The ever-growing demand for water, and its scarcity in many parts of India, are being aggravated by the lack of utilisation of wastewater potential. The importance of advanced wastewater treatment and its diverse applications have gained attention in recent times. Water utilities are adopting new and innovative solutions to improve the efficiency of existing wastewater treatment systems. This has encouraged industry players and technology providers to focus on developing new technologies and systems that can be adapted to current scenarios. They have introduced more evolved, sustainable, cost-effective and digitally updated methods, techniques and processes that can revolutionise the sector. These advancements include the bioremediation process, the thermal hydrolysis process (THP), innovations in pumps used in water network systems, and digital twin- or cloud-based technologies. Most of these are being implemented or planned to be used in the near future. Their growth would also improve the extent of treated wastewater (TWW) reuse for potable or non-potable purposes. However, there are several practical challenges in executing these technologies and meaningfully applying them in India. These need to be addressed to ensure their effective use and open avenues for other emerging technologies, alongside the creation of a robust regulatory framework.
Bioremediation
The process of bioremediation uses a consortium of microbes to break down complex organic pollutants in wastewater. These potent bacteria release enzymes that facilitate biodegradation through biochemical reactions. This process has the advantage of being a low-cost and energy-efficient technology, as it works on natural principles. It also ensures a quality of treatment matching the norms set by the National Green Tribunal and the Central Pollution Control Board. However, it requires proper planning and methodology to design the dosing pattern, which can be ensured by collecting data on the quality and quantity of incoming wastewater at the site.
Several improvements have been made to this technology. These include the use of specialised probiotic bio-culture consortia customised to remediate the target effluent characteristics, automated dosing skids with flow regulating pumps, smart measurement of parameters through internet-of-thing enabled devices and sensors, application of QGIS and satellite imagery for asset mapping, and energy-efficient paddle aerators. Some of these are being implemented in bioremediation projects in India. For instance, paddle aerators have been installed at the oxidation lagoons at Versova wastewater treatment facility (WWTF) in Mumbai by Bioxgreen Technology. The treatment process has helped in the complete breakdown of legacy sludge and the removal of weed in the lagoon. It has also helped to loosen other components such as silt, and improve the depth of the water body from around 1.52 feet to 12.5 feet. Some of the other ongoing bioremediation projects are the rehabilitation of the 180 million litres per day (mld) WWTF in Malad, bioremediation of the 175 mld Aligarh and Jafri drain under Aligarh Nagar Nigam, and bioremediation of the 279 mld Kukrail and GH Canal under Lucknow Nagar Nigam.
Innovative pump designs
Energy consumption by pumps accounts for 20 to 30 per cent of the total energy consumption by sewage treatment plants (STPs). The total energy consumption contributes the majority (more than 50 per cent) of their operational costs. This huge cost implication has pushed the sector to innovate on the design of pumps based on their type and location. The amount and size of biosolids vary from the primary to the tertiary treatment stage, in turn changing the requirements of pump hydraulics. Pump efficiency can be adapted accordingly. For instance, the raw sludge entering an STP for primary treatment typically has up to 4 inches of solids, which goes down to 2 inches when entering the aeration basin for secondary treatment. This further reduces to one inch at the end, and eventually, clear liquid is achieved during tertiary treatment. The pumps must be capable of handling the processing of varying solid sizes and their different types, such as fibrous, bundling, non-bundling, abrasive and non-abrasive.
Furthermore, pumps with variable frequency drives (VFD) are being used to deal with space constraints in multi-storey STPs in densely populated areas. They offer the potential for large energy savings by reducing the speed (or revolutions per minute) of the pump for longer water pipelines. Moreover, their cost has dropped drastically over the last 10 years. They are being used alongside programmable logic controllers (PLC) in both lower and upper basins. For instance, hydraulic modelling by VFD-based pumps has been utilised for water supply works in Hanuman Garhi, Ayodhya. Another 62.5 mld STP in Delawas, Jaipur uses VFD-based blowers in motor pumps and PLC-controlled anaerobic sludge digesters.
Another innovation in pumps is a mechanism that addresses the typical problem of sand build-up near the mechanical seal. These seals prevent water from entering the motor and damaging them. This solution, developed by Kishore Pumps, uses centrifugal force to brush the sand away from the area near the mechanical seal. The company has also adopted a critical practice involving power cables in submersible pumps. Submersible pumps are hermetically sealed, so the power cable is typically installed by the manufacturer in the factory and then sent to the site. However, these pumps may face issues at the STP requiring a change of cable. Therefore, a design has been developed for pumps of varying power whereby the operator can change the cable at the site itself. The pump is dispatched to the site along with a separate cable, which is installed during the commissioning of the STP.
Digital twin technology
A series of functions such as plant management and site data assessment are being explored on cloud-based platforms. One of the most popular emerging cloud-based technologies is the digital twin. It is a process-based technology designed to manage any type of treatment, such as sequential batch reactors (SBR), the activated sludge process and the membrane bio-reactor process. It covers all aspects of the lifecycle of a plant through simulation, including automation, engineering and maintenance. Its application is being explored for sewer management, the creation of a central repository of plant designs and a real-time decision control system for plant operations, and the training of operators. Siemens offers a multi-dimensional digital twin-based solution called Siemens Water (SIWA) Sewer, which uses algorithms to optimise the use of the sewer network and stabilise the inflow of sewage to the STP. It can reduce the discharge of wastewater by more than 85 per cent in some cases. A similar solution is the SIWA Blockage Predictor, which uses artificial intelligence to model the expected level of combined sewer overflow during rainfall. It also applies fuzzy logic to provide a warning system for potential blockages by considering recent levels of rainfall and their deviation from normal levels.
Digital twins are also being used for the optimisation of asset lifecycles. General Process Modelling Systems (gPROMs) are among the waste processing modelling solutions provided by Siemens. gPROMs provides a detailed engineering system in digital form, and generates a simulation of plant operations. The first part of this simulation, wherein the entire data analysis and engineering of processes such as biological, chemical and mechanical reactions take place, is useful for research and development. This data is gathered from the field to create a process twin. The second part involves collecting data from the plant and integrating it with the model. As a result, a feedback loop is created, wherein the real-time parameters or laboratory data are fed into the model to assess the best course of action. An operator training system called SIMIT is also provided by Siemens for plant processes and critical scenarios. It is a process modelling tool that allows energy savings in line with pollutant concentration regulations.
Several initiatives are being taken for deployment of digital twin technology worldwide. For instance, Cyient, a global digital engineering and technology solutions company based in Hyderabad, has developed digital twins for cities in Europe to manage various systems such as water distribution, sewage collection and stormwater drains. These will help their governments in executing projects faster during disaster events. Similarly, Thames Water Utilities Limited in UK is seeking partners to build digital twins for their key water treatment plants (WTPs).
Emerging technologies
Thermal hydrolysis process
The carbon content of soil in India is very low, but can be replenished through the use of sludge as a soil amendment conditioner or fertiliser. This sludge is produced during the primary and secondary treatment of raw sewage in STPs, and can be made fit for reuse through three types of treatment to remove pathogens, namely, class A, B and C treatments. The majority of sludge treatment in India is of the class C variety, wherein the sludge is simply dewatered after thickening, which helps in reducing the volume of solids as well as transportation. The class B option treats the sludge in a digester between the thickener and the dewatering unit. The resulting fertiliser is partially free from pathogens, and meets the sludge treatment norms of the United States Environmental Protection Agency (US EPA). This fertiliser can only be used in areas that have not had public contact for six to 36 months, depending on the type of crop to be grown. This is a huge constraint for end-users, and so class A treatment is being explored, which uses THP. THP is a two-stage process combining high-temperature boiling of sludge at 165 °Celsius at six bar pressure, followed by rapid decompression with a steam explosion. This process disintegrates the biomass by rupturing the cell walls and releasing biogas.
THP meets US EPA norms and has many benefits such as lower lifecycle costs than class B, high-quality pathogen-free fertilisers, and low to no odour. It also offers ease of storage, with 25 to 50 per cent less space required for class A sludge than normal sludge. Furthermore, the digester volume is reduced by 60 to 70 per cent, helping save capex and opex costs and lower the carbon footprint. Moreover, it increases volatile solids destruction by 20 to 50 per cent, in turn increasing biogas production by 20 to 50 per cent, improving dewaterability by 32 to 33 per cent and reducing opex by 30 to 50 per cent. The technology is being researched and developed in India by Cambi and IIT Roorkee. Sludge from various SBR-based STPs is being evaluated for class A treatment in India.
Chlorine radicals-based UV AOP
Wastewater treatment projects in India must first determine the purpose of TWW reuse, following which the treatment process should be decided. The level of contaminant disinfection must be decided in terms of log removal value. Amongst the new technologies that can offer opportunities for advanced wastewater treatment in India is the chlorine radicals-based UV advanced oxidation process (AOP). It is being offered by Trojan Technologies and can be used to improve AOP and reverse osmosis in the treatment stages, and reduce opex costs as well.
Challenges and future opportunities
Water sources such as groundwater and surface water are facing high levels of contamination in India. Safely using them requires different types of treatment based on the amount of pollutant loads and factors such as biological oxygen demand, chemical oxygen demand and the amount of ammonia found in them. However, there is lack of assessment of the type of technology needed for treatment based on the quality of the water received by the WTPs. They are typically designed according to the desired TWW output with no coliform. This does not assure water quality. Moreover, despite the many avenues for the reuse of TWW and the growing interest in potable reuse of wastewater in Indian cities, there is still a lack of regulations to support this. To this end, a revision of the Manual on Sewerage and Sewage Treatment, 2013 has been carried out. Furthermore, the reuse of TWW is considered to be highly expensive. However, advanced treatment for non-potable reuse for industrial purposes, desalination, transportation of water to inland areas and the construction of dams may have equivalent or higher cost implications.
Potable reuse must be considered seriously for water-scarce cities such as Delhi. It can serve as an alternative source of water in times of drought, or if there are disputes regarding the release of water from dams across state borders. It would also help water utilities to expand their portfolio of water sources and manage the demand for water in their cities. Indian cities can learn from many global cities such as Windhoek in Namibia, which has been using sewage as a drinking water source since the 1980s; and Singapore, which meets 30 per cent of its drinking water requirement from advanced treated wastewater. Similarly, many water-scarce US states such as California, Texas and Arizona have developed their own regulations for water reuse, and are implementing wastewater projects based on different parameters.
Based on a presentation and remarks by representatives from Bioxgreen Technology, Cambi India, Kishore Pumps, Siemens and Trojan Technologies at a recent India Infrastructure conference.