Kinetics of phenolic and phthalic acid esters biodegradation in membrane bioreactor (MBR) treating municipal landfill leachate

Recent advances in occurrence, biotreatment, and integrated insights into bacterial degradation of phthalic acid esters in aquatic environments

Phthalic acid esters (PAEs) are prevalent as emerging contaminants owing to their widespread use as plasticizers in industry. Despite their environmental and health risks, a limited understanding of PAE contamination in aquatic environments hinders the practical implementation of biotreatment strategies for their removal. This paper reviews the advances in occurrence, biotreatment, and relevant integrative analysis of bacterial PAE degradation over the past decade. In various aquatic environments, dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) are the predominant PAE pollutants across different regions, with alarming levels reported in Eastern China. PAEs in water usually inhibit the growth and metabolism of surrounding organisms. Meanwhile, various biotreatment techniques have proven effective in removing PAEs from leachate and wastewater. The treatment efficiency can be further enhanced by incorporating suitable physicochemical processes and optimizing key factors, such as the initial pollutant concentration, PAE type, and reaction time. Additionally, a K-means machine learning algorithm and 16S rRNA gene-based evolutionary analysis were employed to reveal that soil is a preferred source for isolating strains, with Gordonia and Pseudomonas being the dominant genera of PAE-degrading bacteria exhibiting high degradation efficiency. Moreover, most PAE hydrolase genes were discovered in these two genera. Different gene clusters facilitated the subsequent degradation pathways under aerobic or anaerobic conditions. This paper presents the latest updates on PAE biotreatment and offers an integrated analysis of the bacterial degradation involved. Future research should apply these insights to enhance the overall effectiveness of PAE removal in water.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Volatile and semi-volatile organic compounds in landfill leachate: Concurrence, removal and the influencing factors

Volatile and semi-volatile organic compounds (VOCs and SVOCs) carried by landfilled wastes may enter leachate, and require appropriate treatment before discharge. However, the driving factors of the entry of VOCs and SOVCs into leachate, their removal characteristics during leachate treatment and the dominant factors remain unclear. A global survey of the VOCs and SOVCs in leachate from 103 landfill sites combined with 27 articles on leachate treatment was conducted to clarify the abovementioned question. The results showed that SVOCs such as polycyclic aromatic hydrocarbons (PAHs), phthalate acid esters (PAEs) and phenols were the most frequently detected in leachate on a global scale. However, four kinds of VOCs, i.e., toluene, ethylbenzene, xylenes and benzene, were frequently detected at high concentrations in landfill leachate as well. The concentrations of VOCs and SVOCs in leachate ranged from 1 × 10° to 1 × 108 ng/L. Solubility was a key factor driving the entry of VOCs and SOVCs into leachate, and higher solubility enables higher detectable concentrations in leachate (P<0.05). It was easiest to remove monocyclic aromatic hydrocarbons (MAHs) from leachate, followed by phenols and PAHs, and it was most difficult to remove PAEs. In terms of removing MAHs, the anoxic/oxic (A/O) process and the sequential batch reactor (SBR) process were comparable to the advanced oxidization process and far superior to the ultrafiltration and nanofiltration processes, and the removal rate increased with an increase in the Henry's constant and/or the hydrophilicity of the contaminants during the A/O and SBR processes (P<0.05). There were no significant differences among biological, advanced oxidation and reverse osmosis processes in the removal of phenolic. In terms of removing PAHs, the A/O process was comparable to the advanced oxidization process and more efficient than the other treatment processes. As to removing PAEs, the membrane bioreactor process was almost the same efficient as the advanced oxidization process and far more efficient than the other biological treatment processes. Future research should focus on the pollution of atmospheric VOCs and SVOCs near aeration units in leachate treatment plants, as well as the health risk assessment of VOCs and SVOCs in the treated leachate effluent. To the best of our knowledge, this is the first review regarding the occurrence and removal of VOCs and SVOCs from landfill leachates worldwide.

Removal of antibiotics from wastewaters by membrane technology: Limitations, successes, and future improvements

Antibiotics and related pharmaceuticals are applied to enhance public health and life quality. A major environmental concern is wastewaters from pharmaceutical industries, which contain significant amounts of antibiotics. Pharmaceutical industries apply conventional processes (biological, filtration, coagulation, flocculation, and sedimentation) for wastewater treatment, but these approaches cannot remove antibiotics completely. Moreover, unmetabolized antibiotics released by humans and animals are dangerous for municipal and effluent wastewater. Besides, antibiotic resistance is another challenge in treatment of wastewater for superbugs. This comprehensive study summarizes different techniques for antibiotic removal with an emphasis on membrane technology in individual and hybrid systems such as chemical, physical, biological, and conditional-based strategies. A combination of membrane processes with advanced oxidation processes (AOPs), adsorption, and biological treatments can be the right solution for perfect removal. Furthermore, this review briefly compares different procedures for antibiotic removal, which can be helpful for further studies with their advantages and drawbacks.

A Combined Catalytic Ozonation-MBR Approach to Remove Contaminants from the Mature Landfill Leachate in the Yellow River Basin

The mature landfill leachate (MLL) is characterized by a large number of fulvic acids and humic acids, which is refractory organic matter and can be cleaned by ozone oxidation. However, the poor property of mass transfer prohibits the widespread use of ozone oxidation in actual leachate treatment. Meanwhile, some combined processes are adopted to treat the mature landfill leachate, which places catalytic ozonation before the membrane bioreactor (MBR) process to enhance the biodegradability of MLL. Thus, this research is conducted to investigate the practicability of applying nano-Fe₃O₄ loaded cow-dung ash (Fe₃O₄@CDA) and biological post-treatment with MBR for the effective removal of pollutants from MLL and puts forward the variation of organics in leachate between catalytic ozonation and MBR. The addition of catalytic ozonation not only improved the removal of hazardous organics but also enhanced the biodegradability of the leachate and favored the subsequent MBR process. Chemical oxygen demand (COD) removal in the catalytic ozonation step was optimized, and 53% removal was obtained at pH = 7, catalyst dosage = 1.0 g/L, and O₃ dosage = 3.0 g/L. After the MBR process, COD in effluent stabilized in the range of 57.85-65.38 mg/L, and the variation range of the ammonia nitrogen (NH₃-N) concentration was 5.98-10.24 mg/L. The catalytic ozonation-MBR integrated process showed strong feasibility in dealing with the biologically pre-treated leachate.

Advances in the application of immobilized enzyme for the remediation of hazardous pollutant: A review

Nowadays, ecofriendly, low-cost, and sustainable alternatives techniques have been focused on the effective removal of hazardous pollutants from the water streams. In this context, enzyme immobilization seems to be of specific interest to several researchers to develop novel, effective, greener, and hybrid strategies for the removal of toxic contaminants. Immobilization is a biotechnological tool, anchoring the enzymes on support material to enhance the stability and retain the structural conformation of enzymes for catalysis. Recyclability and reusability are the main merits of immobilized enzymes over free enzymes. Studies showed that immobilized enzyme laccase can be used up to 7 cycles with 66% efficiency, peroxidase can be recycled to 2 cycles with 50% efficiency, and also cellulase to 3 cycles with 91% efficiency. In this review, basic concepts of immobilization, different immobilization techniques, and carriers used for immobilization are summarized. In addition to that, the potential of immobilized enzymes as the bioremediation agents for the effective degradation of pollutants from the contaminated zone and the impact of different operating parameters are summarized in-depth. Further, this review provides future trends and challenges that have to be solved shortly for enhancing the potential of immobilized systems for large-scale industrial wastewater treatment.

Phthalates in the environment: characteristics, fate and transport, and advanced wastewater treatment technologies

Phthalates are well-known emerging contaminants that harm human health and the environment. Therefore, this review aims to discuss about the occurrence, fate, and phthalates concentration in the various environmental matrices (e.g., aquatic, sediment, soil, and sewage sludge). Hence, it is necessary to treat sources containing phthalates before discharging them to aqueous environment. Various advanced wastewater treatments including adsorption process (e.g., biochar, activated carbon), advanced oxidation processes (e.g., photo-fenton, ozonation, photocatalysis), and biological treatment (membrane bioreactor) have been successfully to address this issue with high removal efficiencies (70-95%). Also, the degradation mechanism was discussed to provide a comprehensive understanding of the phthalate removal for the reader. Additionally, key factors that influenced the phthalates removal efficiency of these technologies were identified and summarized with a view towards pilot-scale and industrial applications.

Biochemical pathways and enhanced degradation of dioctyl phthalate (DEHP) by sodium alginate immobilization in MBR system

As one of the most representative endocrine disrupting compounds, dioctyl phthalate (DEHP) is difficult to remove due to its bio-refractory characteristic. In this study, an immobilization technology was applied in an MBR system to improve the degradation of DEHP. The degradation efficiency of DEHP was significantly improved and the number of degradation genes increased by 1/3. A bacterial strain that could effectively degrade DEHP was isolated from activated sludge and identified as Bacillus sp. The degradation pathway of DEHP was analyzed by GC-MS. DEHP was decomposed into phthalates (DBP) and Diuretic sylycol (DEP), then further to Phthalic acid (PA). PA was oxidized, dehydrogenated, and decarboxylated into protocatechins, further entered the TCA cycle through orthotopic ring opening. The DEHP degrading strain was immobilized by sodium alginate and calcium chloride under the optimized immobilization conditions, and added to MBR systems. The removal rate of DEHP (5 mg/L) (91.9%) and the number of 3, 4-dioxygenase gene copies was significantly improved by adding immobilized bacteria. Micromonospora, Rhodococcus, Bacteroides and Pseudomonas were the dominant genuses, and the results of bacterial community structure analysis show that immobilization technology is beneficial to system stability. The results showed the potential applications of the immobilized technique in DEHP wastewater treatment in MBR.

Use of aged sludge bioaugmentation in two-stage activated sludge system to enhance the biodegradation of toxic organic compounds in high strength wastewater

This research investigates the toxic organic compounds biodegradation efficiency of two-stage activated sludge systems with (bioaugmented) and without aged sludge bioaugmentation (non-bioaugmented). The influent was a mixture of leachate and agriculture wastewater (1:1, v/v), used as the representative high strength wastewater. The bioaugmented and non-bioaugmented systems were operated in parallel, with three levels (low, moderate, and high) of concentrations of organics, nitrogen, and toxic organic compounds in the influent (conditions 1, 2, and 3). The results showed that both systems could efficiently degrade the organic compounds. Nevertheless, the toxic organic compounds biodegradation efficiency of the bioaugmented system was higher than that of the non-bioaugmented one. The bioaugmentation enhanced the overall removal efficiency under conditions 1 and 2. However, the bioaugmented system became less effective under condition 3. Further analysis indicated that the bacterial groups essential to the toxic organic compounds biodegradation were abundant in the aged sludge, including heterotrophic bacteria, heterotrophic nitrifying bacteria, and nitrifying bacteria. The abundance of the effective bacteria improved the biodegradation and wastewater treatment performance of the bioaugmented system. In essence, the aged sludge bioaugmentation is a viable and eco-friendly solution to improving the treatment efficiency of the biological activated sludge system, despite limited biodegradation efficiency in an elevated compounds-concentration environment.

Hydraulic performance and fouling characteristics of a membrane sequencing batch reactor (MSBR) for landfill leachate treatment under various operating conditions

This study investigates the hydraulic performance and the fouling characteristics of a bench-scale membrane sequencing batch reactor (MSBR), treating mature landfill leachate under various time-based operating conditions. The MSBR system operated initially under a high-flux condition (Period 1) which resulted in a rapid trans-membrane pressure (TMP) rise due to intense fouling. Following the characterization of Period 1 as super-critical, the system was subsequently operated under a near-critical condition (Period 2). The overall filtration resistance analysis showed that cake layer formation was the dominant fouling mechanism during Period 1, contributing to 85.5% of the total resistance. However, regarding the MSBR operation during Period 2, adsorption was found to also be a dominant fouling mechanism (Days 1 to 47), contributing to 29.1% of the total resistance. Additionally, the irregular total resistance variation, which was observed during the subsequent operation (Days 48 to 75), and the respective filtration resistance analysis suggested also the formation of an initial sludge cake layer on the membrane surface, contributing to the 47.7% of the total resistance.

Insight into effects of antibiotics on reactor performance and evolutions of antibiotic resistance genes and microbial community in a membrane reactor

A lab-scale anoxic/oxic-membrane bioreactor was designed to treat antibiotics containing wastewater at different antibiotics concentrations (0.5 mg/L, 1 mg/L and 3 mg/L of each antibiotic). Overall COD and NH₄⁺N removal (more than 90%) were not affected during the exposure to antibiotics and good TN removal was also achieved, while TP removal was significantly affected. The maximum removal efficiency of penicillin and chlorotetracycline reached 97.15% and 96.10% respectively due to strong hydrolysis, and sulfamethoxazole reached 90.07% by biodegradation. However, 63.87% of norfloxacin maximum removal efficiency was achieved mainly by sorption. The system had good ability to reduce ARGs, peaking to more than 4 orders of magnitude, which mainly depended on the biomass retaining of the membrane module. Antibiotics concentration influenced the evolution of ARGs and bacterial communities in the reactor. This research provides great implication to reduce ARGs and antibiotics in antibiotics containing wastewater using A/O-MBR.

Toxic compounds biodegradation and toxicity of high strength wastewater treated under elevated nitrogen concentration in the activated sludge and membrane bioreactor systems

This research has assessed the removal efficiencies of toxic compounds in the high strength wastewater (the leachate and agriculture wastewater mixture) using the activated sludge (AS) and membrane bioreactor (MBR) technologies under two carbon to nitrogen (C/N) ratios (C/N 14 and 6) and two toxic compounds concentrations (8-396μg/L and 1000μg/L). In addition, the toxicity evaluations of the AS and MBR effluents to the aquatic environment were undertaken at five effluent dilution ratios (10, 20, 30, 50 and 70% v/v). The findings indicate that the AS treatment performance could be enhanced by the elevation of the nitrogen concentration. Specifically, the C/N 6 environment helps promote the bacterial growth, particularly heterotrophic nitrifying bacteria (HNB) and nitrifying bacteria (NB), which produce the enzymes crucial to the toxic compounds degradation. The improved biodegradation makes the effluents less toxic to the aquatic environment, as evidenced by the lower mortality rates of both experimental fish species raised in the nitrogen-elevated diluted AS effluents. On the other hand, the elevated nitrogen concentration minimally enhances the MBR treatment performance, given the fact that the MBR technology is in itself a biological treatment scheme with very high compounds removal capability. Despite its lower toxic compounds removal efficiency, the AS technology is simple, inexpensive and operationally-friendly, rendering the system more applicable to the treatment operation constrained by the financial, manpower and technological considerations.

Estrogenicity assessment of membrane concentrates from landfill leachate treated by the UV-Fenton process using a human breast carcinoma cell line

Membrane concentrates (MCs) are generated when membranes are used to concentrate landfill leachate. It contains high concentrations of inorganic and organic environmental pollutants, which are highly toxic and carcinogenic. In this paper, the proliferation effect (PE) from MC before and after treatment with the UV-Fenton process was assessed using the human breast carcinoma cell line MCF-7. The highest value of 116% was found at 5% (v/v) concentration after a 10 min reaction. Phthalic acid esters (PAEs) play an important role in the MC estrogenicity. Estrogen simulation solutions (ESS) of PAEs were prepared to simulate the changes in estrogenic active substances during the UV-Fenton process. The ESS degradation conformed to the first-order kinetics model. The estrogenicity decreased after an initial increase until it acted in a non-estrogenic manner. Convincingly, the intermediates were determined by GC/MS, and the estrogenicity was assessed during the degradation process. The estrogenicity was highly related to the generation of intermediates and the PAE concentration. The results provide guidance for UV-Fenton application in MC estrogenicity reduction.

Enhanced biodegradation of phenolic compounds in landfill leachate by enriched nitrifying membrane bioreactor sludge

The role of autotrophic nitrification on the biodegradation of toxic organic micro-pollutants presented in landfill leachate was assessed. A two-stage MBR system consisting of an inclined tube incorporated anoxic reactor followed by aerobic submerged membrane reactor was operated under long sludge age condition in which nitrifying bacteria could be enriched. During the reactor operation, organic removal efficiencies were more than 90% whereas phenolic compounds including bisphenol A (BPA) and 4-methyl-2,6-di-tert-butylphenol (BHT) were removed by 65 and 70% mainly through biodegradation in the aerobic reactor even at high feed concentrations of 1000μg/L for both compounds. Batch experiments revealed that enriched nitrifying sludge with nitrifying activities could biodegraded 88 and 75% of BPA and BHT, largely improved from non-nitrifying sludge and enriched nitrifying sludge with the presence of inhibitor. The first-order kinetic rates of BHT and BPA removal were 0.0108 and 0.096h^-1, also enhanced by 44% from the non-nitrifying sludge.

Degradation behavior of dimethyl phthalate in an anaerobic/anoxic/oxic system

Dimethyl phthalate (DMP) as one of the most important and extensively used Phthalic acid esters (PAEs) is known to likely cause dysfunctions of the endocrine systems, liver, and nervous systems of animals. In this paper, the degradation and behavior of DMP were investigated in a laboratory scale anaerobic/anoxic/oxic (AAO) treatment system. In addition, a degradation model including biodegradation and sorption was formulated so as to evaluate the fate of DMP in the treatment system, and a mass balance model was designed to determine kinetic parameters of the removal model. The study indicated that the optimal operation condition of HRT and SRT for DMP and nutrients removal were 18 h and 15 d respectively, and the degradation rates of anaerobic, anoxic and aerobic zones for DMP were 13.4%, 13.0% and 67.7%, respectively. Under the optimal conditions, the degraded DMP was 73.8%, the released DMP in the effluent was 5.8%, the accumulated DMP was 19.3%, and the remained DMP in the waste sludge was 1.1%. Moreover, the degradation process of DMP by acclimated activated sludge was in accordance with the first-order kinetics equation. The model can be used for accurately modeling the degradation and behavior of DMP in the AAO system.

Effects of hydraulic retention time and carbon to nitrogen ratio on micro-pollutant biodegradation in membrane bioreactor for leachate treatment

This research investigated the biodegradation of the micro-pollutants in leachate by the membrane bioreactor (MBR) system under six treatment conditions, comprising two C/N ratios (6, 10) and three hydraulic retention time (HRT) durations (6, 12, 24h). The experimental results indicated that the C/N 6 environment was more advantageous to the bacterial growth. The bacterial communities residing in the sludge were those of heterotrophic bacteria (HB), heterotrophic nitrifying bacteria (HNB) and ammonia oxidizing bacteria (AOB). It was found that HB and HNB produced phenol hydroxylase (PH), esterase (EST), phthalate dioxygenase (PDO) and laccase (LAC) and also enhanced the biodegradation rate constants (k) in the system. At the same time, AOB promoted the production of HB and HNB. The findings also revealed that the 12h HRT was the optimal condition with regard to the highest growth of the bacteria responsible for the biodegradation of phenols and phthalates. Meanwhile, the longer HRT duration (i.e. 24h) was required to effectively bio-degrade carbamazepine (CBZ), N,N-diethyl-m-toluamide (DEET) and diclofenac (DCF).