Authors: Prof. Makarand M. Ghangrekar, Prof. Brajesh K. Dubey, Mr. Indrajit Chakraborty, Mr. Shreeniwas M. Sathe
Department of Civil Engineering, P. K. Sinha Centre for Bioenergy and Renewable. School of Environmental Science and Engineering. Indian Institute of Technology Kharagpur

Need for water recycling: In the current millennium, rising population and depleting natural resources have compelled governments and other non-government organisations to rethink their national, business and international strategies. This reshaping of the present technologies, business models and government policies have been guided by the sustainable development goals (SDGs) as set by the United Nations. Among the seventeen SDGs framed by United nation as a roadmap, the SDG 6 speaks about clean water and sanitation for all. In addition, the SDGs 3, 9, 11 and 12 are also influenced by the water cycle. For instance, the SDG 3 targets health and well being, which is directly connected to providing clean and potable water to all. Similarly, SDG 9, which talks about industrial innovation and infrastructure development, connects the water recycling industry both in terms of technological innovation for affordable treatment and infrastructural development to support such recycling.

Thus, defining the SDGs and their impact on the water usage and vice-versa, it can be understood that the wastewater treatment and recycling can contribute to the SDGs. Put in simple words, the treated water from the sewage and effluent treatment plants can be treated to such an extent that would enable its recycling for different non potable industrial, institutional, and domestic usage. Such usage would reduce the stress on the fresh water reserves and also the cost of water treatment infrastructure. This would also create more hygienic water practices as presently; large portions of developing nations discharge wastewater in natural water bodies due to lack of proper sewage treatment facilities. Discharge of such untreated water impacts the life on aqua as well as terra. Hence, treatment and recycle would again contribute to the SDG 14 and 15, which talks about reducing pollution load in marine and terrestrial environments.

Hence, building on the SDGs, government agencies as well as private players are adopting to this paradigm change and investing research, resources and framing recycling models for future setups. The Indian scenario is no different and the Government of India has also devised several strategies and projects for conservation of water resources. Pollution control boards, municipal bodies and different local regulatory and civic authorities across the country are focusing on wastewater treatment and reclamation projects as compared to the previous treatment and discharge policies. At this juncture, although such projects can achieve treatment of wastewater, however several factors intimidate the end user towards the reuse of this treated water. The risk of bacteriological and pathogenic contamination, the quality of treated water not meeting the discharge standards and the fear of infringement of personal hygiene reduces the acceptability of such practices. For ensuring reliability and transparency, the designed systems must be well tested prior to implementation in public domain. Additionally, to lure the corporate players the treatment cost offered by such systems should be reasonably low to out-compete other water sources in the water scarce regions of the country.

Glimpses of technologies involved: Different technologies are involved in wastewater treatment for facilitating reuse. The treatment technologies can be broadly classified into primary physical operations, secondary biological and biochemical processes and tertiary adsorption, advanced oxidation, coagulation ion exchange and membrane filtration processes. The list is indicative and with continuous research and development newer technologies are being introduced. In principle, the primary physical operations, such as screens, grit chamber and sedimentation tank, are installed to remove floating objects, gritty materials, and settleable particles, respectively. A certain fraction of organic matter is also removed during sedimentation.

The secondary processes are majorly biological in nature, the mode of operation being either aerobic or anaerobic. In case of aerobic processes, the activated sludge process and its variations, aerated lagoons, oxidation ponds are popular. Within the domain of anaerobic digestion, expanded bed granular reactor, upflow anaerobic sludge blanket reactor, anaerobic baffled reactor, anaerobic sequencing batch reactor etc. can be named. The tertiary treatment processes are often in the form of multigrade filters, membrane filtration for high effluent quality, dialysis for removal of excess dissolved solids, coagulation and flocculation, advanced oxidation processes (AOPs), such as ozonation, chlorination and UV radiation for disinfection. For treating wastewater to reuse quality, the AOPs are popular choice for removal of refractory compounds, that are not removed in secondary biological process.

IIT Kharagpur team and activities: The IIT Kharagpur team consists of Professor Makarand M. Ghangrekar as the Principal Investigator and Prof. Brajesh Kumar Dubey as the co-principal investigator. At IIT Kharagpur, the main theme of research for the WIN Foundation project was the implementation of an effective treatment plant with multistage tertiary treatment to produce treated water of non-potable contact reuse quality without the usage of membrane processes. Hence, the treatment plant designed and commissioned at the sewerage pumping station three inside the IIT Kharagpur campus comprises of two stage biological treatment followed by an optional chemical dosing assisted state-of-the art settler-clarifier unit, dual media filter and three stage disinfection units followed by an pressurized activated carbon filter. The final treated effluent can be either circulated to meeting horiticulture need and an in-house aquaculture pond or can be diverted towards the in-campus agricultural fields  and toilet flushing water, which is proposed as future plan. The block diagram given below describes the process flow diagram. The piping arrangement is designed to enable bypass of any of the operational stage for the tertiary processes. This bypassing arrangement is advantageous to test combination of the installed disinfection/ advanced oxidation processes (AOPs). The three stage AOP consists of ozonation, chlorination and UV radiation.

WIN Foundation modular treatment plant 300 m3 d-1 (a) Layout and (b) Real setup

Operation and monitoring of treatment plant

The 300 KLD treatment plant is under operation since January 2021 and has been continuously monitored for the removal of the organic matter, nutrients, surfactants, pathogens solids and dissolved ions. The results of the operated ETP indicate that the installation is capable of providing adequate treatment to domestic sewage and the water generated can be used for non-potable contact usage. The plant is capable of rendering satisfactory performance for wastewater reuse. The overall performance of the STP is as presented below:

# Most probable number of viable bacteria

The results of the operated STP indicate that the installation is capable of providing adequate treatment to domestic sewage and the water generated can be used for non-potable limited contact usage. The plant is capable of rendering satisfactory performance for wastewater reuse. The capitalised operating expenditure for this plant was estimated as Rs 15.87 per kL of wastewater treated with all three AOP combination. Further identification and monitoring of different trace refractory compounds has to be undertaken in next phase of research.

Broader vision and roadmap: The case studies at IIT Kharagpur provides a roadmap that can be adopted in other parts of the country for providing not only a safe sanitation practice, but also an opportunity for curbing the demand on fresh water reserves. In cities like Bangalore, the current water tariff from tanker supplies soar as high as Rs. 50 per kL of water. Modifying the larger urban apartment complexes with such modular plants capable of producing pathogen free and clean treated water can reduce the cost of water consumption. With the difference in electricity tariffs and accounting for the difference in manpower cost, the cost of such treatment can be kept as low as Rs. 17-18 per kL of water with the present model. Thus replacing the non-potable fraction of water supply with this treated water would lead to considerable savings.

In addition to the work done by IIT Kharagpur, other IITs, state research laboratories and CSIR labs are actively contributing to research on water reuse. A more concerted effort in this direction can be achieved by connecting the stakeholders and experts. The collaborative efforts and knowledge dissemination is a pre-requisite prior to India mobilizing towards such reuse practices. However, the advantageous position of India is that majority of smaller cities and a fraction of the megacities lack proper sewerage network and STPs. Hence designing such STPs and corresponding reuse utlities from scratch would be an easier job than retrofitting older establishments. Moreover, building on the outcome of such case studies of the modular STPs, the city planning and municipal regulations can be reframed to include mandatory and/or incentivised land and building taxes for such buildings that could practice such inhouse treatment of sewage and reuse of treated water. At this stage of planning city planners and urban civic bodies have to be brought onboard. Among other roadmaps towards achieving such paradigm shift of treated water reuse includes convincing the end user towards reuse of such water. This can be achieved by seminars and awareness programs for which, government, corporations and non-government organisations have to be brought in picture.

The advantage of such decentralised modular STPs is that it can be further adopted for peri-urban area and rural communities. However, in such cases, training of local populace to operate the plant and recover fertilizer and manure from the sludge produced and panchayat support towards financial management have to be micro-planned for each specific community. Easier said than done, such efforts of water recycling would require nationwide skilling of environmental engineers and plant operators, educating the general populace about the importance and advantage of such reuse and more importantly convincing the bureaucrats for adopting such policies at district and village panchayat levels.

About Authors:

1. Prof. Makarand M. Ghangrekar, Professor, Department of Civil Engineering Indian Institute of Technology Kharagpur; Head Centre, P. K. Sinha Centre for Bioenergy and Renewables; Head of School, School of Environmental Science and Engineering.https://www.linkedin.com/in/makarand-ghangrekar-3018a024/
   2. Prof. Brajesh K. Dubey,Associate Professor, Department of Civil Engineering Indian Institute of Technology Kharagpur; Faculty, P. K. Sinha Centre for Bioenergy and Renewables; Faculty, School of Environmental Science and Engineering. 
   https://www.linkedin.com/in/brajesh-dubey-716883/
   3. Mr. Indrajit Chakraborty,  PhD Research Scholar, Department of Civil Engineering Indian Institute of Technology Kharagpur https://www.linkedin.com/in/indrajit-chakraborty-7b4a96b6/  
   4. Mr.Shreeniwas M. Sathe,,Research Scholar, Department of Civil Engineering Indian Institute of Technology Kharagpur, https://www.linkedin.com/in/shreeniwas-sathe-851b3b197/

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