Various studies have been conducted over the years which have shown that plants have the ability to purify waste water. Dr MVSS Giridhar of Centre for Water Resources at JNTU-Hyderabad says, “There are certain plant species which are efficient in absorbing nitrates and phosphates present in sewage water. Sewage treatment plants are not capable of removing nitrates and phosphates, that later enter water bodies, resulting in worsening of water parameters like Biochemical Oxygen Demand and Dissolved Oxygen.
While human waste is a main reason behind presence of nitrates in urban sewage, usage of detergents and soaps are reason behind presence of phosphates.
A study conducted by JNTU-Hyderbad researchers to test efficacy of two plant species, Canna indica and Colacasia esculenta on treatment of sewage water found that the plants could reduce nitrates, phosphates, total suspended solids, BOD and other contaminants in the sewage water by 50-70 per cent.
Not just nitrates and phosphates but studies in India and abroad have shown that some plants, known as ‘hyperaccumulators’ have the capability to absorb unusually large amounts of heavy metals like lead, arsenic, mercury and cadmium from contaminated water, in comparison to other plants.