Toxicological characterization of a novel wastewater treatment process using EDTA-Na2Zn as draw solution (DS) for the efficient treatment of MBR-treated landfill leachate

Effect of chloride ions on the simultaneous electrodialysis and electrochemical oxidation of mature landfill leachate

An attempt has been made to improve the treatment efficiency of mature landfill leachate prior to the existing biological treatment. In this study, electrochemical oxidation (EO) was applied as a pre-treatment to remove organic contaminants and was simultaneously combined with electrodialysis (ED) to remove ionic constituents, such as ammonium and phosphate. A laboratory-scale electrochemical reactor was designed by utilizing a carbon graphite anode and a stainless steel cathode and separated by an anion exchange membrane (AEM) and cation exchange membrane (CEM), creating a three-compartment reactor. The oxidation of the organic pollutant would occur in the anodic compartment, while the targeted ammonium and phosphate ions would be migrated and accumulated in the central compartment. The treatment process was performed in a batch recirculation time of 12 h at a constant supplied current of 0.25 A and evaluated by means of the initial leachate pH (i.e., original pH value of 7.85; adjusted pH value of 5.50 and 8.50) and three different initial chloride concentrations. The higher the chloride concentration in the leachate, the higher the removal efficiency, except for total phosphate. The highest chemical oxidation demand (COD) removal was 86.2% (0.88 g W^-1 h^-1), at an initial leachate pH value of 7.85 with the addition of 2 g L^-1 of NaCl. Furthermore, under the same conditions, the ammonium, total phosphate, and chloride removals were 85% (0.44 g W^-1 h^-1), 89% (0.08 g W^-1 h^-1), and 83% (0.69 g W^-1 h^-1), respectively. Also, the concentrated ionic compounds in the central compartment can lower the energy consumption and can possibly be further treated or managed.

Landfill leachate treatment through the combination of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO and membrane filtration processes

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N-NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N-NH₄ to nitrite (N-NO₂) and Nitrate (N-NO₃), and promoting denitrification by converting N-NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.

Hydraulic performance and fouling characteristics of a membrane sequencing batch reactor (MSBR) for landfill leachate treatment under various operating conditions

This study investigates the hydraulic performance and the fouling characteristics of a bench-scale membrane sequencing batch reactor (MSBR), treating mature landfill leachate under various time-based operating conditions. The MSBR system operated initially under a high-flux condition (Period 1) which resulted in a rapid trans-membrane pressure (TMP) rise due to intense fouling. Following the characterization of Period 1 as super-critical, the system was subsequently operated under a near-critical condition (Period 2). The overall filtration resistance analysis showed that cake layer formation was the dominant fouling mechanism during Period 1, contributing to 85.5% of the total resistance. However, regarding the MSBR operation during Period 2, adsorption was found to also be a dominant fouling mechanism (Days 1 to 47), contributing to 29.1% of the total resistance. Additionally, the irregular total resistance variation, which was observed during the subsequent operation (Days 48 to 75), and the respective filtration resistance analysis suggested also the formation of an initial sludge cake layer on the membrane surface, contributing to the 47.7% of the total resistance.

Microbial characteristics of landfill leachate disposed by aerobic moving bed biofilm reactor

An aerobic moving bed biofilm reactor (MBBR) was applied to treat landfill leachate generated from a domestic waste incineration plant. Pollutant removal efficiency of this reactor under stable operating condition was studied. The biomass, bacteria species, and microbial metabolism in this reactor were investigated. These results showed that the average removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen in the aerobic MBBR achieved 64% and 97% in the optimum conditions, respectively. The three-dimensional fluorescence spectrum revealed that the content of soluble microbial byproducts from extracellular polymeric substances extraction in suspended sludge was much higher than that on biofilm, and the types of pollutants were various in different regions of the reactor. It also indicated that the MBBR system had a stable, rich and regular microorganism community, including large amounts of nitrifying bacteria and denitrifying bacteria. Scanning electron microscopy suggested that biofilm attached to the packing provided a good anoxic-aerobic micro environment system to achieve a high metabolic activity, which favored COD and ammonia removal.

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

Landfill leachate contains high concentrations of organic compounds and ammonium, and the presence of heavy metal ions, which normally requires expensive and complex treatment processes. In this study, full-scale experiments were implemented to evaluate the feasibility of mechanical vapor recompression (MVR) treating leachate. Results revealed that despite the drastic changes of influent pollutant concentrations, MVR system possessed the ability to reduce most of the pollutants and guarantee the effluent in compliance with the discharge limits of Chinese Standard. Fouling analyses revealed that the main components in the fouling were crystalline (Mg_0.06Ca_0.94)(CO₃), combining with humus and silicon compounds. A fouling cleaning method was developed with the adding sequence of first sulphamic acid and then NaOH, which could remove 88.62% fouling. Although fouling was inevitable for MVR treating leachate, coagulation pretreatment removed large amounts of COD, BOD₅, total nitrogen, ammonium and total phosphorus, with the respective means of 68.4%, 69.4%, 81.0%, 84.1% and 81.4%, and thereafter reduced the treatment cost 27.4% from 47.06 RMB (6.92 US dollars)/m³ to 34.15 RMB (5.02 US dollars)/m³. These outcomes provided that in addition to the combination method of biological removal process with membrane technology, MVR process was another feasible solution for leachate treatment.

Characterization of residual organic compounds of aerobic degradation of landfill leachate

The purpose of this article is to characterize and compare the residual COD of raw landfill leachate and its low and high molecular weight fractions before and after aerobic degradation process. The low and high molecular weight fractions (<10 kDa and >10 kDa, respectively) were obtained by the use of an ultrafiltration cell. Samples of the fractions with molecular weights 10 kDa, as well as the raw leachate, were characterized in terms of COD, protein, carbohydrate and lipid concentration and by biodegradability test. The compound identification of all samples was carried out using gas chromatography coupled with mass spectrometry (GC/MS). The results show that the landfill leachate studied is constituted of approximately 60% of compounds with molecular weight <10 kDa. Approximately 80% of the compounds identified in the leachate had been degraded. This is an indication that most of the compounds that constitute the significant fraction of residual COD correspond to intermediate products and products of condensation of affluent compounds or had been generated during the degradation (SMP). Similar compounds were identified in all effluents of the degradation assay, suggesting the presence of SMP. These compounds, predominantly aliphatic and esters, are characterized by high molecular weight and probable refractory nature.

A novel forward osmosis system in landfill leachate treatment for removing polycyclic aromatic hydrocarbons and for direct fertigation

Landfill leachate (LL) is harmful to aquatic environment because it contains high concentrations of dissolved organic matter, inorganic components, heavy metals, and other xenobiotics. Thus, the remediation of LL is crucial for environmental conservation. Here, a potential application of the forward osmosis (FO) filtration process with ammonium bicarbonate (NH₄HCO₃) as a draw solution (DS) was investigated to remediate membrane bioreactor-treated LL (M-LL). After the leachate treatment, the toxicity and removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) were evaluated using zebrafish and cultured human cells. The water recovery rate was improved using the current protocol up to 86.6% and 91.6% by both the pressure retarded osmosis (PRO) mode and the forward osmosis (FO) mode. Water flux increased with the increasing DS concentrations, but solution velocities decreased with the operation time. Toxicity tests revealed that the M-LL treated by NH₄HCO₃ had no toxic effect on zebrafish and human cells. Moreover, green fluorescent protein (GFP) expression in the transgenic zebrafish Tg(cyp1a:gfp) induced by PAHs was very weak compared to the effects induced by untreated M-LL. Since the diluted DS met local safety requirements of liquid fertilizer, it could be directly applied as the liquid fertilizer for fertigation. In conclusion, this novel FO system using NH₄HCO₃ as the DS provides a cheap and efficient protocol to effectively remove PAHs and other pollutants in LL, and the diluted DS can be directly applied to crops as a liquid fertilizer, indicating that this technique is effective and eco-friendly for the treatment of different types of LL.

In vivo characterization of hair and skin derived carbon quantum dots with high quantum yield as long-term bioprobes in zebrafish

Carbon quantum dots (CDs) were widely investigated because of their tunable fluorescence properties and low toxicity. However, so far there have been no reports on in vivo functional studies of hair and skin derived CDs. Here, hair derived CDs (HCDs) and skin derived CDs (SCDs) were produced by using human hair and pig skin as precursors. The quantum yields (QYs) of HCDs and SCDs were quite high, compared to citric acid derived CDs (CCDs). HCDs and SCDs possess optimal photostability, hypotoxicity and biocompatibility in zebrafish, indicating that HCDs and SCDs possess the capacity of being used as fluorescence probes for in vivo biological imaging. The long-time observation for fluorescence alternation of CDs in zebrafish and the quenching assay of CDs by ATP, NADH and Fe3+ ions demonstrated that the decaying process of CDs in vivo might be induced by the synergistic effect of the metabolism process. All results indicated that large batches and high QYs of CDs can be acquired by employing natural and nontoxic hair and skin as precursors. To our knowledge, this is the first time to report SCDs, in vivo comparative studies of HCDs, SCDs and CCDs as bioprobes, and explore their mechanism of photostability in zebrafish.