Coke wastewater’s toughest pollutants face a split decision: Fenton chemistry vs. ozone, with carbon polishing

Coke‑oven wastewater is a brew of things biology hates to touch: phenols, quinoline, PAHs (polycyclic aromatic hydrocarbons), cyanides, and thiocyanates, with high COD (chemical oxygen demand). These refractory compounds routinely resist conventional biological treatment, pushing operators toward advanced polishing steps (www.mdpi.com) (www.mdpi.com).

Two workhorses dominate the advanced playbook: AOPs (advanced oxidation processes) and adsorption. AOPs like Fenton chemistry (Fe²⁺ + H₂O₂ generating •OH radicals) aim to break molecules down. Adsorption—often with activated carbon—captures what’s left. The question is which mix gets coke plants to limits like China’s 80 mg/L COD (GB16171‑2012) at a cost they can live with (www.mdpi.com).

Refractory organics and baseline challenge

Because aromatics and nitrogenous species linger after primary/secondary steps, plants often add AOPs to boost biodegradability—typically tracked by BOD₅/COD (biochemical oxygen demand over 5 days divided by COD, a proxy for how “bio‑friendly” the effluent is)—before or after biological treatment (www.mdpi.com).

Fenton chemistry: strong phenol punch, pH caveat

In raw coke wastewater (initial COD ~1000 mg/L), Chu et al. (2012) used iron powder plus 0.3 M H₂O₂ at pH≈3 and achieved ~44–50% COD removal and ~95% total‑phenol removal in 1 hour, with biodegradability rising by ~65% (via increased O₂ uptake) (researchgate.net) (researchgate.net).

In phenolic/oily petrochemical effluent, a Fenton pretreatment at 500 mg/L H₂O₂ and 120 mg/L Fe²⁺ delivered ~89.8% COD removal and boosted B/C (BOD₅/COD) from 0.052 to 0.62 (www.mdpi.com). Typical Fenton performance: high removal of phenolics/aromatics, partial COD removal (often 50–90% at high dose), and iron sludge generation, with a narrow optimum around pH~3 that requires post‑neutralization and sludge disposal (iwaponline.com). Photo‑ or electro‑Fenton variants can improve outcomes but add complexity.

Ozonation: color wins, COD plateaus

Standalone ozonation is less complete on organics. In a bench‑scale coke‑oven test, Chang et al. (2008) saw nearly 100% removal of color and thiocyanate, but only ~30% total organic carbon (TOC) reduction (COD removal similarly low). Cyanide removal was pH‑sensitive (better at neutral/alkaline), and BOD₅/COD rose only modestly (pubmed.ncbi.nlm.nih.gov). As ozonation progressed, the O₃:COD consumption ratio dropped from ~1 to 0.2 (easy targets exhausted), with TOC removal plateauing at ~30% (pubmed.ncbi.nlm.nih.gov).

Enhanced ozone helps. Liu et al. used microbubble‑catalytic ozonation on biotreated coal‑wastewater: ozone aeration alone achieved 42.5% COD removal at 0.44 mg O₃/mg COD with 98% ozone utilization; with subsequent biological polishing, total COD removal reached ~66.7% (effluent ~92 mg/L) (pubmed.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). A state‑of‑art review reports microbubble/catalytic ozone raising BOD₅/COD to ~0.46–0.52 in 100 minutes with ~60–61% COD removal (iwaponline.com).

Trade‑offs remain: ozone systems require high‑energy generators and are less selective—oxidizing widely but often incompletely, with some refractory NICTs remaining (pubmed.ncbi.nlm.nih.gov).

Activated carbon polishing: hydrophobics captured

Adsorption does not destroy organics; it captures them, and is commonly used as a polishing step after AOPs or biology. Xia et al. (2022) treated biologically pretreated coke wastewater with coagulation plus 4 g/L powdered activated carbon (PAC, here meaning powdered activated carbon). The combo delivered 76.8% additional COD removal, yielding ~80 mg/L COD—enough to meet the coke‑industry 80 mg/L limit (GB16171‑2012) (www.mdpi.com) (www.mdpi.com) (www.mdpi.com). In the same study, commercial PAC removed ~48%, underscoring how adsorbent quality and surface chemistry matter (www.mdpi.com).

Hydrophobic, higher‑molecular‑weight species are favored: a coagulation plus SAC (spherical activated carbon) system removed ~77% of hydrophobic COD (www.mdpi.com). A review notes commercial AC can be expensive and that microporous AC has limited uptake of large molecules (pubs.rsc.org) (pubs.rsc.org). By contrast, low‑cost “activated coke” or lignite‑derived adsorbents have shown excellent uptake of refractory organics; An et al. (2017) reported a mesoporous lignite‑coke material that outperformed standard AC for decolorization and refractory removal in coal‑gasification wastewater (pubs.rsc.org), with feedstock costs < $20/ton versus $100+/ton for anthracite (pubs.rsc.org). Recycling coke‑plant byproducts as adsorbents is also promising (iwaponline.com).

Cost hinges on dose. Using 4 g/L (~4 kg/m³) of powdered AC at ~$5/kg implies ~$20/m³ in consumables alone. High‑quality AC can cost hundreds of dollars per ton delivered, and spent carbon requires disposal or thermal regeneration (energy‑intensive). In practice, activated carbon beds or PAC contactors supplement chemistry—coagulation reagents such as coagulants are frequently paired with activated carbon in polishing trains (www.mdpi.com).

Performance and cost snapshot

COD removal varies with chemistry and conditions. Fenton systems have reached ~90% COD removal in strong‑oxidation tests (www.mdpi.com) and ~50% in typical coke effluent trials (researchgate.net). Standalone ozonation often sits lower (e.g., ~30–40%: pubmed.ncbi.nlm.nih.gov), or ~60% under optimized microbubble/catalytic conditions (iwaponline.com). In both cases, BOD₅/COD typically jumps from ~0.05–0.2 to ~0.4–0.6 post‑treatment (www.mdpi.com) (iwaponline.com).

Hybrid AOPs can be powerful. A rotating‑bed O₃/Fenton setup removed essentially 100% of phenol and aniline and 95% of quinoline—and all ammonia—under optimum conditions, far beyond O₃ alone (pubs.rsc.org).

Costs are non‑trivial. Barndõk et al. estimate ~€5/m³ (~$6/m³) for AOP pretreatment to reach ~40% COD removal (pubs.acs.org), translating to ~$1.8–1.9 per kg COD removed for Fenton and $1.96/kg for ozone (www.mdpi.com). Hydrogen peroxide (H₂O₂) is relatively cheap (≈$0.5–1/kg) but dosed heavily; ozone generation is energy‑intensive (~10–20 kWh/kg O₃) and capital‑heavy. Fenton typically removes more COD/phenol per dose and was somewhat cheaper per kg COD than simple O₃ in one study (www.mdpi.com). Still, AOPs are “advanced” for a reason—easy to run in the lab, but with high O&M in practice (iwaponline.com) (iwaponline.com).

What a viable treatment train looks like

AOPs and adsorption are complementary. Fenton chemistry can dismantle phenolics and increase biodegradability but may only partially cut COD and produces iron sludge; ozonation excels on color/thiocyanate and helps BOD₅/COD but can stall on TOC. Adsorption with activated carbon then captures residual hydrophobic, high‑MW organics to meet discharge limits, as shown by the coagulation plus PAC results (76.8% additional COD removal; ~80 mg/L COD effluent) (www.mdpi.com). Designers weigh higher capital/energy for ozone versus reagent costs for Fenton and adsorption, often finishing with biological polishing or biological digestion to capture the biodegradability gains (pubmed.ncbi.nlm.nih.gov).

Sources and standards

Peer‑reviewed studies and industry reviews on coke‑oven wastewater treatment and AOP/adsorption were used. Key data are from chemical engineering journals and standards. For example, Chu et al. (researchgate.net) and Chang et al. (pubmed.ncbi.nlm.nih.gov) report treatment efficiencies for Fenton and ozonation, respectively; Barndõk et al. (pubs.acs.org) and Cheng et al. (www.mdpi.com) provide cost estimates; Xia et al. (www.mdpi.com) and An et al. (pubs.rsc.org) (pubs.rsc.org) demonstrate adsorption performance. Regulatory benchmarks (e.g., COD <80 mg/L) come from national standards (www.mdpi.com). Additional context is drawn from recent reviews (iwaponline.com) (iwaponline.com) (iwaponline.com). The implication is a data‑driven comparison to guide technology choice.

References

Chang et al., J. Hazard. Mater. 156 (2008) 560–567 (pubmed.ncbi.nlm.nih.gov); Chu et al., Chemosphere 86(4) (2012) 409–414 (researchgate.net); Cheng et al., Separations 9(7) (2022) 179 (www.mdpi.com); Barndõk et al., ACS Sustainable Chem. Eng. 6(5) (2018) 5888–5894 (pubs.acs.org); Xia et al., Water 14(15) (2022) 2446 (www.mdpi.com) (www.mdpi.com); Wei et al., RSC Adv. 5 (2015) 93386–93393 (pubs.rsc.org); Duan et al., Water Sci. Technol. 85(1) (2022) 449 (iwaponline.com) (iwaponline.com); Liu et al., Chem. Eng. J. 348 (2018) 191–200 (pubmed.ncbi.nlm.nih.gov); An et al., Environ. Sci.: Water Res. Technol. 3 (2017) 169–174 (pubs.rsc.org) (pubs.rsc.org); and relevant industrial guidelines (GB16171‑2012) (www.mdpi.com).