Municipal wastewater bio-treatment

01Overview and value chain

Markers: [EC: EU Urban Wastewater Treatment Directive + US EPA Clean Water Act secondary treatment standards | OECD: Environmental biotechnology, Circular bioeconomy | Regulator: EPA (USA), ECHA/REACH (EU), MEE (China)]

Municipal wastewater bio-treatment is the biological handling of domestic sewage — the activated-sludge process alone serves the great majority of the world’s city effluent, typically removing 85–95% of biochemical oxygen demand before discharge. The modern stack layers membrane bioreactors (MBR) that deliver reuse-grade filtrate (BOD below 5 mg/L) on a compact footprint, sidestream anammox that cuts aeration energy roughly 60% for nitrogen-rich sludge liquor, thermal hydrolysis plus anaerobic digestion that lifts sludge volatile-solids destruction and turns sewage sludge into biogas and Class A biosolids, and phosphorus recovery that returns a finite nutrient to agriculture. It is a mature, globally deployed industry: every tabled actor is commercial or operating. This article covers municipal sewage only — the biological treatment of toxic industrial effluents (metals, dyes, phenols, oil-and-gas, mining, microelectronics) is covered in Bioremediation of hazardous industrial effluents.

The key directions of municipal wastewater bio-treatment are:

1. Activated sludge and biological nutrient removal (Activated Sludge & BNR): the century-old aerobic suspended-growth workhorse, with nitrification-denitrification for nitrogen and enhanced biological phosphorus removal (EBPR).
2. Membrane bioreactors (Membrane Bioreactors): activated sludge coupled with membrane filtration (Memcor/PVDF) for high-quality effluent and a small footprint, selected for three major English plant expansions in February 2026.
3. Anaerobic digestion of sewage sludge (Anaerobic Sludge Digestion): thermal hydrolysis (Cambi) plus anaerobic digestion converting sludge to biogas and Class A biosolids, as at DC Water’s Blue Plains.
4. Anammox and phosphorus recovery (Anammox & Phosphorus Recovery): anammox shortcutting nitrogen removal with far less aeration, and phosphorus recovery from sludge or ash to close the nutrient loop.

Sectoral value chain

[raw sewage] ──> [primary] ──> [activated sludge/MBR] ──> [nutrient removal]
                                       │
                              (sludge → digestion)
                                       │
                                       ▼
[reclaimed water] <─── [tertiary + disinfection] <─────┘

Value chain levels

Cross-cutting technologies of the sector:

• Smart dosing chemistry (Smart Dosing Chemistry): coagulants and flocculants (Kemira) optimized by real-time sensor feedback for phosphorus removal and sludge dewatering.
• Digital twins and process control (Digital Twin Process Control): model-based aeration and recirculation control cutting energy use.
• Energy recovery (Biogas CHP Energy Recovery): combined heat and power from digester biogas moving large plants toward energy neutrality.

02US

The United States operates some of the world’s largest advanced municipal treatment plants, with thermal-hydrolysis biosolids and membrane bioreactors at the frontier.

advanced WWTP, thermal hydrolysis biosolids, vibrating MBR

• DC Water (Blue Plains): the largest advanced wastewater treatment plant in North America runs Cambi thermal hydrolysis ahead of anaerobic digestion, converting digester gas to steam and electricity and producing the DC Water Bloom Class-A biosolids product returned to land application.
• Evoqua Water Technologies (now part of Xylem): its Memcor MBR systems were selected for three major wastewater treatment plant expansions in England in February 2026, and a July 2026 study validated vibrating membrane bioreactors for enhanced nutrient removal and energy efficiency in municipal service.

03CN

China’s municipal sector is built around membrane bioreactors and large reclaimed-water systems, led by OriginWater and the capital’s drainage utility.

municipal MBR, reclaimed-water systems, capital drainage

• OriginWater (碧水源): a leading membrane-bioreactor supplier (SZSE:300070) providing PVDF MBR and ultrafiltration systems for municipal sewage treatment and reclaimed-water reuse across Chinese cities.
• Beijing Drainage Group and capital reuse: Beijing’s municipal drainage operator runs the city’s reclaimed-water network; 2025 city-wide sewage and reclaimed-water utilization statistics track a municipal system that recycles a large share of its treated effluent.
• National reuse push: China’s water-stressed north relies on reclaimed water for environmental and industrial reuse, anchoring demand for MBR and advanced tertiary treatment.

04EU

Europe pairs the strongest regulatory driver — the Urban Wastewater Treatment Directive and its 2024 revision toward energy neutrality, reuse and micropollutant removal — with leading chemistry and reuse engineering.

water reuse, phosphorus recovery, mainstream anammox

• Suez (France): in April 2026 Suez and Salinity Solutions launched the first industrial pilot of Hybrid Batch Reverse Osmosis; Suez also renewed the Hérault Méditerranée urban-community drinking-water and wastewater contract (January 2026) and is piloting treatment processes for the Biterrois water resource.
• Kemira (Finland): a April 2026 patent-transfer agreement moved phosphorus-recovery technology toward full-scale rollout, Kemira completed its first full-scale US trial of a chlorine-free wastewater treatment solution (March 2026), and a May 2026 study demonstrated near-complete phosphorus valorization from sewage sludge.
• Paques (Netherlands, qualitative): the BIOPAQ and ANAMMOX reactor supplier anchors anaerobic and sidestream-anammox municipal treatment; 2026 academic work advanced mainstream low-carbon anammox toward full-scale application.

05Leading companies and research institutes

06Tech stack and innovations

The stack builds on a century of activated-sludge microbiology, now intensified by membranes, anaerobic sidestreams and nutrient recovery.

1. Biological nutrient removal (Biological Nutrient Removal):
   • nitrification-denitrification and EBPR remove nitrogen and phosphorus to low single-digit mg/L before discharge.
   • case: Evoqua’s vibrating MBR (July 2026) enhanced nutrient removal and energy efficiency in municipal service.
2. Thermal hydrolysis and anaerobic digestion (THP + Anaerobic Digestion):
   • Cambi thermal hydrolysis disintegrates sludge structure before digestion, lifting volatile-solids destruction and biogas yield and yielding Class A biosolids.
   • case: DC Water’s Blue Plains converts digester gas to steam and electricity and markets the DC Water Bloom biosolids product.
3. Anammox and phosphorus recovery (Anammox & P-Recovery):
   • sidestream anammox removes nitrogen from sludge liquor with roughly 60% less aeration; phosphorus is recovered from sludge or ash as fertilizer.
   • case: Kemira’s April 2026 phosphorus-recovery patent transfer and near-complete P valorization from sewage sludge (May 2026).

07Value chains and production pipelines

Industrial pipeline of a municipal wastewater treatment works (EU UWWTD / US EPA 40 CFR 133)

┌───────────────────────────┐      ┌───────────────────────────┐
│ 1. Preliminary & primary  │ ───> │ 2. Biological treatment   │
└───────────────────────────┘      └───────────────────────────┘
                                                 │
                                                 ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 4. THP + digestion        │ <─── │ 3. Nutrient removal (N/P) │
└───────────────────────────┘      └───────────────────────────┘
              │
              ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 5. Biogas + biosolids     │ ───> │ 6. Tertiary + reuse       │
└───────────────────────────┘      └───────────────────────────┘

Stage 1: Preliminary and primary treatment

Raw municipal sewage is screened and de-gritted, then settled in primary clarifiers that remove settleable solids as primary sludge.

Stage 2: Biological treatment

Primary effluent flows to activated-sludge or MBR aeration basins, where a suspended-growth microbial community oxidizes carbonaceous BOD and oxidizes ammonia to nitrate.

Stage 3: Nutrient removal

Nitrification-denitrification zones and EBPR remove nitrogen and phosphorus; Evoqua’s vibrating MBR couples this step with membrane solids separation.

Stage 4: Thermal hydrolysis and digestion

Primary and waste activated sludge pass through Cambi thermal hydrolysis and anaerobic digestion, where thermophilic and mesophilic consortia convert organics to biogas.

Stage 5: Biogas and biosolids

Digester biogas fuels combined-heat-and-power (DC Water’s steam and electricity), and the stabilized, dewatered residue is marketed as Class A biosolids for land application.

Stage 6: Tertiary polishing and reuse

Tertiary filtration, disinfection and (where water is scarce) reverse-osmosis polishing — as in Suez’s Hybrid Batch RO pilot — return reclaimed water for environmental, industrial or non-potable urban reuse.