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

A comparative study of black-box and white-box data-driven methods to predict landfill leachate permeability

Due to the dynamic and complexity of leachate percolation within municipal solid waste (MSW), planning and operation of solid waste management systems are challenging for decision-makers. In this regard, data-driven methods can be considered robust approaches to modeling this problem. In this paper, three black-box data-driven models, including artificial neural networks (ANN), adaptive neuro-fuzzy inference systems (ANFIS), and support vector regression (SVR), and also three white-box data-driven models, including the M5 model tree (M5MT), classification and regression trees (CART), and group method of data handling (GMDH), were developed for modeling and predicting landfill leachate permeability ([Formula: see text]). Based on a previous study conducted by Ghasemi et al. (2021), [Formula: see text] can be formulated as a function of impermeable sheets ([Formula: see text]) and copper pipes ([Formula: see text]). Hence, in the present study, [Formula: see text] and [Formula: see text] were adopted as input variables for the prediction of [Formula: see text] and evaluated for the performance of the suggested black-box and white-box data-driven models. Scatter plots and statistical indices such as coefficient of determination (R²), root mean square error (RMSE), and mean absolute error (MAE) were used for qualitative and quantitative evaluations of the effectiveness of the suggested methods. The outcomes indicated all of the provided models successfully predicted [Formula: see text]. However, ANN and GMDH had higher accuracy between the proposed black-box and white-box data-driven models. ANN with R² = 0.939, RMSE = 0.056, and MAE = 0.017 was marginally better than GMDH with R² = 0.857, RMSE = 0.064, and MAE = 0.026 in the testing stage. Nevertheless, an explicit mathematical expression provided by GMDH to predict k was easier and more understandable than ANN.

Retrofitting a full-scale multistage landfill leachate treatment plant by introducing coagulation/flocculation/sedimentation and ultrafiltration process steps

Considering that landfilling still remains among the most commonly used methods for the confrontation of solid wastes, effective methods should be applied to treat the leachate generated, due to its recalcitrant nature. In this work, a full-scale system consisting of two SBRs operating in parallel (350 m³ each) and two activated carbon (AC) columns operating in series (3 m³ each) was retrofitted by introducing a coagulation/flocculation/sedimentation (C/F/S) unit of 7.8 m³ and an ultrafiltration (UF) membrane of 100 m² to effectively treat landfill leachate. The raw leachate was characterized by high COD and NH₄⁺-N concentration, i.e., 3095 ± 706 mg/L and 1054 ± 141 mg/L respectively, a BOD/COD ratio of 0.22, and high concentrations of certain heavy metals. Leachate processing in this retrofitted multistage treatment system resulted in total COD removal efficiency of 89.84%, with biological treatment, C/F, UF, and AC contributing 46.31%, 4.68%, 15.98%, and 22.87% to the overall organic content removal. The retrofitted scheme achieved an overall NH₄⁺-N and TKN removal of 92.03% and 91.75% respectively, attributed mostly to the activity of an effective nitrifying community. Color number (CN) was reduced by 26.96%, 10.29%, 15.94%, and 5.39% after the activated sludge, the C/F, the UF, and the AC adsorption process respectively, corresponding to a 58.91% overall decrease. Regarding heavy metal removal, all elements examined, apart from Ni, i.e., effluent As, Cd, Co, Cr, Cu, Hg, Mg, Mn, and Pb, were below the legislative limits set by the national authorities for restricted or unrestricted irrigation. Lastly, total operating expenses (OPEX) were estimated as equal to 72,687 €/year or 6.64 €/m³.

Regulating the exposed crystal facets of α-Fe2O3 to promote Fe2O3-modified biochar performance in heavy metals adsorption

α-Fe₂O₃ modified biochar (Fe₂O₃/BC) was prepared to remove Cu(II), Pb(II) and As(V). By adjusting the calcination temperature, the morphology and exposed crystal facets of α-Fe₂O₃ on the biochar were changed which further affected the adsorption performance. The kinetics and isotherms were investigated systematically to reveal adsorption effect of the adsorbent on Cu(II), Pb(II) and As(V). The results indicated that chemisorption process was the dominant adsorption mechanism. Fe₂O₃/BC-350 exhibited superior adsorption capacity for Cu(II) (258.22 mg/g) and Pb(II) (390.60 mg/g), and Fe₂O₃/BC-250 showed relatively good adsorption capacity for As(V) (5.78 mg/g). By adsorption mechanism analysis, electrostatic adsorption, ion exchange, precipitation and complexation were coexisted in the process of removing metal ions by Fe₂O₃/BC. The repeatability test and the effect of ion strength exhibited the strong stability of Fe₂O₃/BC. Meanwhile, density functional theory (DFT) calculations manifested that the (202) facet of α-Fe₂O₃ on Fe₂O₃/BC-350 possessed the lowest adsorption energies of Cu(II) and Pb(II). While for As(V), it was the (104) facet of α-Fe₂O₃ on Fe₂O₃/BC-250 that exhibited the lowest adsorption energy. DFT results revealed that different Fe₂O₃/BC had different adsorption affinities to various heavy metals. In general, this work not only prepared a promising adsorbent via a simple procedure, but also served as a reference for researchers in designing absorbents with specific active facet for efficient heavy metals remediation.

An ISM approach to overcome the participation barriers in the waste source separation-a case study: Urmia University Campus

A procedure developed to identify and facilitate the implementation of waste source separation strategies applicable in higher education centers, as a prerequisite for the expansion of recycling programs. The target materials proper to be separated were selected based on quantitative/qualitative analysis of waste produced on the Nazlou Campus of Urmia University, Iran (as a case study). The barriers to implementation of the program were identified using the interpretive structural modeling (ISM) methodology. Finally, regarding the main obstacles which could be broken down inside the campus complex, an analysis of factors affecting student participation were done. On average, 37.48% of 1.74 tons of waste daily produced on the campus could be recycled. Based on sieve analyses, the categories of non-ferrous metals, glass, and composite packaging have a wider size distribution (i.e., over 150 to under 80 mm) might lead to improper operation of further mechanical separations and be selected as target materials. The weakness of educational programs and persuading the students are considered the main obstacles. A significant relationship was observed between the three training options, namely "installation of announcements," "organizing waste management classes," and "training through holding the exhibition of recycled products" and the student participation in the program (with more emphasis on the last one). Women were estimated to be more likely than men to participate in the program (70 vs 49%). Also, there was a significant relationship between the knowledge and the student's participation. In other words, strengthening public awareness is essential to increase the participation level.

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.

Application of polysaccharide-based metal organic framework membranes in separation science

Polysaccharide/MOF composite membranes have captured the interests of many researchers during decontamination of polluted environments. Their popularity can be attributed to the relatively high chemical and thermal stabilities of these composite membranes. Chitosan is among the polysaccharides extensively used during the synthesis of hybrid membranes with MOFs. The applications of chitosan/MOF composite membranes in separation science are explored in detail in this paper. Researchers have also synthesised mixed matrix membranes of MOFs with cellulose and cyclodextrin that have proved to be effective during separation of a variety of materials. The uses of cellulose/MOF and cyclodextrin/MOF membranes for the removal of environmental pollutants are discussed in this review. In addition, the challenges associated with the use of these mixed matrix membranes are explored in this current paper.

Sensitivity analysis of significant parameters affecting landfill leachate generation rate

A landfill was designed to evaluate leachate quantity's governing factors using the HELP model. As a case study, the proposed methodology was tested in the Nazlou Landfill, Urmia, Iran. Indeed, the main objective was to illuminate the efficacy of executive parameters defined in the model. Lack of the final cover layer in the pre-closure period affects leachate generation as precipitation enters directly into the waste layers and changes their moisture constituents. Concerning the occurrence of the heaviest precipitation condition in the last 30 years in the pre-closure period, leachate leakage might increase to 0.23 m³/tonne of waste. Due to changes in the layers' initial moisture, the effect of precipitation on leachate generation lasts till the landfill post-closure and would change the drained leachate from 0.083 to 0.089 m³/year-tonne of waste (this amount is generally neglected in the leachate collection system design). During pre-closure, the heaviest precipitation causes an increased generated leachate by 37.59% in the first post-closure year, which is vital especially in landfills with limited capacity treatment plants. The impact of operating conditions involves the landfill leachate generation up to different years. However, over five years of averaging, the precipitation trend was consistent with the leachate leakage. Based on the different scenarios defined regarding the meteorological conditions and design parameters, if the geomembrane layer was removed from the final cover, the leachate quantity will be increased by 79.38%. Replacing 76 cm of dense clay can overcome this challenge.

Combined landfill leachate treatment methods: an overview

Landfill leachate is commonly heavily contaminated and consists of high amount of organic compounds, inorganic salts, toxic gases, halogenated hydrocarbons, and heavy metals that exerts a serious threat to public health and the environment. Thus, it requires treatments before direct release into receiving waters. Selecting the efficient method for leachate treatment is still a major challenge. While physicochemical treatment methods such as coagulation-flocculation, adsorption, membrane filtration, ozonation, air stripping, and advanced oxidation processes (AOP) are appropriate for mature leachate, young leachate requires biological treatments including membrane bioreactor (MBR), activated sludge (AS), upflow anaerobic sludge blanket (UASB), and rotational biological contactor (RBC). Recently, the integration of biological processes and physicochemical methods has been demonstrated to be very efficient. It is found that combined coagulation-flocculation/nanofiltration and activated sludge/reverse osmosis are more efficacious than other integrated physicochemical methods and combined physicochemical/biological methods, respectively.