Impact of salinity on organic matter and nitrogen removal from a municipal wastewater RO concentrate using biologically activated carbon coupled with UV/H2O2

Adaptive characteristics of indigenous microflora in an organically contaminated high salinity groundwater

Salinity, a critical factor, could directly or indirectly affect the microbial community structure and diversity. Changes in salinity levels act as environmental filters that influence the transformation of key microbial species. This study investigates the adaptive characteristics of indigenous microflora in groundwater in relation to external organic pollutants under high salinity stress. A highly mineralized shallow groundwater in Northwest China was conducted as the study area, and six representative sampling points were chosen to explore the response of groundwater hydrochemical parameters and microflora, as well as to identify the tolerance mechanisms of indigenous microflora to combined pollution. The results revealed that the dominant genera found in high salinity groundwater contaminated with organic pollutants possess the remarkable ability to degrade such pollutants even under challenging high salinity conditions, including Halomonas, Pseudomonas, Halothiobacillus, Sphingomonas, Lutibacter, Aquabacterium, Thiomicrospira, Aequorivita, etc. The hydrochemical factors, including total dissolved solids (TDS), sulfide, nitrite, nitrate, oxidation reduction potential (ORP), NH3-N, Na, Fe, benzene series, phenols, and halogenated hydrocarbons, demonstrated a significant influence on microflora. High levels of sulphate and sulfide in groundwater can exhibit dual effects on microflora. On one hand, these compounds can inhibit the growth and metabolism of microorganisms. On the other hand, they can also serve as effective electron donors/receptors during the microbial degradation of organic pollutants. Microorganisms exhibit resilience to the inhibitory effects of high salinity and organic pollutants via a series of tolerance mechanisms, such as strengthening the extracellular membrane barrier, enhancing the synthesis of relevant enzymes, initiating novel biochemical reactions, improving cellular self-healing capabilities, responding to unfavorable environmental conditions by migration, and enhancing the S cycle for the microbial metabolism of organic pollutants.

UV-based advanced oxidation of dissolved organic matter in reverse osmosis concentrate from a potable water reuse facility: A Parallel-Factor (PARAFAC) analysis approach

Disposal of reverse osmosis concentrate (ROC) from advanced water purification facilities is a challenge associated with the implementation of reverse osmosis-based treatment of municipal wastewater effluent for potable reuse. In particular, the dissolved organic matter (DOM) present in ROC diminishes the quality of the receiving water upon environmental disposal and affects the toxicity, fate, and transport of organic contaminants. This study investigates UV-based advanced oxidation processes (UV-AOPs) for treating DOM in ROC using a Parallel Factor Analysis (PARAFAC) approach. DOM composition and degradation were tested in UV-only and three UV-AOPs using hydrogen peroxide (H₂O₂), free chlorine (Cl₂), and persulfate (S₂O₈^2-). The four-component PARAFAC model consisted of two terrestrial humic-like components (C_UVH and C_VisH), a wastewater/nutrient tracer component (C_NuTr), and a protein-like (tyrosine-like) component (C_PrTy). Based on the observed loss in the maximum fluorescence intensity of the components, DOM degradation was determined to be dependent on UV fluence, oxidant dose, and dilution factor of the ROC (i.e., bulk DOM concentration). C_VisH was most the photolabile component in the UV-only system, followed by C_NuTr, C_PrTy, and C_UVH, respectively. Furthermore, UV-H₂O₂ and UV-S₂O₈^2- displayed faster overall reaction kinetics compared to UV-Cl₂. The degradation trends suggested that C_NuTr and C_PrTy consisted of chemical moieties that were susceptible to reactive oxygen species (HO^•) but not reactive chlorine species; whereas, C_VisH was sensitive to all reactive species generated in the three UV-AOPs. Compared to other components, C_PrTy was recalcitrant in all treatment scenarios tested. Calculations using chemical probe-based analysis also confirmed these trends in the reactivity of DOM components. The outcomes of this study form a foundation for characterizing ROC reactivity in UV-AOP treatment technologies, to ultimately improve the sustainability of water reuse systems.

Effect of increasing salinity and low C/N ratio on the performance and microbial community of a sequencing batch reactor

The purpose of this study was to investigate the effects of increasing salinity on the performance and microbial community structure in a sequencing batch reactor (SBR) treating low C/N ratio wastewater. The SBR was subjected to a gradual increased salinity from 0 wt% to3.0 wt% under low Chemical Oxygen Demand (COD)/N ratio, operating for 80 days. The study results indicated that high salinity decreased the removal efficiency of ammonium (NH4+-N) from 77.09% (1.0 wt%) to 45.7% (3.0wt%). The organic matter removal are not significantly affected by the high salinity. Non-metric Multi-Dimensional Scaling (NMDS) analysis showed that the gradual increased salinity altered the overall bacterial community structure, and low salinity (1wt%) promoted the bacterial diversity, while high salinity (2 and 3 wt%) significantly decreased the bacterial diversity in low C/N ratio activated sludge system. Further analysis revealed that two genera related to nitrification process (unclassified-Nitrosomonadales and g-Nitrospira) were inhibited, while a genus related to organic removal (Piscicoccus) and three genera related to denitrification (Rodobacteraceae, Denitromonas and Hyphomicrobium) increased significantly at a salinity of 3 wt%. This study provides insights of shifts in the bacteria community under the stress of high salinity in low C/N ratio of activated sludge systems.

Removing organic matters from reverse osmosis concentrate using advanced oxidation-biological activated carbon process combined with Fe3+/humus-reducing bacteria

The high-concentration wastewater produced in the industrial reverse osmosis (RO) process contains a large amount of refractory organic matters, which will have serious impacts on the natural environment and human health. Among them, contaminants can be transformed by humus-reducing bacteria based on humus. In this study, O₃- assisted UV-Fenton method was applied as pretreatment. Biological activated carbon (BAC) technology in which humus-reducing bacteria were the dominant bacteria, enhanced by electron donor and Fe³⁺, was used to dispose of RO concentrate (ROC). The results showed that water treatment process combining oxidation with biological filtration had a positive effect on the removal of stubborn contaminants in ROC. The system was strengthened by adding electron donor and Fe³⁺, and the chemical oxygen demand (COD) removal efficiency was up to 80.1%. However, when the removal efficiency of UV₂₅₄ absorbing pollutants reached optimal value (87.3%), that means only Fe³⁺ was added.

Study on the osmoregulation of "Halomonas socia" NY-011 and the degradation of organic pollutants in the saline environment

"Halomonas socia" NY-011, a new species of moderately halophilic bacteria isolated and identified in our laboratory, can grow in high concentrations of salt ranging from 0.5 to 25%. In this study, the whole genome of NY-011 was sequenced and a detailed analysis of the genomic features was provided. Especially, a series of genes related to salt tolerance and involved in xenobiotics biodegradation were annotated by COG, GO and KEGG analyses. Subsequently, RNA-Seq-based transcriptome analysis was applied to explore the osmotic regulation of NY-011 subjected to high salt stress for different times (0 h, 1 h, 3 h, 6 h, 11 h, 15 h). And we found that the genes related to osmoregulation including excluding Na⁺ and accumulating K⁺ as well as the synthesis of compatible solutes (alanine, glutamate, ectoine, hydroxyectoine and glycine betaine) were up-regulated, while the genes involved in the degradation of organic compounds were basically down-regulated during the whole process. Specifically, the expression trend of genes related to osmoregulation increased firstly then dropped, which was almost opposite to that of degrading organic pollutants genes. With the prolongation of osmotic up-shock, NY-011 survived and gradually adapted to osmotic stress, the above-mentioned two classes of genes slowly returned to normal expression level. Then, the scanning electron microscope (SEM) and transmission electron microscope (TEM) were also utilized to observe morphological properties of NY-011 under hypersaline stress, and our findings showed that the cell length of NY-011 became longer under osmotic stress, at the same time, polyhydroxyalkanoates (PHAs) were synthesized in the cells. Besides, physiological experiments confirmed that NY-011 could degrade organic compounds in a high salt environment. These data not only provide valuable insights into the mechanism of osmotic regulation of NY-011; but also make it possible for NY-011 to be exploited for biotechnological applications such as degrading organic pollutants in a hypersaline environment.

Degradation of non-oxidizing biocide benzalkonium chloride and bulk dissolved organic matter in reverse osmosis concentrate by UV/chlorine oxidation

Non-oxidizing biocide that is used to inhibit the microorganism growth on RO membrane, are observed to be high concentration and toxic in RO concentrate. The synergistic oxidation process (SOP) of UV/chlorine was investigated to simultaneously reduced the content (60.2 %) and toxicity (57.0 %) of a representative biocide dodecylbenzyldimethylammonium chloride (DDBAC) in real RO concentrate, with a UV fluence 1080 mJ/cm² and chlorine dose 20 mg/L. Besides eliminating the DDBAC, UV/chlorine reduced the UVA₂₅₄ and fluorescence of the dissolved organic matters (DOM). The oxidation mechanism was verified to be the radical electrophilic addition rather than the chlorine-electrophilic substitution through the decay of electron-donation moiety and UVA₂₅₄. As results, high molecular weight fractions of DOM (>2k Da, 79.2 %) was cleaved into low molecular weight fractions (<0.4k Da, 18.4 %) and organic halide was formed. Parallel-factor analysis of the fluorescence components suggested that decomposition of the protein-like fluorophore is most likely to surrogate the biocide removal and organic halide formation compared to other fluorophore components and UVA₂₅₄. Accordingly, a portable fluorescence probe with 400 nm excitation and 410-600 nm emission wavelengths was developed as an online surrogate for the DDBAC removal and organic halide formation.

A comparative study of biological activated carbon based treatments on two different types of municipal reverse osmosis concentrates

A study was conducted to understand the impact of reverse osmosis concentrate (ROC) characteristics on the efficacy of biological activated carbon (BAC) based treatments for removing organics and nutrients from two ROC streams (ROC_a derived from municipal waste input with high salinity, and ROC_b derived from domestic waste plus industrial trade waste with markedly lower salinity). Fluorescence excitation and emission matrix spectra and molecular weight analysis demonstrated that ROC_a and ROC_b had a significantly different composition of organic compounds due to the petrochemical processing and abattoir waste compounds in ROC_b. Although the sequence of coagulation, UV/H₂O₂ and BAC gave the highest organic removal from the two ROCs (67% DOC for ROCa and 62% for ROCb), UV/H₂O₂ followed by BAC achieved satisfactory removal (>55%) for both ROC types. Sequential treatment involving coagulation gave better phosphorus removal (>90%) than any single treatment (<65%). Total nitrogen (TN) removal was fairly low (<50%) for all the treatment options and the salinity level had insignificant impact on nitrogen removal. Analysis of bacterial communities suggested that higher phosphorus removal and lower total nitrogen and nitrate removal from ROC_b than ROC_a was related to the presence of various denitrifying or phosphorus accumulating bacteria in the BAC.

A hybrid process of Fe-based catalytic ozonation and biodegradation for the treatment of industrial wastewater reverse osmosis concentrate

This work investigated the feasibility of a hybrid process consisting of catalytic ozonation and biodegradation (i.e., sequencing batch reactor, SBR) for the treatment of the industrial-based reverse osmosis concentrate (ROC) with specific characteristics of high levels of total dissolved solids (TDS) and refractory pollutants. The Fe-based homogeneous and heterogeneous catalytic ozonation was in parallel investigated and compared in terms of contaminant removal efficiency and biodegradability variation. The Fe-based heterogeneous catalyst carried the higher potential to improve the biodegradability of ROC (i.e., 0.32 v. s. 0.27 for B/C, the ratio between BOD₅ and COD) although its direct COD removal efficiency was inferior to the homogeneous one (i.e., 49% v. s. 59% after 25 min' reaction). The ROC pretreated by the Fe-based heterogeneous catalytic ozonation for 5 min was further treated by biodegradation. After the hybrid treatment, the COD concentration reached ∼40 mg/L meeting with the discharge standard (GB, 18918-2002), under the optimal reaction conditions of 2.0 L/min ozone flow rate for catalytic ozonation and 120 min' aeration for biodegradation. The solution pH should not be adjusted by taking both the treatment efficiency and operating cost into consideration. The treatment cost of the hybrid process was estimated to be 0.15 USD/m³. This work could provide a feasible and economic option for the proper management of the industrial-based ROC and should be of interest to the application fields.

Denitrification and microbial community in MBBR using A. donax as carbon source and biofilm carriers for reverse osmosis concentrate treatment

In this study, raw Arundo donax (A. donax) pieces were applied as carbon source and biofilm carriers for denitrification in a lab-scale moving bed biofilm reactor (MBBR) for the treatment of reverse osmosis concentrate gathered from local wastewater reuse plant. At stable phase (about 60 days), efficient denitrification performance was obtained with 73.2% ± 19.5% NO₃^--N average removal and 8.10 ± 3.45 g N/(m³·day) NO₃^--N average volumetric removal rate. Mass balance analysis showed that 4.84 g A. donax was required to remove 1 g TN. Quantitative real-time PCR analysis results showed that the copy numbers of 16S r-RNA, narG, nirS, nosZ and anammox gene of carrier biofilm and suspended activated sludge in the declination phase (BF2 and AS2) were lower than those of samples in the stable phase (BF1 and AS1), and relatively higher copy numbers of nirS and nirK genes with lower abundance of narG and nosZ genes were observed. High-throughput sequencing analysis was conducted for BF2 and AS2, and similar dominant phyla and classes with different abundance were obtained. The class Gammaproteobacteria affiliated with the phylum Proteobacteria was the most dominant microbial community in both BF2 (52.6%) and AS2 (41.7%). The PICRUSt prediction results indicated that 33 predictive specific genes were related to denitrification process, and the relative abundance of 18 predictive specific genes in BF2 were higher than those in AS2.

Coal chemical reverse osmosis concentrate treatment by membrane-aerated biofilm reactor system

Coal chemical reverse osmosis concentrate (ROC), which is characterized by high salinity and high organics, remains as a serious environmental problem. In this study, a lab-scale three-stage membrane-aerated biofilm reactor (MABR) system was designed to treat such a ROC. The effects of influent salinity and operating parameters (pH, DO and HRT) on the treatment efficiency were discussed. The removal efficiencies of COD, NH₄-N and TN under the optimal operating parameters reached to 81.01%, 92.31% and 70.72%, respectively. Simultaneous nitrification and denitrification (SND) as well as shortcut nitrogen removal were achieved. The salinity less than 3% did not induce significant decrease in treatment efficiency and microbial communities. Moreover, the dominant phyla in biofilms were Proteobacteria and Bacteroidetes. This work demonstrated MABR had great potential in ROC treatment.

Enhanced anoxic biodegradation of pyridine coupled to nitrification in an inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR)

Enhanced biodegradation of high-strength pyridine was successfully achieved in the inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR) in this study. Due to the key role of dynamic membrane in biomass retention, NH₄⁺ released from pyridine biodegradation could be effectively nitrified to NO₃^- in oxic zone, which was then recirculated into the anoxic zone to serve as electron acceptor for pyridine biodegradation. Acetate dosage adversely affected pyridine biodegradation, due to the competitive effect of acetate towards NO₃^-. Increase of recirculation ratio positively affected pyridine biodegradation, due to high availability of NO₃^- at high recirculation ratio. At influent pyridine concentration as high as 1500 mg L^-1, effluent turbidity was well maintained below 10 NTU, indicating excellent biomass retention performance of the dynamic membrane. Microbial community analysis confirmed the enrichment of specific functional species in both anoxic and oxic zones. Stable performance during 260 days' operation confirmed the potential of A/O-DMBR for full-scale application.

Investigation into the nitrate removal efficiency and microbial communities in a sequencing batch reactor treating reverse osmosis concentrate produced by a coking wastewater treatment plant

In this study, a biological denitrifying process using a sequencing batch reactor (SBR) was employed to treat reverse osmosis (RO) concentrate with high conductivity produced from a coking wastewater plant. From the results, the average removal efficiencies for chemical oxygen demand, total nitrogen, and nitrate were 79.5%, 90.5%, and 93.1%, respectively. Different microbial communities were identified after sequencing the V1-V3 region of the 16S rRNA gene using the MiSeq platform, and the major bacterial phyla in the SBR system were Proteobacteria and Bacteroidetes. The main microorganisms responsible for denitrification were from the genera Hyphomicrobium, Thauera, Methyloversatilis, and Rhodobacter. Quantitative real-time PCR was used to quantify the absolute levels of denitrifying genes, including narG, nirS, nirK, and nosZ, during the start-up and stable operation of the SBR. The abundances of narG, nirK, and nosZ were lower during stable operation than those in the start-up period. The abundance of nirS at a concentration of 10⁴-10⁵ copies/ng in DNA was much higher than that of nirK, making it the dominant functional gene responsible for nitrite reduction. The higher nitrate removal efficiency suggests that biological denitrification using SBR is an effective technique for treating RO concentrate produced from coking wastewater plants.

Effect of alkaline precipitation on Cr species of Cr(III)-bearing complexes typically used in the tannery industry

Various organic compounds extensively used in the leather industry could influence the performance of alkaline precipitation with Cr(III). This study focused on two typical Cr(III)-bearing complexes (Cr(III)-collagen and Cr(III)-citrate) ubiquitous in tannery effluent yet with distinct treatment efficiencies, as Cr(III) was much more difficult to remove in the Cr(III)-citrate solution. Comprehensive analytical methods were employed to explore the intrinsic mechanism. It was found that a lower removal efficiency towards Cr(III) was significantly associated with higher oligomers. The molecular size of the Cr(III)-citrate complex continued to increase with rising pH, making it larger overall than Cr(III)-collagen species. The growing oligomer moiety of dissolved Cr(III)-complex species could persist in the stronger basic pH range, leading to the large amount of residual Cr(III) in the Cr(III)-citrate system. Combining this result with potentiometric titration and X-ray photoelectron spectroscopy data, it was believed that the polymeric species other than monomers facilitated resisting the attack from hydroxide ions, and the postulated Cr(III)-citrate species towards higher oligomers were discovered. Beyond that, both charge neutralization and sweeping effects were presented among the gradually emerging flocs in the Cr(III)-collagen system together with the electric double layer compression effect derived from salinity, thus resulting in a larger floc size and higher Cr(III) removal efficiency in saline solutions.

Simultaneous removal of organic matter and salt ions from coal gasification wastewater RO concentrate and microorganisms succession in a MBR

A lab-scale membrane bioreactor (MBR) with intermittent aeration was operated to treat the reverse osmosis concentrate derived from coal gasification wastewater. Results showed intermittent aeration represented slight effect on organic matter reduction but significant effect on nitrite and nitrate reduction, with 6h aeration and 6h non-aeration, removal efficiencies of organic matter, chloride, sulfate, nitrite and nitrate reached 48.35%, 40.91%, 34.28%, -36.05% and 64.34%, respectively. High-throughput sequencing showed a microorganisms succession from inoculated activated sludge (S1) to activated sludge in MBR (S2) with high salinity. Richness and diversity of microorganisms in S2 was lower than S1 and the community structure of S1 exhibited more even than S2. The most relative abundance of genus in S1 and S2 were unclassified_Desulfarculaceae (9.39%) and Roseibaca (62.1%), respectively. High salinity and intermittent aeration represented different influence on the denitrifying genus, and non-aeration phase provided feasible dissolved oxygen condition for denitrifying genera realizing denitrification.

UV-based technologies for marine water disinfection and the application to ballast water: Does salinity interfere with disinfection processes?

Water contained on ships is employed in the majority of activities on a vessel; therefore, it is necessary to correctly manage through marine water treatments. Among the main water streams generated on vessels, ballast water appears to be an emerging global challenge (especially on cargo ships) due to the transport of invasive species and the significant impact that the ballast water discharge could have on ecosystems and human activities. To avoid this problem, ballast water treatment must be implemented prior to water discharge in accordance with the upcoming Ballast Water Management Convention. Different UV-based treatments (photolytic: UV-C and UV/H₂O₂, photocatalytic: UV/TiO₂), have been compared for seawater disinfection. E. faecalis is proposed as a biodosimeter organism for UV-based treatments and demonstrates good properties for being considered as a Standard Test Organism for seawater. Inactivation rates by means of the UV-based treatments were obtained using a flow-through UV-reactor. Based on the two variables responses that were studied (kinetic rate constant and UV-Dose reductions), both advanced oxidation processes (UV/H₂O₂ and photocatalysis) were more effective than UV-C treatment. Evaluation of salinity on the processes suggests different responses according to the treatments: major interference on photocatalysis treatment and minimal impact on UV/H₂O₂.

Effect of different salinity adaptation on the performance and microbial community in a sequencing batch reactor

The performance and microbial community profiles in a sequencing batch reactor (SBR) treating saline wastewater were studied over 300days from 0wt% to 3.0wt% salinity. The experimental results indicated that the activated sludge had high sensitivity to salinity variations in terms of pollutants removal and sedimentation. At 2.0wt% salinity, the system retained a good performance, and 95% removal rate of chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH4(+)-N and total phosphorus (TP) could be achieved. Operation before addition salinity revealed the optimal performance and the most microbial diversity indicated by 16S rRNA gene clone library. Sequence analyses illustrated that Candidate_division_TM7 (TM7) was predominant at 2.0 wt% salinity; however, Actinobacteria was more abundant at 3.0wt% salinity.