Removing Diazepam from global recycled water and wastewater in bulk at low cost

A low-cost and efficient one-step method to remove the anxiety drug Diazepam from recycled water and wastewater using titanium dioxide nanofibres has been developed by researchers headed by the University of Johannesburg’s Professor Vinod Kumar Gupta, located in Johannesburg, South Africa. Used worldwide for anxiety disorders, as anticonvulsants and anti-epileptics, and for terminally ill people as part of essential medicines list from the World Health Organisation (WHO), Diazepam is a member of the benzodiapezine drug group.

Prescription drugs like Diazepam tend to slip through traditional wastewater treatment plants as they are not designed to remove the thousands of different pharmaceuticals in use globally. As drug use increases, legal and illegal pharmaceuticals enter the environment through treated sewage and wastewater discharged from drug manufacturing.

“Existing processes that can remove Diazepam and other drugs at large scale from wastewater are expensive, time consuming, inefficient, or all three. Some also consume a lot of energy in multiple steps, or use toxic and hazardous compounds unfriendly to the environment,” Professor Gupta, from the Department of Applied Chemistry at the university, said. “Also, Diazepam is not easy to remove from wastewater using traditional methods. It is partially soluble and has a small particle size. For efficient, targeted removal, advanced hybrid nanomaterials are needed.”


Used everywhere

In 2017 a team headed by a researcher from New York State University, New York, United States (U.S.) announced a new method to simultaneously test for 89 legal neuropsychiatric pharmaceuticals and illicit drugs in unfiltered wastewater and freshwater. Diazepam and several other benzodiapezines are included in the list.

Also, in 2017, a review of seven psychoactive drugs, and to what extent they show up in the aquatic environment, was published by Rio de Janeiro State University (UERJ), Rio de Janeiro, Brazil. The review analysed research about Diazepam and five other benzodiapezines.

The researchers found that the presence and concentration of psychoactive drugs such as Diazepam was roughly the same in treated wastewater and untreated wastewater. They found that lower-income countries are worse affected. Moreover, in surface water, psychoactive drugs tested for were “mostly within the range that caused measurable toxic effects in ecotoxicity assays.”


The big thirst

As the world rapidly urbanises, city populations grow significantly in short timescales. In some regions this means that fresh water resources become more constrained. In South Africa, Cape Town residents dread its imminent “Day Zero”, the day the authorities will have to turn off the taps because there will be too little water left in the city’s dams and reservoirs.

As a city’s options for fresh water become more limited, re-using waste water, even for drinking purposes, becomes a more important option. However, for a city in a developing country, removing pharmaceuticals from waste water needs to happen in an efficient, cost-effective and speedy way. The treated water can then be added back in low volumes to the city’s water supply, as is done already in Orange County in California, Singapore and Perth.


Faster, low cost wastewater treatment

“Implementing this water treatment in municipal wastewater treatment plants should be relatively quick and simple,” Professor Gupta added.

Titanium dioxide nanofibres remove Diazepam and related drugs in a targeted way, during the photocatalytic decomposition process. The fibres can be used as filters in municipal or industrial treatment plants, he stated.

The filter and screen will be made up of hybrid nanomaterials which are highly efficient in the removal of noxious pharmaceutical and other inorganic and organic impurities from municipal and industrial wastewater, co-author Dr Ali Fakhri from the Department of Chemistry at Islamic Azad University, Tehran, Iran, said.

“We use a modified hydrothermal manufacturing method, which produces a dense chain network of hollow fibres. The fibres are cross-linked and stable, so there is low risk for fibres to be emitted in the purified wastewater,” Dr Fakhri added.

The nanofibres can be used to remove industrial dyes and other organic pollutants as well. However they need to optimise some important parameters on the fibre structure first, he continued.

“The process to make the fibres is also simple and cost-effective. We are planning a pilot plant at the University of Johannesburg to manufacture these nanofibres. Every aspect of the pilot plant is planned to minimise nanofibre pollution to the environment,” Professor Gupta concluded.  “Later the pilot plant will be followed by a demonstration wastewater treatment plant, to show how nanotechnology can remove a range of pharmaceutical impurities efficiently, rapidly, and at low cost.”