Salt inhibition on partial nitritation performance of ammonium-rich saline wastewater in the zeolite biological aerated filter

Single-stage versus two-stage partial nitritation - anammox reactor systems for deammoniafication under hypersaline conditions

The production of increasing amounts of high salinity wastewaters in our industrialized society has prioritized their treatment to prevent environmental pollution. The partial nitritation - anammox (PN/A) process for nitrogen removal has been little investigated for hypersaline wastewaters (salinity greater than 3%). In the investigation presented here, single-stage versus two-stage partial nitritation - anammox (PN/A) reactor systems for deammonification at 4% (40 g/kg) saline conditions were investigated and compared in completely mixed fixed bed reactors. In the two-stage system, the first stage reactor achieved a nitritation rate of 1.9 gN/L-reactor/d. Effluent from the partial nitritation reactor was then fed to the second two-stage anammox reactor and the maximal nitrogen removal of 0.8 g/L-reactor/d was achieved. The dominant microbial species for the ammonia oxidizing and anammox reactions in the nitritation (first) reactor and the second reactor were identified as Nitrosococcus oceani and Candidatus Scalindua wagneri, respectively, both obligate halophiles. In the single-stage reactor, deammonification rates reached 0.6 gN/L-reactor/d. Nitrosomonas marina and Candidatus Scalindua wagneri were the dominant AOB and anammox bacteria, respectively. Maintaining free ammonia (FA) concentrations above 1 mg/L was found to selectively inhibit nitrite oxidizing bacteria (NOB) and resulted in long term stable nitritation. At FA concentrations lower than 1 mg/L, nitrate began to appear after 20 days of reactor operation. Nitritation was recovered after increasing FA in the reactor to inhibitory concentrations. Overall N2O emissions were shown to be significantly lower in the single-stage PN/A reactor than the two stage PN/A reactor system.

Effective recovery of the nitritation process through hydrogen peroxide

This study successfully achieved stable nitritation by adding hydrogen peroxide (H2O2) to the nitrification sludge whose nitritation stability had been destroyed. The batch experiment demonstrated that, the activity of ammonia-oxidizing bacteria (AOB) was restored more rapidly than that of nitrite oxidizing bacteria (NOB) after the addition of H2O2, thereby selectively promoting AOB enrichment and NOB washout. When the H2O2 concentration was 6.25 mg/L, the NOB activity was significantly reduced and the nitrite accumulation rate (NAR) was more than 95% after 18 cycles of nitrifying sludge restoration. As a result, H2O2 treatment enabled a nitrifying reactor to recover stable nitritation performance via H2O2 treatment, with the NAR and ammonia removal efficiency (ARE) both exceeding 90%. High-throughput sequencing analysis revealed that H2O2 treatment was successful in restoring nitritation, as the relative abundance of Nitrosomonas in the nitrifying reactor increased from 6.43% to 41.97%, and that of Nitrolancea decreased from 17.34% to 2.37%. Recovering nitritation by H2O2 inhibition is a low operational cost, high efficiency, and non-secondary pollution nitritation performance stabilization method. By leveraging the varying inhibition degrees of H2O2 on AOB and NOB, stable nitrification can be efficiently restored at a low cost and without causing secondary pollution.

Effect of salinity on biological nitrogen removal from wastewater and its mechanism

The nitrogen discharge from saline wastewater will cause significant pollution to the environment. As a high-efficiency and low-cost treatment method, biological treatment has a promising application prospect in the removal of nitrogen from high-salt wastewater. However, the inhibitory effect of high salt on microorganisms increases the difficulty of its treatment. This review discusses the influence of salinity on the nitrogen removal process, considering both traditional and novel biological techniques. Common methods to enhance the effectiveness of biological nitrogen removal processes and their mechanisms of action in engineering practice and research, including sludge acclimation and inoculation of halophilic bacteria, are also introduced. An outlook on the future development of biological nitrogen removal processes for high-salt wastewater is provided to achieve environmentally friendly discharge of high-salt wastewater.

Applying response surface methodology to optimize partial nitrification in sequence batch reactor treating salinity wastewater

In this study, the operation parameters of a partial nitrification process (PN) treating saline wastewater were optimized using the Box-Behnken design via the response surface methodology (BBD-RSM). A novel strategy based on the control of the carbon/nitrogen ratio (C/N), alkalinity/ammonia ratio (K/A), and salinity in three stages was used to achieve PN in a sequence batch reactor. The results demonstrated that a high and stable PN was completed after 50 d with an ammonia removal efficiency (ARE) of 98.37 % and nitrite accumulation rate (NAR) of 85.93 %. Next, BBD-RSM was applied, where ARE and NAR were the responses. The highest responses from the confirmation experiment were 99.9 % ± 0.04 and 95.25 % ± 0.32 when the optimum C/N, K/A, and salinity were identified as 0.84, 2, and 5.5 (g/L), respectively. The results were higher than those for the nonoptimized reactor. The developed regression model adequately forecasts the PN performance under optimal conditions. Therefore, this study provides a promising strategy for controlling the PN process and shows how the BBD-RSM model can improve the PN performance.

Improved insights into the adaptation and selection of Nitrosomonas spp. for partial nitritation under saline conditions based on specific oxygen uptake rates and next generation sequencing

Partial nitritation (PN) is a bioprocess that is essential for developing cost-effective biological nitrogen removal processes. Understanding the abundant bacterial communities responsible for nitrification under salt stress conditions is important to achieve a stable PN system for treating saline wastewater. Therefore, in this study, we identified the core nitrifying communities and investigated their correlations with the process parameters in a nitrifying bioreactor that was used for treating saline high-strength ammonia wastewater. A PN system worked efficiently under saline conditions with varying operational factors, such as temperature, dissolved oxygen (DO), and alkalinity. Interestingly, the specific oxygen uptake rate (SOUR) became similar under salt-free and saline media after the salt adaption. Next generation sequencing results suggested that the inactivation of Nitrobacter winogradskyi was a key factor for the PN reaction under salt stress conditions. We also found that Nitrosomonas europaea, a freshwater type ammonia-oxidizing bacteria (AOB), was predominantly found under both salt-free and saline conditions, whereas other halotolerant or halophilic AOB species, including Nitrosomonas nitrosa and Nitrosomonas mobilis, became selectively abundant under saline conditions. This implies that adaptation (training of N. europaea) and selection (presence of N. nitrosa and N. mobilis) were simultaneously attributed to selective ammonia conversion for the PN reaction. The redundancy analysis showed that the salinity and ammonia loading rates were statistically significant process parameters that determined the nitrifying bacterial community, suggesting that these parameters drive the adaptation and selection of the core AOB species during the PN reaction. Furthermore, the correlation analysis revealed that the abundance of N. nitrosa and N. mobilis was critically correlated with the specific oxygen uptake rates in saline media containing ammonia.

The noteworthy chloride ions in reclaimed water: Harmful effects, concentration levels and control strategies

Chloride ions (Cl^-), which are omnipresent in reclaimed water, can cause various problems in water reuse systems, especially during water transmission and at end use sites. Although reverse osmosis (RO) is considered as an effective technology to reduce chloride, its high investment and complex maintenance requirements hinder its application in many water reclamation plants (WRPs). Recently, several technologies bringing new options to better deal with chloride have gained increased attention. This review provides detailed information on the harmful effects, concentration levels, and sources of chloride in reclaimed water and summarizes and discusses various chloride removal technologies, including non-selective methods (e.g., membrane filtration, adsorption and ion exchange, oxidation, and electrochemical methods) and selective methods (e.g. precipitation and specially designed electrochemical methods). Among these, Friedel's salt precipitation and capacitive deionization showed attractive development potential. This review also proposes a holistic framework for chloride control from aspects of "Fit-for-Purpose" planning, technical system development, and whole process optimization, which could facilitate the planning and operation of long-term sustainable water reuse practices.

Effect of low salinity on nitrogen removal from municipal wastewater via a double-anammox process coupled with nitritation and denitratation: Performance and microbial structure

Saline wastewater present in municipal pipe networks poses challenges to biological nitrogen removal due to its inhibition on microorganisms. This study focuses on the effects of low salinity (0.0%, 0.4%, 0.7% and 1.0%) on a system featuring a combination of nitritation/anammox in oxic stage and denitratation/anammox in anoxic stage (double-anammox) in a step-feed SBR for municipal wastewater over a period of 130 days. The results showed that a maximum nitrogen removal efficiency of 81.2% was achieved at a salinity of 1.0% with anammox contribution of 76.5%. Analysis of anammox contribution and sludge activities discovered that low salinity promoted both nitritation and denitratation, further enhancing the coupling with anammox. Further, microbial analysis confirmed that Ca. Brocadia was enriched on biofilms from 0.21% to 0.51% and Nitrosomonas was enriched in flocs from 0.50% to 1.04%. Overall, the double-anammox process appears to be a promising method for the treatment of saline wastewater.

Bioaugmented constructed wetlands for efficient saline wastewater treatment with multiple denitrification pathways

Six laboratory-scale constructed wetlands (CWs) were used to quantify the nitrogen removal (NR) capacity in the treatment of saline wastewater at high (6:1) and low (2:1) carbon-nitrogen ratios (C/N), with and without bioaugmentation of aerobic-denitrifying bacterium. Sustained high-efficiency nitrification was observed throughout the operation. However, under different C/N ratios, although the bioaugmentation of aerobic-denitrifying bacterium promoted the removal of NO₃^--N and TN, there were still great differences in denitrification. Molecular biology experiments revealed ammonia-oxidizing archaea, together with the Nitrosomonas and Nitrospira, led to highly efficient nitrification. Furthermore, aerobic-denitrifying bacterium and sulfur-driven denitrifiers were the core denitrification groups in CWs. By performing these combined experiments, it was possible to determine the optimal CW design and the most relevant NR processes for the treatment of salty wastewater. The results suggest that the bioaugmentation of salt-tolerant functional bacteria with multiple NR pathways are crucial for the removal of salty wastewater pollutants.

Partial nitrification performance and microbial community evolution in the membrane bioreactor for saline stream treatment

Effects of salinity level and gradient on partial nitrification performance, sludge properties and microbial activities were investigated using partial nitrification membrane bioreactors (PN-MBRs). PN-MBRs obtained stable nitrite accumulation rate of 91.1% and ammonia removal of 64.8% at 10 g/L NaCl. 10 g/L NaCl obtained higher oxygen uptake rate than 5 g/L, and promoted the differentiation of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria. Salinity increased sludge flocs size, stimulated secretion of extracellular polymeric substances with high carbohydrates contents, but had insignificant impact on sludge settleability and dewaterability. Salt level and gradient were both important for microbial community evolution to salt-tolerant bacteria. PN-MBRs enriched aerobic AOBs (Nitrosomonas and norank_f_Nitrosomonadaceae) and anaerobic AOBs (Candidatus_Kuenenia and Candidatus_Brocadia) for partial nitrification, while salt gradients resulted in different metabolism pathways for nitrification even at the same salinity. Increasing salinity promoted hydroxylamine oxidizer in nitrification process evolving from Candidatus_Kuenenia and Candidatus_Brocadia to aerobic AOBs.

The performance of freshwater one-stage partial nitritation/anammox process with the increase of salinity up to 3.0

The freshwater anammox-based process would usually experience performance fluctuation and need adoption period when subjected to saline wastewater according to previous studies. In this study, the performance of nitrite-limited freshwater one-stage partial nitritation/anammox (PNA) process subjected to saline wastewater was investigated. The results showed that the nitrite-limited freshwater system could smoothly adapt to the salinity of 0.25%. The stable nitrogen removal could be achieved until the salinity of 2.5%, at which the desirable average NRR of 0.74 ± 0.1 kg/m³/d was achieved. The microbial community analysis showed that during the whole experiment, the main functional microbes were from genus Nitrosomonas and genus Kuenenia, which were through to be the crucial factors for achieving the excellent performance. This study indicates the nitrite-limited strategy is admissible for stabilizing the performance of freshwater one-stage PNA process subjected to saline wastewater in actual application.

Biological nitrogen removal via combined processes of denitrification, highly efficient partial nitritation and Anammox from mature landfill leachate

The combined processes of pre-denitrification, highly efficient partial nitritation and Anammox were developed to treat mature landfill leachate. In the partial nitritation stage, an outstanding nitrite production rate (NPR) of approximately 1.506 kg·(m³ day)^-1 of mature landfill leachate was achieved in a zeolite biological aerated filter (ZBAF) due to the inhibition of nitrite-oxidizing bacteria (NOB) by free ammonia (FA) and free nitrous acid (FNA). With respect to the nitrogen removal performance of the combined process, remarkable nitrogen removal efficiencies (NRE) and nitrogen removal rates (NRR), which exceeded 90.0% and 0.490 kg·(m³ day)^-1, respectively, were detected based on the stable and efficient partial nitritation performance and reasonable control of effluent nitrite to ammonium ratios (at approximately 1.2) in the ZBAF. High-throughput sequencing analysis further revealed that the dominant bacteria genera Paracoccus and Comamonas in the denitrification reactor, Nitrosomonas in the ZBAF and Candidatus Kuenenia and Candidatus Anammoxoglobus in the Anammox reactor were demonstrated to be responsible for denitrification, partial nitritation and Anammox process, respectively.

Efficient nitrogen removal in a modified sequencing batch biofilm reactor treating hypersaline mustard tuber wastewater: The potential multiple pathways and key microorganisms

This study first compared the efficiencies and mechanisms of the nitrogen removal in an aerobic sequencing batch biofilm reactor (SBBR) treating mustard tuber wastewater from high salt (30 gNaCl L^-1) to ultra-high salt (70 gNaCl L^-1). High-efficiency maintaining of nitrification was observed. Despite of high BOD₅/TN (5.5-9), distinct denitrification decline for lack of carbon in response to salt stress was observed. Considering the high concentrations of sulfate in mustard wastewater, and the existence of sulfur-reducing bacteria (SRB) and sulfur-driven denitrifiers (DNSOB) in the aerobic SBBR, sulfate reduction-sulfur autotrophic denitrification process is a feasible idea to solve this problem. By modified to intermittent aeration mode, sulfur cycle was developed in SBBR. The average removal efficiency of COD, TN reached 85.20% and 98.56%, respectively. By batch activity tests and microbial community analysis, ammonia oxidation activity by ammonia-oxidizing archaea (AOA) was observed, and high abundance of AOA (Arch-amoA/AOB amoA: 2.38 × 10²) together with ammonia-oxidizing bacteria (AOB) of Nitrosomonas_halophila (1.23%) ensured the high efficient nitrification. After running mode change, specific sulfur-driven NO₃^--N reduction rate increased and the abundance of dominant SRB and DNSOB rose from 3.95% to 10.79% and 2.22% to 9.95%, respectively. The sulfate-reducing process during anaerobic phase provided electron donors for subsequent autotrophic denitrification, making outlet NO₃^--N concentrations reduced from 18.26 mg L^-1 to 1.93 mg L^-1. The sulfur activity batch test showed that 73.80%∼80.92% of sulfate were circulation utilized, and rest of them conversed to the gaseous H₂S and S⁰. In addition to DNSOB, anoxic denitrifier of Halomonas (22.91%), aerobic denitrifier of Phaeodactylibacter (2.75%) and endogenous denitrifier of Defluviicoccus (3.18%) were also dominant heterotrophic bacteria (all halophilic or halotolerant) in the intermittent aeration SBBR. Batch activity tests and periodic laws have also verified the existence of corresponding denitrification pathways. This study shows that the enrichment of special halophilic functional bacteria with multiple nitrogen removal pathways is a good idea for the efficient treatment of high-concentrated hypersaline industrial wastewater.

Partial nitritation performance and microbial community in sequencing batch biofilm reactor filled with zeolite under organics oppression and its recovery strategy

Influences of organics on partial nitritation performance were investigated in a lab-scale sequencing batch biofilm reactor filled with zeolite. Significant differences in nitrite production rate (NPR) were observed between different dosages of glucose. With influent COD/N ratio from 0 to 1.5, NPR declined from 0.4 to 0.05 kg/(m3·d). Meanwhile, an appropriate NO2--N/NH4+-N ratio (1.4 ± 0.5) could be obtained for simultaneous anammox denitrification at COD/N ratio of 0.5. Increasing airflow rate was found as an effective recovery strategy. Other than competition of heterotrophs with nitrifiers for dissolved oxygen, it has been verified that addition of organics generated higher free ammonia, and then further inhibitedammonium oxidizing bacteria (AOB). Moreover, three-dimensional excitation-emission matrix (3D-EEM) results revealed that protein-like and humic acid-like substances were the main components in extracellularpolymericsubstances (EPS). And high-throughput sequencing analysis demonstrated that the relative abundance of AOB decreased.

Application of zeolites for biological treatment processes of solid wastes and wastewaters - A review

This review reports the use of zeolites in biological processes such as anaerobic digestion, nitrification, denitrification and composting, review that has not been proposed yet. It was found that aerobic processes (activated sludge, nitrification, Anammox) use zeolites as ion-exchanger and biomass carriers in order to improve the seattlebility, the biomass growth on zeolite surface and the phosphorous removal. In the case of anaerobic digestion and composting, zeolites are mainly used with the aim of retaining inhibitors such as ammonia and heavy metals through ion-exchange. The inclusion of zeolite effect on mathematical models applied in biological processes is still an area that should be improved, including also the life cycle analysis of the processes that include zeolites. At the same time, the application of zeolites at industrial or full-scale is still very scarce in anaerobic digestion, being more common in nitrogen removal processes.

Characterization of solidification for disposal of hazardous waste landfill leachate

Hazardous waste landfill leachate (HWLL) with high concentrations of salt and pollutants has created a bottleneck at hazardous waste landfills. This study applied a cement-based curing method to the disposal of HWLL. The highest contaminant fixing rate was achieved by adjusting the composition and proportion of the curing base, the content of additives, and the liquid-solid (L/S) ratio of the leachate to the curing base. The fixing rates for chemical oxygen demand and salt content in HWLL reached the highest values of 95.1% and 86.1%, respectively, when the Portland cement to metakaolin ratio was 3:2; the L/S was 1; and diatomite and activated carbon were added at 0.5% and 0.25%, respectively. The addition of glass fiber to the curing base improved the crack resistance of the solidified product. A simulated landfill experiment further indicated that after 116 days of leaching, the leachate effluent pollutant concentrations of the landfill column were lower than the effluent standard. Solidification is a feasible method for HWLL disposal.

Establishing simultaneous nitrification and denitrification under continuous aeration for the treatment of multi-electrolytes saline wastewater

Simultaneous nitrification and denitrification (SND) was established under continuous aeration (6 mgO₂ L^-1) aiming at achieving a feasible and simple operational strategy for treating multi-electrolyte saline wastewaters. Two Structured Fixed-Bed Reactors (SFBR) were used to assess SND performance with (Saline Reactor, SR) and without (Control Reactor, CR) salinity interference. Salinity was gradually increased (from 1.7 to 9 atm) based on the composition of water supplied in arid regions of Brazil. At 1.7 atm, N-NH₄⁺ oxidation and Total Nitrogen (TN) removal efficiencies of 95.9 ± 2.8 and 65.76 ± 7.5%, respectively, were obtained. At osmotic pressure (OP) of 9 atm, the system was severely affected by specific salt toxicity and OP. High chemical oxygen demand (COD) removal efficiency was achieved at all operational conditions (97.2 ± 1.6 to 78.5 ± 4.6%). Salinity did not affect microbial diversity, although it modified microbial structure. Halotolerant genera were identified (Prosthecobacter, Chlamydia, Microbacterium, and Paenibacillus).