Isotherm-kinetic equilibrium investigations on absorption remediation potential for COD and ammoniacal nitrogen from leachate by the utilization of paper waste sludge as an eco-friendly composite filler

The paper industry is a major environmental polluter due to paper waste sludge (PWS), often disposed of in hazardous ways. The techniques are employed to disposing of PWS are posing significant environmental hazards and risks to well-being. This study aims to evaluate PWS as a potential replacement for commercial adsorbents like AC and ZEO in treating stabilized leachate. Contact angle analysis of PWS was 92.60°, reveals that PWS to be hydrophobic. Batch adsorption experiments were conducted with parameters set at 200 rpm stirring speed, 120 min contact time, and pH 7. Optimal conditions for COD and NH3-N removal were identified at 120 min contact time, 200 rpm stirring speed, pH 7, and 2.0 g PWS ratio. Removal percentages for COD and NH3-N were 62% and 52%, respectively. Based on the results of the isotherm and kinetic studies, it was observed that the Langmuir and Pseudo second order (PSO) model exhibited greater suitability compared to the Freundlich and Pseudo first order (PFO) model, as indicated by higher values of R-squared (R2). The R-squared of Langmuir for COD and NH3-N were 0.9949 and 0.9919 and for Freundlich model were 0.9855 and 0.9828 respectively. Whereas the R-squared of PFO for COD and NH3-N were 0.9875 and 0.8883 and for PSO were 0.9987 and 0.9909 respectively.

Humic acid recovery from stabilized leachate: Characterization and interference with chemical oxygen demand-colour removal

Heterogeneous combinations of organic compounds (humic acid (HA) and fulvic acid) are the prime factor for the high concentration of colour and chemical oxygen demand (COD) in semi-aerobic stabilized landfill leachate. These organics are less biodegradable and cause a severe threat to environmental elements. Microfiltration and centrifugation processes were applied in this study to investigate the HA removal from stabilized leachate samples and its corresponding interference with COD and colour. The three-stage extraction process recovered a maximum of 1412 ± 2.5 mg/L (Pulau Burung landfill site (PBLS) leachate), 1510 ± 1.5 mg/L (Alor Pongsu landfill site (APLS leachate) at pH 1.5 and 1371 ± 2.5 mg/L (PBLS) and 1451 ± 1.5 mg/L (APLS) of HA (about 42% of the total COD concentration) at pH 2.5, which eventually indicates the process efficiency. Comparative characteristics analysis of recovered HA by scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy, and Fourier transform infrared significantly indicate the existence of identical elements in the recovered HA compared with the previous studies. The higher reduction (around 37%) in ultraviolet (UV) absorbance values (UV254 and UV280) in the final effluent indicates the elimination of aromaticity and conjugated double-bond compounds from leachate. Moreover, 36 and 39% COD and 39 and 44% colour removal exhibit substantial interference.

Sanitary landfill leachate treatment by aerated electrochemical Fenton process

The aerated electrochemical Fenton procedure was investigated as a viable treatment approach for electrolytic degradation and decolourization of sanitary landfill leachate. The optimization effects of initial pH, applied voltage, H₂O₂ concentration and combination of iron electrodes on detoxification were demonstrated by COD and colour removal from stabilized leachate, respectively. The study illustrates that, under the optimum experimental parameters voltage of 4.5 V, electrolysis time of 90 min, H₂O₂ dosage of 5 g/L, pH 3, 99% of chemical oxygen demand (COD) and 100% colour are removed from stabilized leachate, and the biodegradability ratio of the five-day biochemical oxygen demand (BOD₅) to COD increases from 0.1 to 0.72. In addition, the pure catalytic metallic iron anode and cathode electrode used in the electrochemical Fenton process was first electro-oxidized to Fe²⁺ for use during the Fenton reaction, then with Fe³⁺ that was reverted back to Fe²⁺ under the applied electrochemical-magnetic field, resulting in the iron dissolution and regeneration circuit (Fe²⁺/Fe³⁺/Fe²⁺). Additionally, Fe²⁺/Fe³⁺ served as bridges for agglomerates to coalesce into big, closely packed particles for better filterability and sedimentation action. As a preparatory step for the biochemical treatment, this technology has been effectively used to treat stabilized landfill leachate containing toxic refractory recalcitrant organics on a large scale. Additionally, by estimating the scientific experiment with a regression model approach for the outcomes, RSM software was employed in order to standardize the ECF treatment process, significantly reducing the number of test cases and trials.

Post-treatment of stabilized landfill leachate by upflow gravel filtration and granular activated carbon adsorption

Stabilized leachates from sanitary landfills generally display high levels of recalcitrant organic matter, sometimes requiring a combination of biological and physicochemical treatment processes. This study evaluated the post-treatment by Upflow Gravel Filtration (UGF) followed by Granular Activated Carbon Adsorption (GACA) on a pilot scale of two different landfill leachates previously treated by biological processes. The system design was proven technically feasible for a continuous flow post-treatment in relation to recalcitrant organic matter removal efficiency. The UGF experiments presented 83.9% and 82.0% COD removals for leachates A and B, respectively, with residual values of 107 and 194 mg L^-1. The UGF-GACA experiments, in turn, produced effluents with residual COD values of 67 and <60 mg L^-1 for leachates A and B, respectively, corresponding to 89.9% and >94.6% efficiencies.

Leachate treatment: comparison of a bio-coagulant (Opuntia ficus mucilage) and conventional coagulants using multi-criteria decision analysis

The main aim of this research was to compare a bio-coagulant, organic coagulant, and a conventional coagulant applied to the treatment of leachates. Coagulant options were Stage 1 FeCl₃, Stage 2 Polyamine, and Stage 3 Opuntia ficus mucilage (OFM). Optimal conditions for maximum chemical oxygen demand (COD) removal were determined by experimental data and Response Surface Methodology. The application of Multiple Criteria Decision Analysis using Multi-Criteria Matrix (MCM) was explored by evaluating the Coagulation–Flocculation processes. Maximum COD removal (%) and the best MCM scores (on a scale from 0 to 100) were: Stage 1: 69.2±0.9 and 48.50, Stage 2: 37.8±1.1 and 79.0, and Stage 3: 71.1±1.7, and 81.5. Maximum COD removal using FeCl₃ and OFM was not statistically different (p 0.15 < 0.05). OFM extraction process was evaluated (yield 0.70 ± 1.17%, carbohydrate content 32.6 ± 1.18%). MCM allows the evaluation of additional technical aspects, besides oxygen COD removal, as well as economic aspects, permitting a more comprehensive analysis. Significant COD removals indicate that the use of OFM as a coagulant in the treatment of stabilized leachate was effective. Opuntia ficus cladodes, a residue, were used to treat another residue (leachates).

Hollow fiber vs. flat sheet MBR for the treatment of high strength stabilized landfill leachate

The Membrane Bioreactor (MBR) technology is increasingly becoming a prominent process in the treatment of high-strength wastewater such as leachate resulting from the decomposition of waste in landfills. This study presents a performance comparative assessment of flat sheet and hollow fiber membranes in bioreactors for the treatment of relatively stable landfill leachate with the objective of defining guidelines for pilot/full scale plants. For this purpose, a laboratory scale MBR system was constructed and operated to treat a leachate with Chemical Oxygen Demand (COD) (3900-7800mg/L), Biochemical Oxygen Demand (BOD5) (∼440-1537mg/L), Total Phosphorus (TP) (∼10-59mg/L), Phosphate (PO4(3)(-)) (5-58mg/L), Total Nitrogen (TN) (1500-5200mg/L), and ammonium (NH4(+)) (1770-4410mg/L). Both membranes achieved comparable BOD (92.2% vs. 93.2%) and TP (79.4% vs. 78.5%) removals. Higher PO4(3)(-) removal efficiency or percentage (87.3% vs. 81.3%) and slightly higher, but not statistically significant, COD removal efficiency were obtained with the hollow fiber membrane (71.4% vs. 68.5%). On the other hand, the flat sheet membrane achieved significantly higher TN and NH4(+) removal efficiencies (61.2% vs. 49.4% and 63.4% vs. 47.8%, respectively), which may be attributed to the less frequent addition of NaOCl compared to the hollow fiber system.