This special issue contains 7 articles that are disseminating the physical, chemical and biological process techniques and tools for pollution prevention and sustainability. They are selected from the presentations made at the 13th annual international conference on the “Challenges in Environmental Science and Engineering”, CESE-2020 that was held online on the 7th and the 8th of November 2020. There were 177 delegates from 18 countries and regions participated in CESE-2020. This special issue covers the removal of chemical species such as phosphorus from water and related effects, recovery of chemical species such as copper and nickel, carbon capture using activated carbon, utilization of hydrogels, detection technology and inverter technology.

One article on chemical species removal discusses about fixed-bed column dynamics of ultrasound and Na-functionalized diatomite (U-D-Na) to remove phosphate from water. The U-D-Na was functionalized by the inexpensive NaCl reagent after simple ultrasonic purification of diatomite. The maximum removal rate of phosphate was found to be more than 95%, and a thrice loop of effective regeneration was achieved with 0.1 M hydrochloric acid eluent and deionized water. Therefore, the authors concluded that the U-D-Na could be used as a better alternative phosphate adsorbent for wastewater in a continuous column sorption process. The next article on chemical species removal discusses the reduction of N2O generation during denitrifying phosphorus removal with propionate as carbon source in sequencing batch reactors. The study found that the nitrogen removal was 40.6% lower when propionate was used as the carbon source instead of acetate, while phosphorus removal was similar. Enrichment of glycogen-accumulating organisms in the acetate system suggested to cause higher N2O production in the acetate system. The lower nitrite accumulation in the propionate system compared to the acetate system was found to be the dominant factor leading to the lower N2O production. The article on recovery deals with the competitive effect of copper and nickel recovery with carbonate in the fluidized-bed homogeneous granulation process (FBHGP). It aims to recover copper and nickel from the wastewater originating from printed circuit boards (PCB) processes using a FBHGP. FBHGP is an advanced green technology that removes copper and nickel and transforms the sludge into a hard granule. The study found that the copper has been successfully recovered from synthetic PCB wastewater using FBHGP. However, the nickel needs a multi-step fluidized bed reactor.

The article on hydrogels focusses on the shape stable poly(vinyl alcohol) (PVA) hydrogels with immobilized metal hexacyanoferrates for radioactive caesium removal from waters. The metal hexacyanoferrates with transition metal ions to replace ferric ions in the face-centred cubic structure of Prussian blue (PB) crystals (a total of eight PB analogue particles in two families M3[Fe(III)(CN)6]2 (MFe(III)) or M4[Fe(II)(CN)6]2 (MFe(II)) with M = Zn, Ni, Cu, or Co synthesized in this study) are candidate adsorbents for caesium ions. The PVA-CoFe(III) was found to be the best candidate for enhanced Cs removal. The article on carbon capture investigates the production and characterization of bamboo-based activated carbon through single-step H3PO4 activation for CO2 capture. A single-stage phosphoric acid (H3PO4) activation is adopted at a constant temperature and holding time. The prepared activated carbon via 50 wt% H3PO4 activation shows the highest BET surface area and carbon dioxide (CO2) adsorption capacity of 1.45 mmol g−1 at 25 °C/bar and 9.0 mmol g−1 at 25 °C/30 bar.

The article on detection technology investigates a new electrode constructed via the anodic electropolymerization of poly-(L-serine) (PLS) on a reduced graphene oxide (rGO) − Nafion–modified glassy carbon electrode (GCE) for the detection of the emerging organic contaminant naproxen (NPX). The synergistic effect of PLS and rGO − Nafion was found to facilitate the catalytic oxidation of NPX on PLS/rGO − Nafion/GCE greatly. The modified electrode exhibited excellent linearity with respect to NPX concentration in the range of 4.3 to 87 μM, and the limit of detection was 0.23 μM.

The article on inverter technology elaborates the CC-LA: Determining Optimal Switching Angles in Cascaded H-bridge Multilevel Inverter with the aid of Binary Cat Cubpool-based Lion Algorithm. The objective of optimizing the switching angle is to generate the needed fundamental voltage and minimize the harmonic content.

The guest Editors of this special issue are thankful to the Editor-in-Chief of Environmental Science and Pollution Control Journal, Professor Garrigues, and the publishing editor Alexandrine Cheronet for providing an opportunity to publish selected peer-reviewed papers that were presented at CESE-2020. Thanks are also due to Ms. Fanny Creusot, Editorial Assistant, and the entire production team of the journal for their valuable support in bringing out this issue successfully. Last but not least, our sincere appreciation to all the reviewers for their invaluable and critical review comments on manuscripts that were submitted for this special issue.