ENG421 (4c) – Water Quality Management Water Treatment Plant - for surface water - for groundwater - for residual management

Water Treatment Plant for Surface Water (1 of 9) Alternative water treatment trains may be used depends on : quality of surface water water standard to be met conventional water treatment direct- and inline filtration treatment direct-microfiltration treatment reverse-osmosis treatment

Water Treatment Plant for Surface Water (2 of 9) Conventional Water Treatment used for surface waters with : high turbidity (> 20 NTU) high colour (> 20 cu) high Total Organic Carbon (TOC > 4 mg/L) process : coagulation flocculation sedimentation granular media filtration disinfection advantages : good operational flexibility hydraulically stable low operator attention disadvantage : low surface loading rates → large process surface area requirements consider land availability

Water Treatment Plant for Surface Water (3 of 9) Conventional Water Treatment (cont)

Water Treatment Plant for Surface Water (4 of 9) Direct- and Inline Filtration Treatment used for higher quality surface waters with : low turbidity (< 15 NTU) moderate to low colour (< 20 cu) low Total Organic Carbon (TOC < 4 mg/L) process : flash mixing flocculation granular media filtration (often coarse deep bed monomedia filters) disinfection Inline Filtration same as direct filtration except flocculation occurs in pipe (not in flocculation basin) used for excellent quality surface waters with : very low turbidity (< 5 NTU) low colour (< 10 cu)

Water Treatment Plant for Surface Water (5 of 9) Direct- and Inline Filtration Treatment (cont)

Water Treatment Plant for Surface Water (6 of 9) Direct-microfiltration Treatment used for good quality surface waters with : low turbidity (< 10 NTU) moderate to low colour (< 10 cu) low Total Organic Carbon (TOC < 4 mg/L) process : screening system cartridge filters or microscreens (and maybe coarse screens) microfiltration membranes configured in modules disinfection advantage : plant may be readily automated good for small or isolated sites

Water Treatment Plant for Surface Water (7 of 9) Direct-microfiltration Treatment (cont)

Water Treatment Plant for Surface Water (8 of 9) Reverse-osmosis treatment used for desalination of seawater (35 g/L) brackish water (0.5 – 30 g/L) specific contaminant removal e.g. natural organic matter (NOM) from surface water colour from groundwater process : screening system cartridge filters or microscreens reverse osmosis (RO) membranes disinfection

Water Treatment Plant for Surface Water (9 of 9) Reverse-osmosis treatment (cont)

Water Treatment Plant for Groundwater (1 of 9) Alternative water treatment trains may be used depends on : quality of groundwater water standard to be met conventional lime-softening treatment membrane water softening gas removal treatment iron and manganese treatment

Water Treatment Plant for Groundwater (2 of 9) Conventional Lime-softening Treatment used to remove hardness from groundwater hard water has total hardness > 150 mg/L hardness is total of carbonate and noncarbonate hardness high mineral content due to calcium (Ca2+) and magnesium (Mg2+) process : when hardness is mainly calcium (magnesium < 40 mg/L) lime (and/or soda ash) is added (single stage process) soda ash removes noncarbonate hardness coagulation/flocculation/sedimentation may occur in single basin

Water Treatment Plant for Groundwater (3 of 9) Conventional Lime-softening Treatment (cont)

Water Treatment Plant for Groundwater (4 of 9) Membrane Water Softening used to remove hardness from groundwater colour total organic carbon (TOC) disinfection by-products (DBP) process : nanofiltration (more common) membranes configured in modules removes divalent ions may be automated good for small, remote plants reverse osmosis removes monovalent ions disadvantage : disposal of concentrated waste stream

Water Treatment Plant for Groundwater (5 of 9) Membrane Water Softening (5)

Water Treatment Plant for Groundwater (6 of 9) Gas Removal Treatment (aka air stripping) used for groundwaters with : undesirable gases hydrogen sulphide volatile organic compounds (VOC) concentrations above maximum contaminant level (MCL) process : stripping tower pressurised granular media filtration disinfection disadvantage : must consider (and treat) off-gas from stripping tower

Water Treatment Plant for Groundwater (7 of 9) Gas Removal Treatment (cont)

Water Treatment Plant for Groundwater (8 of 9) Iron and Manganese Treatment used for groundwaters containing inorganic iron and magnesium process : oxidation oxidants used : chlorine (when iron < 2 mg/L, little manganese) potassium permanganate (when iron and manganese are present) oxygen (effective with iron) ozone precipitation on pressure filters disinfection

Water Treatment Plant for Groundwater (9 of 9) Iron and Manganese Treatment (cont)

Treatment Processes for Residual Management (1 of 2)

Treatment Processes for Residual Management (2 of 2)

References MWH, 2005, Water Treatment Principles and Design, 2nd ed., John Wiley and Sons, New York (TD430 .W375 2005), pages 221 - 285