Advances in Wastewater Treatment: Energy Efficiency, Micropollutants, and Circular Resource Recovery

Abstract

Wastewater treatment is progressing from conventional removal of organic load toward integrated multi-barrier systems that also address nutrients, pathogens and persistent trace contaminants.

This review compares established and emerging treatment approaches, including activated sludge, biological nutrient removal, advanced oxidation processes, membrane technologies and hybrid treatment trains. The comparison considers treatment function, operational complexity, energy demand, integration requirements and potential contribution to water reuse and resource recovery.

Persistent contaminants—including pharmaceuticals, endocrine-disrupting compounds and per- and polyfluoroalkyl substances—may require tertiary or quaternary treatment beyond conventional biological processing. The appropriate barrier depends strongly on contaminant chemistry and matrix composition. Oxidation processes may be effective for some organic micropollutants, whereas highly persistent species such as many PFAS often require targeted separation, concentration or specialized destruction strategies. Technologies discussed include ozonation and other oxidation processes, hydrodynamic cavitation, photocatalysis, membrane-based separations, cold plasma, microbial electrochemical concepts and controlled-release oxidants.

The review frames advanced wastewater-treatment plants as systems that may combine pollution control with water reuse, energy recovery and recovery of nutrients or other resources where technically and economically justified. Its central recommendation is coordinated treatment-train integration rather than selection of isolated technologies solely from laboratory-scale removal percentages.

Treatment-system framework

Core biological and physicochemical treatment

Conventional treatment remains responsible for hydraulic management, solids separation, organic-load removal and, where configured, biological nitrogen and phosphorus removal. Its performance defines the matrix entering any downstream polishing stage.

Micropollutant and pathogen barriers

Advanced oxidation, adsorption, membrane separation and disinfection can provide complementary barriers for compounds or organisms that are insufficiently controlled by conventional treatment. Selection depends on contaminant properties, water-matrix effects, by-product formation, residual-stream management and the intended discharge or reuse standard. Removal from the aqueous phase must be distinguished from chemical destruction or mineralization.

Energy and resource recovery

Anaerobic digestion, biogas utilization, nutrient precipitation, water reuse and other recovery routes can improve resource utilization where the recovered stream meets a defined specification and has a credible outlet. Recovery potential must be evaluated together with product quality, contaminants, internal energy demand, chemical use, residual handling, storage, transport and market or reuse requirements.

Monitoring and digital optimization

Sensors, process analytics, predictive control and digital models can support treatment stability and energy optimization. Their usefulness depends on measurement quality, representative training or calibration data where relevant, model verification and validation, data governance, operator integration, fail-safe operation and clear decision or control objectives.

Engineering selection principles

• define influent variability, target contaminants, discharge or reuse requirements and treatment reliability before selecting technologies;
• evaluate the complete treatment train rather than isolated removal results from idealized laboratory water;
• include energy and chemical demand, membrane or catalyst replacement, fouling and cleaning, sludge and concentrate management, residual disposal or recovery, and operator workload;
• assess transformation products, disinfection by-products and toxicity rather than relying only on disappearance of the parent contaminant;
• distinguish contaminant destruction from transfer into another phase or residual stream;
• verify hydraulic, reaction, mass-transfer and separation limits at representative scale;
• connect resource recovery to a defined product specification, contaminant limit, quality-assurance method and outlet or reuse pathway.

Treatment-function interpretation

Treatment, polishing, reuse preparation and resource recovery are different engineering functions. A unit operation that reduces a contaminant concentration may not destroy the contaminant, and a process that transfers material into sludge, concentrate, spent adsorbent or another residual stream still requires management of that residual.

Water reuse requires performance to be assessed against the intended use and its relevant chemical, microbiological and operational quality criteria. Resource recovery likewise requires a defined recovered product, quality specification, contaminant limits and destination; recovery yield alone is not sufficient evidence of a useful circular pathway.

Scope and evidence boundary

The paper is a narrative synthesis rather than a formally registered systematic review or meta-analysis. Technology comparisons are therefore suitable for orientation and framework development, not for deriving universal performance rankings.

Removal efficiency, destruction efficiency, energy demand and cost depend on wastewater composition, contaminant concentration, dissolved organic matter, alkalinity, suspended solids, temperature, hydraulic loading, reactor design, dose, residence time, mass-transfer conditions and downstream separation. Values from one matrix or operating regime should not be transferred to another without an explicit applicability assessment.

Laboratory activity does not establish full-scale feasibility. Implementation requires representative-water testing, closed mass and energy balances, by-product and toxicity assessment, residual-stream management, process safety, operability analysis, reliability and maintenance assessment, and representative pilot-scale validation. Software calculations and short-duration tests support development decisions but do not substitute for system-specific validation.

The paper discusses regulatory developments available during its preparation in March 2026. Current legal requirements, standards, discharge permits and water-reuse criteria must be verified for the relevant jurisdiction and project date.

Relation to the AOP kinetic–process framework

This review provides the broader treatment-train and resource-recovery context. The companion AOP kinetic–process framework addresses a narrower modelling problem: screening how kinetics, water-matrix effects and process conditions influence oxidative-treatment performance.

The two resources therefore operate at different levels. A kinetic or energy-normalized AOP screening result does not by itself establish treatment-train suitability, reuse compliance, residual management, toxicity control, process safety or full-scale economics.

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Licence and reuse

The deposited paper is available under the Creative Commons Attribution 4.0 International licence .

The licence permits sharing and adaptation, including commercial reuse, provided appropriate attribution is given, a link to the licence is supplied and any changes are indicated.

Recommended citation

Saylam, A. (2026). Advances in Wastewater Treatment: Energy Efficiency, Micropollutants, and Circular Resource Recovery. Zenodo. https://doi.org/10.5281/zenodo.19438613

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