Process Engineer, Ben Hazard, of Te-Tech Process Solutions, discusses the results of pilot plant trials looking at the removal of an anti-inflammatory, an anticonvulsant and an antibiotic using an advanced oxidation process.

Trace levels of anthropogenic micropollutants in water are a growing concern, and active pharmaceutical ingredients (APIs), excreted by users of medications, are a major contributor since most are not easily removed in conventional wastewater treatment processes; indeed some can actually threaten the activated sludge bacteria on which treatment relies. A recent study1 concluded that 13% of UK wastewater treatment works were releasing APIs including Ibuprofen, diclofenac, ethinyloestradiol, clarithromycin and azithromycin at concentrations which would exceed their predicted no effect concentrations (PNEC) in receiving waters.

The Water Industry National Environment Plan (WINEP) favours catchment and nature-based solutions to prevent pollution of watercourses, but APIs are so widely used – antibiotics, anti-inflammatories, contraceptives, anticonvulsants and so on – that, unless there is a huge change in our lifestyles, we will continue to rely on technology-based solutions at wastewater treatment facilities. The most effective technologies for the destruction of these recalcitrant organic molecules are advanced oxidation processes, which use various reactive oxygen species including peroxide, ozone and free hydroxyl radicals. These species have very high oxidation potentials and can oxidise most organic compounds via proton transfer.

Advanced Oxidation

Austrian environmental engineers SFC Umwelttechnik have developed technology using non-thermal plasma generated by passing atmospheric air through an electrical glow discharge, which produces a range of reactive oxygen species including peroxide, ozone and free hydroxyl radicals. The plasma containing the reactive oxygen species is introduced into the wastewater either by a submerged turbine or via a diffuser system. Working with the Department of Environmental, Process, and Energy Engineering at MCI, Innsbruck, SFC investigated the effect of using the technology to remove three APIs from treated wastewater at the Bad Reichenhall municipal wastewater treatment works in Innsbruck. The three APIs were: Diclofenac, an anti-inflammatory, Carbamazepine, an anticonvulsant and antibiotic, Sulfamethoxazole.

The pilot plant at Bad Reichenhall consisted of a feed tank to collect final effluent from the works and pump it to a te-mem submerged hollow fibre ultrafiltration module, a permeate collection tank and a te-ion non thermal plasma unit injecting the plasma into a continuous stirred tank reactor (CSTR). The pilot plant was operated under a range of conditions varying the volumetric ratio of plasma air flow to water, hydraulic retention time in the CSTR and the plasma generation electrical frequency. Each experimental run was carried out twice; with and without pre-treatment by ultrafiltration, in order to eliminate the effect of particulate suspended solids and any macromolecules that might interfere with the oxidation process. The three target APIs all have molecular weights in the range 250 – 300 Da so would not be removed by ultrafiltration unless bound to the larger particulate matter.

Significant Results

The results2 showed that, with a residence time in the CSTR of 30 minutes and a plasma air:water volume ratio of 10 it was possible to achieve 90% removal of the three target APIs, well below the PNEC in the receiving watercourse. The power consumption for the te-ion plasma generator was typically around 0.5 kWh/m3. This makes te-ion an attractive option for the destruction of anthropogenic micropollutants including APIs and industrial chemicals. With electricity produced by sludge digestion or other renewables, it is a sustainable solution. The te-ion™ and te-mem™ technologies are available in the UK from Te Tech Process Solutions, a partner of SFC.

1 Comber S et al Active pharmaceutical ingredients entering the aquatic environment from wastewater treatment works: A cause for concern?, Sci Total Environ, 613–614 (2018) 538-547

2 Back J O et al Combining ultrafiltration and non-thermal plasma for low energy degradation of pharmaceuticals from conventionally treated wastewater Jour Env Chem Eng 6 (2018) 7377-7385