Remove pharmaceutical residues from water
Pharmaceutical residues are increasingly important contaminants for wastewater treatment operators, pharmaceutical manufacturers, water utilities and environmental engineers.
Compounds such as diclofenac, carbamazepine, ibuprofen, antibiotics and other medicinal substances can enter wastewater systems and remain detectable after conventional biological treatment.
Although these substances are often present at very low concentrations, some are biologically active and may raise environmental concerns when discharged into rivers and other receiving waters.
Conventional wastewater treatment processes can remove certain pharmaceutical compounds effectively. However, other substances are relatively resistant to biological degradation.
Advanced ozonation is one of the available technologies for reducing selected pharmaceutical micropollutants in water.
The effectiveness of this treatment depends on the molecular structure of each compound, wastewater quality, ozone demand and the presence of competing contaminants.
For UK industrial and municipal wastewater operators, the objective is to determine whether ozone can provide measurable additional treatment while maintaining acceptable operating costs and controlling oxidation by-products.
Why are pharmaceutical residues found in water?
Pharmaceutical compounds can enter the water environment through several pathways.
Following the administration of medicines, some active substances or their metabolites are excreted and enter wastewater collection systems.
Additional contamination can originate from healthcare facilities, pharmaceutical manufacturing, research laboratories and the disposal of unused medicines.
The main sources include:
- Municipal wastewater containing residues from household medicine use.
- Hospital and healthcare facility wastewater.
- Pharmaceutical manufacturing and formulation effluents.
- Laboratory and research facility discharges.
- Wastewater containing veterinary medicinal residues.
- Surface water receiving treated wastewater discharges.
Concentrations vary depending on the origin of the wastewater, the compounds involved and the treatment processes already installed.
Some pharmaceuticals are readily biodegradable. Others can remain detectable after conventional treatment.
The presence of pharmaceutical residues does not automatically mean that drinking water is unsafe.
In the UK, drinking-water suppliers assess risks associated with source water and implement treatment and monitoring programmes under the applicable regulatory framework.
The principal engineering challenge addressed here is reducing selected pharmaceutical contaminants before treated wastewater is discharged or reused.
Which pharmaceutical compounds can be treated with ozone?
Pharmaceutical compounds differ considerably in their chemical properties and their susceptibility to oxidation.
Some react rapidly with molecular ozone, while others are less reactive and may require advanced oxidation processes or alternative technologies.
Diclofenac: a widely studied anti-inflammatory compound
Diclofenac is a non-steroidal anti-inflammatory drug frequently investigated as a pharmaceutical micropollutant.
Its molecular structure contains functional groups that react readily with ozone.
Consequently, ozonation can substantially reduce the concentration of the original diclofenac molecule under appropriate operating conditions.
However, oxidation can generate transformation products that must be considered when assessing environmental performance.
A reduction in diclofenac concentration should not be interpreted as complete mineralisation.
Carbamazepine: a persistent pharmaceutical compound
Carbamazepine is used in the treatment of epilepsy and certain neurological conditions.
It is frequently studied because of its relatively poor removal in conventional biological wastewater treatment systems.
Carbamazepine reacts rapidly with molecular ozone and is commonly used as an indicator compound in advanced wastewater treatment studies.
Ozonation can effectively transform the original molecule, although transformation products may remain detectable after treatment.
Additional monitoring or downstream treatment may therefore be appropriate.
Sulfamethoxazole: an antibiotic micropollutant
Sulfamethoxazole is an antibiotic frequently investigated in pharmaceutical wastewater treatment studies.
It can react relatively rapidly with ozone, making ozonation a potentially effective treatment approach.
Actual removal performance depends on wastewater composition and operating conditions.
When antibiotic resistance is also a concern, the chemical removal of antibiotics and the reduction of antibiotic-resistant bacteria or resistance genes must be evaluated separately.
Ibuprofen: different oxidation characteristics
Ibuprofen is another widely used pharmaceutical compound.
Unlike diclofenac and carbamazepine, it reacts relatively slowly with molecular ozone under typical water treatment conditions.
Its degradation may depend more strongly on reactions involving hydroxyl radicals.
Consequently, conventional ozonation may not achieve the same performance for ibuprofen as for more ozone-reactive pharmaceutical compounds.
Advanced oxidation processes or alternative treatment technologies may therefore need to be considered.
Other pharmaceutical compounds
Other substances that may be relevant to wastewater treatment investigations include:
- Naproxen.
- Clarithromycin.
- Trimethoprim.
- Metoprolol.
- Atenolol.
- Venlafaxine.
- Erythromycin.
- Selected hormones and endocrine-active pharmaceuticals.
The removal efficiency of each substance must be assessed individually.
Why do pharmaceutical residues remain after biological wastewater treatment?
Most municipal and industrial wastewater treatment plants were originally designed to remove biodegradable organic matter, suspended solids and specific nutrients.
Typical treatment processes include:
- Activated sludge.
- Sequencing batch reactors.
- Membrane bioreactors.
- Biological filtration.
- Sedimentation.
- Physical and chemical separation.
These technologies can achieve substantial treatment of conventional wastewater pollutants.
However, certain pharmaceutical compounds have molecular structures that resist biological degradation.
A wastewater treatment plant may therefore achieve satisfactory BOD and COD performance while continuing to discharge trace concentrations of pharmaceuticals.
A low final effluent COD value does not demonstrate the complete absence of pharmaceutical residues.
Targeted analytical testing is required to determine which substances remain in the treated water.
For related applications, see our article on ozone removal of pollutants from wastewater.
How does ozone remove pharmaceutical residues from water?
Ozone (O₃) is a powerful oxidising agent generated on site using specialised equipment.
It is introduced into water through an injection and gas–liquid contact system.
Two principal mechanisms contribute to pharmaceutical oxidation.
Direct oxidation by molecular ozone
Molecular ozone reacts selectively with certain chemical functional groups.
Compounds containing reactive double bonds, electron-rich aromatic structures or specific nitrogen- and sulphur-containing functional groups may react rapidly with ozone.
Diclofenac, carbamazepine and sulfamethoxazole are examples of pharmaceuticals that can exhibit relatively high reactivity towards molecular ozone.
These reactions change the structure of the original molecules.
Indirect oxidation by hydroxyl radicals
Ozone decomposition in water can generate hydroxyl radicals (•OH).
These highly reactive species can oxidise a broader range of organic compounds.
Hydroxyl radical oxidation is particularly relevant when the target pharmaceutical reacts slowly with molecular ozone.
Treatment performance depends on pH, dissolved organic carbon, alkalinity and other substances that compete for oxidants.
Advanced oxidation processes can be considered where conventional ozonation does not provide sufficient performance.
Further information is available in our article on ozone and associated oxidation processes in water treatment.
Does ozonation completely eliminate pharmaceutical contaminants?
Not necessarily.
It is important to distinguish between four different outcomes:
- Removal of the original pharmaceutical molecule.
- Formation of oxidation transformation products.
- Reduction in the biological activity or toxicity of the treated water.
- Complete mineralisation of the organic substance.
A pharmaceutical compound may become undetectable in a targeted analysis while other oxidation products remain present.
Some products may be biodegradable, while others may require further investigation.
For this reason, pharmaceutical removal cannot be demonstrated solely through COD, oxidation-reduction potential or residual ozone measurements.
An appropriate analytical programme should examine the target substances and, where relevant, their transformation products and environmental effects.
Which treatment configuration is most appropriate?
Several treatment arrangements may be considered depending on the wastewater characteristics and treatment objectives.
Biological treatment followed by ozonation
Process: biological treatment → ozone contact reactor → treated effluent
This configuration may be suitable when the objective is to reduce specific pharmaceutical residues remaining after conventional wastewater treatment.
Direct discharge after ozonation must be assessed against the required water quality, transformation products and applicable discharge conditions.
Biological treatment followed by ozone and biofiltration
Process: biological treatment → ozonation → biological filtration → final effluent
Ozonation can transform certain organic molecules into compounds that are more readily biodegradable.
A downstream biological stage may then remove part of the biodegradable organic matter formed.
This configuration can improve overall treatment performance when properly designed and validated.
Ozonation followed by activated carbon
Process: biological treatment → ozonation → activated carbon → final effluent
Granular activated carbon can provide additional adsorption of selected contaminants and transformation products.
Biological activity within an activated carbon filter may also contribute to the removal of biodegradable organic substances.
Performance depends on the contaminants, competing dissolved organic matter and operating conditions.
Ozone combined with hydrogen peroxide
The O₃/H₂O₂ process can increase hydroxyl radical formation.
This approach may be relevant for compounds with limited direct reactivity towards molecular ozone.
However, peroxide consumption, radical scavenging, operating costs and by-product formation must be considered.
An advanced oxidation process should be selected on the basis of comparative testing rather than assumed to outperform conventional ozonation.
Can pharmaceutical residues be removed from drinking water?
Advanced water treatment technologies, including ozonation and activated carbon, can reduce selected organic micropollutants in source water.
However, drinking-water treatment has different regulatory and operational requirements from industrial wastewater treatment.
In the UK, water suppliers monitor drinking-water quality and assess potential risks associated with contaminants.
The Drinking Water Inspectorate has reported that the very low concentrations of pharmaceuticals generally identified in drinking water do not represent an appreciable risk to human health.
The detection of trace pharmaceutical substances must therefore not be interpreted automatically as a drinking-water safety problem.
Any proposed ozone process must be evaluated in the context of existing treatment barriers, drinking-water standards and the potential formation of oxidation by-products.
Further information is available in our article on ozone treatment of drinking water.
Which UK facilities may benefit from pharmaceutical micropollutant treatment?
Municipal wastewater treatment works
Municipal wastewater treatment works receive mixtures of pharmaceutical residues from domestic, commercial and healthcare sources.
Tertiary ozonation can be investigated where selected pharmaceutical compounds remain after biological treatment.
Hospitals and healthcare facilities
Hospital wastewater may contain pharmaceutical residues, disinfectants and other contaminants.
The feasibility of treatment depends on whether a dedicated wastewater stream or the entire facility discharge is being considered.
Targeted treatment of specific waste streams may sometimes be preferable to treating the total wastewater volume.
Pharmaceutical manufacturing plants
Pharmaceutical manufacturing and formulation activities may produce wastewater containing active ingredients and chemical intermediates.
These effluents can have substantially higher contaminant concentrations than municipal wastewater.
Source segregation, equalisation and pre-treatment should be evaluated before considering an ozone treatment stage.
Industrial wastewater treatment plants
Industrial effluent treatment plants may receive wastewater containing pharmaceutical substances or other persistent organic compounds.
Where biological treatment is insufficient, tertiary ozonation may provide additional removal of selected micropollutants.
Water reuse projects
Advanced treatment may also be relevant to projects involving the reuse of treated industrial or municipal wastewater.
The proposed process must be designed around the intended reuse application and the applicable chemical and microbiological requirements.
Explore our article about industrial water reuse using ozone.
What information is required to design an ozone treatment system?
Before selecting equipment, the wastewater should be characterised and the treatment objectives clearly defined.
Important parameters include:
- Average and peak flow rate in m³/h.
- Existing wastewater treatment processes.
- COD and BOD5.
- Dissolved organic carbon (DOC).
- Total organic carbon (TOC).
- Suspended solids and turbidity.
- pH and temperature.
- Nitrite and bromide concentrations.
- Identified pharmaceutical compounds and their concentrations.
- Required removal performance.
- Applicable discharge conditions.
- Available installation space and utilities.
Pharmaceutical concentrations are often measured using specialised analytical methods such as liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS).
Depending on the application, transformation products and ecotoxicological indicators may also need to be examined.
How is an ozone generator sized for pharmaceutical removal?
An initial mass balance can be calculated using:
Applied ozone (g/h) = water flow (m³/h) × applied ozone dose (mg/L)
This calculation provides the theoretical mass of ozone applied to the water.
It does not establish the dose required to remove any particular pharmaceutical.
Example of tertiary treatment at 30 m³/h
Consider an industrial wastewater treatment plant with the following hypothetical conditions:
| Parameter | Illustrative value |
|---|---|
| Treated wastewater flow | 30 m³/h |
| Applied trial ozone dose | 6 mg/L |
| Theoretical applied ozone | 180 g/h |
| Treatment objective | Reduction of selected pharmaceuticals |
The calculation is:
30 × 6 = 180 g O₃/h
This is an illustrative mass-balance calculation, not a recommended treatment dose.
Actual ozone demand depends on wastewater composition and the pharmaceutical compounds involved.
The final generator capacity must account for gas–liquid transfer efficiency, contact time, peak flow rates, residual ozone management and process control.
Ozone demand should ideally be investigated through laboratory or pilot testing on representative wastewater.
Which factors influence pharmaceutical removal efficiency?
Dissolved organic matter
Dissolved organic matter competes with pharmaceutical compounds for ozone and hydroxyl radicals.
This competition can increase ozone consumption and reduce treatment efficiency.
Nitrite concentration
Nitrite reacts readily with ozone.
Elevated nitrite concentrations may therefore increase the ozone demand of tertiary wastewater treatment.
pH and alkalinity
The pH influences ozone decomposition and the relative contribution of direct and radical-based oxidation reactions.
Alkalinity and other dissolved constituents can influence hydroxyl radical availability.
Bromide and oxidation by-products
When bromide is present, the formation of bromate must be evaluated.
Depending on the wastewater composition, other oxidation by-products may also require investigation.
Ozone transfer and contact time
Treatment performance depends on effective transfer of ozone from the gas phase into the water.
The ozone generator, injection system, contact reactor and process controls must therefore be considered together.
Why are laboratory and pilot trials recommended?
Pharmaceutical removal performance should be demonstrated using representative wastewater rather than relying exclusively on published removal data.
A structured trial can establish:
- Initial pharmaceutical concentrations.
- Actual ozone demand.
- Pollutant removal at different ozone doses.
- Changes in COD, DOC and UV254 absorbance.
- Formation of relevant oxidation by-products.
- Performance of downstream polishing systems.
- Ozone consumption and energy requirements.
- Preliminary operating costs.
Where pharmaceutical concentrations are particularly low, laboratory detection limits must be appropriate for the required treatment objectives.
Pilot testing also helps establish whether ozone should be used alone or combined with activated carbon, biological filtration or another treatment process.
What are the limitations of ozone treatment?
Although ozone can effectively transform certain pharmaceutical compounds, it should not be considered a universal treatment solution.
Important limitations include:
- Different oxidation reaction rates between pharmaceutical compounds.
- Possible formation of transformation products.
- Incomplete mineralisation of some contaminants.
- Competition from dissolved organic substances.
- Potential formation of bromate or other by-products.
- Additional treatment requirements in certain applications.
- Energy consumption and maintenance costs.
- Workplace safety requirements associated with ozone gas.
Industrial ozone systems require appropriate ambient ozone detection, ventilation, off-gas destruction and safe operating procedures.
A suitable risk assessment should also address applicable UK workplace health and safety requirements, including COSHH where relevant.
UK environmental and regulatory considerations
Pharmaceutical wastewater treatment must be assessed within the regulatory framework applicable to the facility.
In England, relevant wastewater discharges may be regulated through environmental permits issued by the Environment Agency.
Trade effluent discharged into a public sewer generally requires consent or other authorisation from the relevant sewerage undertaker.
Different regulatory arrangements apply in Scotland, Wales and Northern Ireland.
The installation of an ozone treatment stage does not automatically establish compliance.
Operators must demonstrate that the process meets their applicable discharge conditions and does not create unacceptable environmental risks.
Drinking-water applications must also comply with the relevant drinking-water quality regulations and treatment requirements.
OXYTRADING UK: engineering-led ozone treatment solutions
OXYTRADING UK supports industrial wastewater operators, pharmaceutical manufacturers, water treatment specialists and engineering consultancies investigating the removal of pharmaceutical micropollutants.
Our approach focuses on technical feasibility, process engineering and practical integration.
Depending on the project, our services can include:
- Preliminary technical assessment.
- Review of wastewater analysis.
- Identification of target micropollutants.
- Laboratory and pilot-scale testing.
- Ozone generator selection and sizing.
- Oxygen supply and ozone injection systems.
- Gas–liquid contact reactor design.
- Instrumentation and process control.
- Off-gas destruction and safety systems.
- Installation and commissioning support.
- Operator training and maintenance.
The objective is to determine whether ozonation can deliver measurable treatment improvements before recommending a full-scale installation.
Request a technical assessment of your wastewater
Are you managing wastewater containing diclofenac, carbamazepine, antibiotics or other pharmaceutical residues?
Do you need to improve treatment performance after an existing biological wastewater treatment process?
OXYTRADING UK can help assess whether tertiary ozonation is suitable for your treatment objectives.
For an initial review, please provide:
- The wastewater source.
- Average and maximum flow rates.
- Available analytical results.
- Pharmaceutical substances of concern.
- Existing treatment equipment.
- Required discharge or reuse objectives.
These details will help establish whether a laboratory assessment, pilot trial or further engineering study is appropriate.
Contact OXYTRADING UK to discuss pharmaceutical residue treatment →