1. Introduction
Green technology presents technology and science-based solutions that reduce negative effects on the environment and human beings in various industries, including agriculture, manufacturing, and energy [1,2,3,4]. Green technologies can be used in these areas, thus providing comprehensive solutions for sustainable development.
The result of increased water and wastewater treatment costs due to stricter regulation has become an emerging challenge since rapid industrialization, and population growth has significantly reduced the availability of water resources [5,6,7,8]. In addition, the considerable amount of wastewater discharged by industries is an issue for human beings and a significant concern for the next generations [9,10]. In recent years, there has been an increase in severe environmental pollution, which is driving industries and governments to re-examination their conventional water and wastewater purification technologies and is propelling them toward green technology development for a sustainable future [11].
In the aspect of sustainable water and wastewater purification technologies, many researchers in several sciences and engineering groups have focused their research efforts on sustainable water and wastewater treatment using greener materials and cost-effective and highly efficient techniques. They have demonstrated the elimination of organic and inorganic contaminants in water and wastewater treatment plants (WWTP) using green technologies, such as physical (e.g., eco-friendly adsorbents), biological (e.g., activated sludge), and chemical processes (e.g., oxidant and catalyst) [12,13].
This Special Issue aimed to provide an update on recent trends in green technologies for sustainable water and wastewater treatment fields. The published papers in this Special Issue deal with critical environmental problems, removing organic and inorganic contaminants in WWTP by biological treatment technologies [14,15], applying biochar for water and wastewater purification [16,17], and eliminating pesticides in rainwater runoff via oxidative processes [18].
2. Short Review of the Contributions in This Issue
Five research articles can be classified into three categories on sustainable water and wastewater purification technologies.
The first category is the cost-effective, highly efficient, and environmentally friendly biological treatment technologies to remove organic and inorganic contaminants in WWTP. Um-e-Habiba et al. revealed the significance and usefulness of designing a new beverage wastewater treatment technique via an anaerobic sludge system or operations for existing anaerobic-sludge-based methods to treat wastewater from the beverage industry [14]. Furthermore, the influence of bacteria growth on the degradation of organic matter (COD removal efficiency = 99.31% for 13 days) and the operating conditions of an anaerobic batch reactor, along with the efficiency of wastewater treatment, were estimated via microbial kinetics. Lian et al. investigated the combination mechanism of heavy metal ions and extracellular polymeric substances (EPSs) of different molecular weights in activated sludge via three-dimensional fluorescence spectroscopy [15]. The authors suggested that the application of EPSs was promising to effectively combine heavy metals from activated sludge, while it could also decrease the volume of the excess activated sludge.
The second category is the waste recycling technologies of carbon-rich substances through biomass pyrolysis for water and wastewater purification. The application of several types of biochar for the removal of various contaminants co-existing in water and wastewater was introduced in this Special Issue. Son et al. evaluated the effects of tangerine peel biochar (TB) on the removal efficiency of phosphate ions (PO43−) in the aqueous phase with/without chemical activation using CaCl2 (CTB) and FeCl3 (FTB) [16]. The experimental results presented that chemical-activated TB was enhanced in the adsorption capacities of PO43− (FTB (1.655 mg/g) > CTB (0.354 mg/g) > TB (0.104 mg/g)). Furthermore, the adsorptive removal of PO43− for the FTB was more effective than that of the TB and CTB under various pH and ionic strength conditions. These findings imply that the chemical activation with FeCl3 might be a promising option to make the TB more relevant for removing PO43− in water and wastewater. Lee et al. fabricated the engineered biochar using peanut shells (PSB) and successive chemical modifications with KMnO4 and KOH (PSBOX-A) [17]. The specific surface area of PSBOX-A was approximately 21 times greater than that of PSB after sequential chemical modification, which considerably promoted the removal efficiencies of three fungicides (i.e., carbendazim, pyrimethanil, and tebuconazole) in water.
The final category is the efficient oxidative treatment technologies of non-point source pollution in rainwater runoff. Ochir et al. investigated the removal efficiencies of selected pesticides, such as alachlor (ALA), carbendazim (CAR), diuron (DIU), pyrimethanil (PYR), and tebuconazole (TEB), in rainwater on the oxidative treatment processes by comparing their relative reactivities of three different oxidants (i.e., chlorine (HOCl), ozone (O3), and ozone/hydrogen peroxide (O3/H2O2)) under various oxidant dosages, reaction times, pH conditions, and the co-existence of organic and inorganic matters [18]. CAR, DIU, and PYR removal efficiencies by HOCl treatment were more effective than those of O3 and O3/H2O2 treatments. O3/H2O2 treatment was the most efficient oxidative technology for removing ALA and TEB. In addition, the reactivities of the selected pesticides toward the HOCl, O3, and O3/H2O2 treatments increased due to deprotonation when the pH condition of the rainwater was higher than the pKa values of the selected pesticides.
3. Conclusions
This Special Issue systematically discusses the state-of-the-art results in the range of sustainable water and wastewater purification for the accomplishment of green technology and innovative water and wastewater treatment development. Furthermore, the developments of green technology contribute to the usage of environmentally friendly materials and cost-effective and highly efficient water and wastewater treatment using biological and chemical techniques. The primary purpose of these studies is to provide valuable insights into the effective removal of organic and inorganic contaminants in various water conditions and the application of efficient green technologies in water and wastewater treatment plants.
Y.-G.L. and K.C. The authors contributed equally to this work (Conceptualization, writing—review and editing). All authors have read and agreed to the published version of the manuscript.
We would like to give special thanks to all the authors who contributed to the collection of scientific research papers in this Special Issue.
The authors declare no conflict of interest.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Details
1 Department of Environmental Engineering, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon-si 24341, Gangwon-do, Korea
2 Department of Environmental Engineering, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon-si 24341, Gangwon-do, Korea; Department of Integrated Energy and Infra System, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon-si 24341, Gangwon-do, Korea