Application of Adsorbents for Water Pollution Control

The most important application of activated carbon adsorption where large amounts of activated carbons are being consumed and where the consumption is ever increasing is the purification of domestic and industrial waste water. More than 800 specific organic and inorganic chemical compounds have been identified in ground and surface waters. Many of these compounds are carcinogenic and cause many other ailments. Several methods such as coagulation, aeration, oxidation and activated carbon adsorption have been used for the treatment of water but the activated carbon adsorption has been found to be the best broad spectrum technology available at the present moment. The more important parameters that influence and determine the adsorption of inorganics from aqueous solutions are the acidic carbon-oxygen surface groups present on the carbon surface and the pH of the solutions. These two parameters determine the nature and concentration of the ionic and molecular species in the solutions. Electrokinetic studies have shown that the nature and the extent of the carbon surface charge can be modified by changing the pH of the carbon-solution system. The adsorption of metal ions, therefore, mainly involves electrostatic attractive interactions between the metal ionic species in the solution and the negative sites on the carbon surface. The adsorption of organics, however, is quite different. The organic compounds present in water can be polar or non-polar so that not only electrostatic interactions but also dispersive interactions will play an important role. In addition the porous structure of the carbon surface which includes the existence of mesopores shall also be an important factor for the adsorption of essentially non-polar organic molecules.

This chapter aims at presenting the most common models describing the adsorption at solid/solution interfaces. Considerations are limited to the batch-type adsorption systems. The presented models are divided into two groups: models related to the equilibrium state and those describing the time-evolution of the adsorption system ('kinetic models'). A special emphasis is put on the relation between the physical models and the empirical and/or semi-empirical mathematical expressions. The issue of interpretation of the experimental data is also briefly discussed in the context of various models.

Development of new technology for drinking water and wastewater treatment is a matter of concern for researchers and decision makers worldwide. Despite the various applications of iron oxides in the fields of energy and the environment, the application of iron oxide nanoadsorbents for water and wastewater treatment has been a relatively recent area of research. This chapter focuses on the removal of various pollutants from wastewater by adsorption method using different phases of iron oxide nanoadsorbents. The chapter highlights the main synthesis techniques of iron oxide nanoadsorbents, their types, advantages, and adsorption mechanism. The effect of various operating and experimental conditions on adsorptive removal is reported; including: particle size, contact time, solution pH, temperature, and coexisting pollutants. Further, adsorption isotherms, thermodynamic studies and fixed-bed column adsorption are reported as well. The reported data are in well agreement to both Freundlich and Langmuir models. Different thermodynamic parameters, such as changes in standard Gibbs free energy (ΔG°_ads), enthalpy (ΔH°_ads) and entropy (ΔS°_ads) are also reported and supported that the adsorption process is feasible, spontaneous, and could be endothermic or exothermic in nature. Thomas and BDST are the best-fit models for the fixed-bed breakthrough. The review concludes that, after taking a precautionary approach and advanced attention, iron oxide nanoadsorbents have the potential to be employed as an alternate treatment for future wastewater treatment technologies.

This chapter provides a brief introduction of current strategies in water remediation based on nanotechnology. It describes different surface engineering strategies for enhanced and/or selective removal of different inorganic/organic pollutants from water bodies. Different factors like surface properties at nanoscale level, types of the molecules used for surface modification etc. affect the adsorption process significantly. Small molecules like, organic acids, amphiphiles to polymers and biomolecules are being used for the surface modification of nanomaterials These surface engineering strategies are crucial in water remediation technologies and are discussed thoroughly in this chapter along with recent research progress in this field.

Layered double hydroxides (LDHs) otherwise referred as hydrotalcite-like (HTlike) materials are potential sorbents that are explored widely in the field of waste water remediation of noxious anions. The structural features of LDHs makes them effective sorbents for these anions through different mechanism like surface adsorption, anionexchange, reconstruction and surface precipitation. This chapter presents a discussion about LDHs, their synthesis methodologies, physicochemical characterization and their potential in the removal of environmentally undesired oxoanions like phosphate, borate and chromate from aqueous solutions. The optimization of the various parameters like sorbate concentration, pH, temperature, time, extent of removal in the co-presence of competitive anions and reusability are discussed in respective sections. A comparison of the anionexchange capacity of LDHs with commercial anion exchangers is also discussed. Different mechanisms involved in the removal of phosphate, borate and chromate anions by LDHs are addressed.

In this chapter, the development of novel, highly ordered, mesoporous materials, which can be used to provide active sorbents for mitigation of environmental pollutants, has been discussed. Specifically, focus was given on the use of these materials for water pollution remediation through the extraction of metal ions and phosphate ions (as these are the most important pollution problems in industrialised regions). Also, a review is presented on some of the recent works in this field including some of our most recent studies. A variety of porous materials were synthesised including mesoporous particles and macroporous spheres and these were characterised using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and nitrogen adsorption techniques to establish the pore diameters, material morphology, packing of the pores and specific surface areas of the materials. Pure silica materials have limited efficacy in these applications and it was necessary to modify their properties with a selection of ligands and metal ion dopants to tailor their sorptive properties towards the selected applications. The extraction efficiencies of each sorbent was quantified using a number of analytical procedures depending on the nature of the pollutant studied.

In this chapter, the feasibility of kaolinite like alternative adsorbent for wastewater treatment has been discussed. Kaolinite is widely used in various industrial processes. Besides these applications, kaolinite has also been used in the environmental applications, with special emphasis on the treatment of industrial effluents. Due to its low cost and efficient adsorptive character, its utilization has been studied for the removal of flotation reagents in iron mineral processing and dyes from wastewater in textile industry. A detailed characterization of kaolinite is presented. The results demonstrated that kaolinite has higher potential for these organic compounds which makes it a good alternative for the wastewater treatment. The adsorption kinetics and isotherms have also been discussed.

In this study, the use of a common clay mineral, montmorillonite and its modified derivatives for adsorptive removal of toxic heavy metals from aqueous system has been reviewed. The modification of clay was primarily done by pillaring with various polyoxy cations of Zr₄₊, Al₃₊, Si₄₊, Ti₄₊, Fe₄₊, Cr₃₊ or Ga₃₊, etc. Some quaternary ammonium cations, viz, tetramethylammonium-, tetramethylphosphonium-, trimethylphenylammonium-, etc. are also used for pillaring purposes. Moreover the acidactivation of montmorillonite is also reported. The adsorption of toxic metals, namely, Cd, Cr, Co, Cu, Fe, Pb, Ni, Zn, etc. have been studied predominantly. Various experimental parameters, like, pH of metal solution, amount of montmorillonite, initial metal ion concentration, interaction time, temperature, etc. are considered for adsorption process. Application of models as given by the Freundlich, Langmuir etc. has been shown by many authors and these have also been reviewed. The review aims to give a comprehensive picture on the studies of isotherm of adsorption for metal removal on montmorillonites during the last few years.

There are abundant natural materials in the world with diverse field applications. Some of these are well known and familiar to mankind from the earliest days of civilization. Some of these are used as adsorbents in water and wastewater treatment. Adsorption effectively removes specific pollutants from wastewaters and adsorption phenomena in solution systems play important roles in many areas of practical environmental technology. In this chapter, the classification and structure of natural materials and their uses, specifically in relation to adsorption are discussed. Economic aspects of natural materials are also evaluated.

The aim of this chapter was to show how the concentration of some organic compounds may be reduced by means of natural zeolites as sorbents. Among many chemicals found in natural water systems, here we focused on humic acids, phenylureas and triazines herbicides. Zeolites such as phillipsite and chabazite were found to exhibit a marked ability to sorb humic acids, in particular, when their surface is enriched in calcium ions; the latter act as a bridge between the negative surface of the mineral and the humic macromolecules. Sorption of humic acids is also influenced by reaction time, pH and ionic strength of the solution. Organo-zeolites aggregates (humic acids – phillipsite/chabazite aggregates) were found to be efficient sorbents for phenylureas herbicides by a partition process; the uptake increases with the hydrophobicity of the chemical. Atrazine is efficiently removed from water using acid-modified zeolites. The presence of H₊ on the aluminosilicate surface favours the protonation of the azo and amino nitrogen atoms of atrazine and consequently its electrostatic bonding to the negative charged surface of the mineral phase. Experiments carried out on aqueous samples simulating natural water systems revealed that different organic compounds can be simultaneously sequestered combining different types of zeolites. Basing on the above results, natural zeolites may be considered effective sorbents for organic compounds occurring in natural water.

In this chapter, we have reviewed the results of different studies on the removal of aquatic pollutants especially heavy metals and organics by various biosorbents. Among several sorbents used by different researchers, only agricultural solid wastes without any chemical treatments, i.e. identified as “low cost adsorbents”, are considered. In the adsorption process, the effect of different parameters such as: pH, dose of adsorbent, initial pollutant concentration, contact time, adsorbent particle size, temperature, etc. have been investigated. Among them, pH was found to play an important role in the removal of pollutants by biosorbents. The optimum value of pH for maximum adsorption is reported based on the results of various studies. In some cases, the best adsorption isotherms and kinetic models are also introduced for the prediction of adsorbent behavior. This summary information would help in selecting and deciding suitable cheap biosorbents based on local agricultural wastes for the removal of common pollutants globally.

In this chapter, biochars used as a low-cost adsorbent for wastewater treatment have been summarized including the concept, methods of production, property of structure, capacity and mechanism of adsorption for hazardous materials and some recommendations for future work.

This chapter addresses the application of rice husk and bagasse ash as adsorbents to remove dyes from textile and printing wastewater and heavy metals, such as nickel, from electroplating wastewater. Rice husk was used in removal of basic, direct and acid dyes. A study on the adsorption of basic dyes onto rice husk involved electrostatic interactions. Evidence showed that lignin, cellulose and hemi-cellulose were the main components involved in dye adsorption. Because of alterations to active –CH, −OH, ketone and carboxylate functional groups, heating decreases the ability of rice husk to adsorb direct and acid dyes. Rice husk has also been used to adsorb nickel from electroplating wastewater. Rice husk modified by 0.1 M NaOH can adsorb nickel higher than original rice husk, thus confirming the mechanism as chemical adsorption involving ion exchange. Decolorization of sugar syrup and vegetable oil by these agricultural residues was also studied. Production of activated carbon from rice husk and bagasse ash was characterized and used for decolorization of vegetable oils such as rice bran oil. Bagasse ash was also applied in the decolorization of sugar syrup via a mechanism involving electrostatic interactions. Bagasse ash was used as an adsorbent in the treatment of wastewater containing water-based ink. In addition, bagasse ash can be used to adsorb dyes in wastewater before it is discharged into natural water systems.

This chapter discusses the use of Electric Arc Furnace (EAF) slag as a safe, effective and inexpensive end-of-pipe add-on solution for improving the treatment of urban stormwater runoff. Stormwater comprises a complex mixture of constituents, which at elevated concentrations can be very harmful to receiving surface waters. Its treatment therefore requires an optimal mix of technologies or treatment train that achieves acceptable end-point water quality prior to its discharge into an aquatic environment. Existing popular stormwater treatment measures such as grassed swales, detention ponds and constructed wetlands, while effective in removing certain components such as suspended solids, have not fared very well in dealing with dissolved nutrients and heavy metals. In the right concentrations, these become pollutants and find their way to water bodies downstream where they have been known to create a host of health and economic challenges for the communities that rely on these water supplies for their upkeep and well-being. Dissolved phosphorus is of particular interest as it has been known to cause an over-enrichment of nutrients in freshwater habitats around the world, and the subsequent degradation of those water systems. Thus the need for safe, effective and affordable add-on solutions to address this stormwater treatment gap is an important research focus. Industrial by-products, such as EAF slag from the steel recycling industry, provide an interesting option for this treatment challenge in the communities where they are produced. They are largely inexpensive, locally available and present in very large quantities. Their use also lessens the environmental costs of waste disposal for the manufacturing company, and creates additional revenue. This chapter looks at dissolved phosphorus and different studies that conclude the general effectiveness of these industrial materials to remove dissolved phosphorus from solution. Particular interest is paid to EAF slag due to its vast availability in the region under discussion (North America). However, these findings may be extended to other locations around the world where EAF slag, or materials of similar composition and characteristics, are available in significant quantities. The discussions on EAF slag presented in this chapter conclude that it is a low-cost adsorbent with vast potential to effectively sequester dissolved phosphorus from stormwater. This means that EAF slag can act as a viable end-of-pipe add-on technology to existing stormwater treatment systems for improved effluent quality.

Victorian lignite, a cheap natural energy resource from southeast Australia, has previously shown very high adsorption capacity for cationic methylene blue dye in aqueous solutions without the need of any pretreatment. The kinetics of the adsorption process was examined using both pseudo first order and pseudo second order models. By combining the results of linear and non-linear regression, it was concluded that the pseudo second order model predicted the chemisorption process of methylene blue the best, while a general first order model by Annadurai and Krishnan fitted the experimental data well, except for the initial stage. Further analysis of the adsorption mechanisms suggested that the external film diffusion was the rate-controlling step only at the initial stage of the adsorption. As the initial dye concentration increased, the length of this stage was reduced. After 6 to 40 minutes, depending on the initial dye concentration, mass transfer by intraparticle diffusion became the limiting mechanism before reaching equilibrium.

Bone char is traditionally used in sugar industry for color and turbidity removal. Due to its excellent adsorptive character, it has been applied for the removal of metals from mining and metallurgical effluents, dyes from textile industry wastewater, flotation reagents in iron mineral processing and defluoridation of water. A detailed characterization of bone char was conducted in the present study. Thermodynamic and kinetics aspects of adsorption using bone char in these systems are presented. The results depict a high affinity of bone char for both organic and inorganic compounds which makes it a potential adsorbent for chemically complex solutions. The adsorption mechanisms are also discussed.

This note briefly summarizes the progress and advances in adsorption technology for water remediation. Although numerous adsorbents have been developed and examined in water treatment, their potential needs to be further assessed on pilot scale with real surface/ground water and/or wastewater. Development of some synthetic, hybrid and nano-scale adsorbents show high efficiency towards specific pollutants removal, but more research is needed prior to their use in full-scale application in water and wastewater treatment.