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. 2023 Mar 11;11(3):109673. doi: 10.1016/j.jece.2023.109673

Comparative evaluation of advanced oxidation processes (AOPs) for reducing SARS-CoV-2 viral load from campus sewage water

Rinka Pramanik a,1, Narendra Bodawar b,1, Aashay Brahme b, Sanjay Kamble b,⁎, Mahesh Dharne a,⁎
PMCID: PMC10008039  PMID: 36937242

Abstract

Presence of SARS-CoV-2 in wastewater is a major concern as the wastewater meets rivers and other water bodies and is used by the population for various purposes. Hence it is very important to treat sewage water in an efficient manner in order to reduce the public health risk. In the present work, various advanced oxidation processes (AOPs) have been evaluated for disinfection of SARS-CoV-2 from sewage water collected from STP inlet of academic institutional residential. The sewage water was subjected to ten AOPs, which include Ozone (O3), Hydrodynamic cavitation (HC), Ultraviolet radiation (UV), and their hybrid combinations like HC/O3, HC/O3/H2O2, HC/H2O2, O3/UV, UV/H2O2, UV/H2O2/O3, and O3/H2O2 to reduce SARS-CoV-2 viral load. Further, AOP treated sewage water was subjected to total nucleic acid isolation followed by RT-qPCR for viral load estimation. The sewage water treatment techniques were evaluated based on their viral concentration-reducing efficiency. It was found that ozone and ozone-coupled hybrid AOPs showed the most promising result with more than 98 % SARS-CoV-2 viral load reducing efficiency from sewage water. Interestingly, the best six AOPs used in this study significantly reduced both the SARS-CoV-2 and PMMoV (faecal indicator) viral load and improved water quality in terms of increasing DO and decreasing TOC.

Keywords: AOPs and hybrid AOPs, Ozonation, Hydrodynamic cavitation, SARS-CoV-2, PMMoV, Sewage water treatment

Graphical Abstract

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1. Introduction

The first detection of the SARS-CoV-2 virus responsible for causing COVID-19 infection was found in Wuhan, China, in December 2019 [1], [2], [3]. The COVID-19 outbreak was declared a public health emergency of international concern by the World Health Organization (WHO) on 30th January 2020. The SARS-CoV-2 virus is mainly transmitted through tiny respiratory droplets [4]. COVID-19-infected patients, both symptomatic as well as asymptomatic excrete the SARS-CoV-2 virus through faeces and other body secretion (sputum, saliva, urine) that are released via the restroom or lavatory and is introduced into the sewage treatment plant (STP) [1], [5], [6], [7]. SARS-CoV-2 RNA can survive in wastewater for around eight days, and it can remain inactive at 4 °C for approximately 19 days [8], [9]. Therefore, sewage water from the inlet of STPs can be used to extract SARS-CoV-2 viral RNA, and its presence and quantification can be determined using RT-qPCR. Wastewater-based epidemiology (WBE) estimates the prevalence of diseases and works as an early warning system for population-wide infectious diseases [10], [11], [12]. It was already proven to be an effective tool during the Influenza A (H1N1) outbreak and other studies like the presence of Norovirus, Hepatitis A and E virus, adenovirus, and rotavirus [11].

The water released from the outlet of STPs plays an essential role in protecting public health as it has been used for irrigation, recreational purposes, or discharged in rivers [6], [13]. The presence of SARS-CoV-2 genetic material influences the quality of water in many ways. Such sewage water can cause many public health risks and environmental issues if released without proper treatment from STP’s outlet to the environment. Hence, an effective treatment method for reducing viral load from sewage water is crucial for the environment [1], [13], [14]. Many studies demonstrate the presence of SARS-CoV-2 throughout the STPs as well as in treated wastewater around the globe like India, China, Paris, Germany, Japan, USA, Italy, and Spain [1], [8], [11], [15], [16], [17], [18], [19], [20]. Primary or secondary STP treatments cannot wholly remove SARS-CoV-2 RNA from raw sewage water; hence tertiary or advanced treatment techniques must be investigated [1]. As the primary treatment involves the removal of suspended solids, the complete removal of SARS-CoV-2 RNA is unachievable in this stage [21]. Besides, the virus can easily survive the primary disinfection techniques because of their size; therefore, chemical disinfection is the alternate approach for eliminating viruses [4], [22]. Mainly chlorine-based disinfection strategies are used to remove SARS-CoV-2 RNA from sewage water [23]. However, the generation of eco-toxic by-products, such as chloroform, halo acetic acids, and trihalomethanes, sets a significant limitation to this method. Other disinfecting techniques have their merits and demerits, as they are not equally effective for inactivating viral particles [24], [25]. Therefore, it is crucial to explore and develop a proper treatment strategy for contaminated sewage water in battling this kind of pandemic situation.

Advanced oxidation processes (AOPs) are the latest wastewater treatment techniques that efficiently disinfect viruses by generating oxidant species [26]. The fundamental mechanism for the disinfection of viruses by AOPs occurs via the generation of reactive oxygen species (ROS) like Hydroxyl (OH•) radicals, superoxide (O2 •), etc. [27], [28]. These ROS are responsible for the degradation of lipids and proteins, resulting in oxidative damage of Membrane glycoprotein, envelope protein, and nucleocapsid of SARS-CoV-2 viral structure. Apart from the structural damage, RNA content of SARS-CoV-2 is also degraded with the help of these ROS generated during AOP treatment of sewage water, which leads to the elimination of SAR-CoV-2 from sewage water [22].

This study aims to examine and evaluate advanced oxidation processes (AOPs) and their hybrid combinations for disinfecting SARS-CoV-2 from sewage water. The AOPs used in this study are ozonation, ultraviolet radiation (80 W lamp of wavelength 254 nm), hydrodynamic cavitation (HC), as well as their hybrid techniques like HC/O3, HC/O3/H2O2, HC/H2O2, O3/UV, UV/H2O2, UV/H2O2/O3 and O3/H2O2 for reducing the SARS-CoV-2 viral load from sewage water. The raw sewage water sample and AOPs treated sewage water samples were subjected to RT-qPCR to discern SARS-CoV-2 viral load. Subsequent comparison of the viral load of treated sewage water with that of raw sewage water, giving six best treatment techniques were shortlisted for further experimentation. Additionally, the effect of ozone dose on these above techniques was studied to establish the optimum ozone dose required. Further selected six best techniques were used to treat three distinct sewage water samples collected on different dates to validate their efficacy for disinfection of SARS-CoV-2 ( Fig. 1).

Fig. 1.

Fig. 1

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Experimental scheme illustrating treatment of raw sewage water samples (from STP) with different treatment techniques for reduced SARS-Cov-2 viral load.

The sewage water treatment techniques would be most effective if they also reduce faecal matter and other enteric viruses from outlets of STPs. Therefore, during the final screening of raw sewage water treatment techniques, we also investigated the reduction of Pepper mild mottle virus (PMMoV). It is the most prevalent virus (up to 109 viruses/gram dry stool) in human faecal samples, as it is a plant virus with the dietary origin of humans from various pepper species [29], [30], [31]. Therefore, it is counted as a viral indicator of faecal contamination in sewage water because of its relatively stable nature and ability to move through the gut quickly [30].

2. Material and methods

2.1. Experimental setup

2.1.1. Setup for hydrodynamic cavitation and hybrid hydrodynamic cavitation technique

The experimental setup used for hydrodynamic cavitation and hybrid hydrodynamic cavitation for disinfection of SARS-CoV-2 from sewage water is shown in Fig. 2. The cavitation setup consists of an effluent holding tank (EHT) having a capacity of 5 litres, a centrifugal pump (P) power rating of 2 kW (CNP YE2–80M1–2: 2830 rpm, 415 V, 50 Hz A.C.), ½ inch control valves (ball valves) and pressure gauges PG1 and PG2. The venturi throat of diameter (6 mm) was used as cavitation device in the present setup. The sewage water was circulated from the EHT through the line consisting of a venturi device and back into the EHT using a positive displacement pump, and a bypass line was provided to control the circulation flow rate if required. The temperature of sewage water in the EHT tank is controlled by circulating the cold water through helical coils submerged in the EHT tank. The entire setup was fabricated using stainless steel 316. This experimental setup was used to disinfect SARS-CoV-2 from the sewage water using hydrodynamic cavitation and hybrid hydrodynamic cavitation techniques such as HC/O3, HC/O3/H2O2, and HC/H2O2.

Fig. 2.

Fig. 2

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Setup for hydrodynamic cavitation and its hybrid techniques.

2.1.2. Setup for hybrid photocatalytic and ozonation processes

As shown in Fig. 3, an annular glass reactor comprising a quartz candle placed inside the annular glass reactor was used for disinfection of SARS-CoV-2 from raw sewage water. The volume of the glass reactor is 1 litre, with an annular effective volume of 500 ml. The disinfection of SARS-CoV-2 takes place in the annular volume formed between the glass rector and the quartz candle placed in it. The required ozone flow is introduced from the bottom of the glass reactor through a ring air sparger. Ozone generator supplied by Ozonics India Ltd, Pune, India, was used in the present experimental work. It can be operated upto a maximum current of 0.15 A. The generator produces ozone using dry air as a feed gas. The ozone generator was operated within a current range of 0.08 A to 0.15 A, producing ozone at a flow rate of 8 gm/hr and 15 gm/hr, respectively. The quartz candle is equipped with a cooling water inlet and outlet to maintain the temperature of the sewage water in the reactor. The hollow inner space inside the quartz candle is used to place the UV lamp. The UV lamp having 80 W capacity and wavelength of 254 nm was used.

Fig. 3.

Fig. 3

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Setup for UV/ozonation and its hybrid processes.

2.2. Sampling of sewage water sample and sampling site

Raw sewage water samples were collected from the inlet of the Sewage Treatment Plant (Phytorid- STP) located at CSIR-National Chemical Laboratory (CSIR-NCL) campus, Pune, Maharashtra, India (18°32'31.2"N 73°48'43.2"E). The STP receives around 0.15 MLD of wastewater daily from Colony residents, hostel. Raw sewage water sample was collected following Standard Operating Procedure of wastewater surveillance by Center for disease control and prevention (CDC, USA) in a sterile container and stored at 4 °C until it gets subjected to the following disinfection techniques. 20 litres of raw sewage water samples were collected for primary treatment and secondary treatment on 27th July 2022 and 18th September 2022, respectively. Whereas for evaluating the efficacy of the six best AOP techniques, three different sewage water samples (20 litres each) were collected on 30th August 2022, 1st September 2022, and 2nd September 2022.

2.3. Treatment procedure

2.3.1. Hydrodynamic cavitation and hybrid hydrodynamic cavitation technique

The known quantity of sewage water collected from STP was fed to the effluent holding tank (EHT), as shown in Fig. 2. The physiochemical characteristics like Total Organic Carbon (TOC), Total dissolved solids (TDS), Dissolve Oxygen (DO), and pH were estimated before and after treatment of raw sewage water by AOPs. Hydrodynamic cavitation was induced using a pump of power rating 2KW, as the pressure induced by the pump generates the required suction across the venturi that enables the formation of cavities resulting in the formation of OH• radicals. The sewage water was circulated using this pump from the EHT through the line consisting of a venturi device and back into the EHT using a centrifugal pump. The known quantity of ozone gas was introduced at the venturi throat depending on the requirement of disinfection techniques. In the case of hybrid techniques such as ozonation/H2O2/HC and ozonation/HC ozone gas is induced at the venturi throat, while in the case of HC and HC/H2O2 ozone gas is not induced. The sewage water was kept in recirculation mode for 90 min for treatment and the samples were taken and subsequently analysed for their physiochemical characteristics along with viral load. TOC also was measured using total organic carbon analyser TOC-L (Shimadzu model 00114). The pH, TDS, and DO were measured using electrodes provided by HANNA instruments (HI5521 and HI5522).

2.3.2. Ozonation and hybrid techniques

Fig. 3 shows a schematic of the annular glass reactor used for UV, ozonation, and hybrid techniques such as UV/H2O2, UV/ozonation, UV/ozonation/H2O2, and ozonation/H2O2. A known quantity of sewage water (500 ml) was added to the annular glass reactor having an annular space volume of 1 litre. The UV lamp of 80 W, having a wavelength of 254 nm, is placed in the inner quartz tube hollow candle, which will be used for UV and hybrid techniques such as UV/H2O2, UV/ozonation, UV/ozonation/H2O2. The reaction temperature was constantly maintained by circulating the chilled water from the annular space between the lamp with the help of JULABO chiller FP-50 MA. The ozone gas with the desired flow rate was supplied through a ring sparger situated at the bottom of the reactor. The sewage water samples were taken from the reactor to estimate physiochemical characteristics and viral load. The disinfection experiment was performed for 90 min.

2.4. Isolation of total nucleic acids

Wizard® Enviro Wastewater TNA kit (Promega Corp., USA) was used to purify Total Nucleic Acid (TNA) from the raw sewage water (unpasteurised) as well as AOPs treated water samples at the same time to compare the difference in the viral concentration. TNA was isolated using the manufacturer protocol, which consists of 2 Steps: In the first step, TNA is captured on PureYield™ Midi Binding Column (Promega Corp., USA) and then eluted in 1 ml of pre-warmed (60 °C) nuclease-free water (NFW); in the second one eluted TNA was further purified using a Mini spin column and concentrated in 40 µL volume.

2.5. Viral reverse transcriptase-quantitative PCR assay (RT-qPCR)

2.5.1. Quantification of SARS-CoV-2 RNA

The isolated TNA was subjected to SARS-CoV-2 RNA screening using GenePath Dx CoViDx One v2.1.1TK-Quantitative multiplex RT-qPCR kit (Achira Labs, India). This kit targets nucleocapsid (N), RNA-dependent RNA Polymerase (RdRp), and Envelope (E) regions of the SARS-CoV-2 genome along with human control gene (RNAase P). 15 µL of amplification reaction was composed of 10 µL of reaction master mix and 5 µL TNA. NFW was used as a no-template control (NTC), and extraction control was analysed with each plate. Experiments were performed on 7500 Fast Real-Time PCR system (Applied Biosystems, Foster City, USA) with the following cycling conditions: Pre-incubation for 5 min at 37 °C, Reverse transcription for 7 min at 52 °C, R.T. inactivation for 3 min 30 s at 95 °C, and 40 cycles of denaturation at 5 s at 95 °C and extension 35 s at 35 °C. RT-qPCR was performed in duplicates for each sample. The quantitation of the SARS-CoV-2 viral load in the samples was done using the Covid-19 Viral Load Calculation Tool (RUO).

2.5.2. Quantification of PMMoV RNA

Quantification of PMMoV RNA was screened using the GenePath Dx Wastewater monitoring for Covid-19 (RUO) (Achira Labs, India) on a 7500 Fast Real-Time PCR system (Applied Biosystems, Foster City, USA). Three standards of PMMoV (of concentration 5000 copies/µL, 500 copies/µL, 50 copies/µL) were amplified along with experimental samples to construct a standard curve for PMMoV quantification. 5 µL of extracted TNA was mixed with 10 µL reaction master mix to make 15 µL amplification reaction. 5 µL of NFW was used as an NTC. Reactions were performed with the following cycling conditions: Pre-incubation for 5 min at 37 °C, Reverse transcription for 7 min at 52 °C, R.T. inactivation for 3 min 30 s at 95 °C, and 40 cycles of denaturation at 5 s at 95 °C and extension 35 s at 35 °C. RT-qPCR was performed in duplicates for each sample. The concentration of PMMoV was estimated using the standard curve.

3. Results and discussion

SARS-CoV-2 viral load in sewage water started to rise from the first week of July 2022. The escalated viral load in sewage water from the inlet of STP was needed to evaluate the best sewage water treatment techniques. Therefore, these experiments were accomplished from August 2022 to September 2022, when the viral load of sewage water was elevated. The disinfecting techniques like hydrodynamic cavitation (HC), UV and ozonation, as well as their hybrid combinations like HC/O3, HC/O3/H2O2, HC/H2O2, O3/UV, UV/H2O2, UV/H2O2/O3 and O3/H2O2 for reducing the SARS-CoV-2 viral load from sewage water, were used in this study. The experiments were divided into three parts: 1) Primary screening of AOPs and hybrid AOPs, 2) Variation of ozone dose for optimum efficiency, 3) Treatment of three different sewage water samples using selected six best AOP techniques.

3.1. Primary screening

Around ten AOPs, including hybrids techniques were screened for effective disinfection of the SARS-CoV-2 from raw sewage water ( Fig. 4). The ozone flow rate of 8 gm/hr during the initial screening was kept constant. TNA was isolated from a sewage water sample (raw and treated) and subjected to RT-qPCR, which were analysed by cycle threshold (Ct) and viral load. AOP treated sewage water having Ct value < 35 for any two target genes of SARS-CoV-2 were considered SARS-CoV-2 Positive (according to the kit’s instruction), and they were less efficient in reducing SARS-CoV-2 from sewage water (Supplementary Table: 1).

Fig. 4.

Fig. 4

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Bar plot illustrating evaluation of disinfecting efficiency of different AOPs for reduced viral load. (Experimental conditions: 8 gm/hr ozone flow rate, 400 mg/L H2O2 and ultraviolet radiation (254 nm) were set for 90 min in respective AOPs treatments on X-axis.).

The viral load of raw sewage water used in the initial screening was 382 copies/µL. During the initial screening, UV was used as one of the disinfection techniques because it can eradicate biological pollutants from wastewater [32], [33] and SARS-CoV-2 from infected surfaces like doors and handles of windows [34], [35]. UV-C of wavelength 254 nm was used in the treatment process, which effectively breaks the bonds within the biological molecules by generating high numbers of OH• radicals and is widely used for disinfection [36], [37]. Therefore, eradication of SARS-CoV-2 RNA was done by exposing sewage water to UV for 90 min, giving a 75.5 % reduction in RNA concentration which is 105 copies/µL. SARS-CoV-2 RNA was reduced to 86.7 copies/µL with disinfecting efficiency of 77.3 % when UV was combined with hydrogen peroxide (400 mg/L); the synergetic effect of the combination of UV/H2O2 lead to more generation of hydroxyl radical which resulted in high disinfecting efficiency [38]. Dular et al. [39] studied sewage water treatment using hydrodynamic cavitation technique and found that it reduces waterborne enteric viruses from sewage water treatment plants. Similarly, Bui et al. [40] also investigated HC as an efficient and economical treatment technique that generates no by-products. In the present study, HC treatment of sewage water for 90 min scaled down the SARS-CoV-2 RNA viral load to 12.2 copies/µL with 96.80 % disinfecting efficiency. But when HC was combined with hydrogen peroxide (400 mg/L) and Ozone (8 gm/h) to treat the sewage water, the RNA concentration was reduced to 10.4 copies/µL and 6.71 copies/µL, respectively. Besides this, a hybrid of HC, ozone (8 gm/h), and hydrogen peroxide (400 gm/l) brought the SARS-CoV-2 RNA concentration down to 3.7 copies/µL with 99.02 % disinfecting efficiency because the combination of HC with other AOPs are more effective for sewage water treatment as the number of hydroxyl radical generated are more due to the addition of hydrogen peroxide and ozone [41], [42]. To the best of our knowledge, this is the first study to implicate hydrodynamic cavitation for reducing SARS-CoV-2 viral load from sewage water. SARS-CoV-2 RNA concentration in sewage water was scaled down to 1.66 copies/µL when treated with ozone at an 8 gm/hr flow rate for 90 min. The combination of ozone (8 gm/hr) with UV and hydrogen peroxide (400 mg/L) was also used to treat sewage water, resulting in the diminution of SARS-CoV-2 RNA concentration to 0.984 copies/µL and 1.21 copies/µL, respectively. In addition, a hybrid treatment of ozone (8 gm/h), UV and hydrogen peroxide (400 mg/L) was also used to treat sewage water and decline the SARS-CoV-2 RNA concentration to 1.13 copies/µL. All ozone and ozone based AOPs sewage water techniques shown more than 99.00 % disinfecting capability, as it is highly reactive to viruses because of its oxidising property, and it can eradicate enveloped as well as non-enveloped viruses [41], [43], [44], [45].

3.2. Secondary screening

Variations of ozone dose were given to the six most effective techniques from the primary screening. The ozone dose variation was selected based on the minimum and maximum operating capacity of the ozone generation device used in this study. The least and maximum flow rate provided by the ozone generator is 8 gm/hr and 15 gm ozone/hr, respectively. UV-C light of wavelength 254 nm and H2O2 loading of 400 mg/L were used to perform the secondary screening experiments. In this screening, ozonation/UV, ozonation/UV/H2O2, HC/ozonation, and ozonation/HC/H2O2 proved to be most effective when the ozone dose was 15 gm/hr ( Fig. 5). The ozone flow rate of 8 gm/hr worked best for ozonation and ozonation/H2O2. However, both ozone flow rates significantly reduced the SARS-CoV-2 RNA concentration (Fig. 5), and treatment with the least ozone flow rate is always economical as the operating cost of the process will be less.

Fig. 5.

Fig. 5

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Variations of initially screened treatment techniques using raw sewage water samples. The Y-axis at the left shows the viral load (copies/µL) of raw sewage water (red bar), and the secondary Y-Axis axis depicts the viral load (copies/µL) of AOP treated sewage water.

3.3. Evaluation of six best AOP techniques for reduction of SARS-CoV-2 and PMMoV

These six best AOP techniques were further tried to treat three different sewage water samples collected on different days. The purpose of the treatment of three different sewage water samples was to certify the efficacy and consistency of all selected six best AOP techniques for the reduction of SARS-CoV-2 RNA concentration. It was found that all treatment techniques show SARS-CoV-2 RNA viral load reduction to the desired level ( Fig. 6).

Fig. 6.

Fig. 6

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Graphical representation of the SARS-CoV-2 viral load reduction for the three different sewage water samples collected on different days using six best AOP techniques. The Y-axis at the left shows the viral load (copies/µL) of raw sewage water (checkered pattern bar), and the secondary axis represents the viral load (copies/µL) of AOP treated water.

Additionally, PMMoV RNA reduction was also evaluated for the three different sewage water samples collected on different days using the six best AOP techniques. PMMoV is the most abundant RNA virus in human faeces and an indicator of faecal contamination [30]. GenePathDx Wastewater monitoring for Covid-19 (RUO) (Achira Labs, India) was used to evaluate PMMoV RNA reduction and compared with raw sewage water sample ( Fig. 7). PMMoV RNA was more than 1900 copies/µL in raw sewage water got reduced to < 600 copies/µL after AOPs treatment, hence we can say that these treatment techniques are also effective in reducing the faecal contamination along with SARS-CoV-2 RNA from sewage water [46].

Fig. 7.

Fig. 7

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PMMoV RNA (copies/µL) reduction. After treatment of the three different sewage water samples collected using the six best AOP techniques.

3.4. Water quality improved after AOP treatment

The physicochemical characteristics of raw sewage water before and after the AOPs were estimated and shown in Table 1. The TOC of the treated sewage water decreases from 27 mg/L to below 5 mg/L for all treatment techniques (Table 1). This reflects a direct correlation between reduction in SARS-CoV-2 RNA, PMMoV, and other microbes in the sewage water and reduction in total organic carbon load as all these viruses and bacteria contain organic carbons [47], [48]. Also, reduction in TOC helps lower the risk of forming hazardous toxic by-products such as chloroform, halo acetic acids, and trihalomethanes formed by the reaction of organic matter with chlorine which is used as a primary disinfectant in conventional STPs [23]. The AOP techniques also help in increasing the DO content of the sewage water as O2 is generated along with the OH. radicals that help in the degradation of the SARS-CoV-2 RNA [28]. Also, ozone gas that is used as one of the primary oxidizing agents in degrading the SARS-CoV-2 RNA has a very short half-life in water, due to which, if not consumed, gets converted to O2, which in turn helps in further degradation and increasing the DO content of the water. The dissolved oxygen (DO) level of treated sewage water has increased from 5 mg/L to 15 mg/L, which is a good indicator of water quality. Aquatic life depends on sufficient oxygen to live; hence, a drop in dissolved oxygen below the limit will result in the loss of fish and plants. Therefore, water quality can be estimated by measuring dissolved oxygen level. As per the Environmental Protection Agency (EPA) guideline, if dissolved oxygen concentration reaches 3 mg/L, it is considered to be danger zone for aquatic life and levels below 1 mg/L are unfavourable to aquatic life, whereas dissolved oxygen level concentration 8–9 mg/L support all aquatic life (fish and plants) [49], [50]. The above AOPs were performed for the first time to reduce SARS-CoV-2 from sewage water, and further studies are essential to implement these techniques for the treatment of sewage water at actual STP.

Table 1.

Physical properties of untreated and treated sewage water using AOPs.

Physiochemical Parameters TOC (mg/L) TDS (mg/L) DO (mg/L) pH
Raw sewage water 27.06 336.4 5.9 7.5
HC/Ozonation 1.13 253.3 8.38 9
UV/Ozonation 5.58 261.3 12.7 8.7
H2O2/Ozonation 1.17 238.7 13.77 8.8
Ozonation 1.39 212.3 13.8 8.8
UV/Ozonation /H2O2 3.12 238.4 14.62 9
HC/Ozonation/H2O2 3.37 268.8 9.37 8.4
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3.5. Cost comparison of six best AOP techniques

Process economics is the major part that decides the merit for commercialization of the process. The Operating expenses (OpEx) comparison of six best AOPs will help understand the OpEx dynamics. Along with the SARS-CoV-2 reducing efficiency of treatment techniques, the cost analysis of the AOPs will be beneficial while scaling up the treatment processes. The operating cost for each of the six best AOPs is calculated by taking the sum of electricity cost (ozone generator, UV lamp, and pumps), labour cost, chemical cost, equipment maintenance cost, and analysis cost. Sample calculation for one of the hybrid AOP (UV/O3/H2O2) was done (Supplementary Information). Operating expenses estimation of all six hybrid AOPs were calculated similarly and comparatively evaluated in Table 2 for the treatment of 1 m3 sewage water.

Table 2.

Operating cost comparison of six best AOPs.

Items HC/O3 UV/O3 H2O2/O3 O3 UV/O3/H2O2 HC/O3/H2O2
Labour cost ($/m3) 1.44 1.44 1.44 1.44 1.44 1.44
Analysis cost ($/m3) 1.80 1.80 1.80 1.80 1.80 1.80
Equipment maintenance cost ($/m3) 0.007 0.045 0.004 0.003 0.046 0.007
Ozone generator electricity cost ($/m3) 1.32 1.32 0.63 0.63 1.32 1.32
UV lamp electricity cost ($/m3) 0.00 7.68 0.00 0.00 7.68 0.00
Pump electricity cost ($/m3) 0.71 0.71 0.71 0.71 0.71 0.71
Chemical cost ($/m3) 0.00 0.00 0.14 0.00 0.14 0.14
Overall total cost ($/m3) 5.27 13.00 4.73 4.58 13.14 5.42
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3.6. Limitations of the AOPs for the treatment of SARS-CoV-2 containing sewage water and further research scope

Compared to other pathogens, viruses exhibit mixed resistances and react differently to wastewater treatment methods, contributing to their longevity and prevalence in the environment. Hence, a better understanding of how viruses behave in STP will serve as a model for future viral elimination studies and help mitigate and reduce disease outbreaks. Furthermore, a crucial step in this approach is thoroughly identifying and evaluating viral pollutants and the wastewater treatment procedure. To enhance and maximize the virus eradication in STPs, the following influence elements should be considered:

  • a)

    A deviation between the lab-scale experiments and large-scale treatment of sewage water can be observed, leading to difficulties in verifying the treatment efficiencies. Thus, the stability of the process, when implemented on a large scale for long-term operation in STP, is an important aspect that needs to be analyzed and tested, particularly for hybrid AOPs.

  • b)

    Ozone dose variation in this study was based on the ozone generator's minimum and maximum operating capacity·H2O2 loading was kept constant at 400 mg/L during all treatments. Optimizing experimental parameters such as ozone flow rate, H2O2 loading, and HC inlet pressure can thus be further investigated to eliminate SARS-CoV-2 from wastewater efficiently.

  • c)

    To further optimize the HC-based hybrid AOPs, several hydrodynamic cavitation devices types, such as orifice, venturi, and vortex diode can be investigated.

  • d)

    In this study, there is an insignificant removal of TDS from treated sewage water because AOPs are effective in degrading only organic molecules rather than any inorganic salts in the water. As TDS comprises inorganic salts and a small amount of organic matter, their effective removal can only be achieved by combining AOPs with techniques like physical adsorption, reverse osmosis (RO), distillation, precipitation, membrane filtration, etc [51].

  • e)

    By installing tiny STPs in apartment buildings and housing complexes, it is possible to implement the AOPs to treat sewage water efficiently at the point of generation. The treated water can be utilized for gardening or as toilet flush water.

4. Conclusions

This is the first kind of study showing the effective use of AOPs for sewage water treatment to reduce SARS-CoV-2. In Primary screening, all AOPs techniques effectively reduced SARS-CoV-2 from sewage water, of which ozonation, hydrodynamic cavitation (HC) and hybrid AOPs show more than 95 % SARS-CoV-2 virus reduction. The study highlights that ozone and ozone-based hybrid AOPs techniques showed 99 % effectiveness in disinfecting SARS-CoV-2. These AOPs treatment combinations not only reduced SARS-CoV-2 but also effectively reduced PMMoV RNA concentration and enhanced water quality by increasing dissolved oxygen and decreasing the TOC of treated water. Although this is a preliminary study with a limited number of samples, the observations and experimental evidence highlighted the importance of AOP techniques in reducing SARS-CoV-2 viral load in sewage water. The results of our investigation could be instrumental for further studies dealing with the prospection of AOPs for the reduction of other viruses and pathogens from the sewage water.

CRediT authorship contribution statement

Rinka Pramanik: Conceptualization, Methodology, Experimentation, Validation, Investigation, Writing – original draft, Writing – review & editing. Narendra Bodawar: Conceptualization, Methodology, Experimentation, Validation, Investigation, Writing – original draft, Writing – review & editing. Aashay Brahme: Experimentation. Sanjay Kamble: Conceptualization, Methodology, Validation, Investigation, Resources, Writing – review & editing, Supervision. Mahesh Dharne: Conceptualization, Methodology, Validation, Investigation, Resources, Writing – original draft, Writing – review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

Authors are thankful to the Director, CSIR National Chemical Laboratory for support. This work funded by CSIR through project E3OW (MLP102326B) and National Chemical Laboratory, Pune (MLP 038526). Authors would like to express thanks to Engineering Division of National Chemical Laboratory for support during sample collection. Authors also acknowledge https://biorender.com/for creation of images. Manuscript has been checked for plagiarism using iThenticate licensed version. The Preprint of this manuscript is available in medRXIV.

Editor: Stefanos Giannakis

Footnotes

Appendix A

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.jece.2023.109673.

Appendix A. Supplementary material

Supplementary material

mmc1.docx (32.1KB, docx)

.

Data Availability

Data will be made available on request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary material

mmc1.docx (32.1KB, docx)

Data Availability Statement

Data will be made available on request.

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