Municipal Tail-Water Polishing Without Extra Chemical Dosing: What a Dedicated Ozone Catalyst Changes

Upgrading a municipal WWTP is a different problem from treating industrial effluent. The COD is low, the flow is enormous, and the pollutants that actually fail consent — humic substances, trace pharmaceuticals, endocrine disruptors, geosmin and MIB — sit at concentrations a conventional oxidation step barely touches. Plants then reach for powdered carbon or a bigger chemical room, both of which push sludge handling costs in the wrong direction.

SINOKLE took the other route and built a municipal-dedicated heterogeneous ozone catalyst around that specific water quality. The result is a medium tuned for low-COD, trace-pollutant duty rather than for bulk COD destruction, and it behaves differently from the industrial grades in several useful ways.

What municipal water does to a catalyst

Two mechanisms shorten media life in municipal service. The first is scaling: calcium and magnesium salts precipitate inside the pores, and once the pore mouth narrows, the accessible surface collapses and activity follows. The second is biological fouling — extracellular polymer and biofilm build up inside the pore network during months of uninterrupted running, which is why many plants end up dismantling reactors far more often than the media supplier predicted.

The municipal grade uses a porous inorganic composite substrate formed by staged temperature-controlled sintering, with a connected multi-level micropore structure above 250 m2/g and dual-acidic active sites on the surface. Manganese, iron and copper carry the transition-metal function; precious metal can be added on some models. Atomic-deposition super-hydrophilic modification is what addresses scaling and slime: the surface holds a water film that calcium salts, colloids and microbial polymer struggle to anchor to. Active components are high-temperature anchored, so metal-ion leaching is not a concern for reclaimed water.

On the chemistry side, the multi-metal system drops the activation energy for ozone decomposition and drives radical formation at roughly 2–5 times the rate of ozone alone. ·OH then cleaves the humic and pharmaceutical fraction non-selectively, which is what produces the simultaneous decolorisation, deodorisation and UV254 reduction that plant operators notice first.

The specification sheet in plain terms

• Form: red-brown spherical granules, standard 2–4 mm, customisable.
• Strength: single-granule compressive strength ≥100 N, annual wear ≤0.3%.
• pH window: 6–11, matching neutral-to-weak-alkaline municipal water, with short-term swings tolerated.
• Ozone conversion: decomposition utilisation ≥97%.
• Removal: comprehensive COD removal ≥45% on secondary effluent at incoming COD 40–120 mg/L; colour ≥95%; odour substances ≥92%.
• Life: beyond 5 years, regenerated by acid wash plus water wash after scaling or adsorption saturation.
• Duty: 24 h continuous high-flow operation.

Three duty cycles, three results

Secondary effluent pushed to approximate Class IV

A prefecture-level municipal WWTP of 50,000 m3/d was discharging secondary effluent at COD 55–80 mg/L with 40–60-fold colour and a clear earthy odour, and needed approximate surface-water Class IV at COD≤30 mg/L for river ecological replenishment. At 10 mg/L ozone, 5 g/L catalyst and 20 min hydraulic retention, COD removal came out at 48% and effluent stabilised at 28 mg/L, with colour inside 10-fold and geosmin-class odorants down 93%. The downstream BAC filter load dropped noticeably.

Tail water prepared for industrial reuse

An industrial-park WWTP producing secondary effluent at COD 60–95 mg/L needed COD≤40 mg/L for circulating cooling make-up. At 7 mg/L ozone, 4 g/L catalyst and 15 min retention, COD removal was 46% and effluent held at 35 mg/L. UV254 fell sharply, UF organic fouling slowed, and the membrane chemical-cleaning interval doubled.

Combined-sewer overflow in wet weather

Overflow from a combined-sewer network, CSO duty, is a nasty one: COD 90–160 mg/L, high suspended solids, high colour and violent short-term swings in both flow and quality. At 15 mg/L ozone, 6 g/L catalyst and 25 min retention, COD removal was 44% and colour removal 94% — enough to knock the receiving-water impact down without building a wet-weather tank.

Where it sits in the flowsheet

The catalyst is rarely the first unit. In the Class IV configuration the train is filtration, then CDOF ozone catalytic oxidation charged with the municipal medium, then BAC to mineralise the small-molecule intermediates the ozone stage leaves behind. In the reuse configuration a CDFU swirl-air-flotation filtration stage replaces conventional pre-treatment, skid-mounted and compact, with ozone catalysis acting as membrane pre-treatment. Either way the front end removes suspended solids so the catalyst is not buried in grit.

Smaller applications follow the same logic: small and mid-sized municipal upgrades chasing Grade 1-A, park wastewater carrying a minor industrial component, circulating-water make-up pre-treatment, WWTP deodorisation coupling, and centralised rural domestic sewage destined for landscape reuse or irrigation.

Operating economics

Because ozone decomposition utilisation stays above 97%, plants cut ozone dosing at equal effluent standards, which reduces both generator capacity and per-tonne power — energy consumption at the ozone system drops over 35% in the cases above. Chemical sludge falls as flocculent and decolorant dosing is reduced or removed entirely. Media lasts beyond 5 years and regenerates, wear is ≤0.3% a year, and the skid can be installed on-line without a full plant shutdown. Where BAC or UF sits downstream, the reduced organic load extends media and membrane life as well.

Instrumentation covers online COD, UV254, pH, ozone concentration, flow and pressure; feed distribution, catalytic reaction, gas-water backwash and tail-gas ozone destruction are all automatic and remotely monitored, so the O&M burden stays small. SINOKLE backs the package with R&D, process design, commissioning and catalyst regeneration services under high-tech enterprise, specialised-innovation, ISO three-system and multiple ozone-catalysis invention-patent qualifications. For municipal operators facing tighter colour, odour and micropollutant limits, the choice is usually between building a bigger chemical room and changing the oxidation chemistry — this is an argument for the second.