Treatment of Landfill Leachate Reverse Osmosis Concentrate from by Catalytic Ozonation with γ-Al 2 O 3

Abstract

To develop a technology for the degradation of the toxic and refractory pollutants contained in landfill leachate reverse osmosis (RO) concentrate, a γ-Al₂O₃/O₃ system was set up in this study. Landfill leachate RO concentrate was rejected from RO of biologically pretreated raw landfill leachate. First, its key operational parameters, including γ-Al₂O₃ dosage, ozone dosage, reaction temperature, treatment time, and initial pH value, were optimized through single-factor experiments. Under the optimal conditions, the chemical oxygen demand (COD) (70%) and color (100%) removal efficiencies could be obtained by the γ-Al₂O₃/O₃ process. Meanwhile, the ratio of biochemical oxygen demand (BOD₅) to COD (B/C ratio) was enhanced from 0.01 to 0.2, which suggests that its biodegradability was improved to some extent. Decomposition or transformation of organic pollutants in landfill leachate RO concentrate was analyzed by ultraviolet-visible spectroscopy, excitation–emission matrix fluorescence spectroscopy, and fourier transform infrared (FTIR) spectroscopy. Furthermore, the synergetic effect between ozone and alumina was investigated. Collectively, these analyses suggest that γ-Al₂O₃/O₃ process will be a promising technology for the treatment of landfill leachate RO concentrate if the problem of the desorption of pollutants could be solved economically.

Introduction

Landfilling is one of the most common methods used to manage urban solid wastes (Renou et al., 2008). Rainwater percolating through the landfill, together with the production of liquids during the stabilization of the solid wastes, generates landfill leachate (Oulego et al., 2015). Leachate from mature landfills is typically characterized by high ammonium concentration, low biodegradability, and high fraction of recalcitrant and large organic molecules such as humic and fulvic acids (Cortez et al., 2011). Other compounds such as heavy metals, chlorinated organic compounds, benzene, toluene, and xylenes also occur in the landfill leachate (Oulego et al., 2015).

Plenty of treatment technologies, including physical–chemical process (Chu et al., 2015; Kattel et al., 2016; Silva et al., 2016, 2017; Jung et al., 2017; Kattel and Dulova, 2017) and biological treatment (Ahmed and Lan, 2012; Chys et al., 2015; Syron et al., 2015), has been investigated to treat the landfill leachate. Biological processes are commonly used to treat landfill leachate due to its low cost. However, biological processes may not be effective enough to treat the refractory and hazardous organic contaminants contained in landfill leachate (Fernandes et al., 2015).

As a result, membrane filtration technologies, including membrane bioreactor, nanofiltration (NF), and reverse osmosis (RO), as a main posttreatment step in leachate treatment, seem to be one of the most promising and efficient methods for the treatment of landfill leachate (Renou et al., 2008; Hasar et al., 2009; Wang et al., 2014; Zayen et al., 2016). However, the generation of toxic and biorefractory landfill leachate RO concentrate was the major problem of these processes. Therefore, proper treatment of landfill leachate RO concentrate is helpful to avoid the secondary pollution of the above processes (i.e., NF and RO).

Currently, many physicochemical methods, including noncatalytic wet oxidation (Oulego et al., 2015), electrochemical advanced oxidation process (Moreira et al., 2016), photo-Fenton (Barndõk et al., 2016), Fenton process (Gupta et al., 2014), activated carbon adsorption (Kurniawan and Lo, 2009), Fenton-like process (Martins et al., 2012), microwave-enhanced persulfate oxidation (Chou et al., 2015), were proposed for the treatment of the recalcitrant pollutants contained in wastewater.

To degrade the toxic and refractory pollutants contained in landfill leachate RO concentrate, many methods have been investigated, such as solidification/stabilization process (Hunce et al., 2012), Fenton process (Wu et al., 2011), electro-peroxone process (Li et al., 2013), electrochemical oxidation (Zhou et al., 2016), and anodic oxidation combined with electro-Fenton processes (Labiadh et al., 2016). However, these processes suffer the limit of high cost or low efficiency.

In recent years ozonation has been applied widely in the oxidation treatment of landfill leachate (Bila et al., 2005; Ntampou et al., 2006; Chys et al., 2015; Oloibiri et al., 2015; Amaral-Silva et al., 2016). However, Jung and his colleagues had found that Fenton oxidation exhibited a better treatment performance than ozonation due to the production of unselective and more active oxidants [i.e., hydroxyl radicals (HO•)], and O₃ tended selectively reacted with the organics in landfill leachate (Jung et al., 2017). Compared with ozone (E⁰ = 2.07 V), HO• is a stronger oxidant (E⁰ = 2.33 V) (Kasprzyk-Hordern et al., 2003).

Furthermore, the catalytic ozonation with the catalyst (e.g., Al₂O₃, FeOOH, MnO₂, CeO₂) was developed to enhance the oxidation capacity of ozonation (Nawrocki and Kasprzyk-Hordern, 2010). In other words, ozone can be decomposed into the reactive oxygen species (ROS), including O• and HO• on the surface of the catalyst. For example, Vittenet et al. reported the involvement of HO• during catalytic ozonation with γ-Al₂O₃ for the treatment of 2,4-dimethylphenol (2,4-DMP), and its total organic carbon removal was 32% higher than single ozonation process under the operational condition: 2,4-DMP₀ = 50 mg/L, γ-Al₂O₃ dosage = 2 g/L, O₃ flow rate = 40 L/h, treatment time = 5 h, volume of solution = 1.5 L (Vittenet et al., 2015).

According to the previous reports, possibility reaction mechanism of γ-Al₂O₃/O₃ process has been proposed. On the one hand, γ-Al₂O₃ was able to adsorb ozone and to decompose it into free radicals by interacting with the hydroxyl groups of the materials (Vittenet et al., 2015). Compared with ozone, free radicals are unselective and more active oxidants. On the other hand, some pollutants were adsorbed on the surface of γ-Al₂O₃ then attacked by the adsorbed ozone directly (Qi et al., 2013). Therefore, the catalytic ozonation with γ-Al₂O₃ may have a better treatment efficiency for the landfill leachate RO concentrate compared with ozonation.

In this study, a catalytic ozonation with γ-Al₂O₃ was set up to decompose the toxic and refractory organics in landfill leachate RO concentrate. First, the key operational parameters (e.g., γ-Al₂O₃ dosage, O₃ dosage, initial pH, reaction temperature, and treatment time) were optimized through single-factor experiments. Furthermore, two control processes (i.e., γ-Al₂O₃ alone and O₃ alone) were set up to confirm the high treatment efficiency of catalytic ozonation with γ-Al₂O₃. Meanwhile, ultraviolet-visible (UV-vis), excitation–emission matrix (EEM), fourier transform infrared (FTIR) spectra, and B/C ratio were used to evaluate the degradation of the organic pollutants in landfill leachate RO concentrate and its improvement of biodegradability. Finally, the operational life and catalytic mechanism of γ-Al₂O₃ were investigated thoroughly.

Experimental Protocols

Reagents

γ-Al₂O₃ particles from Chengdu Kelong chemical reagent factory were used in the experiment, whose diameter was ∼50 μm and Brunner–Emmet–Teller (BET) surface area was about 172.7 m²/g. The pH_pzc of γ-Al₂O₃ was about 8.5. All the chemicals used in the experiment were analytical grades. Deionized water was used throughout the whole experiment process.

Landfill leachate RO concentrate

Landfill leachate RO concentrate used in this study was obtained from an old landfill site (over 10 years) located in southwest China, which was rejected from RO of biologically pretreated landfill leachate (chemical oxygen demand [COD] = 372 mg/L). Its environmental characterizations are shown in Table 1.

Table 1.

Characteristics of Landfill Leachate Reverse Osmosis Concentrate

Item	Units	Values
COD	mg/L	1,317.5
BOD₅	mg/L	20
B/C ratio	—	0.01
Colority	Times	2,000
Suspended solids	mg/L	57
pH	—	7.3
Conductivity	μS cm⁻²	9,086
Turbidity	NTU	5.5
Cl⁻	mg/L	2,030
Bicarbonate	mg/L	943.2
Alkalinity	mmol/L	15.5
Co²⁺	mg/L	0.1
Ni²⁺	mg/L	0.2
Cu²⁺	mg/L	0.4
Zn²⁺	mg/L	0.2
Fe²⁺	mg/L	2.1
Cd²⁺	mg/L	0.003
Cr³⁺	mg/L	0.3

BOD₅, biochemical oxygen demand; COD, chemical oxygen demand.

Batch experiments

During the γ-Al₂O₃/O₃ treatment system, the key effect factors, such as γ-Al₂O₃ dosage, ozone dosage, and initial pH of landfill leachate RO concentrate, were investigated thoroughly through batch experiments.

In each batch experiment, 300 mL landfill leachate RO concentrate with different adjusted initial pH (3.0–10.0), alumina powders (0–50.0 g/L) were added in a 500 mL flat bottom beaker, and the reaction solution was stirred by a mechanical stirrer with a speed of 300 r/min. Simultaneously, ozone gas was generated onsite from pure compressed dry oxygen (99.9%, v/v) by a laboratory model ozone generator (10 g/h; Chengdu Yifeng Co., Ltd., China) and continuously dispersed into the reacting solution through a gas diffuser. And the concentration of the generated ozone was about 53.88 mg/L. After the treatment process of 30 min, the solution samples were withdrawn and filtered through a polytetrafluoroethylene (PTFE) syringe filter disc (0.45 μm); some of the samples were diluted by deionized water if necessary.

Finally, COD, UV-vis, and EEM spectra of the samples were measured, respectively. All experiments were carried out in triplicate.

Analytical methods

Transition metal ions and chloride contained in landfill leachate RO concentrate were determinated by inductively coupled plasma mass spectrometry (ICP-MS) (NexION 300X; Perkin Elmer) and ICS-90 (Daian, China), respectively. COD and biochemical oxygen demand (BOD₅) were determined using COD analyzer (Lianhua, China) and BOD₅ analyzer (OxiTop IS12, WTW, Germany), respectively. The initial pH and the pH of the effluent were measured by pHS-3C meter (Rex, China).

The UV-vis spectra (Shimadzu, Japan) of the influent and effluent were carried out in 10 mm quartz cuvettes, and the UV-vis spectra were recorded from 190 to 450 nm using deionized water as blank. The EEM spectra were measured by a luminescence spectrometry (F-7000 spectrophotometer, Hitachi, Japan), and the EEM spectra were collected with the corresponding scanning emission spectra from 200 to 550 nm at 5 nm increments by varying the excitation wavelength from 200 to 400 nm at 5 nm sampling intervals. The excitation and emission slits were kept at 10 nm, and the scanning speed was set at 1,200 nm/min (Ren et al., 2016).

Meanwhile, all samples were filtered and diluted 100 times by ultrapure water before the analysis of EEM fluorescence spectroscopy. FTIR was used to assess the differences in general functional groups of organics that exist in the influent and effluent of landfill leachate RO concentrate, as well as on the surface of γ-Al₂O₃. Samples were dried and grinded with KBr in a motor with 1:100 rations. The power mixture was compressed into tablet under 10 t force for 1 min. And each sample was scanned four times between the wavelengths of 4,000–500 cm⁻¹ using a Nicolet 6700 FTIR spectrometer (Ren et al., 2016). Colority of the samples was measured using dilution ratio method. Ozone concentration was measured by the iodometric method (Xiong et al., 2016b).

The alkalinity and bicarbonate of the landfill leachate RO concentrate were measured by chemical method of analysis. The BET surface area of γ-Al₂O₃ was detected by a surface area analyzer (ASAP 2020; Micromeritics). The pH_pzc of γ-Al₂O₃ was determined by mass titration method as described by Ikhlaq (Ikhlaq et al., 2012).

Results and Discussion

Influence of operational parameters on performance in γ-Al₂O₃/O₃ system

Effects of γ-Al₂O₃ dosage on COD removal

Batch experiments were conducted on a condition that different dosages of γ-Al₂O₃ were used to treat 300 mL landfill leachate RO concentrate with the initial pH (7.3) and 16.5 mg/min of O₃ for 30 min at temperature 30°C.

As shown in the Fig. 1a, the COD removal efficiency of landfill leachate RO concentrate was enhanced from 28% to 60% with the increasing of γ-Al₂O₃ dosage from 0 to 50 g/L. However, the γ-Al₂O₃ dosage was not a limited factor when it reached 50 g/L. For example, when γ-Al₂O₃ dosage was further increased to 80 g/L, only 62% of COD removal efficiency was obtained. The increase of γ-Al₂O₃ dosage would increase its total surface area and number of active sites, which could improve its adsorption and catalytic capacity. Thus the rapid increase of COD removal was mainly attributed to the combined action of adsorption and catalytic ozonation.

FIG. 1.

Effects of γ-Al₂O₃ dosage (a), O₃ dosage (b), initial pH (c), reaction temperature (d), and treatment time (e) on COD removal and effluent pH of landfill leachate after γ-Al₂O₃/O₃ treatment. COD, chemical oxygen demand.

The similar results have been found by Vittenet and his colleagues when catalytic ozonation with γ-Al₂O₃ was used to degrade the refractory organics in water (Vittenet et al., 2015). Thus the γ-Al₂O₃ dosage of 50 g/L was chosen in the following experiments.

In addition, Fig. 1a also shows that all the effluent pH values of the batch experiments with different γ-Al₂O₃ dosage (0–80 g/L) were similar to their initial pH (=7.3) after 30 min treatment. The results suggest that accumulation of the organic acids as intermediates did not occur after 30 min treatment (Kasprzyk-Hordern et al., 2003; Zhao et al., 2008; Nawrocki and Kasprzyk-Hordern, 2010). The generated organic acids might be further decomposed rapidly or adsorbed by γ-Al₂O₃. The carboxylates can be adsorbed and accumulated on γ-Al₂O₃, which could decrease its Al-OH basic sites and catalytic activity (Pocostales et al., 2011; Vittenet et al., 2015).

Effects of O₃ dosage on COD removal

Since the consumption of ozone was a crucial parameter for the operating cost and treatment efficiency, it is necessary to optimize O₃ dosage. Figure 1b shows that the COD removal efficiency increased rapidly from 27% to 70% with the increasing of O₃ dosage from 0 to 22 mg/min and then it elevated slowly when O₃ dosage exceeded 22 mg/min. An increase of ozone concentration could improve the generation of HO•, which could accelerate the decomposition of the pollutants in landfill leachate RO concentrate. Meanwhile, the pollutants can also be transformed directly by the ozone. Nevertheless, the degradation of the pollutants was dominantly controlled by the rate of chemical reaction when the ozone concentration in the liquid phase approached its maximum value at a fixed temperature (Ruan et al., 2010).

According to the previous research (Xiong et al., 2016a), we can obtain the general concentration of dissolved ozone indirectly based on COD removal efficiency. Figure 1b shows that the COD removal efficiency remained unchanged when the O₃ dosage is above 33 mg/min. That is to say, the dissolved ozone in solution was almost saturated when the O₃ dosage is above 33 mg/min. The further increase of ozone dosage (>22 mg/min) had no significant contribution to the degradation of pollutants. Therefore, the ozone dosage of 22 mg/min was chosen in the subsequent experiments from the economical strategy and practical point of view.

Effects of initial pH on COD removal

Figure 1c shows that the COD removal efficiency (∼70%) was maintained when the initial pH increased from 3.0 to 7.3, but it dropped to 57% rapidly when the initial pH reached 10.0. In γ-Al₂O₃/O₃ system, contributions to the COD removal efficiency came from following parts: (I) the ozonation effect in aqueous solution, (II) reactions between the ozone and organic compounds after they were adsorbed on the surface of γ-Al₂O₃ and became concentrated (Qi et al., 2013), and (III) the γ-Al₂O₃ adsorption effect of the oxidation by-products produced by ozone in aqueous solution (Aboussaoud et al., 2014). It is well known that the presence of OH⁻ ions in water leads to ozone decomposition and generation of HO•, which then reacts with organics in a nonselective way (Ikhlaq et al., 2012).

Therefore, the contribution to COD removal efficiency of part (I) was improved to some extent with the increasing of pH. Pollutants occur in the landfill leachate RO concentrate and the intermediates from ozonation process contain many carboxyl groups. Under alkaline condition, these carboxyl groups are under carboxylate form. Carboxylates can hardly be adsorbed on the surface of γ-Al₂O₃, which is fully populated with OH⁻ ions when the pH of solution is above its pH_PZC (∼8.5) (Ikhlaq et al., 2012). Therefore, the contributions to COD removal efficiency of part (II) and part (III) were reduced strongly. At last, the total COD removal efficiency decreased when the pH is above γ-Al₂O₃ pH_PZC during γ-Al₂O₃/O₃ process.

Meanwhile, some constituents of the landfill leachate RO concentrate had scavenging effects, such as CO₃²⁻, HCO₃⁻ (Vicente et al., 2011; Zhao et al., 2016). Under neutral or acidic condition, the solution contained less or little CO₃²⁻, HCO₃⁻, so the γ-Al₂O₃/O₃ system could accumulate more HO• and obtain a better COD removal efficiency. Therefore, the initial pH 7.3 without any adjustments was chosen in the subsequent experiments from the economical strategy and practical point of view.

Effects of reaction temperature on COD removal

Experiments were carried out with different reaction temperatures (i.e., 20–70°C). Figure 1d shows that the high COD removal efficiency (∼69%) was maintained when the reaction temperature was between 20°C and 60°C, while it dropped rapidly to 58% when the reaction temperature reached 70°C. The phenomenon is attributed to two reverse factors of the reaction temperature in catalytic ozonation process.

First, high activation energy of diffusion-controlled or chemical-controlled reactions could be overcome when the treatment process was carried out under the higher operating temperature (Lien and Zhang, 2007). In other words, the high reaction temperature usually could facilitate the chemical reactions, which enhance the degradation efficiency of pollutants (Ahn et al., 2008). Second, the increasing reaction temperature would also lead to a decrease of ozone solubility in aqueous phase of the catalytic ozonation process and then impair the COD removal efficiency. The above two opposite effects compete with each other with the increase of reaction temperature.

However, the dominant reaction mechanism was controlled by the second factor when the temperature reached 70°C, which resulted in the decrease of treatment efficiency. Consequently, the room temperature (30°C) was chosen in the following experiments from the economical point of view.

Effects of treatment time on COD removal

The landfill leachate RO concentrate was treated for 120 min by γ-Al₂O₃/O₃ process in this experiment. Figure 1e shows that the COD removal efficiency reached 70% only after 30 min treatment. However, the COD removal efficiency just reached 86% at the cost of fourfold treatment time and ozone dosage. Since the fourfold treatment time would cause much more treatment cost, the optimal treatment time should be 30 min.

Control experiments

To compare the effects of three processes (γ-Al₂O₃ adsorption, O₃ oxidation alone, and the combination of γ-Al₂O₃ and O₃), three control experiments and a sequential treatability experiment were conducted under the above optimal conditions (COD₀ = 1,317.5 mg/L, γ-Al₂O₃ dosage of 50 g/L, O₃ dosage of 22 mg/min, initial pH of landfill leachate RO concentrate without any adjustments, reaction temperature of 30°C, and the treatment time of 30 min) in triplicate. The sequential treatability experiment was that first treated landfill leachate RO concentrate with γ-Al₂O₃ alone and then ozonized the γ-Al₂O₃ treated effluent.

Degradation of the pollutants and its improvement of biodegradability

Figure 2a shows that the COD removal efficiency obtained by γ-Al₂O₃/O₃ process (70%) was higher compared with γ-Al₂O₃ (27%) and O₃ (48%). The COD removal efficiency of the sequential treatability experiment was 70%, which is equal to γ-Al₂O₃/O₃ process. It could be illustrated that the removal efficiency by O₃ alone was enhanced by transition metal ions originally contained in landfill leachate RO concentrate.

FIG. 2.

COD removal and color removal efficiencies, BOD₅/COD ratios (a), and UV-vis spectra (b) of the influent and effluents by different treatment processes under the optimal conditions (COD₀ = 1,317.5 mg/L, γ-Al₂O₃ dosage = 50 g/L, O₃ dosage = 22 mg/min, initial pH = 7.3, reaction temperature = 30°C, treatment time = 30 min). BOD₅, biochemical oxygen demand; UV-vis, ultraviolet-visible.

Transition metal ions of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Cd²⁺, Cr³⁺ in landfill leachate RO concentrate were determinated by ICP-MS and the concentrations of them are as shown in Table 1. The effect of transition metal ions on catalysis of ozone was studied in previous literatures (Kasprzyk-Hordern et al., 2003). Furthermore, the adsorption COD of γ-Al₂O₃ alone process was 356 mg/L, which also had contribution to the removal of the pollutants.

Recalcitrant matter transformation could be determined by analyzing color changes during the treatment. The initial dark brown color of the landfill leachate RO concentrate, which can be attributed to the presence of humic substances, became light yellow or even colorless by γ-Al₂O₃ process, γ-Al₂O₃/O₃, and O₃ process, respectively. In addition, Fig. 2a shows the color removal efficiencies obtained by γ-Al₂O₃/O₃ process (100%), O₃ alone (99%), γ-Al₂O₃ alone (88%), which suggested that the decolorization of landfill leachate RO concentrate was primarily attributed to the combination of ozone oxidation and adsorption of γ-Al₂O₃. Within a short time, ozone could directly attack the carbon-double bonds in the chromophoric and product compounds like aliphatic acids, ketones, and aldehydes, which are colorless, thus increase the color removal efficiencies (Ntampou et al., 2006).

Figure 2a shows that the B/C ratio was increased from 0.01 to 0.2 after 30 min treatment by γ-Al₂O₃/O₃ process under the optimal conditions, which was higher compared with O₃ alone (0.1) and γ-Al₂O₃ alone (0.02). The result indicates that the toxic and refractory pollutants in landfill leachate RO concentrate could be effectively degraded or transformed by γ-Al₂O₃/O₃ process, and its biodegradability was improved to some extent, which could facilitate the subsequent biological treatment. Meanwhile, the higher B/C ratio (0.2) obtained by γ-Al₂O₃/O₃ process was mainly attributed to the catalytic action of γ-Al₂O₃ and transition metal ions originally contained in landfill leachate for the decomposition of ozone.

UV-vis analysis

After 30 min treatment under the optimal conditions, the changes in UV-vis absorbance characteristics of influent and effluents by the γ-Al₂O₃/O₃ process and two control experiments from 190 to 450 nm are shown in Fig. 2b. With regard to the UV-vis spectrum of the landfill leachate RO concentrate, the absorbance peaks at the wavelength of about 190 nm can be assigned to the C═O or —OH. The strong peaks between 220 and 230 nm represent the C═C conjugated bond. Meanwhile, the weaker adsorption intensities above 255 nm are related to C═C aromatic group (Mecozzi et al., 2009).

Figure 2b shows that all the adsorption peaks (190–450 nm) of the three effluents were reduced to some extent, but the intensity of the adsorption between 250 and 450 nm has decreased to 0 in the γ-Al₂O₃/O₃ system, which suggests that almost all the aromatics were adsorbed, decomposed, or transformed. Therefore, the residual peaks located between 190 and 250 nm probably due to the by-products (i.e., aldehydes, ketones, and esters) after the decomposition and transformation of the aromatic pollutants (Xu et al., 2008). In addition, the intensity of all the peaks for the effluent of the γ-Al₂O₃/O₃ system was much lower compared with the two control experiments. The results also confirm that the γ-Al₂O₃/O₃ system had a higher treatment efficiency for the landfill leachate RO concentrate.

EEM spectral analyses

EEM fluorescence spectroscopy is a rapid and sensitive technique for the analysis of dissolved organic matter, and it had been used to detect the transformations of aromatic pollutants in previous works (Shao et al., 2009; Wu et al., 2012; Xi et al., 2012).

Figure 3 shows the EEM spectra of the influent and effluents of the γ-Al₂O₃/O₃ process and two control experiments. Their fluorescence parameters and total fluorescence intensities are listed in Table 2. Three peaks were identified for the landfill leachate RO concentrate; peak A (λ_ex/λ_em = 320/405 nm), peak B (λ_ex/λ_em = 275/410 nm), and peak C (λ_ex/λ_em = 250/450 nm) are attributed to biorefractory humic-like materials (He et al., 2011; Xi et al., 2012). Peak D (λ_ex/λ_em = 225/327 nm) fell in the region defined by shorter excitation wavelength (<250 nm), and shorter emission wavelength (<350 nm) is related to the aromatic protein region (Shao et al., 2009).

FIG. 3.

Excitation–emission matrix spectra of the influent (a) and effluents by different treatment processes (b) γ-Al₂O₃, (c) O₃, (d) γ-Al₂O₃/O₃.

Table 2.

Dissolved Organic Matter of Influent and Effluents by Different Treatment Processes

	Peak A		Peak B		Peak C		Peak D
Treatment processes	Ex/Em (nm)	Intensity (a.u.)	Ex/Em (nm)	Intensity (a.u.)	Ex/Em (nm)	Intensity (a.u.)	Ex/Em (nm)	Intensity (a.u.)	Total intensity (a.u.)	Removal efficiency (%)
Influent	320/405	1,724	275/410	1,694	250/450	2,622	—	—	6,040	0
γ-Al₂O₃	325/405	1,365	285/390	1,392	250/450	2,420	—	—	5,177	14
O₃	—	—	—	—	—	—	225/310	116.4	116.4	98
γ-Al₂O₃/O₃	—	—	—	—	—	—	225/327	110.8	110.8	98

I_Total = I_A+ I_B+ I_C+ I_D, COD₀ = 1,317.5 mg/L, γ-Al₂O₃ dosage = 50 g/L, O₃ dosage = 22 mg/min, initial pH = 7.3, reaction temperature = 30°C, treatment time = 30 min.

As shown in Table 2, the total fluorescence intensity removal efficiency (14%) was obtained in γ-Al₂O₃ alone process. Meanwhile, the intensities of peak A, peak B, and peak C were decreased to some extent and no new peaks appeared. The results confirm that the γ-Al₂O₃ shows the ability of adsorption in γ-Al₂O₃ alone process. As shown in Fig. 3c, d, three initial peaks disappeared and a new peak named peak D appeared after the treatment by ozone alone or the γ-Al₂O₃/O₃ process.

According to Table 2, the fluorescence intensity removal efficiencies by O₃ process (98%) and γ-Al₂O₃/O₃ process (98%) were obtained, which suggested that both of them had great abilities for the removal of fluorescence compounds. According to the previous work, it can be proposed that the fluorescence compounds could be degraded by destructing conjugated structure of the pollutants (He et al., 2011). Because landfill leachate RO concentrate contains transition metal ions (i.e., Co²⁺, Ni²⁺, Cu²⁺), an all-right fluorescence intensity removal efficiency could be obtained by O₃ process without γ-Al₂O₃.

FTIR spectra analysis

Figure 4 shows the FTIR spectrum of the landfill leachate RO concentrate. According to prior literatures (Hua et al., 2013; Yang et al., 2015; Lenz et al., 2016; Li et al., 2016), these absorbance bands could be interpreted as follows: the board and intense band at 3,435 cm⁻¹ is due to the O—H stretching of hydroxyl and carboxyl groups and the N—H stretching of amide.

FIG. 4.

FTIR spectra of 500–4,000 cm⁻¹ region of influent (a) and effluent (b) by γ-Al₂O₃/O₃ process (COD₀ = 1,317.5 mg/L, γ-Al₂O₃ dosage = 50 g/L, O₃ dosage = 22 mg/min, initial pH = 7.3, reaction temperature = 30°C, treatment time = 30 min). FTIR, fourier transform infrared.

The methyl/methylene C—H stretching bands typically appeared around 2,930–2,734 cm⁻¹, and the band at 2,395 cm⁻¹ might be associated with bonds of C≡N, N═C═O, and N═C═S; the sharp peak at 1,763 cm⁻¹ was attributed to the carboxylic acids of the humic substances; the band at 1,643 cm⁻¹ corresponded to aromatic rings (the typical C═C skeleton vibration in conjugated aromatic systems); the broad and particularly intense band at 1,384 cm⁻¹ was attributed to NO₂ stretch vibration of nitrite, which revealed the high nitrogen concentration contained in the landfill leachate RO concentrate; the band at 1,267 cm⁻¹ can be attributed to the amino groups (C—N stretching vibration) and oxygenated groups (C—O and C—O—C stretching of carboxylic acids, phenols, aromatic and unsaturated ethers); the characteristic band at 1,109 cm⁻¹ was C—O groups of alcohols; and the bands at 824 and 863 cm⁻¹ could be assigned to the substituted benzene.

As shown in Fig. 4, intensities of the main bands at 1,100 cm⁻¹–1,170 cm⁻¹ were decreased obviously and band at 1,267 cm⁻¹ disappeared completely. Meanwhile, the band intensity ratio between bands around 1,385 cm⁻¹ and 1,763 cm⁻¹ increased from 27.4 (A₂/A₁) to 56.7 (B₂/B₁). The results reveal that the benzene ring had been opened, and some pollutants were transformed or decomposed. In addition, it could be observed that the band at 863 cm⁻¹ almost disappeared, which suggests that nitrogen and aromatic compounds were transformed or decomposed.

Reuse of γ-Al₂O₃ in successive ozonation reactions

To investigate the durability of γ-Al₂O₃ during ozonation, the γ-Al₂O₃ had been reused in five successive runs with and without ozone under the same operational conditions. As shown in Fig. 5a, the COD removal efficiencies progressively decreased during the continuous runs of γ-Al₂O₃ alone, and it was decreased from 29% to 10% after five successive runs. The results suggest that the adsorption capacity of γ-Al₂O₃ would be decreased after recycling utilization.

FIG. 5.

Reuse times of γ-Al₂O₃ in the γ-Al₂O₃/O₃, γ-Al₂O₃ alone processes (a) and γ-Al₂O₃/O₃, γ-Al₂O₃/O₃/US processes (b) (COD₀ = 1,317.5 mg/L, γ-Al₂O₃ dosage = 50 g/L, O₃ dosage = 22 mg/min, initial pH = 7.3, reaction temperature = 30°C, treatment time = 30 min).

In the γ-Al₂O₃/O₃ process, the COD removal efficiencies decreased rapidly from 70% to 53% after three runs and then it was maintained at about 50% in the subsequent treatment batches. The results might be explained that some pollutants or their intermediates adsorbed on the surface of γ-Al₂O₃/O₃ were hard to be mineralized completely or desorbed easily in the γ-Al₂O₃/O₃ process, which would occupy the catalytic activity sites of γ-Al₂O₃/O₃ to inhibit the catalytic decomposition of ozone. Thus, the treatment efficiency of the γ-Al₂O₃/O₃ process would be decreased after three batch experiments.

In the previous work, it was reported that the pollutants deposited on the surface of Zero-valent iron (ZVI) particles could be removed rapidly by ultrasonic irradiation. So, the ZVI particles could maintain their surface activity (Hung et al., 2000; Lai et al., 2013). To solve the above problem, therefore, the ultrasonic irradiation was used to intensify the γ-Al₂O₃/O₃ process.

However, Fig. 5(b) shows that the treatment efficiency of the γ-Al₂O₃/O₃ process was not improved in the presence of ultrasonic irradiation. The results suggest that the pollutants or their intermediates adsorbed on the surface of γ-Al₂O₃/O₃ could also not be desorbed by the ultrasonic irradiation. Furthermore, the adsorption of the organic compounds by γ-Al₂O₃ might occur through a ligand exchange with Al-OH groups forming Al-O(CO)R groups (Vittenet et al., 2015). Therefore, the strong adsorption of γ-Al₂O₃ for some compounds would decrease its catalytic sites and limit the treatment efficiency of the γ-Al₂O₃/O₃ process.

Regeneration of γ-Al₂O₃

As shown in Fig. 6, the ratio of band intensity between bands around 1,638 cm⁻¹ and 2,929 cm⁻¹ of the γ-Al₂O₃ of γ-Al₂O₃ alone process (A₂/A₁ = 11.9) is close to that of landfill leachate RO concentrate (9.6). Therefore, we can conclude that initial pollutants were adsorbed on the γ-Al₂O₃ surface directly in γ-Al₂O₃ alone process. However, the ratio of the γ-Al₂O₃ of γ-Al₂O₃/O₃ process (B₂/B₁ = 24.8) is much higher compared with landfill leachate RO concentrate (9.6). The result further confirms that the intermediates from ozonation process in aqueous solution were adsorbed on the surface of γ-Al₂O₃ in the γ-Al₂O₃/O₃ process. Meanwhile, some pollutants were adsorbed on the surface of γ-Al₂O₃ then attacked by ozone and the generated ROS from the decomposition of ozone.

FIG. 6.

FTIR spectra of 500–4,000 cm⁻¹ region of the reproduced γ-Al₂O₃ (calcined under 500°C for 2 h) after three times reuse in γ-Al₂O₃/O₃ process (c), γ-Al₂O₃ after three times reuse in γ-Al₂O₃/O₃ process (b), and γ-Al₂O₃ after three times reuse in γ-Al₂O₃ alone process (a).

After three runs of ozonation, γ-Al₂O₃ particles were removed from the solution and dried at 75°C then calcined at 500°C for 2 h. The same dosage (50 g/L) of calcined γ-Al₂O₃ was used in another ozonation experiment and showed a similar COD removal efficiency (70%) to the unused γ-Al₂O₃ (70%). The result suggests that a calcination at 500°C can remove the adsorbed pollutants on the surface of γ-Al₂O₃ completely realizing regeneration of γ-Al₂O₃. However, the high cost of this regeneration method limits the application of γ-Al₂O₃ to catalyzing ozonation for the treatment of landfill leachate RO concentrate.

Summaries

In this study, the landfill leachate RO concentrate was treated by γ-Al₂O₃/O₃ process, and the optimal operational parameters (γ-Al₂O₃ dosage of 50 g/L, ozone dosage of 22 mg/min, initial pH of 7.3, reaction temperature of 30°C, treatment time of 30 min) were obtained in this study. Under the optimal conditions, the γ-Al₂O₃/O₃ system reached 70% COD and 100% color removal efficiencies. Meanwhile, B/C ratio was enhanced from 0.01 to 0.2, which suggests that its biodegradability was improved to some extent. In addition, the treatment ability of γ-Al₂O₃/O₃ process was higher than other two control experiments, and the superiority of this process was further confirmed by the analysis results of UV-vis, EEM, and FTIR spectra. Subsequently, we found that the intermediates of pollutants were absorbed on the surface of γ-Al₂O₃ in the γ-Al₂O₃/O₃ process.

At the same time, some pollutants were adsorbed on the surface of γ-Al₂O₃ then degraded by ozone and the generated ROS from the decomposition of ozone. Finally, calcination was confirmed to be an effective method for the regeneration of γ-Al₂O₃ but the high cost might limit its wider application. If the desorption of pollutants from γ-Al₂O₃ could be obtained economically, then, γ-Al₂O₃/O₃ process will be a promising technology for the treatment of landfill leachate RO concentrate.

Footnotes

Acknowledgments

The authors acknowledge the financial support from Funds for Innovation and Entrepreneurship Training for College Students (Sichuan University) and Science and Technology Project of Sichuan Province (2016JY0154).

Author Disclosure Statement

No competing financial interests exist.

References

Aboussaoud

, Manero

M.-H.

, Pic

J.-S.

, and Debellefontaine

(2014). Combined ozonation using alumino-silica materials for the removal of 2,4-dimethylphenol from water. Ozone Sci. Eng., 36, 221.

Ahmed

F.N.

, and Lan

C.Q.

(2012). Treatment of landfill leachate using membrane bioreactors: A review. Desalination, 287, 41.

Ahn

S.C.

, Oh

S.-Y.

, and Cha

D.K.

(2008). Enhanced reduction of nitrate by zero-valent iron at elevated temperatures. J. Hazard. Mater., 156, 17.

Amaral-Silva

, Martins

R.C.

, Castro-Silva

, and Quinta-Ferreira

R.M.

(2016). Ozonation and perozonation on the biodegradability improvement of a landfill leachate. J. Environ. Chem. Eng., 4, 527.

Barndõk

, Blanco

, Hermosilla

, and Blanco

. (2016). Heterogeneous photo-Fenton processes using zero valent iron microspheres for the treatment of wastewaters contaminated with 1,4-dioxane. Chem. Eng. J., 284, 112.

Bila

D.M.

, Filipe Montalvão

, Silva

A.C.

, and Dezotti

(2005). Ozonation of a landfill leachate: Evaluation of toxicity removal and biodegradability improvement. J. Hazard. Mater., 117, 235.

Chou

Y.-C.

, Lo

S.-L.

, Kuo

, and Yeh

C.-J.

(2015). Microwave-enhanced persulfate oxidation to treat mature landfill leachate. J. Hazard. Mater., 284, 83.

Chu

Y.-Y.

, Zhu

M.-H.

, and Liu

(2015). Electrochemical treatment of biotreated landfill leachate using a porous carbon nanotube-containing cathode: Performance, toxicity reduction, and biodegradability enhancement. Environ. Eng. Sci., 32, 445.

Chys

, Oloibiri

V.A.

, Audenaert

W.T.M.

, Demeestere

, and Van Hulle

S.W.H.

(2015). Ozonation of biologically treated landfill leachate: Efficiency and insights in organic conversions. Chem. Eng. J., 277, 104.

10.

Cortez

, Teixeira

, Oliveira

, and Mota

(2011). Evaluation of Fenton and ozone-based advanced oxidation processes as mature landfill leachate pre-treatments. J. Environ. Manage., 92, 749.

11.

Fernandes

, Pacheco

M.J.

, Ciríaco

, and Lopes

(2015). Review on the electrochemical processes for the treatment of sanitary landfill leachates: Present and future. Appl. Catal. B Environ., 176, 183.

12.

Gupta

, Zhao

, Novak

J.T.

, and Douglas Goldsmith

(2014). Application of Fenton's reagent as a polishing step for removal of UV quenching organic constituents in biologically treated landfill leachates. Chemosphere. 105, 82.

13.

Hasar

, Unsal

S.A.

, Ipek

, Karatas

, Cınar

, Yaman

, and Kınacı

(2009). Stripping/flocculation/membrane bioreactor/reverse osmosis treatment of municipal landfill leachate. J. Hazard. Mater., 171, 309.

14.

X.-S.

, Xi

B.-D.

, Wei

Z.-M.

, Jiang

Y.-H.

, Yang

, An

, Cao

J.-L.

, and Liu

H.-L.

(2011). Fluorescence excitation—Emission matrix spectroscopy with regional integration analysis for characterizing composition and transformation of dissolved organic matter in landfill leachates. J. Hazard. Mater., 190, 293.

15.

Hua

, Ma

, and Zhang

(2013). Degradation process analysis of the azo dyes by catalytic wet air oxidation with catalyst CuO/γ-Al2O3. Chemosphere. 90, 143.

16.

Hunce

S.Y.

, Akgul

, Demir

, and Mertoglu

(2012). Solidification/stabilization of landfill leachate concentrate using different aggregate materials. Waste Manage. 32, 1394.

17.

Hung

H.M.

, Ling

F.H.

, and Hoffmann

M.R.

(2000). Kinetics and mechanism of the enhanced reductive degradation of nitrobenzene by elemental iron in the presence of ultrasound. Environ. Sci. Technol., 34, 1758.

18.

Ikhlaq

, Brown

D.R.

, and Kasprzyk-Hordern

(2012). Mechanisms of catalytic ozonation on alumina and zeolites in water: Formation of hydroxyl radicals. Appl. Catal. B Environ., 123, 94.

19.

Jung

, Deng

, Zhao

, and Torrens

(2017). Chemical oxidation for mitigation of UV-quenching substances (UVQS) from municipal landfill leachate: Fenton process versus ozonation. Water Res. 108, 260.

20.

Kasprzyk-Hordern

, Ziółek

, and Nawrocki

(2003). Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment. Appl. Catal. B: Environ., 46, 639.

21.

Kattel

, and Dulova

(2017). Ferrous ion-activated persulphate process for landfill leachate treatment: Removal of organic load, phenolic micropollutants and nitrogen. Environ. Technol., 38, 1223.

22.

Kattel

, Trapido

, and Dulova

(2016). Treatment of landfill leachate by continuously reused ferric oxyhydroxide sludge-activated hydrogen peroxide. Chem. Eng. J., 304, 646.

23.

Kurniawan

T.A.

, and Lo

W.-H.

(2009). Removal of refractory compounds from stabilized landfill leachate using an integrated H2O2 oxidation and granular activated carbon (GAC) adsorption treatment. Water Res. 43, 4079.

24.

Labiadh

, Fernandes

, Ciríaco

, Pacheco

M.J.

, Gadri

, Ammar

, and Lopes

(2016). Electrochemical treatment of concentrate from reverse osmosis of sanitary landfill leachate. J. Environ. Manage., 181, 515.

25.

Lai

, Chen

Z.Y.

, Zhou

Y.X.

, Yang

, Wang

J.L.

, and Chen

Z.Q.

(2013). Removal of high concentration p-nitrophenol in aqueous solution by zero valent iron with ultrasonic irradiation (US-ZVI). J. Hazard. Mater., 250, 220.

26.

Lenz

, Böhm

, Ottner

, and Huber-Humer

(2016). Determination of leachate compounds relevant for landfill aftercare using FT-IR spectroscopy. Waste Manage. 55, 321.

27.

, Wang

, Liu

, Wei

, and Chen

(2016). Advanced treatment of municipal wastewater by nanofiltration: Operational optimization and membrane fouling analysis. J. Environ. Sci., 43, 106.

28.

, Yuan

, Qiu

, Wang

, Pan

, Wang

, and Zuo

(2013). Effective degradation of refractory organic pollutants in landfill leachate by electro-peroxone treatment. Electrochim. Acta, 102, 174.

29.

Lien

H.-L.

, and Zhang

W.-X.

(2007). Nanoscale Pd/Fe bimetallic particles: Catalytic effects of palladium on hydrodechlorination. Appl. Catal. B: Environ., 77, 110.

30.

Martins

R.C.

, Lopes

D.V.

, Quina

M.J.

, and Quinta-Ferreira

R.M.

(2012). Treatment improvement of urban landfill leachates by Fenton-like process using ZVI. Chem. Eng. J., 192, 219.

31.

Mecozzi

, Pietroletti

, Gallo

, and Conti

M.E.

(2009). Formation of incubated marine mucilages investigated by FTIR and UV–VIS spectroscopy and supported by two-dimensional correlation analysis. Marine Chem. 116, 18.

32.

Moreira

F.C.

, Soler

, Fonseca

, Saraiva

, Boaventura

R.A.R.

, Brillas

, and Vilar

V.J.P.

(2016). Electrochemical advanced oxidation processes for sanitary landfill leachate remediation: Evaluation of operational variables. Appl. Catal. B Environ., 182, 161.

33.

Nawrocki

, and Kasprzyk-Hordern

(2010). The efficiency and mechanisms of catalytic ozonation. Appl. Catal. B Environ., 99, 27.

34.

Ntampou

, Zouboulis

A.I.

, and Samaras

(2006). Appropriate combination of physico-chemical methods (coagulation/flocculation and ozonation) for the efficient treatment of landfill leachates. Chemosphere, 62, 722.

35.

Oloibiri

, Ufomba

, Chys

, Audenaert

W.T.M.

, Demeestere

, and Van Hulle

S.W.H.

(2015). A comparative study on the efficiency of ozonation and coagulation—Flocculation as pretreatment to activated carbon adsorption of biologically stabilized landfill leachate. Waste Manage. 43, 335.

36.

Oulego

, Collado

, Laca

, and Díaz

(2015). Tertiary treatment of biologically pre-treated landfill leachates by non-catalytic wet oxidation. Chem. Eng. J., 273, 647.

37.

Pocostales

, Álvarez

, and Beltrán

F.J.

(2011). Catalytic ozonation promoted by alumina-based catalysts for the removal of some pharmaceutical compounds from water. Chem. Eng. J., 168, 1289.

38.

, Xu

, Chen

, Feng

, Zhang

, and Sun

(2013). Catalytic ozonation of 2-isopropyl-3-methoxypyrazine in water by γ-AlOOH and γ-Al2O3: Comparison of removal efficiency and mechanism. Chem. Eng. J., 219, 527.

39.

Ren

, Yuan

, Lai

, Zhou

, and Wang

(2016). Treatment of reverse osmosis (RO) concentrate by the combined Fe/Cu/air and Fenton process (1stFe/Cu/air-Fenton-2ndFe/Cu/air). J. Hazard. Mater., 302, 36.

40.

Renou

, Givaudan

J.G.

, Poulain

, Dirassouyan

, and Moulin

(2008). Landfill leachate treatment: Review and opportunity. J. Hazard. Mater., 150, 468.

41.

Ruan

X.-C.

, Liu

M.-Y.

, Zeng

Q.-F.

, and Ding

Y.-H.

(2010). Degradation and decolorization of reactive red X-3B aqueous solution by ozone integrated with internal micro-electrolysis. Sep. Purif. Technol., 74, 195.

42.

Shao

Z.-H.

, He

P.-J.

, Zhang

D.-Q.

, and Shao

L.-M.

(2009). Characterization of water-extractable organic matter during the biostabilization of municipal solid waste. J. Hazard. Mater., 164, 1191.

43.

Silva

T.F.C.V.

, Fonseca

, Saraiva

, Boaventura

R.A.R.

, and Vilar

V.J.P.

(2016). Scale-up and cost analysis of a photo-Fenton system for sanitary landfill leachate treatment. Chem. Eng. J., 283, 76.

44.

Silva

T.F.C.V.

, Soares

P.A.

, Manenti

D.R.

, Fonseca

, Saraiva

, Boaventura

R.A.R.

, and Vilar

V.J.P.

(2017). An innovative multistage treatment system for sanitary landfill leachate depuration: Studies at pilot-scale. Sci. Total Environ., 576, 99.

45.

Syron

, Semmens

M.J.

, and Casey

(2015). Performance analysis of a pilot-scale membrane aerated biofilm reactor for the treatment of landfill leachate. Chem. Eng. J., 273, 120.

46.

Vicente

, Santos

, Romero

, and Rodriguez

(2011). Kinetic study of diuron oxidation and mineralization by persulphate: Effects of temperature, oxidant concentration and iron dosage method. Chem. Eng. J., 170, 127.

47.

Vittenet

, Aboussaoud

, Mendret

, Pic

J.-S.

, Debellefontaine

, Lesage

, Faucher

, Manero

M.-H.

, Thibault-Starzyk

, Leclerc

, et al. (2015). Catalytic ozonation with γ-Al2O3 to enhance the degradation of refractory organics in water. Appl. Catal A Gen., 504, 519.

48.

Wang

, Fan

, Wu

, Qin

, Zhang

, Gao

, and Meng

(2014). Anoxic/aerobic granular active carbon assisted MBR integrated with nanofiltration and reverse osmosis for advanced treatment of municipal landfill leachate. Desalination, 349, 136.

49.

, Zhang

, Shao

L.-M.

, and He

P.-J.

(2012). Fluorescent characteristics and metal binding properties of individual molecular weight fractions in municipal solid waste leachate. Environ. Pollut., 162, 63.

50.

, Zhou

, Zheng

, Ye

, and Qin

(2011). Mathematical model analysis of Fenton oxidation of landfill leachate. Waste Manage. 31, 468.

51.

B.-D.

, He

X.-S.

, Wei

Z.-M.

, Jiang

Y.-H.

, Li

, Pan

H.-W.

, and Liu

H.-L.

(2012). The composition and mercury complexation characteristics of dissolved organic matter in landfill leachates with different ages. Ecotoxicol. Environ. Safety, 86, 227.

52.

Xiong

, Cao

, Yang

, Lai

, and Yang

(2016a). Coagulation-flocculation as pre-treatment for micro-scale Fe/Cu/O3 process (CF-mFe/Cu/O3) treatment of the coating wastewater from automobile manufacturing. Chemosphere, 166, 343.

53.

Xiong

, Yue

, Bo

, Yang

, and Zhou

(2016b). Mineralization of ammunition wastewater by the micron-size Fe0/O3 process (mFe0/O3). RSC Adv. 6, 55726.

54.

, Zhao

, Shi

, Zhang

, and Ni

(2008). Electrolytic treatment of C.I. Acid Orange 7 in aqueous solution using a three-dimensional electrode reactor. Dyes Pigm., 77, 158.

55.

Yang

, Han

D.H.

, Lee

B.-M.

, and Hur

(2015). Characterizing treated wastewaters of different industries using clustered fluorescence EEM–PARAFAC and FT-IR spectroscopy: Implications for downstream impact and source identification. Chemosphere, 127, 222.

56.

Zayen

, Schories

, and Sayadi

(2016). Incorporation of an anaerobic digestion step in a multistage treatment system for sanitary landfill leachate. Waste Manage. 53, 32.

57.

Zhao

, Ji

, Kong

, Lu

, Zhou

, and Yin

(2016). Simultaneous removal of bisphenol A and phosphate in zero-valent iron activated persulfate oxidation process. Chem. Eng. J., 303, 458.

58.

Zhao

, Ma

, Sun

, and Zhai

(2008). Mechanism of influence of initial pH on the degradation of nitrobenzene in aqueous solution by ceramic honeycomb catalytic ozonation. Environ. Sci. Technol., 42, 4002.

59.

Zhou

, Yu

, Wei

, Long

, Xie

, and Wang

(2016). Electrochemical oxidation of biological pretreated and membrane separated landfill leachate concentrates on boron doped diamond anode. Appl. Surf. Sci., 377, 406.

Treatment of Landfill Leachate Reverse Osmosis Concentrate from by Catalytic Ozonation with γ-Al 2 O 3

Abstract

Abstract

Introduction

Experimental Protocols

Reagents

Landfill leachate RO concentrate

Batch experiments

Analytical methods

Results and Discussion

Influence of operational parameters on performance in γ-Al2O3/O3 system

Effects of γ-Al2O3 dosage on COD removal

Effects of O3 dosage on COD removal

Effects of initial pH on COD removal

Effects of reaction temperature on COD removal

Effects of treatment time on COD removal

Control experiments

Degradation of the pollutants and its improvement of biodegradability

UV-vis analysis

EEM spectral analyses

FTIR spectra analysis

Reuse of γ-Al2O3 in successive ozonation reactions

Regeneration of γ-Al2O3

Summaries

Footnotes

Acknowledgments

Author Disclosure Statement

References

Influence of operational parameters on performance in γ-Al₂O₃/O₃ system

Effects of γ-Al₂O₃ dosage on COD removal

Effects of O₃ dosage on COD removal

Reuse of γ-Al₂O₃ in successive ozonation reactions

Regeneration of γ-Al₂O₃