Treatment of mature landfill leachate by electrocoagulation followed by Fenton or UVA-LED photo-Fenton processes

Combination of electrocoagulation with solar photo Fenton process for treatment of landfill leachate

The aim of the present work was to provide a viable and active way to remove COD and colour from landfill leachate treated by adopting combined process of electrocoagulation and solar photo Fenton process. Coagulating agents such as metal hydroxides are created by the electrolysis process through self-sacrificial electrodes. Aluminium and iron dissolves at the anode and hydrogen gas are generated at the cathode when aluminium and iron electrodes are utilised. The contaminants interact with the coagulating agent to generate enormous organic flocs. The leachate was obtained from a landfill in Madurai and then it was characterised in terms of its major predominant pollutants. In this study, the electrocoagulation process was used in conjunction with the solar photo Fenton process to treat the leachate under ideal conditions of pH = 7, NaCl = 2 g/L, voltage = 4 V, Al & Fe electrodes and inter electrode distance = 3 cm with a COD and colour removal effectiveness of 75% and 76%, respectively. Furthermore, the effluent from the electrocoagulation process was treated using a solar photo Fenton process at pH = 3, H2O2 = 10 g/L and Fe2+ = 1 g/L with COD and colour reduction effectiveness of 90% and 91%, respectively. In this combination of treatment systems, leachate biodegradability increased from 0.35 to 0.73, favouring the biological oxidation process in conventional treatment plants. This research demonstrates that employing this paired electrocoagulation-solar photo Fenton to treat landfill leachate can achieve consistent treatment effects with high removal efficiencies, and that it is an acceptable treatment technique for landfill leachate.

Pd/MIL-100(Fe) as hydrogen activator for FeIII/FeII cycle: Fenton removal of sulfamethazine

Masses of iron sludge generated from engineering practice of classic Fenton reaction constraints its further promotion. Accelerating the FeIII/FeII cycle may be conducive to reducing the initial ferrous slat dosage and the final iron sludge. Based on the reduction of Pd/MIL-100(Fe)-activated hydrogen, an improved Fenton system named MHACF-MIL-100(Fe) was developed at ambient temperature and pressure. 97.8% of sulfamethazine, the target pollutant in this work, could be degraded in 5 min under the conditions of 20 mM H2O2, 25 μM ferrous chloride, initial pH 3.0, 2 g·L-1 composite catalyst Pd/MIL-100(Fe) and hydrogen gas 60 mL·min-1. Combining density functional theory (DFT) calculation and intermediate detection, the degradation of this antibiotic was inferred to start from the cleavage of N-S bond. The catalytic of Pd/MIL-100(Fe), demonstrated by the removal efficiency of SMT and the catalyst morphology, remained intact after six reaction cycles. The present study provides an insight into the promotion of Fenton reaction.

Modelling and optimisation of electrocoagulation/flocculation recovery of effluent from land-based aquaculture by artificial intelligence (AI) approaches

This study examined the modelling and optimisation of the electrocoagulation-flocculation (ECF) recovery of aquaculture effluent (AQE) using aluminium electrodes. The response surface methodology (RSM), artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) were used for the modelling, while the optimisation tools were the numerical RSM and genetic algorithm (GA). Furthermore, the kinetics of the ECF process was studied to provide insight into the mechanism governing the ECF of AQE. The experimental design was performed using the central composite design (CCD) of the RSM. The ANFIS modelling was accomplished via the Grid Partition (GP) of the data set, while the ANN used the multi-layer perceptron (MLP) based feed-forward system. Statistically, the prediction accuracy of the models followed the order: ANFIS (R²: 0.9990), ANN (R²: 0.9807), and RSM (R²: 0.9790). The process optimisation gave optimal turbidity (TD) removal efficiencies of 98.98, 97.81, and 96.01% for ANFIS-GA, ANN-GA, and RSM optimisation techniques, respectively. The ANFIS-GA gave the best optimization result at optimum conditions of pH 4, current intensity (3 A), electrolysis time (7.2 min), settling time (23 min), and temperature (43.8 °C). In the kinetics study, the experimental data was analysed using pseudo-first-order (0.8787), pseudo-second-order (0.9395), and Elovich (R²: 0.9979) kinetic models; the Elovich model gave the best correlation with the experimental data showing that the process is governed by electrostatic interaction mechanism. This study effectively demonstrated that ECF recovery of AQE can effectively be modelled using RSM, ANN, and ANFIS and be optimised using RSM, ANN-GA, and ANFIS-GA techniques, and the order of performance is ANFIS > ANN > RSM and ANFIS-GA > ANN-GA > RSM, respectively.

Tertiary treatment of bio-treated landfill leachate by a two-step electrochemical process including electrooxidation and electrocoagulation: a bench-scale trial

A two-step electrochemical process including electrooxidation (EO) and electrocoagulation (EC) was proposed for the tertiary treatment of bio-treated landfill leachate (BTLL). The operating conditions of sole EO and EC technology were optimized via batch tests. Batch tests indicate that EO displayed superior removal efficiency towards color (89%) and UV₂₅₄ (64%) under optimal experimental conditions. EC with the electrode combinations Fe-Fe-Fe-Fe (four plates, anode-cathode-anode-cathode) performed better than the other electrode combinations (Fe-Al-Fe-Al, Al-Fe-Al-Fe, Al-Al-Al-Al) and showed excellent removal efficiency towards COD (60%) and color (85%). In continuous-flow tests of 13 h, compared to sequential EC-EO process, the sequential EO-EC process was more effective than the sequential EC-EO process in reducing organic matters (COD, TOC) and residual chlorine. The sequential EO-EC process could remove 50% COD, 55% TOC, 72% UV₂₅₄, and 96% color. The average concentration of residual chlorine in the final effluent of EO-EC process (147 mg/L) was significantly lower than that of EC-EO process (463 mg/L). UV-vis and GC-MS analyses indicate that the BTLL mainly contained humic acid and fulvic acid-like substances with unsaturated bonds. Conjugated unsaturated organics could be degraded into organic of small molecular weight after the sequential EO-EC process. EEM spectroscopic analysis revealed that soluble microbial byproducts became the predominant organics in the final effluent. This work verifies the synergism between EO and EC and provides some insights into the removal and degradation performance of organic substances in BTLL during the sequential EO-EC treatment.

Optimization and kinetic modeling of phosphate recovery as struvite by electrocoagulation from source-separated urine

Phosphorus recovery is indispensable due to the rapid depletion of its natural reserves and excessive utility in agriculture. Though human urine has high nutrient content including phosphate, nitrogen and potassium; direct use as a fertilizer is restricted due to hygienic, environmental, social and ethical issues. To overcome these limitations, the nutrients are precipitated by the external addition of magnesium (Mg) to form a slow-releasing fertilizer called struvite. The present study aims to maximize phosphate recovery through optimizing struvite production by an emerging electrocoagulation technique. A maximum of 95% phosphate recovery was achieved using inter-electrode distance of 0.5 cm, 2 A current from undiluted urine using Mg-Mg electrodes in a reaction time of 30 min. Further, kinetic modeling of phosphate recovery through electrocoagulation was conducted to comprehend the intended mechanism through the order of kinetics. The results revealed that the data best correlated with first-order kinetics with a correlation coefficient of 0.95. Electrocoagulation improved the supernatant quality by reducing the ion concentrations other than phosphate (30-50%), salinity (40-45%), and microbial population (99%). Qualitative assessment of the precipitate through sophisticated analysis further confirmed the presence of struvite crystals.

Leachate decontamination through biological processes coupled to advanced oxidation: A review

The landfill leachate is considered a toxic effluent composed of recalcitrant contaminants that requires innovative alternatives for its decontamination. Coupling between advanced oxidation processes (AOPs) and aerobic biological treatments are highlighted in this research. Therefore, a bibliographic review of the research made from 2010 to 2021 was developed. These combined alternatives were applied in leachates, and it is oriented toward the analysis of knowledge gaps, trends, and future proposals of the treatment combined that contribute to researchers who wish to work on the subject. These kinds of treatments were chosen due to a bibliometric analysis made. Also, the information was searched in several scientific database. This work was found to be unpublished, as no reviews were found so far that agglomerate studies of coupling between photocatalytic and aerobic biological processes to treat leachates. Besides, AOPs are ideal for treating wastewater of complex composition, however, when it is used as the only treatment, they are usually unprofitable, which justifies their coupling with biological treatments. Subsequently, it was determined that the knowledge main gap is the lack of documentation of treatment costs, which makes it difficult to implement on a real scale. In addition to this, the couplings trends are toward doping with metallic and nonmetallic ions of the catalyst used in the photocatalytic process to improve the efficiency of these. Finally, future research should work on finding alternatives that allow the optimization of the resources used in the combined systems and on promoting the recovery of existing products in the leachate.Implications: Leachates generate several environmental impacts due to their toxic composition. Even when coupling between heterogeneous photocatalysis and biologic treatment can solve them, issues like cost analysis and the scaling-up factor have not been developed, and futures researchers should work on that. Besides, the trend founded in almost all investigations was the catalyst doping with metals and nonmetals ions, particularly when they use TiO2 because it gives the possibility of improving efficiencies just with a structural variation. Finally, these treatment combinations require more analyses and comparison of their remotion over emerging pollutants and their performance with new designs.

Treatment of Olefin plant spent caustic by combination of Fenton-like and foam fractionation methods in a bench scale

Spent Merox caustic (SMC) is a hazardous waste that is produced during the Merox desulfurization process in the petroleum refinery industry and should be treated before discharging to environment. In the present study, treatment of SMC was investigated by three methods including Fenton-like process, foam fractionation, and a combination of both processes. Immobilized TiO₂/Fe⁰ on modified silica nanoparticles was used as a heterogeneous Fenton-like catalyst. The chemical and physical characteristics of the catalyst were determined using Fourier-transform infrared spectroscopy, X-ray diffraction, diffuse reflectance spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and transmission electron microscopy techniques. The treatment performance of the combined method was measured as a cost-effective method with chemical oxygen demand (COD) removal percentage. The effect of parameters including pH, gas flow rate, surfactant type and concentration of hydrogen peroxide, catalyst, and chelate were investigated. It is found that the prepared heterogeneous catalyst has high activity for the treatment of SMC. In addition, the results showed that the combined method achieved 97.6 ± 0.5% COD removal, while the measured values for Fenton or foam fractionation methods alone did not exceed 85.5 ± 1% and 47.2 ± 0.4%, respectively. The advantage of combination process over foam fractionation was the use of an advanced oxidation process in the separating column to eliminate or reduce the secondary phase contamination load. Besides, the role of the column in the effective contact of contaminants with the rising bubbles improved the degradation performance of the proposed process and reduced the consumption of hydrogen peroxide by 46% compared to the Fenton-like method.

Micro- and Macroelements Content of Plants Used for Landfill Leachate Treatment Based on Phragmites australis and Ceratophyllum demersum

One of the key problems associated with the functioning of landfills is the generation of leachate. In order to reduce their negative impact on the environment, various treatment technologies are applied. Among them, solutions based on the use of phytotechnology deserve special attention. The aim of this study was to evaluate the impact of landfill leachate on the content of micro- and macroelements in plant material. The research was carried out in four municipal waste landfills located in Poland. Emergent macrophytes (P. australis) and submergent macrophytes (C. demersum) were used in this research. The migration and distribution of pollutants reaching the roots and shoots of P. australis from water solutions were also studied. The concentrations of heavy metals in the studied plants were low in all analysed cases. Higher metal contents could often be observed in roots rather than in shoots, but these differences were insignificant. The chemical composition of the studied plant samples was primarily related to the source of origin of the treated leachate (landfill), as clearly demonstrated by cluster analysis. In the conducted studies, no important differences were noted in the accumulation of the studied components between submergent plants (C. demersum) and emergent macrophytes (P. australis).

Investigating the Electrocoagulation Treatment of Landfill Leachate by Iron/Graphite Electrodes: Process Parameters and Efficacy Assessment

Electrocoagulation is a widely used method for treating leachate since it is cost effective and eco-friendly. In the present study, the electrocoagulation process was employed to remove chemical oxygen demand (COD), NH4+, total dissolved solids (TDS), total suspended solids (TSS), turbidity, and color from landfill leachate. At first, lime was used as a pretreatment, then the Fe/Gr and Ti/PbO2/steel electrodes were used, and the optimum electrode was selected. Afterwards, the effects of some variables, including pH, current density, temperature, the inter-electrode distance, and the type of electrolyte were investigated. Results showed that COD, NH4+, TSS, TDS, electrical conductivity (EC), turbidity, color, and pH of effluent pretreatment chemical reached 22,371, 385, 884, 21,820 (mg/L), 13.8 (ms/cm3), 1355 (NTU), 8500 (TCU) and 10, respectively (the removal efficiency was 0, 20.37, 32.4, 61.99, 59.18, and 56.6 percent). With the Fe/Gr electrode, the optimal condition was observed as follows: pH of 7.5, current density of 64 mA/cm2, inter-electrode distance was equal to 1.5 cm, temperature at 20 °C, and retention time 2–4 h. Overall, the electrocoagulation with the Fe/Gr electrode was a suitable technology for landfill leachate treatment due to its effectiveness for the removal of both COD and NH4+, with advantageous performance indicators.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Combining Coagulation and Electrocoagulation with UVA-LED Photo-Fenton to Improve the Efficiency and Reduce the Cost of Mature Landfill Leachate Treatment

This study focused on the reduction of the treatment cost of mature landfill leachate (LL) by enhancing the coagulation pre-treatment before a UVA-LED photo-Fenton process. A more efficient advanced coagulation pretreatment was designed by combining conventional coagulation (CC) and electro-coagulation (EC). Regardless of the order in which the two coagulations were applied, the combination achieved more than 73% color removal, 80% COD removal, and 27% SUVA removal. However, the coagulation order had a great influence on both final pH and total dissolved iron, which were key parameters for the UVA-LED photo-Fenton post-treatment. CC (pH = 5; 2 g L^-1 of FeCl₃6H₂O) followed by EC (pH = 5; 10 mA cm^-2) resulted in a pH of 6.4 and 100 mg L^-1 of dissolved iron, whereas EC (pH = 4; 10 mA cm^-2) followed by CC (pH = 6; 1 g L^-1 FeCl₃6H₂O) led to a final pH of 3.4 and 210 mg L^-1 dissolved iron. This last combination was therefore considered better for the posterior photo-Fenton treatment. Results at the best cost-efficient [H₂O₂]:COD ratio of 1.063 showed a high treatment efficiency, namely the removal of 99% of the color, 89% of the COD, and 60% of the SUVA. Conductivity was reduced by 17%, and biodegradability increased to BOD₅:COD = 0.40. With this proposed treatment, a final COD of only 453 mg O₂ L^-1 was obtained at a treatment cost of EUR 3.42 kg COD^-1.