Full-scale treatment of landfill leachate by using the mechanical vapor recompression combined with coagulation pretreatment

Simultaneous nitrification and denitrification in a hybrid activated sludge-membrane aerated biofilm reactor (H-MABR) for nitrogen removal from low COD/N interflow: A pilot-scale study

There are a large number of simple landfills in hilly areas, and the results of previous studies have shown that pollutants in landfills can spread via interflow and cause surface source pollution. The hybrid activated sludge-membrane aerated bioreactor (H-MABR) developed in a previous study can be used for the treatment of interflow with a low chemical oxygen demand (COD)/total nitrogen (TN) ratio, and it has been shown to be effective in laboratory simulations. To investigate the effectiveness of the H-MABR in treating interflow around landfills in real-world applications, an in-situ pilot-scale evaluation of the effectiveness of H-MABR operation was conducted at a landfill. The results indicated that the removal efficiencies of COD, TN, and ammonia nitrogen in interflow by H-MABR were 87.1 ± 6.0%, 80.9 ± 7.9%, and 97.9 ± 1.4%, respectively. The removal rate of TN reached 148.6-205.6 g-N/m3·d. The concentration of each pollutant in the effluent was in accordance with China's "Standard for pollution control on the landfill site of municipal solid waste (GB16889-2008)," wherein the COD, TN, and ammonia nitrogen of effluent should be less than 100 mg/L, 40 mg/L, and 25 mg/L, respectively. The results of community composition analysis and PICRUSt analysis based on 16S rRNA gene sequencing showed that there were different dominant functional bacteria between the inner and outer rings, but functional genes involved in the nitrification-denitrification, assimilated nitrate reduction, and dissimilated nitrate reduction pathway were all detected. Furthermore, except for the nitrite oxidation gene narG, the abundance of which did not significantly differ between the inner and outer rings, the abundance of the other functional genes was higher in the outer ring than in the inner ring. An economic evaluation revealed that the operation cost of interflow treatment by the H-MABR was as low as ¥2.78/m3; thus, the H-MABR is a shock-load-resistant and cost-effective technology for interflow treatment.

Gas-liquid contact evaporation of concentrate leachate from disk-tube reverse osmosis treatment in waste incineration plant

In order to utilize waste heat such as exhaust steam and hot air passing through air preheater in the waste incineration plant to heat air used for evaporating leachate concentrate (LC) by gas-liquid contact evaporation technology, hot air of 600 °C, 450 °C and 250 °C was used to evaporate LC in a laboratory-scale evaporator to obtain purified condensate used for supplying water for circulating cooling water system. The influence of pH, hot air temperature and evaporation rate on COD and NH3-N in condensate were investigated to identify the optimum operation of this technology. The results showed that COD concentration in condensate obviously decreased with increase in hot air temperature. Higher hot air temperature led to higher initial evaporation temperature, and evaporation rate of water was significantly greater than that of small molecular organic matter with lower boiling point than water with increasing hot air temperature. Reduction in contents of phenol, ketone and benzene was responsible for COD decreasing in condensate. COD in condensate decreased with increase in pH, as the amount of volatile organic matter such as fatty acids escaped from LC to condensate decreased. The pH had little influence on the DOM in condensate according to EEM spectra analysis. Evaporation rate had little influence on COD in the condensate water. NH3-N concentrations in condensate in all experimental groups were far away from the limit value (10 mg/L) in the water quality standard. Under the premise of meeting water quality standard, the lowest temperature (450 °C) of hot air was selected to save energy and use lower grade waste heat. Therefore, the optimum condition was 450 °C of hot air, pH = 7 of LC and CF = 10. At this condition, molecular weight of DOM in the condensate was smaller and humification degree and aromaticity of DOM were lower according to UV-visible absorption spectrum analysis.

Effective treatment of leachate concentrate from waste incineration plant by combination of coagulation and direct contact evaporation

In order to verify that coagulation as pre-treatment can reduce the temperature of the hot air used for direct contact evaporating the leachate concentrate (LC) and low-grade waste heat such as exhaust steam in the waste incineration plant can be used to evaporate the LC. The supernatants after coagulation using polymerized ferrous sulfate (PFS), polymeric-aluminum (PAC), polymeric silicate aluminum ferric (PSAF) and poly-aluminum ferric chloride (PAFC) as coagulants were further treated in a lab-scale direct contact evaporation system. The results showed that the best performance with removal efficiencies of COD and NH3-N of 58.70% and 29.09% was achieved after coagulation when PAFC dosage = 15 g/L, PAM dosage = 30 mg/L and initial pH of supernatant = 6. After coagulation, a large amount of the fulvic-like acid and aromatic heterocyclic compounds were removed and the degree of complexity and aromaticity of organics decreased. After direct contact evaporation, using PAFC as coagulant still was the best selection due to its lowest concentrations of COD and NH3-N (22 mg/L and 1.02 mg/L) in the condensate produced by this two-stage treatment when initial pH of supernatant was 6 during evaporation and the condensate produced by this two-stage treatment met the water quality standard for using as supplying water for circulating cooling water system when temperature of hot air used for heating LC was at low temperature (250 °C). The fulvic-like acid and aromatic heterocyclic compounds in the condensate continuously reduced. Phenol, adamantane, 1-isocyanato, phthalic anhydrid, tri(2-chloroethyl) phosphat, Heptadecane, 2-methyl, ginsenol and Octadecane, 2-methyl- in the condensate obviously decreased. The effect of four coagulants as pretreatment on reducing the temperature of hot air used for evaporating LC was ranked as PAFC > PFS > PAC > PSAF. PSAF was not recommended due to the large amount of NH3-N produced when using PSAF to treat the LC.

Evaluation of volatile fatty acids and ammonia recovery approach from landfill leachate using pilot-scale mechanical vapor recompression

Treatment of landfill leachate is still a current problem due to the high treatment costs in addition to the difficulty of meeting the discharge criteria. However, there is a more important issue that should be underlined; it is also valuable compounds that leachate contains. Conventional methods used for treatment of leachate such as membrane filtration, advanced oxidation processes, biological processes and their combinations have largely focused on treatment. However, the recovery of ammonia and volatile organic acids (VFA) in leachate is a promising approach both to overcome high treatment costs and to sustainably manage leachate. In this study, leachate treatment potential was investigated by mechanical vapor recompression (MVR) process, which offers an operational opportunity to recover high value-added products from leachate while providing an effective treatment for wastewater. Optimum operating conditions for the pilot-scale MVR process have been determined by laboratory-scale studies. VFAs were recovered as organic acid salts from the pilot-scale MVR distillate, while ammonia recovery was accomplished as ammonium sulfate from a highly contaminated concentrate stream. VFA and ammonia recovery rates were 89% and 99%, respectively. The treatment cost of leachate with MVR process was calculated according to the data obtained in pilot scale MVR studies considering the operating cost, chemical cost and economical contribution of value-added products. The results showed that the integrated MVR-crystallization process, all treatment costs are covered, with a net gain of 3.8 USD/m3. Consequently, MVR integrated crystallization process offers an economical and sustainable solution for the treatment of leachate by recovering valuable products.

Simultaneous production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from recovered volatile fatty acid with treatment of leachate by Pilot-Scale Mechanical Vapor Recompression

Serious global problems faced due to many petroleum-based materials in the last century, which is called the plastic age, constitute the main motivation of this research. Considering wastewater treatment from this perspective, both the recovery of organic acids from wastewater and their conversion into bioplastics are extremely important in terms of reducing petroleum dependency. In this study, while the treatment of landfill leachate was provided with biological process integrated into Mechanical Vapor Recompression (MVR), simultaneously PHBV production was carried out with 84.9% recovered VFA as carbon source. The effects of C/N/P ratio and feeding regime on PHBV storage were investigated by Cupriavidus necator. PHBV storage of 96% (g PHBV/g DCW) was maximized by 2-stage feeding and nitrogen restriction. The ratio of 3HV to 3HB of PHBV was 45%. In addition, extracted PHBV was compared with standard PHA in terms of thermal and chemical properties with FTIR, XRD, TGA and DSC analyses.

Critical role of Photo-electrode with Ce-g-C3N4 in multi-stage microbial fuel cells cascade reactor treating diluted hyper-saline industrial wastewater rich in amines

Treatment of chemical industrial wastewater often faces problems of large volume occupation, high cost, and long processing time. In this study, low-content Ce-modified g-C₃N₄ was prepared and used as a catalyst on stainless steel mesh photo-cathode in constructing a multi-stage cascade microbial fuel cell system to reduce treatment costs in an energy-saving way. The large specific surface area (332.5 m² g^-1) and mesoporous structure of the material, is favorable for catalytic reactions, in which Ce elements were mainly present in single atoms. The characterized catalyst indicated a pronounced effect of Ce species in increasing photo-current and the synergistic pollutant removal, microbial bio-degradation and cascade operation stability. In Batch-mode (light illumination, aeration, total HRT (hydraulic residence time) of 54 h) treatment through three cascade reactors, removed 88% COD (Chemical Oxygen Demand). With 0.5 mM PMS (peroxymonosulfate), 94% COD and 86% NH₄⁺-N of the system were removed. The cascade net average COD removal capacity reached 16.04 kg per kg catalyst per day. The addition of PMS also enhanced the electricity generation. In continuous-mode, in totally 18 h treatment through the three-stages cascade reactors without PMS, overall, 83% COD and 78% TOC (Total Organic Carbon) were removed, reaching a net calculated system average COD removal capacity of 19.29 kg per kg catalyst per day. With Ce-g-C₃N₄ catalyst, the batch or continuous multi-stage cascade system demonstrated great technical flexibility and economic potential in treating high-strength, high-salinity amine-rich industrial wastewater.

Challenges and engineering application of landfill leachate concentrate treatment

Landfill leachate concentrate (LLC) is a concentrated waste stream from landfill leachate treatment systems and has been recognized as a key challenge due to its high concentration of salts, heavy metals, organic matters, etc. Improper management of LLC (e.g. reinjection) would exacerbate the performance of upstream treatment processes and pose risks to the surrounding environments near landfill sites. Addressing the challenge and recovering resources from LLC have thus been attracting considerable attention. Although many LLC treatment technologies have been developed, a comprehensive discussion about the challenges still lacks. This review critically evaluates mainstream LLC treatment technologies, namely incineration, coagulation, advanced oxidation, evaporation and solidification/stabilization. We then introduce a geopolymer-based solidification (GS) process as a promising technology owning to its simple casting process and reusable final product and summarizes engineering applications in China. Finally, we suggest investigating hybrid systems to minimize LLC production and achieve the on-site reuse of LLC. Collectively, this review provides useful information to guide the selection of LLC treatment technologies and suggests a sustainable alternative for large-scale application, while also highlighting the need of joint efforts in the industry to achieve efficient, ecofriendly and economical on-site management of landfill waste streams.

Pilot-scale treatment of municipal garbage mechanical dewatering wastewater by an integrated system involving partial nitrification and denitrification

The municipal solid waste (MSW) with high water content can be pre-treated by the mechanical dewatering technology to significantly decrease the leachate generation in sequential landfill treatment or to improve the efficiency for solid waste incineration, which has attracted great concerns recently. However, the generated mechanical dewatering wastewater (MDW) containing high organics and nitrogenous content has been one of the big challenges for the sustainable treatment of MSW. In this study, a pilot-scale integrated system composed of physiochemical pretreatment, anaerobic sequencing batch reactor (ASBR), partial nitrification SBR (PN-SBR), denitrification SBR (DN-SBR), and UV/O₃ advanced oxidation process, with a capacity of 1.0 m³/d to treat MDW containing over 34000 mg-chemical oxygen demand (COD)/L organics pollutant and 850 mg/L NH₄⁺-N, was successfully developed. By explorations on the start-up of this integrated system and the process conditions optimization, after a long-term system operation, the findings demonstrated that this integrated system could reach the removal efficiency in the COD, NH₄⁺-N and total nitrogen (TN) in the MDW of 99.7%, 98.2% and 96.9%, respectively. Partial nitrification and denitrification were successfully obtained for the TN removal with the nitrite accumulation rate of over 80%. The treatment condition parameters were optimized to be 800 mg/L polyaluminum chloride (PAC) and 2 mg/L polyacrylamide (PAM) under a pH of 9 for pretreatment, 36 h hydraulic retention time (HRT) for ASBR, 24 h for PN-SBR, and 2 h for UV/O₃ unit. The organic sources in the MDW were also found to be feasible for the DN-SBR. Consequently, the resulting final effluent was stably in compliance with the discharge standard with high stability and reliability.

A Recent Progress in the Leachate Pretreatment Methods Coupled with Anaerobic Digestion for Enhanced Biogas Production: Feasibility, Trends, and Techno-Economic Evaluation

Landfill leachate (LFL) treatment is a severe challenge due to its highly viscous nature and various complex pollutants. Leachate comprises various toxic pollutants, including inorganic macro/nano components, xenobiotics, dissolved organic matter, heavy metals, and microorganisms responsible for severe environmental pollution. Various treatment procedures are available to achieve better effluent quality levels; however, most of these treatments are nondestructive, so pollutants are merely transported from one phase to another, resulting in secondary contamination. Anaerobic digestion is a promising bioconversion technology for treating leachate while producing renewable, cleaner energy. Because of its high toxicity and low biodegradability, biological approaches necessitate employing other techniques to complement and support the primary process. In this regard, pretreatment technologies have recently attracted researchers' interest in addressing leachate treatment concerns through anaerobic digestion. This review summarizes various LFL pretreatment methods, such as electrochemical, ultrasonic, alkaline, coagulation, nanofiltration, air stripping, adsorption, and photocatalysis, before the anaerobic digestion of leachate. The pretreatment could assist in converting biogas (carbon dioxide to methane) and residual volatile fatty acids to valuable chemicals and fuels and even straight to power generation. However, the selection of pretreatment is a vital step. The techno-economic analysis also suggested the high economic feasibility of integrated-anaerobic digestion. Therefore, with the incorporation of pretreatment and anaerobic digestion, the process could have high economic viability attributed to bioenergy production and cost savings through sustainable leachate management options.

Release of soluble ions and heavy metal during fly ash washing by deionized water and sodium carbonate solution

Two municipal solid waste incineration fly ashes were selected for washing by deionized water and Na₂CO₃ solution for comparison. Results showed that the benefits of washing were two folds: (1) Washing was able to reduce the contents of Cl^- and SO₄^2- while increased the contents of CaO, SiO₂, Al₂O₃ etc.; (2) Washing by Na₂CO₃ solution showed increased stability of heavy metals (Cr, Ni, Cd, Cu, Zn and Pb) and fly ash was safe for later reuse. Release of Cl^- was high at more than 90% regardless of washing solution. SO₄^2- and Ca²⁺ removal was highly dependent on the dissolution and precipitation equilibriums. Na₂CO₃ washing promoted the formation of CaCO₃. Thus SO₄^2- was washed off instead of precipitating as CaSO₄ and retained in fly ash solid. SO₄^2- removal was raised to more than 80% by Na₂CO₃ washing as compared with about 30% by deionized water. At the same time, Ca removal by Na₂CO₃ dropped to 1-2%. In addition, the basicity of fly ash was important as high basicity helped SO₄^2- removal. Overall, washing by Na₂CO₃ appears to be a promising option for fly ash treatment.

Technical and economic aspects of a sequential MF + NF + zeolite system treating landfill leachate

This work explores the techno-economic aspects of landfill leachate treatment by an integrated scheme composed of microfiltration (MF), nanofiltration (NF), and zeolite application for carbon and nitrogen removal. In bench-scale experiments, MF and NF were investigated, and zeolite batch tests were carried out to determine optimum conditions. A preliminary economic analysis is presented for a 200 m³ d^-1 full-scale treatment facility based on the data obtained from experimental tests and literature surveys. The maximum removals of 92%, 94%, and 79% for chemical oxygen demand (COD), absorbance at 254 nm, and ammonium nitrogen (NH₄⁺-N) were achieved in bench experiments, respectively. It was possible to reach the local discharge standard for COD (200 mg L^-1), but it was not possible to reach the Brazilian disposal requirement for NH₄⁺-N (20 mg L^-1). The total cost of the integrated MF + NF + zeolite system was estimated at 19.89 US$m^-3. In this study, the costs of the zeolite application account for around 70% of the total costs of the integrated scheme. Membrane process integration was an adequate strategy for removing organic compounds at low operating costs; However, further NH₄⁺-N depuration is needed to meet discharge requirements.

Membrane cleaning in membrane distillation of reverse osmosis concentrate generated in landfill leachate treatment

As a thermally induced membrane separation process, membrane distillation (MD) has drawn more and more attention to the advantages of treating hypersaline wastewaters, especially the concentrate from the reverse osmosis (RO) process. One of the major obstacles in widespread MD application is the membrane fouling. We investigated the feasibility of direct contact membrane distillation (DCMD) for landfill leachate reverse osmosis concentrate (LFLRO) brine treatment and systematically assessed the efficiency of chemical cleaning for DCMD after processing LFLRO brine. The results showed that 80% water recovery rate was achieved when processing the LFLRO brine by DCMD, but membrane fouling occurred during the DCMD process, and manifested as the decreasing of permeate flux and the increasing of permeate conductivity. Analysis revealed that the serious flux reduction was primarily caused by the fouling layer, which consisted of organic matter and inorganic salts. Five cleaning methods were investigated for membrane cleaning, including hydrogen chloride (HCl)-sodium hydroxide (NaOH), ethylene diamine tetraacetic acid (EDTA)-NaOH, citric acid, sodium hypochlorite (NaClO) and sodium dodecyl sulphate (SDS) cleaning. Among the chemical cleaning methods investigated, the 3 wt.% SDS cleaning showed the best efficiency at recovering the performance of fouled membranes.

A Novel Alternative Methods for Decalcification of Water Resources Using Green Agro-Ashes

The strategic idea in this work was to increase pH values by employing natural alkali sources (i.e., HCO3- and CO32-) from four tested agro-ashes as an alternative to chemicals (i.e., lime or soda ash). The considerable proportion of carbonates and bicarbonates in the investigated ash products had remarkable features, making them viable resources. All ash materials showed a significant ability for Ca ion elimination at high initial Ca ion concentrations. A slight quantity of ash (10 g/L) was sufficient for usage on very hard water contents up to 3000 ppm. Finally, the tested agro-ash was free of cost. Furthermore, unlike other conventional precipitants, such as NaOH, Ca(OH)2, NaHCO3, Na2CO3, and CaO, they are cost effective and ecologically sustainable. There is no need to employ any additional chemicals or modify the agro-ash materials throughout the treatment process. The benefits of the manufactured ash were assessed using a SWOT analysis.

Technical and economic evaluation of the integration of membrane bioreactor and air-stripping/absorption processes in the treatment of landfill leachate

A membrane bioreactor inoculated with commercial baker's yeast (Saccharomyces cerevisiae) (MBRy) integrated to an air-stripping/absorption (AS/AB) as pre-treatment (aiming ammonia recovery) or a post-treatment (polishment step) was assessed for the landfill leachate treatment. The effect of chemical oxygen demand (COD) and nitrogen (N) ratio (C:N) on the performance of the MBRy was also investigated. At high COD/N ratio, high organic matter removal in terms of COD (71 ± 4%) and ammonia removal (97 ± 3%) was observed. Lower COD/N ratio favored yeast growth in the mixed liquor even under adverse conditions. The results of ammonia removal and recovery, and economic analysis demonstrated that the best way to integrate the AS/BS processes is as pre-treatment of MBRy. The ammonia concentration in the AS/AB process feed was a key factor to achieve the market specification. Although pH and temperature adjustment were adequate to promote ammonia removal/recovery, the AS operation at high temperatures showed the highest ammonia removal rate (99%). Therefore, the integration of AS/AB with MBRy allows obtaining a permeate with a final concentration of 2902 ± 374 mg L^-1 of COD and 9 ± 7.5 mg L^-1 of ammonia. Although it was possible to reach the Brazilian discharge standard for ammonia (20 mg L^-1), it was not possible to reach the standard for COD, where the remaining fraction is recalcitrant organic matter, requiring the integration of a physico-chemical process. It should be noted that the proposed route allowed recovery 7 kg of ammonia per m³ of treated leachate.

Landfill Leachate Treatment Through Coagulation-flocculation with Lime and Bio-sorption by Walnut-shell

Due to the environmental consequences corresponding to leachate penetration, a sequence of inexpensive conventional processes proposed leachate treatment. The main objective was maximizing the COD and heavy metal removal efficiencies while minimizing generated sludge volume and material consumption rate. Walnut-shell adsorption complements lime treatment by eliminating heavy metals and low molecular-weight organic compounds. Samples gathered from Nazlou-landfill, Urmia, Iran. The relative significance of independent variables (lime and walnut-shell dosages and pH) on the removal efficiency was investigated using response surface methodology. By estimating the gradient of relative equations of the experimental results, the ideal direction of independent variable change was found as such increasing COD removal. A new variable called OSVLDR was utilized for measuring the ratio of the observed sludge volume to used lime dosage. The proposed sequence resulted in 43.24% COD removal under optimal conditions (i.e., 6.83, and 25 g/L of lime and walnut-shell dosage and pH values of 6, and 4 for two sets). Furthermore, effective removal in heavy metal concentrations was observed, i.e., 98.17, 67.45, 91.03, and 88.02% for nickel, cadmium, zinc, and lead, respectively. The results showed that a change in variables' amount affects associated costs while making a variation at removal efficiency. Reducing the initial pH value of leachate to 3.50 might decrease the consumed raw materials and OSVLDR value, resulting in a considerable decline in material costs (by 10%). Also, the inactive walnut-shell surface with a more crushing degree was used to reduce costs in walnut-shell set experiments rather than the activated surface.

Importance of Combined Electrochemical Process Sequence and Electrode Arrangements: A Lab-scale Trial of Real Reverse Osmosis Landfill Leachate Concentrate

Reverse osmosis (RO) is a widely applied technique for wastewater effluent reuse and landfill leachate treatment. The latter generates a refractory RO leachate concentrate (ROLC), for which cost-effective treatment is required. This study focuses on a two-step electrochemical method consisting of aluminum-based electrocoagulation (EC), and simultaneous electrooxidation-electrocoagulation with a titanium-based lead dioxide (Ti/ß-PbO₂) anode and aluminum cathode (EO_EC) assembly. The sequence and electrode arrangements of the combined electrochemical process were investigated to determine the organic transformation, Ti/ß-PbO₂ anode viability, and energy consumption. Series-based EC-EO_EC decreased the total chemical oxygen demand (COD) from 8750 mg L^-1 to 380 mg L^-1, a 96% removal efficiency, in 3.5 hours at 141 A m^-2. Under a low energy consumption of 28.7 kWh kg_COD^-1, the ROLC biodegradability (BOD₅/COD) significantly increased from 0.015 to 0.530, which was ascribed to aromatic removal (e.g., -C=C) and an increase in -COOH functional groups. Furthermore, the rapid removal of natural organic matter and increase in pH elevation from EC suppressed the dissolution of Pb from the Ti/ß-PbO₂ anode during the subsequent EO_EC, thereby leaving 0.061 mg L^-1 in the ROLC after treatment. The treatment cost was 3.86 USD kg_COD^-1, which was approximately 34% lower than that of previously reported electrochemical processes for ROLC treatment. These findings obtained with a real RO concentrate provide a foundation for scaling up this new electrochemical treatment approach.

Enhanced Pb and Zn stabilization in municipal solid waste incineration fly ash using waste fishbone hydroxyapatite

The present research focused on evaluating the role of waste fishbone hydroxyapatite (FB-HAP) in stabilizing heavy metals, particularly Pb and Zn, in incineration fly ash (IFA). Bones were collected from various fish species and processed for batch experiments. A commercial apatite product (Apatite II™) was also obtained for a comparative analysis. The experiments were performed at fishbone/fly ash ratios of 0.0 (control group) and 1:10 (by weight), settling times of 6, 12, 24, and 672 h (28 days), and W/S ratios of 1.0 and 1.5 mL/g. The highest Pb removal efficiency reached 86.39% at 28 days settling periods, when the FB-HAP dose was only 10% at W/S 1.5 mL/g. FB-HAP was found noticeably more effective (approximately 1.5 to 2 times) than Apatite II™, particularly at shorter settling periods. Stabilization of Zn was efficient at longer settling period (28 days) using FB-HAP. The highest stabilization rate of Zn was 62.67% at W/S 1.0 mL/g. The results indicated that settling time and W/S ratio were the most important factors to enhance the stabilization of Pb and Zn in IFA. Utilization of waste fishbone is expected to be a low-cost and eco-friendly technology.

Assessing an Integral Treatment for Landfill Leachate Reverse Osmosis Concentrate

An integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation treatment, which best results were obtained using a dosage of 5 g L−1 of ferric chloride at an initial pH = 6 (removal of the 76% chemical oxygen demand (COD), 57% specific ultraviolet absorption (SUVA), and 92% color). The second step is a photo-Fenton process, which resulted in an enhanced biodegradability (i.e., the ratio between the biochemical oxygen demand (BOD5) and the COD increased from 0.06 to 0.4), and an extra 43% of the COD was removed at the best trialed reaction conditions of [H2O2]/COD = 1.06, pH = 4 and [H2O2]/[Fe]mol = 45. An ultra violet-A light emitting diode (UVA-LED) lamp was tested and compared to conventional high-pressure mercury vapor lamps, achieving a 16% power consumption reduction. Finally, an optimized 30 g L−1 lime treatment was implemented, which reduced conductivity by a 43%, and the contents of sulfate, total nitrogen, chloride, and metals by 90%. Overall, the integral treatment of LLROC achieved the removal of 99.9% color, 90% COD, 90% sulfate, 90% nitrogen, 86% Al, 77% Zn, 84% Mn, 99% Mg, and 98% Si; and significantly increased biodegradability up to BOD5/COD = 0.4.

Interactions among low-molecular-weight organics, heavy metals, and Fe(III) during coagulation of landfill leachate nanofiltration concentrate

The generation of landfill leachate nanofiltration concentrate (LLNC) has been a dilemma for leachate treatment plants because it contains large amounts of refractory organics with low molecular weight (LMWO), as well as heavy metals (HMs), and is difficult to handle. The coagulation removal of LMWOs is a significant challenge, as is the removal of HMs bonded to LMWOs. In this study, coagulation through the dosing of FeCl₃ was used to remove LMWOs and HMs from LLNC. The results interestingly demonstrated that the removal rates of dissolved organic carbon (DOC), Cr, Ni, and As reached up to 84.1% ± 3.9%, 91.0 ± 1.1%, 73.1 ± 2.2%, and 96.9 ± 1.5%, respectively. The partition of LMWO components, as well as the interactions among the LMWOs, HMs, and Fe(III) were investigated to determine the mechanism behind the LMWO and HM removal. LMWOs with a high degree of humification, including humic and fulvic acid-like components, were preferentially removed through aggregation and electrostatic attraction originating from the specialistic adsorption of Fe₂(OH)₂⁴⁺ and Fe₃(OH)₄⁵⁺. In addition to being removed, a portion of these two components was dissociated into aromatic protein I, aromatic protein II, and soluble microbial by-product-like materials due to an acid effect and the formation of inner-sphere complexes. A redundancy analysis revealed that As, Cr, and Ni are mainly removed through the electrostatic attraction of Fe(III), bonding to humic substances and hydrophilic organics, respectively. The outcomes provide a new understanding on the coagulation removal of LMWOs and HMs.

Combined processes of ozonation and supercritical water oxidation for landfill leachate degradation

Leachate is a highly variable, heterogeneous and recalcitrant wastewater generated in landfills which may contain high concentrations of many organic and inorganic compounds, hampering the application of a single technique in its treatment. Therefore, this paper assessed leachate degradation through supercritical water oxidation (ScWO) as well as combined processes of ozonation and supercritical water oxidation (O₃/ScWO and ScWO/O₃), a yet innovative combination. Ozonation was carried out at different reaction times (30-120 min). ScWO was developed at 600 °C, 23 MPa, and spatial time (τ) from 29 to 52 s. A combination of ozonation (30 min) and supercritical water oxidation process (O₃-30'/ScWO) was the most efficient technique for the degradation of the leachate assessed. These conditions enabled to remove high values of apparent and true color (92% and 97%, respectively), biochemical oxygen demand (BOD_5,20) (95%), chemical oxygen demand (COD) (92%), total organic carbon (TOC) (79%), nitrite (78%), nitrate (84%), total (96%), dissolved (96%) and suspended (94%) solids. In addition, the combined process presented significant decrease in electric conductivity (EC) (68%) and less leachate turbidity removal (43%). Except for ammonia and nitrite, all parameters of the leachate treated by O₃-30'/ScWO met the specifications of Brazilian legislation (CONAMA Resolutions No. 357/2005 and No. 430/2011) for the disposal of wastewater in water bodies. Besides, both processes are considered to be clean technologies. This shows the great possibility of applying the O₃/ScWO combination to landfills leachates.

Supercritical water gasification of landfill leachate for hydrogen production in the presence and absence of alkali catalyst

Gasification of landfill leachate in supercritical water using batch-type reactor is investigated. Alkali such as NaOH, KOH, K₂CO₃, Na₂CO₃ is used as catalyst. The effect of temperature (380-500 °C), retention time (5-25 min), landfill leachate concentration (1595 mg L^-1-15,225 mg L^-1), catalyst adding amount (1-10 wt%) on hydrogen mole fraction, hydrogen yield, carbon gasification rate, COD, TOC, TN removal efficiency are investigated. The results showed that gaseous products mainly contained hydrogen, methane, carbon dioxide and carbon monoxide without addition of catalyst. However, the main gaseous products are hydrogen and methane with addition of NaOH, KOH, K₂CO₃, Na₂CO₃. In the absence of alkali catalyst, the effect of temperature on landfill leachate gasification is positive. Hydrogen mole fraction, hydrogen yield, carbon gasification ratio increase with temperature, which maximum value being 55.6%, 107.15 mol kg^-1, 71.96% is obtained at 500 °C, respectively. Higher raw landfill leachate concentration leads to lower hydrogen production and carbon gasification rate. The suitable retention time is suggested to be 15 min for higher hydrogen production and carbon gasification rate. COD, TOC and TN removal efficiency also increase with increase of temperature, decrease of landfill leachate concentration. In the presence of catalyst, the hydrogen production is obviously promoted by addition of alkali catalyst. the effect of catalysts on hydrogen production is in the following order: NaOH ＞ KOH ＞ Na₂CO₃ ＞ K₂CO₃. The maximum hydrogen mole fraction and hydrogen yield being 74.40%, 70.05 mol kg^-1 is obtained with adding amount of 5 wt% NaOH at 450 °C, 28 MPa, 15 min.