An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus.

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

Enhanced bioenergy and nutrients recovery from wastewater using hybrid anodes in microbial nutrient recovery system.

BACKGROUND: The combined microbial fuel cell-microbial nutrient recovery system has lately been thoroughly explored from an engineering standpoint. The relevance of microbial communities in this process, on the other hand, has been widely underestimated. RESULTS: A lab-scale microbial nutrients recovery system was created in this work, and the microbial community structure was further defined, to give a thorough insight into the important microbial groups in the present system. We reported for the first-time different hybrid anodes of activated carbon and chitosan that were used in the microbial nutrient recovery system for bioenergy production, and, for the removal of COD and recovery of nutrients present in the wastewater. The hybrid anodic materials were studied to adapt electrochemically active bacteria for the recovery of nutrients and energy generation from wastewater without the need for an external source of electricity. The potential of the created hybrid anodes in terms of nutrients recovery, chemical oxygen demand elimination, and energy generation from municipal wastewater was thoroughly examined and compared with each other under similar operating conditions. When the COD loading was 718 mg/L, a total COD removal of ~ 79.2% was achieved with a hybrid activated carbon and chitosan anode having an equal ratio after 10 days of the operation cycle. The maximum power density estimated for hybrid anode (~ 870 mWm-2) was found. CONCLUSION: Overall, this work reveals a schematic self-driven way for the collection and enrichment of nutrients (~ 72.9% phosphorus recovery and ~ 73% ammonium recovery) from municipal wastewater, as well as consistent voltage production throughout the operation.

Effect of modified anode on bioenergy harvesting and nutrients removal in a microbial nutrient recovery cell.

The microbial nutrient recovery cell i.e. modified microbial fuel cell containing a middle recovery chamber can be used to purify wastewater and remove valuable nutrients, while simultaneously generating electricity. The study investigated nutrient removal and microorganism interactions with carbon (CB- HT and CB- APTES) and stainless steel (SSB-HT) modified anodes used in microbial nutrient recovery cells. The removal efficiencies of ammonium ions were found higher in carbon-based CB-APTES (~98%) and CB-HT (~98.27%) systems in comparison to SSB-HT (~87.16%) system. On comparing further, the removal efficiencies of chemical oxygen demand (~99.5%) and total phosphorus (~99%) in CB- APTES system were superior to the cases of CB- HT, and SSB- HT systems. Besides, the CB-APTES based microbial fuel cell (MFC) displayed an average stable voltage of 0.5 V and a maximum power density of ~ 850 mW/m2.

Adsorption, degradation, and mineralization of emerging pollutants (pharmaceuticals and agrochemicals) by nanostructures: a comprehensive review.

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

Understanding the factors affecting the adsorption of Lanthanum using different adsorbents: A critical review.

Over the past few decades, removal and recovery of Lanthanum (La) have received great attention due to its significance in different industrial processes. In this review, the application of various adsorbents viz. biosorbents, commercial and hybrid materials, nanoparticles, nanocomposites etc. have been summarized in terms of the removal and recovery of La. The influence of various operating parameters including pH, dosage, contact time, temperature, coexisting ions, adsorption kinetics, isotherm and thermodynamics were investigated. Statistical analysis of the obtained data revealed that 60% and 70% of the authors reported an optimum pH of 4-6 and a dose of 1-2 g/L, respectively. It can be concluded on the basis of an extensive literature survey that the adsorbent materials (especially hybrids nanocomposites) containing carboxyl, hydroxyl and amine groups offered efficient La removal over a wide range of pH with higher adsorption capacity as compared to other adsorbents (e.g., biosorbents and magnetic adsorbents). Also, in most cases, equilibrium and kinetics were followed by Langmuir and pseudo second-order model and adsorption was endothermic in nature. To evaluate the adsorption efficiency of several adsorbents towards La, desorption and regeneration of adsorbents should be given due consideration. The main objective of the review is to provide an insight into the important factors that may affect the recovery of La using various adsorbents.

N- and O- ligand doped mesoporous silica-chitosan hybrid beads for the efficient, sustainable and selective recovery of rare earth elements (REE) from acid mine drainage (AMD): Understanding the significance of physical modification and conditioning of the polymer.

Silica-chitosan hybrid beads were synthesized via three different methods to investigate the selective recovery of REE from AMD. The influence of amino/non-amino silanes, high molecular weight/high viscous chitosan and N-/O- based ligands were studied and their effects on REE removal efficiencies were analyzed. The adsorption efficiencies of three various groups of modified beads were inspected with respect to feed pH, in a single and a multi-component system, and their affinities towards the light and heavy rare earth elements (LREE/ HREEs) were interpreted to understand the intra-series REE separation behavior. The focus of the study was mainly directed towards utilizing these fabricated beads for the recovery of valuable REEs from the real AMD obtained at three different sampling depths which was found rich in iron, sulfur and aluminum. Moreover, the selectivity of the beads towards REEs improved with silanized and ligand immobilized gels and their impacts on REE recovery in the presence of competing ions were successfully presented in this paper. Also, the synthesized beads showed rapid REE adsorption and recovery within a process time of 5 min. Group II adsorbents, synthesized by forming silica-chitosan hybrid beads followed by PAN/acac modifications, showed superiority over the other groups of adsorbents.

Chemically immobilized and physically adsorbed PAN/acetylacetone modified mesoporous silica for the recovery of rare earth elements from the waste water-comparative and optimization study.

This study was aimed at the investigation of Rare Earth Element (REE) recovery from aqueous solution by silica gels with 1-(2-Pyridylazo) 2-naphthol (PAN) and acetyl acetone (Acac) modifications. The two different methods of silica gel chelation, such as chemical immobilization with the help of silane coupling agents (3-aminopropyl triethoxysilane (APTES) and 3-aminopropyl trimethoxysilane (APTMS) in this study) and direct physical adsorption onto the silica surface, is compared in terms of their REE removal efficiency. A comparative analysis between adsorption of different REEs for different silica gels is performed and the influence of parameters such as pH, contact time, temperature and initial concentration has been reported. The effect of calcined adsorbents on the adsorption process is also investigated. Characterization studies on silica gels by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and zeta potential analysis are performed to better understand the relation between physical/chemical attributes of the adsorbents and their impact on the adsorption process. The experimental results are evaluated and optimal conditions for REE adsorption are identified. Chemically immobilized gels demonstrated immense potential for all the REE under study except Sc, for which, physically loaded gels seemed to be more efficient. The removal of REEs could be achieved at lower pHs by chemically immobilized PAN/Acac gels, making it suitable for many practical applications. The amine functionalized gels before chemical immobilization step were compared with PAN/Acac chemically immobilized gels in single as well as multi element system and the significance of chemical immobilization after amine functionalization is also stated.