Catalytic ozonation-biological coupled processes for the treatment of industrial wastewater containing refractory chlorinated nitroaromatic compounds

Abstract

A treatability study of industrial wastewater containing chlorinated nitroaromatic compounds (CNACs) by a catalytic ozonation process (COP) with a modified Mn/Co ceramic catalyst and an aerobic sequencing batch reactor (SBR) was investigated. A preliminary attempt to treat the diluted wastewater with a single SBR resulted in ineffective removal of the color, ammonia, total organic carbon (TOC) and chemical oxygen demand (COD). Next, COP was applied as a pretreatment in order to obtain a bio-compatible wastewater for SBR treatment in a second step. The effectiveness of the COP pretreatment was assessed by evaluating wastewater biodegradability enhancement (the ratio of biology oxygen demand after 5 d (BOD(5)) to COD), as well as monitoring the evolution of TOC, carbon oxidation state (COS), average oxidation state (AOS), color, and major pollutant concentrations with reaction time. In the COP, the catalyst preserved its catalytic properties even after 70 reuse cycles, exhibiting good durability and stability. The performance of SBR to treat COP effluent was also examined. At an organic loading rate of 2.0 kg COD/(m(3)xd), with hydraulic retention time (HRT)=10 h and temperature (30+/-2) degrees C, the average removal efficiencies of NH(3)-N, COD, BOD(5), TOC, and color in a coupled COP/SBR process were about 80%, 95.8%, 93.8%, 97.6% and 99.3%, respectively, with average effluent concentrations of 10 mg/L, 128 mg/L, 27.5 mg/L, 25.0 mg/L, and 20 multiples, respectively, which were all consistent with the national standards for secondary discharge of industrial wastewater into a public sewerage system (GB 8978-1996). The results indicated that the coupling of COP with a biological process was proved to be a technically and economically effective method for treating industrial wastewater containing recalcitrant CNACs.

Fig. 1

X-ray diffraction (XRD) pattern (a), X-ray photoelectron spectroscopy (XPS) Co 2p (b) and Mn 2p (c) spectra of the fresh catalyst CPS: counts per second; BE: binding energy

Fig. 1

X-ray diffraction (XRD) pattern (a), X-ray photoelectron spectroscopy (XPS) Co 2p (b) and Mn 2p (c) spectra of the fresh catalyst CPS: counts per second; BE: binding energy

Fig. 1

X-ray diffraction (XRD) pattern (a), X-ray photoelectron spectroscopy (XPS) Co 2p (b) and Mn 2p (c) spectra of the fresh catalyst CPS: counts per second; BE: binding energy

Fig. 2

Scheme of the experimental set-up 1: ozone generator; 2: rotameter; 3: porous titanium plate; 4: catalysts layer; 5: bubble column reactor; 6: KI absorption; 7: three-way valve; 8: input ozone gas detection; 9: off gas detection

Fig. 3

GC-MS analysis of organic contaminants in industrial wastewater Peak identities are as follows: 1: 2-ClA, 2: 4-ClNB, 3: 2-ClNB, 4: 4-NP, 5: 2-Cl-4,6-DNP (speculated)

Fig. 4

COD, TOC and NH₃-N removal profiles against the operating time in SBR1 Experimental conditions: organic load rate 2.0 kg COD/(m³·d), hydraulic retention time (HRT)=10 h, T=(30±2) °C

Fig. 5

Typical HPLC chromatograms of the influent (a) and the effluent (b) in SBR1

Fig. 5

Typical HPLC chromatograms of the influent (a) and the effluent (b) in SBR1

Fig. 6

Color comparison of deionized water (a), SBR2 effluent (b), and SBR1 effluent (c)

Fig. 7

Time-evolution profiles of major pollutants (a), Cl⁻, NO₃ ⁻ and NH₃-N (b) in catalytic ozonation Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 7

Time-evolution profiles of major pollutants (a), Cl⁻, NO₃ ⁻ and NH₃-N (b) in catalytic ozonation Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 8

Evolution of pH and ORP during catalytic ozonation of industrial CNACs-containing wastewater Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 9

UV-Vis spectra of the raw wastewater and treated water with 5 times of dilutions as a function of time Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 10

Evolution of biodegradability (a), total organic carbon (TOC), chemical oxygen demand (COD), average oxidation (AOS), and carbon oxidation state (COS) (b) as a function of ozonation time Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 10

Evolution of biodegradability (a), total organic carbon (TOC), chemical oxygen demand (COD), average oxidation (AOS), and carbon oxidation state (COS) (b) as a function of ozonation time Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 11

Effect of catalyst reuse times on TOC removal in catalytic ozonation process Experimental conditions: initial pH 12.9, temperature 25 °C, and 55.76 mg/min of applied ozone dose

Fig. 12

COD concentration variations in COP and subsequent SBR2 during steady-running 23 cycles Experimental conditions: 1.15 mg O₃/mg COD-applied specific ozone dose at COP stage, while at SBR2 stage, organic load rate 2.0 kg COD/(m³·d); hydraulic retention time (HRT)=10 h, T=(30±2) °C