total (especially the contribution of electricity). The environmental impact of climate change due to greenhouse gas (GHG) emissions is important in the assessment of HWWT due to the energy-intensive nature of the processes involved. Therefore, GHG accounting should be included in the assessment, and mitigation strategies should be explored, such as the integration of renewable energy sources (e.g., solar or wind-powered systems) to reduce the environmental burden. In addition, the electricity consumption per m³ of wastewater treated is an important indicator to be considered in this case. Additionally, future LCA studies should expand their scope to include broader environmental criteria, such as the presence of pharmaceutical residues and antibiotic-resistant genes (ARGs) in receiving water bodies, risks to environmental safety, and the generation and management of waste byproducts like sludge. Including these aspects will lead to more holistic and policy-relevant environmental assessments.

Similar to environmental assessment, economic studies should also focus on the entire life cycle of the treatment plant by considering the operational and investment costs of the different primary, secondary, and tertiary techniques needed for the complete treatment of hospital wastewater (HWW). In other words, economic evaluations should provide a long-term financial outlook by integrating Life Cycle Costing (LCC) analysis. By considering both capital expenditure (CAPEX) (or investment) and operational costs, LCC allows for a more realistic assessment of HWWT processes. For example, while advanced membrane-based treatments, such as membrane bioreactors (MBRs) and electrochemical oxidation (EO), may have higher initial investment costs (as shown in previous studies), they could lead to lower long-term expenses due to reduced energy dependence and chemical usage. Therefore, future research should consider LCC models to compare the long-term sustainability of different treatment options, ensuring cost-effective and financially viable wastewater management strategies. The efficiency of each technique should also be considered. Indicators used for this assessment can rely on operational costs (in euros or dollars per m³ of wastewater treated) and investment costs (in euros or dollars per year, depending on the treatment capacity).

It is worth mentioning that energy consumption and cost may vary based on the treatment capacity and hospital size. In fact, larger hospitals typically benefit from economies of scale, leading to lower energy and costs per cubic meter of wastewater treated. Future research should focus on comparative studies across different hospital sizes to better normalize these figures for decision-making.

4.2. Recommendations for Social Assessment of HWWT

Social assessment differs significantly from other types of assessments due to its qualitative nature. However, in order to facilitate a comparison between the different treatment techniques, it is important to quantitatively measure the indicators.

From the literature studies discussed above, several indicators have been identified as significant for HWWT techniques. These indicators can be classified into two types based on the different stakeholders affected:

• Workers: workers’ health and safety, sustainable behavior
• Community & society: public health and safety, effluent quality, open space availability

Workers’ health and safety indicators can be quantified, for example, by calculating the total number of work fatalities, total risks of occupational diseases, implementation of standard procedures and guidelines, and number of personnel who have received training regarding different policies and procedures. The sustainable behavior indicator can be quantified through surveys measuring the awareness and engagement of staff with sustainability-related practices, such as proper chemical handling and energy-saving behavior, to prevent health and environmental risks. Quantitative data can also be collected by tracking the number of personnel attending sustainability training programs or workshops and monitoring initiatives undertaken to increase their awareness of the societal importance of their work. These metrics can help connect behavioral awareness to actual performance outcomes in the management of hospital wastewater.

Public health and safety can be quantified by identifying the different effects caused or prevented by the operation of the plant or by calculating the potential impacts of the plant’s design on the public. The effluent quality can be quantified by comparing the composition of the effluent with the values established in specific regulations or laws. Finally, the open space availability indicator was quantified by determining the land available in square meters per m³ of wastewater per day.

Although originally developed in the context of municipal systems, spatial indicators such as open space availability can also be relevant in hospital settings, especially when decentralized or nature-based treatment units are considered. These systems may require dedicated land areas within or near hospital facilities, which can impact their design feasibility, public safety, and acceptability. While municipal indicators were used as a reference, only those relevant to hospital wastewater treatment were retained, and the specific challenges hospitals face, such as pathogen risks and antibiotic resistance, were acknowledged.

Nevertheless, future research is needed in order to adopt a common and adapted set of social quantitative indicators, especially those significant for HWWT techniques. The social life cycle (S-LCA) framework, which assesses human health, occupational safety, employment conditions, and social well-being along the life cycle of a system, is interesting to use and adapt to HWWT [76]. Additionally, in the effort to establish hospital-specific social indicators, some other well-established frameworks might be tested, such as Stakeholder Analysis (SA) [77], Community Perception Surveys [78], and Health Impact Assessment (HIA) [79]. Finally, the adopted quantitative set of social indicators meaningful for HWWT should be tested in real-case studies.

4.3. Summary of Recommendations for HWWT Sustainability Assessment

Our primary recommendation is to use the life cycle sustainability assessment framework (LCSA) [80] as an integrated methodological approach to evaluate the environmental, economic, and social impacts of an HWWT system throughout its entire life cycle. Adapting its key components (E-LCA for environmental assessment, LCC for economic assessment, and S-LCA for social assessment) to HWWT systems will facilitate greater harmonization and comparability across studies.

Achieving comparability across separate studies requires adopting the life cycle approach and addressing the following key aspects identified in this review:

• Technical assessment: defining the most representative HWW pollutants to be measured in order to determine the efficiency of a certain technique. Selecting these pollutants requires scientific and technological expertise to determine the most appropriate indicators—whether they are easier to measure, pose higher risks to human and ecological health, or exhibit greater persistence in the environment.
• Environmental assessment: using LCA and including detailed inventory data (e.g., electricity, chemical usage, removal efficiencies), in addition to environmental impact results of at least the climate change impact category (kg CO₂-eq/m³) and energy consumption (kWh/m³), among others.
• Economic assessment: using LCC, including both investment and operational costs for a specific technology.
• Social assessment: defining a common set of quantitative social indicators meaningful for HWWT. Further research is needed to test and adapt existing social indicators from other assessment frameworks, such as the HIA, to ensure their applicability to hospital wastewater treatment.

It is important to mention the capacity of the studied plant or technology in all these assessments, as most of them can be affected by it, especially environmental and economic assessments.

By applying these measures, future studies can ensure greater comparability and consistency in the assessments of HWWT technologies, thus gaining knowledge on the different dimensions of sustainability assessment and helping to develop more sustainable HWWT facilities.

Table 6. Summary of recommendations for harmonization of sustainability studies on HWWT.

Sustainability Dimension	Additional Research Needed	Key Indicators	Measurement	Integration Into Decision-Making
Technical	Determine common representative pollutants to measure	Pollutant Removal Efficiency	% Removal	Helps in selecting the most effective technology or strategy
Environmental a	no	Climate change Electricity consumption	kg CO2-eq/m3,	Informs decisions on eco-friendly technology or strategy
Economic a	no	investment + operational costs	Cost per m3 treated wastewater	Informs long-term financial feasibility
Social	Adapting meaningful social quantitative indicators	Related to: Health and Safety, Community Acceptance	not yet defined	Ensures health & safety compliance and public acceptance

^a The capacity/size of the evaluated plant or technology should always be reported.

summarizes the proposed guidelines for the harmonization of each sustainability dimension, including information on additional research needed, key indicators, measurement units, and how they can be integrated into decision-making processes.

5. Conclusions

In this first-of-its-kind review, detailed literature studies on the technical, environmental, economic, and social assessment of hospital wastewater treatments (HWWTs) are provided, as no complete sustainability assessment currently exists.

The technical assessment shows that the activated sludge process (ASP) and membrane bioreactor (MBR) are the most effective biological techniques, achieving 90% removal of the biological oxygen demand (BOD) and chemical oxygen demand (COD). ASP also removed 95% of ibuprofen and up to 97% of certain pharmaceutically active compounds (PhACs). Environmental assessments have revealed that electricity use is the dominant contributor to these impacts. Therefore, energy-efficient options such as ASP with electrochemical oxidation (EO) or sand filtration are preferable, requiring only 1.5 kWh/m³ and 0.579 kWh/m³, respectively. Economically, costs vary with equipment and energy requirements. Membrane technologies generally have higher operational costs than ASP when used as a secondary treatment. Social assessment remains a significant gap. No studies have directly evaluated the social implications of HWWT, although relevant indicators such as workers’ and public health and safety, effluent quality, sustainable behavior, and open space availability have been proposed in the general wastewater treatment (WWT) literature and could be adapted to HWWT.

The main limitations of these results are their geographical coverage and dependence on plant size/capacity. Most studies focus on Europe, North America, and parts of Asia, with limited representation in developing regions. Regarding plant size, only one of the nine environmental assessments and none of the economic assessments explicitly mentioned the capacity of the treatment plant. These limitations primarily affect environmental and economic assessment results, as treatment capacity significantly influences energy consumption, cost estimation, and overall sustainability outcomes.

The review results highlight two primary research gaps: (i) the lack of comprehensive sustainability assessments of HWWT options and (ii) the difficulty in comparing results across studies evaluating the technical, environmental, economic, and social dimensions of sustainability. Improving the comparability among studies will facilitate a more efficient understanding of HWWT sustainability, ultimately aiding in the design of more sustainable treatment alternatives for specific applications. This review offers practical recommendations for addressing these gaps and guiding future sustainability assessments.

These recommendations identify research needs and emphasize the type of information and indicators that should be incorporated across the four sustainability dimensions. The main suggestions for future research include: (i) identifying the most representative pollutants in hospital wastewater (HWW) to be measured and targeted for removal; (ii) following the proposed recommendations to ensure comparability in environmental and economic assessments in future studies; and (iii) establishing a standardized set of quantitative social indicators adapted to HWWT for social assessment. By applying these recommendations, future research and policy can move toward more consistent, effective, and sustainable hospital wastewater treatment practices.