Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the Anammox process

Enhanced methane production from waste activated sludge by microbial electrolysis cell assisted anaerobic digestion: Fate and effect of humic substances

Humic substances as major components of waste activated sludge are refractory to degrade and have inhibition in traditional anaerobic digestion (AD). This study for the first time investigated the feasibility and mechanism of microbial electrolysis cell assisted anaerobic digestion (MEC-AD) to break the recalcitrance and inhibition of humic substances. The cumulative methane production of AD decreased from 134.7 to 117.6 mL/g-VS with the addition of humic acids and fulvic acids at 25.2-102.1 mg/g-VS. However, 0.6 V MEC-AD maintained stable methane production (155.5-158.2 mL/g-VS) under the effect of humic substances. 0.6 V MEC-AD formed electrical stimulation on microbial cells, provided anodic oxidation and cathodic reduction transformation pathways for humic substances (acting as carbon sources and electron shuttles), and aggregated functional microorganisms on electrodes, facilitating the degradation of humic substances and generation of methane. This study provides a theoretical basis for improving the energy recovery and system stability of sludge treatment.

Drivers to improve metal(loid) phytoextraction with a focus on microbial degradation of dissolved organic matter in soils

Bioaugmentation of soils can increase the mobilization of metal(loid)s from the soil-bearing phases. However, once desorbed, these metal(loid)s are mostly complexed to the dissolved organic matter (DOM) in the soil solution, which can restrict their availability to plants (roots mainly taking up the free forms) and then the phytoextraction performances. Firstly the main drivers influencing phytoextraction are reminded, then the review focuses on the DOM role. After having reminding the origin, the chemical structure and the lability of DOM, the pool of stable DOM (the most abundant in the soil) most involved in the complexation of metal(loid)s is addressed in particular by focusing on carboxylic and/or phenolic groups and factors controlling metal(loid) complexation with DOM. Finally, this review addresses the ability of microorganisms to degrade metal(loid)-DOM complexes as an additional lever for increasing the pool of free metal(loid) ions, and then phytoextraction performances, and details the origin of microorganisms and how they are selected. The development of innovative processes including the use of these DOM-degrading microorganisms is proposed in perspectives.

Insights to Fe(II) on the fate of humic acid and humic acid Fe complex with biogeobattery effect in simultaneous partial nitritation, anammox and denitrification (SNAD) system

The role of Fe(II) on the humic acid (HA) transformation and the effects of humic acid Fe (HA-Fe) on simultaneous partial nitrification, anammox and denitrification (SNAD) system were investigated. After adding Fe(II), the HA content decreased and the HA inhibition on the SNAD system was released. Results showed that Fe(II) and HA formed the lower water-soluble HA-Fe, promoting the HA removal. HA-Fe with stronger electron transfer capacity constituted the interface with microorganisms to forming the biogeobattery effect. This accelerated the microbial electron transfer, as well as improved the key enzymes and ATP, indicating that HA-Fe stimulated the microbial activity of the SNAD system. Microbial community and quorum sensing analysis further demonstrated that HA-Fe enhanced the mutual symbiosis between electroactive and nitrogen removal bacteria, to ensure the stability of the SNAD system. The study provided references for efficient HA removal and revealed the biogeobattery effect of HA-Fe in the SNAD system.

Exploiting refractory organic matter for advanced nitrogen removal from mature landfill leachate via anammox in an expanded granular sludge bed reactor

Anammox is an efficient low-carbon nitrogen removal technology for mature landfill leachate (MLL). However, it produces 11 % nitrate theoretically, which needs further removal. In this study, the mechanisms of exploiting refractory organic matter (ROM) from an MLL as an inner carbon source for advanced nitrogen removal via anammox were systematically analyzed, and the effects of hydraulic retention time on nitrogen and ROM removal/utilization were investigated. Without any external carbon source, a total nitrogen and organic carbon removal efficiency of 94.50 % and 27.12 %, respectively, were achieved, with a nitrogen loading rate of 2.4 kg N/(m³·d). The abundances of norank_f_norank_o_SBR1031, OLB13, and norank_f_A4b, which had the capacity to degrade ROM, increased from 21.63 % to 49.21 %. This study reveals that the ROM in an MLL can be exploited for synchronous advanced nitrogen and organic matter removal.

A review on characterizing the metabolite property of anammox sludge by spectroscopy

As one of the most promising autotrophic biological nitrogen removal technology, anaerobic ammonia oxidation (anammox) has gained intense attention for the past decades and several full-scale facilities have been implemented worldwide. However, anammox bacteria are easily affected by disturbed external environmental factors, which commonly leads to the fluctuations in reactor performance. The response of anammox sludge to external stress results in changes in components and structural characteristics of intracellular and extracellular polymer substances. Real-time and convenient spectral analysis of anammox sludge metabolites can give early warning of performance deterioration under external stresses, which is of great significance to the stable operation of bioreactor. This review summarized the research progress on characterizing the intracellular and extracellular metabolites of anammox sludge through spectroscopic techniques. The correlation between anammox sludge activity and its key metabolites was analyzed. Also, the limitations and future prospects of applying spectral analytical techniques for anammox bioreactor monitoring were discussed and outlooked. This review may provide valuable information for both scientific study and engineering application of anammox based nitrogen removal technology.

Influential mechanism of water occurrence states of waste-activated sludge: Potential linkage between water-holding capacity and molecular compositions of EPS

The water occurrence states in waste-activated sludge (WAS) are crucial to its dewaterability and significantly influenced by the water-retaining capacity of extracellular polymeric substances (EPS) matrix. Accordingly, the non-selective •OH-oxidation processes were widely reported for the sludge dewaterability improvement, just because it can non-selectively destruct complex structure units of EPS, no matter these structure units are crucial to EPS water-holding capacity or not. But these non-selective processes may also require the large consumption of oxidant chemicals, which limits their wide application. This study specifically focused on the •OH-induced variation in molecular compositions of EPS and the corresponding effects on water occurrence states of WAS, which is expected to lay a foundation for optimizing the efficiency of oxidation-based sludge conditioning. Especially, through a novel method based on the equilibrium dialysis with alkaline titration, the typical hydrophilic functional groups of EPS were quantitatively analyzed. The results indicated that the free amino group (-NH2) had the greater impact on the water-holding capacity of EPS than the acidic hydroxyl groups (-OH). Nevertheless, by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), the hydrophilic heteroatom classes (e.g. N:Cw) were found to be less sensitive to the varying oxidant dosage than the molecular saturation degree (e.g. weighted averages of double bond equivalents (DBEw) and aromatic index (AImod,w)). •OH modified the nitrogen-containing or oxygen-containing functional groups, but could not completely remove these hydrophilic functional groups from EPS macromolecules. Therefore, the potential competition for •OH between the hydrophilic functional groups and the unsaturated structure units of EPS was clarified, which guides directions that developing highly-efficient sludge conditioning approaches should be based on the selective removal of hydrophilic functional groups instead of improving •OH production efficiency.

Deciphering effects of humic acid in landfill leachate on the simultaneous nitrification, anammox and denitrification (SNAD) system from performance, electron transfer and microbial community

Simultaneous nitrification, anammox and denitrification (SNAD) system is effective for landfill leachate treatment. However, humic acid (HA) as both an organic pollutant and electron shuttle in landfill leachate, its effects on the SNAD system remain unknown. This study demonstrated that HA initially inhibited NH₄⁺-N removal efficiency due to HA inhibition on anammox bacteria (the lowest fell to 90.89% from 100%), but the HA inhibition was released after adaption in the SNAD system. Hence, the mechanism of releasing HA inhibition in the SNAD system was established from performance, electron transfer and microbial community. Firstly, HA could be effectively removed by an adsorption-biodegradation process in the SNAD system, which avoided deteriorated performance caused by HA accumulation. Electrochemical analysis demonstrated that HA stimulated riboflavin and flavin mononucleotide (FMN) secretion to promote electron transfer efficiency. With the improved electron transfer efficiency, ETSA and ATP values significantly increased, indicating that HA enhanced the microbial metabolism activity of the SNAD system. Further analysis by enzymatic activity assay showed that the HAO (39.68 to 69.53 U/L), AMO (242.94 to 308.36 U/L), HZO (133.73 to 169.65 U/mL), NXR (24.63 to 54.52 U/L), NAR (94.40 to 114.36 U/L) and NIR (104.40 to 123.74 U/L) activities were improved with the HA increased from 0 to 200 mg/L, manifesting that HA enhanced nitrogen metabolism in the SNAD system. Besides, more reasonable metabolic division of labor in functional bacterial and enrichment of heterotrophic bacteria achieved efficient simultaneous removal of HA and nitrogen. Overall, efficient HA biodegradation, faster electron transfer efficiency and better metabolic division of microbial communities released HA inhibition, making the SNAD system more resistant to HA stress. This study shed light on the effects of HA on the SNAD system and provided a new insight for the SNAD system to landfill leachate treatment.

Combining electrochemical nitrate reduction and anammox for treatment of nitrate-rich wastewater: A short review

Treatment of nitrate-rich wastewater is important but challenging for the conventional biological denitrification process. Here, we propose combining the electrochemical reduction and anaerobic ammonium oxidation (anammox) processes together for treatment of nitrate-rich wastewater. This article reviews the mechanism and current research status of electrochemical reduction of nitrate to ammonium as well as the mechanism and applicability of the anammox process. This article discusses the principles, superiorities and challenges of this combined process. The feasibility of the combined process depends on the efficiency of electrochemical nitrate reduction to ammonium and the conditions in the anammox process to use the reduced ammonium as the substrate to achieve deep nitrogen removal. The article provides a feasible strategy for using the electrochemical reduction and anammox combined process to treat nitrate-rich wastewater.

Emerging onsite electron donors for advanced nitrogen removal from anammox effluent of leachate treatment: A review and future applications

Partial nitrification-anammox process is promising in leachate treatment, but the 11% residue nitrate limits the total nitrogen removal efficiency. Denitrification or partial denitrification and anammox are both practical polishing processes of anammox effluent, requiring extra electron donors. Fortunately, there are organic matter, sulfide and methane in leachate or produced by leachate treatment, which can serve as onsite electron donors. In this review, the mechanisms and processes using these three kinds of electron donors for residue nitrate reduction in anammox effluent of leachate are systematically summarized and discussed. It can be concluded that, biodegradable organic matter is an effective electron donor, sulfide is a promising electron donor, methane is a potential electron donor. Two possible applications in future based on anammox treatment of fresh and mature leachate using sulfide and methane as onsite electron donors are proposed. Through sulfide reutilization, energy-saving with about 14% of aeration reduction can be achieved.

Deciphering and predicting anammox-based nitrogen removal process under oxytetracycline stress via kinetic modeling and machine learning based on big data analysis

Anaerobic ammonium oxidation (anammox) is an advanced nitrogen removal process that is widely used in the nitrogen removal of various antibiotic containing wastewaters due to its high efficiency and energy saving characteristics. However, as a widely used antibiotic, the inhibitory effect of oxytetracycline (OTC) on anammox is unclear. In this study, the effect of OTC on the anammox-based nitrogen removal process was revealed by kinetic model and machine learning models. Statistical analysis showed that anammox started to be inhibited when the OTC concentration reached 2 mg/L. The inhibition and recovery periods were simulated under OTC stress. During the inhibition period, the R² fitted by Exp model was higher, and the simulated maximum nitrogen removal rate (NRR) was between 0.47 and 17.05 kg/(m³·d). During the recovery period, both Boltzmann and Gauss models fit well. In addition, the machine learning model of the artificial neural network predicted the NRR more accurately, indicating that the importance of environmental factors was lower than the effluent parameters. Spearman correlation analysis showed that the NRR was negatively correlated with OTC under both short-term and long-term OTC stress. Furthermore, the hydraulic retention time and water quality parameters played an important role in the short-term and long-term experiment, respectively. Finally, redundancy analysis demonstrated that the abundance of nitrogen functional genes, such as hydrazine dehydrogenase, nitrite/nitric oxide oxidoreductase and hydrazine synthase, was negatively correlated with the amount of OTC, while antibiotic resistance genes showed the opposite trend.

Interactions between Humic Substances and Microorganisms and Their Implications for Nature-like Bioremediation Technologies

The state of the art of the reported data on interactions between microorganisms and HSs is presented herein. The properties of HSs are discussed in terms of microbial utilization, degradation, and transformation. The data on biologically active individual compounds found in HSs are summarized. Bacteria of the phylum Proteobacteria and fungi of the phyla Basidiomycota and Ascomycota were found to be the main HS degraders, while Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes were found to be the predominant phyla in humic-reducing microorganisms (HRMs). Some promising aspects of interactions between microorganisms and HSs are discussed as a feasible basis for nature-like biotechnologies, including the production of enzymes capable of catalyzing the oxidative binding of organic pollutants to HSs, while electron shuttling through the utilization of HSs by HRMs as electron shuttles may be used for the enhancement of organic pollutant biodegradation or lowering bioavailability of some metals. Utilization of HSs by HRMs as terminal electron acceptors may suppress electron transfer to CO2, reducing the formation of CH4 in temporarily anoxic systems. The data reported so far are mostly related to the use of HSs as redox compounds. HSs are capable of altering the composition of the microbial community, and there are environmental conditions that determine the efficiency of HSs. To facilitate the development of HS-based technologies, complex studies addressing these factors are in demand.

Simultaneous Stripping of Ammonia from Leachate: Experimental Insights and Key Microbial Players

Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.

Fate of dissolved organic nitrogen during the Anammox process using ultra-high resolution mass spectrometry

Anaerobic ammonium oxidation (Anammox) is a cost-effective process for treating highly nitrogenous wastewater. However, the fate of organic nitrogen during Anammox treatment is still unclear, which limits its practical application. In this work, the changes in the quality of dissolved organic nitrogen (DON) in coal liquefaction wastewater (CLW) during Anammox were studied in relation to its chemical composition, which was determined by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The molecular-level characterization of extracellular polymeric substances (EPS) in the Anammox sludge is also reported for the first time in this paper. The relative contribution of N-containing compounds to the total dissolved organic matter (DOM) determined by summating the normalized intensities exceeded 30%, highlighting the complexity of the nitrogenous compounds in the influent. Additionally, Anammox appeared to be better suited to removing DON compounds with fewer carbonyl or carboxyl groups, more aromatic structures, and higher oxidative properties. Lignin-like substances were verified as the predominant component of N-containing compounds in Anammox EPS, followed by protein and substances with condensed aromatic structures. DON compounds with higher degrees of saturation, lower molecular weight, and higher lignin-like properties were more prone to absorption by Anammox EPS. A series of microbe-mediated pathways were demonstrated to be responsible for DON biodegradation, which revealed the organic and inorganic nitrogen removal mechanisms in the Anammox reactor. The obtained results provide great support to the ongoing efforts to optimize the Anammox process.

Kinetic aspects of humic substances derived from macrophyte detritus decomposition under different nutrient conditions

Autochthonous particulate organic carbon (POC) is an important precursor of humic substances (HS), and macrophytes represent the major source of POC in tropical aquatic ecosystems. Autochthonous HS influence the carbon supply, light regime, and primary production within freshwater systems. This study addresses the conversion of POC from two macrophyte species into HS and their mineralization under different nutrient conditions (oligotrophic to hypereutrophic). A first-order kinetic model was adopted to describe the conversion routes. The POC conversion rate to HS for detritus derived from Paspalum repens was similar under different nutrient conditions, but eutrophication decreased the k_R (global coefficient reaction) for detritus from Pistia stratiotes due to its high detritus quality (C:N:P ratio). Fulvic acids were the main fraction of HS in both plants. The mineralization of humic acids from P. stratiotes was inhibited at higher nutrient availability, while eutrophication increased the mineralization of fulvic acids from P. repens. The main route of POC cycling is humification through fulvic acid formation (up to 40% of POC). The intrinsic characteristics of the source detritus were the main forcing functions that stimulated the cycling of HS. In tropical aquatic ecosystems, the degradation of autochthonous carbon decreased due to eutrophication, thus contributing to the diagenetic process in the long term.

A review of landfill leachate induced ultraviolet quenching substances: Sources, characteristics, and treatment

Landfill leachate contains extremely diverse mixtures of pollutants and thus requires appropriate treatment before discharge. Co-treatment of landfill leachate with sewage in wastewater treatment plants is a common approach because of low cost and convenience. However, some recalcitrant organic compounds in leachate can escape biological treatment processes, lower the UV transmittance of waste streams due to their UV-quenching properties, and interfere with the associated disinfection efficacy. Thus, the leachate UV quenching substances (UVQS) must be removed or reduced to a level that UV disinfection is not strongly affected. UVQS consist of three major fractions, humic acids, fulvic acids and hydrophilics, each of which has distinct characteristics and behaviors during treatment. The purpose of this review is to provide a synthesis of the state of the science regarding UVQS and possible treatment approaches. In general, chemical, electrochemical, and physical treatments are more effective than biological treatments, but also costlier. Integration of multiple treatment methods to target the removal of different fractions of UVQS can aid in optimizing treatment. The importance of UVQS effects on wastewater treatment should be better recognized and understood with implemented regulations and improved research and treatment practice.

Selection of seeding strategy for fast start-up of Anammox process with low concentration of Anammox sludge inoculum

The long start-up time and large demand of Anammox seed sludge limit the practical application of Anammox process. In this study, the seeding strategy of fast start-up of Anammox process using 2.0 g VSS L^-1 of anaerobic granular sludge (AGS) or activated sludge (AS) with various low concentration of Anammox sludge as inoculum was investigated. In laboratory scale, the start-up (achieving 70% TN removal) was shortened from 21 days to 5 days when Anammox sludge concentration increased from 0.02 g VSS L^-1 to 0.2 g VSS L^-1 with 2 g VSS L^-1 AS as inoculum, and 16S rDNA analysis indicated the enrichment of Anammox bacteria, while the start-up failed with AGS. In pilot scale, the start-up was achieved in 10 days using 0.02 g VSS L^-1 of Anammox sludge and 2.0 g VSS L^-1 of AS, confirming the fast start-up of Anammox process with low concentration of Anammox sludge.

Using combined multiple techniques to characterize refractory organics during anammox process with mature coal chemical wastewater as influent

This study combined spectroscopy techniques to assess the composition of refractory organics and highlighted the potential application of excitation-emission matrix (EEM) fluorescence spectroscopy within future monitoring of coal chemical wastewater treatment by the anammox process. The results showed that the anammox process could effectively degrade refractory organic substances, with fulvic-like, UV-humic acid, and Vis-humic acid component removal efficiencies of 43.61, 53.93, and 100%, respectively. In this study, EEM fluorescence spectroscopy was proven to be an effective method of assessing the removal of dissolved organic nitrogen during anammox treatment of mature coal chemical wastewater. Furthermore, remarkable accumulation (9.3-16.2%) of Ca. Kuenenia occurred in the anammox granules that underwent long-term cultivation in mature coal chemical wastewater, which provided the high nitrogen removal rate. The abundance of Anaerolineaceae and Bacteroides was vital in refractory organic degradation.

Composition characterization and transformation mechanism of refractory dissolved organic matter from an ANAMMOX reactor fed with mature landfill leachate

This study applied combined spectroscopy techniques to assess rDOM compositional characteristic and investigated its transformation mechanisms during the treatment of mature landfill leachate by ANAMMOX process. A novel rDOM metabolism mechanism was proposed in this study for the first time. A stable, high nitrogen removal rate of 5.95 kg N/m³/day and a rDOM conversion efficiency of 51% were achieved in ANAMMOX reactor (AR). In additionally, the initial rDOM removal was closely related to sludge adsorption, with the adsorption force mainly originating from electrostatic interaction and hydrophobicity. As the operating time increased, the removal mechanism of rDOM in the AR changed from adsorption to adsorption-biodegradation and finally stabilized. Furthermore, Anaerolineaceae, associated with the hydrophobic reaction, were the primary degraders for the rDOM and Candidatus Kuenenia dominated the nitrogen consumption. rDOM removal efficiency was suggested to be increased by a moderate enhancement of Anaerolineaceae content in the AR.

Leachate/domestic wastewater aerobic co-treatment: A pilot-scale study using multivariate analysis

Multivariate analysis was used to identify the variables affecting the performance of pilot-scale activated sludge (AS) reactors treating old leachate from a landfill and from domestic wastewater. Raw leachate was pre-treated using air stripping to partially remove the total ammoniacal nitrogen (TAN). The control AS reactor (AS-0%) was loaded only with domestic wastewater, whereas the other reactor was loaded with mixtures containing leachate at volumetric ratios of 2 and 5%. The best removal efficiencies were obtained for a ratio of 2%, as follows: 70 ± 4% for total suspended solids (TSS), 70 ± 3% for soluble chemical oxygen demand (SCOD), 70 ± 4% for dissolved organic carbon (DOC), and 51 ± 9% for the leachate slowly biodegradable organic matter (SBOM). Fourier transform infrared (FTIR) spectroscopic analysis confirmed that most of the SBOM was removed by partial biodegradation rather than dilution or adsorption of organics in the sludge. Nitrification was approximately 80% in the AS-0% and AS-2% reactors. No significant accumulation of heavy metals was observed for any of the tested volumetric ratios. Principal component analysis (PCA) and partial least squares (PLS) indicated that the data dimension could be reduced and that TAN, SCOD, DOC and nitrification efficiency were the main variables that affected the performance of the AS reactors.

Decomposition characteristics of humic-like matters with the hollow ellipsoid structure sludge inoculated from decayed soil in mature landfill leachate

The organics in mature leachate are mainly humic-like matters, which account for over 80% weight of the total organics. In this work, the microorganisms in decayed soil were found to be capable of decomposing the humic-like matters evidently using an anaerobic-aerobic/anoxic bioprocess in two sequencing bio-reactors. The 3D excitation-emission matrix and Fourier transform infrared (FT-IR) were applied to characterize the variation of dissolved organic matters in mature leachate while sludge morphology was characterized by scanning electron microscopy. The intensities of fluorescence peaks A and C of leachate effluents were 71.66% and 48.75% lower than those of influents, respectively, which indicated the extraordinary degradation ability of microorganisms inoculated from the decayed soil. Meanwhile a kind of distinctive hollow ellipsoid structure sludge organized by tiny soil particles was observed, which might favour the humic-like matters' decomposition and has never been reported before as we know. The formation mechanisms of hollow ellipsoid structure sludge will need further study.

Characterization of dissolved organic matter in landfill leachate during the combined treatment process of air stripping, Fenton, SBR and coagulation

A combined treatment process of air stripping+Fenton+sequencing batch reactor (SBR)+ coagulation was performed to remove the pollutants in landfill leachate. Molecular weight (MW) distribution and fractions of dissolved organic matter (DOM) were discussed to study the characteristics. The experiment showed that the removal rate of chemical oxygen demand (COD), five day biological oxygen demand (BOD5) and ammonia nitrogen (NH3N) by the combined process were 92.8%, 87.8% and 98.0%, respectively. Humic acid (HA) and fulvic acid (FA) were the main fractions in raw leachate with 81.8% of the total COD concentration, while hydrophilic organic matter (HyI) was the dominant fraction in the final effluent of the combined process with 63.5% of the total COD concentration. After the combined treatment process, the removal rate of DOM and fractions HA, FA, HyI were 91.9%, 97.1%, 95.8% and 71.7%, respectively. Organic matters of MW<2k and MW>100k were removed with 90.5% and 97.9% COD concentration after the treatment. The ultraviolet-visible spectra (UV-vis), Fourier transform infrared spectra (FTIR) and three-dimensional excitation-emission matrices spectra (EEMs) indicated that benzene materials and phenol compounds were preferentially removed in air stripping. High MW matters, aromatic rings, conjugated moieties and some functional groups were mainly removed by Fenton. While smallMW fractions, carboxylic acids, alcohols and protein-like materials were preferentially biodegraded via SBR. Fulvic-like and humic-like materials were mainly destroyed via Fenton oxidation and coagulation.

Co-treatment of landfill leachate and domestic wastewater using a submerged aerobic biofilter

This study used a pilot-scale submerged aerobic biofilter (SAB) to evaluate the co-treatment of domestic wastewater and landfill leachate that was pre-treated by air stripping. The leachate tested volumetric ratios were 0, 2, and 5%. At a hydraulic retention time of 24 h, the SAB was best operated with a volumetric ratio of 2% and removed 98% of the biochemical oxygen demand (BOD), 80% of the chemical oxygen demand (COD) and dissolved organic carbon (DOC), and 90% of the total suspended solids (TSS). A proposed method, which we called the "equivalent in humic acid" (Eq.HA) approach, indicated that the hardly biodegradable organic matter in leachate was removed by partial degradation (71% of DOC Eq.HA removal). Adding leachate at a volumetric ratio of 5%, the concentration of the hardly biodegradable organic matter was decreased primarily as a result of dilution rather than biodegradation, which was confirmed by Fourier transform infrared (FTIR) spectroscopy. The total ammoniacal nitrogen (TAN) was mostly removed (90%) by nitrification, and the SAB performances at the volumetric ratios of 0 and 2% were equal. For the three tested volumetric ratios of leachate (0, 2, and 5%), the concentrations of heavy metals in the treated samples were below the local limits.

Long-term performance and microbial ecology of a two-stage PN-ANAMMOX process treating mature landfill leachate

Long-term performance of a two-stage partial nitritation (PN)-anaerobic ammonium oxidation (ANAMMOX) process treating mature landfill leachate was investigated. Stable partial nitritation performance was achieved in a sequencing batch reactor (SBR) using endpoint pH control, providing an effluent with a ratio of NO2(-)-N/NH4(+)-N at 1.23 ± 0.23. High rate nitrogen removal over 4 kg N/m(3)/d was observed in the ANAMMOX reactor in the first three months. However, during long-term operation, the ANAMMOX reactor can only stably operate under nitrogen load of 1 kg N/m(3)/d, with 85 ± 1% of nitrogen removal. The ammonium oxidizing bacteria (AOB) in the PN-SBR were mainly affiliated to Nitrosomonas sp. IWT514, Nitrosomonas eutropha and Nitrosomonas eutropha, the anaerobic ammonium oxidizing bacteria (AnAOB) in the ANAMMOX reactor were mainly affiliated to Kuenenia stuttgartiensis.

The effect of humic acids on the reverse osmosis treatment of hazardous landfill leachate

This study deals with the treatment of hazardous waste landfill leachate with the help of reverse osmosis. The landfill is located in an abandoned brown coal pit in northern Bohemia. The leachate contained 7.2 g/L of dissolved inorganic salts. Among other contaminants were heavy metals, arsenic, ammonia nitrogen and associated organic pollutants, especially chlorinated compounds. A mobile membrane unit (LAB M30) equipped with a spiral wound element (FILMTEC SW30-4040), with a membrane area equaling 7.4 m2 was used for the pilot plant experiments. All experiments were carried out in batch mode. 94% conversion of the input stream into the permeate was achieved by use of a two-stage arrangement. Removal efficiencies of the monitored contaminants in the feed ranged from 94% for ammonia nitrogen to 99% for the two-valent ions. Removal efficiency for total dissolved solids was 99.3% on average. Due to varying levels of humic acids in the leachate throughout the year, fouling experiments were performed to investigate the separation process under different conditions than those used in the pilot plant. Leachates containing different concentrations of added humic acids were separated using a thin film composite on a propylene membrane. The added humic acids were obtained from samples of contaminated oxihumolite.

Impact of reactor configuration on anammox process start-up: MBR versus SBR

Anaerobic ammonium oxidation (anammox) is an energy saving biological nitrogen removal process which was limited to slow growth rate of anammox bacteria during start-up period. This study investigated the start-up of anammox process by a laboratory sequential batch reactor (SBR) for 218 days and subsequently modified the reactor as a membrane bioreactor (MBR) for 178 days. Modification of a SBR as MBR with installation of an external membrane module resulted in acceleration of specific anammox activity by 19 times. The acceleration of specific anammox activity with MBR was further confirmed by starting-up another MBR for a 242 day period. Molecular microbial analyses showed that Candidatus "Brocadia anammoxidans" and Candidatus "Kuenenia stuttgartiensis" were the dominant species in the inocula and biomass developed in the reactor. The start-up with MBR appeared to be more effective than SBR for the enrichment of anammox bacteria due to high sludge retention property of MBR configuration.