Water Quality Engineering and Wastewater Treatment III

1. Introduction

The provision of clean water is a vital element to ensure life sustainability; this can be achieved by designing and implementing effective prevention and control measures to protect water resources. Designing efficient wastewater technologies is a crucial tool to prevent potential pollution releases into water resources, whereas setting controls on pollution can be achieved by designing efficient remediation technologies that mitigate the spread of the contaminants of concern. Despite the huge accumulated knowledge in the field of water quality engineering and wastewater treatment, this field is still challenged by difficulties in addressing emerging contaminants [1], the need to improve the efficiency for conventional technologies to meet the strengthen regulatory standard on effluent releases [2,3,4], and need to advance innovative technologies for large-scale applications [5].

2. Overview on This Special Issue

This Special Issue includes this editorial and 13 papers (eight research papers and five review papers) {C1–C13}. The focus of this Special Issue is directed towards addressing recent advances in wastewater treatment technologies, including chemical precipitation {C4}, flocculation {9}, biological treatment {C3,C5,C8}, sorption {C2,C7,C12}, and a combination of advanced oxidation process (AOP) with sorption {C1}. Moreover, the control of pollution sources toward achieving better water quality is addressed in this Special Issue in four papers that focus on the mitigation of sewage system corrosion {C6}, analyzing the knowledge gap to mitigate the micro-plastic pollution {C10}, the use of permeable barriers to control water pollution {C11}, and leachate treatment {C13}.

Advances in primary wastewater treatment methods, i.e., chemical precipitation and flocculation, are addressed in two papers {C4,C9}. The first studies Hg removal from dry gas cleaning by-products from sinter plants in the steel industry {C4}. Hg concentration values in the leachate of the by-products were measured, and its removal efficiency by chemical precipitation with organic or sodium sulfides followed by filtration was determined. The study reveals the efficiency of the process in the high salt concentration conditions, and referrers to the importance of the precipitator dosage optimization to mitigate the Hg re-dissolution {C4}. A review paper addressed the potential role of the microbial flocculants (MBF), as eco-friendly materials, in the treatment of wastewater {C9}. An overview of the state of the art of the MBF sources, categories, production, and their performance and mechanisms is presented. MBF applications in the removal of suspended solids, dyes, and heavy metals from municipal and industrial effluents were presented. The challenges that face the wide applications of these materials were summarized, and the way forward, towards the advancement of the technology’s readiness, is outlined {C9}.

Three papers present the advances in the secondary wastewater treatment, where research on the optimization of biogas production in an anaerobic digester (AD), enhanced biological removal of phosphorus, and optimizing the implementation of the innovative moving bed bio-film reactor (MBBR) are included {C3,C5,C8}. In this respect, an analysis was conducted to compare and assess the performance of 34 AD implemented in the domestic wastewater treatment plants in Austrian alpine region {C3}. The study addressed the reactor shapes, mixing methods, energy efficiency, and biogas production. That work highlights that the process optimization can enhance the role of the AD technology as green energy source by increasing the gas production and reducing the operating costs and gas losses {C3}. In another work, a design for an enhanced biological phosphorus removal (EBPR) process was studied, where a culture of phosphorous accumulating organisms (PAO) were grown in a membrane–bioreactor-activated sludge system. The process was optimized by assessing the effect of the substrate on the PAO growth {C5}. The results indicate that increasing the dosage of the propionate substrate has linear correlation with the PAO concentration {C5}. In the last paper in under this topic, the optimization of the innovative MBBR technology to improve the capacity of the wastewater treatment plant in Dojran, North Macedonia, was presented {C8}.The analytical hierarchy process (AHP) was used to optimize the design of the plant; the analysis considered, among other factors, the condition assessment and efficiency of the existing plant, the available space at the site, and financial parameters. The results reveal that the optimal solution to improve the capacity of the existing plant is the construction of a new MBBR with 6000 equivalent inhabitants capacity {C8}.

The use in the tertiary and quaternary treatment technologies in the removal of methyl red (MR) dye, chromium, and emerging contaminant (EC) is presented in four papers {C1,C2,C7,C12}. The use of biochar derived from Rumex-abyssinicus for the removal of MR was investigated {C2}. In that work, the biochar was prepared, characterized, and tested to identify the effect of the operating conditions on the removal performance. The study concluded on the feasibility of using this biochar for the treatment of industrial wastes containing MR {C2}. In another study, Cr removal using pre-treated clinoptilolite was studied, where the compliance with the discharge limits and regeneration feasibility were investigated {C7}. The study reveals the ability of the pre-treated clinoptilolite to treat the wastewater in compliance with relevant regulations {C7}. The third paper is a review paper that addresses the EC and their removal from aqueous media using sorbents {C12}. It overviewed the performance of different conventional (e.g., activated carbon, clay) and non-conventional (e.g., industrial and agro residues) materials in EC removal. The study highlights the promising role of agro-industrial residues in EC removal, and linked that to their availability, low toxicity, and sorption capacities {C12}. The combined implementation of Photo-Fenton and use of Granular Activated Carbon (GAC) was assessed for the removal of micro-contaminants from wastewater effluents {C1}. The study encompassed the investigation of four advanced oxidation process scenarios coupled with GAC filtration. The analysis of the toxicity and phyto-toxicity of the treated wastewater proves the efficiency of the tested processes {C1}.

A research paper addressed the mitigation of the sewage system corrosion by controlling the hydrogen sulfide (H₂S) via biological oxidation {C6}. The experimental data showed that the conductive concrete is providing electron pathway for biological oxidation of H₂S {C6}. In another work, the knowledge gap to mitigate micro-plastic pollution was reviewed {C10}. That work analyzed related literature to support the prioritization of the efforts to reduce this pollution type. It concluded that the knowledge gaps include, among others, a lack of information about non-standardized test methodologies addressing life-cycle impacts and real hotspots {C10}. Another review paper presented the role of permeable concrete barriers in controlling the water pollution {C11}. It overviewed the advances in the studying the mix-design of conventional and innovative permeable concrete, their characterization techniques, and their performance in the pollution control. The work recommended the optimization of the mix-design of the permeable reactive barriers in a way that balances the performance measures and the durability of the barrier over its service life {C11}. In the last paper in this Special Issue, techniques for municipal solid landfill leachate remediation were reviewed {C13}. This work focused on the use of contemporary techniques to remediate leachate of high COD content, colored, and NH₃-N with low biodegradability. Finally, the challenges and future prospects for the semi-aerobic landfill design were presented {C13}.