Biotransformation of sulfamethoxazole (SMX) by aerobic granular sludge: Removal performance, degradation mechanism and microbial response

Densely Stacked CoCu-MOFs Coated with CuAl/LDH Enhance Sulfamethoxazole Degradation in PMS-Activated Systems

As the most promising techniques for refractory antibiotic degradation in wastewater management, sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted considerable attention. However, systematic studies on potassium peroxymonosulfate (PMS) activation by MOF-derived metal oxides coated with LDH materials are still lacking. In this work, a series of catalysts consisting of CoCu-MOFs coated with CuAl/LDH were synthesized for PMS activation in the removal of sulfamethoxazole (SMX). As expected, CoCu-MOFs coated with CuAl/LDH catalyst showed high SMX removal and stability in PMS activation. In the CoCu/LDH/PMS reaction, the SMX removal was nearly 100% after 60 min, and the mineralization reached 53.7%. The catalyst showed excellent catalytic stability and low metal leaching concentrations (Co: 0.013 mg/L, Cu: 0.313 mg/L), as detected by ICP. Sulfate radicals and hydroxyl radicals were identified as the dominant reactive species in the CoCu/LDH/PMS system. Moreover, the presence of 1O2 in the process revealed the coupling of non-radical and radical processes. The XPS results showed that the layered structure of CoCu/LDH promoted the recycling of metal ions (high and low valence), which facilitated heterogeneous PMS activation. The effects of different reaction conditions and reuse cycles were also determined. The SMX oxidation pathways were proposed based on the intermediates identified by LC/MS. The high activity and stability of CoCu/LDH provide a new mechanistic understanding of PMS activation catalysts and their potential utilization in practical wastewater treatment.

Enhancement of aerobic denitrification process on antibiotics removal: Mechanism and efficiency: A review

Traditionally, the removal of nitrogenous pollutants from wastewater relied on conventional anaerobic denitrification as well as aerobic nitrification and anoxic denitrification. However, anaerobic denitrification is complicated since it requires stringent environmental conditions as well as a large land, therefore, denitrification and nitrification were performed in two separate reactors. Although high pollutant removal efficiency has been achieved via aerobic nitrification and anoxic denitrification, the demerits of this approach include high operational costs. Other traditional nitrogen removal methods include air stripping, reverse osmosis, adsorption, ion exchange, chemical precipitation, advanced oxidation process, and breakpoint chlorination. Traditional nitrogen removal methods are not only complicated but they are also uneconomical due to the high operational costs. Researchers have discovered that denitrification can be carried out by heterotrophic nitrification-aerobic denitrification (HNAD) microorganisms which remove nitrogen in a single aerobic reactor that does not require stringent operating conditions. Despite the significant effort that researchers have put in, there is still little information known about the mechanisms of antibiotic removal during HNAD. This review begins with an update on the current state of knowledge on the removal of nitrogenous pollutants and antibiotics from wastewater by HNAD. The mechanisms of antibiotic removal via HNAD were examined in detail. Followed by, the enhancement of antibiotics removal via co-metabolism and oxidation of sulfamethoxazole (SMX) as well as the response of microbial communities to antibiotic toxicity. Lastly, the conditions favorable for antibiotic biodegradation and mechanisms for nitrogen removal via HNAD were examined. The findings in this review show that co-metabolism and oxidation of SMX were the main antibiotic biodegradation mechanisms, pathways for antibiotic removal by co-metabolism and oxidation of SMX were also proposed in the discussion. This research indicated the potential of aerobic denitrification in the removal of antibiotics from wastewater. Understanding the mechanisms and pathways of antibiotic removal by HNAD helps wastewater engineers and researchers apply the technology more efficiently. PRACTITIONER POINTS: The mechanisms of antibiotic removal via HNAD were examined in detail. Co-metabolism and oxidation of SMX were the main antibiotic biodegradation mechanisms. Pathways for antibiotic removal by co-metabolism and oxidation of SMX were also proposed. Conditions favorable for antibiotic biodegradation were examined. This research indicated the potential of aerobic denitrification in the removal of antibiotics from wastewater.

The role of cationic bridges in enhancing sulfamethoxazole adsorption onto montmorillonite

The coexistence and interaction of free metal cations in the environment can significantly affect the migration of organic pollutants, leading to varied effects depending on environmental conditions. However, the mechanisms affecting the adsorption of organic pollutants in the presence of metal ions remain poorly understood due to limited molecular-level studies. This study investigated the adsorption behavior of sulfamethoxazole (SMX) on montmorillonite (MT) at different pH values (1.6, 3.0, and 5.0) in the presence of three metal cations with different valences: Na+, Ca2+, and Cr3+. At pH 5.0, the adsorption of SMX by MT at pH 5.0 in Ca2+ and Cr3+ systems increased significantly-by 7.25 times and 47 times, respectively, compared to those at pH 1.6. In contrast, Na+ had a less pronounced effect on SMX adsorption. Density functional theory (DFT) calculations indicated that as the pH value increases, the interaction between SMX, metal ions, and MT strengthens. Furthermore, the adsorption binding energy of SMX in the high-valence Cr3+ system (- 94.51 kcal/mol) was significantly lower than in the low-valence Na+ system (- 36.55 kcal/mol). As pH and cation valency increased, the bonding density of cation bridges also increased, leading to a more substantial enhancement in SMX adsorption. This study provides insights into the adsorption mechanism of SMX on MT in the presence of metal cations, contributing valuable understanding of the environmental behavior of organic pollutants under varying cationic conditions.

The response to shock loads of Ni-MOF and NiO NPs on aerobic granular sludge and algal-bacterial aerobic granular sludge

Currently, the increasing use of nickel metal-organic frameworks (Ni-MOF) and nickel oxide nanoparticles (NiO NPs) has raised concerns regarding their potential environmental impact on wastewater treatment systems. Herein, the responses of aerobic granular sludge (AGS) and algal-bacterial aerobic granular sludge (AB-AGS) to Ni-MOF and NiO NPs were investigated. The results showed that Ni-MOF concentrations of 50, 100, and 200 mg/L significantly reduced nutrient removal in both systems, particularly affecting ammonia, nitrite, and phosphorus removal, while denitrification processes remained stable. AB-AGS exhibited greater tolerance to nickel than AGS, likely due to its higher content of extracellular polymeric substances (EPSs), in which the algae were embedded, indicating a robust bacterial-algal symbiotic system. Conversely, NiO NPs had no adverse effects on bioreactor performance, likely due to their insolubility and integration into the sludge matrix. This research provides valuable insights into the potential future applications of AGS and AB-AGS technologies for treating wastewater contaminated with nickel and other heavy metals, highlighting the superior resilience of AB-AGS to nickel exposure.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

Peroxymonosulfate activation by nanocomposites towards the removal of sulfamethoxazole: Performance and mechanism

Heterogeneous activation of peroxomonosulfate (PMS) has been extensively studied for the degradation of antibiotics. The cobalt ferrite spinel exhibits good activity in the PMS activation, but suffers from the disadvantage of low PMS utilization efficiency. Herein, the nanocomposites including FeS, CoS2, CoFe2O4 and Fe2O3 were synthesized by hydrothermal method and used for the first time to activate PMS for the removal of sulfamethoxazole (SMX). The nanocomposites showed superior catalytic activity in which the SMX could be completely removed at 40 min, 0.1 g L-1 nanocomposites and 0.4 mM PMS with the first order kinetic constant of 0.2739 min-1. The PMS utilization efficiency was increased by 29.4% compared to CoFe2O4. Both radicals and non-radicals contributed to the SMX degradation in which high-valent metal oxo dominated. The mechanism analysis indicated that sulfur modification, on one hand, enhanced the adsorption of nanocomposites for PMS, and promoted the redox cycles of Fe2+/Fe3+ and Co2+/Co3+ on the other hand. This study provides new way to enhance the catalytic activity and PMS utilization efficiency of spinel cobalt ferrite.

Microbial Ecology of Granular Biofilm Technologies for Wastewater Treatment: A Review

Nowadays, the discharge of wastewater is a global concern due to the damage caused to human and environmental health. Wastewater treatment has progressed to provide environmentally and economically sustainable technologies. The biological treatment of wastewater is one of the fundamental bases of this field, and the employment of new technologies based on granular biofilm systems is demonstrating success in tackling the environmental issues derived from the discharge of wastewater. The granular-conforming microorganisms must be evaluated as functional entities because their activities and functions for removing pollutants are interconnected with the surrounding microbiota. The deep knowledge of microbial communities allows for the improvement in system operation, as the proliferation of microorganisms in charge of metabolic roles could be modified by adjustments to operational conditions. This is why engineering must consider the intrinsic microbiological aspects of biological wastewater treatment systems to obtain the most effective performance. This review provides an extensive view of the microbial ecology of biological wastewater treatment technologies based on granular biofilms for mitigating water pollution.

Unraveling the Role of Microalgae in Mitigating Antibiotics and Antibiotic Resistance Genes in Photogranules Treating Antibiotic Wastewater

Harnessing the potential of specific antibiotic-degrading microalgal strains to optimize microalgal-bacterial granular sludge (MBGS) technology for sustainable antibiotic wastewater treatment and antibiotic resistance genes (ARGs) mitigation is currently limited. This article examined the performance of bacterial granular sludge (BGS) and MBGS (of Haematococcus pluvialis, an antibiotic-degrading microalga) systems in terms of stability, nutrient and antibiotic removal, and fate of ARGs and mobile genetic elements (MGEs) under multiclass antibiotic loads. The systems exhibited excellent performance under none and 50 μg/L mixed antibiotics and a decrease in performance at a higher concentration. The MBGS showed superior potential, higher nutrient removal, 53.9 mg/L/day higher chemical oxygen demand (COD) removal, and 5.2-8.2% improved antibiotic removal, notably for refractory antibiotics, and the system removal capacity was predicted. Metagenomic analysis revealed lower levels of ARGs and MGEs in effluent and biomass of MBGS compared to the BGS bioreactor. Particle association niche and projection pursuit regression models indicated that microalgae in MBGS may limit gene transfers among biomass and effluent, impeding ARG dissemination. Moreover, a discrepancy was found in the bacterial antibiotic-degrading biomarkers of BGS and MBGS systems due to the microalgal effect on the microcommunity. Altogether, these findings deepened our understanding of the microalgae's value in the MBGS system for antibiotic remediation and ARG propagation control.

Effect of minute amounts of arsenic on the sulfamethoxazole removal and microbial community structure via the SBR system

In this study, the effect of arsenic on the sulfamethoxazole (SMX) removal efficiency and microbial community structure was investigated over 60 days using the SBR process. The results showed that the presence of arsenic had no significant impact on the system performance, the removal efficiencies of two reactors, R1 (the control test) and R2 (with the addition of arsenic), were 13.36 ± 5.71 and 14.20 ± 5.27%, which were attributed to the adsorption of SMX by fulvic acid-like substances and tryptophan-like proteins of extracellular polymeric substances. Compared to the seed sludge, the species number indicated that R2 possessed the richer diversity, while R1 possessed the lower diversity on day 60, which might be relative to the transferring of antibiotic resistance genes (ARGs) in sludge bacterial communities; the minute amounts of arsenic could make the relative levels of Sul1 and Sul2 genes which encode ARGs of sulfonamides in R2 (2.07 and 2.47%) be higher than that in R1 (1.65 and 1.27%), which made the bacterial community of the R2 system more adaptable to SMX stress. Therefore, the minute amounts of arsenic weakened the effect of SMX on the system and enhanced the stability of the microbial community structure.