Key Takeaways & Executive Findings
- •• • The two-stage A/O–MBBR system achieved average NH4+-N and COD removal efficiencies of 97.7% and 66.8%, respectively, under influent NH4+-N up to 1800 mg·L−1, demonstrating robust resistance to shock loads and suitability for high-strength leachate. • • Coupling Anammox with partial nitrification-denitrification contributed 13–16% to nitrogen removal, elevating total nitrogen (TN) removal to 93.9%, significantly outperforming conventional biological processes in energy and carbon source savings. • • High-throughput sequencing confirmed Proteobacteria as dominant (>50%), with denitrifying genera Azoarcus and Thauera enriched; Planctomycetota increased from 0.6% to 3.7%, and Candidatus Kuenenia was detected, evidencing successful Anammox biofilm colonization. • • The multi-stage spatial configuration and biofilm microenvironment enabled simultaneous organic oxidation, nitrification, denitrification, and Anammox, overcoming limitations of traditional processes for high C/N and toxic leachate, offering a practical low-carbon treatment pathway.
Abstract
Landfill leachate, characterized by high ammonia nitrogen, high organic load, complex toxic components, and low nitrogen removal efficiency, poses significant environmental challenges. To achieve efficient nitrogen removal, a continuous-flow two-stage anoxic/oxic (A/O) moving-bed biofilm reactor (MBBR) system coupled with anaerobic ammonium oxidation (Anammox) was constructed and operated for long-term treatment of actual landfill leachate. After biofilm attachment and multi-gradient acclimation, influent concentrations were gradually increased from low levels (NH4+-N ~200 mg·L−1, COD ~2500–3000 mg·L−1) to high levels (NH4+-N ~1800 mg·L−1, COD ~8500 mg·L−1). During stable operation, average removal efficiencies of NH4+-N and COD reached 97.7% and 66.8%, respectively, with total nitrogen (TN) removal efficiency improving to 93.9%. Along the reactor, the first A/O stage achieved major organic degradation and ammonia oxidation, while the second stage facilitated nitrite accumulation and promoted Anammox for synergistic nitrogen removal. High-throughput sequencing revealed Proteobacteria as the dominant phylum (>50%), with denitrifying genera such as Azoarcus and Thauera significantly enriched. Planctomycetota abundance increased from 0.6% to 3.7%, and Candidatus Kuenenia was detected, confirming successful Anammox colonization and participation in nitrogen removal. This study validates the efficient combined nitrogen removal mechanism of the A/O–MBBR system with Anammox, providing theoretical basis and technical support for engineering treatment of high-ammonia wastewater.
1. Introduction
Landfill leachate, particularly from mature landfills, presents a formidable challenge to conventional biological nitrogen removal due to its high ammonia nitrogen concentrations (often exceeding 2000 mg·L−1), recalcitrant organic matter, and imbalanced carbon-to-nitrogen ratios. Traditional nitrification-denitrification processes require substantial aeration and external carbon sources, leading to high energy consumption and operational costs. Physicochemical methods such as ammonia stripping and membrane separation are energy-intensive and generate secondary pollution. These limitations underscore the urgent need for more sustainable and efficient nitrogen removal technologies.
Anammox-based processes offer a promising alternative, reducing aeration energy by approximately 50% and eliminating the need for external carbon sources. However, their application to real wastewater has been hindered by the sensitivity of anammox bacteria to environmental conditions and the difficulty of achieving stable nitrite supply. This study addresses these bottlenecks by integrating a two-stage A/O–MBBR system with anammox, creating distinct zones for organic removal, partial nitrification, and anammox. The system successfully treated actual landfill leachate with high ammonia loads, achieving over 93% total nitrogen removal, demonstrating a robust and practical solution for high-strength wastewater treatment.
Loading authentic research manuscript (Pages 1–5)...
LIU Jianxi, LIU Hongtao, TAN Yong, GUO Juncheng, LIU Sichen, TAN Cong (2026). Enhanced Nitrogen Removal from Landfill Leachate via a Two-Stage A/O–MBBR System Coupled with Anammox. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202508006
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What are the critical operational parameters (e.g., DO, pH, temperature) required to maintain stable Anammox activity in the continuous-flow system, and how were they controlled?
The system maintained stable Anammox activity by creating a low-DO environment in the second anoxic zone (A2) to facilitate nitrite accumulation and Anammox. Although specific DO values are not detailed in the text, the design ensured that the second-stage anoxic zone received minimal oxygen, promoting partial denitrification and Anammox. The system operated at ambient temperatures typical for leachate treatment, and pH was maintained near neutral (influent pH 8±0.5). The successful colonization of Candidatus Kuenenia indicates that conditions were suitable for Anammox bacteria.
How does the two-stage A/O–MBBR configuration contribute to the high nitrogen removal efficiency compared to single-stage systems?
The two-stage configuration separates organic degradation and ammonia oxidation in the first A/O stage from nitrite accumulation and Anammox in the second stage. This spatial segregation allows optimization of conditions for each microbial group, preventing competition between heterotrophs and autotrophs. The MBBR biofilm provides a protected microenvironment for slow-growing Anammox bacteria, enhancing their retention and activity. This design achieved a TN removal of 93.9%, significantly higher than typical single-stage systems.
What is the contribution of Anammox to overall nitrogen removal, and how was it quantified?
Anammox contributed 13–16% to nitrogen removal, as determined by mass balance calculations and microbial community analysis. This contribution was stable during operation, indicating a reliable synergy between partial denitrification and Anammox. The presence of Candidatus Kuenenia and the increase in Planctomycetota abundance from 0.6% to 3.7% corroborate the activity of Anammox bacteria.
What are the potential scalability challenges of this system for full-scale landfill leachate treatment, and how can they be addressed?
Scalability challenges include maintaining stable biofilm formation on MBBR carriers, controlling DO gradients across large reactors, and managing the sensitivity of Anammox bacteria to environmental fluctuations. These can be addressed by using appropriate carrier materials, implementing robust process control (e.g., online DO and pH monitoring), and gradually acclimating the system to high loads. The successful operation at pilot scale (39 L) suggests that the design is feasible for scale-up, but further validation at larger scales is needed.
How does the system handle the high organic load (COD) in landfill leachate without inhibiting Anammox activity?
The system achieved 66.8% COD removal, primarily in the first A/O stage, which reduces the organic load entering the Anammox zone. This prevents heterotrophic competition and potential inhibition of Anammox bacteria by high organic concentrations. The second stage operates under low COD conditions, favoring autotrophic Anammox activity. This staged approach effectively manages the high organic load while maintaining high nitrogen removal.
Related Chinese Research & Cross-Citations
Analysis of National and Local Policies for Medical Waste Treatment and Disposal in China
The escalating generation of medical waste, driven by healthcare expansion and frequent medical activities, poses significant environmental and public health risks. Under the framework of ecological civilization, China is developing a comprehensive policy system for medical waste treatment and disposal, yet the current framework remains nascent and exhibits inconsistencies between national and local policies. This study systematically analyzes the status of national and local policies from 2003 to 2024, collecting 413 policy documents (166 from national ministries and 247 from provincial governments). The analysis examines temporal evolution, regional distribution, and policy focus, alongside the influence of medical waste output, treatment technologies, facility infrastructure, and major epidemic responses. Findings reveal distinct policy phases: initial self-disposal, exploratory management, foundational system building, and rapid development. Regional disparities are pronounced, with eastern coastal areas showing more advanced policies due to greater technical and financial resources. The surge in medical waste, particularly during the COVID-19 pandemic, underscores the need for enhanced regulatory guidance. Non-incineration technologies are gaining traction for their environmental and cost benefits, and facility coverage has improved but remains uneven. The study proposes five policy principles to foster technological innovation and industrial upgrading, ensuring safe medical waste management and environmental protection.
Kinetic Analysis and Simulation of Pollutant Removal in Sewage Networks
This study investigates pollutant removal characteristics and kinetic behaviors in sewage networks, and analyzes their impact on the carbon-to-nitrogen ratio (C/N, as COD/TN) of influent to wastewater treatment plants. Source water quality sampling at drainage outlets revealed spatial and temporal variations in C/N, with domestic sewage exhibiting higher C/N than industrial sewage, and diurnal peaks reaching 6.92 versus 4.71 during off-peak hours. Using a pilot-scale adjustable sewage network system in Kunshan, experiments were conducted under high (0.491 m·s−1) and low (0.089 m·s−1) flow velocities, monitoring pollutant removal over 144 hours. Pseudo-first-order kinetics were applied to model COD and TN removal. Results showed that COD (including SCOD and PCOD), BOD5, and SS achieved approximately 80% removal within 144 h, with higher removal at low flow velocity. TN, NH3-N, and TP exhibited lower overall removal rates. Kinetic fitting revealed that COD removal rate constants (kCOD) were significantly higher than those for TN (kTN), and both decreased with increasing flow velocity: at low velocity, kCOD=0.0167 h−1 and kTN=0.0029 h−1; at high velocity, kCOD=0.0127 h−1 and kTN=0.0020 h−1. Simulations based on actual source pollutant concentrations indicated that the time for C/N to drop to the denitrification critical value of 4.50 was 12.24 h at high velocity, but shortened to 9.49 h at low velocity. These findings demonstrate that increasing flow velocity effectively retards the decline of C/N. Therefore, regulating network flow velocity to reduce hydraulic retention time is a key strategy for maintaining adequate C/N at the terminal and ensuring denitrification efficiency in wastewater treatment plants.
Preparation of Trimetallic-Carbon Composite Catalysts and Their Application in Catalytic Ozonation of Industrial Wastewater
Advanced oxidation processes (AOPs) are promising for degrading organic pollutants in water treatment. Heterogeneous catalytic ozonation (HCO) has gained attention due to its high oxidation efficiency, strong interference resistance, and low secondary pollution. In this study, a series of trimetallic-carbon composite ozone catalysts were prepared via an organic precursor calcination method using γ-Al2O3 as support. This method enhanced catalytic activity and mechanical strength while overcoming the limitations of carbon materials (low mechanical strength) and metal-based materials (poor mass transfer). The optimized catalyst, CA-FeCoCu, comprising Fe, Co, Cu, carbon, and alumina, exhibited excellent performance in phenol degradation and real industrial wastewater treatment. Characterization revealed that the synergistic effect of trimetals and the introduction of multiple carbon types increased specific surface area and hydroxyl radical (·OH) generation. In a pilot-scale fixed-bed reactor, the CA-FeCoCu/O3 system reduced COD from 120 mg·L−1 to below 40 mg·L−1, with an O3 consumption ratio (O/C) of less than 1, effectively lowering operational costs. This work provides a new strategy for developing efficient and stable heterogeneous O3 catalysts and offers a reference for the practical application of HCO in industrial wastewater treatment.
Differentiated Characteristics of Suspended Particulate Matter and Their Effects on Water Quality in the Middle and East Routes of the South-to-North Water Diversion Project
This study investigates the spatiotemporal differentiation of suspended particulate matter (SPM) characteristics, sources, and their impacts on water quality between the Middle Route (closed artificial channel) and East Route (open natural water system) of the South-to-North Water Diversion Project. Thirty sampling sites (13 on the Middle Route, 17 on the East Route) were established, and samples were collected during dry and wet seasons. Water quality parameters and SPM characteristics were analyzed, including particle size distribution, total suspended solids (TSS), chlorophyll a, and stable carbon and nitrogen isotopes. Results show that the Middle Route maintains good and stable water quality, with SPM dominated by coarse particles (>63 μm, 61.43%–94.68%), total phosphorus (TP) <0.01 mg·L−1, and a significant positive correlation between chlorophyll a and coarse particles (r=0.60), indicating algal aggregation dominates particle formation. In contrast, the East Route exhibits high and fluctuating nitrogen and phosphorus concentrations, with SPM dominated by fine particles (<20 μm, 51.26%–88.61%), TP ranging from 0.03 to 1.11 mg·L−1, and a positive correlation with fine particles, suggesting significant external inputs. Carbon and nitrogen isotope analysis reveals that Middle Route SPM primarily originates from autochthonous algae (contribution >46.75%), while East Route SPM is influenced by both terrestrial C3 plants and algae. The distinct engineering and management approaches of the two routes lead to significant differences in SPM characteristics and sources, thereby affecting water quality dynamics. The Middle Route requires an 'algal reduction and hydrodynamic optimization' strategy to control algal-derived coarse particle deposition, whereas the East Route benefits from 'retention-sedimentation and wetland purification' to reduce external fine particles and pollutant inputs. This research provides theoretical support and practical guidance for differentiated SPM management in long-distance water diversion systems.
Combined Ozone Micro-Nano Bubble Oxidation and Powdered Activated Carbon Adsorption for Removal of Taste and Odor Compounds from Drinking Water
Algal-derived taste and odor compounds (2-methylisoborneol, 2-MIB, and geosmin, GSM) in drinking water sources are poorly removed by conventional treatment. This study systematically evaluated the standalone and combined performance of ozone micro-nano bubbles (O3-MNBs) oxidation and powdered activated carbon (PAC) adsorption for removing 2-MIB, GSM, and algal cells from source water. Results showed that O3-MNBs pre-oxidation achieved >97.5% removal of odorants at 400 ng·L−1 and 67.2% algal cell removal within 30 min. When applied as a deep treatment stage, the degradation rate constant (k) was 10.1%–25.6% higher than in pre-oxidation due to lower background matrix interference. Both pre-oxidation and deep treatment reduced effluent concentrations of 2-MIB and GSM to below 10 ng·L−1, with oxidation kinetics fitting pseudo-first-order models (R²>0.95). PAC adsorption of both compounds followed pseudo-second-order kinetics (R²>0.99), with GSM equilibrium adsorption capacity approximately 20.0% higher than that of 2-MIB. In pure water, adsorption capacity increased by >10.0% compared to raw water. Based on kinetic models, a quantitative prediction method was established for O3-MNBs oxidation and PAC adsorption processes, aiming to achieve efficient odorant removal and cost optimization, providing theoretical support for advanced drinking water purification and smart water plant construction.
Pulsed Electric Field Enhancement of Nitrogen Removal Performance and Microbial Community Structure Response in Anammox Granular Sludge
This study investigated the effects of a ring-shaped pulsed electric field (PEF) (1.5 V, 4 h on-time per cycle) on nitrogen removal performance and microbial community structure of anammox granular sludge (AnGS). Two anaerobic sequencing batch reactors (R1 control, R2 with PEF) were operated under stepwise increasing nitrogen loading rates (NLR). At NLR below 1,155 mg·(L·d)−1, R2 exhibited total nitrogen removal efficiency (TRE) 7.5%–17.0% higher than R1, with biomass, specific anammox activity (SAA), and extracellular polymeric substances (EPS) increased by 5%–7%, 21%–71%, and 54%–77%, respectively. However, at NLR above 1,320 mg·(L·d)−1, the toxic effect of nitrite dominated, and PEF enhancement diminished or even reversed to inhibition. Microbial community analysis revealed that at low-to-moderate NLR, PEF increased the relative abundance of Planctomycetes and key anammox bacteria (Candidatus Brocadia and Candidatus Jettenia), along with enhanced community richness (Chao1) and diversity (Shannon/Simpson indices). At high NLR, PEF decreased microbial richness compared to R1. Principal component analysis and redundancy analysis indicated that PEF was the key factor driving community differences at low-to-moderate NLR, whereas nitrite concentration became the dominant factor at high NLR. This study provides theoretical support for enhancing the resilience and engineering application of anammox processes.