Tetracycline-induced decoupling of symbiosis in microalgal-bacterial granular sludge

Exploring the influence of sulfadiazine-induced stress on antibiotic removal and transformation pathway using microalgae Chlorella sp

Sulfadiazine (SDZ) is a kind of anti-degradable antibiotics that is commonly found in wastewater, but its removal mechanism and transformation pathway remain unclear in microalgal systems. This study investigated the effects of initial algae concentration and SDZ-induced stress on microalgal growth metabolism, SDZ removal efficiency, and transformation pathways during Chlorella sp. cultivation. Results showed that SDZ had an inhibitory effect on the growth of microalgae, and increasing the initial algal biomass could alleviate the inhibitory effect of SDZ. When the initial algal biomass of Chlorella sp. was increased to 0.25 g L-1, the SDZ removal rate could reach 53.27%-89.07%. The higher the initial algal biomass, the higher the SOD activity of microalgae, and the better the protective effect on microalgae, which was one of the reasons for the increase in SDZ removal efficiency. Meanwhile, SDZ stress causes changes in photosynthetic pigments, lipids, total sugars and protein content of Chlorella sp. in response to environmental changes. The main degradation mechanisms of SDZ by Chlorella sp. were biodegradation (37.82%) and photodegradation (23%). Most of the degradation products of SDZ were less toxic than the parent compound, and the green algae were highly susceptible to SDZ and its degradation products. The findings from this study offered valuable insights into the tradeoffs between accumulating microalgal biomass and antibiotic toxic risks during wastewater treatment, providing essential direction for the advancement in future research and full-scale application.

Microalgal-bacterial consortia for the treatment of livestock wastewater: Removal of pollutants, interaction mechanisms, influencing factors, and prospects for application

The livestock sector is responsible for a significant amount of wastewater globally. The microalgal-bacterial consortium (MBC) treatment has gained increasing attention as it is able to eliminate pollutants to yield value-added microalgal products. This review offers a critical discussion of the source of pollutants from livestock wastewater and the environmental impact of these pollutants. It also discusses the interactions between microalgae and bacteria in treatment systems and natural habitats in detail. The effects on MBC on the removal of various pollutants (conventional and emerging) are highlighted, focusing specifically on analysis of the removal mechanisms. Notably, the various influencing factors are classified into internal, external, and operating factors, and the mutual feedback relationships between them and the target (removal efficiency and biomass) have been thoroughly analysed. Finally, a wastewater recycling treatment model based on MBC is proposed for the construction of a green livestock farm, and the application value of various microalgal products has been analysed. The overall aim was to indicate that the use of MBC can provide cost-effective and eco-friendly approaches for the treatment of livestock wastewater, thereby advancing the path toward a promising microalgal-bacterial-based technology.

Effects of Intestinal Microbiota on the Biological Transformation of Arsenic in Zebrafish: Contribution and Mechanism

Both the gut microbiome and their host participate in arsenic (As) biotransformation, while their exact roles and mechanisms in vivo remain unclear and unquantified. In this study, as3mt-/- zebrafish were treated with tetracycline (TET, 100 mg/L) and arsenite (iAsIII) exposure for 30 days and treated with probiotic Lactobacillus rhamnosus GG (LGG, 1 × 108 cfu/g) and iAsIII exposure for 15 days, respectively. Structural equation modeling analysis revealed that the contribution rates of the intestinal microbiome to the total arsenic (tAs) and inorganic As (iAs) metabolism approached 44.0 and 18.4%, respectively. Compared with wild-type, in as3mt-/- zebrafish, microbial richness and structure were more significantly correlated with tAs and iAs, and more differential microbes and microbial metabolic pathways significantly correlated with arsenic metabolites (P < 0.05). LGG supplement influenced the microbial communities, significantly up-regulated the expressions of genes related to As biotransformation (gss and gst) in the liver, down-regulated the expressions of oxidative stress genes (sod1, sod2, and cat) in the intestine, and increased arsenobetaine concentration (P < 0.05). Therefore, gut microbiome promotes As transformation and relieves As accumulation, playing more active roles under iAs stress when the host lacks key arsenic detoxification enzymes. LGG can promote As biotransformation and relieve oxidative stress under As exposure.

Microalgal-bacterial biofilms for wastewater treatment: Operations, performances, mechanisms, and uncertainties

Microalgal-bacterial biofilms have been increasingly considered of great potential in wastewater treatment due to the advantages of microalgal-bacterial synergistic pollutants removal/recovery, CO2 sequestration, and cost-effective biomass-water separation. However, such advantages may vary widely among different types of microalgal-bacterial biofilms, as the biofilms could be formed on different shapes and structures of attachment substratum, generating "false hope" for certain systems in large-scale wastewater treatment if the operating conditions and pollutants removal properties are evaluated based on the general term "microalgal-bacterial biofilm". This study, therefore, classified microalgal-bacterial biofilms into biofilms formed on 2D substratum, biofilms formed on 3D substratum, and biofilms formed without substratum (i.e. microalgal-bacterial granular sludge, MBGS). Biofilms formed on 2D substratum display higher microalgae fractions and nutrients removal efficiencies, while the adopted long hydraulic retention times were unacceptable for large-scale wastewater treatment. MBGS are featured with much lower microalgae fractions, most efficient pollutants removal, and acceptable retention times for realistic application, yet the feasibility of using natural sunlight should be further explored. 3D substratum systems display wide variations in operating conditions and pollutants removal properties because of diversified substratum shapes and structures. 2D and 3D substratum biofilms share more common in eukaryotic and prokaryotic microbial community structures, while MGBS biofilms are more enriched with microorganisms favoring EPS production, biofilm formation, and denitrification. The specific roles of stratified extracellular polymeric substances (EPS) in nutrients adsorption and condensation still require in-depth exploration. Nutrients removal uncertainties caused by microalgal-bacterial synergy decoupling under insufficient illumination, limited microbial community control, and possible greenhouse gas emission exacerbation arising from microalgal N2O generation were also indicated. This review is helpful for revealing the true potential of applying various microalgal-bacterial biofilms in large-scale wastewater treatment, and will provoke some insights on the challenges to the ideal state of synergistic pollutants reclamation and carbon neutrality via microalgal-bacterial interactions.

Assessing the Ecotoxicity of Eight Widely Used Antibiotics on River Microbial Communities

Global prevalence of antibiotic residues (ABX) in rivers requires ecotoxicological impact assessment. River microbial communities serve as effective bioindicators for this purpose. We quantified the effects of eight commonly used ABXs on a freshwater river microbial community using Biolog EcoPlates™, enabling the assessment of growth and physiological profile changes. Microbial community characterization involved 16S rRNA gene sequencing. The river community structure was representative of aquatic ecosystems, with the prevalence of Cyanobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes. Our findings reveal that all ABXs at 100 µg/mL reduced microbial community growth and metabolic capacity, particularly for polymers, carbohydrates, carboxylic, and ketonic acids. Chloramphenicol, erythromycin, and gentamicin exhibited the highest toxicity, with chloramphenicol notably impairing the metabolism of all studied metabolite groups. At lower concentrations (1 µg/mL), some ABXs slightly enhanced growth and the capacity to metabolize substrates, such as carbohydrates, carboxylic, and ketonic acids, and amines, except for amoxicillin, which decreased the metabolic capacity across all metabolites. We explored potential correlations between physicochemical parameters and drug mechanisms to understand drug bioavailability. Acute toxicity effects at the river-detected low concentrations (ng/L) are unlikely. However, they may disrupt microbial communities in aquatic ecosystems. The utilization of a wide array of genetically characterized microbial communities, as opposed to a single species, enables a better understanding of the impact of ABXs on complex river ecosystems.

Revealing mechanisms of triclosan on the removal and distribution of nitrogen and phosphorus in microalgal-bacterial symbiosis system

Microalgal-bacterial symbiosis (MABS) system performs synergistic effect on the reduction of nutrients and carbon emissions in the water treatment process. However, antimicrobial agents are frequently detected in water, which influence the performance of MABS system. In this study, triclosan (TCS) was selected to reveal the effects and mechanisms of antimicrobial agents on MABS system. Results showed that the removal efficiencies of chemical oxygen demand, NH4+-N and total phosphorus decreased by 3.0%, 24.0% and 14.3% under TCS stress. In contrast, there were no significant decrease on the removal effect of total nitrogen. Mechanism analysis showed that both the growth rate of microorganisms and the nutrients retention capacity of extracellular polymeric substances were decreased. The intracellular accumulation for nitrogen and phosphorus was promoted due to the increased cytomembrane permeability caused by lipid peroxidation. Moreover, microalgae were dominant in MABS system with ratio between microalgae and bacteria of more than 5.49. The main genus was Parachlorella, with abundance of more than 90%. Parachlorella was highly tolerant to TCS, which might be conductive to maintain its survival. This study revealed the nutrients pathways of MABS system under TCS stress, and helped to optimize the operation of MABS system.

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.

Adsorption of oxytetracycline on subalpine meadow soil from Zoige Plateau, China: Effects of the coexisting Cu2

Subalpine meadow soil with high moisture and humus content is a unique soil type in the Zoige Plateau. Oxytetracycline and copper are common soil contaminants which interact to form compound pollution. Oxytetracycline's adsorption on natural subalpine meadow soil and its components (humin and the soil without iron and manganese oxides) was studied in the laboratory with and without the presence of Cu2+. The effects of temperature, pH and Cu2+ concentration were documented in batch experiments, allowing deduction of the main sorption mechanisms. The adsorption process had two phases: one rapid, taking place in the first 6 h, and another slower, reaching equilibrium at around 36 h. The adsorption kinetics were pseudo-second-order, and the adsorption isotherm conformed to the Langmuir model at 25 °C. Higher concentrations oxytetracycline increased the adsorption, but higher temperature did not. The presence of Cu2+ had no effect on the equilibrium time, but the amount and rate adsorbed were much greater with Cu2+ concentration increased (except for the soil without iron and manganese oxides). The amounts adsorbed with/without Cu2+ were in the order the humin from subalpine meadow soil (7621 and 7186 μg/g) > the subalpine meadow soil (7298 and 6925 μg/g) > the soil without iron and manganese oxides (7092 and 6862 μg/g), but the difference among those adsorbents was slight. It indicates that humin is a particularly important adsorbent in the subalpine meadow soil. The amount of oxytetracycline adsorbed was greatest at pH 5-9. In addition, Surface complexation through metal bridging was the most important sorption mechanism. Cu2+ and oxytetracycline formed positively-charged complex that was adsorbed and then formed a ternary complex "adsorbent-Cu(II)-oxytetracycline", in which Cu2+ acted as a bridge. These findings provide a good scientific basis for soil remediation, and for assessing environmental health risks.

Exploring resistomes and microbiomes in pilot-scale microalgae-bacteria wastewater treatment systems for use in low-resource settings

Antibiotic resistance genes (ARGs) released into the environment are an emerging human and environmental health concern, including ARGs spread in wastewater treatment effluents. In low-to-middle income countries (LMICs), an alternate wastewater treatment option instead of conventional systems are low-energy, high-rate algal ponds (HRAP) that use microalgae-bacteria aggregates (MABA) for waste degradation. Here we studied the robustness of ARG removal in MABA-based pilot-scale outdoor systems for 140 days of continuous operation. The HRAP system successfully removed 73 to 88 % chemical oxygen demand and up to 97.4 % ammonia, with aggregate size increasing over operating time. Fourteen ARG classes were identified in the HRAP influent, MABA, and effluent using metagenomics, with the HRAP process reducing total ARG abundances by up to 5-fold from influent to effluent. Parallel qPCR analyses showed the HRAP system significantly reduced exemplar ARGs (p < 0.05), with 1.2 to 4.9, 2.7 to 6.3, 0 to 1.5, and 1.2 to 4.8 log-removals for sul1, tetQ, blaKPC, and intl1 genes, respectively. Sequencing of influent, effluent and MABAs samples showed associated microbial communities differed significantly, with influent communities by Enterobacteriales (clinically relevant ARGs carrying bacteria), which were less evident in MABA and effluent. In this sense, such bacteria might be excluded from MABA due to their good settling properties and the presence of antimicrobial peptides. Microalgae-bacteria treatment systems steadily reduced ARGs from wastewater during operation time, using sunlight as the energetic driver, making them ideal for use in LMIC wastewater treatment applications.

Cultivation of algal-bacterial granular sludge and degradation characteristics of tetracycline

Due to the increasing use of antibiotics, tetracycline was frequently detected in wastewater. As a novel technology, algal-bacterial granular sludge process is expected to be widely used in wastewater treatment. However, the degradation effect of tetracycline by algal-bacterial granular sludge process and its degradation path is still unknown. In this study, mature and stable algal-bacterial granular sludge was cultured and the degradation of tetracycline by it was investigated. The results showed that the removal amount of 1-25 mg/L tetracycline by algal-bacterial granular sludge was 0.09-1.45 mg/g volatile suspended solids (VSS), in which the adsorption amount was 0.06-0.17 mg/g VSS and the degradation amount was 0.03-1.27 mg/g VSS. Tetracycline biosorption was dominant at its concentration of 1-3 mg/L, while biodegradation was predominant at 5-25 mg/L of tetracycline. At tetracycline concentration of 3-5 mg/L, the contribution of biosorption and biodegradation to tetracycline removal by algal-bacterial granular sludge process was almost equal. Algal-bacterial granular sludge could effectively degrade tetracycline through demethylation, dehydrogenation, deacylation, and deamination or their combination. In addition, the degradation products were nontoxic and hardly pose a threat to environmental health. The research results of this paper provide a solid theoretical basis for tetracycline removal by algal-bacterial granular sludge and a reference for the development of algal-bacterial granular sludge process for wastewater treatment in the presence of tetracycline. PRACTITIONER POINTS: Mature and stable algal-bacterial granular sludge was cultured. Tetracycline was removed by algal-bacterial granular sludge through biosorption and biodegradation. Algal-bacterial granular sludge could degrade tetracycline through demethylation, dehydrogenation, deacylation, and deamination or their combination. The degradation products were nontoxic.

Effect of GR24 concentrations on tetracycline and nutrient removal from biogas slurry by different microalgae-based technologies

A biogas slurry composed of carbon, nitrogen, phosphorus, and antibiotics was generated. Investigations into the nutrient and tetracycline removal performance of four microalgae-based contaminant removal technologies, including Chlorella vulgaris, C. vulgaris co-cultured with endophytic bacteria, C. vulgaris co-cultured with Ganoderma lucidum, and C. vulgaris co-cultured with G. lucidum and endophytic bacteria, were conducted. The algal-bacterial-fungal consortium with 10^-9 M strigolactone (GR24) yielded the maximum growth rate and average daily yield for algae at 0.325 ± 0.03 d^-1 and 0.192 ± 0.02 g L^-1 d^-1, respectively. The highest nutrient/ tetracycline removal efficiencies were 83.28 ± 7.95 % for chemical oxygen demand (COD), 82.62 ± 7.97 % for total nitrogen (TN), 85.15 ± 8.26 % for total phosphorus (TP) and 83.92 ± 7.65 % for tetracycline. Adding an algal-bacterial-fungal consortium with an optimal synthetic analog GR24 concentration is seemingly an encouraging strategy for enhancing pollutant removal by algae, possibly overcoming the challenges of eutrophication and antibiotic pollution.

Pervasive Selection for Clinically Relevant Resistance and Media Adaptive Mutations at Very Low Antibiotic Concentrations

Experimental evolution studies have shown that weak antibiotic selective pressures (i.e., when the antibiotic concentrations are far below the minimum inhibitory concentration, MIC) can select resistant mutants, raising several unanswered questions. First, what are the lowest antibiotic concentrations at which selection for de novo resistance mutations can occur? Second, with weak antibiotic selections, which other types of adaptive mutations unrelated to the antibiotic selective pressure are concurrently enriched? Third, are the mutations selected under laboratory settings at subMIC also observed in clinical isolates? We addressed these questions using Escherichia coli populations evolving at subMICs in the presence of either of four clinically used antibiotics: fosfomycin, nitrofurantoin, tetracycline, and ciprofloxacin. Antibiotic resistance evolution was investigated at concentrations ranging from 1/4th to 1/2000th of the MIC of the susceptible strain (MICsusceptible). Our results show that evolution was rapid across all the antibiotics tested, and selection for fosfomycin- and nitrofurantoin-resistant mutants was observed at a concentration as low as 1/2000th of MICsusceptible. Several of the evolved resistant mutants showed increased growth yield and exponential growth rates, and outcompeted the susceptible ancestral strain in the absence of antibiotics as well, suggesting that adaptation to the growth environment occurred in parallel with the selection for resistance. Genomic analysis of the resistant mutants showed that several of the mutations selected under these conditions are also found in clinical isolates, demonstrating that experimental evolution at very low antibiotic levels can help in identifying novel mutations that contribute to bacterial adaptation during subMIC exposure in real-life settings.

Adsorption performance and optimization by response surface methodology on tetracycline using Fe-doped ZIF-8-loaded multi-walled carbon nanotubes

Herein, an iron-doped ZIF-8-loaded multi-walled carbon nanotube (FZM) was synthesized and its adsorption performance on tetracycline (TC) was investigated. The experimental conditions (solution pH, temperature, adsorbent dose) were optimized by Box-Behnken design (BBD) in response surface methodology (RSM). The results show that the adsorption effect of TC by FZM is optimal under the conditions of temperature = 298 K, pH = 6, and contact time = 360 min. The adsorption processes of TC by FZM follow the pseudo-second-order (PSO) kinetic and Freundlich isotherm models, indicating that chemisorption is the dominant factor and the adsorption reaction is multi-layer, with a theoretical maximum saturation capacity of 1111.11 mg/g at 298 K. The adsorption thermodynamic results indicate that the adsorption of TC by FZM is a spontaneous and endothermic process. The mechanism of TC adsorption by FZM possibly occurs through hydrogen bonding, surface complexation, π-π interaction, and electrostatic interaction. From the statistical results, the optimal adsorption capacity of TC by FZM is 599.78 mg/g at a pH of 7.1, a temperature of 312.5 K, and an adsorbent dose of 64.43 mg/L, with a deviation of 1.73% from the actual value. Furthermore, regeneration experiments demonstrate that FZM has excellent reusability with a 15% loss of adsorption capacity after four cycles. This study provides some insights to study the adsorption behavior of TC by MOFs and the optimization of the adsorption experimental conditions, and also shows the potential of FZM for TC removal.

Effect of live and inactivated Chlamydomonas reinhardtii on the removal of tetracycline in aquatic environments

With the development of medical drugs, the widely used tetracycline has brought many adverse effects on the ecosystem and human health. Tetracycline pollution of water environment is becoming more and more serious, and has become an emerging environmental problem. As single celled organisms, microalgae are not only model organisms for risk assessment of aquatic ecosystems, but also can efficiently purify sewage. Microalgae-mediated pollutant remediation has attracted more and more attention from researchers. In this paper, Chlamydomonas reinhardtii (C. reinhardtii) was used to remove tetracycline in aqueous solution, and the removal efficiency and mechanism of microalgae on tetracycline were studied. The results showed that the removal rates of tetracycline by active and inactivated microalgae at a density of 5 × 10⁶ cells·mL^-1 were 81.9% and 89.8%, respectively. C. reinhardtii removed tetracycline through biosorption and nonmetabolic processes. Microalgal cell supernatant and hydroxyl radicals could significantly promote the removal of tetracycline. The positively charged tetracycline was electrostatically adsorbed on the microalgae surface and extracellular polymeric substances. Microalgae biomass can promote the production of ROS and enhance the ability of microalgae to remove tetracycline.

Advanced insights on removal of antibiotics by microalgae-bacteria consortia: A state-of-the-art review and emerging prospects

Antibiotics abuse has triggered a growing environmental problem, posing a major threat to both ecosystem and human health. Unfortunately, there are still several shortcomings to current antibiotics removal technologies. Microalgae-bacteria consortia have been shown to be a promising antibiotics treatment technology owing to advantages of high antibiotics removal efficiency, low operational cost, and carbon emission reduction. This review aims to introduce the removal mechanisms, influencing factors, and future research perspectives for using microalgae-bacteria consortia to remove antibiotics. The interaction mechanisms between microalgae and bacteria are comprehensively revealed, and their exclusive advantages have been summarized in a "Trilogy" strategy, including "reinforced physical contact", "upgraded substance utilization along with antibiotics degradation", and "robust biological regulation". What's more, the relationship between different interaction mechanisms is emphatically analyzed. The important influencing factors, including concentration and classes of antibiotics, environmental conditions, and operational parameters, of antibiotics removal were also assessed. Three innovative treatment systems (microalgae-bacteria fuel cells (MBFCs), microalgae-bacteria membrane photobioreactors (MB-MPBRs), and microalgae-bacteria granular sludge (MBGS)) along with three advanced techniques (metabolic engineering, machine learning, and molecular docking and dynamics) are then introduced. In addition, concrete implementing schemes of the above advanced techniques are also provided. Finally, the current challenges and future research directions in using microalgae-bacteria consortia to remove antibiotics have been summarized. Overall, this review addresses the current state of microalgae-bacteria consortia for antibiotics treatment and provides corresponding recommendations for enhancing antibiotics removal efficiency.

Adaptation responses of microalgal-bacterial granular sludge to polystyrene microplastic particles in municipal wastewater

Microplastics are frequently detected in wastewater treatment plants, but the knowledge of their effects on microalgal-bacterial granular sludge (MBGS) is still unknown. This study investigated the performance and adaptive response of MBGS exposed in municipal wastewater in the presence of polystyrene (PS) microplastic particles with different sizes (i.e., 100 nm, 5 μm, and 10 μm). Results indicated that the average removal efficiency of influent organics, ammonia, and phosphorus by MBGS process was stable at above 85%, showing insignificant difference between three sizes of microplastic particles. The community richness of MBGS was reduced by nano-sized (i.e., 100 nm) and micro-sized (i.e., 5 μm) PS microplastic particles, while the community diversity decreased in all types. Although filamentous cyanobacteria were broken by PS microplastic particles, the performance of MBGS process was insignificantly affected due to the stimulated extracellular polymeric substances, which could act as adaptive responses and protect MBGS from stress damage. This study proves that MBGS process can be operated in the presence of prevalent PS microplastic particles.

Photocatalytic degradation of organic pollutants in water by N-doping ZnS with Zn vacancy: enhancement mechanism of visible light response and electron flow promotion

In order to improve the visible light response, N-doping ZnS (N-ZnS) nanospheres with Zn vacancy and porous surface were prepared by a simple one-pot hydrothermal method. Characterizations and density functional theory simulations showed excellent visible light response of N-ZnS. N-doping introduced impurity energy levels, which led to orbital hybridization and changed the original dipole moment. The presence of ortho Zn vacancy (O-Znv) can effectively reduce e--h+ recombination and photocorrosion. Furthermore, O-Znv caused lattice distortion (twisted the -S-Zn-N-(O-Znv)-S-Zn-S- chemical bond chain), resulting in "vacancy effect" to accelerate e- flow. Under visible light, the photocatalytic degradation efficiency of tetracycline (TC) and 2,4-dichlorophenol (2,4-DCP) was 90.31% and 60.84%, respectively. TOC degradation efficiency was 31.4% and 25.6%, respectively. Combined with Fukui index and LC-MS methods, it was found that TC and 2,4-DCP were degraded under the constant attack of active substances such as ·OH. This work can provide a reference for the application of catalytic materials in the field of visible light photocatalysis.

Progress in microalgal mediated bioremediation systems for the removal of antibiotics and pharmaceuticals from wastewater

Worldwide demand for antibiotics and pharmaceutical products is continuously increasing for the control of disease and improvement of human health. Poor management and partial metabolism of these compounds result in the pollution of aquatic systems, leading to hazardous effects on flora, fauna, and ecosystems. In the past decade, the importance of microalgae in micropollutant removal has been widely reported. Microalgal systems are advantageous as their cultivation does not require additional nutrients: they can recover resources from wastewater and degrade antibiotics and pharmaceutical pollutants simultaneously. Bioadsorption, degradation, and accumulation are the main mechanisms involved in pollutant removal by microalgae. Integration of microalgae-mediated pollutant removal with other technologies, such as biodiesel, biochemical, and bioelectricity production, can make this technology more economical and efficient. This article summarizes the current scenario of antibiotic and pharmaceutical removal from wastewater using microalgae-mediated technologies.

Sustainability and carbon neutrality trends for microalgae-based wastewater treatment: A review

As the global economy develops and the population increases, greenhouse gas emissions and wastewater discharge have become inevitable global problems. Conventional wastewater treatment processes produce direct or indirect greenhouse gas, which can intensify global warming. Microalgae-based wastewater treatment technology can not only purify wastewater and use the nutrients in wastewater to produce microalgae biomass, but it can also absorb CO₂ in the atmosphere or flue gas through photosynthesis, which demonstrates great potential as a sustainable and economical wastewater treatment technology. This review highlights the multifaceted roles of microalgae in different types of wastewater treatment processes in terms of the extent of their bioremediation function and microalgae biomass production. In addition, various newly developed microalgae cultivation systems, especially biofilm cultivation systems, were further characterized systematically. The performance of different microalgae cultivation systems was studied and summarized. Current research on the technical approaches for the modification of the CO₂ capture by microalgae and the maximization of CO₂ transfer and conversion efficiency were also reviewed. This review serves as a useful and informative reference for the application of wastewater treatment and CO₂ capture by microalgae, aiming to provide a reference for the realization of carbon neutrality in wastewater treatment systems.

Calcium ions-effect on performance, growth and extracellular nature of microalgal-bacterial symbiosis system treating wastewater

Microalgal-bacterial symbiosis (MABS) system treating wastewater has attracted great concern because of its advantages of carbon dioxide reduction and biomass energy production. However, due to the low density and negative surface charge of microalgae cells, the sedimentation and harvesting performance of microalgae biomass has been one limitation for the application of MABS system on wastewater treatment. This study investigated the performance enhancement of microalgae harvesting and wastewater treatment contributed by calcium ions (i.e., Ca²⁺) in the MABS system. Results showed that a low Ca²⁺ loading (i.e., 0.1 mM) promoted both COD and nutrients removal, with growth rates of 11.95, 6.53 and 1.21% for COD, TN and TP compared to control, and chlorophyll a was increased by 64.15%. Differently, a high Ca²⁺ loading (i.e., 10 mM) caused removal reductions by improving the aggregation of microalgae, with reduction rates of 34.82, 3.50 and 10.30% for COD, NH₄⁺-N and TP. Mechanism analysis indicated that redundant Ca²⁺ adsorbed on MABS aggregates and dissolved in wastewater decreased the dispersibility of microalgae cells by electrical neutralization and compressed double electric layer. Moreover, the presence of Ca²⁺ could improve extracellular secretions and promoted flocculation performance, with particle size increasing by 336.22%. The findings of this study may provide some solutions for the enhanced microalgae biomass harvest and nutrients removal from wastewater.

An overview on microalgal-bacterial granular consortia for resource recovery and wastewater treatment

Excessive generation of wastewater is a matter of concern around the globe. Wastewater treatment utilizing a microalgae-mediated process is considered an eco-friendly and sustainable method of wastewater treatment. However, low biomass productivity, costly harvesting process, and energy extensive cultivation process are the major bottleneck. The use of the microalgal-bacteria granular consortia (MBGC) process is economic and requires less energy. For efficient utilization of MBGC, knowledge of its structure, composition and interaction are important. Various microscopic, molecular and metabolomics techniques play a significant role in understating consortia structure and interaction between partners. Microalgal-bacteria granular consortia structure is affected by various cultivation parameters like pH, temperature, light intensity, salinity, and the presence of other pollutants in wastewater. In this article, a critical evaluation of recent literature was carried out to develop an understanding related to interaction behavior that can help to engineer consortia having efficient nutrient removal capacity with reduced energy consumption.

Occurrence of antibiotics in waters, removal by microalgae-based systems, and their toxicological effects: A review

Global antibiotics consumption has been on the rise, leading to increased antibiotics release into the environment, which threatens public health by selecting for antibiotic resistant bacteria and resistance genes, and may endanger the entire ecosystem by impairing primary production. Conventional bacteria-based treatment methods are only moderately effective in antibiotics removal, while abiotic approaches such as advanced oxidation and adsorption are costly and energy/chemical intensive, and may cause secondary pollution. Considered as a promising alternative, microalgae-based technology requires no extra chemical addition, and can realize tremendous CO₂ mitigation accompanying growth related pollutants removal. Previous studies on microalgae-based antibiotics removal, however, focused more on the removal performances than on the removal mechanisms, and few studies have concerned the toxicity of antibiotics to microalgae during the treatment process. Yet understanding the removal mechanisms can be of great help for targeted microalgae-based antibiotics removal performances improvement. Moreover, most of the removal and toxicity studies were carried out using environment-irrelevant high concentrations of antibiotics, leading to reduced guidance for real-world situations. Integrating the two research fields can be helpful for both improving antibiotics removal and avoiding toxicological effects to primary producers by the residual pollutants. This study, therefore, aims to build a link connecting the occurrence of antibiotics in the aquatic environment, the removal of antibiotics by microalgae-based processes, and the toxicity of antibiotics to microalgae. Distribution of various categories of antibiotics in different water environments were summarized, together with the antibiotics removal mechanisms and performances in microalgae-based systems, and the toxicological mechanisms and toxicity of antibiotics to microalgae after either short-term or long-term exposure. Current research gaps and future prospects were also analyzed. The review could provide much valuable information to the related fields, and provoke interesting thoughts on integrating microalgae-based antibiotics removal research and toxicity research on the basis of environmentally relevant concentrations.

Towards environment-sustainable wastewater treatment and reclamation by the non-aerated microalgal-bacterial granular sludge process: Recent advances and future directions

Currently, we are increasingly aware of the environmental unsustainability of the conventional wastewater treatment processes, e.g. extensive energy consumption and greenhouse gases emission. As such, the light-motivated non-aerated microalgal-bacterial granular sludge (MBGS) process has drawn extensive attention recently. This review aims to offer the important recent advances and future directions on the emerging non-aerated MBGS process for wastewater treatment and reclamation. The formation mechanism of MBGS from activated sludge is revealed to be the mobility under environmental stress such as shear force and nutrient deficiency. The key environmental factors affecting the non-aerated MBGS process are analyzed in terms with light, temperature, stirring and influent composition. Furthermore, sceneries of future outdoor processes by non-aerated MBGS are outlined. In turns out that the non-aerated MBGS offers a harmonious ecosystem to enrich the pollutants from wastewater to biomass, which can be potentially utilized as biofertilizer and feed for plant and animal, respectively. This review is expected to deepen our insights into the emerging non-aerated MBGS process for environment-sustainable wastewater treatment and reclamation.

Microalgal-Bacterial Granular Sludge Process in Non-Aerated Municipal Wastewater Treatment under Natural Day-Night Conditions: Performance and Microbial Community

The microalgal-bacterial granular sludge (MBGS) process is expected to meet the future requirements of municipal wastewater treatment technology for decontamination, energy consumption, carbon emission and resource recovery. However, little research on the performance of the MBGS process in outdoor treatment was reported. This study investigated the performance of the MBGS system in treating municipal wastewater under natural alternate day and night conditions in late autumn. The results showed that the average removal efficiencies of Chemical oxygen demand (COD), NH4+-N and PO43−-P on daytime before cooling (stage I, day 1−4) could reach 59.9% ± 6.8%, 78.1% ± 7.9% and 61.5% ± 4.5%, respectively, while the corresponding average removal efficiencies at night were 47.6% ± 8.0%, 56.5% ± 17.9% and 74.2% ± 7.6%, respectively. Due to the dramatic changes in environmental temperature and light intensity, the microbial biomass and system stability was affected with fluctuation in COD and PO43−-P removal. In addition, the relative abundance of filamentous microorganisms (i.e., Clostridia and Anaerolineae) decreased, while Chlorella maintained a dominant position in the eukaryotic community (i.e., relative abundance > 99%). This study can provide a theoretical basis and technical support for the further engineering application of the MBGS process.