Degradation of refractory organics in concentrated leachate by the Fenton process: Central composite design for process optimization

doi:10.1007/s11783-020-1294-1

Front. Environ. Sci. Eng.

2021, Vol. 15

Issue (1) : 2 https://doi.org/10.1007/s11783-020-1294-1

RESEARCH ARTICLE

Degradation of refractory organics in concentrated leachate by the Fenton process: Central composite design for process optimization

Senem Yazici Guvenc(

), Gamze Varank

Department of Environmental Engineering, Yıldız Technical University, Davutpaşa Campus, Esenler, Istanbul 34220, Turkey

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Abstract

• 90% total COD, 95.3% inert COD and 97.2% UV₂₅₄ were removed.

• High R² values (over 95%) for all responses were obtained with CCD.

• Operational cost was calculated to be 0.238 €/g COD_removed for total COD removal.

• Fenton oxidation was highly-efficient method for inert COD removal.

• BOD₅/COD ratio of leachate concentrate raised from 0.04 to 0.4.

The primary aim of this study is inert COD removal from leachate nanofiltration concentrate because of its high concentration of resistant organic pollutants. Within this framework, this study focuses on the treatability of leachate nanofiltration concentrate through Fenton oxidation and optimization of process parameters to reach the maximum pollutant removal by using response surface methodology (RSM). Initial pH, Fe²⁺ concentration, H₂O₂/Fe²⁺ molar ratio and oxidation time are selected as the independent variables, whereas total COD, color, inert COD and UV₂₅₄ removal are selected as the responses. According to the ANOVA results, the R² values of all responses are found to be over 95%. Under the optimum conditions determined by the model (pH: 3.99, Fe²⁺: 150 mmol/L, H₂O₂/Fe²⁺: 3.27 and oxidation time: 84.8 min), the maximum COD removal efficiency is determined as 91.4% by the model. The color, inert COD and UV₂₅₄ removal efficiencies are determined to be 99.9%, 97.2% and 99.5%, respectively, by the model, whereas the total COD, color, inert COD and UV₂₅₄ removal efficiencies are found respectively to be 90%, 96.5%, 95.3% and 97.2%, experimentally under the optimum operating conditions. The Fenton process improves the biodegradability of the leachate NF concentrate, increasing the BOD₅/COD ratio from the value of 0.04 to the value of 0.4. The operational cost of the process is calculated to be 0.238 €/g COD_removed. The results indicate that the Fenton oxidation process is an efficient and economical technology in improvement of the biological degradability of leachate nanofiltration concentrate and in removal of resistant organic pollutants.

Keywords Concentrated leachate Fenton oxidation Central composite design Biodegradability Inert COD

Corresponding Author(s): Senem Yazici Guvenc

Issue Date: 24 July 2020

Cite this article:

Senem Yazici Guvenc,Gamze Varank. Degradation of refractory organics in concentrated leachate by the Fenton process: Central composite design for process optimization[J]. Front. Environ. Sci. Eng., 2021, 15(1): 2.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-020-1294-1
https://academic.hep.com.cn/fese/EN/Y2021/V15/I1/2

Tab.1 Characterization of concentrated leachate

Tab.2 Independent variables and their coded levels for CCD experimental design and experimental responses

Tab.3 ANOVA results of quadratic models

Fig.1 Plots of actual values versus predicted values for COD (a), Color (b), Inert COD (c) and UV₂₅₄ (d) removal responses.

Fig.2 Response surface plots on the effects of pH and Fe²⁺(a), pH and H₂O₂/ Fe²⁺ (b), pH and Oxidation time (c), H₂O₂/Fe²⁺ and Oxidation time (d) for COD removal.

Fig.3 Response surface plots on the effects of pH and Fe²⁺ (a), pH and H₂O₂/Fe²⁺ (b), pH and Oxidation time (c), H₂O₂/Fe²⁺ and Oxidation time (d) for Color removal.

Fig.4 Response surface plots on the effects of pH and Fe²⁺ (a), pH and H₂O₂/ Fe²⁺ (b), pH and Oxidation time (c), H₂O₂/Fe²⁺ and Oxidation time (d) for inert COD removal.

Fig.5 Response surface plots on the effects of pH and Fe²⁺ (a), pH and H₂O₂/Fe²⁺ (b), pH and Oxidation time (c), H₂O₂/Fe²⁺ and Oxidation time (d) for UV₂₅₄ removal.

Wastewater type	Process type	Characterization of WW	Independent variables	Optimum conditions	Max. Removal Efficiency (%)	Operation Cost	Reference
Leachate Nanofiltration Concentrate	Only Fenton	UV₂₅₄: 3860 mg/L COD: 7000 mg/L Inert COD: 6120 mg/L Color: 11400 Pt/Co	pH: 2–4, Fe²⁺: 30–150 mmol/L, H₂O₂/Fe²⁺: 0.5–3.5 and oxidation time: 30?110 min	pH: 3.99, Fe²⁺: 150 mmol/L, H₂O₂/Fe²⁺: 3.27 oxidation time: 84.8 min	COD: 90	0.238 €/g COD_removed	This study
Leachate Nanofiltration concentrate	Only Fenton	COD: 4500 mg/L TOC: 1600 mg/L Chromaticity: 250	Initial pH: 2?5 H₂O₂ (mol/L): 0.10–1.00 Fe²⁺ concentration (mmol/L): 10–25	Initial pH: 2 H₂O₂: 1 mol/L Fe⁺²:17.5 mmol/L	COD: 69.6 TOC: 68.9 Chromaticity: 100	NA	^{Xu et al. (2017)}
Leachate Nanofiltration concentrate	Fenton and UV-Fenton	COD:2172 mg/L Color: 5600 PtCo	pH: 2–3 H₂O₂: 4%(v/v) FeSO₄·7H₂O: 2 g/L Time: 120 min	NA	COD: 89.68	NA	Wang et al. (2016b)
Leachate Nanofiltration concentrate (A), Leachate Nanofiltration concentrate (B)	Fenton-Photo Fenton	COD(A): 1330 mg/L COD(B): 3450 mg/L TOC(A): 715 mg/L TOC(B): 1426 mg/L Color (Dilution)(A): 400 Color (Diluation)(B): 500 Total PAHs (A): 18.57 µg/L Total PAHs (B): 5.40 µg/L	pH: 2–7 H₂O₂: 0–60 mmol/L Fe⁺²: 3–10 mmol/L Time: 2 h	pH:5 H₂O₂:10 mmol/L Fe⁺²: 4 mmol/L Time: 2 h	COD: 70 PAHs-2 ring (A):58 PAHs-2 ring (B): 45 PAHs-3 ring (A): 30 PAHs-3 ring (B): 44	NA	^{Li et al. (2016)}
Leachate Nanofiltration concentrate	Fenton-UV Fenton	COD: 724 mg/L BOD5: 43 mg/L NH₄-N: 11.3 mg/L Conductivity: 11.3 mS/cm Cl: 2925.7 mg/L Suspended solids: 128 mg/L	pH: 2–3 H₂O₂: (4%? v/v) FeSO₄·7H₂O: (2 g/L) Time: 0–120 min	NA	COD: 80.1	NA	^{Wang et al. (2016a)}
Leachate UF and NF concentrate	Fenton	COD: 3060 mg/L BOD₅: 288 mg/L	pH range of 2–6.5 H₂O₂/Fe²⁺: 1–15 Fe²⁺: 100–1000 mg/L Time: 20?200 min	Temperature: ~20°C Fe²⁺ :400 mg/L pH:3 Time:2 h H₂O₂/Fe²⁺: 9	COD:>60	NA	^{He et al. (2015)}
Leachate RO concentrate	Microwave (MW)-Fenton	COD: 2494 mg/L BOD₅/COD: 0.13	pH: 5.0 Fe²⁺: 0.04 mol/L H₂O₂/Fe²⁺ ratio:8 Time: 3 h	pH:5.0 Fe²⁺: 0.04 mol/L H₂O₂/Fe²⁺: 8 Time: 3 h MW power: 390 W-8 min	COD: 75 BOD₅/COD: 0.62	NA	^{Zhang et al. (2018)}
Leachate NF concentrate	Fenton UV-Fenton UV-H₂O₂	COD: 1280 mg/L BOD₅: 121 mg/L	pH: 2.0–7.5 FeSO₄.7H₂O:1.8–14.4 mmol/L, H₂O₂:100–400 mmol/L Time:0–180 min. Temperature:15°C–45°C	pH:3.0, FeSO₄.7H₂O: 7.2 mmol/L, H₂O₂ dosage: 400 mmol/L Temperature: 25°C	COD: 92.7 BOD₅/COD: 0.44	NA	^{Zhao et al. (2020)}
Concentrated Leachate	MW-Fe⁰ /H₂O₂	COD: 1501 mg/L BOD₅: 23.4 mg/L BOD/COD: 0.02	initial pH: 2–8 Fe⁰: 0.10 to 0.50 g/L H₂O₂: 1 to 25 mL/L MW: 200 to 700 W	Temperature: 85°C, initial pH of 2.0, Fe⁰: 0.5 g/L, H₂O₂: 20 mL/L MW: 400 W Time: 14 min	COD:58.70 UV₂₅₄:85.69 CN:88.30 BOD₅/COD:0.41	0.56 CNY/t	^{Chen et al. (2018)}
Memebrane Concentrate Landfill Leachate	Fenton	COD: 3300 mg/L TOC: 1080 mg/L BOD₅: 48.4 mg/L	H₂O₂: 1–18 mL Time: 0–120 min pH: 2?6 H₂O₂/Fe(II) molar ratio 1?5	H₂O₂ = 9.0 mL/200 mL H₂O₂/Fe(II) molar ratio: 3.0 pH= 3.0 time= 40 min	COD: 78.9±1.3 TOC: 70.2±1.4 UV₂₅₄: 90.64±1.6	NA	^{Teng et al. (2020)}

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