Advanced Biotechnologies for Water and Wastewater Treatment

1. Introduction

The use of biotechnology to control and prevent the contamination of water resources has a long track record that goes back to the beginning of the 20th century. In that early stage of development, activated sludge technology was developed and implemented for the treatment of wastewater [1]. This technological breakthrough, at that time, was a result of several efforts to enhance the performance of the innovative biological filter [1,2]. Since then, scientists and engineers have started a quest to improve the effective implementation of this technology in partial or full stabilization of biodegradable contaminants, i.e., organic contaminants [3]. This led to the development of several technologies that use varied modes of contact between the wastewater and the biological mass in the presence or absence of air [3]. The wide implementation of biological treatment technologies in the management of several industrial waste streams can be attributed to the efficiency of these technologies, the competitive construction and operational costs, the low energy requirements, the operational flexibility, and the reduced environmental impacts.

Recently, the advancements in the applications of biotechnologies for water and wastewater treatment are being investigated as a part of the quest to improve the sustainability of integrated water and wastewater management systems. These technologies are directed not only to improve the conventional secondary treatment of wastewater, i.e., biological treatment, but also extended to address the tertiary treatment, i.e., sorption [4] and photodegradation [5]. The advances in this field cover not only the use of bacteria but also algae and fungi [6] and advances in improving sludge management and contact technologies, e.g., microbial fuel cells [7], but is also extended to cover the removal of toxic elements, e.g., heavy metals. This Special Issue is directed to present the recent advances in the implementation of biotechnology in water and wastewater treatment with a focus on aspects related to the sustainability of the technologies, i.e., improved efficiency, reduced costs, and minimized energy consumption.

2. Summary of Contributions

This Special Issue includes 11 papers (Contributions 1 to 11) and this editorial. Improving biomass management by using thermal degradation to valorize the biomass or sludge separation to enhance recyclability was addressed in two research papers {C2, C4}. In the first paper, the integration of the pyrolysis and gasification technologies was proposed to improve the management process {C2}. In that context, the results of pilot-scale trials were presented to valorize the biomass via the production of biochar. The feasibility of the presented technology was investigated by coupling the energy analysis and preliminary techno-economic assessments. The work concludes on the efficiency of the proposed system to remove emerging contaminants, e.g., PFAS, from the product, scrubber water and gaseous emissions. Moreover, the optimization conditions for operating self-sufficient energy were presented {C2}. In the second paper, the improvement of the granulation of the activated sludge with poor settle ability was investigated for variable high-strength effluent {C4}. In this respect, a microbial selection strategy to form aerobic granules was implemented via the use of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor. The work reveals that the granulated sludge has significantly lower resistance compared to the seed sludge due to pore blockage and has significantly higher sustainable flux. The research work recommends the implementation of adequate influent pretreatment technology to improve the performance of the adopted strategy in the granulation of the activated sludge {C4}.

Heavy metal removal from water and wastewater is one of the challenging problems that affect the applicability of biotechnologies in this field. In this Special Issue, five research papers addressed the effect of the presence of these metals on the biomass and the improvement in the removal performance and the optimization of the process {C3, C5, C6, C10, C11}. Insights into the effect of the presence of lead in municipal wastewater on the symbiosis of algal–bacterial granular activated sludge were provided in a research paper {C10}. This effect was studied for initial lead concentration in the range of 2.5–10 ppm. Within that range, the study reveals that the presence of lead has little effect on the performance of the algal–bacterial granular sludge {C10}. The optimization of the Cr removal performance in microbial fuel cells was investigated in a research paper by using an adaptive neuro-fuzzy inference system (ANFIS) and artificial ecosystem optimization (AEO) {C11}. The study considered the effect of the Cu(II)/Cr(VI) ratio, the substrate concentration, and the external resistance during the optimization process and concluded that the integration between ANFIS and AEO to model and optimize the process led to increasing both the power density and the Cr removal considerably {C11}. Another research paper addressed the process modeling for the treatment of water contaminated by Cr via using bacterial cellulose biomass {C3}. Lab-scale and pilot-scale experiments were conducted in that research work to study the removal of chromium using the biomass. In addition, the reusability of the biomass was investigated by studying biomass elution using EDTA. The work concluded on the applicability of the used biomass to remove heavy metals from aqueous solutions {C3}. The fourth paper investigated the use of biotechnology in the removal of Cr from aqueous solutions using transformed E. crassipes biomass with sodium Tripolyphosphate (TPP){C6}. In that respect, the sorption capacity and the cost were investigated, and the elution performance to reuse the used biomass was determined. The results suggest that E. crassipes biomass, enhanced with PTT and through EDTA elutions, could be proposed as a suitable water remediation technology based on sorption technology. The last research paper that covered the removal of heavy metals investigated the construction of a genetically engineered Escherichia coli cell factory for the removal of Cd {C5}. In this respect, molecular biology techniques were adopted to fuse the recombinant human ferritin (rHF) gene and the synthetic phytochelatin (EC) gene. The work shows the successful soluble expression of the recombinant fusion protein in E. Coli cells that can remove 9.2 μmol of Cd²⁺in vitro over a wide range of temperatures (16–45 °C) and in slightly acidic–slightly neutral pHs (5–9). The main emphasis of that work is on the synthesis of multivalent chelating peptides in E. coli cells to enhance Cd removal {C5}.

Finally, improving the degradation of organic contaminants in the tertiary treatment was presented in four papers {C1, C7–C9}. The first paper addressed the effect of the preparation conditions of the ZnO nano-particles on their photo-catalytic activity {C1}. The work addresses the effect of the calcination temperature during the preparation of ZnO nanoparticles on the structural, morphological, and optical properties of the prepared material. The study demonstrates that the calcination temperature affects photo-catalytic activity, and the performance of the optimized material in the degradation of RhodamineB was investigated under different operating conditions, either solely or combined with H₂O₂oxidation. The study concluded on the optimized conditions to fully degrade the Rhodamine B {C1}. Another study assessed the potential use of the immobilized enzymes, i.e., Horseradish Peroxidase (HRP) and Myoglobin (MB), in sodium alginate for the treatment of organic pollutants {C7}. The prepared material was tested for its potential use in the degradation of aniline, phenol, and p-nitrophenol. The paper concludes on the resilience of the enzymes to the changes in the temperature and pH and on the promising reusability performance {C7}. The third paper in this category studied the removal of Xenobiotics by Trametes hirsute LE-BIN 072 activated carbon-based Mycelial pellets {C8}. In that context, the roles of fungal mycelium and fungal enzymes in the sorption and biodegradation of the dye were evaluated. The work reveals that laccases were proposed as the main contributing enzymes in the degradation process, where RT-qPCR measurements demonstrated an increase in transcription for the two laccase genes—lacA and lacB. It has been proven that the composite Mycelial pellets of T. hirsute show improved sorption ability, which emphasizes the role of fungal mycelium in improving dye removal {8}. Finally, the last paper investigated phenol degradation using immobilized Alcaligenes faecalis strain JH1 in Fe₃O₄-modified biochar from pharmaceutical residues{C9}. In that work, four types of biochar were used as carriers to immobilize different Alcaligenes faecalis strains to have insights into the removal mechanism of phenol and the reusability of the material was investigated. The study indicated that the immobilization process improves the tolerance of the bacteria to the operating conditions. The durability of the material, its stability, and reproducibility were proven, and the role of Fe₃O₄nano-particle in enhancing the removal was concluded.

3. Conclusions

Despite the use of biotechnology in water and wastewater treatment having a long operational track, innovation in this field is directed to improve the overall performance of the technologies and ensure their sustainability. The presented research papers in this Special Issue cover these motivations, where biomass management, improving the performance of heavy metal removal, and organic contaminant degradation were experimentally and theoretically investigated. The presented papers highlighted the possibility of improving the practice of treatment and balancing the sustainability measures, e.g., cost-effectiveness, energy efficiency, and reduced environmental impacts. Yet efforts are still needed to synergize the sustainability performance indicators with the technical assessment during the feasibility assessment of the use of different biotechnologies in water and wastewater treatment.