Recent Trends and Innovations in Sustainable Treatment Technologies for Heavy Metals, Dyes and Other Xenobiotics

One of the most important issues in recent times is the remediation of wastewater discharged from different industries. Several of the growing economies have been investing heavily to reduce the discharged waste content for economic and environmental sustainability. The wastewater when discharged into natural water bodies harms the flora and fauna of the surrounding environment, which in turn disrupts the ecosystem and affects the food chain. It also increases and possesses a variety of health risks to human beings. To eliminate the potential threats, a critical analysis of the past research and upcoming remediation technologies is necessary. Over the years, a lot of advancements have been made to curb the disruption of the natural ecology from effluent discharges by different industries like the leather industry wastewater, Rice mill wastewater, pharmaceutical industry wastewater and Coke Oven wastewater. The common characterization techniques that are employed in all of them are to measure the COD and BOD levels, pH, odor, TSS, organic and inorganic materials. Subsequently, the common technologies that are in use to treat these wastewaters are mainly physicochemical treatments like adsorption, electrocoagulation/ flocculation, nanofiltration, Fenton’s oxidation or biological treatments like aerobic/anaerobic microbial degradation. An important requirement is to understand the situation currently prevalent in wastewater treatment to develop better and advanced methods for increased efficiency and waste removal. The aim of this chapter is to give a detailed account on the composition, characterization, and treatment strategies of the discharged effluent to enhance the knowledge of available resources and instigate ideas of future improvements.

Conventional technologies such as stripping, liquid-liquid extraction, chemical precipitation, adsorption, and the advanced oxidation process among others have been applied for the treatment of wastewater. The imposition of stricter regulations on discharge limits has led to a search for novel technologies to make the conventional wastewater treatment technologies efficient and cost-effective. High gravity technology uses centrifugal force to create artificial gravity which is hundreds of times the terrestrial gravitational force. Equipment working in high gravity environment intensifies the rate of mass transfer, micromixing and allows a higher amount of fluid to flow through the devices. The usefulness of high gravity technology for enhancing the performance of wastewater treatment processes has been discussed. 

Heavy metals, dyes and xenobiotic compounds are the primary environmental contaminants that are accumulating at higher rates attributed to increased industrialization and uncontrolled release without treatment. These pollutants have also raised serious concerns about life on earth, attributed to their recalcitrance and tenacity in the environment. The treatment strategies currently utilize chemical methods, such as advanced oxidation processes (AOPs) and catalytic processes, whereas biological processes such as adsorption and accumulation are also predominant. However, AOPs and catalytic processes are proven to be the potential methods for heavy metals, dyes, and xenobiotic pollutant remediation in large-scale applications. Identification and synthesis of novel molecules/ materials that can effectively recover and remediate heavy metals, dyes and xenobiotic compounds from wastewater remain one of the key approaches. This chapter highlights the success of AOPs and catalytic processes in the degradation of dyes, pharmaceuticals compounds, and heavy metal ions from different water environments and possible future prospects.

Anthropogenic activities have led to widespread pollution in aquatic bodies due to extensive dissemination of refractory contaminants such as heavy metals, dyes, and xenobiotics. Adsorption is well recognized as a suitable technology for the removal of these pollutants. The major objective of this book chapter is to summarize recent advancement in this field. Accordingly, the book chapter starts with a brief introduction explaining the potential of the technology as compared to other competitive operations, followed by the identification of thrust areas to work on and the construction of a “template” to evaluate the progress in the technology. Next, recent developments in the preparation of various types of adsorbents (activated carbon-based traditional adsorbents, zeolites and clay minerals, adsorbents of biological origin, composite adsorbents having nanoparticles impregnated in a suitable matrix) have been elaborated. The chapter then focuses on how different process parameters may affect the efficiency of these adsorbents in removal of heavy metals, dyes, and xenobiotics. Finally, a comprehensive discussion has been made about how different mathematical models have been applied in recent times to fit experimental equilibrium and kinetic data obtained from the batch adsorption experiments, along with a critical evaluation of frequently used models. The chapter ends with a recommendation regarding future trends in adsorption technology.

The present review draws on a wide range of resources available on bioderived, bioconjugated, chemisorption technologies and strategies known for degradation of heavy metals. The prevalent escalation in application of heavy metals, chemically synthesized dyes and xenobiotic compounds has created major environmental disruptions. Industries, mining, vehicles, and household activities release heavy metals and their derivatives into a multitude of water resources. Contaminated water provides an easy ingress of these contaminants into human and animal system resulting in exposure related disorders like mutagenesis, carcinogenesis and other serious health issues. Minimization and management of such chemicals demands high end technology, equipment, time, effort and cost. Thus, the less demanding but more effective strategy would be adoption of biosorption, using whole plant/microbial cells, components, derived and/or synthesized materials to convert toxic compounds/metals into less toxic forms. This review documents, critically analyses and collates heavy metals from mining, processing and industrial effluents followed by remediation technologies based on plants and microbes. Each section in the latter is discussed in detail with relevant examples that illustrate biosorption, bioderived, bioconjugated, chemisorptions, and bioremediation strategies. In the final analysis, though plant materials exhibit efficient removal strategies, particularly when augmented by nanomaterial conjunction, the commercial scale and viability remain to be validated

Over 100 tons of dyes are released per year into the wastewaters without prior treatment which adds to the contamination of freshwater resources globally. Thus, the development of economical, and sustainable control measures to avoid the pollution of natural resources remains imperative. In the present scenario, recent advancements in biological approaches have escalated bioremediation as a potential strategy for treatment of dyes and associated derivatives. These biological approaches utilize simple to complex microorganisms, plants, and wastes generated from different animal products as tools to remediate and remove dye molecules from wastewater. This particular chapter targets to address the recent advancements in the past three to four years in the sustainable treatment of dye molecules from wastewater using bioremediation approaches. The study also includes the prevailing hurdles, and research prospects in the bioremediation techniques utilized for the reduction of dyes from wastewater. 

This chapter covers bottlenecks in various sustainable physio-chemical processes including membrane filtration, activated carbon filtration, adsorption, advanced oxidation processes, dissolved air floatation, coagulation-flocculation and sedimentation, and electrocoagulation process for removing heavy metal ions, dyes, and xenobiotics from the aquatic environment. The approach taken in this chapter is to give a quick overview of each phase before focusing on the bottlenecks that these processes face when it comes to removing metal ions and organic matter from wastewater. Performance, cost, and sustainability criteria for sustainable wastewater treatment technologies are also covered in this chapter for each process. 

Exponential growth in population associated with changing lifestyle patterns and industrial upheaval has led to the degradation of the most valuable renewable resource i.e. water. Contamination of water bodies of varying sizes across the world has resulted in mass-scale deterioration of health and environmental adversaries. Uninhibited disposal of domestic, municipal and industrial effluents onto water bodies has severely impacted the flora and fauna, in turn affecting human health globally. If unchecked, this would lead to an unmitigated disaster, which would be detrimental to the very existence of humans on the planet. Wastewater remediation, therefore, is of paramount importance to safeguard water bodies and prevent them from excessive pollution. To that end, novel, sustainable technologies for elevated nutrient removal from wastewater are the need of the hour. Bioremediation of wastewater is one of the most prolific and novel approaches directed towards the efficient elimination of contaminants coupled with their subsequent conversion into value-added products. Over the last few decades, microbial treatment processes have gained increasing momentum due to their ease and high efficiency compared to conventional treatment technologies. The chapter provides a detailed overview of various biological wastewater treatment methodologies such as bacterial, fungal, microalgal and microalgae-bacteria consortium-mediated bioremediation.