Landfill leachate sludge use as soil additive prior and after electrocoagulation treatment: A cytological assessment using CHO-k1 cells

Ecotoxicological impacts of landfill sites: Towards risk assessment, mitigation policies and the role of artificial intelligence

Waste disposal in landfills remains a global concern. Despite technological developments, landfill leachate poses a hazard to ecosystems and human health since it acts as a secondary reservoir for legacy and emerging pollutants. This study provides a systematic and scientometric review of the nature and toxicity of pollutants generated by landfills and means of assessing their potential risks. Regarding human health, unregulated waste disposal and pathogens in leachate are the leading causes of diseases reported in local populations. Both in vitro and in vivo approaches have been employed in the ecotoxicological risk assessment of landfill leachate, with model organisms ranging from bacteria to birds. These studies demonstrate a wide range of toxic effects that reflect the complex composition of leachate and geographical variations in climate, resource availability and management practices. Based on bioassay (and other) evidence, categories of persistent chemicals of most concern include brominated flame retardants, per- and polyfluorinated chemicals, pharmaceuticals and alkyl phenol ethoxylates. However, the emerging and more general literature on microplastic toxicity suggests that these particles might also be problematic in leachate. Various mitigation strategies have been identified, with most focussing on improving landfill design or leachate treatment, developing alternative disposal methods and reducing waste volume through recycling or using more sustainable materials. The success of these efforts will rely on policies and practices and their enforcement, which is seen as a particular challenge in developing nations and at the international (and transboundary) level. Artificial intelligence and machine learning afford a wide range of options for evaluating and reducing the risks associated with leachates and gaseous emissions from landfills, and various approaches tested or having potential are discussed. However, addressing the limitations in data collection, model accuracy, real-time monitoring and our understanding of environmental impacts will be critical for realising this potential.

Treatment of nanofiltration concentrate of landfill leachate using advanced oxidation processes incorporated with bioaugmentation

Advanced oxidation processes have been broadly applied in wastewater treatment, but few studies have focused on its degradative effect on refractory organic contaminants in membrane concentrates of landfill leachate. In this study, the treatment effects of advanced oxidation processes including electrocoagulation (EC), ozone (OZ), anodic oxidation (AO) and electro-Fenton (EF) incorporated with genetically engineered nitrifying bacteria Rhodococcus erythropolis expressing Nirs and AMO (rRho-NM) on nanofiltration concentrate (NFC) of old landfill leachate were investigated in a lab-scale experiment. The results showed that advanced oxidation processes degraded the refractory organic contaminants including coagulation-resistant substances (CRS), humic acid (HA), fulvic acid (FvA), macro molecular organics (MMOs) and benzene ring compounds (BRCs) and increased the biodegradability in NFC of old landfill leachate. Compared to activated sludge (AS), rRho-NM exhibited an excellent removal performance for total organic carbon (TOC), ammonia nitrogen (NH₄-N), total nitrogen (TN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) for advanced oxidation processes-treated NFC of old landfill leachate. Advanced oxidation processes incorporated with bioaugmentation demonstrated an outstanding degradation performance for removing refractory organic contaminants, TOC, NH₄-N, TN, BOD, COD and heavy metal in NFC of old landfill leachate. In addition, OZ incorporated with rRho-NM (OZ-rRho-NM) showed the optimal removal efficacy in reduction of refractory organic contaminants, TOC, NH₄-N, TN, BOD and COD, the shortest hydraulic retention time (HRT) and the minimum energy consumption in NFC of landfill leachate. Furthermore, the cheapest treatment cost for NFC could be achieved by EC incorporated with rRho-NM (EC-rRho-NM). More impressively, rRho-NM remained stable in expressing Nirs and AMO genes, increased nitrification and denitrification rate, and improved MBR effluent quality in the treatment of NFC. In conclusion, this work provides new insights into the application of advanced oxidation processes incorporated with bioaugmentation using rRho-NM for the treatment of NFC of old landfill leachate.

Evaluation of scrap metallic waste electrode materials for the application in electrocoagulation treatment of wastewater

The constant need for sacrificial electrodes is one of the limitations of applying the EC in wastewater treatment. Accordingly, this study proposes a sustainable alternative in reusing scrap metallic wastes as electrode materials. Four different types of metallic wastes (beverage cans, used aluminum (Al) foil, scrap iron, and scrap mild steel) are proposed as sacrificial electrodes for grey water (GW) treatment using the EC technique. At electrical current densities (CD) ranging between 5 and 20 mA/cm², the treatment performance was evaluated for a reaction time of 10 min in terms of the removal efficiency of some key parameters such as color, turbidity, chemical oxygen demand (COD), and electrical conductivity, energy and material consumption, and metal contamination of GW from electrodes. The results demonstrated that using metallic wastes as sacrificial electrodes can achieve a considerable reduction in color, turbidity, COD, and electric conductivity of about 97.2%, 99%, 88%, and 89%, respectively. However, their reuse as electrodes revealed some important concerns. Al foil undergoes quick and substantial perforation and loss of surface area during electrolysis. The scrap iron and scrap mild steel were found to cause metal contamination by increasing Fe ions in the treated GW. Generally, metal scrap wastes can serve effectively as alternative sustainable electrodes. However, further research is recommended regarding the operating costs, which are considered crucial aspects of the EC process in terms of energy consumption and the most efficient method of fabricating the metallic wastes into a form suitable for reuse in the EC technique.

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.

Investigation on the improved electrochemical and bio-electrochemical treatment processes of soilless cultivation drainage (SCD)

The soilless crop cultivation under cover generates wastewater called soilless cultivation drainage (SCD), being a nutrient-rich overflow. The average concentration of phosphorus- and nitrogen-based pollutants from soilless tomato cultivation usually ranges from 35.4 to 104.0 mg P/L and from 270.0 to 614.9 mg N/L, respectively. In bio-electrochemical reactors, nitrogen and phosphorus are removed via biological denitrification, electrochemical nitrate reduction, bio-electrochemical reduction, and electrocoagulation. The novelty of this study is due to the use of alternating current (AC), which can both mitigate the corrosion on the anode and solve the issue of insoluble oxide build-up on the cathode. Additionally, and crucially, it promotes bacterial growth and activity. The aim of the present study was to determine (1) the effectiveness of soilless cultivation drainage treatment methods that employ biological and electrochemical processes, with consideration given to (2) the quantity and quality of the produced sludge as a potential nutrient-rich product. The bio-electrochemical reactor proved more effective than the electrochemical one and ensured a high TP and TN removal efficiency exceeding 97% and 66%, respectively. The resulting sludge was rich in such elements as calcium, potassium, carbon, phosphorus, and nitrogen, and as such may serve as a viable alternative to conventional mineral fertilizers.

Review on electrochemical system for landfill leachate treatment: Performance, mechanism, application, shortcoming, and improvement scheme

Landfill leachate is a type of complex organic wastewater, which can easily cause serious negative impacts on the human health and ecological environment if disposed improperly. Electrochemical technology provides an efficient approach to effectively reduce the pollutants in landfill leachate. In this review, the electrochemical standalone processes (electrochemical oxidation, electrochemical reduction, electro-coagulation, electro-Fenton process, three-dimensional electrode process, and ion exchange membrane electrochemical process) and the electrochemical integrated processes (electrochemical-advanced oxidation process (AOP) and biological electrochemical process) for landfill leachate treatment are summarized, which include the performance, mechanism, application, existing problems, and improvement schemes such as cost-effectiveness. The main objective of this review is to help researchers understand the characteristics of electrochemical treatment of landfill leachate and to provide a useful reference for the design of the process and reactor for the harmless treatment of landfill leachate.

Comparison between sinusoidal AC coagulation and conventional DC coagulation in removing Cu2+ from printed circuit board wastewater

A new Electrocoagulation (EC) technique, sinusoidal AC coagulation (SACC), is creatively put forward for Cu²⁺ removal in the wastewater from the printed circuit board (PCB) production in this paper. The removal efficiency of Cu²⁺ from PCB wastewater and energy consumption are compared by SACC and conventional direct current coagulation (DCC). The optimal process parameters were established through analysis of response surface methodology (RSM). The coagulations containing Cu²⁺ was characterized by SEM, EDS, TEM，BET, XRD and FTIR. The nano-ferrum collosol, mainly composed of goethite (α-FeOOH) and magnetite (γ-Fe₂O₃), absorbs the Cu²⁺ and coagulates to remove Cu²⁺. The results show that the removal rates of Cu²⁺ by SACC and DCC are 99.86％ and 98.21％, respectively, and the energy consumption is 2.76 × 10^-2 kWh⋅m^-3 for SACC and 4.42 × 10^-2 kWh⋅m^-3 for DCC under the optimal process conditions of c₀ (Cu²⁺) = 41.99 mg⋅dm^-3, pH = 7.14, j = 0.293 A⋅m^-2, t = 16.7 min. The pilot tests indicate that the SACC technique is feasible in industrial application. Cu²⁺ removal were completed through electrodeposition of Cu²⁺ on iron electrode, the deposition of Cu(OH)₂ and the adsorption of Cu²⁺ by ferrum collosol. The adsorption follows the pseudo-second order kinetics model well. The maximum saturated adsorption capacity (q_max) of Cu²⁺ on ferrum collosol produced by SACC is larger than that by DCC. The adsorption of Cu²⁺ on the ferrum collosol prepared by SACC and DCC are in accordance with Langmuir's adsorption isotherms. The novel SACC technique is a promising technique for the highly-efficient treatment of Cu²⁺ from PCB wastewater.

Investigating landfill leachate toxicity in vitro: A review of cell models and endpoints

Landfill leachate is a complex mixture characterized by high toxicity and able to contaminate soils and waters surrounding the dumpsite, especially in developing countries where engineered landfills are still rare. Leachate pollution can severely damage natural ecosystems and harm human health. Traditionally, the hazard assessment of leachate is based on physicochemical characterization but the toxicity is not considered. In the last few decades, different bioassays have been used to assess the toxicity of this complex matrix, including human-related in vitro models. This article reviews the cell bioassays successfully used for the risk assessment of leachate and to evaluate the efficiency of toxicity removal of several processes for detoxification of this wastewater. Articles from 2003 to 2018 are covered, focusing mainly on studies that used human cell lines, highlighting the usefulness and adequacy of in vitro models for assessing the hazard involved with exposure to leachate, particularly as an integrative supporting tool for chemical-based risk assessment. Leachate is generally toxic, mutagenic, genotoxic and estrogenic in vitro, and these effects can be measured in the cells exposed to already low concentrations, confirming the serious hazard of this wastewater for human health.