Introduction To Water Treatment PDF

**INTRODUCTION TO WATER TREATMENT** **REASONS FOR WATER TREATMENT** - Two main reason (1. remove contaminants harmful to health and 2. remove contaminants that affect the waters' look, taste, or smell bad) - ***Aesthetics*** - pleasant in appearance, color, and taste - ***Turbidity...

**INTRODUCTION TO WATER TREATMENT** **REASONS FOR WATER TREATMENT** - Two main reason (1. remove contaminants harmful to health and 2. remove contaminants that affect the waters' look, taste, or smell bad) - ***Aesthetics*** - pleasant in appearance, color, and taste - ***Turbidity*** - caused by the presence of suspended matter, results in scattering and absorpotion of light rays - ***Hydrogen Sulfide Gas***- from bacterial anaerobic decay. Strong rotten egg odor - ***Hardness*** - caused primarily by calcium and manganese ions - ***Acute***- rapid with low levels of exposures - ***Chronic*** - prolonged and repeated exposures - ***Disinfection by products***- formed by the reaction of disinfectant with contaminants in water **MOST COMMON CONTAMINANTS** - ***Giardia*** -- excreted by animals (6-18 micrometers) - ***Cryptosporidium*** -- " (4-6 micrometers) - ***Total Trihalomethanes (TTHM)*** -- formed when natural organic substances from decaying vegetation and soil react with chlorine - ***HAA5 (five Haloacetic Acids)*** **BASIC WATER TREATMENT UNIT PROCESSES** Biological Activated Carbon -- biological process removes contaminants from potable water - ***Oxidation*** -- add oxy, removes hydrogen -removal of inorganic contaminants (***iron, manganese, and arsenic***) -prior to other process to improve the removal of inorganics, particulates, taste or odor \- most commonly used oxidants (**chlorine and potassium permanganate**) \- chlorine is supplied in gas,solid, and liquid form \- potassium permanganate is supplied as a fine granular solid material that is dissolved in water \- in operation, **free chlorine** is used \- oxidants are injected as gas or liquid \- the speed or reaction time depends on pH, type of oxidant, contaminants, and water temp -**lower pH or temp = slow oxidation** \- rate slowed/demand increased by the presence of iron/manganese -used of chlorine as oxidants can formed a disinfection byproducts (TTH or total\ trihalomethane or HAA5 or Haloacetic acids (5) \- ammonia = chloramines - a much weaker oxidant and slow oxidation \- the proper amount of oxidant is visible in slight pink - ***Coagulation*** -- destabilization or decreasing the stability of colloids in water \- results from adding salts in iron, aluminum, or cationic polymer \- colloidal material (**hydrophobic** - water fearing, **hydrophilic** - water loving and common source of color in water) \- organic material that will pass through a 0.45 micrometer membrane filter can be dissolved ( **humic and fulvic** acids which causes water color) \- organic carbon - comes from plant/animal sources \- **Total Organic Carbon (TOC)** - both larger and smaller than 0.45 micrometers \- **Dissolved Organic Carbon (DOC)** - fraction of organic material smaller than 0.45 micro \- opposing forces\ \> **Stability factors**- help to keep colloids dispersed \> **Instability factors** - contribute to natural removal of colloids \- **Polymer** is high molecular weight that forms ions when dissolved in water (polyelectrolytes) \> primary coagulant and is long sting-like chain molecules \> Polymeric - small molecules \> **Cationic Polymers** - positive charged polymeric \> **Anionic Polymers** - negative charged polymeric \> **Nonionic Polymers** - no charge \- Common coagulants (**aluminum sulfate, sodium aluminate, ferric sulfate, ferrous sulfate, ferric chloride, Polyaluminum chloride, cationic polymers**) \- **simplest coagulation process** (Alum placed in water then chemical reaction occurs which produces positive charged ions and it will attached to the negative charged colloid then the overall result in reduction of negative surface charge and subsequent formation of agglomerate) \- 4 factors that influence the coagulation is **pH, turbidity, temperature & alkalinity** \- **Alkalinity** - waters ability to neutralize an acid \- Metal salts must be thoroughly dispresed into the stream within 1-2 seconds for effective treatment \- Most common type of flash mixers \> **Pump Diffusion systems** - uses jets to inject coagulant into raw water stream \- produces no additional headloss \- additional electric power consumption and maintenance \> **Inline static** - No electric power and very little maintenance \- mixing efficiency varies with flow rate and headloss can be 2 ft or more \- appropriate detention times are required for completion before water is filtered or additional chemicals (**10-20 mins**) and detention occurs in piping, reaction vessels and in the head space in the filter \- **Gang mixer or jar test apparatus** is used to determine correct chemical dosage (6 mixers connected together and 6 one-liter beakers) \- Samples of the water and various dosages of coagulants are added to the jars, the jars then is stirred to duplicate the flash mix then slowly -proper dosage is determined by observing best performing **floc** (small gelatinous masses formed liquid by coagulant + thereto) , pH and turbidity settled/ filtered - Disinfection - control pathogenic organisms - Flocculation -- gentle stirring either mechanical or hydraulic means - Sedimentation - removal of solid particles from water by settling induced by gravity - Adsorption - gathering a gas or dissolved substance onto the surface of a solid - Precipitate - substance in a liquid phase fall or passes out into a solid form