Saline Wastewater Treatment Research Articles

Validation of Recycled Nanofiltration and Anion-Exchange Membranes for the Treatment of Urban Wastewater for Crop Irrigation.

One of the alternative sources to tackle the problem of water shortage is the use of reclaimed water from wastewater treatment plants for irrigation purposes. However, when the wastewater has a high conductivity value, it becomes unusable for crop irrigation and needs a more specific treatment. In this work, recycled nanofiltration (rNF) membranes and anion-exchange membranes (rAEMs) obtained from end-of-life RO membranes were validated to evaluate their application capability in saline wastewater treatment. The use of recycled membranes may represent an advantage due to their lower cost and reduced environmental impact associated with their production, which integrates membrane-based technology into a circular economy model. Both recycled membranes were tested in crossflow filtration and electrodialysis (ED) systems. The results of the rNF membrane showed a high selective rejection of divalent ions (SO42− (>96%) and Ca2+ and Mg2+ (>93%)). In the case of the ED process, the comparison between rAEMs and commercial membranes showed an appropriate demineralization rate without compromising the power consumption. Finally, the quality of both system effluents was suitable for irrigation, which was compared to the WHO guideline and validated by the 7-week lettuce crop study.

Evaluating the effects of chloride on the performance of microbial fuel cells for wastewater treatment

Up to 5% of wastewater generated worldwide is highly saline effluent. Microbial fuel cells (MFCs) have been considered as a promising saline wastewater treatment, which uses microorganisms to convert organic compounds into electrical energy. This study investigated lab-scale MFCs to evaluate the effect of chloride at different concentrations (0, 5, 10 and 20 g/l NaCl) on the performance of the MFC by examining its electrical generation and wastewater treatment efficiency. Increasing NaCl concentration led to a decrease in power generation with maximum power at 30, 18.7, 18.8, and 5.2 mW/m2 corresponding to 0, 5, 10, and 20 g/l of NaCl, respectively. The COD removal efficiency of the four treatments did not significantly vary (p>0.05) and reached 65.9% to 78.7%. Acidovorax spp. was isolated from the treatment without NaCl while Pseudomonas citronellolis was isolated from the treatments containing 10 and 20 g/l NaCl. Pseudomonas citronellolis can be used as a potential inoculum for MFCs treating highly saline wastewater based on its high electrical generation ability (606.8 mW/m2) based on inoculation of this pure strain into the mini MFC.

Insights into the response of anammox sludge to the combined stress of nickel and salinity

Anaerobic ammonium oxidation (anammox) is a promising technology applied to treat industrial wastewater, while the commonly coexistent heavy metals and salinity usually become a challenging issue to be addressed. In this study, the responses of anammox sludge in terms of performance, activity, functional enzyme and extracellular polymeric substance (EPS) to the combined stress of Ni(II) and salinity (20 ‰) were investigated holistically. It turned out that low Ni(II) concentration (0.2 mg·L−1) together with salinity (20 ‰) showed an insignificant effect on the anammox performance, while a decreased nitrogen removal by 46.96 % was observed with the increased Ni(II) concentration to 1 mg·L−1. It should be pointed out that the anammox system exhibited good robustness evidenced by rapid recovery to achieve 89.13 % of nitrogen removal efficiency and 1.21 kg·m−3·d−1 of nitrogen removal rate after the elimination of stress factors within 40 days. Ni(II) concentration was revealed to play a more important role in the specific activity of anammox sludge. The functional enzymes related to nitrogen removal, e.g. nitrite reductase (NIR), hydrazine oxidase (HZO) and heme c were found to be inhibited by the combined stress of Ni(II) and salinity, with decreased activity by 49.54 %, 39.39 % and 45.88 %, respectively. However, the enzyme related to assimilation, e.g. alkaline phosphatase (AKP) and nitrate reductase (NAR) appeared to be enhanced. The EPS content was found to decrease by 55.19 % under the combined stress. Detailed analysis of 3D-EEM and FTIR spectra further revealed that the combined stress of Ni(II) and salinity could change both the quantity and composition of EPS in anammox sludge. These results are expected to offer insights into the combined effect of nickel and salinity on the anammox system, and benefit the application of anammox technology for industrial metal-rich saline wastewater treatment.

Comparison on the photogranules formation and microbial community shift between the batch and continuous-flow mode for the high saline wastewater treatment

The application of biological process for the high saline mariculture wastewater treatment was hindered primarily by salinity and settleability. Photogranule is an effective wastewater treatment technology with excellent settleability and resistance to environmental changes. In this study, internal circulating photogranular membrane bioreactor (IC-PMBR) and internal circulating photogranular sequencing batch bioreactor (IC-PSBR) were constructed to cultivated photogranules. The result showed that mature photogranules quickly formed within one month for both photobioreactors. IC-PMBR exhibited more excellent pollutants removal performance than IC-PSBR. The removal efficiencies of TN, PO43- and TOC in IC-PMBR were 95 ± 3%, 78 ± 6% and 85 ± 3%, respectively. The excellent nitrogen removal in both bioreactors was ascribed to the enrichment of Proteobacteria and Cyanobacteria. Interestingly, the increasing abundance of Leucothrix could enhance the denitrification in the IC-PMBR. The removal of phosphate was achieved by phosphate accumulating organisms (PAOs) (mainly Thiothrix) and cyanobacteria in the IC-PMBR, while only p-accumulation microalgae dominated the phosphate intake in the IC-PSBR. Moreover, the synergy of heterotrophic bacterial and microalgae improved the removal efficiency of organics in both bioreactors. Morphology observation and community analysis revealed that the key players in photogranules from IC-PMBR was Phormidium sp. acting as backbones and interweaving a mat on the surface of granules. In contrast, an integrated Leptolyngbya sp. with false branching was observed in photogranules from the IC-PSBR acting as an interior core and mat-like structure was absent. Noticeably, an anaerobic region was detected in photogranules from both bioreactors with different proportion, primary Rhodobacteraceae and Thiotrichaceae. Therefore, this study demonstrated that cultivating photogranules in continuous-flow membrane photobioreactor provided an alternative option for high saline wastewater treatment.

Thermodynamic simulation and experiment research of the solar air evaporating separation system for saline wastewater treatment with thermal collector–evaporator integrated unit

Solar driven air evaporating separation (AES) technology has extensive application in the field of saline wastewater treatment due to its energy saving and cleanliness. However, these current systems generally utilize solar collectors to heat working fluids (air and wastewater), and then pass these heat carrying fluids into the evaporator to complete the mass transfer evaporation process, so as to realize the separation of the wastewater. This conventional process inevitably leads to the mismatch between heat and mass transfer of two working fluids in evaporator, which limits the efficient utilization of the energy. Accordingly, a novel thermal collector–evaporator integrated unit, in which the collecting process and evaporating process are carried out at the meantime and the collected heat directly supplies the latent heat consumed by this evaporation process, is designed to couple with the solar air evaporating separation system for saline wastewater treatment in this paper. Meanwhile, the system thermodynamic simulation model is established and detailed system performance experimental investigations are carried out. The results show that this system is feasible, and this special design is indeed conducive to improve the system thermal utilization (compared with the traditional system, the average irradiation utilization efficiency ηi can be increased by 21.2%). Furthermore, by comparing the experimental and simulation results, the thermodynamic model can effectively predict various system state parameters during operation (errors are all basically within ±10%). More importantly, from the system dynamic characteristic analysis results, the stored wastewater has the phenomenon of heat storage and heat release, which is beneficial to prolong the duration of maintaining high GOR, evaporation efficiency (EE) and system energy utilization efficiency (ηsys). Even under experimental conditions in winter, this system can still sustain high wastewater treatment performance and energy efficiency (When c=10%, three average indicator: GOR= 3.99, EE= 6.97 kg/kWh, ηsys=73.8%).

Characterization of a novel salt-tolerant strain Sphingopyxis sp. CY-10 capable of heterotrophic nitrification and aerobic denitrification

A novel heterotrophic nitrification and aerobic denitrification (HN-AD) strain CY-10 was isolated and identified as Sphingopyxis sp. When ammonium, nitrate or nitrite was used as the sole nitrogen source (300 mg/L), the maximum nitrogen removal efficiency of strain CY-10 were 100%, 91.1% and 68.5%, respectively. The optimal salinity for ammonia nitrogen removal by strain CY-10 was in the range of 0–5%. At the salinity of 5%, a maximum nitrogen removal rate of 6.25 mg/(L·h) was realized. Metabonomics data showed that the metabolic levels of sucrose and D-tagatose increased significantly at 5% salinity condition, enabling the strain to regulate osmotic pressure and survive in high-salt environments. Functional genes were successfully amplified by quantitative PCR, and HN-AD pathway of strain CY-10 followed NH4+-N → NH2OH → NO2–-N → NO → N2O → N2. These findings show that strain CY-10 has great potential in nitrogen removal treatment of saline wastewater.

Microbial behaviours inside alternating anaerobic-anoxic environment of a sulfur cycle–driven EBPR system: A metagenomic investigation

Denitrifying sulfur conversion-assisted enhanced biological phosphorus removal (DS-EBPR) was recently developed for saline wastewater treatment. However, the main functional bacteria and the interrelationship of functional bacteria of the DS-EBPR have not been defined and identified so far. This study used metagenomics and multivariate statistics to deduce the functional microbial community and distribution of functional genes associated with the critical metabolic pathways of carbon (C), nitrogen (N), phosphorus (P) and sulfur (S), particularly regarding how they would behave under the alternating anaerobic-anoxic conditions inside a long-term DS-EBPR system. An analysis of the metagenomics and metabolic functions identified 11 major microbial species which were classifiable into four groups: sulfate reducing bacteria (SRB, 0.8–2.2%), sulfur oxidizing bacteria (SOB, 31.9–37.7%), denitrifying phosphate accumulating organisms (DPAOs, 10.0–15.8%) and glycogen accumulating organisms (GAOs, 3.7–7.7%). The four groups of microorganisms performed their respective metabolisms synergistically. In terms of distribution of functional genes, SRB (Desulfococcus and Desulfobacter) and SOB (Chromatiaceae and Thiobacillus) are not only encoded by the related sulfur conversion genes (sqr, dsrAB, aprAB and sat), but also encoded by the necessary ppx and ppk1 gene for P removal that they can be considered as the potential S-related PAOs. Between the anaerobic and anoxic conditions, the metagenome-based microbial community remained structurally similar, but the functional genes, which encode various key enzymes for the P, N, and S pathways, changed in abundance. This study contributes to our understanding on the interactions and competition between the SRB, SOB, DPAOs, and GAOs in a DS-EBPR system.

Bio-nanocrystallization of NaCl using saline wastewaters through biological treatment by Yarrowia lipolytica

This study deals with the biological treatment of saline wastewaters generated by olive oil and fish canning industries using Yarrowia lipolytica. The ability of the halophilic yeast Y. lipolytica was studied on the dephenolated olive mill wastewater (DOMW)/ tuna wash processing wastewater (TWPW) mixtures at different proportions. Our results showed that DOMW/TWPW (75:25) is the suitable mixture for the highest Y. lipolytica biomass production reaching 11.3 g L−1 after 7 days. In addition, our results showed significant removal of chemical oxygen demand (COD) and phosphorus of 97.49 % and 98.90 %, respectively. As well as, a total removal of nitrogen was observed at the end of the experiment. On the other hand, Y. lipolytica was found to be effective in removing salts from these mixtures reaching 92.21 %. Moreover, the analytical results using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed the biosorption of NaCl on the surface of the yeast as nanocrystals form. Hence, Y. lipolytica can be considered as a promising candidate for the simultaneous remediation and desalination of saline food wastewater.

Effect of filamentous algae in a microalgal-bacterial granular sludge system treating saline wastewater: Assessing stability, lipid production and nutrients removal

In this study modified microalgal-bacterial granular sludge (MBGS) was constructed and employed to compare the performance for treating 1%-5% saline wastewater with aerobic granular sludge (AGS). Filamentous algae were found to flourish at 1% salinity when nutrients were temporarily restricted to low level (COD 0, N 10 mg/L, P 0.5 mg/L). A significant improvement of granule stability was detected as the integrity coefficients of MBGS was only 0.12–0.24 rather than 0.19–0.48 of AGS under 1%-5% salinities, which reduced the risk of particle disintegration. Filamentous algae including Leptolyngbya and Geitlerinema occupied 91.2% of identified algae, and were beneficial for enhancing the biomass content and lipid production to about 1.27–1.37, 3.1–5.0 times than AGS. The MBGS had best nitrogen and phosphorus removal efficiencies of 93.4% and 64.6% at 1% salinity, and showed higher resistance to 3%-5% salinities. This study could provide meaningful information for using this modified MBGS technology in practice.

High Salinity Wastewater Treatment Study Using an Automated Pilot Combining Anaerobic and Aerobic Biofilm Processes

A 20-ft containerized biological pilot system consisting of both an anaerobic expended granular sludge bed (EGSB) and an aerobic biofilm continuous flow intermittent clean (CFIC®) system has been designed, constructed, and delivered onsite at a pharmaceutical wastewater producer for a wastewater treatment study. The pilot was operated for a total of 317 days, including 147 days of adaptive phase and 170 days of testing phase. A pilot adaptive phase feeding wastewater COD concentration from 2 to 50 g/L with salinity up to 16 g/L was carried out, achieving EGSB where COD removal reached over 80 to 95% at OLR up to 22 kg COD/m3·d. In the testing phase, with repressive practical wastewater, the EGSB can remove over 97% of feed COD (with up to 82% acetic acid) at an average 16.3 kg COD/m3·d. The high wastewater salinity at 20 g/L did not inhibit COD removal efficiency by the system. The complete system with EGSB and aerobic stage was very stable and removed over 90–97% of the total COD dependent on the wastewater composition. The pilot was demonstrated as a valuable tool because of its user-friendly nature with high automation level, as well as its high efficiency in treating specific wastewater under varying operational conditions. This study provides critical information for full-scale system design and offers training for the customer in handling a previously unfamiliar process in a confident manner.

The Impact of Operational Parameters on Polypropylene Membrane Performance during the Separation of Oily Saline Wastewaters by the Membrane Distillation Process

In the present study, membrane distillation (MD) was applied for the treatment of oily saline wastewaters produced on ships sailing the Baltic Sea. For comparison purposes, experiments were also carried out with model NaCl solutions, the Baltic Seawater and oil in water emulsions. The commercial Accurel PP V8/2 membranes (Membrana GmbH, Germany) were used. In order to investigate the impact of the operational parameters on the process performance, the experiments were conducted under various values of the feed flow velocity (from 0.03 to 0.12 m/s) and the feed temperature (from 323 to 343 K). The obtained results highlight the potential of PP membranes application for a stable and reliable long-term treatment of oily wastewater. It was demonstrated that the permeate flux increased significantly with increasing feed temperature. However, the lower temperature ensured the limited scaling phenomenon during the treatment of oily wastewaters. Likewise, increasing the feed flow velocity was beneficial to the increase in the flux. Moreover, it was found that performing a cyclic rinsing of the module with a 3% HCl solution is an effective method to maintain a satisfactory module performance. The present study sheds light on improving the MD for the treatment of oily wastewaters.

The effect of salinity on ammonium-assimilating biosystems in hypersaline wastewater treatment

The ammonium-assimilating biosystem is a promising solution to improve the susceptible biological nitrogen removal (BNR) and to achieve nitrogen recovery in saline wastewater treatment. However, the treatment performance and functional stability of ammonium-assimilating biosystems have not been fully illuminated in hypersaline wastewater. In this study, although the dramatic decrease of removal efficiency of NH4+-N and PO43−-P was observed in ammonium-assimilating biosystems under the salinity from 3% to 7%, the direction of nitrogen conversions through assimilation was insusceptible to high salinity. The extremely low concentrations of nitrite and nitrate accumulation and abundances of nitrification functional genes confirmed that the process of nitrification was negligible in all biosystems. Ammonium-assimilating biosystems maintained robustness and functional stability in hypersaline wastewater. The increase of salinity stimulated the production of EPS and changed the microbial community by enriching Proteobacteria and halophilic genera. We anticipate that the ammonium-assimilating biosystem could be a promising strategy for hypersaline wastewater treatment and future practical applications.

Exerting applied voltage promotes microbial activity of marine anammox bacteria for nitrogen removal in saline wastewater treatment

To date, the application of marine anammox bacteria (MAB) is still a challenge in saline wastewater treatment due to the low growth rate and high sensitivity. Herein, bioelectrochemical system with applied voltage was exerted for the first time to promote the activity of MAB for removing nitrogen from saline wastewater. At the optimal voltage of 1.5 V, the mean total nitrogen removal rate (TNRR) reached the maximum of 0.65 kg/m3•d, which was 27.45% higher than that without applied voltage. Besides, applied voltage reduced the microbial diversity of MAB-based consortia, but the relative abundance of Candidatus Scalindua increased by 4.63% at 1.5 V compared with that without applied voltage. Also, proper applied voltage promoted the secretion of EPS and heme c, which resulted in the enhancement of MAB activity. Based on the remodified Logistic model analysis, the lag time of the nitrogen removal process was shortened by 0.72 h at the voltage of 1.5 V. Furthermore, it was found that higher voltage (> 2.0 V) had a negative effect on the MAB activity for low TNRR of 0.33 kg/m3•d (2.5 V). However, TNRR increased back to 0.61 kg/m3•d after removing the high applied voltage, which implied that the bioactivity was recoverable after being inhibited. These findings demonstrated that external electrical stimulation is an effective strategy to promote nitrogen removal and MAB activity for treating saline wastewater.

Recovery of NaCl and Na2SO4 from high salinity brine by purification and evaporation

High salinity brine is the main resource for NaCl and Na2SO4. An industrial production test and application for Na2CO3-NaOH brine purification methods were carried out and operated for different periods. The total concentration of Ca2+ and Mg2+ was reduced from 513.49 mg/L to 12.01 mg/L at the optimal doses of NaOH = 0.25 g/L and Na2CO3 = 1.3 g/L. This extended the production periods from 60 to 70 days to 90–100 days during the industrial application. In addition, the degree of CO32− accumulation in the circulating feed brine was decreased, and the deposition of CaCO3 was inhibited. Narrow NaCl and Na2SO4 crystals with good anti-caking properties were prepared from high salinity brine by regulating the evaporation temperature and pressure in a multi-effect evaporation system. Moreover, the crystal growth direction of NaCl and Na2SO4 was observed by optical microscopy at different supersaturation degrees. The long-term, low-energy operation of brine purification and evaporative crystallization industrial production were realized, which are of great significance to the treatment of salinity wastewater in the chemical industry and metallurgy fields.

ZIF-8 derived defect-rich nitrogen-doped carbon with enhanced catalytic activity for efficient non-radical activation of peroxydisulfate.

The non-radical oxidation processes of persulfate activation by carbon materials have shown great potential for industrial and saline wastewater treatment. Recently, metal-organic frameworks (MOFs) as an emerging precursor have been widely used for fabricating functional carbon materials. Herein, we reported ZIF-8 derived defect-rich nitrogen-doped carbon (ZCNs) via NaCl-assisted pyrolysis for efficient non-radical activation of peroxydisulfate to degrade rhodamine B (RB). All samples exhibited excellent catalytic activity, and ZCN-900 (pyrolyzed at 900°C) was found to be the most active, able to degrade 96% of RB quickly within 10min. Quenching tests and electron paramagnetic resonance (EPR) analyses suggested that the singlet oxygen (1O2) dominated the degradation process by a non-radical pathway. Furthermore, the effect of anions and water quality on RB oxidation were investigated, and ZCN-900/PDS system showed great resistance to the anions and natural organic matters (NOM). This work may provide a significant addition to MOF-based functional materials for environmental remediation based on the results above.

Assessment of High Salinity Wastewater Treatment with Dewatered Alum Sludge-Aerobic Membrane Reactor

Abstract The discharge of wastewater containing both high salinity and high organic content without prior treatment is detrimental to aquatic life and water hygiene. In order to integrate the advantages of membrane treatment and biological treatment, and exert the phosphorus removal efficiency of dewatered alum sludge, in this study, an aerobic membrane reactor based on dehydrated alum sludge was used to treat mustard tuber wastewater with salinity of 6.8-7.3 % under the conditions of 30 °C, 20 kPa trans-membrane pressure (TMP) and chemical oxygen demand (COD) of 3300-3900 mg/L. Three replicate reactors were applied to assess the operational performance under different organic loading rate (OLR). The results showed that all reactors were effective in removing COD, ammonia nitrogen (NH4 +-N) and soluble phosphate (SP) under the conditions of 30 °C and 20 kPa of TMP. Meanwhile, the effluent concentration of COD, NH4 +-N and SP all increased while OLR was changed from 1.0 to 3.0 kg COD/m3/day, and the effluent COD and NH4 +-N concentration except for SP could reach the B-level of Chinese “Wastewater quality standards for discharge to municipal sewers” when OLR was less than 3.0 kg COD/m3/day. This indicates that dewatered alum sludge-based aerobic membrane reactor is a promising bio-measure for treating high salinity wastewater.

Ammonium-assimilating microbiome: A halophilic biosystem rationally optimized by carbon to nitrogen ratios with stable nitrogen conversion and microbial structure

The contradiction between theoretical metabolism of ammonium assimilation and experiential understanding of conventional biosystems makes the rational optimization of the ammonium-assimilating microbiome through carbon to nitrogen (C/N) ratios perplexing. The effect of different C/N ratios on ammonium-assimilating biosystems was investigated in saline wastewater treatment. C/N ratios significantly hindered the nutrient removal efficiency, but ammonium-assimilating biosystems maintained functional stability in nitrogen conversions and microbial communities. With sufficient biomass, higher than 86% ammonium and 73% phosphorus were removed when C/N ratios were higher than 25. Ammonium assimilation dominated the nitrogen metabolism in all biosystems even under relatively low C/N ratios, evidenced by the extremely low abundances of nitrification functional genes. Different C/N ratios did not significantly change the bacterial community structure of ammonium-assimilating biosystems. It is anticipated that the ammonium-assimilating biosystem with advantages of clear metabolic pathway and easy optimization can be applied to nutrient removal and recovery in saline environments.

Enhanced aerobic granular sludge by static magnetic field to treat saline wastewater via simultaneous partial nitrification and denitrification (SPND) process

Saline wastewater poses a threat to biological nitrogen removal. This study investigated whether and how static magnetic field (SMF) can improve the salt-tolerance of aerobic granular sludge (AGS) in two simultaneous partial nitrification and denitrification (SPND) reactors. Results confirmed that the SMF improved the mean size and settleability of granules, stimulated secretion of extracellular polymeric substances with high protein content, in turn enhancing the aerobic granulation. Although high salt stress inhibited functional microorganisms, the SMF maintained better SPND performance with average COD removal, TN removal and nitrite accumulation ratio finally recovering to 100%, 72.9% and 91.1% respectively. High throughput sequencing revealed that functional bacteria evolved from Paracoccus to halotolerant genera Xanthomarina, Thauera, Pseudofulvimonas and Azoarcus with stepwise increasing salinity. The enhanced salt-tolerance may be because the SMF promoted the activity of these halotolerant bacteria. Therefore, this study proposes an economic, effective and environmental biotechnology for saline wastewater treatment.

On the potential of halophiles enriched from hypersaline sediments for biohydrogen production from saline wastewater

Halophiles are key microorganisms to potentially overcome the salinity-induced limitation in anaerobic bioremediation of organic pollutants and energy recovery when using conventional inoculums. This study aimed to enrich halophiles from hypersaline sediment and optimize their use as alternative inoculum for fermentative hydrogen production. Batch assays of 15 combinations (i.e., pH 6–10, salinity of 10–70 g-NaCl/L, and iron concentration of 0.2–1.0 g-FeSO4/L) were conducted using glucose as a substrate. To potentially boost the efficiency via optimization of operational conditions, response surface methodology (RSM) was employed. The maximum obtained hydrogen yield (HY) of 151 mL/g-COD (1.29 mol-H2/mol-glucose) was achieved at pH 6.0, 40 g-NaCL/L, and 0.6 g-FeSO4/L. The results further emphasize the negative impacts of salinity <25 g-NaCl/L and pH > 8, along with the beneficial role of iron supplementation (0.3–1.0 g-FeSO4/L). By using and validating a multivariate optimization model using desirability function, towards maximum HY, the predicted value was 155 mL/g-COD at pH 6.65, 70 g-NaCl/L, and 0.2 g-FeSO4/L. The microbial community analysis revealed that the enrichment of raw sediment enhanced the biodiversity, and then showed that Halobacteroidaceae bacteria were the key players in producing H2 from glucose. Overall, with respect to the achieved competitive HY (1.29 mol/mol-glucose), the use of halophiles-based inoculum is feasible to overcome the limitations of DF when treating saline wastewater, and future studies/implications with real effluents are worthy.

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.