Pilot study of nitrogen removal from landfill leachate by stable nitritation-denitrification based on zeolite biological aerated filter

Nitrogen in landfills: Sources, environmental impacts and novel treatment approaches

Nitrogen (N) accumulation in landfills is a pressing environmental concern due to its diverse sources and significant environmental impacts. However, there is relatively limited attention and research focus on N in landfills as it is overshadowed by other more prominent pollutants. This study comprehensively examines the sources of N in landfills, including food waste contributing to 390 million tons of N annually, industrial discharges, and sewage treatment plant effluents. The environmental impacts of N in landfills are primarily manifested in N2O emissions and leachate with high N concentrations. To address these challenges, this study presents various mitigation and management strategies, including N2O reduction measures and novel NH4+ removal techniques, such as electrochemical technologies, membrane separation processes, algae-based process, and other advanced oxidation processes. However, a more in-depth understanding of the complexities of N cycling in landfills is required, due to the lack of long-term monitoring data and the presence of intricate interactions and feedback mechanisms. To ultimately achieve optimized N management and minimized adverse environmental impacts in landfill settings, future prospects should emphasize advancements in monitoring and modeling technologies, enhanced understanding of microbial ecology, implementation of circular economy principles, application of innovative treatment technologies, and comprehensive landfill design and planning.

Achieving simultaneous removal of carbon and nitrogen by an integrated process of anaerobic membrane bioreactor and flow-through biofilm reactor

In this study, a combined system consisting of an anaerobic membrane bioreactor (AnMBR) and flow-through biofilm reactor/CANON (FTBR/CANON) was developed to simultaneously remove carbon and nitrogen from synthetic livestock wastewater. The average removal efficiencies of total nitrogen (TN) were 64.2 and 76.4% with influent ammonium (NH4 +-N) concentrations of approximately 200 and 500 mg/L, respectively. The COD removal efficiencies were higher than 98.0% during the entire operation. Mass balance analysis showed that COD and TN were mainly removed by the AnMBR and FTBR/CANON, respectively. The anammox process was the main nitrogen removal pathway in the combined system, with a contribution of over 80%. High functional bacterial activity was observed in the combined system. Particularly, an increase in the NH4 +-N concentration considerably improved the anammox activity of the biofilm in the FTBR/CANON. 16S rRNA high-throughput sequencing revealed that Methanosaeta, Candidatus Methanofastidiosum, and Methanobacterium were the dominant methanogens in the AnMBR granular sludge. In the CANON biofilm, Nitrosomonas and Candidatus Kuenenia were identified as aerobic and anaerobic ammonium-oxidizing bacteria, respectively. In summary, this study proposes a combined AnMBR and FTBR/CANON process targeting COD and nitrogen removal, and provides a potential alternative for treating high-strength wastewater.

Microbial interactions and nitrogen removal performance in an intermittently rotating biological contactor treating mature landfill leachate

Developing efficient landfill leachate treatment is still necessary to reduce environmental risks. However, nitrogen removal in biological treatment systems is often poor or costly. Studying biofilms in anoxic/aerobic zones of rotating biological contactors (RBC) can elucidate how microbial interactions confer resistance to shock loads and toxic substances in leachate treatment. This study assessed the nitritation-anammox performance in an intermittent-rotating bench-scale RBC treating mature leachate (diluted). Despite the leachate toxicity, the system achieved nitritation with an efficiency of up to 34 % under DO values between 0.8 and 1.8 mg.L-1. The highest average ammoniacal nitrogen removal was 45.3 % with 10 h of HRT. The 16S rRNA sequencing confirmed the presence of Nitrosonomas, Aquamicrobium, Gemmata, and Plantomyces. The coexistence of these bacteria corroborated the selective pressure exerted by leachate in the community structure. The microbial interactions found here highlight the potential application of RBC to remove nitrogen in landfill leachate treatment.

Response of partial nitritation and denitrification processes to high levels of free ammonia in a pilot mature landfill leachate treatment system: Stability and microbial community dynamics

The high levels of free ammonia (FA) challenge the application of partial nitritation (PN) and denitrification (DN) in the treatment of ammonia-rich wastewater. This study explored the impact of high levels of FA on the PN and DN stability and microbial community dynamics. By reducing reflux and increasing influent load, the concentrations of FA in PN and DN reactors increased from 28.9 mg/L and 140.0 mg/L to 1099.8 mg/L and 868.4 mg/L, respectively. During this process, the performance of PN and DN remained stable. The microbial analysis revealed that the Nitrosomonas exhibited strong tolerance to high levels of FA, and its relative abundance was positively correlated with amoABC (R2 0.984) and hao (R2 0.999) genes. The increase in microbial diversity could enhance the resistance ability of PN against the FA impact. In contrast, high levels of FA had scant influence on the microbial community and performance of DN.

Performance and mechanism of simultaneous nitrification and denitrification in zeolite spheres internal loop airlift reactor

An internal loop airlift reactor was constructed with zeolite spheres as biofilm carriers (ZS-ALR), and the performance and mechanism of nitrogen removal were investigated. The results indicated that the TN, NH₄⁺-N and TOC removal efficiencies of ZS-ALR reached 96.12%, 100% and 94.54% under appropriate conditions (HRT of 6-8 h, aeration rates of 80-120 mL/min, C/N ratios of 4-6), and the highest TN removal rate constant was 0.01156 min^-1. Further investigating the influence of ammonia-N concentrations on nitrogen removal and biofilm stability revealed that catabolism was important in TN removal, and the prominent genera for nitrogen removal included Sphaerotilus (42.20%), Flavobacterium (17.47%) and Fusibacter (6.14%). Meanwhile, the abundance of amoA, napA, narG and nosZ genes was markedly influenced by ammonia-N concentrations. The nitrogen removal of ZS-ALR was mainly through ammonia-N adsorption by zeolite spheres and simultaneous nitrification and denitrification by biofilm.

Treatment of raw sanitary landfill leachate using a hybrid pilot-scale system comprising adsorption, electrocoagulation and biological process

The effectiveness of a three-stage pilot approach using adsorption (AD), electrocoagulation (EC) and biological (BIO) processes for the treatment of raw sanitary landfill leachate (SLL) was investigated. SLL is loaded with hazardous substances such as organic load and heavy metals with high ammonium nitrogen (NH₄⁺-N) concentrations and is also produced in large quantities, causing serious risks to both living organisms and the environment. In this study, column adsorption experiments were initially performed to examine the removal of toxic NH₄⁺-N using different initial NH₄⁺-N concentrations and recirculation flow rates. The adsorption process was then examined as a pre-treatment step in two sequential treatment scenarios, i.e., AD-EC-BIO and AD-BIO-EC, to determine which achieved the highest removal of pollutants and leachate toxic potential, thus ensuring the biosafety of these processes during the release of the respective effluents into surface waters. The overall removal efficiencies of NH₄⁺-N, color, dissolved chemical oxygen demand (d-COD), manganese (Mn), nickel (Ni), zinc (Zn) and iron (Fe) achieved after the application of the AD-EC-BIO system were 95.5 ± 0.1%, 98.8 ± 0.1%, 85.7 ± 0.8%, 100 ± 0.1%, 71.4 ± 1.7%, 63.8 ± 1.9% and 94.2 ± 0.2%, respectively, while the values for the AD-BIO-EC system were 98.5 ± 0.2%, 98.7 ± 0.1%, 85.7 ± 0.4%, 98.9 ± 1.2%, 67.7 ± 1.7%, 76.1 ± 1.6% and 94.8 ± 0.1%, respectively. In accordance with the latter, the assessment of leachate toxic potential using a Thamnocephalus platyurus bioassay revealed that the AD-EC-BIO system could be considered a promising treatment strategy for the purification of raw SLL.

Nitrogen Removal from the Simulated Wastewater of Ionic Rare Earth Mining Using a Biological Aerated Filter: Influence of Medium and Carbon Source

In engineering application, a two-stage biological aerated filter (BAF) has been deployed to achieve the steady nitrogen removal of the wastewater from the mining area of ionic rare earth with a low carbon to nitrogen (C/N) ratio. However, the cost-efficiency of the medium and carbon source casts a shadow over further development. In this study, the influences of four media (i.e., volcanic, zeolite, quartz, and ceramisite) and three soluble carbon sources (i.e., acetate, glucose, and methanol) on the N removal were systematically compared. Applying volcanic and quartz showed a favorable start-up performance due to the biophilic surface and dense packing, respectively. However, regardless of medium type, with [NH4+-N]0 = 50 and [NO3−-N]0 = 30 mg/L, the C/N ratio of 3 was required to meet the discharge standards of NH4+-N, TN, and COD, and acetate was confirmed applicable for all the selected medium-packed BAFs. Introduction of sweet potato residues as the solid carbon source decreased the amount of added acetate by more than 13%. The 16S rRNA high-throughput gene sequencing revealed that Sphingomonas and Nitrospira were abundant in the aerobic stages of the volcanic and zeolite-packed BAFs, respectively. Such a community integrated with the extensively distributed Thauera, Clostridium_sensu_stricto, and Proteiniclasticum in the anoxic stage accounted for the efficient N removal. Thus, deploying volcanic as the medium and acetate as the soluble carbon source was proposed. These findings will provide valuable references for the selection of medium and carbon source and, consequently, further optimize the operational performance.

Advanced nitrogen removal in a single return anaerobic/aerobic/anoxic/aerobic (AnOAO) bioreactor treating municipal wastewater through hydroxylamine addition: Performance and microbial community

The NH₂OH dosing strategy for nitrogen removal was investigated in a single return continuous-flow anaerobic/aerobic/anoxic/aerobic (A_nOAO) reactor fed with real municipal wastewater. A high nitrite accumulation ratio of 98% was achieved in only two days by continuously adding 10 mg/L NH₂OH. When gradually reducing dosing frequency to one day every four days, effluent total nitrogen was as low as 4.8 ± 2.2 mg N/L with removal efficiency of 88.7 ± 5.3%, under aerobic HRT of 4.6 h, DO below 1.0 mg/L, and C/N of 2.8 without external carbon sources. Batch test showed that nitrite oxidizing bacteria (NOB) activity decreased by 81% after adding NH₂OH, while ammonia oxidizing bacteria (AOB) activity remained stable. qPCR confirmed that NOB abundance decreased, and 16S rRNA sequencing further showed that g_Nitrospira belonging to NOB decreased significantly (P < 0.001). Overall, this study provides a novel strategy for advanced nitrogen removal from municipal wastewater in continuous flow systems.

An Innovative Process for Mature Landfill Leachate and Waste Activated Sludge Simultaneous Treatment Based on Partial Nitrification, In Situ Fermentation, and Anammox (PNFA)

An innovative partial nitrification, in situ fermentation, and Anammox (PNFA) system was developed to achieve mature landfill leachate and waste activated sludge simultaneous treatment. Three separate sequencing batch reactors (SBRs) were used for partial nitrification (PN-SBR), integrated fermentation-denitrification (IFD-SBR), and partial nitrification-Anammox (PNA-SBR). After 200 days of continuous operation, a satisfactory nitrogen removal efficiency (NRE) of 99.2 ± 0.1% was obtained, with an effluent total nitrogen (TN) of 15.2 ± 3.2 mg/L. In IFD-SBR, the volatile fatty acids generated from fermentation drove efficient denitrification, obtaining sludge and nitrogen reduction rates of 4.2 ± 0.7 and 0.61 ± 0.04 kg/m³·day, respectively. Furthermore, unwanted fermentation metabolites (134.1 mg/L NH₄⁺-N) were further treated by PNA-SBR using a combination of step-feed and intermittent aeration strategies. In PNA-SBR, Anammox significantly contributed to 82.1% nitrogen removal, and Anammox bacteria (Candidatus Brocadia, 2.3%) mutually benefited with partially denitrifying microorganisms (Thauera, 4.2%), with 66.3% of generated nitrate reduced to nitrite and then reutilized in situ by Anammox. Compared with the conventional nitrification-denitrification process, PNFA reduced oxygen energy consumption, external carbon source dosage, and CO₂ emission by 21.3, 100, and 38.9%, respectively, and obtained 50.1% external WAS reduction efficiency.

Influence of seasonal temperature change on autotrophic nitrogen removal for mature landfill leachate treatment with high-ammonia by partial nitrification-Anammox process

In this study, a denitrification (DN)-partial nitritation (PN)-anaerobic ammonia oxidation (Anammox) system for the efficient nitrogen removal of mature landfill leachate was built with a zone-partitioning self-reflux biological reactor as the core device, and the effects of changes in seasonal temperature on the nitrogen removal in non-temperature-control environment were explored. The results showed that as the seasonal temperature decreased from 34°C to 11.3°C, the total nitrogen removal rate of the DN-PN-Anammox system gradually decreased from the peak value of 1.42 kg/(m³•day) to 0.49 kg/(m³•day). At low temperatures (<20°C), when the nitrogen load (NLR) of the system is not appropriate, the fluctuation of high NH₄⁺-N concentration in the landfill leachate greatly influenced the stability of the nitrogen removal. At temperatures of 11°C-15°C, the NLR of the system is controlled below 0.5 kg/(m³•day), which can achieve stable nitrogen removal and the nitrogen removal efficiency can reach above 96%. The abundance of Candidatus Brocadia gradually increased with the decrease of temperature. Nitrosomonas, Candidatus Brocadia and Candidatus Kuenenia as the main functional microorganisms in the low temperature.

Multi-omics analysis reveals structure and function of biofilm microbial communities in a pre-denitrification biofilter

The highly complex microbial communities in biofilm play crucial roles in the pollutant removal performance of wastewater treatment plants (WWTPs). In the present study, using multi-omics analysis, we studied microbial structure, key enzymes, functional traits, and key metabolic pathways of pre-denitrification biofilter in an urban WWTP in China. The analysis results of metagenomic and metaproteomic showed that Betaproteobacteria and Flavobacteriia were dominant in biofilms. The integrated metagenomic and metaproteomic data showed that the expression of nitrogen metabolism genes was high, and the high proportion of denitrification module indicating that denitrification was the main nitrogen removal pathway. The most abundant denitrifying bacterial genera were: Dechloromonas, Acidovorax, Bosea, Polaromonas, and Chryseobacterium. And microorganisms with denitrification potential may not be able to denitrify in the actual operation of the filter. The integrated analysis of metaproteomic and metabolomic showed that there was a correlation between biofilm microorganisms and metabolites. Metabolomic analysis indicated that metabolic profiles of biofilms varied with layer height. This study provides the first detailed microbial communities and metabolic profiles in a full-scale pre-denitrification biofilter and clarifies the mechanism of denitrification.

Application of membrane separation technology in the treatment of leachate in China: A review

To comprehensively investigate the application of membrane separation technology in the treatment of landfill leachate in China, the performance of nearly 200 waste management enterprises of different sizes in China were analyzed, with an emphasis on their scale, regional features, processes, and economic characteristics. It was found that membrane separation technologies, mainly nanofiltration (NF), reverse osmosis (RO), and NF + RO, have been used in China since 2004. The treatment capacity of the two most dominant membrane separation technologies, i.e., NF and RO, were both almost 60,000 m³/d in 2018, and both technologies are widely used in landfills and incineration plants. Their distribution is mainly concentrated in eastern and southwestern China, where the amount of municipal solid waste (MSW) is relatively high and the economy is developing rapidly. Membrane separation technology is the preferred technique for the advanced treatment of leachate because more contaminants can be effectively removed by the technology than by other advanced processes. However, the membrane retentate that is produced using this technology-commonly known as leachate concentrate-is heavily contaminated due to the enrichment of almost all the inorganic anions, heavy metals, and organic matter that remain after bioprocessing. An economic cost analysis revealed that the operating cost of membrane separation technology has stabilized and is between 1.77 USD/m³ and 4.90 USD/m³; electricity consumption is the most expensive cost component. This review describes the current problems with the use of membrane separation technology and recommends strategies and solutions for its future use.