The "salinity red line" in biological treatment of high-salinity wastewater: 1%, 3%, and 22 g/L are all correct, because they are not the same thing.

The "Salinity Red Line" in Biological Treatment of High-Salinity Wastewater: 1%, 3%, and 22 g/L Are All Correct, Because They Are Not the Same Thing

— "Salt-tolerant bacteria" and "halophilic bacteria" are two completely different types of bacteria; mixing them up leads to the wrong selection; acclimation can buy you steady-state width, but not shock resistance; and the biological stage is not responsible for desalination from start to finish

I. Salt does four things to a biological system, not one

Attributing salinity inhibition simply to "osmotic pressure" is the first-layer reason for the commissioning failure of many high-salinity systems. Osmotic shock is indeed what happens first: the osmotic pressure inside microbial cells roughly corresponds to 0.9% NaCl (about 9 000 mg/L). When external salinity rises to 30 000~50 000 mg/L, the extracellular osmotic pressure is 3~5 times the intracellular value. Water molecules exude massively according to the van 't Hoff relationship, cells lose water, the protoplast shrinks, and the cell membrane separates from the cell wall. But osmotic pressure is only the opening act; three other things happen simultaneously afterward.

The second is ion toxicity. Na⁺ competes with the metal cofactors (Mg²⁺, K⁺) at enzyme active centers, while Cl⁻ interacts with the hydrophobic regions of proteins. A set of data from industry technical materials can serve as an order-of-magnitude reference: under 40 000 mg/L NaCl conditions, the dehydrogenase activity of ordinary activated sludge is only 15%~20% of the salt-free control—the tricarboxylic acid cycle and electron transport chain are blocked, and even if the cells are alive, they cannot obtain ATP. This is the direct biochemical reason for the decline in COD removal efficiency.

The third is the reduction of extracellular polymeric substances (EPS), that is, floc disintegration. In a hyperosmotic environment, cells prioritize energy for synthesizing compatible solutes rather than EPS, while the expression of EPS synthesis genes is downregulated. Some materials show that when salinity rises from 0 to 30 000 mg/L, total EPS decreases by 40%~60%, and the ratio of polysaccharides to proteins drops from 1.2 to 0.5; an increased protein proportion makes the flocs more hydrophilic and reduces their flocculation ability. The macroscopic manifestations are SVI rising from the normal 80~120 mL/g to above 200 mL/g, while SV₃₀ instead decreases (because the flocs do not settle at all), sludge washout from the secondary clarifier, and effluent TSS soaring from below 30 mg/L to 150~300 mg/L. There is a vicious cycle here: floc disintegration releases adsorbed organic matter back into the water, and effluent COD may "falsely" rise to even approach or exceed the influent value.

The fourth is the decline in dissolved oxygen, and this one is most easily overlooked. According to Henry's law, the higher the salinity of water, the lower the solubility of oxygen. The industry convention is that for every 10 000 mg/L increase in salinity, oxygen transfer efficiency decreases by about 15%. This means that under the same aeration rate, the actually available oxygen in a high-salinity system is significantly less—many high-salinity projects "still lack oxygen even with aeration at maximum," and the root cause lies here, not in the blowers.

There is one more thing that is not a mechanism but must be known: synergistic toxicity. High salinity changes cell membrane permeability, allowing toxic substances that originally could not enter to flow in massively. Under normal conditions, the half-inhibitory concentration of copper ions for activated sludge is 10 mg/L; under 30 000 mg/L salinity, it may drop to 2 mg/L. Therefore, the judgment that "this stream is high in salt but has no other toxicants" must be made only after completing bench-scale testing.

II. The first misuse: is "salt-tolerant bacteria" actually salt-tolerant, or halophilic?

This is the most important section of the entire article. In Chinese, "salt-tolerant bacteria" is used as a generic term, but in the English classification system, halotolerant and halophile are two different things: halotolerant bacteria are bacteria that can grow normally without salt but can additionally tolerate high salinity; halophiles, on the other hand, are bacteria that must have salt to survive. The engineering consequences of this distinction are very direct—if the "halophiles" you purchased are introduced into a system with a salinity of only 0.3%, they may not gain dominance at all; conversely, if ordinary halotolerant bacteria are still present in the high-salinity stage of 3%, their specific degradation rate may be only a fraction of that of halophiles.

What is even more troublesome is that the "moderately halophilic" range itself has four definitions. Although all refer to "moderately halophilic," the classic systems of Kushner and Kamekura are two separate systems, and the MDPI review and the IntechOpen review each have their own as well, with the difference between the highest and the lowest being nearly twofold.

Applying this table to procurement and selection, at least three questions can be raised: Is what is reported for the microbial agent the "upper salinity tolerance limit" or the "optimal salinity range"? Is the criterion "can survive" or "meets the degradation rate target"? Is the microbe salt-out type or salt-in type (which determines whether it can still function in the low-salinity range)?

III. The Second Mix-Up: The Four Variables Within the Salinity Red Line

Putting the scope problem from the previous section into numbers explains why the "salinity tolerance upper limit" given by public sources can range all the way from 1% to 33 g/L.

Variable One: Which Salinity Is Being Measured

Cl⁻, TDS, NaCl, and electrical conductivity (EC) are four scopes that are often used interchangeably. The "salinity 10~40 g/L" of tannery wastewater is explicitly on a TDS basis; the "salt content 1%~15%" of pickle wastewater is converted in the literature to Cl⁻ of 10 000~150 000 mg/L; while another citation for tannery wastewater states "salinity 21~57 g/L." The same stream of water can differ by a factor of two simply because of a different scope. If the design document only writes "salt content" and the operating log only records conductivity, the two sides will never reconcile.

Variable Two: Whose Salinity Is Being Measured

"Influent salinity," "mixed liquor salinity in the tank," and "single-step surge magnitude" are three different quantities. Return liquor, cooling tower blowdown, equipment rinse water, and different stages of batch production all cause influent salinity to vary within the same shift. System collapse is often not caused by high steady-state salinity, but by a salinity jump in a particular batch of water.

Variable Three: Which Indicator Is Being Looked At

This one is the decisive factor in selection.Nitrifying bacteria are far more salt-sensitive than heterotrophic bacteria.The literature gives a tolerance upper limit of about 33 g NaCl/L for ammonia-oxidizing bacteria (AOB) and about 20 g NaCl/L for nitrite-oxidizing bacteria (NOB); the industry technical scope is even stricter—most AOB show a 80% activity decline at salinity >15 000 mg/L, and NOB are already severely inhibited at >10 000 mg/L. At the same time, heterotrophic COD removal can still be maintained at 93%~96% under 3% salinity. So the statement "this water can be handled biologically" must be supplemented with "which indicator it can handle."

Variable Four: Which Biological Form Is Being Used

Suspended-growth activated sludge is the most fragile: conventional activated sludge works normally when TDS is below about 10 g/L, and actual tannery wastewater at 10~40 g/L already exceeds its capacity. Biofilm reactors are significantly more resistant because mass transfer within the biofilm is slow and salinity within the biofilm changes gradually—in a semi-industrial pilot test of tannery wastewater, MBBR could stably maintain COD removal when TDS did not exceed 22 g/L, and only showed a significant decline when it exceeded 22 g/L. Granular sludge falls between the two, relying on its dense structure.

Putting these ten numbers side by side, the conclusion is actually quite plain:the salinity red line is not one line, but a family of lines. It is a combination of "which indicator + which form + which scope + what fluctuation magnitude," and changing one condition changes the line. Any technical solution that gives only a single number is worth first asking clearly which coordinate system it is speaking in.

IV. Acclimation Can Buy Steady State, But Not Shock Resistance

Incremental salinity acclimation is effective and has clear mechanistic support. Research on SBBR treating pickle wastewater shows that after incremental salinity acclimation, the system operates stably at 3.0% salinity, while the community structure undergoes directional succession: the halotolerant phylum Actinobacteriota becomes the dominant population, whereas NOB is strongly inhibited, with its abundance rapidly declining until it disappears, and the main nitrogen removal pathway shifts from complete nitrification–denitrification to Partial Nitrification–Denitrification (PND). Similar evidence exists on the anaerobic side: an AnMBR treating high-salinity pickled mustard tuber wastewater gradually raised salinity from 12.9 g/L to 33.5 g/L, and the COD removal rate and biogas yield showed a "decrease first, then increase" pattern, ultimately stabilizing above 75% and 300 mL/gCOD; after the loading rate was increased to approximately 7.6 kgCOD/(m³·d), COD removal was approximately 80%, biogas yield was 330~380 mL/gCOD, and VFA/ALK remained below 0.15 throughout. In an AnMBR treating textile wastewater, the microbial community shifted from salt-sensitive groups (Aminiphilus, Caldatribacterium, Mesotoga, Methanosaeta, etc.) to halotolerant groups (Longilinea, Ignavibacterium, Rhodovarius, Bosea, Flexilinea), reaching a new equilibrium at 20 g/L.

However, what acclimation buys is steady-state width, not shock resistance. The same system may perform well at a steady state of 3%, yet a single sudden salinity spike can cause metabolic activity to drop immediately and effluent COD to rise, with the mechanism being osmotic shock-induced cell dehydration, membrane dysfunction, and even lysis. Industry data give a very specific recovery cost: after a salinity shock, even if water quality returns to its original level, the COD removal rate requires 3~4 weeks to return to 50%, and in many cases the system is permanently damaged and must be re-inoculated. Another quantitative relationship is: for conventional Activated Sludge, once salinity exceeds 20 000 mg/L, for every 5 000 mg/L increase in salinity, the COD removal rate decreases by an average of 10~15 percentage points.

There is another cost here that is easily overlooked. The "success" of acclimation is sometimes achieved at the expense of extremely low biomass. In the study published in Environmental Science on screening halophilic bacteria from the sediment of the Dalian Lüshun salt field, the MLSS after SBR acclimation at 3.5% salinity averaged only 600 mg/L—an order of magnitude lower than conventional Activated Sludge, and in engineering terms this concentration cannot support any loading. The same study provides finer boundaries: sludge SOUR was 10.36 mg/(g·h) for endogenous respiration and 29.09 mg/(g·h) for exogenous respiration, indicating that activity was indeed not poor; at salinity 3.5%, the NH₄⁺-N removal rate was 61%, but when salinity was raised to 5.0%, it dropped directly to 31%. Therefore, the conclusion of "acclimated to 3.5%" must be considered together with "how much biomass is present and whether ammonia nitrogen can meet standards."

V. The biological stage only accounts for organic loading; salt must be handled separately

This section is where mistakes are most likely to be made in the entire article. A semi-industrial pilot MBBR treating tannery wastewater ran continuously for three months, with an overall COD removal rate of approximately 70% (of which MBBR contributed 35.5% and secondary chemical polishing contributed 15.1%), but the paper contains a very firm conclusion: no significant TDS decrease occurred in the system throughout the study period, and the final effluent salinity remained at approximately 22 g/L. Neither biological oxidation nor chemical precipitation removes dissolved salts—this statement should be written into the design specification of every high-salinity project.

Looking at the impressive desalination figures in commercial cases makes this even clearer: in one fine chemicals project, "salinity was reduced from 6.1% to below 0.3%," and what accomplished this was MVR evaporation, not the biological stage; in one coal chemical Zero Liquid Discharge project, "the produced water reuse rate was >98%, with annual recovery of approximately 5 000 t of sodium sulfate and approximately 3 000 t of sodium chloride," relying on "UF + two-stage RO + DTRO concentration to a TDS of approximately 15% (volume reduction of more than 90%) + salt separation evaporation crystallization," while the biological stage was only responsible for reducing organic matter to within the tolerance range of the membrane system. Therefore, "high-salinity wastewater treatment" should be divided in design into two independent lines: the organic loading line is borne by the biological stage, and the salt line is borne by membranes, Electrodialysis, evaporation crystallization, or compliant discharge. The indicators, costs, and responsible parties of the two lines should not be mixed together.

By the way, note a counterintuitive phenomenon: "which indicator holds up" depends on which degradation pathway the pollutant takes. For textile wastewater AnMBR, as salinity rises from 0 to 20 g/L, COD removal drops from 92% to 73%, but dye removal is barely affected, remaining at 90%~96% throughout. The reason is that dye removal relies mainly on adsorption and anaerobic reduction, and does not depend on that salt-sensitive metabolism inhibited by salinity. Therefore, when evaluating the biological stage in high-salinity scenarios, one cannot look only at COD as a single overall indicator—the overall indicator may drop by 19 percentage points while the target pollutant does not drop at all; and vice versa.

VI. The Real Ledger: Eleven High-Salinity Projects with Traceable Sources

VII. Process Selection: Where Are the Salt-Tolerance Boundaries of Different Biological Forms

VIII. Five Engineering Truths

References

1. Fadaei Tehrani M R, Taheri S. Efficiency of Biological Treatment Processes in the Leather Industry under Wastewater Salinity. Indexed by FAO AGRIS, 2026. (Semi-industrial MBBR pilot: real tannery wastewater TDS 19~24 g/L, MLSS approx. 1 500 mg/L, COD:N:P=100:5:1, acclimation 3~6 d, continuous operation 3 months; overall COD approx. 70%, MBBR contribution 35.5%, polishing 15.1%; stable at TDS ≤22 g/L, decline at >22 g/L; effluent salinity still approx. 22 g/L; also notes conventional Activated Sludge works normally at TDS <approx. 10 g/L, real tannery wastewater 10~40 g/L) https://agris.fao.org/search/zh/records/6a3a5e1b7cd15b8235a88c0c
2. Treatment of Pickle Wastewater under Varying Salinity Conditions within the Sequencing Batch Biofilm Reactor System. Water, 2024, 16(9): 1312. (College of Architecture and Environment, Sichuan University; Sichuan Academy of Eco-Environmental Sciences; pickle wastewater salt content 1%~15%, i.e. 10 000~150 000 mg/L Cl⁻; at 3.0% salinity, COD approx. 96%, TN approx. 93%, NH₄⁺-N approx. 99%; NOB abundance decreased to disappearance, PND became the main pathway; Actinobacteriota became dominant bacteria; the paper cites "osmotic shock may occur when salinity is higher than 1%") https://doi.org/10.3390/w16091312
3. Performance, sludge characteristics and microbial community in a salt-tolerant aerobic granular SBR by seeding anaerobic granular sludge. International Biodeterioration & Biodegradation, 2021. (At 3% salinity, COD 93.3±1.3%, NH₄⁺-N 92±6.5%, TN 76±8.4%; dominant bacteria Xanthomarina, Vitellibacter; AOB was Nitrosomonas, denitrifying bacteria Defluviimonas, NOB (Nitrospira) abundance very low; decreased nirS/nirK abundance led to NO₂⁻-N accumulation; the paper cites fish farming wastewater approx. 30 g/L, tannery wastewater 21~57 g/L)
4. Bassin J P, et al. Ammonia-Oxidizing Bacteria (AOB) tolerance upper limit 33 g NaCl/L, Nitrite-Oxidizing Bacteria (NOB) tolerance upper limit 20 g NaCl/L, 2011. (cited via reference 3)
5. Study on Direct Acclimation of Halophilic Bacteria for Treatment of High-Salinity Wastewater. Environmental Science. (Halophilic bacteria screened from sediment of Dalian Lüshun Salt Field; acclimated at 3.5% salinity in SBR, average MLSS 600 mg/L; endogenous SOUR 10.36 mg/(g·h), exogenous 29.09 mg/(g·h); under conditions of salinity 3.5%, COD 240~340 mg/L, cycle 12 h, aeration 0.6 L/min, SRT 18 d, COD removal >95%, NH₄⁺-N 61%, TP 55%; at salinity 5.0%, NH₄⁺-N only 31%) https://www.hjkx.ac.cn/
6. Wu X, Du Y G, Qu Y, Du D Y. Ternary cycle treatment of high saline wastewater from pesticide production using a salt-tolerant microorganism. Water Science and Technology, 2013. PMID 23656938, doi:10.2166/wst.2013.072 (Bacillus sp. SCUN; optimal pH 6.0~8.0, immobilized microbial agent 1.5 g/L, 30℃, NaCl 0~3%, after acclimation can grow at 4% NaCl; ternary cycle COD removal approx. 58.3%)
7. Wang K, Zhang H, Shen Y, et al. Impact of salinity on anaerobic ceramic membrane bioreactor for textile wastewater treatment: Process performance, membrane fouling and machine learning models. Journal of Environmental Management, 2023, 345: 118717. (Sichuan University, Zhejiang University of Technology, Shaoxing Water Group; UASB-configuration AnMBR + flat-sheet ceramic membrane; four stages of salinity 0/5/10/20 g/L; COD removal 92%→73%, dye removal 90%~96%; 5 g/L promoted gas production, >10 g/L inhibited; SMP and membrane fouling rate peaked at 10 g/L, declined at 20 g/L; microbial community shifted from salt-sensitive groups to salt-tolerant groups)
8. Long-term operation of a pilot-scale AnMBR for treatment of high-salinity low-load municipal sewage (Falconara Marittima wastewater treatment plant, Italy, whole plant 80 000 PE/30 000 m³/d; Horizon 2020 "SMART-Plant" No. 690323). Separation and Purification Technology, 2020. (Increased salinity caused deterioration of membrane filtration: when Na⁺ increased from 8 g/L to 20 g/L, TMP rose to 350 mbar, biomass particle size decreased by one order of magnitude; biogas production decreased by 27% under seawater intrusion conditions; salt-induced floc/particle disintegration and biomass loss)
9. Operational Performance and Membrane Fouling Characteristics of AnMBR for Treatment of High-Salinity Pickled Mustard Tuber Wastewater. Chinese Journal of Environmental Engineering. doi:10.12030/j.cjee.202004134 (National Natural Science Foundation of China 21506076, 51678279; Shanghai Chengtou Science and Technology Innovation Program CTKY-ZDXM-2018-009) (At salinity 12.9→33.5 g/L, loading 0.5~1.0 kgCOD/(m³·d), COD removal rate and biogas yield first decreased then increased with salinity, finally stabilizing above 75% and 300 mL/gCOD; when loading was increased to approx. 7.6 kgCOD/(m³·d), COD removal approx. 80%, biogas 330~380 mL/gCOD, VFA/ALK <0.15; during sludge discharge phase COD 83%, biogas approx. 400 mL/gCOD and favorable for mitigating membrane fouling; SEM-EDX showed inorganic salt crystals on membrane surface, recommended NaClO cleaning + acid cleaning combination)
10. Engineering Case of Resource Recovery Treatment of High-Salinity, High-COD Chemical Wastewater. Environmental Engineering Journal. (Electrodialysis fresh water influent NaNO₃ 93 500 mg/L, COD 103 400 mg/L → effluent NaNO₃ 1 430 mg/L, COD 95 800 mg/L; concentrated water effluent NaNO₃ 107 500 mg/L, COD 5 940 mg/L; (fresh water) three-stage UASB + A/O influent COD 45 000, TN 531, TP 10 mg/L → effluent 297, 47, 4 mg/L; total investment 2 089.17 万yuan, operating cost 123.37 元/m³; three-stage UASB biogas supplied to plant hot water boiler, MVR produced NaNO₃ approx. 10 t/d for recovery) [Volume/Issue to be supplemented]
11. Resource Recovery Treatment Process for High-Salinity High-COD Chemical Wastewater. Wastewater Treatment Engineering Network, 2025-09-18. (Itemized costs and commissioning records of the same project: chemical cost 0.39 元/m³; pretreatment/biological/odor control/sludge treatment installed capacity 191.6 kW, load factor 0.80 converted to actual 153.3 kW, power consumption 29.5 kWh/m³, electricity price 0.52 元/kWh converted to electricity cost 15.34 元/m³; labor 15 persons × 3 500 元/month converted to 14 元/m³; maintenance cost calculated at 1.5% of fixed assets as 0.41 元/m³; Ultrafiltration 0.78, Electrodialysis 34.07, evaporation crystallization electricity cost 37 + steam cost 9.6 元/m³; commissioning issues were high COD in Electrodialysis concentrate chamber affecting MVR sodium nitrate salt separation purity, UASB acidification solved by controlling load and adding alkali; effluent implements Henan Province DB41/1135—2016)
12. Commissioning and Operation of High-Salinity Wastewater Treatment Plant in Xuwei New Area, daily treatment capacity 3.75 万 tons. Website of the CPC Jiangsu Provincial Committee, 2021-02-02. (Lianyungang Xuwei New Area; daily treatment 3.75 万 m³/d, divided into two treatment trains, land area 57.6 mu, approved total investment approx. 3.36 亿yuan; treats concentrated water from reclaimed water reuse of industrial project wastewater in the petrochemical park; core process is Aerobic carrier moving bed + Ozonation coupled biofilm; built in 2020-12, Activated Sludge acclimation and cultivation carried out during commissioning period 2021-02; after meeting standards discharged to compliant tail water purification project, ultimately discharged to natural water bodies through deep-sea discharge pipeline; annual COD reduction approx. 2 000 t)
13. Effect of Salinity in Dye Industry Wastewater on Biochemical Process Performance. Industry operational data analysis. (Under salinity steps of 0.5425%/0.894%/1.064%/1.36%, Hydrolysis Acidification tank CODCr consumption decreased to 58%, 21% of baseline, Aerobic tank decreased to 23.6%, 39%; volumetric loading 1.595 → 1.17 → 0.65 kgCOD/(m³·d); at <1% sludge showed large flocs, at 1.064% supernatant turbid, SV₃₀ decreased, sludge visible disintegration, at 1.36% sludge severely disintegrated, settling ratio without obvious interface, settling still poor after adding flocculant) [Industry source, recommend tracing back to plant operational records]
14. Why High-Concentration Saline Wastewater Inhibits Ordinary Activated Sludge. Industry technical material. (Three mechanisms: osmotic pressure imbalance/plasmolysis, ion-specific toxicity (Cl⁻ inhibits dehydrogenase, Na⁺ disrupts membrane ion balance and ATP synthesis), Henry's law reducing oxygen solubility; ordinary Activated Sludge long-term adapted to low-salt environment typically refers to chloride ion <2 000 mg/L) [Industry technical material, qualitative mechanisms usable, numerical values to be verified]
15. High-Concentration Chemical Wastewater Treatment: Biochemical Efficiency Enhancement Solutions for High-Salinity Systems. Industry technical article. (Ordinary Activated Sludge salinity tolerance upper limit approx. 2%, beyond which COD removal rate drops precipitously, >5% unacclimated microbial community almost completely loses degradation capacity; when salinity exceeds 20 000 mg/L, for every increase of 5 000 mg/L, COD removal rate decreases by 10~15 percentage points on average; when salinity increases from 0 to 30 000 mg/L, total EPS decreases by 40%~60%, polysaccharide/protein ratio decreases from 1.2 to 0.5; SVI increases from 80~120 mL/g to above 200 mL/g, effluent TSS increases from <30 mg/L to 150~300 mg/L; most AOB activity decreases by 80% at salinity >15 000 mg/L, NOB more sensitive; gradient acclimation weekly increase 0.5%~1%, period 1~3 months, acclimation period 40~60 天 when inoculated with ordinary municipal sludge; sludge concentration should be 30%~50% higher than conventional) [Industry technical article, numerical values recommended to trace back to original literature]
16. Under 40000 mg/L NaCl conditions, dehydrogenase activity of ordinary Activated Sludge is only 15%~20% of the no-salt control; for every increase of 10 000 mg/L salinity, oxygen transfer efficiency decreases by approx. 15%; under normal conditions, EC₅₀ of copper ions to Activated Sludge is 10 mg/L, which may decrease to 2 mg/L at 30 000 mg/L salinity. Industry technical material. [Industry source, must be calibrated by on-site bench tests]
17. Halophilic microorganism classification system proposed by Kushner D J, Kamekura M, et al. Cited via Microbiology and Molecular Biology Reviews, 1998, 62(2): 504 ("Biology of Moderately Halophilic Aerobic Bacteria") and IntechOpen "Kinetics of Halophilic Enzymes" review. (Non-halophiles optimum <0.2 M NaCl; slight halophiles 0.2~0.5 M; moderate halophiles 0.5~2.5 M; borderline extreme halophiles 2.5~4.0 M; extreme halophiles 4.0~5.9 M; halotolerant bacteria can grow without salt, ≥2.5 M called extreme halotolerant; also note salt requirement and tolerance vary with temperature and medium composition)
18. Ventosa A, Arahal D R. (optimum growth >3% for halophiles, 3%~15% for moderate, >15% to salt saturation for extreme); Ollivier B, et al. (salt concentration ≥150 g/L i.e. 15%, 2.5 M to be counted as halophiles); Encyclopedia MDPI "Biodiversity of Hypersaline Environments" (slight 0.2~0.85 M/1%~5%, moderate 0.85~3.4 M/5%~20%, extreme 3.4~5.1 M/20%~30%; applicable groups of salt-out and salt-in strategies); IntechOpen "Kinetics of Halophilic Enzymes" (mild 1%~6%, moderate 7%~15%, extreme 15%~30%).
19. Plant Growth-Promoting Halobacteria and Their Ability to Protect Crops from Abiotic Stress. Agronomy, 2022, 12(4): 804. (Halotolerant bacteria can survive at 0~25% NaCl, halophiles require salt for growth; slight halophiles 1%~3%, moderate 3%~15%, extreme 15%~25%) https://doi.org/10.3390/agronomy12040804
20. Extremophiles · Halotolerant Organism Classification Entry. Wikiwand aggregated entry. (Halotolerant organisms 2%~12% (0.2~2.5 mol/L), extreme halotolerant >12%; halophiles require minimum 0.2 M salt concentration; slight halophiles 2%~3%, moderate halophiles 3%~12%, extreme halophiles 12%~30%) [Aggregated source, for terminology reference only, not to be used as design basis]
21. Salt-Tolerant Bacteria Enhanced SBR for Treatment of Simulated High-Salinity Wastewater. Chinese journal. (SBR dosed with salt-tolerant bacteria at 3% salinity achieved COD degradation rate of approx. 93%, significantly higher than control group; at salinity ≤3%, average NH₄⁺-N removal rate stabilized at 90%; at salinity >3%, simultaneous Nitrification and Denitrification was significantly inhibited, excessive salinity led to microbial death)
22. Industrial Wastewater Treatment Workers' Response to Inhibitory Effects of High-Salinity Wastewater on Activated Sludge: Salinity Acclimation and Sludge Discharge Strategy. Industrial Wastewater Treatment Worker Vocational Skills Network. (Gradual salt increase, influent salinity increase not exceeding 1 000 mg/L/week; selective sludge discharge when SV₃₀ exceeds 80% and continuously deteriorates; maintain DO >4 mg/L; one plant successfully acclimated from 2 000 → 8 000 mg/L in stages, stabilizing for two weeks per stage) [Industry skills material, rate basis differs from literature 15 by more than 5 times, must be calibrated by on-site bench tests]
23. Fine Chemical High-COD Intermediate Wastewater Treatment Project. Commercial engineering material. (MBR uses 0.1 μm PVDF membrane to replace secondary clarifier, sludge concentration increased to 8 000 mg/L; influent COD average 40 600 mg/L → effluent 85 mg/L (99.8%), ammonia nitrogen 332 → 12 mg/L (96.4%), TP 15.3 → 0.3 mg/L (98%); salinity reduced from 6.1% to below 0.3% (accomplished by MVR); cost per ton water 42 元 (chemicals 18, electricity 12, labor 5, maintenance 7); annual revenue from salt resource recovery and biogas recovery approx. 120 万yuan) [Commercial source, to be verified]
24. Pharmaceutical High-Salinity Wastewater Treatment Project (a pharmaceutical company in Zhejiang 500 m³/d). Commercial technical material. (Influent COD 20 000 mg/L, total salt 30 000 mg/L; process flow: equalization tank → iron-carbon micro-electrolysis → Fenton → PSB photosynthetic bacteria biochemical → A/O; PSB salt tolerance 3 万~6 万 mg/L, high-concentration organic wastewater COD removal 70%~80%, footprint 20%~25% of conventional Activated Sludge; final effluent COD stably <500 mg/L, meeting GB 8978—1996 Class III standard) [Commercial source, to be verified]
25. Chinese Scientists Construct Novel Engineered Bacterial Strain Capable of Simultaneously Degrading Five Organic Pollutants. China.com.cn citing CCTV report / Nature, 2025-05-07. (Dai Junbiao of Shenzhen Institute of Advanced Technology, CAS and Tang Hongzhi team of Shanghai Jiao Tong University; using salt-tolerant chassis "Vibrio natriegens Vmax" to construct regulatable efficient natural transformation strain VCOD-2, further constructing five artificial metabolic pathways covering mono-cyclic to poly-cyclic pollutants to obtain VCOD-15; within 48 h, removal rates of five typical aromatic pollutants (biphenyl, phenol, naphthalene, dibenzofuran, toluene) all exceeded 60%, biphenyl completely degraded, toluene and dibenzofuran degradation rates near 90%, improved by 2~3 times compared to natural strains)