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Water Parameters – Technical Illustrations

WATER PARAMETERS

Technical illustrations per chapter — water treatment & water quality

H01

Overview — Water Parameters

pH pH Unit: pH units (0–14) Corrosion · scaling · disinfection H⁺ activity in water ALK Alkalinity Unit: mg/L as CaCO₃ pH buffering · corrosion control HCO₃⁻ / CO₃²⁻ / OH⁻ capacity TH Total Hardness Unit: mg/L as CaCO₃ Scaling · membrane fouling Ca²⁺ and Mg²⁺ concentration EC Conductivity Unit: µS/cm or mS/cm Ionic strength · process control Total dissolved ions ORP ORP / Redox Unit: mV (millivolt) Disinfection · redox chemistry Oxidising/reducing capacity NH₃ Ammonia Unit: mg/L as NH₃-N Toxicity · nitrification load NH₃ (free) + NH₄⁺ (ionic form) NO₂⁻ Nitrite Unit: mg/L as NO₂⁻-N Alarm · toxicity · instability Intermediate nitrification product NO₃⁻ Nitrate Unit: mg/L as NO₃⁻-N Nutrient load · compliance Final oxidation product PO₄³⁻ Phosphate Unit: mg/L as PO₄-P Biofouling · algal bloom Nutrient + precipitation behaviour Physical-chemical parameters — Nitrogen cycle parameters — Nutrients & precipitation
H02

pH — Hydrogen Ion Activity

H⁺ dominant (acidic) ←————————————————————————————————————————————————————→ OH⁻ dominant (basic) Strongly corrosive Corrosion risk Acidic / unstable OPTIMAL 6.5 – 8.5 Scaling risk Strongly basic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Drinking water (6.5–8.5) NH₃ toxicity increases CaCO₃ precipitation risk increases pH = −log[H⁺] · Neutral point: pH 7 (25 °C)
H03

Alkalinity — Acid Binding Capacity

Carbonate equilibrium (pH-dependent) CO₂ + H₂O Carbon dioxide ⇌ H₂CO₃ Carbonic acid ⇌ HCO₃⁻ + H⁺ Bicarbonate ← BUFFER ⇌ CO₃²⁻ + 2H⁺ Carbonate (high pH) ⇌ OH⁻ Hydroxide (pH>10) ← low pH high pH → LOW ALKALINITY (<50 mg/L) Limited buffer capacity → pH spikes during dosing → Increased corrosion risk → Unstable process chemistry ⚠ Recommended: increase via NaHCO₃ or Ca(OH)₂ dosing MODERATE (50–150 mg/L) Stable buffer capacity → Controlled pH chemistry → Favourable for process control → Corrosion inhibition active ✓ OPTIMAL ZONE HIGH ALKALINITY (>150 mg/L) Strongly buffered system → Risk of CaCO₃ precipitation → Scaling upon heating → CO₂ stripping raises pH ⚠ Monitor when hardness >150 mg/L CaCO₃ combination
H04

Total Hardness — Ca²⁺ and Mg²⁺

SOFT WATER <70 mg/L CaCO₃ Full flow cross-section Pipe wall HARD WATER >210 mg/L CaCO₃ Lime deposit (CaCO₃) Reduced flow rate Scaling reaction Ca²⁺ + CO₃²⁻ → CaCO₃↓ Risk increases with: ↑ temperature ↑ pH ↑ hardness Hardness scale SOFT MODERATELY HARD HARD / SCALING RISK 70 mg/L 210 mg/L 0 500+ mg/L CaCO₃
H05

Conductivity — Dissolved Ions

WATER SAMPLE Na⁺ Ca²⁺ Mg²⁺ K⁺ Fe²⁺ Cl⁻ SO₄²⁻ HCO₃⁻ NO₃⁻ Cations (+) Anions (−) current conducted by ions CONDUCTIVITY SCALE 0 µS/cm — Deionised / permeate 10 µS/cm — RO permeate 500 µS/cm — Typical drinking water 2,500 µS/cm — Lightly contaminated 50,000 µS/cm — Seawater ⚠ Always temperature-correct to 25 °C
H06

ORP / Redox Potential — Oxidising Capacity

ORP scale in millivolts (mV) — pH 7, 25 °C REDUCING MILDLY REDUCING OXIDISING STRONG OX. 0 mV −400 −200 +200 +400 +600 +800 Anoxic / sulphide reduction H₂S formation, biocorrosion Aerobic nitrification zone NH₄⁺ → NO₂⁻ → NO₃⁻ Strong disinfection zone Chlorine, ozone active REDUCING ENVIRONMENT (low ORP) Substance donates electrons → e⁻ donor Fe²⁺, H₂S, organic matter present Corrosion tendency, biological growth OXIDISING ENVIRONMENT (high ORP) Substance accepts electrons → e⁻ acceptor O₂, chlorine, ozone present Disinfection active, iron oxidation → ORP increases
H07

Ammonia — NH₃ / NH₄⁺ Equilibrium

Distribution of NH₃ (free, toxic) vs NH₄⁺ (ionic form) as a function of pH — at 20 °C 100% 75% 50% 25% 0% 5 6 7 8 9 10 11 pH → NH₄⁺ (ammonium) Low toxicity · stable NH₃ (free ammonia) ⚠ TOXIC to aquatic organisms pKa ≈ 9.3 (20 °C) 50/50 point ⚠ pKa decreases at higher temperature → more NH₃ at same pH
H08

Nitrite — Nitrification Intermediate

Aerobic nitrification pathway — nitrogen oxidation in two steps NH₄⁺ Ammonium (influent) Nitrosomonas + O₂ (aerobic oxidation) ⚠ ALARM PARAMETER NO₂⁻ Nitrite — unstable intermediate Acutely toxic · incomplete conversion Nitrobacter + O₂ (aerobic oxidation) NO₃⁻ Nitrate (stable end product) Oxygen consumption — nitrification Step 1: NH₄⁺ + 1½O₂ → NO₂⁻ + H₂O + 2H⁺ | Step 2: NO₂⁻ + ½O₂ → NO₃⁻ Elevated NO₂⁻: O₂ deficiency, toxic inhibition or biological imbalance
H09

Nitrate — Nitrogen Cycle

Nitrogen cycle — nitrification and denitrification in water treatment Organic N Proteins, urea, biomass NH₄⁺ Ammonium NO₂⁻ Nitrite (⚠ alarm) NO₃⁻ Nitrate (end product) N₂ Nitrogen gas (atmosphere) ammonification Nitrosomonas (+ O₂) Nitrobacter (+ O₂) denitrification (anoxic) N₂ fixation (biological) Nitrification requires: aerobic conditions (O₂ present), pH 6.5–8.5 Denitrification requires: anoxic conditions (no O₂), carbon source
H10

Phosphate — Biofouling and Precipitation

PO₄³⁻ Phosphate in solution BIOLOGICAL PATHWAY Nutrient uptake by micro-organisms Algal bloom / bacterial growth Biofouling / biofilm membrane fouling, heat exchangers ⚠ Also eutrophication of surface water CHEMICAL PATHWAY 3Ca²⁺ + 2PO₄³⁻ → Ca₃(PO₄)₂↓ Poorly soluble precipitate Scaling / deposits on membranes, pipes, heat exchangers Risk increases with high Ca²⁺ + higher pH ✓ Controlled orthophosphate dosing in distribution networks → corrosion inhibition on lead pipes
H11

Indicative Assessment Frameworks — Zones per Parameter

PARAMETER LOW ZONE NORMAL ZONE HIGH / CRITICAL ZONE pH pH units <6.5 — corrosion risk,metal solubility 6.5 – 8.5drinking water/industry >8.5 — scaling risk,altered NH₃ chemistry Alkalinity mg/L as CaCO₃ <50 — limited buffering,pH instability 50 – 150well manageable >150 — precipitation athard water conditions Total Hardness mg/L as CaCO₃ <70 — soft water,low scaling risk 70 – 210common range >210 — elevated scalingrisk on membranes Conductivity µS/cm Very low — deionised/permeatequality Application-dependent Sharp rise — possiblecontamination/breakthrough ORP / Redox mV Low/negative — reducingconditions Process-specificsetpoint High — strongly oxidising,check dosing Ammonia mg/L NH₃-N Not detectable orvery low (desired) Traces possibledepending on source Elevated — toxicity orincomplete conversion Nitrite mg/L NO₂⁻-N Ideally not detectable(drinking water standard) Low traces atstart-up ⚠ ALARM — incompletenitrification Nitrate mg/L NO₃⁻-N Low — desired in drinkingwater Moderate,source-dependent High — complianceissue, eutrophication Phosphate mg/L PO₄-P Low — fouling-sensitive systems Controlled dosing High — biofouling, algal bloom
H12

Relevance per Application — Critical Parameters

Critical Relevant Less relevant pH Alka-linity Hard-ness Conduc-tivity ORP Ammo-nia Nitrite Nitrate Phos-phate Drinking Water health, taste, corrosion Cooling Water corrosion, scaling, biofouling Boiler Feed Water deposits, corrosion, efficiency RO / Demineralised membrane performance, scaling Biological Treatment nitrification, process control Aquatic Systems toxicity, buffering, species Indicative overview — exact threshold values are application- and installation-specific
H13

Measurement & Interpretation Notes — Sensor Use

pH ORP EC T° Water Sample Continuous inline measurement Temperature Correction Always correct EC to 25 °C ORP/pH also temperature-dependent Regular Calibration pH: buffer pH 4.0 / 7.0 / 10.0 ORP: Zobell solution (+228 mV) ⚠ Monitor for Drift Sensor fouling = erroneous trending Maintenance + reference measurement NH₃ Interpretation Always combine with pH and T° Free NH₃ determines toxicity Combination of pH + alkalinity + hardness + EC + T° gives the best predictive value for scaling and corrosion