Integrating landfill bioreactors, partial nitritation and anammox process for methane recovery and nitrogen removal from leachate

Unveiling long-term combined effect of salinity and Lead(II) on anammox activity and microbial community dynamics in saline wastewater treatment

The study assessed the effect of salinity and lead (Pb(II)) on the anammox sludge for nitrogen removal from saline wastewater. Results showed decreased nitrogen removal and specific anammox activity (SAA) with elevated salinity and Pb(II). SAA reduced from 541.3 ± 4.3 mg N g-1 VSS d-1 at 0.5 mg/L Pb(II) to 436.0 ± 0.2 mg N g-1 VSS d-1 at 30 g/L NaCl, further to 303.6 ± 7.1 mg N g-1 VSS d-1 under 30 g/L NaCl + 0.5 mg/L Pb(II). Notably, the combined inhibition at salinity (15-20 g/L NaCl) and Pb(II) (0.3-0.4 mg/L) exhibited synergistic effect, while higher salinity and Pb(II) aligned with independent inhibition models. Combined inhibition decreased protein/polysaccharides ratio, indicating more severe negative effect on anammox aggregation capacity. Metagenomics confirmed decreased Candidatus Kuenenia, and enhanced denitrification under elevated salinity and Pb(II) conditions. This study offers insights into anammox operation for treating saline wastewater with heavy metals.

Utilization of microbial fuel cells as a dual approach for landfill leachate treatment and power production: a review

Landfill leachate, which is a complicated organic sewage water, presents substantial dangers to human health and the environment if not properly handled. Electrochemical technology has arisen as a promising strategy for effectively mitigating contaminants in landfill leachate. In this comprehensive review, we explore various theoretical and practical aspects of methods for treating landfill leachate. This exploration includes examining their performance, mechanisms, applications, associated challenges, existing issues, and potential strategies for enhancement, particularly in terms of cost-effectiveness. In addition, this critique provides a comparative investigation between these treatment approaches and the utilization of diverse kinds of microbial fuel cells (MFCs) in terms of their effectiveness in treating landfill leachate and generating power. The examination of these technologies also extends to their use in diverse global contexts, providing insights into operational parameters and regional variations. This extensive assessment serves the primary goal of assisting researchers in understanding the optimal methods for treating landfill leachate and comparing them to different types of MFCs. It offers a valuable resource for the large-scale design and implementation of processes that ensure both the safe treatment of landfill leachate and the generation of electricity. The review not only provides an overview of the current state of landfill leachate treatment but also identifies key challenges and sets the stage for future research directions, ultimately contributing to more sustainable and effective solutions in the management of this critical environmental issue.

Effective partial denitrification of biological effluent of landfill leachate for Anammox process: Start-up, influencing factors and stable operation

Partial denitrification combined with Anammox is a promising approach for simultaneous removal of ammonium and nitrate from wastewaters. In this study, the start-up, influencing factors and stable operation of partial denitrification for treating biological effluent from landfill leachate were investigated. High nitrate loads (3.85 kg N m^-3 d^-1) and short hydraulic retention time (0.66 h) were obtained in the partial denitrification process, yielding a suitable ratio of NO₂^--N/NH₄⁺-N in the effluent for downstream Anammox process. The study also revealed the importance of carbon sources, COD/NO₃^--N ratio and salinity in the partial denitrification. Acetate-type carbon source, COD/NO₃^--N ratio of about 3.0 and salinity lower than 1% favored high-efficient partial denitrification. The endogenous carbon sources from high-rate partial denitrification sludge contributed to low COD consumption in the process. During the partial denitrification, the dominant genus of Thauera was enriched, and shifted to Pseudomonas with the increase of organic removal rates.

Progress and prospects in mitigation of landfill leachate pollution: Risk, pollution potential, treatment and challenges

The escalating loads of municipal solid waste (MSW) end up in open dumps and landfills, producing continuous flows of landfill leachate. The risk of incorporating highly toxic landfill leachate into environment is important to be evaluated and measured in order to facilitate decision making for landfill leachate management and treatment. Leachate pollution index (LPI) provides quantitative measures of the potential environmental pollution by landfill leachate and information about the environmental quality adjacent to a particular landfill. According to LPI values, most developing countries show high pollution potentials from leachate, mainly due to high organic waste composition and low level of waste management techniques. A special focus on leachate characterization studies with LPI and its integration to treatment, which has not been focused in previous reviews on landfill leachate, is given here. Further, the current review provides a summary related to leachate generation, composition, characterization, risk assessment and treatment together with challenges and perspectives in the sector with its focus to developing nations. Potential commercial and industrial applications of landfill leachate is discussed in the study to provide insights into its sustainable management which is original for the study.

Microbial community and performance of a partial nitritation/anammox sequencing batch reactor treating textile wastewater

Implementation of onsite bioremediation technologies is essential for textile industries due to rising concerns in terms of water resources and quality. Partial nitritation-anaerobic ammonium oxidation (PN/A) processes emerged as a valid, but unexplored, solution. In this study, the performance of a PN/A pilot-scale (9 m3) sequencing batch reactor treating digital textile printing wastewater (10-40 m3 d-1) was monitored by computing nitrogen (N) removal rate and efficiencies. Moreover, the structure of the bacterial community was assessed by next generation sequencing and quantitative polymerase chain reaction (qPCR) analyses of several genes, which are involved in the N cycle. Although anaerobic ammonium oxidation activity was inhibited and denitrification occurred, N removal rate increased from 16 to 61 mg N g VSS-1 d-1 reaching satisfactory removal efficiency (up to 70%). Ammonium (18-70 mg L-1) and nitrite (16-82 mg L-1) were detected in the effluent demonstrating an unbalance between the aerobic and anaerobic ammonia oxidation activity, while constant organic N was attributed to recalcitrant azo dyes. Ratio between nitrification and anammox genes remained stable reflecting a constant ammonia oxidation activity. A prevalence of ammonium oxidizing bacteria and denitrifiers suggested the presence of alternative pathways. PN/A resulted a promising cost-effective alternative for textile wastewater N treatment as shown by the technical-economic assessment. However, operational conditions and design need further tailoring to promote the activity of the anammox bacteria.

Impact of low temperature on ex situ nitritation/in situ denitritation in field pilot-scale landfill for postclosure care of leachate treatment and gas content

Leachates and landfill gas (LFG) are the major problems for closed landfills (CL) and cause significant threats to receiving waterbody and ambient air quality. In this study, a field pilot-scale CL with ex situ nitritation/in situ denitritation process was constructed and operated continuously under wide temperature variations. The effect of low temperature on leachate treatment, and LFG content was studied. Results showed that the combined process can efficiently remove nitrogen and organic matters from leachate, and change LFG content under low-temperature condition. In the ex situ nitritaion, maximum removal efficiencies of ammonia and chemical oxygen demand (COD) were over 99% and 85%, respectively. The loading rate of nitrogen and COD reached 0.5 kg N m^-3 d^-1 and 0.7 kg COD m^-3 d^-1, respectively. The inhibitions of free ammonia (FA) and free nitrous acid (FNA), and low temperature were the key factors affecting nitritation. With recirculating nitrified leachate, total oxidized nitrogen (TON) was completely reduced, and the refuse decomposition was accelerated. Denitritation was the main reaction responsible in the CL. Additionally, methane content was observed lowly at non-inhibitory TON loading rate of 5.8 ± 3.7 g N ton^-1 TS d^-1. This decrease was not caused by the increased of TON loading, but a carbon source competition by denitrificans. The estimated COD consumption and methane reduction were 55.0 kg d^-1 by TON reduction, and 20 m³ d^-1, respectively. Hence, this study served a potential strategy for postclosure care of landfills under low temperature variation.

Kinetic affinity index informs the divisions of nitrate flux in aerobic denitrification

Aerobic denitrification is attracting increasing attention since its advantage of complete nitrogen removal in a single aerobic reactor with simplified configurations. This study investigated the nitrate kinetic affinity (half-saturation index, K_m) by an isolated aerobic denitrifier named P. balearica strain RAD-17. It turned out that strain RAD-17 had a high K_m of 162.5 mg-N/L and maximum nitrate reduction rate of 21.7 mg-N/(L•h), enabling it to treat high-strength nitrogen wastewater with high efficiency. Further analysis illustrated that K_m was the critical value for the change of growth yield rate along initial nitrate concentrations. Nitrogen balance results elucidated an opposite nitrogen flux to cell synthesis and nitrogen loss during aerobic denitrification. Moreover, the expression of functional genes provided proofs for these phenotypic results at transcriptional level. Consequently, K_m could be an indicator for nitrate flux division directing to respiration and assimilation in aerobic denitrifiers, shedding light on its regulation for wastewater treatment.

Beyond Energy Balance: Environmental Trade-Offs of Organics Capture and Low Carbon-to-Nitrogen Ratio Sewage Treatment Systems

Several life-cycle assessments (LCAs) have evaluated the environmental impacts (EIs) of different wastewater treatment (WWT) configurations, attempting resource recovery and energy efficiency. However, a plant-wide LCA considering up-concentration primary treatment and low carbon-to-nitrogen (C/N) ratio sewage at the secondary biological treatment (SBT) has not yet been conducted. This study identifies the environmental trade-offs and hotspots for the chemically enhanced primary treatment (CEPT) and low C/N ratio SBT emerging processes compared to conventional WWT. The life-cycle inventories were calculated using a stoichiometric life-cycle inventory framework that couples stoichiometry and kinetics to obtain site-specific water, air, and soil emissions. The midpoint results of LCA show that CEPT with anaerobic digestion (AD) for sludge treatment achieves energy self-sufficiency, but increases marine eutrophication (MEu) by 1 order of magnitude compared to conventional WWT. A mainstream anaerobic fluidized-bed bioreactor and a partial nitritation-anammox fluidized-bed membrane bioreactor which can reduce all environmental impacts by 17-47%, including MEu, are proposed as the SBT of the low-carbon CEPT settled sewage. Integrating the standardized S-LCI framework resulted in a site-specific LCA that aids decision-makers on choosing between higher reductions in most EIs at the expense of high MEu or less but consistent reductions in all EI categories.

A review on mainstream deammonification of municipal wastewater: Novel dual step process

The conventional biological nitrogen removal process is receiving increasing pressure partially due to its energy-negative operation. To address this challenge, various mainstream deammonification processes have been explored for energy-neutral municipal wastewater treatment, whereas these processes appear challenging to be sustainably and stably achieved in conventional process configurations. Therefore, this review aimed to provide a comprehensive analysis of the state-of-the-art of mainstream deammonification, while highlighting the major technical challenges. It appeared that recently developed novel dual step process, i.e. A-B processes, could provide a feasible engineering option for mainstream deammonification, where A-stage is designed for COD capture with the aim to enhance energy recovery, and B-stage is tailored for nutrient removal/recovery. This indeed may lead to a promising integrated mainstream deammonification process towards energy-efficient and environmentally sustainable nitrogen removal. Meanwhile, this review also offered an opinion on future municipal wastewater treatment, aiming for concurrent water reclamation and energy recovery.

Towards mainstream deammonification of municipal wastewater: Partial nitrification-anammox versus partial denitrification-anammox

The mainstream deammonification has been believed as a viable technology for the energy-neutral municipal wastewater treatment, which can be realized through two approaches known as partial nitrification-anammox (PN/AMX) and partial denitrification-anammox (PDN/AMX). However, large-scale applications of these deammonification processes for municipal wastewater treatment have been rarely reported thus far. Given such a situation, this review examined the mainstream PN/AMX and PDN/AMX processes with the focus on their engineering feasibility, economic viability and potential challenges. It was revealed that soluble COD and stable nitrite production were the main challenges for mainstream deammonification. Pre-capture of COD was essential for mitigating the competition between denitrifiers and anammox bacteria on nitrite, while NOB suppression and partial denitrification control to nitrite stage were critical issues for stable nitrite production in PN and PDN processes respectively. Compared to nitrification-denitrification, the unit oxygen demand for nitrogen removal in PN/AMX and PDN/AMX could be reduced by 57.3% and 47.7%, while the sludge production could also be cut off by 83.7% and 66.3% in PN/AMX and PDN/AMX respectively. These clearly showed the greater economic viability and environmental sustainability of PN/AMX against PDN/AMX. Consequently, more effort is needed to improve the engineering feasibility of large-scale mainstream deammonification for municipal wastewater treatment.

Comparison of nitrous oxide emission between a partial and full nitrification enriched ammonia-oxidising culture

Nitrification systems are known to be a source of nitrous oxide (N₂O) emission, however, the contribution from partial and full nitrification systems remains controversial. In this study, N₂O emission from a partial and full nitrification culture was investigated. In all tests, nitrite, dissolved oxygen concentration and pH levels were controlled within a similar range limiting ammonium concentration to be the only variable. The results reveal with the same amount of ammonium removed, the full nitrification culture produced far greater N₂O than the partial nitrification culture for both pulse (25-36 times) and continuous feeding modes (2-110 times). The relative gene expression data indicate that under pulse feeding there is a decreasing trend of nirK and norB genes for the partial and full nitrification culture respectively while under continuous feeding, increasing norB trends were observed for both. This possibly indicated the hydroxylamine pathway was favoured for the partial nitrification culture while the hybrid N-nitrosation pathway maybe the major contributor for the full nitrification culture. These findings improve our understanding on N₂O production pathways and enable researchers to propose better mitigation strategies.

Free nitrous acid (FNA) induced transformation of sulfamethoxazole in the enriched nitrifying culture

The sulfonamide antibiotics sulfamethoxazole (SMX) has been frequently detected in the wastewater. It has been reported that part of SMX can be transformed by the co-metabolism of ammonia oxidizing bacteria (AOB) during nitrifying process. However, previous studies reported inconsistent or even contradictory results in terms of SMX degradation and/or transformation. Literature study revealed that nitrite may play certain role in SMX transformation, which has been neglected previously. In this study, the transformation behavior of SMX was investigated with and without the presence of nitrite in an enriched nitrifying culture. The results clearly show that the elimination of SMX occurred with the presence/accumulation of nitrite, and a linear regression was observed between SMX elimination efficiency and free nitrous acid (FNA) concentration, indicating that FNA was the major factor responsible for the SMX transformation. By reacting with FNA, SMX transformation products, such as 4-nitro-SMX, desamino-SMX and hydroxylated SMX, were detected. However, when FNA concentration decreased, these intermediates may be retransformed back to SMX. These findings improved our understanding on SMX transformation in a biological system and highlighted the role of nitrite/FNA in the sulfonamide antibiotics degradation.

Mainstream anammox in a novel A-2B process for energy-efficient municipal wastewater treatment with minimized sludge production

The conventional biological processes for municipal wastewater are facing the challenges of high energy consumption and production of excessive sludge. To address these two emerging issues, this study demonstrated the feasibility to integrate mainstream anammox into an A-2B process for municipal wastewater treatment towards energy-efficient operation with reduced sludge production. In the proposed A-2B process, an anaerobic fixed bed reactor (AFBR) served as A-stage for COD capture, an anammox moving bed biofilm reactor (MBBR) was employed as B2-stage, which received effluent containing nitrite from a sequencing batch reactor (SBR) at B1-stage. The results showed that under the operation conditions studied, 58% of influent COD was converted methane gas at A-stage, and 87% total inorganic nitrogen (TIN) removal was achieved with the effluent TIN concentration of 6.5 mg/L. Moreover, it was shown that at least 75% of sludge reduction was obtained due to the COD capture at A-stage. The high-throughput sequencing analysis further revealed that Candidatus Kuenenia was the dominant genus responsible for the observed anammox at B2-stage MBBR. This study clearly demonstrated a novel process configuration for sustaining mainstream anammox for municipal wastewater reclamation towards energy-efficient operation with minimized sludge production.

The effects of manganese oxide octahedral molecular sieve chitosan microspheres on sludge bacterial community structures during sewage biological treatment

This study examines the effects of manganese oxide octahedral molecular sieve chitosan microspheres (Fe₃O₄@OMS-2@CTS) on anaerobic and aerobic microbial communities during sewage biological treatment. The addition of Fe₃O₄@OMS-2@CTS (0.25 g/L) resulted in enhanced levels of operational performance for decolourization dye X-3B. However, degradation dye X-3B inhibition in the presence of Fe₃O₄@OMS-2@CTS was recorded as greater than or equal to 1.00 g/L. Illumina MiSeq high throughput sequencing of the 16 S rRNA gene showed that 108 genera were observed during the anaerobic process, while only 71 genera were observed during the aerobic process. The largest genera (Aequorivita) decreased from 21.14% to 12.65% and the Pseudomonas genera increased from 10.57% to 12.96% according to the abundance in the presence of 0.25 g/L Fe₃O₄@OMS-2@CTS during the anaerobic process. The largest Gemmatimonas genera decreased from 21.46% to 11.68% and the Isosphaerae genera increased from 5.8% to 11.98% according to the abundance in the presence of 0.25 g/L Fe₃O₄@OMS-2@CTS during the aerobic process. Moreover, the X-ray photoelectron spectroscopy results show that the valence states of Mn and Fe in Fe₃O₄@OMS-2@CTS changed during sewage biological treatment.