Chapter 2 PP2.pdf

Water Treatment Foundations WWWT 1120 Section 2.3 Reservoirs  Water Demand As population increases so does the need for water Local water sources may not be able to meet increased demands This Photo by Unknown Author is licensed under CC BY-SA-NC  Wa...

Water Treatment Foundations WWWT 1120 Section 2.3 Reservoirs  Water Demand As population increases so does the need for water Local water sources may not be able to meet increased demands This Photo by Unknown Author is licensed under CC BY-SA-NC  Water Demand  To make up for any shortfall water is diverted.  Reservoirs and dams are constructed to hold the diverted water.  Primary use as a water supply for domestic potable water.  Reservoir Uses Secondary uses include:  Flood control  Hydroelectric power  Regulating downstream releases  Recreation  Agriculture  Municipal water  Industry  Manmade Factors Affecting Water Quality Include:  Acid rain  Wastewater  Agricultural run off  Livestock grazing  Mining  Urban runoff  Industry Discharges Reservoir Contamination Leads to decreased:  Physical water quality  Chemical water quality  Biological water quality  Reservoir Quality Natural factors affecting water quality are:  Climate  Watershed & drainage areas  Wild fires  Reservoir construction  Water Shed Conditions Major portion of surface runoff into a reservoir occurs during a very short periods of time Following a storm Spring run off These condition can increase, possibly in a very short amount of time, turbidity = shorten filter times, high chlorine demand, nutrient loading = Algae blooms, and organic loading = THM’S depending on the landscape within the water shed.  Stratification In a reservoir or lake, layers can form that act as barriers to water mixing. These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers.  Thermal Stratification The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water's density with temperature  Lake Stratification http://moodlehubpreview.remc.org/pluginfile.php/8406/mod_page/content/1/DZ_L3ActB_water-temp-graphic-web.jpg  Thermal Stratification Cold water is denser than warm water and the top of the lake generally consists of water that is not as dense as the water in the bottom layer. However, the temperature of maximum density for freshwater is 4 °C.  Thermal Stratification In temperate regions where lake water warms up and cools through the seasons, a cyclical pattern of overturn occurs that is repeated from year to year as the cold dense water at the top of the lake sinks.  Thermal Stratification  Upper layer: Epilimnion = mixing  Middle layer: Metalimnion = rapid temperature change with depth  Lowest layer Hypolimnion = denser water  Thermal Stratification Upper layer = Epilimnion = mixing Middle layer = Metalimnion = rapid temperature change with depth Lowest layer = Hypolimnion = denser water Water Treatment  Thermal Stratification  Once lake turn over has occurred, major changes in water quality begin to take place.  Biochemical oxygen demand may lead to total dissolved oxygen depletion.  Resulting in anaerobic conditions Thermal Stratification Smmr.c! r Fall 1LIT1iK.IY!H'  Nutrients Many problems in domestic water supplies occur in waters containing moderate or large quantities of nutrients.  Nutrients Types of are: Cause:  Phosphate  Act as a fertilizer  Nitrate  Stimulating algae  Organic growth nitrogen compounds  Nutrients There are three types of nutrient classifications for lakes and reservoirs:  Eutrophic  Oligotrophic  Mesotrophic  Eutrophic Rich in nutrients Able to support large amounts of:  Aquatic vegetation  Aquatic creatures  Oligotrophic Poor in nutrients Supports:  Little vegetation  Few aquatic creatures  Mesotrophic Moderate nutrients levels Supports moderate levels of:  Plant life  Animal life  Littoral Zone  Shallow water  Abundant vegetation  Bank of rivers or lakes  Productive Water Bodies Support large populations of:  Phytoplankton  Zooplankton  Phytoplankton A sudden large increase in plankton populations is referred to as an algal blooms Size of bloom depends on:  Light  Temperature  Nutrient conditions  Algal Blooms Can contain several different algae types May last:  Several days  Several weeks  Several months  Algal Blooms Can cause:  Taste & odor problems  Shorter filter runs  Increased pH  Organic loading  Dissolved oxygen depletion  Algal Blooms Taste and Odor complaints.:  Fishy  Aromatic  Grassy  Septic  Musty  Earthy TON Profiles can help.  Odor Complaints More noticeable in hot water Areas odors are detected more often include:  Showers  Cooking  Dishwashing Chlorine can combine with organics to make the odor worse  Odors In thermal layer blooms the strongest odors are generally located in the upper layer Blooms can occur even when the reservoir is frozen over  Odors During thermal turnover the concentrated obnoxious tastes & odors are redistributed through out the whole reservoir  Algae Control Primary Purpose:  Prevent taste & odors resulting from algal blooms Secondary purposes:  Reduce biological activity  Reduce D.O. depletion  Shortened Filter Runs Clogging of filters is the second major issue with Algal blooms. Normal run time ( maximum in Alberta is 72 hours) can decrease to the point where more water is being used to backflush(water use to clean the filters) then water being produced.  pH  Algal blooms increase pH  From 7.0 to greater than 9.0  Chlorine efficiency reduced  Increased chemical costs (Alum)  pH  Increases during the day due to photosynthesis ( decrease in CO2)  Decreases at night due to respiration ( increase in CO2)  Diurnal cycle  Organic Loading Notable impacts because of algae blooms include:  Increased color  Increased chlorine demand  Increased THM’s Dissolved Oxygen Depletion  Occurs after major algal blooms  When the blooms die off bacteria feeding off dead algae use up all of the oxygen  Fish kills occur ( No DO and Algae in gills)  Consumer complaints  Anaerobic Conditions  Anaerobic = no free oxygen  Can occur after thermal stratification  Can occur in the Metalimnion or Hypolimnion  Cause water quality complaints  Anaerobic Conditions Cause:  Rotten egg odor can by Hydrogen Sulfide (H2S)  Iron or Manganese passed into solution leading to dirty looking water Neither is acceptable to consumers Questions? Please Review Check Your Understanding Page 78 and 84.