TERI advanced oxidation technology (TADOX^®) for treatment and rejuvenation of open drains and surface water bodies: making habitats sustainable

Larger towns and modern-day cities in developing countries have the requisite infrastructure to tackle sewage management and managing water resources; however, rural areas, villages and satellite towns lack resources for efficient wastewater treatment and management of water resources. Many of these villages are adjoining big cities and are developing very fast into peri-urban areas where economic activities are prevalent but there are also rural community areas where there are typical issues such as open defecation, animal husbandry and allied activities, agricultural activities, common bathing and washing areas that lead to multiple sources of pollution into nearby lakes, and surface water bodies.

Open drains also face continuous ecological and climatic effects and experience anthropogenic activities leading to a high risk of infection and transmission of communicable diseases. In this regard, microbiology parameters like Escherichia coliform, total coliform and total aerobic count are important to be investigated and treated suitably. Open drains from such peri-urban areas also contain high biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), sulfides, nitrates, ammonical nitrogen and phosphates, and micropollutants such as steroids, antihistamines, analgesics, antibiotics, pesticides and fertilizers (Giannakis et al. 2015; Bagheri et al. 2017; Fawzi Suleiman Khasawneh & Palaniandy 2019; Liang et al. 2019; Khasawneh & Palaniandy 2021; Krishnan et al. 2021; Yacouba et al. 2021; Yin & Shang 2020; Żyłła et al. 2019). Such open drains easily find their way based on natural topology and drainage patterns into natural ponds, lakes and rivers which are important water resources.

Moreover, several of these peri-urban areas have small-scale industries, cottage industries and small-scale workshops that are insignificant polluters on an individual basis however cumulatively account for a large pollution load into the water bodies, thus leading to a quality which is highly heterogeneous and difficult to treat. Therefore, it is of utmost importance to treat these drains before they join the natural water bodies; however, it is a difficult challenge as open drains are mostly untraceable and are easily created based on the topography of the area, climate of the area, etc. Furthermore, open drains could also be seasonal (only visible in monsoon season), could be prone to shock loads in terms of quality/quantity and could have the ability to alter water course with slight changes in drainage pattern of the area due to anthropogenic activities. Therefore, these open drains are difficult to be tapped into the centralized as well as decentralized wastewater treatment plants (STPs/DWWT) being run by the urban local bodies (ULBs). Severely contaminated open drains could percolate several micropollutants, dissolved organics or toxic compounds into the groundwater of the area causing immediate exposure/ingestion by the population. This situation is potentially hazardous for human health, occupational health and ecological health.

Conventional treatment technologies like chemical coagulation treatment followed by anaerobic–aerobic biological treatment systems cannot be directly integrated into such drains and streams with the intermittent flow and seasonal variations. These technologies require a homogenous flow and load influent on the treatment systems. For this reason, Shrivastava et al. (2020) supported the installation of either decentralized approaches or an in situ constructed wetland (CW) as an approach for enhancing the self-purification of surface water bodies; CW is also a promising approach given that there is limited operation and maintenance. Though this may be a potential abatement plan, CW may not efficiently remove low biodegradable organics, and micropollutants and cannot disinfect coliforms from sewage water. Several researchers have published reports on various technological interventions in mitigating these challenges, such as Wang et al. reported use of diffused aeration by placement of aerators into the Qing River, Beijing, China (Md Anawar & Chowdhury 2020); while another report evaluated the use of physicochemical treatment in Lake Rusalka, Poland through systematic addition of FeSO₄ to the lake (Md Anawar & Chowdhury 2020).

Advanced oxidation processes (AOPs) have shown to be promising in simultaneous removal of microbial toxicity and micropollutants wherein a significant removal was observed in 2 h, and the authors concluded that AOP could be a viable strategy to facilitate drain disposal of contaminated waters (Phillips et al. 2020). While not many advanced oxidation-based treatments have been used at a large scale for the abatement of polluted rivers, lakes and water bodies. A recent report by Tabla-Hernandez et al. (2020) discussed continuous diffused O₂ and O₃ purging directly through a floating reactor system into the Valsequillo reservoir in Puebla, Mexico for 5 months to reduce COD, BOD and increase DO levels. To the best of our knowledge, this has been the most recent and large-scale non-point-source pollution abatement strategy at this real scale. Whereas there are limited reports available on real-time treatment of a flowing open drain; none of the reports study the treatment of these small open drains/nallahs.

This report shows a case study where an open untreated drain passing through The Energy and Resources Institute (TERI) Gwal Pahari campus at Gurugram, Haryana, India has been treated using TERI Advanced Oxidation Technology (TADOX^®); this drain is highly discoloured and has a strong and pungent odour throughout its flow in TERI campus. TADOX^® utilizes an advanced coagulation–flocculation-based primary treatment, nanotechnology-enabled heterogeneous photocatalysis (UV/n-TiO₂) and nanomaterial recovery as tertiary treatment (Bahadur 2015, 2021; Bahadur & Bhargava 2019, 2022; Bahadur et al. 2020; Das et al. 2020). The treatment efficiency has been evaluated in terms of physicochemical characteristics; pathogens like E. coli and faecal coliforms; micropollutants like caffeine, acetaminophen, ibuprofen, naproxen, sulfamethoxazole, diclofenac, bisphenol-A (BPA) and pesticides.

As shown in Figure 2, the wastewater is slightly discoloured and there is intermittent flow at the point of collection of wastewater. About 5,000 L of sewage flows every day from the village and is only naturally aerated, ultimately the drain joins the city drain channelized to the common sewage treatment plant of Gurugram.

Technical information and detailed methodology of the TADOX^® technology-based pilot scale plant treating 100 litres per day (LPD) and its operation has been published in another recent article. Details of plant operation, analysis of the wastewater quality parameters, computation of energy requirements and evaluation of the figures of merit have been already given in the earlier publication of this series of case studies (Kumar & Mathur 2004, 2006; Bahadur 2015, 2021; Bahadur & Bhargava 2019, 2022; Bahadur et al. 2020; Das et al. 2020). It involves UV/TiO₂ photocatalysis as the secondary treatment followed by nanomaterial recovery at the source. Such a photocatalytic treatment has been established to be useful in dye intermediates, basic organics, dye molecules, synthetic textile effluent, real textile and dyeing wastewater treatment systems and has been successful in eliminating the need of biological treatment at any stage (Kumar & Mathur 2004, 2006; Bahadur et al. 2010, 2020; Kumar et al. 2014; Bahadur 2015, 2021; George et al. 2016; Bahadur & Bhargava 2019, 2022; Das et al. 2020).

pH, electrical conductivity and total dissolved solids (TDS) were analysed by Pocket Pro Plus multi-tester by HACH, USA. UV–Vis spectra were recorded on UV–Vis spectrophotometer model DR6000 by HACH, USA. Analysis of other wastewater quality parameters was carried out at National Accreditation Board for Testing and Calibration Laboratories, India (NABL) Accredited laboratory as per ISO/IEC 17025:2017. Micropollutants and pathogens were analysed as per standard methods given in Standard Methods for the Examination of Water and Wastewater by American Public Health Association (APHA) 23 edition 2017 (Rice et al. 2017). The analysis took place in triplicates so that relative standard deviation (RSD) and other statistical inferences could be drawn.

The wastewater characteristics of the untreated and TADOX^® treated open drain have been given in Table 1, which clearly indicates a significant reduction in various physicochemical parameters like COD, BOD, TDS, TKN - total Kjeldahl nitrogen and phosphates along with microbiological parameters and hazardous micropollutants like caffeine, acetaminophen, ibuprofen, naproxen, sulfamethoxazole, diclofenac, bisphenol-A and pesticides.

Tabulated data in Table 1 clearly shows that TADOX^® was able to reduce all primary pollutants such as COD, BOD, TSS, etc. This quality of water also meets the regulatory requirements laid down by the Central Pollution Control Board (CPCB), Government of India and National Green Tribunal (NGT) which requires COD less than 50 mg/L and BOD less than 10 mg/L with TSS below 20 mg/L before the treated water can be discharged onto surface water bodies (Ministry of Environment & Forests 1986a, 1986b; Kumar & Goyal 2020).

TADOX^® also led to a substantial reduction in total nitrogen and phosphorus content of untreated drain water, which are the potential reasons for downstream eutrophication in water bodies, where total nitrogen reduction of 61% and phosphate reduction of 96% was observed within 5 h of treatment. In addition, a nitrate reduction of 24% was also found, while there was a marginal increase in the level of nitrite after the treatment. Reduction in nitrate level and increase in nitrite level might have occurred due to the photolysis of nitrates under UV light that causes the generation of hydroxyl ions and nitrite ions as a by-product (Vinge et al. 2020).

Moreover, TADOX^® treatment resulted in a 3 log unit E. coli reduction and 4 log unit total coliform bacteria reduction and a 4 log unit reduction in the total count (CFU/ml). Significance of these reported values are shown in Table 2 which shows the designated best use of the surface water bodies as per the regulatory body, i.e. Central Pollution Control Board, India (CPCB) (Central Pollution Control Board n.d.; Ministry of Environment & Forests 1986a, 1986b). The extent of pathogen inactivation is an essential parameter to decide the end use of the untreated and treated stream. Due to the promising pathogen inactivation presented in this work, the treated water quality as shown in Table 1 has been compared to the Class A quality as per water quality criteria shown in Table 2.

TADOX^® treatment may be directly compared with several other studies that report the rejuvenation of surface water bodies in different ways. One such study evaluated the use of direct placement of aerators into the Qing River in Beijing, China; this resulted in 60% removal of BOD while the DO concentration increased from negligible to 6 mg/L which led to improvement in aquatic life in the water body (Md Anawar & Chowdhury 2020). Another study has also evaluated the use of chemical coagulation and flocculation to reduce phosphorus and nitrogen concentration in water to avoid eutrophication in Lake Rusalka, Poland through the systematic addition of FeSO₄ to the lake (Tabla-Hernandez et al. 2020). Another interesting report from Swarzędzkie Lake, Poland shows a 38% reduction in phosphorus and improvement in aquatic life indicated by cyanobacteria through a chemical-cum-biological treatment (Md Anawar & Chowdhury 2020; Tabla-Hernandez et al. 2020).

A more recent laboratory-scale study on feasibility of sequential batch (SBR) operation under aerobic (SBRAe) and aerobic-anoxic (SBRAex) microenvironments was done in Siripuram village, Telangana, India showed 76.2% of organic fraction, 73.3% of phosphate and 81.6% of nitrate removal and concluded that the modified biological treatment systems could be utilized as a decentralized treatment system to implement community-level ZLD (Kopperi et al. 2023).

AOP has been utilized for similar compounds degradation on a laboratory scale study by Phillips et al. (2020) wherein three different AOPs UV/H₂O₂, O₃/H₂O₂ and electrochemical oxidation (boron-doped diamond (BDD) anode) have been compared to treat herbicides, pesticides, pharmaceuticals and flame retardant (Phillips et al. 2020). For most of the contaminants, AOPs were able to degrade about 100% parent compounds within 2 h of treatment which showed a viable strategy towards AOP as an approach to pretreat contaminated water prior to biological treatment. This study was only done for tap water and had the usual background matrix, which does not emulate the actual sample treatment (Phillips et al. 2020).

While not many advanced oxidation-based treatments have been used at a large scale for the abatement of polluted rivers, lakes and water bodies but a recent report from Valsequillo reservoir in Puebla, Mexico which is a highly polluted body of water shows the use of a combined O₂ + O₃ purging as a promising method (Tabla-Hernandez et al. 2020). The study shows the use of three large vessels, which injected 144 tons of O₃ and 300 tons of O₂ in 5 months at various locations in the reservoir. This led to oxidative degradation of various alkenes and phenols with successful degradation of 20–65% in heavy metal content and reduction of up to 20% in terms of COD and BOD. The study is very crucial as this is the only report of AOP-based non-point-source abatement of surface water (Tabla-Hernandez et al. 2020).

In comparison with the global trends in surface water pollution abatement, TADOX^® can degrade primary pollutants such as COD, BOD and TSS in a much more efficient and easy manner while at the same time requiring less space, deployment time, residence time and treatment time. One of the major challenges that TADOX^® was able to overcome is the mobility of the system and its speed of deployment. TADOX^® is designed to be modular and can be manoeuvred within the surface water body as per requirements, while other technologies require a lot of plant and machinery, and it may be difficult for these plants to manoeuvre. For treatment of open drains, TADOX^® plant could be installed adjacent to the drain and the upstream flow could be channelized to the TADOX^® system and the downstream flow could be sent back to the surface body thereby tapping, cleaning and restoring the drain simultaneously. Therefore, the presented study opens tremendous scope for non-point water pollution abatement in an affordable, easy and sustainable manner. This could influence policymakers to come out with specific policies and action plans to restore/rejuvenate surface water bodies while laying special emphasis on the permissible levels of physicochemical, microbiological, specific contaminants and micropollutants in the surface water body.

This study shows that the flowing open drains containing raw sewage and other mixed wastewater pose a serious environmental and occupational health hazard. Most importantly, the TADOX treatment was end-to-end, bypassing the requirement of any biological treatment technology. The overall 5-h end-to-end treatment resulted in significant removal of primary pollutants such as 63.5% COD, 99% BOD, 96% phosphate and 61% TKN with a double increase in DO concentration. It simultaneously led to a 3 log reduction in E. coli and a 4 log reduction in total coliform values, which represent microbial contamination load in the open drain. This results in treated water complying to Class A of designated water reuse criteria defined by CPCB, India. Moreover, TADOX treatment led to a reduction in micropollutant (MP) pollution load by 93.5% in acetaminophen, 96% in sulfamethoxazole, 96% in ibuprofen and 89% in caffeine. This reduction has not been reported elsewhere during surface water rejuvenation using AOPs. The remarkable reduction in persistent organic pollutants (POPs), pathogens, hazardous micropollutants and contaminants of emerging concern (CECs) shows that modern-day wastewater challenges need advanced interventions. TADOX Technology based on heterogeneous photocatalysis utilizing UV/TiO₂ holds tremendous potential as highly efficient, clean, green and future ready technology for wastewater treatment. Such a study will also open avenues for bringing in regulatory compliance and policy norms for the discharge of MPs in open drains and surface water bodies.

Authors gratefully acknowledge the support of Perfact Researchers Pvt Ltd, New Delhi and Sigma Test & Research Centre, New Delhi in collection, preservation, transportation and analysis of all wastewater samples. National Mission for Clean Ganga (NMCG), Ministry of Jal Shakti, Government of India, is acknowledged for funding such studies on pollution abatement under the NMCG-TERI Centre of Excellence (CoE) on Water Reuse [Ref. No: Mi/31/2021-PMC-NMCG].

National Mission for Clean Ganga (NMCG), Ministry of Jal Shakti, Government of India, is acknowledged for funding such studies on pollution abatement under the NMCG-TERI Centre of Excellence (CoE) on Water Reuse [Ref. No: Mi/31/2021-PMC-NMCG].

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.