Engineering Guide
Quaternary Treatment Upgrade for EU Directive 2045 Compliance: The Complete Engineering Guide
A practical guide to designing the quaternary treatment upgrades that EU urban wastewater treatment plants must deliver between 2033 and 2045 under Directive (EU) 2024/3019, with technology comparison, cost ranges, and a compliance timeline grounded in the legal text and the JRC cost study.
What Quaternary Treatment Means for Wastewater Engineers
Quaternary treatment is the additional stage of urban wastewater treatment that removes a broad spectrum of organic micropollutants — pharmaceutical residues, cosmetic ingredients, and other persistent organic chemicals that pass through conventional primary, secondary, and tertiary stages. Under Directive (EU) 2024/3019, quaternary treatment is defined as “treatment of urban wastewater by a process which reduces a broad spectrum of micropollutants in urban wastewater.”[1]
For wastewater engineers in the European Union, quaternary treatment is no longer an emerging requirement. It is a binding obligation on a defined compliance trajectory. By 31 December 2045, all urban wastewater treatment plants serving a load of 150 000 population equivalent (p.e.) or above must apply quaternary treatment, with interim milestones in 2033 and 2039. Additional treatment plants serving agglomerations of 10 000 p.e. and above must also apply quaternary treatment where they discharge into areas identified as sensitive to micropollutant pollution.[1][3]
Key Insight: The Directive imposes the quaternary treatment requirement on the basis of the precautionary principle, combined with a risk-based approach. Even at low concentrations of micrograms per litre or below, certain micropollutants are hazardous for public health and the environment.[1] The Directive treats the cost of quaternary treatment as a polluter-pays obligation: producers of pharmaceuticals and cosmetics that generate the micropollutants must cover at least 80% of the treatment cost through extended producer responsibility (EPR) schemes.[1]
The practical implication for engineering and consulting firms: a quaternary treatment upgrade is not a future research topic. It is the dominant capital project on the European wastewater roadmap for the next two decades, with a defined deadline, defined technologies named in the Directive, and a defined risk-assessment methodology that determines which 10 000–150 000 p.e. plants must also comply.
The Regulatory Framework Engineers Are Designing Against
The legal basis for quaternary treatment is Directive (EU) 2024/3019 of the European Parliament and of the Council of 27 November 2024 concerning urban wastewater treatment (recast), published in the Official Journal on 12 December 2024 and entered into force on 1 January 2025.[1] Member States must transpose the substantive provisions into national law by 31 July 2027.[3] The legal framework engineers must work within sits across three reinforcing layers: scope, compliance deadlines, and producer responsibility.
Scope: which plants and which substances
Article 8 of the Directive establishes two scope triggers for quaternary treatment. The first is plant size: every urban wastewater treatment plant treating a load of 150 000 p.e. or above is required to apply quaternary treatment.[1] The second is risk-based: agglomerations of 10 000 p.e. and above that discharge into areas where the concentration or accumulation of micropollutants represents a risk for the environment or human health are also covered. Such areas include catchments used for the abstraction of drinking water, bathing waters, areas of aquaculture activity, lakes, rivers with a dilution ratio below 10, Natura 2000 sites, and coastal, transitional, and marine waters where a risk assessment confirms the need.[1]
Compliance is measured by removal performance. Annex I, Table 3 of the Directive requires a minimum 80% removal of indicator micropollutants, calculated as the average of the specific percentages of removal of substances drawn from two categories: Category 1 (substances that can be very easily treated, including amisulpride, carbamazepine, citalopram, clarithromycin, diclofenac, hydrochlorothiazide, metoprolol, and venlafaxine) and Category 2 (substances that can be easily disposed of, including benzotriazole, candesartan, irbesartan, and a 4/5-methylbenzotriazole mixture).[1]
Compliance deadlines: the 2033–2045 trajectory
The Directive establishes a progressive compliance trajectory with binding interim milestones, not a single 2045 deadline. For plants treating 150 000 p.e. and above, the schedule is:
- 31 December 2033: 20% of these treatment plants must apply quaternary treatment
- 31 December 2039: 60% of these treatment plants must apply quaternary treatment
- 31 December 2045: all of these treatment plants must apply quaternary treatment[1]
For agglomerations of 10 000 p.e. and above that discharge into listed sensitive areas, the trajectory is more granular: 10% by 31 December 2033, 30% by 31 December 2036, 60% by 31 December 2039, and 100% by 31 December 2045.[1] Member States must establish the list of sensitive areas by 31 December 2030 and review it every six years thereafter.[1]
Extended Producer Responsibility (Article 9)
To cover the additional costs imposed by quaternary treatment, Article 9 of the Directive requires Member States to put in place an Extended Producer Responsibility (EPR) system by 31 December 2028. Producers placing on the EU market the products listed in Annex III — currently medicinal products for human use and cosmetic products — must cover at least 80% of the full costs of quaternary treatment, including investment and operational costs and the monitoring of micropollutants.[1]
Exemptions apply where a producer places less than one tonne per year of the relevant substances on the market, or where the substances are rapidly biodegradable in wastewater or do not generate micropollutants at the end of life. Producers must exercise their responsibility collectively through nationally recognised Producer Responsibility Organisations, which are subject to annual independent audits.[1] The Commission must review the Annex III product list under Article 30 by 2033 at the latest, and may extend EPR to additional sectors based on monitoring data and scientific evidence.[2]
📋 EU Implementation Detail
The Directive specifies that quaternary treatment must focus first on organic micropollutants, “which represent a significant part of the pollution and for which removal technologies have already been designed.”[1] Member States may go beyond the minimum requirements set out in the Directive, including applying deadlines or thresholds more stringent than the Union baseline or broadening the spectrum of products subject to extended producer responsibility.[1]
Sampling, monitoring, and pass/fail criteria
For plants subject to quaternary treatment, the Directive sets monitoring frequencies based on plant size. Plants treating 50 000 to 149 999 p.e. require two micropollutant samples per month; plants treating 150 000 p.e. and above also require two samples per month for micropollutants, alongside more frequent sampling for other parameters.[1] Each sampling event takes a sample at both the inlet and the outlet of the urban wastewater treatment plant. Time-based samples used to monitor micropollutants must be 48-hour samples rather than the 24-hour samples used for other parameters.[1]
Compliance is assessed by averaging the specific percentages of removal of all single substances used in the calculation. At least six substances must be measured, and the number of Category 1 substances must be twice the number of Category 2 substances.[1]
Engineering Implication: The Directive is explicit that requirements more stringent than those in Annex I “shall be applied where necessary to ensure that the receiving waters fulfil the requirements” laid down in the Water Framework Directive, the Marine Strategy Framework Directive, the Environmental Quality Standards Directive, and the Bathing Water Directive.[1] Design teams that scope only to the 80% Annex I removal threshold without checking the receiving-water status of every applicable directive risk a non-compliant outcome at commissioning.
Quaternary Treatment Technology Options
The Directive does not prescribe a single technology. Recital 18 identifies the design space at the policy level: quaternary treatment should focus on organic micropollutants, “for which removal technologies have already been designed.”[1] In the European technical evidence base — most importantly the Joint Research Centre cost-model comparison published in 2025 and the underlying Swiss and Italian data sets — three technology families dominate the implementation conversation: ozonation, granular activated carbon (GAC), and powdered activated carbon (PAC).[2]
Ozonation
Ozonation oxidises micropollutants by introducing ozone into the treated effluent, typically followed by a biological or physical post-treatment step such as sand filtration to manage transformation products. In the JRC analysis of the Swiss VSA data set covering plants operating from 2014 to 2023, ozonation plants concentrate along the lower end of the cost-versus-size curve.[2] The Italian Politecnico di Milano analysis cited in the JRC report indicates that levelized cost ranges from approximately 9 EUR/p.e./year at 50 000 p.e. to approximately 6 EUR/p.e./year at plants above 50 000 p.e., with the ozonation curve representing the cheapest of the three technology families in the comparison.[2]
Granular Activated Carbon (GAC)
GAC removes micropollutants by adsorption onto a fixed bed of carbon media that is periodically regenerated or replaced. In the PoliMi data set referenced by the JRC, GAC cost is sensitive to regeneration interval — 6, 12, 24, and 36-month regeneration cycles produce a wide spread of operational costs.[2] At long regeneration intervals, GAC is competitive with ozonation; at short intervals, costs rise materially.
Powdered Activated Carbon (PAC)
PAC is dosed into the treatment train as a slurry, providing fast adsorption kinetics but generating a sludge stream that must be managed. In the PoliMi analysis, PAC consistently presents as the most expensive of the three technology families, with cost driven by the dose and the percentage of waste/extracted sludge.[2]
How the technologies compare across plant size
Quaternary treatment cost per p.e. drops sharply with plant size — the economies of scale are pronounced. The JRC report documents that unit costs (EUR/p.e./year) decline from roughly 20–25 EUR at 10 000 p.e. to roughly 7–10 EUR at 100 000 p.e. and approach 7 EUR at one million p.e. in the Swiss data set.[2] The Danish ENVIDAN/TI/DANVA model gives a comparable shape: roughly 12 EUR/p.e./year at 50 000 p.e. declining to roughly 7 EUR/p.e./year at 300 000 p.e.[2]
| Technology | Cost profile (per JRC 2025) | Dominant cost driver | Key constraint |
|---|---|---|---|
| Ozonation (+ post-treatment) | Lowest of the three in PoliMi data | Ozone dose (2, 5, or 10 mg/L) | Transformation product management; energy |
| Granular Activated Carbon (GAC) | Mid-range; sensitive to regeneration interval | GAC regeneration time (6 to 36 months) | Spent media management; bed sizing |
| Powdered Activated Carbon (PAC) | Highest of the three in PoliMi data | PAC dose and waste-sludge fraction | Sludge volume; disposal cost |
| Conventional secondary + tertiary alone | Not compliant with quaternary requirement | — | Does not achieve 80% removal of the Annex I indicator substances |
The Directive does not require any single technology. Member State competent authorities, in consultation with operators, identify the most appropriate quaternary treatment technologies through the dialogues required by Article 10.[1] The technology choice is plant-specific and must be validated against feed-water characterization, footprint constraints, sludge management capacity, and the receiving-water sensitivity classification under Article 8.
The Quaternary Treatment Design Process
A defensible quaternary treatment design starts with regulatory and risk-assessment analysis, not with equipment selection. The process below structures the most consequential decisions first.
Confirm scope under Article 8
Determine whether the plant is captured by the unconditional 150 000 p.e. threshold, or by the risk-based trigger for plants of 10 000 p.e. and above discharging into a sensitive area. For 10 000–149 999 p.e. plants, the Article 8 risk assessment is the controlling document and must be referenced to the formal list of sensitive areas published by the Member State.[1] National transposition law may impose stricter scope than the Union baseline.
Anchor the project to the compliance milestone
Identify which interim milestone in the 2033–2045 trajectory the plant is assigned to under the national implementation programme. Member States must establish national implementation programmes by 1 January 2028 and submit them to the Commission.[1] The programme determines whether the plant must be online by 2033, 2039, or 2045 — and therefore when procurement, engineering, and construction must begin.
Characterize the feed water and the indicator substances
Sample the plant influent and effluent for the Annex I, Table 3 indicator substances across operating conditions. Quantify the existing removal achieved by primary, secondary, and (where present) tertiary stages, so that the quaternary treatment design is dimensioned for the residual load, not the gross load. The Directive requires that the 80% removal performance be calculated as the average across at least six substances, with the Category 1 count being twice the Category 2 count.[1]
Generate multiple treatment chain options
Evaluate several candidate configurations rather than committing to a single technology. The JRC cost evidence indicates ozonation is typically the lowest-cost family, GAC mid-range with sensitivity to regeneration interval, and PAC the most expensive.[2] Hybrid configurations (ozonation followed by a biological or adsorption polishing step) are common in the Swiss reference data set.[2] Each candidate must meet the 80% removal requirement on the Annex I indicator panel.
Model lifecycle cost in line with the JRC reference range
For each candidate, model levelized cost over the plant lifetime — CAPEX, OPEX, energy, consumables, residuals management, and monitoring. Use the JRC reference range (95% to 138% of the inflation-adjusted impact assessment estimate at EU level) as a sanity check on unit costs.[2] Energy is a significant share of OPEX and is partly offset by the Article 11 energy neutrality targets — 20% renewable share by 2030, 40% by 2035, 70% by 2040, and 100% by 2045.[1]
Coordinate with the Article 9 EPR funding pathway
Up to 80% of the quaternary treatment costs are covered by the EPR scheme paid by pharmaceutical and cosmetic producers.[1] The producer responsibility organisation determines the cost-recovery mechanism in each Member State. Engineering teams should align project cost reporting with the EPR data-gathering format so that the operator can recover eligible costs from the producer responsibility organisation without retrospective rework.
Document traceable design justification
Every design decision should be traceable to a specific Article, Annex, or risk assessment finding. The Directive establishes a national implementation programme review every six years and a Commission evaluation in 2033 and 2040 that will look at the appropriateness of the Annex III product list, the feasibility of extending EPR to PFAS and microplastics, and the achievement of the energy neutrality objective.[1] Designs that are auditable today survive those reviews; designs that rely on tribal knowledge do not.
Cost Ranges and Treatment Economics
The JRC technical report published in 2025 (JRC144745) provides the most recent and most authoritative cost reference for quaternary treatment at EU scale.[2] It compares the cost function used in the impact assessment of the recast Directive with five alternative cost models drawn from Swiss (VSA), Italian (Politecnico di Milano), German (UBA), and Danish (ENVIDAN/TI/DANVA) evidence.
The headline finding: when the full quaternary treatment requirement is implemented by 2045, the total annual cost for the EU is expected to fall in the range of 1.48 to 1.8 billion EUR per year at 2025 prices, representing between -5% and +15% relative to the impact assessment estimate adjusted for inflation (1.56 billion EUR per year).[2] The upper-bound “worst case” cost without correcting for Swiss price levels is 2.15 billion EUR per year.[2]
Per-citizen cost: If 80% of total costs are recovered through the Article 9 EPR scheme and passed on to consumers, the JRC estimates the additional cost per EU citizen at 2.64 to 3.20 EUR per year by 2045 — less than 1% of the average per-capita expenditure on pharmaceuticals and non-durable medical goods, which EuroStat data places at approximately 557 EUR per year in current prices.[2]
At the plant level, the JRC report quantifies the cost-versus-size relationship using five cost functions. The pattern across all five is the same: unit cost (EUR/p.e./year) drops sharply with plant size. The “average” Swiss VSA curve suggests roughly 25 EUR/p.e./year at 10 000 p.e., declining to roughly 10 EUR/p.e./year at 100 000 p.e. and roughly 7.5 EUR/p.e./year at one million p.e.[2] The Danish model produces a similar shape with roughly 12 EUR/p.e./year at 50 000 p.e. declining to 6.8 EUR/p.e./year above 300 000 p.e.[2]
For a 150 000 p.e. plant, the inflation-adjusted impact-assessment function returns roughly 7.6 EUR/p.e./year (1300 × 150 000^-0.45), implying a total annual cost of approximately 1.14 million EUR per year for that plant. The Swiss “average” curve at the same size returns approximately 8 EUR/p.e./year. The two anchor estimates converge within 10–15% at the 150 000 p.e. threshold and diverge more at smaller and larger plant sizes.[2]
Three factors will reduce these costs over the implementation period and should be reflected in any project-level economic model:
- Energy neutrality targets under Article 11 progressively reduce the energy share of OPEX as renewable generation comes online at and around the treatment plant.[2]
- Economies of scale at the EU market level — as quaternary treatment is deployed across all 150 000+ p.e. plants, equipment and consumable costs are expected to decline with market maturity.[2]
- The implementation trajectory itself: between 2025 and 2045, the average annual cost is approximately 40% of the final 2045 cost at current prices, because only a fraction of plants is online in each interim period.[2]
⚠️ Cost Modelling Reality
The JRC explicitly notes that costs estimated from cost functions of this type are not plant-specific and should be used only for aggregated estimations.[2] A project-level cost model must be built from the specific site conditions: feed-water matrix, footprint, available utilities, sludge management capacity, and the procurement environment of the Member State. The JRC cost ranges are the upper-level sanity check; they are not the budget.
Worked Example: Quaternary Treatment Upgrade
The following worked example illustrates the design logic for a quaternary treatment upgrade, applying the regulatory thresholds and cost evidence drawn from the cited authorities.
Project Context
- EU Member State urban wastewater treatment plant treating a load of 200 000 p.e.
- Current configuration: primary, secondary biological, and tertiary nitrogen and phosphorus removal
- Captured by the unconditional 150 000 p.e. scope under Article 8(1) — quaternary treatment required regardless of receiving-water risk assessment[1]
- National implementation programme assigns this plant to the 60% milestone — quaternary treatment must be operational by 31 December 2039[1]
- Receiving water is a river feeding a downstream drinking water abstraction; Article 8(2) sensitive-area classification confirmed
Treatment Chain Comparison
| Configuration | Annex I removal performance | Indicative unit cost | Residuals to manage |
|---|---|---|---|
| Ozonation + sand filtration | Designed for ≥80% across Annex I indicator panel[1] | Approx. 6–9 EUR/p.e./year (PoliMi range)[2] | Transformation products in effluent; manageable sludge from sand filter |
| GAC adsorption (24-month regeneration) | Designed for ≥80% across Annex I indicator panel[1] | Approx. 7–8 EUR/p.e./year at 24-month regen (PoliMi)[2] | Spent GAC requiring regeneration or disposal |
| PAC dosing + sand filtration | Designed for ≥80% across Annex I indicator panel[1] | Approx. 8 EUR/p.e./year (PoliMi)[2] | PAC-laden sludge requiring disposal; higher sludge volume |
| Ozonation + GAC polish (hybrid) | Designed for ≥80% across Annex I indicator panel[1] | Higher; combines two technology families | Spent GAC + transformation product management |
Design Logic Applied
Regulatory basis: Article 8(1) imposes quaternary treatment unconditionally because the plant exceeds 150 000 p.e.[1] The 31 December 2039 deadline is fixed by the national implementation programme. Annex I, Table 3 establishes the 80% removal performance threshold across the indicator substances.[1]
Technology choice: The receiving water feeds a drinking-water abstraction, so Article 8(2)(a) confirms the sensitive-area classification.[1] Ozonation plus sand filtration is the lowest-cost configuration in the PoliMi data, with the second-lowest unit cost in the Swiss VSA reference set.[2] Sand filtration after ozonation addresses transformation-product management before discharge.
Cost envelope: At 200 000 p.e., the JRC inflation-adjusted impact assessment function returns approximately 6.8 EUR/p.e./year, implying roughly 1.36 million EUR per year. The Swiss VSA average curve at the same size returns approximately 9 EUR/p.e./year (1.8 million EUR per year). The PoliMi ozonation curve returns approximately 6 EUR/p.e./year (1.2 million EUR per year).[2] The expected envelope is therefore in the range 1.2 to 1.8 million EUR per year.
EPR funding: Article 9 requires that producers cover at least 80% of these costs through the Producer Responsibility Organisation by 31 December 2028.[1] The remaining 20% is covered by the operator and recovered through water tariffs.
Procurement timing: A 31 December 2039 operational deadline implies that engineering procurement should be locked by 2034–2035 to allow for design, tendering, construction, commissioning, and the at-least-six-month sampling period required to demonstrate the 80% removal performance.[1]
Your Quaternary Treatment Design Checklist
Before committing to a quaternary treatment upgrade design, ensure the following are documented and traceable:
☐ Article 8 Scope Confirmed — Unconditional scope at 150 000 p.e. and above, or risk-based scope under Article 8(2) for 10 000–149 999 p.e. plants discharging into listed sensitive areas.[1]
☐ National Compliance Milestone Identified — Plant assignment under the 2033/2039/2045 trajectory documented in the national implementation programme submitted by 1 January 2028.[1]
☐ Indicator Substance Panel Characterized — Influent and effluent concentrations measured across the Annex I, Table 3 Category 1 and Category 2 substances, with at least six substances and Category 1 count = 2 × Category 2 count.[1]
☐ Multiple Treatment Chain Configurations Evaluated — At least three candidate configurations among ozonation, GAC, PAC, and hybrid variants, compared on the 80% removal threshold, lifecycle cost, footprint, and residuals burden.[2]
☐ Cost Envelope Benchmarked Against JRC Range — Project-level cost compared against the inflation-adjusted impact assessment function and at least one alternative (VSA, PoliMi, or Danish) cost model from the JRC 2025 report.[2]
☐ Receiving-Water Status Cross-Checked — Compliance with the Water Framework Directive, Marine Strategy Framework Directive, Environmental Quality Standards Directive, and Bathing Water Directive confirmed, with stricter Annex I requirements applied where receiving-water quality so requires.[1]
☐ Article 9 EPR Funding Pathway Aligned — Cost-reporting format coordinated with the national Producer Responsibility Organisation to ensure at least 80% cost recovery through the EPR scheme.[1]
☐ Energy and Residuals Plan Documented — Energy audit consistent with Article 11 and the 2030/2035/2040/2045 renewable energy trajectory; residuals disposal pathway documented for spent media or transformation products.[1]
☐ Audit Trail and Traceability Documentation — Every design decision linked to an Article, Annex, or risk-assessment finding that an external reviewer can verify against the Directive text and the national implementation programme.
💡 Pro Tip
Build a single regulatory requirements matrix at the start of the project: one row per applicable Article and Annex of Directive (EU) 2024/3019, one column for the plant-specific application, citation, and milestone. Populate each cell with the design response and the supporting evidence. This matrix becomes the single source of truth for the project lifecycle, from preliminary design through commissioning, monitoring, and the six-year national implementation programme review cycle.
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Sources & References
[1] European Parliament and Council, Directive (EU) 2024/3019 of 27 November 2024 concerning urban wastewater treatment (recast), Official Journal of the European Union, OJ L, 12.12.2024 — Directive (EU) 2024/3019 (EUR-Lex)
[2] Pistocchi, A. (Joint Research Centre), Updated estimation of the costs of quaternary wastewater treatment in the EU — A comparison of cost models, Publications Office of the European Union, Luxembourg, 2025 (JRC144745) — JRC Cost Study on Quaternary Treatment (2025)
[3] European Parliament Legislative Observatory, Urban wastewater treatment. Recast — 2022/0345(COD) — Final act, 12 December 2024 — Legislative Observatory Procedure 2022/0345(COD)
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