The Menace of High TDS in Chemical Intermediates- Halophiles at rescue
Salts are one of the most omnipotent components present on Earth. Their presence and absence are significant in almost every chemical, physical, or biological process. Their concentration either depletes or enhances biological growth, preservation, and destruction. However, in effluent treatment plants, salts always have a destructive effect. High TDS in chemical intermediates is never welcomed by any ETP operator as it comes with operational ineffectiveness, damage to infrastructure, extreme difficulty in handling the effluent, non-compliance and high OPEX/CAPEX. Elevated TDS not only jeopardizes downstream operations, leading to scaling, corrosion, and product contamination, but also complicates effluent management, often forcing plants to deploy energy-intensive physicochemical treatments such as Multi-Effect Evaporators (MEE) and Reverse Osmosis (RO).
Although MEE/RO is effective, but is cost-intensive! so, what might be the alternative? Well, here is the answer, HALOPHILES! Also known as halophilic bacteria, these salt-loving microbes offer a promising solution. This blog will help readers explore how halophiles in the form of microbial culture can help industries achieve operational excellence and reduce the effects and cost.
For more information or to discuss how our solutions can assist your operations, please contact us
The Impacts of High TDS :
High TDS streams in chemical intermediates plants often arise from:
- Salt‐based reactants and catalysts: e.g., chlorides, sulfates, nitrates
- Neutralization and pH control: addition of acid/base produces salts
- Process by-products: dissolved organics, chelating agents, metal complexes
Operational Challenges
Effects of high TDS in chemical intermediates include:
- Scaling & Fouling
- Precipitation of sparingly soluble salts (e.g., CaSO₄, BaSO₄) on heat‐exchange surfaces leads to reduced heat transfer and frequent downtime.
- Corrosion
- Chloride‐rich brines attack stainless steels and other alloys, raising maintenance costs.
- Product Quality Risks
- Carryover of salts compromises the purity of intermediates, requiring additional downstream purification.
Hampers Biological treatment:
- Due to high TDS, most of the biological wastewater treatment processes fail to generate effective biomass, hence hampering the efficiency.
Regulatory and Discharge Constraints
- Effluent quality limits: Most jurisdictions cap TDS in discharge at 2,000–5,000 mg/L.
- Brine disposal: Concentrated RO or evaporator brines often exceed tolerable disposal limits, leading to high disposal fees or zero-liquid discharge (ZLD) mandates.
- Membrane/Equipment Damages: Due to hampered biological wastewater treatment efficiency, most of the COD and dead biomass is carried into RO membranes results into their scaling or fouling in MEE.
Physicochemical Solutions: MEE & RO
Reverse Osmosis (RO)
Principle: Semi-permeable membranes allow water to pass under pressure while retaining salts.
- Recovery ratio (R):
- Typical performance: Recovery up to 75–85% for moderate TDS (<10,000 mg/L).
Pros:
- Modular and relatively compact
- High salt rejection (>99%)
Cons:
- Membrane fouling/scaling requiring frequent cleaning
- High‐pressure energy costs (2–6 kWh/m³)
- Brine at 15–30% of feed volume
Multi‐Effect Evaporator (MEE)
Principle: A Series of evaporators reuses steam from one stage as the heating medium for the next, concentrating brine.
- Steam economy: up to 8–10 kg steam/kg water evaporated.
Pros:
- Handles very high TDS (>100,000 mg/L) and organics
- Robust to feed variability
Cons:
- Large footprint and capex
- High thermal energy demand (often >500 kWh thermal/m³)
- Generates a highly concentrated sludge
Halophilic Biocultures: A Biological Alternative
What Are Halophiles?
- Definition: Microorganisms—including bacteria, archaea, and some fungi—that not only tolerate but require high salt concentrations (≥3% w/v NaCl) for optimal growth.
- Types:
- Moderate halophiles: 3–15% w/v NaCl
- Extreme halophiles: 15–30% w/v NaCl
Mechanisms of Pollutant Removal
- Organic Degradation
- Many halophiles express salt-stable enzymes (e.g., dehydrogenases, esterases) that mineralize refractory organics, aiding in biological TDS reduction.
- Biosorption of Inorganics
- Cell walls and extracellular polymeric substances (EPS) bind heavy metals and ammonium ions, reducing dissolved load.
- Biomineralization
- Certain strains precipitate metal sulfides or carbonates, facilitating solids separation.
Case Study: Halomonas spp. in High-Salinity Effluent:
| Parameter | Untreated Effluent | After Halophilic Treatment | Removal Efficiency |
|---|---|---|---|
| TDS (mg/L) | 45,000 | 28,000 | 38% |
| COD (mg/L) | 5,200 | 1,100 | 79% |
| NH₄⁺-N (mg/L) | 310 | 45 | 85% |
In a pilot study, a consortium dominated by Halomonas elongata achieved near‐complete organic removal and 30–40% TDS reduction within 48 hours, showcasing the potential of TDS reduction using microorganisms.
Integration Strategies:
4.1 Hybrid Biological‐Physicochemical Systems
- Pre‐treatment with Halophiles + RO
- Step 1: Use halophilic bioreactor to ingest organics and bind metals, lowering fouling precursors.
- Step 2: Send biologically pre-treated stream to RO, extending membrane life and improving recovery.
- Post‐MEE Biological Polishing
- Concentrate via MEE to moderate brine TDS (e.g., 80,000 mg/L → 120,000 mg/L).
- Dilute and treat with halophiles to remove residual COD and ammonia, enabling partial recycling.
4.2 Reactor Configurations
- Sequencing Batch Reactors (SBR): Ideal for flexible loading and high-salt adaptation cycles.
- Membrane Bioreactors (MBR): Combine biomass retention with ultrafiltration, ensuring high mixed liquor suspended solids (MLSS).
- Fixed-Film Reactors (e.g., Biofilm Carriers): EPS‐rich biofilms on carriers that thrive in saline feed.
Design & Operational Best Practices:
| Aspect | Recommendation |
|---|---|
| Salinity Gradients | Gradual acclimation: start at 3% NaCl, ramp to process levels over 2–3 weeks. |
| pH Control | Maintain 7.5–8.5; extremes impair enzymatic activity. |
| Nutrient Supplementation | C:N:P ratio of ~100:5:1 for robust growth. |
| Temperature | 30–37 °C to optimize halophilic metabolism. |
| Hydraulic Retention Time | 24–72 hours, depending on target removal efficiencies. |
| Mixing & Oxygenation | Ensure DO ≥2 mg/L for aerobic halophiles; N₂ sparging for anaerobic strains. |
Economic & Environmental Benefits:
| Metric | Conventional MEE/RO Only | Hybrid with Halophiles |
|---|---|---|
| Energy Consumption (kWh/m³) | 6–10 (electrical) + 500 (thermal) | 3–5 (electrical) + 300 (thermal) |
| Membrane Cleaning Frequency | Every 2–4 weeks | Every 8–12 weeks |
| Brine Volume for Disposal (%) | 20–30 | 10–15 |
| Chemical Usage (antiscalants) | High | Moderate |
| Carbon Footprint (kg CO₂e/m³) | 15–20 | 8–12 |
By biologically reducing foulants and salinity, plants can halve brine volumes, extend membrane life, and cut overall energy and chemical costs by up to 30%. Moreover, the biodegraded organics lessen the environmental hazards of any unavoidable discharges, promoting eco-friendly chemical processing.
Conclusion:
High TDS in chemical intermediates has traditionally been corralled by MEE and RO—solutions that are effective but capital- and energy-intensive, and that generate challenging brines. Halophilic biocultures, however, offer a compelling biological route to alleviate TDS and organic loads, enhancing and de-risking conventional treatment trains. By integrating salt-adapted microbes—either as a pretreatment before RO or as a polishing step after evaporation—plants can achieve lower energy footprints, reduced chemical consumption, and more manageable brine streams.
As the industry seeks sustainability and cost-efficiency, harnessing the power of halophiles represents a strategic pivot: one that turns the very menace of high salinity into an opportunity for greener, sharper operations.
Are high TDS levels threatening your effluent compliance? Discover how a customized biological approach can turn the tide. Contact us to discuss a no-obligation site assessment and see how TeamOne’s expertise can optimize your industrial wastewater treatment.
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