Water treatment: The key to water conservation
Have you ever wondered why Earth is called the blue planet? It’s because water covers about 70% of its surface. Considering this amount of water available, it seems obvious that it is abundant. However, 97% of the Earth’s water is saline consisting of 1,335 million km3, and 2% is frozen freshwater locked up in glaciers, polar ice caps, soil etc. and is unavailable for use. As a result, there is only 2,04,000 km3 of freshwater available for consumption, which is about 0.5 to 1% of the total freshwater available. Water is mainly used for agriculture, industry, and domestic purposes.
IGlobally, freshwater withdrawals in 2017 totalled 3,880 km3, of which India drew 647 km3. It is estimated that industrial activities require between 2 and 20% of the total amount of water. According to one of the references, India uses 14 km3 of water for industrial purposes, 48 km3 for domestic, and 586 km3 for agricultural purposes. The demand for water in agriculture exceeds 80% of total consumption; therefore, it is crucial to increase water efficiency. As agriculture runoff is a non-point source, its treatment and reuse are difficult. Sewage can be reused, and it can become one of the sources of water. However, in our country, only 1/3rd of sewage is treated. The discharge of untreated wastewater pollutes natural water bodies. Due to the growing demand and limited availability of water, India, China, and a few European and African countries are expected to experience water scarcity by 2025.
In case of scarcity, water supply to industries would be restricted. Considering the rising water demand in India, an additional 7 km3 of water could be made available even if 50% of wastewater is recycled by industries. This volume is equivalent to more than five years of water requirement of New Delhi.
Lack of uniform distribution of water resources across the globe, erratic climate changes, and poor water conservation and management strategies are major causes of water scarcity. It is expected that water scarcity can be physical, where there is not enough water available to meet the demand, or economic, where there is enough water available but not the proper means to produce desirable water quality. Hence, industries must achieve and sustain wastewater recycling to the maximum extent possible. Ideally, Zero Liquid Discharge (ZLD) of all liquid streams should be targeted. There are many factors affecting the effluent treatment process, such as changing effluent quality and quantity, different combinations of constituents from various manufacturing processes, and uncertainty about the effectiveness of conventional treatments.
The ongoing technological advancements and augmentation in manufacturing processes are changing the composition of wastewater. Thus, efficient industrial wastewater treatment plays a critical role in water quality management. It is possible to treat a wide range of effluents by integrating conventional and new technologies. For example, conventional treatment can reduce organic constituents and inorganic solids from coke oven wastewater, whereas novel adsorbents can reduce source-specific constituents. Thus, such hybrid treatment would help to recycle tough-to-treat wastewaters.
ZLD is considered an emerging alternative to reduce the water demand of the industry. As the name indicates, ‘Zero Liquid Discharge’ eliminates all liquid waste from the system. In ZLD, wastewater is treated, reused, and the residues are concentrated and disposed of in solid form. Bioprocesses and membrane filtration-based solutions are adopted for the treatment of industrial wastewater. Thermal technologies like multi effect evaporator (MEE) and mechanical vapour recompression (MVR) are used to concentrate inorganic constituents. This helps the industries to maximise water recovery.
There are a multitude of measures that citizens, industries, and authorities can adopt to bring about a notable change in the water conservation scenario. The first step, however, is to acknowledge that water is a valuable resource and implement water reuse on an organisational as well as individual level. Every drop counts!
– Nandan Prabhune and Sayali Jadhav, Water and Waste Solutions
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