CHE 574: Industrial Wastewater Pollution Control
Estimated study time: 10 minutes
Table of contents
Sources and References
Primary texts — Eckenfelder, W.W., Ford, D.L., and Englande, A.J., Industrial Water Quality, 4th ed., McGraw-Hill, 2009; Metcalf & Eddy / AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed., McGraw-Hill, 2014.
Supplementary texts — Davis, M.L., Introduction to Environmental Engineering, 6th ed., McGraw-Hill, 2021; Crittenden, J.C. et al., MWH’s Water Treatment: Principles and Design, 3rd ed., Wiley, 2012.
Online resources — MIT OCW 1.85 “Water and Wastewater Treatment Engineering”; US EPA Effluent Guidelines database; Environment and Climate Change Canada industrial wastewater regulations; IWA open-access publications; BAT reference documents (BREFs) public summaries.
Chapter 1: Industrial Wastewater Characterization
1.1 Composition and Variability
Industrial effluents span extreme pH, high salinity, high organic load, toxic inorganics, colored dyes, emulsified oils, recalcitrant synthetics. Variability is extreme—flow and composition vary by shift, batch, season. Characterization must capture averages and peaks: 24-hour composite samples, grab samples at process events, continuous monitoring of key parameters (pH, conductivity, TOC).
1.2 Regulatory Parameters
- BOD (biochemical oxygen demand, 5-day): biodegradable organic content.
- COD (chemical oxygen demand): total oxidizable organics (BOD + recalcitrant).
- TOC (total organic carbon): instrumental measure.
- TSS (total suspended solids), TDS (total dissolved solids).
- Nitrogen forms: TKN, NH\(_3\)-N, NO\(_3\)\(^-\), total N.
- Phosphorus: ortho, total.
- Specific contaminants: heavy metals, phenol, CN\(^-\), specific organics per industry.
1.3 Industry-Specific Streams
- Metal finishing: heavy metals (Cr, Ni, Cu, Zn, Cd), cyanides, oil and grease, variable pH.
- Pulp and paper: high BOD, color (chlorinated lignins), adsorbable organic halides (AOX).
- Petroleum refining: oil, H\(_2\)S, NH\(_3\), phenols, high salinity (desalter).
- Food and beverage: high BOD, nutrients, oil and grease, seasonal.
- Textile: dyes (color), surfactants, salts, heat.
- Pharmaceutical: recalcitrant organics, APIs (trace toxicity), solvent mixtures.
Chapter 2: Waste Minimization
2.1 Source Reduction
Process modifications to reduce wastewater generation at source: substitution of hazardous reagents, countercurrent rinsing, closed-loop cooling, segregation of concentrated vs. dilute streams. Pays dividends by reducing both treatment load and raw material losses.
2.2 Rinsewater Circuit Design
Electroplating lines and semiconductor fabs use cascade (countercurrent) rinsing to minimize water use. For \( N \) stages in series with dragout \( D \) from plating bath:
\[ \frac{C_N}{C_0} = \frac{1}{r^N}, \quad r = \frac{Q}{D}, \]where \( Q \) is freshwater feed. Three-stage rinse at \( r = 100 \) achieves \( 10^{-6} \) dilution; a single-stage rinse at the same water use cannot approach this.
2.3 Water Pinch Analysis
Analogous to heat pinch: composite water-demand and water-supply curves reveal minimum freshwater and maximum reuse. Mass-transfer-based pinch for contaminant-free operations; source-sink allocation for process design. Industrial retrofits routinely find 30-50% freshwater reduction without capital-intensive treatment upgrades.
2.4 Zero Liquid Discharge
ZLD combines extensive reuse, evaporation, and crystallization to eliminate liquid effluent. Applied where water scarcity, regulatory pressure (e.g., China’s industrial water norms), or salt-sensitive receiving waters mandate it. Energy-intensive; driven by multi-effect evaporators, mechanical vapor recompression, and forced-circulation crystallizers.
Chapter 3: Chemical Treatment
3.1 Neutralization
pH adjustment with lime (Ca(OH)\(_2\)), caustic (NaOH), soda ash (Na\(_2\)CO\(_3\)), sulfuric or hydrochloric acid. Automatic control essential because pH is non-linear; pH-titration curves and buffering must be characterized. Two-stage neutralization (coarse + fine) handles streams with wide pH swings.
3.2 Precipitation for Heavy Metal Removal
Hydroxide precipitation:
\[ M^{2+} + 2 OH^- \to M(OH)_2\downarrow. \]Minimum solubility pH varies by metal: Cu ~9, Ni ~10, Zn ~10, Cd ~11, Cr(III) ~8. For streams with multiple metals, compromise pH may leave residuals; two-stage or sulfide precipitation (M\(^{2+}\) + S\(^{2-}\) → MS↓, more insoluble) can meet stringent limits.
Chromium(VI) requires pre-reduction to Cr(III) with SO\(_2\), bisulfite, or ferrous before precipitation.
3.3 Coagulation and Flocculation
Colloids (clay, organic matter, emulsions) stabilized by surface charge resist gravity settling. Coagulants (alum, ferric chloride, polyaluminum chloride, PAC) neutralize charge; flocculants (high-molecular-weight polymers) bridge destabilized particles into flocs > 100 µm. Jar testing optimizes dose, mixing intensity, and sequencing.
3.4 Oxidation
Chlorine (Cl\(_2\), NaOCl) for cyanide destruction, disinfection; hydrogen peroxide; ozone; persulfate. Advanced oxidation processes (AOP) generate hydroxyl radicals (O\(_3\)/H\(_2\)O\(_2\), UV/H\(_2\)O\(_2\), photocatalysis) to degrade recalcitrant organics. Cost per unit of contaminant removed is high; used for polishing or targeted compounds.
Chapter 4: Physical Separations
4.1 Sedimentation and Flotation
Rectangular or circular clarifiers settle flocs under gravity; overflow rate \( Q/A \) [m/h] governs design. Dissolved air flotation (DAF) attaches microbubbles to particles, floating them; preferred for oily, low-density, or buoyant solids.
4.2 Ion Exchange
Cation exchangers (sulfonated styrene-divinylbenzene, strong acid; weak acid carboxylate) swap Na\(^+\), H\(^+\) for metal cations. Anion exchangers swap OH\(^-\) or Cl\(^-\) for anions. Regeneration with acid/base/brine; spent regenerant is a concentrated waste stream needing downstream treatment. Common for demineralization, metal recovery, and selective removal (chromate, selenate, perchlorate).
4.3 Membrane Separation
Microfiltration (0.1-1 µm): suspended solids, some bacteria. Ultrafiltration (1-100 nm): macromolecules, colloids. Nanofiltration (~1 nm): divalent salts, small organics. Reverse osmosis (non-porous): salts, most organics. Transmembrane pressures 1-100 bar; energy dominated by RO. Concentration polarization and fouling dictate cross-flow operation and pretreatment. Spiral wound and hollow fiber modules prevail.
4.4 Adsorption
Granular activated carbon (GAC) columns remove dissolved organics. Breakthrough curves, mass transfer zone (MTZ), empty bed contact time (EBCT) characterize design. Regeneration by steam (for solvents) or thermal reactivation; powdered activated carbon (PAC) is single-use. Selective resins target specific compounds (PFAS, phenol).
Chapter 5: Biological Treatment of Organic Aqueous Waste
5.1 Activated Sludge
Suspended-growth biomass oxidizes biodegradable organics in aerated tank; settling tank separates biomass for recycle. Steady-state Monod + mass balance:
\[ \tau_c = \frac{1}{\mu - k_d}, \]with solid retention time \( \tau_c \), yield \( Y \), endogenous decay \( k_d \). F/M ratio, MLSS, SVI, and \( \tau_c \) are operational parameters. Extended aeration, contact-stabilization, oxidation ditches are variants.
5.2 Attached-Growth Systems
Trickling filters, rotating biological contactors (RBCs), moving-bed biofilm reactors (MBBR), integrated fixed-film activated sludge (IFAS). Biofilms handle lower biodegradable loads per unit area than suspended-growth but are robust to toxic shocks and variable flow.
5.3 Anaerobic Processes
Anaerobic digestion converts organics to biogas (60-70% CH\(_4\), 30-40% CO\(_2\)) in sequence: hydrolysis, acidogenesis, acetogenesis, methanogenesis. Up-flow anaerobic sludge blanket (UASB), expanded granular sludge bed (EGSB), and anaerobic MBR handle high-strength industrial effluents (brewery, sugar, pulp mill) with positive energy balance.
5.4 Nutrient Removal
Nitrification-denitrification: autotrophic NH\(_4\)\(^+\) → NO\(_3\)\(^-\) (aerobic) followed by heterotrophic NO\(_3\)\(^-\) → N\(_2\) (anoxic). Anammox: anaerobic ammonium oxidation, NH\(_4\)\(^+\) + NO\(_2\)\(^-\) → N\(_2\), saves > 60% energy. Biological phosphorus removal: alternating anaerobic/aerobic zones luxury-uptake P into biomass. Enhanced biological nutrient removal (EBNR) is standard in advanced municipal and industrial plants.
Chapter 6: Integrated Treatment and Sludge Management
6.1 Treatment Train Design
Typical order: screening, flow equalization, primary (physical/chemical), secondary (biological), tertiary (filtration, disinfection), advanced (nutrient removal, membrane, AOP). Each stage tailored to the preceding stream’s characteristics. Capacity balanced against redundancy and resilience to upsets.
6.2 Sludge Handling
Primary, secondary (WAS), and chemical sludges thicken, digest, dewater, and dispose. Digestion (anaerobic or aerobic) stabilizes and reduces volume; dewatering (centrifuge, belt press, filter press) reduces moisture from ~98% to ~70%. Incineration, landfill, land application, and valorization (biochar, construction fill) are disposal paths; regulatory pathways (biosolids Class A/B, EQ) govern beneficial reuse.
6.3 Energy and Resource Recovery
Wastewater contains more energy (via anaerobic digestion) and nutrients than ordinary treatment releases. Recent trend: wastewater treatment plants as water resource recovery facilities. Phosphorus recovery as struvite, nitrogen as ammonia sulfate, energy from biogas and hydrothermal processes, and water reuse for industrial or non-potable uses.
6.4 Monitoring and Control
Regulatory: flow, pH, BOD, TSS, COD, nutrients, specific pollutants. On-line: pH, ORP, DO, conductivity, turbidity, ammonia, nitrate. Advanced: COD, TOC, respirometry. Process control with SCADA; anomaly detection and soft sensors integrated in modern digital water platforms.
