| 1. |
- Ren, Zhongfei, et al.
(author)
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Combination of adsorption/desorption and photocatalytic reduction processes for PFOA removal from water by using an aminated biosorbent and a UV/sulfite system
- 2023
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In: Environmental Research. - : Elsevier. - 0013-9351 .- 1096-0953. ; 228
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Journal article (peer-reviewed)abstract
- Per- and polyfluoroalkyl substances (PFAS) are stable organic chemicals, which have been used globally since the 1940s and have caused PFAS contamination around the world. This study explores perfluorooctanoic acid (PFOA) enrichment and destruction by a combined method of sorption/desorption and photocatalytic reduction. A novel biosorbent (PG-PB) was developed from raw pine bark by grafting amine groups and quaternary ammonium groups onto the surface of bark particles. The results of PFOA adsorption at low concentration suggest that PG-PB has excellent removal efficiency (94.8%–99.1%, PG-PB dosage: 0.4 g/L) to PFOA in the concentration range of 10 μg/L to 2 mg/L. The PG-PB exhibited high adsorption efficiency regarding PFOA, being 456.0 mg/g at pH 3.3 and 258.0 mg/g at pH 7 with an initial concentration of 200 mg/L. The groundwater treatment reduced the total concentration of 28 PFAS from 18 000 ng/L to 9900 ng/L with 0.8 g/L of PG-PB. Desorption experiments examined 18 types of desorption solutions, and the results showed that 0.05% NaOH and a mixture of 0.05% NaOH + 20% methanol were efficient for PFOA desorption from the spent PG-PB. More than 70% (>70 mg/L in 50 mL) and 85% (>85 mg/L in 50 mL) of PFOA were recovered from the first and second desorption processes, respectively. Since high pH promotes PFOA degradation, the desorption eluents with NaOH were directly treated with a UV/sulfite system without further adjustment. The final PFOA degradation and defluorination efficiency in the desorption eluents with 0.05% NaOH + 20% methanol reached 100% and 83.1% after 24 h reaction. This study proved that the combination of adsorption/desorption and a UV/sulfite system for PFAS removal is a feasible solution for environmental remediation.
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| 2. |
- Uwayezu, Jean Noel, et al.
(author)
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Combination of separation and degradation methods after PFAS soil washing
- 2023
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In: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 907
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Journal article (peer-reviewed)abstract
- The current study evaluated a three-stage treatment to remediate PFAS-contaminated soil. The treatment consisted of soil washing, foam fractionation (FF), and electrochemical oxidation (EO). The possibility of replacing the third stage, i.e., EO, with an adsorption process was also assessed. The contamination in the studied soils was dominated by perfluorooctane sulfonate (PFOS), with a concentration of 760 and 19 μg kg−1 in soil I and in soil II, accounting for 97 % and 70 % of all detected per-and polyfluoroalkyl substances (PFAS). Before applying a pilot treatment of soil, soil washing was performed on a laboratory scale, to evaluate the effect of soil particle size, initial pH and a liquid-to-soil ratio (L/S) on the leachability of PFAS. A pilot washing system generated soil leachate that was subsequently treated using FF and EO (or adsorption) and then reused for soil washing. The results indicated that the leaching of PFAS occurred easier in 0.063–1 mm particles than in the soil particles having a size below 0.063 mm. Both alkaline conditions and a continual replacement of the leaching solution increased the leachability of PFAS. The analysis using one-way ANOVA showed no statistical difference in means of PFOS washed out in laboratory and pilot scales. This allowed estimating twenty washing cycles using 120 L water to reach 95 % PFOS removal in 60 kg soil. The aeration process removed 95–99 % PFOS in every washing cycle. The EO and adsorption processes achieved similar results removing up to 97 % PFOS in concentrated soil leachate. The current study demonstrated a multi-stage treatment as an effective and cost-efficient method to permanently clean up PFAS-contaminated soil.
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| 3. |
- Uwayezu, Jean Noel, et al.
(author)
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Combining electrochemistry and ultraviolet radiation for the degradation of per- and poly-fluoroalkyl substances in contaminated groundwater and wastewater
- 2023
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In: Journal of Water Process Engineering. - : Elsevier. - 2214-7144. ; 54
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Journal article (peer-reviewed)abstract
- Electrochemical and ultraviolet-based methods are advanced oxidation processes emerging as viable water and wastewater treatment options. In this study, a combination of these two methods (EO-UV) using boron-doped diamond (BDD) electrodes and ultraviolet radiation at both 185 and 254 nm was assessed for the degradation of poly-fluoroalkyl substances (PFAS). Sodium persulfate (Na2S2O8) and sodium sulfate (Na2SO4) were used as electrolytes. The method was investigated on model solutions containing perfluorooctanoic acid (PFOA) and perfluorosulfonic acid (PFOS). The method's effectiveness was assessed by comparing PFAS removal efficiencies and energy demands associated with the use of separate and combined treatments. The results showed that the highest removal of PFOA and PFOS was 96 % and 85 % respectively, which was achieved using EO-UV and persulfate electrolytes. Average removal efficiencies were 1.5–2 times higher in EO-UV than in EO and 4–6 times higher than in UV treatment. The degradation of PFAS under EO-UV and persulfate applied to PFAS-contaminated groundwater and wastewater reached 94 % PFOA and 88 % PFOS in groundwater and 51 % and 63 % in wastewater. The removal of the sum of eleven PFAS was 86 % and 66 % in groundwater and wastewater, respectively. The combination of EO, UV and persulfate was the most effective option for PFAS treatment at lower energy consumption.
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| 4. |
- Uwayezu, Jean Noel
(author)
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Remediation of PFAS-contaminated soil and wastewater : Feasibility of chain treatment applying destructive techniques
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals ubiquitously distributed in soil and aquatic media, resulting from their wide range of industrial applications. Today, PFAS is a global concern due to their persistence in the environment and their adverse effects on humans and the ecosystem. Despite the considerable efforts to develop PFAS treatment methods, a viable solution has not yet been established.This Ph.D. thesis investigated the potential of applying electrochemical oxidation (EO) and UV radiation assisted with persulfate (PS/UV), both individually and in combination(EO-UV), for PFAS degradation in solutions. Furthermore, integrating destructive technique showing the most promising results, i.e., EO, within a treatment chain comprising soil washing (SW) and foam fractionation (FF) was assessed to eliminate PFAS from contaminated soil. Perfluorooctanesulfonic acid (PFOS) accounted for 97% of the PFAS contamination in the soil. The EO and PS/UV showed the potential to break down PFAS in spiked solutions. Removal of 99 % perfluorooctanoic acid (PFOA) was found at a current density of 23.4 mA cm-2 and 4 h whereas 80% PFOA, 60% PFOS, and 57% perfluorobutanoic acid (PFBA) were removed in 4 h and in the presence of 5 g L-1 Na2S2O8. By transferring the best experimental conditions for the treatment of PFAS-contaminated wastewater, the removal of 56% ∑11PFAS was reached using EO whereas PS/UV led to an increase in the concentration of PFAS. It was highlighted that optimizing EO would lead to higher removal and reduce energy consumption. Nevertheless, PFAS removal from groundwater using PS/UV treatment was almost as effective as in synthetic solutions, highlighting its potential for treating PFAS in matrix-free water. Combining EO and UV led to substantial removal improvements due to degradation processes in both systems, probably due to synergistic effects. Adding FF to soil SW led to an average removal of 82% and 92% ∑11PFAS in soil and leachate respectively, at the L/S of 5 (five washing cycles) and pH 11.5. As per estimations, employing 20 treatment cycles could result in 94% and 91% of PFAS removal in soil and leachate. The EO at 60 mA cm-2 and 2 h removed 88.3% of ∑11PFAS, which was contained in wastewater resulting from the FF process. Overall, the SW-FF-EO three-stage treatment led to the removal of 67% ∑11PFAS, estimated to be 88% if the SW-FF consecutive treatments are repeated 20 times. Incorporating FF in the treatment chain enabled leachate recycling and reduced water volume needs in the soil treatment process, but also concentrated PFAS in a smaller water volume, thereby allowing the EO step to be more cost-effective.
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| 5. |
- Uwayezu, Jean Noel, et al.
(author)
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Validation of UV/persulfate as a PFAS treatment of industrial wastewater and environmental samples
- 2023
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In: Journal of Water Process Engineering. - : Elsevier. - 2214-7144. ; 53
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Journal article (peer-reviewed)abstract
- The contamination of natural water and industrial wastewater with per- and polyfluoroalkyl substances (PFAS) occurs globally. Thus, proper technologies are required to reduce PFAS in the environment and mitigate the adverse effects of these pollutants on human health and the environment. This study used a 23 full factorial design to evaluate the importance of operating factors including the level of persulfate (PS), the initial concentration of PFAS, and the time to the photochemical degradation of PFAS via ultraviolet irradiation at 185/254 nm assisted with persulfate (PS/UV method) in spiked solution. The method was then applied to break down PFAS in industrial wastewater, landfill leachate and groundwater samples using the highest factor levels applied in the 23 full factorial design. The results showed that the three investigated factors played an important role in the degradation of PFAS. The highest PFAS degradation was 57 % perfluorobutanoic acid (PFBA), 80 % perfluorooctanoic acid (PFOA) and 60 % perfluorooctane sulfonate (PFOS) using 10 mg L−1 PFAS, 5 g L−1 PS for 4 h. The defluorination also increased in the presence of PS but decreased in the presence of potassium hydrogen phthalate, nitrates, and chlorides. The PS/UV method decreased the concentration of PFAS in wastewater samples by 20–25 % PFOS and 13–15 % perfluorohexane sulfonate (PFHxS). PFAS degradation in wastewater improved with increasing treatment time. Under the PS/UV treatment, the degradation of major PFAS in groundwater was 94 % 6–2 FTS, 75 % PFOA, 62 % PFOS and 61 % PFHxS. The removal of major compounds in landfill leachate reached up to 12 % PFHxA, 32 % PFPeA, 56 % PFOA and 43 % PFOS. Our study indicated matrix effects leading to decreased PFAS degradation in different contaminated waters. The level of PS should also be controlled to an optimal value because higher levels led to a decrease in treatment efficiency.
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