There has been a significant decline in and deterioration of freshwater resources in recent times. This points to an impending water crisis in India. According to the Water Technology Centre of the Indian Agricultural Research Institute, the projected demand for industrial water in 2050 is likely to exceed the 2025 levels by 170 per cent. As per the estimates of the Central Water Commission, the projected water demand for 2025 is around 843 billion cubic metres. The water demand is expected to be the highest for the irrigation sector, followed by drinking water, industry, energy and other sectors.
The reuse and recycling of industrial wastewater has the potential to alleviate water scarcity; however, the process involves high costs. The water policies drafted by the Ministry of Environment, Forest and Climate Change, and the Central Pollution Control Board encourage industries to adopt zero liquid discharge (ZLD) treatment processes. Moreover, the desalination process, which is referred to as seawater reverse osmosis (SWRO), is being promoted to transition to net zero emissions.
Companies such as Danfoss and IDE Technologies are offering innovative solutions such as energy-efficient axial pumps, life cycle assessment (LCA) methods, and carbon capture technology in ZLD and desalination processes to improve efficiency and reduce costs.
Energy recovery
Danfoss provides energy-efficient axial piston pumps and energy recovery devices that are tailored for the reverse osmosis (RO) and ZLD processes. It has successfully completed around 24,000 SWRO and ZLD installations worldwide. Membrane-based technologies such as RO can help reduce energy consumption and costs.
With innovative processes involving RO, around 60 per cent of water can be treated through industrial processes and 40 per cent through unsustainable thermal treatment methods. In the absence of the RO process, the entire water volume will have to be treated through thermal energy processes, which will involve high energy consumption as well as significant costs. The RO step in the ZLD process works through a semi-permeable membrane and has a resultant product of salt water as brine. This rejected brine contains high concentrations of salts and other dissolved solids. The brine is sent to an evaporation system, often using mechanical vapour compression or multi-effect distillation. These systems evaporate water from the brine, leaving behind solid waste. For instance, Danfoss has an energy recovery device which can capture this energy by pumping a higher flow of water at a higher pressure to the RO membrane. This reduces the energy consumption required to generate by-products. The use of energy recovery devices for brine thus becomes an energy-efficient and cost-effective solution.
Pumping solutions
Axial piston pumps have the ability to deliver a constant flow which is unaffected by changes in outlet pressure. These pumps guarantee high performance, and are a reliable and efficient pumping solutions.They offer advantages such as lower energy costs, quieter working conditions that enhance productivity and comfort, reduced service costs, and up to 15 to 20 per cent reduction in energy consumption. These pumps are more efficient than their next best alternatives such as centrifugal pumps.
In addition to this, ceramic axial piston pumps are gaining traction. These pumps offer robustness and efficiency. The internal parts of the pump which are vulnerable to wear and tear are replaced with technical ceramics. This helps the pumps to endure high compressional strength which is useful in crushing bigger particles. One of the benefits of ceramic axial piston pumps is reduced inspection and service intervals. Also, filtration was earlier undertaken in stages where the first stage was 10 microns absolute and the second stage was 5 microns absolute. Now, these stages have been clubbed into a single stage, which involves a standard filtration of 5 microns nominal. As a result, the costs of filtration and service have been reduced.
Danfoss has used ceramic axial piston pumps in various projects. The company achieved power savings of 40 per cent for a plant of capacity 164 cubic metres per day in the Andaman & Nicobar Islands. Similarly, in Visakhapatnam, the company achieved power savings of around 40 per cent for a plant having a capacity of 2,184 cubic metres per day.
Life cycle assessment
LCA is an ISO tool that helps to quantify the environmental impact of a manufacturing process. For desalination, it involves the evaluation of the environmental impact of a desalination plant throughout its life cycle. The LCA considers factors such as energy consumption, water intake, and usage and discharge of chemicals. The assessment helps to compare the carbon footprint of energy alternatives, enabling desalination plant operators and stakeholders to optimise resource efficiency and promote sustainability throughout the life cycle of the plant. The four main stages of the LCA practice are defining scope and goals, life cycle inventory, life cycle impact assessment, and interpretation based on data analysis. IDE Technologies is a pioneer in implementing LCA tools for assessing SWRO plants.
Global sustainable SWRO practices
The global desalination market is implementing a variety of high potential carbon-negative solutions.
Green steam
The usage of green steam from biomass to operate high power pumps with direct connection to a steam turbine is gaining traction globally. It eliminates the need for a generator or a motor. This direct drive approach can reduce the SWRO carbon footprint by 60-70 per cent. Earlier, energy production involved exploitation of fossil fuels to generate steam, which was used to turn the turbines and generate electricity. Green steam, meanwhile, involves connecting the turbine directly to one of the pumps. This eliminates a couple of intermediary steps and improves the efficiency of the process. The direct drive solution also eliminates inherent inefficiencies of generators, motors, variable frequency drives and transmission.
Carbon capture
Carbon capture facilitates the generation of carbon dioxide on site from the by-products of the treatment process such as flue gases. It helps to cut costs by reducing the overall operating expenses and also leads to a reduction in carbon footprint.
Electrochlorination system
Another sustainable method involves the usage of an Electrochlorination system to facilitate the generation of hypochlorite from saline water. It improves sustainability outcomes, reduces cost and ensures improved plant safety by avoiding storage of large quantities of hypochlorite. Thus, on-site generation of chemicals or gases helps to reduce transportation costs in remote areas which account for 70-80 per cent of the cost of chemicals.
Green chemicals
IDE Technologies has incorporated the use of green chemicals and the production of chemicals on-site in various projects. It has helped the company reduce the expenses on chemical procurement.
This sustainable solution can maximise carbon capture potential as well as generate an additional revenue stream.
Adoption of renewable energy
The use of renewable energy in powering a desalination plant reduces its carbon footprint. This can be achieved by on-site power generation through solar panels or wind turbines, or by power purchase agreements with relevant renewable energy operators. For instance, around 70 per cent of the energy required at the Western Galilee SWRO desalination plant is supplied by a renewable energy source. IDE Technologies has also used this solution at its Sorek B project in Israel.
Future potential
Desalination is a costly process but has a wide scope, especially in India. It can be a viable solution for coastal cities that are facing impending water crises. With the help of innovative technologies and sustainable processes, desalination can be used to conserve the environment and reduce costs. As the country explores the adoption of SWRO and ZLD, global best practices and the lessons learnt can help guide it to obtain better and sustainable outcomes. This will improve the affordability of water and solve the problem of inequitable geographical distribution of water.
Based on a presentation by Pravin Abnave, Simulation Specialist, High Pressure Pumps, Danfoss; and Nayan Shah, Director, Sales & Marketing, IDE Technologies India, at a recent India Infrastructure conference
