Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min−1 providing a sample throughput of more than 15 samples h−1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.

The proper management of municipal solid waste for the reduction of its potential impacts on the environment is one of the most challenging issues faced by the world. In this study, a comprehensive characterization of leachate and groundwater was carried out surrounding the Oum Azza sanitary landfill in Morocco to assess their potential risks to human health. The groundwater quality was analysed using quality indices and chemometric expertise. For this purpose, spatiotemporal variation of sixteen (16) physico-chemical parameters and nine (9) heavy metals (Cd, Pb, Ni, Cu, Cr, Hg, Ni, Zn, and Fe) in groundwater and leachate were studied. Experimental data showed elevated leachate contamination potential (LPI = 29.14) surpassed the permissible limits for discharge of leachate. Besides, the application of WQI (27.47–214.58), Nemerow index (0.72–6.17), irrigation quality indices (SAR, MHR, %Na, KI, and PI), and spatial distribution revealed the unsuitability of most of the groundwater samples in vicinity of the landfill area for drinking and irrigation purposes. However, the carcinogenic and non-carcinogenic risks are still within acceptable limits for residential receptors. The multivariate statistical (PCA and HCA) analysis suggested that the deterioration of groundwater quality was mainly originated from anthropogenic sources related to landfill leachate. This study proved an alarming threat of the groundwater in vicinity of the sanitary landfills due to leachate pollution. It is important to note that despite the fact that the landfill is a sanitary landfill and provided with liners, leachate contamination potential is inevitable. Thus, it is important to continuously monitor the groundwater quality surrounding the landfill. The study also recommended emphasizing on the status and conditions of geomembrane used in the landfill liner systems to prevent leachate percolation into the groundwater.

The escalating loads of municipal solid waste (MSW) end up in open dumps and landfills, producing continuous flows of landfill leachate. The risk of incorporating highly toxic landfill leachate into environment is important to be evaluated and measured in order to facilitate decision making for landfill leachate management and treatment. Leachate pollution index (LPI) provides quantitative measures of the potential environmental pollution by landfill leachate and information about the environmental quality adjacent to a particular landfill. According to LPI values, most developing countries show high pollution potentials from leachate, mainly due to high organic waste composition and low level of waste management techniques. A special focus on leachate characterization studies with LPI and its integration to treatment, which has not been focused in previous reviews on landfill leachate, is given here. Further, the current review provides a summary related to leachate generation, composition, characterization, risk assessment and treatment together with challenges and perspectives in the sector with its focus to developing nations. Potential commercial and industrial applications of landfill leachate is discussed in the study to provide insights into its sustainable management which is original for the study.

Landfill leachate has created significant environmental issues throughout the world. Most of the developed countries have strict guidelines for the management of solid waste landfills as opposed to the open waste dumps commonly used in developing countries. Karadiyana is an open dumpsite which is in operation for nearly 20 years, located in the Western Province of Sri Lanka with a total area of about 25 acres. This open dumpsite is located very close to the Weras Ganga - Bolgoda Lake wetland system. A small stream known as Meda Ela runs parallel to the site A of the dump receives landfill leachate as overland flows and as leachate contaminated groundwater polluting its waters. Meda Ela intercepts the Weras Ganga - Bolgoda Lake adjacent to the dumpsite and delivers most of its polluted waters to the lake. In this paper, the water quality of Meda Ela and two ground water monitoring wells were investigated to assess the impact of the dumpsite on water quality deterioration. Water quality parameters; electrical conductivity (EC), pH, ORP, dissolved oxygen concentration, total dissolved solids (TDS), ammonia, nitrate, Cu, Mn, Fe, Zn, Cr and Cd were studied over two years. Investigational analysis of experimental data was carried out with principal component analysis, box plots, and ANOVA to identify the degree of water quality deterioration. Comprehensive pollution index method has been carried out with eleven (11) water quality parameters to determine the overall water quality of Meda Ela which categorized its water as moderately polluted water. PCA was used to identify four principal components demonstrating 89.8 % cumulative variance. The concentration of ammonia, nitrate and phosphate in monitoring wells were significantly higher with average values 346 ± 39 mg L−1, 151 ± 48 mg L−1 and 62 ± 11 mg L−1 respectively.

Halloysite nanoclay was utilized to retain aqueous oxytetracycline (OTC) which is extensively used in the veterinary industry. The micro-structure and functionality of the nanoclay were characterized through spectroscopic techniques before and after adsorption. The OTC removal experiments were performed at different pH conditions (pH 3.0–9.0), ionic strengths (0.001, 0.01, 0.1 M NaNO3) and contact time (up to 32 h) at an initial 25 mg/L OTC concentration with 1.0 g/L halloysite. Oxytetracycline adsorption was pH dependent, and the best pH was observed in the range of pH 3.5–5.5 at a 0.001 M ionic strength. At pH 3.5, the maximum OTC adsorption amount was 21 mg/g which translated to 68% removal of the initial OTC loading. Positively charged inner lumen and negatively charged outer lumen of the tubular halloysite structure led to form inner-sphere complexes with the anionic and cationic forms of OTC, respectively. A rapid adsorption of OTC was observed in the kinetic study where 62% OTC was adsorbed in 90 min.. Pseudo-second order equation obeyed by the kinetic data indicated that the adsorption was governed by chemisorption, whereas Hill isotherm equation was the most fitted with a maximum adsorption capacity of 52.4 mg/g indicating a cooperative adsorption phenomenon.

In this paper, we investigate the release of heavy metals from sludge produced from an electrical industry using both organic and inorganic acids. Single and sequential extractions were conducted to assess heavy metals in different phases of the sludge. Metal release from sludge was investigated in the presence of three inorganic acids (nitric, sulfuric, and phosphoric) and three organic acids (acetic, malic, and citric) at concentrations ranging from 0.1 to 2.0 mol L−1. Sequential extraction indicated the presence of Cu primarily in the carbonate fraction, Pb in the residual fraction, and Ni in the FeMn oxide fraction. The cumulative release rates of heavy metals (i.e., Pb, Cu, and Ni) by 1.0 mol L−1 of acid increased with the use of the following acids in the order of: malic < sulfuric < acetic < phosphoric < citric < nitric. Acetic acid exhibited the highest release of Cu, at a rate of 72.62 × 10−11 mol m−2 s−1 at pH 1, and malic acid drove the release of Pb at a maximum rate of 3.90 × 10−11 mol m−2 s−1. Meanwhile, nitric acid provided the maximum rate of Ni release (0.23 × 10−11 mol m−2 s−1) at pH 1. The high rate of metal release by organic acids is explained through ligand-promoted mechanisms that enhance the release of metal ions from the sludge. The results from our study emphasize that an understanding of the metal release mechanism is key to selecting the optimal acid for the maximum recovery of heavy metals.

Excessive amounts of fluoride ions and other heavy metals in drinking water instigate a solemn threat to human health. Even though materials with specific binding ability towards these ions have been developed, it is yet a challenge to meet the practical utility of developing an efficient remedy as such. With this regard, a novel tri-metal composite incorporated polyacrylamide (TCIP) has developed. TCIP has shown a significant binding efficiency towards arsenate, chromate and fluoride ions in the presence of the other competing anions. The maximum adsorption capacities (qmax) of 43.85, 42.25 and 107.52 mg/g were achieved for arsenate, chromate and fluoride respectively at 300 K and in pH 7.00. Arsenate, chromate and fluoride adsorption is highly pH dependent. Monolayer adsorption of arsenate, chromate and fluoride ions was observed and adsorption data were found well behaved with the Langmuir adsorption isotherm. Arsenate, chromate and fluoride adsorption to TCIP has shown pseudo-second order adsorption kinetics, and no leaching of metal ions was observed from the metal composite into the aqueous medium.

The focus of this research was to synthesize novel clay-biochar composites by incorporating montmorillonite (MMT) and red earth (RE) clay materials in a municipal solid waste (MSW) biochar for the adsorptive removal of tetracycline (TC) from aqueous media. X-ray Fluorescence Analysis (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Powder X-ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM) were used for the characterization of the synthesized raw biochar (MSW-BC) and clay-biochar composites (MSW-MMT and MSW-RE). Results showed that minute clay particles were dispersed on biochar surfaces. The FTIR bands due to Si-O functional group vibrations in the spectra of the clay-biochar composites provided further evidence for successful composite formation. The kinetic TC adsorption data of MSW-MMT were well fitted to the Elovich model expressing high surface activity of biochar and involvement of multiple mechanisms in the adsorption. The kinetic TC adsorption data of MSW-BC and MSW-RE were fitted to the pseudo second order model indicating dominant contribution of chemisorption mechanism during the adsorption. The adsorption differentiation obtained in the kinetic studies was mainly due to the structure of the combined clay material. The adsorption isotherm data of all the adsorbents were well fitted to the Freundlich model suggesting that the adsorption of TC onto the materials occurred via both physisorption and chemisorption mechanisms. In comparison to the raw biochar and MSW-RE, MSW-MMT exhibited higher TC adsorption capacity. Therefore, MSW-MMT clay-biochar composite could be applied in the remediation of TC antibiotic residues in contaminated aqueous media.