The Indian chemical industry is currently caught in a catch-22 situation.
On one side, it is one of the best performing sectors in the nation. It is an engine of growth for the country and remains one of the most diversified industries in the world with over 70,000 chemical products. Between 2006 and 2019, the Indian chemical industry grew at a CAGR of 15% against the global average of 8%. In total, it contributes around 3% of the GDP of the world’s sixth-largest economy.
For all its achievements, the industry also poses a serious challenge to the nation’s water resources due to the amount of water pollution it creates.
According to reports, the number of Grossly Polluting Industries (GPIs) in Inda gas doubled between 2011 to 2019. GPIs are establishments that discharge more than 1,00,000 liters of wastewater and harmful chemicals into the rivers and other freshwater sources.
India’s chemical industry, which includes basic chemicals and their intermediates, petrochemicals, fertilizers, paints, pesticides, bulk drugs, and pharmaceuticals, is one of the most diversified industrial sectors covering more than 70,000 commercial products
The dangers of chemical discharge
Chemical industry wastewater is highly toxic, carcinogenic, and highly reactive. Wastewater from a chemical plant has a complex composition. It contains many non-biodegradable compounds. Additionally, different chemical production plants have different processes. Hence, there is variation in the composition of the wastewater.
Composition of chemical plant wastewater
- High BoD and CoD
- High concentration of salts, dissolved metals
- High toxicity
- Non-biodegradable organic pollutants
Chemical plant wastewater is marked by a high degree of non-biodegradable chemical and metallic components and contains very little to no suspended solids.
Wastewater treatment for the chemical industry
The design of water treatment plants varies according to the components of process water. In some cases, factors such as biodegradability and molecular size of the pollutants in water also affect the setup of the water treatment process.
Key technologies used in wastewater
Activated sludge
The activated sludge mechanism generally consists of an aeration tank and a secondary clarifier. In the aeration tank, there are microorganisms that will digest the biodegradable matter in process water. The tank is aerated with diffuser systems to provide oxygen to the microorganisms.
To balance the process, some microorganisms are settled down in the secondary clarifier. Flocculants are added so that these microbes clump together in particles and settle down as activated sludge. Some of the activated sludge is then recycled back to the aeration basin. With this process, the microorganisms in the raw process water can be increased by up to 30 times. This process helps ensure the biodegradation of material in a confined space.
Activated sludge is an effective but older water treatment technology. Studies in China found that activated sludge reduces the BoD count of the process water, but it cannot deliver compliance in line with strict regulatory norms Local river water had to be used to dilute the treated chemical effluent and bring it within the limits.
Chemical treatment
A combination of biological pretreatment and chemical oxidation is used to reduce the CoD in chemical plant wastewater by around 80%. The residual COD in the effluent of the biological pre-treatment section belongs to refractory chemicals which cannot be removed by the normal biological process. The biodegradability of such chemicals is boosted using chemicals. In addition, methods such as chemical oxidation and BCB treatment are also used.