Comprehensive Study Notes – Water Quality, Standards & Treatment

Introduction to Water Quality

  • Water supply systems demand water that meets specific physical, chemical, biological and other quality criteria.
  • Conventional treatment steps: screening → grit removal → aeration → coagulation → flocculation → sedimentation → filtration → fluoridation → disinfection → conditioning.
  • Certain contaminants (e.g.
    • \text{Na}, \text{Mg}, \text{NO3^-}, \text{SO4^{2-}}, heavy metals) cannot be fully removed by conventional methods and require special/advanced treatment such as algae control, pre-chlorination, ozonation, activated-carbon adsorption or specialised sludge handling.

Recommended Raw-Water Quality & Monitoring

  • Parameters divided into Groups I–V (microbial, general physical–chemical, toxic metals, pesticides & herbicides, radioactivity).
  • Monitoring frequency codes
    • W = weekly M = monthly Y/4 = once every 3 months Y = annual WN = when necessary.
  • Illustrative limits (surface / ground / direct impounding)
    • Total coliform: 5{,}000\;\text{MPN\,or\,CFU}/100\text{ mL} (Group I – microbial).
    • Turbidity: 1{,}000\;\text{NTU} (raw water upper limit).
    • Colour: 300\;\text{TCU}.
    • pH range: 5.5{-}9.0.
    • Dissolved solids: 1{,}500\;\text{mg/L}.
    • Key toxic elements (Group III) & limits: \text{Hg}=0.001, \text{Cd}=0.003, \text{Se}=0.01, \text{As}=0.01, \text{Pb}=0.05 (\text{mg/L}).
    • 40 parameters in raw-water list, 131 in treated-water list.
  • Samples must be taken more frequently if source is known/suspected to exceed limits.

Drinking-Water Quality Standards (Plant Outlet → Reservoir → Distribution)

  • Microbiological
    • Total coliform & E.\,coli: “not detected” in any 100\text{ mL} sample.
    • Faecal streptococci, clostridia, viruses, protozoa, helminths: absent in 100\text{ mL}.
  • Physical
    • Turbidity \le 5\;\text{NTU}.
    • Colour \le 15\;\text{TCU}.
    • pH 6.5{-}9.0.
    • Free residual chlorine 0.2{-}5.0\;\text{mg/L}; combined residual \ge 1.0\;\text{mg/L}.
  • Inorganic chemicals (examples of maximum acceptable values)
    • Total dissolved solids \le 1{,}000\;\text{mg/L}.
    • Chloride \le 250\;\text{mg/L}.
    • Ammonia \le 1.5\;\text{mg/L\,(as\,N)}.
    • Nitrate \le 10\;\text{mg/L\,(as\,N)}.
    • Iron \le 0.3\;\text{mg/L}; Manganese \le 0.1\;\text{mg/L}.
    • Hardness: design target 100\;\text{mg/L}, absolute \le 500\;\text{mg/L}.
    • Aluminium \le 0.2\;\text{mg/L}.
  • Organic/radiological
    • Trihalomethanes (THMs): sum of ratios \le 1; key individual limits – chloroform 0.2\;\text{mg/L}, bromoform 0.1\;\text{mg/L}.
    • Gross \alpha: 0.1\;\text{Bq/L}, Gross \beta: 1.0\;\text{Bq/L}.

Physical Quality Parameters

Colour

  • Natural waters are ideally colourless.
  • Caused by humic/fulvic compounds; acceptable
    • Raw water <300\,\text{TCU} (conventional treatment handles <75\,\text{TCU}).
    • Drinking water <15\,\text{TCU}.
  • Measured spectrophotometrically (expressed as TCU).

Turbidity

  • Results from suspended solids (silt, clay, FDOM).
  • Signifies clarity & possible microbial shielding.
    • Raw water permissible peak 1{,}000\,\text{NTU}.
    • Finished water \le 5\,\text{NTU} (regulatory).
  • Measured with nephelometric turbidimeter (NTU units).

Taste & Odour

  • Trace organics/inorganics (e.g. algae by-products, hydrogen sulphide, chlorophenols) impair palatability.
  • Control options: aeration, chemical pre-treatment (algaecides), pre-chlorination, activated-carbon adsorption.

Suspended Solids & TDS

  • Suspended solids – plankton, clay, silt; correlate with turbidity.
  • TSS often elevate TDS; TDS \le 1{,}500\,\text{mg/L} (design aim 1{,}000\,\text{mg/L} to assure taste, hardness & corrosion control).

Temperature

  • Ideal potable water temperature 10{-}15^{\circ}\text{C}; extremes affect taste and treatment chemistry.
  • Source selection should consider seasonal variation.

Chemical Quality Parameters

Inorganic Contaminants (selected)

  • Arsenic: limit 0.05\,\text{mg/L}; sources—pesticides, mining; conventional limit same for raw water.
  • Cadmium: 0.005\,\text{mg/L}; plating, photography; removed at \text{pH}>8 via coagulation.
  • Chromium (VI): 0.05\,\text{mg/L}; industrial.
  • Cyanide: 0.1\,\text{mg/L}; mining effluent; chlorine treatment removes 90{-}100\%.
  • Fluoride: problem >1.5\,\text{mg/L}; conventional removal ineffective → seek alternate source.
  • Lead: 0.05\,\text{mg/L}; corrosion of plumbing; alum coagulation helpful.
  • Mercury: 0.001\,\text{mg/L}; mostly inorganic in water; removed by activated-carbon.
  • Nitrate-N: 10\,\text{mg/L} (equiv. 45\,\text{mg/L\,NO_3^-}); high levels cause infant methaemoglobinaemia (blue-baby syndrome). Sources: fertilisers, animal waste.
  • Selenium: 0.01\,\text{mg/L}; copper smelters; toxicity threshold 0.01{-}0.1\,\text{mg kg}^{-1}\text{/day} body weight.

Organic Contaminants

  • Natural organics: humic/fulvic acids (0–30\,\text{mg/L}) → precursors to disinfection by-products.
  • PAHs: tar, incomplete combustion; limit 0.0002\,\text{mg/L} in treated water.
  • Pesticides & herbicides (e.g. aldrin/dieldrin 0.00003\,\text{mg/L}, atrazine 0.002\,\text{mg/L}) monitored quarterly or as required.
  • Trihalomethanes (THMs): formed when chlorine reacts with organic matter; control by organic precursor removal pre-chlorination.

Microbiological Quality Parameters

  • Raw water indicators: total coliform (TC) & faecal coliform (FC).
    • High TC → general sewage contamination; high FC/E.\,coli → human/animal faecal origin.
    • Raw water alert: if 1{-}10 coliforms/100\,\text{mL} consistently detected, urgent mitigation.
    • Raw water maxima: TC=5{,}000\,\text{MPN}/100\,\text{mL}.
  • Drinking water standard: TC=0 and E.\,coli=0 per 100\,\text{mL}.

Other Important Parameters

  • pH: raw waters generally 4{-}9; treated water recommended 6.5{-}9.0 (≈60\% of Malaysian rivers between 6.5{-}8.5).
  • Biochemical Oxygen Demand (BOD): indicator of organic pollution.
    • Raw water guideline <6\,\text{mg/L}.
    • Classification: 0{-}4 clear; 4{-}8 mildly; 8{-}12 moderately; >12 grossly polluted.
  • Ammoniacal-N: impacts chlorine demand.
    • Treated water target <0.5\,\text{mg/L}.
    • Removal: breakpoint chlorination or biological nitrification.
  • Aluminium (residual): <0.2\,\text{mg/L}; excess arises from over-dosing alum.
  • Chloride: taste/corrosion; drinking limit 250\,\text{mg/L} (desalination expensive → prefer low-Cl- sources).
  • Hardness: carbonate & non-carbonate; Malaysian rivers mostly <60\,\text{mg/L}, design standard 100\,\text{mg/L}; accept up to 500\,\text{mg/L} in raw water.
  • Iron: rivers 1{-}5\,\text{mg/L}; treat if >0.3\,\text{mg/L} (prechlorination, aeration + coagulation).
  • Manganese: treated limit 0.1\,\text{mg/L}; sometimes oxidised by \text{KMnO_4} dosing.

Malaysian Legislation & Classification

  • National Water Quality Standards (NWQS, MWA 2021) align with WHO but adapt to local conditions (tropical climate, monsoon run-off).
  • DOE Water Quality Index (WQI)
    • Six parameters: DO, BOD, COD, TSS, NH$_3$-N, pH.
    • Water-class linkage:
    • Class I: pristine; drinking after minimal treatment; fishery I (very sensitive species).
    • Class IIA: conventional treatment; fishery II.
    • Class IIB: recreational body-contact.
    • Class III: extensive treatment; fishery III; livestock.
    • Class IV: irrigation; Class V: non-classified.
    • WQI score interpretation
    • >92.7 Class I 76.5{-}92.7 Class II 51.9{-}76.5 Class III 31{-}51.9 Class IV <31 Class V.
    • Pollution status
    • Clean 81{-}100, slightly polluted 60{-}80, polluted 0{-}59.
  • Real-time dashboard (24 Feb 2025): 30 stations – 18 clean, 11 slightly polluted, 1 polluted (Sg. Klang WQI 58).

Water Supply Issues & Sustainability

  • Finite freshwater despite perception of abundance; spatial & temporal scarcity exacerbated by:
    • Rapid urbanisation & population growth.
    • Inadequate/aged infrastructure ⇒ high non-revenue water (NRW).
    • Low consumer tariffs → under-financing O & M.
    • Pollution from industrial, agricultural, domestic sources.
    • Climate change introduces hydrological uncertainty and irreversible ecosystem shifts.

Ethical, Practical & Cross-lecture Connections

  • Public-health ethics: ensuring safe, palatable water prevents water-borne disease; failure disproportionately hurts vulnerable communities.
  • Economic implications: cost of advanced treatment vs. preventive watershed protection.
  • Engineering design: choice of source, process selection (advanced oxidation, membrane filtration) hinges on parameter exceedance highlighted above.
  • Policy tie-in: complying with WHO 1993/96 guidelines (chemical updates) and adopting adaptive management under Malaysian Environmental Quality Act.

Key Numerical References (LaTeX format examples)

  • \text{Turbidity}{\text{raw}}\le 1{,}000\;\text{NTU} \text{Turbidity}{\text{drink}}\le 5\;\text{NTU}
  • \text{Colour}{\text{drink}}
  • \text{TDS}_{\text{limit}}=1{,}500\;\text{mg/L} (design target 1{,}000\;\text{mg/L})
  • \text{pH}_{\text{drink}}=6.5{-}9.0
  • \text{Nitrate\,(as\,N)}_{\max}=10\;\text{mg/L}
  • E.\,coli_{\max}=0\;\text{MPN}/100\,\text{mL}

Study Tips & Real-World Relevance

  • Memorise Group I microbial zero-tolerance for treated water – most exam questions target this critical health criterion.
  • Understand why some contaminants (e.g. fluoride, sodium, sulphate) pass through conventional plants → know which advanced processes address them (e.g. ion exchange, RO).
  • Link WQI classifications to treatment depth: Class IIA → conventional; Class III → ext. treatment; exam scenarios frequently ask to recommend process trains.
  • Watch for units: many limits switch between \text{mg/L\,(as\,N)} and \text{mg/L\,(NO_3^-)}.
  • Ethical dimension: balancing affordability with stringent standards; rate-setting and NRW reduction feature in policy essays.