High rate nitrogen removal by ANAMMOX internal circulation reactor (IC) for old landfill leachate treatment

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

Boosting the denitrification efficiency of iron-based constructed wetlands in-situ via plant biomass-derived biochar: Intensified iron redox cycle and microbial responses

Considering the unsatisfied denitrification performance of carbon-limited wastewater in iron-based constructed wetlands (ICWs) caused by low electron transfer efficiency of iron substrates, utilization of plant-based conductive materials in-situ for improving the long-term reactivity of iron substrates was proposed to boost the Fe (III)/Fe (II) redox cycle thus enhance the nitrogen elimination. Here, we investigated the effects of withered Iris Pseudacorus biomass and its derived biochar on nitrogen removal for 165 days in ICWs. Results revealed that accumulate TN removal capacity in biochar-added ICW (BC-ICW) increased by 14.7 % compared to biomass-added ICW (BM-ICW), which was mainly attributed to the synergistic strengthening of iron scraps and biochar. The denitrification efficiency of BM-ICW improved by 11.6 % compared to ICWs, while its removal capacity declined with biomass consumption. Autotrophic and heterotrophic denitrifiers were enriched in BM-ICW and BC-ICW, especially biochar increased the abundance of electroactive species (Geobacter and Shewanella, etc.). An active iron cycle exhibited in BC-ICW, which can be confirmed by the presence of more liable iron minerals on iron scraps surface, the lowest Fe (III)/Fe (II) ratio (0.51), and the improved proportions of iron cycling genes (feoABC, korB, fhuF, TC.FEV.OM, etc.). The nitrate removal efficiency was positively correlated with the nitrogen, iron metabolism functional genes and the electron transfer capacity (ETC) of carbon materials (P < 0.05), indicating that redox-active carbon materials addition improved the iron scraps bioavailability by promoting electron transfer, thus enhancing the autotrophic nitrogen removal. Our findings provided a green perspective to better understand the redox properties of plant-based carbon materials in ICWs for deep bioremediation in-situ.

Insights on pretreatment technologies for partial nitrification/anammox processes: A critical review and future perspectives

For almost 20 years, partial nitrification-anammox (PN/A) has been the subject of intensive study and development. Pretreatment of wastewater for PN/A is crucial because the inhibitory substances in the influent may reduce the performance of PN/A. In this review, the current PN/A pretreatment technologies are comprehensively summarized. The selection of pretreatment technology for PN/A depending on the source of the wastewater and its main characteristics (high-strength wastewater or municipal wastewater, organic matters, suspended solids). Comparison of pretreatment technologies through multiple perspectives including wastewater characteristics, the objectives of the wastewater treatment (treating requirement, energy and resource recovery demand), reactor configuration of PN/A. Based on the discussion, two integrated processes, HRAS + one-stage PN/A and advanced AD + two-stage PN/A, are recommended as the preferred processes for treating municipal wastewater and wastewater with a high-strength ammonium, respectively. This review aims to provide guidance for future research and development of PN/A.

Achieving superior nitrogen removal in an air-lifting internal circulating reactor for municipal wastewater treatment: Performance, kinetic analysis, and microbial pathways

Anticipated growth in living standards has accentuated higher requirements for effluent quality from municipal wastewater treatment. In this study, an air-lifting internal circulating reactor with a high internal circulation ratio (36:1) was established to treat municipal wastewater with a long-term operation. In the bioreactor, the average effluent chemical oxygen demand, total nitrogen, and ammonium nitrogen could be 13.1, 5.7, and lower than 1 mg/L, respectively. Further analysis of nitrogen removal showed that traditional nitrification and denitrification, simultaneous nitrification and denitrification (SND), and nitrogen assimilation accounted for 27.4 %, 68.7 %, and 3.9 % respectively. The proportion of aerobic bacteria (Saprospiraceae) and facultative bacteria (Comamonadaceae) were significantly increased, indicating a higher capacity for organic degradation in the reactor. The relative abundance of denitrifying bacteria and bacterial groups with SND (Comamonadaceae) increased. These results suggested the air-lifting internal circulating reactor could be a viable and efficient option for superior nitrogen removal in wastewater treatment.

Strategy of nitrate removal in anaerobic ammonia oxidation-dependent processes

The anaerobic ammonium oxidation (anammox), a microbial process that is considered as a low-cost and high efficient wastewater treatment, has received extensive attention with an attractive application prospect. The anammox process reduces nitrite (NO₂^-) to nitrogen gas (N₂) with ammonium (NH₄⁺) as the electron donor. However, some nitrate (NO₃^-) equivalent to 11% of total nitrogen (TN) is generated in this process, which limits the development of anammox. To overcome this problem, many efforts have been made in this regard, mainly combining with other biological treatment methods (denitrification, denitrifying anaerobic methane oxidation, etc.), introducing the substance into anammox process, etc. Herein, we summarized a detailed review of previous researches on the removal of NO₃^- in the anammox-dependent processes. It is hoped that this review could serve as valuable guidance in future research and practical applications of anammox.

Characterization of Enrichment Cultures of Anammox, Nitrifying and Denitrifying Bacteria Obtained from a Cold, Heavily Nitrogen-Polluted Aquifer

Anammox bacteria related to Candidatus Scalindua were recently discovered in a cold (7.5 °C) aquifer near sludge repositories containing solid wastes of uranium and processed polymetallic concentrate. Groundwater has a very high level of nitrate and ammonia pollution (up to 10 and 0.5 g/L, respectively) and a very low content of organic carbon (2.5 mg/L). To assess the potential for bioremediation of polluted groundwater in situ, enrichment cultures of anammox, nitrifying, and denitrifying bacteria were obtained and analyzed. Fed-batch enrichment of anammox bacteria was not successful. Stable removal of ammonium and nitrite (up to 100%) was achieved in a continuous-flow reactor packed with a nonwoven fabric at 15 °C, and enrichment in anammox bacteria was confirmed by FISH and qPCR assays. The relatively low total N removal efficiency (up to 55%) was due to nonstoichiometric nitrate buildup. This phenomenon can be explained by a shift in the metabolism of anammox bacteria towards the production of more nitrates and less N₂ at low temperatures compared to the canonical stoichiometry. In addition, the too high an estimate of specific anammox activity suggests that N cycle microbial groups other than anammox bacteria may have contributed significantly to N removal. Stable nitrite production was observed in the denitrifying enrichment culture, while no "conventional" nitrifiers were found in the corresponding enrichment cultures. Xanthomonadaceae was a common taxon for all microbial communities, indicating its exclusive role in this ecosystem. This study opens up new knowledge about the metabolic capabilities of N cycle bacteria and potential approaches for sustainable bioremediation of heavily N-polluted cold ecosystems.

Electrocoagulation followed by sound agitation for removal of nitrogen and carbon-based pollutants from industrial wastewater

The herculean imprecation of nitrogen-based pollutant like ammoniacal nitrogen (AN) and chemical oxygen demand (COD) on aquatic milieu is now a concern for the dye, pharma and fertiliser industries. Wastewater from these is characterised with high concentration of AN, COD and total dissolved solids (TDS), treatment of which is of utmost importance for a cleaner environment. In the current research work, an attempt was made to apply integrated electro-coagulation (EC) - sonication process for the removal of COD and AN from highly acidic dye intermediate wastewater containing high to very high concentration of COD and AN. Systematic laboratory experiments were conducted for the treatment of dye intermediate wastewater and influences of pH (5-11), applied voltage (0.5-4V) and electrolysis time (30-120 min) were investigated. A Response Surface Methodology (RSM) was used for optimization of major operating parameters for EC. The conditions for minimum fraction remaining (C/C0), was found to be same for both COD and AN, i.e. pH 7, time 90 min and applied voltage 2V. The C/Co value for COD and AN were 0.244 and 0.302, respectively. The C/Co value of COD and AN in combined EC-Sonication process with optimum operating conditions were 0.145 and 0.228 respectively with sonication time 60 min at a frequency of 33 kHz. Thus, EC - sonication process is an efficacious process for their removal from dye industrial wastewater.

Effect of organic matter on the anammox performance of constructed rapid infiltration systems

Anaerobic ammonia oxidation (anammox) process was achieved in a constructed rapid infiltration (CRI) system and the effect of organic matter on the anammox performance and microbial community structure was investigated. The results showed that the removal efficiencies of NH4+-N, NO2-N and TN were 99.7 ± 0.3%, 99.8 ± 0.2% and 91.3 ± 0.2% respectively after 83 days of acclimation without the presence of organic matter in the influent. The average TN removal efficiency increased by 3.2%-7.7% due to the synergistic effect of anammox and denitrification at a low level of organic matter concentration (10-30 mg COD/L). At medium or high organic matter concentration (50-100 mg COD/L), denitrification gradually replaced anammox as the predominant nitrogen removal route due to its stronger ability to compete with substrate, resulting in a significant decline in anammox activity. The contribution rate of anammox to nitrogen removal dropped by 70.3% with the influent COD increased from 0 to 100 mg/L, and the TN removal efficiency decreased to 68.4 ± 3.6% since the anammox was seriously suppressed. 16S rRNA high-throughput sequencing analysis illustrated that the genus Candidatus Kuenenia was the predominant anammox bacteria (AAOB) with a relative abundance of 12.63% when no organic matter was applied. While the heterotrophic denitrifying bacteria (DNB) Thauera gradually dominated the community with the elevated organic matter introduction. The findings of this study provide useful information for the stable operation and optimal regulation of anammox in the CRI system when the influent contains organic matter.

Recovery and dormancy of nitrogen removal characteristics in the pilot-scale denitrification-partial nitrification-Anammox process for landfill leachate treatment

The pilot-scale partial nitrification-anaerobic ammonia oxidation (PN-Anammox) process for landfill leachate treatment has been running stably for 2 years. The degradation characteristics of nitrogen removal performance of PN-Anammox in this system were discussed during shutdown, and different recovery strategies were analyzed from the perspective of economy and easy implementation. The results showed that during the 166 d dormancy period, the decrease in Anammox bacteria activity occurred earlier than that of Anammox bacteria, and both tended to slow down after 128 d. The recovery strategy of simulated wastewater was the fastest, followed by the pretreated landfill leachate recovery strategy with inoculation of some corresponding functional sludges, while the worst strategy was the direct pretreated landfill leachate recovery strategy. The recovery start-up of the pilot-scale PN-Anammox process further showed that microbial activities were difficult to recover simultaneously during operation using raw wastewater directly due to the presence of high NH₄⁺-N levels and the coupling process, which easily led to the accumulation of NH₄⁺-N or NO₂^-N, thereby inhibiting microbial activity. The addition of some functional bacteria was more conducive to the rapid recovery of microbial activity. This study provides a new strategy for the rapid recovery of microbial activity for the engineering application of the PN-Anammox process.

Bacterial community composition of internal circulation reactor at different heights for large-scale brewery wastewater treatment

This study analyzed bacterial community structure for large-scale brewery wastewater treatment at different heights in internal circulation (IC) reactor. Proteobacteria, Bacteroidetes and Chloroflexi were dominant bacteria, which accounted for 64.17%, 64.04%, 59.87% and 55.79% in phylum level, respectively. The unidentified bacteria were accounted for a large proportion in genus level, available data showed that Longilinea, Desulfomicrobium, Caldithrix, Geobacter and Syntrophorhabdus were relatively abundant. Organic fermentation, hydrolysis, and acidification were mainly completed at the bottom, and production of hydrogen and methane were completed in the upper and middle part of reactor. Alpha diversity and cluster distance analysis showed the bacterial community could be divided into bottom, middle and upper part of IC reactor. The IC reactor possessed the COD_Cr removal efficiency of 80% - 84.09%, and BOD₅ of 77.50% - 86% for brewery wastewater. This study would provide bacterial analysis references of IC reactor for industrial wastewater treatment in future.

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.

Flocs are the main source of nitrous oxide in a high-rate anammox granular sludge reactor: insights from metagenomics and fed-batch experiments

Nitrous oxide (N₂O) emissions from anammox-based processes are well documented but insight into source of the N₂O emission in high-rate anammox granular sludge reactors (AGSR) is limited. In this study, metagenomics and fed-batch experiments were applied to investigate the relative contributions of anammox granules and flocs to N₂O production in a high-rate AGSR. Flocs, which constitute only ~10% of total biomass contributed about 60% of the total N₂O production. Granules, the main contributor of nitrogen removal (~95%), were responsible for the remaining ~40% of N₂O production. This result is inconsistent with reads-based analysis that found the gene encoding clade II type nitrous oxide reductase (nosZ_II) had similar abundances in both granules and flocs. Another notable trend observed was the relatively higher abundance of the gene for NO-producing nitrite reductase (nir) in comparison to the gene for the nitric oxide reductase gene (nor) in both granules and flocs, indicating nitric oxide (NO) may accumulate in the AGSR. This is significant since NO and N₂O pulse assays demonstrated that NO could lead to N₂O production from both granules and flocs. However, since anammox bacteria, which were shown to be in higher abundance in granules than in flocs, have the capacity to scavenge NO this provides a mechanism by which its inhibitory effects can be mitigated, limiting N₂O release from the granules, consistent with experimental observation. These results demonstrate flocs are the main source of N₂O emission in AGSR and provide lab-scale evidence that NO-dependent anammox can mitigate N₂O emission.

Unclassified Anammox bacterium responds to robust nitrogen removal in a sequencing batch reactor fed with landfill leachate

Treatment of landfill leachate was conducted in a lab-scale sequencing batch reactor (SBR). The SBR was started through inoculating activated sludge with controlling dissolved oxygen of 0.5-1.0 mg/L. Anammox reaction took place within around three months. The SBR established robust nitrogen removal with incremental NLRs of 0.25-2.17 kg N/m³/d. At the final phase, it achieved elevated nitrogen removals of 1.68-1.91 kg N/m³/d. 16S rRNA gene amplicon sequencing analysis revealed Nitrosomonas, unclassified Anammox bacterium, and diverse denitrifying populations coexisted and accounted for 4.02%, 20.05% and 34.69%, respectively. Phylogenic analysis and average nucleotide identity comparison jointly suggested the unclassified Anammox bacterium potentially pertained to a novel Anammox lineage. The functional profiles' prediction suggested sulfate reduction, arsenate reduction and eliminations of antibiotics and drugs likely occurred in the SBR. The finding from this study suggests contribution of unclassified Anammox bacteria in influencing nitrogen budget in natural and engineering systems is currently being underestimated.

Anammox, biochar column and subsurface constructed wetland as an integrated system for treating municipal solid waste derived landfill leachate from an open dumpsite

This study aims to treat nitrogen-rich landfill leachate from Karadiyana open dumpsite, Sri Lanka, through an integrated treatment train consists of an anammox process, Municipal Solid Waste derived biochar column followed by a biochar embedded subsurface constructed wetland. Characterization of leachate was done and the leachate pollution index (LPI) was estimated. Meanwhile, leachate was treated through a treatment system comprising an anammox reactor having 140 mm diameter and 250 mm height, a biochar reactor having the same dimensions with 1.3 kg of MSW biochar, and a laboratory-scale constructed wetland of 1 × 0.3 × 0.45 m. The influent and effluent quality was assessed for the samples taken in 24 h intervals. The analysis indicated that the leachate was high in COD (4000-14,000 mg/L), ammonia (760-900 mg/L), nitrate (60-126 mg/L), and phosphorus (33-66 mg/L). Ammonia and nitrite were removed 94 and 99% by anammox unit, respectively. Nitrate, phosphate, COD and conductivity were significantly removed by the constructed wetland system in 78, 70, 65 and 61%, respectively, whereas biochar barricades extended support for removal of the contaminants and color. The combined treatment system demonstrated treatment efficiencies as 100% of ammonia, 98.7% of nitrite, 98.2% of nitrate, 80.9% of phosphate, 79.7% of COD, and 69.9% of conductivity. Thus, it can be concluded that the anammox, combined with biochar embedded treatment train is promising to treat landfill leachate, having a high pollutant index.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Metagenomics reveals microbial community differences lead to differential nitrate production in anammox reactors with differing nitrogen loading rates

Nitrate production during anammox can decrease total nitrogen removal efficiency, which will negatively impact its usefulness for the removal of nitrogen from waste streams. However, neither the performance characteristics nor physiological shifts associated with nitrate accumulation in anammox reactors under different nitrogen loading rates (NLRs) is well understood. Consequently, these parameters were studied in a lower NLR anammox reactor, termed R1, producing higher than expected levels of nitrate and compared with a higher NLR reactor, termed R2, showing no excess nitrate production. While both reactors showed high NH₄⁺-N removal efficiencies (>90%), the total nitrogen removal efficiency (<60%) was much lower in R1 due to higher nitrate production. Metagenomic analysis found that the number of reads derived from anammox bacteria were significantly higher in R2. Another notable trend in reads occurrence was the relatively higher levels of reads from genes predicted to be nitrite oxidoreductases (nxr) in R1. Binning yielded 27 high quality draft genomes from the two reactors. Analysis of bin occurrence found that R1 showing both a decrease in anammox bacteria and an unexpected increase in nxr. In-situ assays confirmed that R1 had higher rates of nitrite oxidation to nitrate and suggested that it was not solely due to obligate NOB, but other nxr-containing bacteria are important contributors as well. Our results demonstrate that nitrate accumulation can be a serious operational concern for the application of anammox technology to low-strength wastewater treatment and provide insight into the community changes leading to this outcome.

Semi-continuous feeding combined with traditional domestication improved anaerobic performance during treatment of cassava stillage

The effects of feeding pattern were studied during anaerobic digestion of cassava stillage. Continuous feeding and semi-continuous feeding, were adopted in two internal circulation (IC) reactors (A and B, respectively). The reactors showed different performance in the anaerobic digestion process. The maximum difference, was observed for the soluble chemical oxygen demand (SCOD) removal rate and the biogas production, which were 23.2% and 95.7 L/2 d higher in reactor B than reactor A, respectively. The overall VFAs level of reactor A was higher than that of reactor B. Microbial community analyses indicated that the abundances of dominant bacteria and methanogens became higher in the reactor B than in reactor A as the digestion process progressed. Hence, semi-continuous feeding showed superior performance than continuous feeding for SCOD removal rate, biogas production, and the relative abundances of methanogens in the case of high OLR.

Effects of vibration on anammox-enriched biofilm in a high-loaded upflow reactor

An upflow biofilm reactor was operated for 211 days to investigate the effects of vibration on anammox treatment performance. With vibration, the highest nitrogen removal rates (20 kg-N·m^-3·d^-1) were obtained on day 180. Since the vibration could directly applied on the biofilm, it could release the dinitrogen gas accumulated in the biofilm timely and reduce the internal mass transfer resistance sharply. The specific anammox activity increased by more than 3 times with a higher vibration intensity. Meanwhile, the unique random motion caused by mechanical vibration promotes the production of extracellular proteins. Moreover, the VSS reached 20.97 g·L^-1 which was 1.6 times higher than the control reactor. Such enrichment method resulted in a hard and thick anammox biofilm with a special granular morphology, and the nitrite tolerance concentration could reach 500 mg-N·L^-1. Operated with an adequate vibration intensity could maintain the biofilm thickness and conducive to improve the stability of the reactor. In addition, this technique also allowed the microorganisms inside the biofilm and those on the surface to reach the same culture conditions. Base on the batch experiments, intermittent vibration caused a decrease in energy consumption from about 7.757 (kW·h)·(kg-N)^-1 in group 0-Lv7(60-60) to 0.912 (kW·h)·(kg-N)^-1 in group 0-Lv7(5-60). Compared to the internal recycle without vibration, the energy consumption fell by a slice over 65%. Furthermore, the high-throughput sequencing results showed that the relative abundance of Candidatus Kuenenia in reactor 1 increased from 13.2% to 43.9%.

New direction in biological nitrogen removal from industrial nitrate wastewater via anammox

Anaerobic ammonium oxidation (anammox) is an important scientific discovery in the field of wastewater treatment. This process is a sustainable option in nitrogen removal due to its energy-efficient and cost-effective advantage. Great effort has been made recently to remove ammonium from industrial and municipal wastewater via the anammox process with a preceding partial nitrification (PN) converting part of NH₄⁺ to NO₂^-. Anammox process is seldom involved in the nitrate removal. Nitrate (NO₃^-), one of the main nitrogen compounds produced from various industries, is typically converted to nitrogen gas via denitrification process where a large amount of carbon source is consumed. Within this context, we reviewed the current technologies for high-strength nitrate wastewater treatment. It is found that nitrite accumulation often occurs during nitrate reduction, and its accumulating level would be increased at certain conditions (i.e., low C/N ratio and high pH). Hence, this provides a great opportunity to employ the anammox process to further convert nitrite in a more sustainable way. In this review, we highlight a new approach for industrial nitrate wastewater treatment via partial denitrification coupled with anammox process (PD-A). We also discuss the conditions to achieve successful PD-A process, economic and environmental benefits, and potential challenges as well as the future perspectives in practical application.

Recent advances in nitrogen removal from landfill leachate using biological treatments - A review

Landfill leachate, generated from the wastes in a landfill, is a type of wastewater with high concentrations of ammonia and organics, causing a serious environmental pollution. Because of its complex and changing characteristics, it is difficult to remove nitrogen from landfill leachate economically and effectively. Hence, nitrogen removal is a significant research priority of landfill leachate treatment in recent years. Biological processes are known to be effective in nitrogen removal. In this work, the biological nitrogen removal treatments were divided into the following processes: conventional nitrification-denitrification process, nitritation-denitritation process, endogenous denitritation process, and anaerobic ammonium oxidation (Anammox) process. This manuscript summarized the theories and applications of these approaches in detail, and concluded that appropriate processes should be selected in accordance with different characteristics of landfill leachate, in order to effectively remove nitrogen from all stages of landfill leachate and reduce disposal costs. Finally, perspective on the challenges and opportunities of biological nitrogen removal from landfill leachate was also presented.

Treatment of Landfill Leachate Using Activated Sludge Technology: A Review

Landfill leachate contains a large amount of organic matter and ammoniacal nitrogen. As such, it has become a complex and difficult issue within the water treatment industry. The activated sludge process has been found to be a good solution with low processing costs and is now therefore the core process for leachate treatment, especially for nitrogen removal. This paper describes the characteristics and treatment of leachate. Treatment of leachate using the activated sludge process includes the removal of organic matter, ammoniacal nitrogen, and total nitrogen (TN). The core method for the removal of organic matter involves anaerobic treatment supplemented with an aerobic process. Ammoniacal nitrogen is commonly removed using a conventional aerobic treatment, and advanced TN removal is achieved using endogenous denitrification or an anaerobic ammonium oxidation (ANAMMOX) process. Since biological processes are the most economical method for TN removal, a key issue is how to tap the full potential of the activated sludge process and improve TN removal from leachate. This complex issue has been identified as the focus of current scholars, as well as an important future direction for leachate research and development.

Release behavior of chloride from MSW landfill simulation reactors with different operation modes

The chloride ion (Cl^-), a very common monatomic anion, has high ecological toxicity at high concentrations because of its non-biodegradability, and can easily migrate from landfill site into the surrounding environment. Four lab-scale landfill simulation reactors were established to investigate Cl^- release behavior: the anaerobic landfill mode (R1), the semi-aerobic landfill mode (R2), the anaerobic landfill with leachate re-circulation mode (R3), and the semi-aerobic landfill with leachate re-circulation mode (R4). The landfill operation modes had a great influence on the release of Cl^-. In 256 days, the cumulative release amounts of Cl^- in the four reactors were 64.52, 132.07, 56.10, and 33.1 g for R1-R4, respectively. Once air enters anaerobic landfill, the leachate Cl^- concentration may sharply increase. The highest leachate Cl^- concentrations were 6.6 g L^-1 in anaerobic reactor and 18 g L^-1 in semi-aerobic reactor. However, the leachate re-circulation can maintain the release of Cl^- at dynamic equilibrium state. Theoretically, the Cl^- release behavior from anaerobic landfill with leachate re-circulation (R3) will be continuous. In contrast, under the other conditions, it can be anticipated to occur once the leachate recirculation stops (R1) or when the landfill encounters air incursion (R2 and R4). The semi-aerobic operation modes had significantly lower COD/Cl and NH₄-N/Cl ratios than the anaerobic modes. This indicates that the Cl^- pollution risk from semi-aerobic modes is lower than that from anaerobic modes.

Microbial electricity driven anoxic ammonium removal

Removal of nitrogen, mainly in form of ammonium (NH₄⁺), in wastewater treatment plants (WWTPs) is a highly energy demanding process, mainly due to aeration. It causes costs of about half a million Euros per year in an average European WWTP. Alternative, more economical technologies for the removal of nitrogen compounds from wastewater are required. This study proves the complete anoxic conversion of ammonium (NH₄⁺) to dinitrogen gas (N₂) in continuously operated bioelectrochemical systems at the litre-scale. The removal rate is comparable to conventional WWTPs with 35 ± 10 g N m^-3 d^-1 with low accumulation of NO₂^-, NO₃^-, N₂O. In contrast to classical aerobic nitrification, the energy consumption is considerable lower (1.16 ± 0.21 kWh kg^-1 N, being more than 35 times less than for the conventional wastewater treatment). Biotic and abiotic control experiments confirmed that the anoxic nitrification was an electrochemical biological process mainly performed by Nitrosomonas with hydroxylamine as the main substrate (mid-point potential, E_ox = +0.67 ± 0.08 V vs. SHE). This article proves the technical feasibility and reduction of costs for ammonium removal from wastewater, investigates the underlying mechanisms and discusses future engineering needs.

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.