1 Chapter 2 Environmental Measurements 2 1 a During drinking water treatment 17 lb of chlorine Cl are added daily to disinfect 5 million gallons of water What is the aqueous concentration of chlorine in mg L b The chlorine demand is the concentration of chlorine used during disinfection The chlorine residual is the concentration of chlorine that remains after treatment so the water maintains its disinfecting power in the distribution system If the residual concentration is 0 20 mg L what is the chlorine demand in mg L Solution a 17 lb chlorine added to 5 million gallons of water Chlorine dosage in mg L 17 lb day 454 g 1000 mg 1 gal 0 41 mg L 6 5 10 gal day 1 lb 1g 3 78 L b Chlorine demand 0 41 mg L 0 20 mg L 0 21 mg L 2 2 2 A water sample contains 10 mg NO3 L What is the concentration in a ppmm b moles L c mg NO3 N L and d ppbm Solution 10 g NO3 L in various units a 1 L water 1 kg water in water mg L ppm 10 mg L 10 ppm as NO3 1 kg L b 62 grams NO3 1 mole NO310 mg 1g 1 mole 1 6 10 4 moles NO3 L L 1 000 mg 62 g c 62 grams NO3 1 mole NO3 14 grams N 1 mole N 1 mole NO3 1 mole N 10 mg NO3 1 mole NO3 1 mole N 14 g N 2 3 mg NO3 N L L 62 g NO3 1 mole NO3 1 mole N d 1 L water 1 kg water 1 kg 106 mg 1 billion 103 million 10 mg L 1000 million 10 000 ppb as NO3 1 kg L 1 billion 3 2 3 A liquid sample has a concentration of iron Fe of 5 6 mg L The density of the liquid is 2 000 g L What is the Fe concentration in ppmm Solution 2000 g 2 kg 5 6 mg L 2 8 ppm 2 0 kg L 4 2 4 Coliform bacteria for example E coli are excreted in large numbers in human and animal feces Water that meets a standard of less than one coliform per 100 mL is considered safe for human consumption Is a 1 L water sample that contains 9 coliforms safe for human consumption Solution Standard requires 1 coliform 100 mL or 10 coliform 1 L L 9 coliforms 0 9 coliforms 100 mL L 10 coliforms 100 mL This value is 1 coliform 100 mL therefore water is safe 5 2 5 The treated effluent from a domestic wastewater treatment plant contains ammonia NH3 at 9 0 mg N L and nitrite NO2 at 0 5 mg N L Convert these concentrations to mg NH3 L and mg NO2 L Solution 17 g NH3 1 mole NH3 46 g NO2 1 mole NO21 mole N 1 mole NH3 1 mole NO29 0 mg NH 3 N 1 mole N 1 mole NH 3 17 g NH 3 10 9 mg NH 3 L L 14 g N 1 mole N 1 mole NH 3 0 5 mg NO 2 N 1 mole N 1 mole NO 2 46 g NO 2 1 6 mg NO 2 L L 14 g N 1 mole N 1 mole NO 2 6 2 6 Nitrate concentrations exceeding 44 3 mg NO3 L are a concern in drinking water due to the infant disease methemoglobinemia Nitrate concentrations near three rural wells were reported as 0 01 mg NO3 N L 1 3 mg NO3 N L and 20 0 mg NO3 N L Do any of these three wells exceed the 44 3 ppmm level Solution Convert the regulatory value to units of as N Then compare to the measured concentrations 44 3 mg NO3 1 mole NO3 1 mole N 14 0 g N 10 0 mg NO3 N L L 62 0 g NO3 1 mole NO3 1 mole N The third well 20 0 mg NO3 N L exceeds the 10 ppm level 7 2 7 Mirex MW 540 is a fully chlorinated organic pesticide that was manufactured to control fire ants Due to its structure mirex is very unreactive thus it persists in the environment Lake Erie water samples have had mirex measured as high as 0 002 g L and lake trout samples with 0 002 g g a In the water samples what is the aqueous concentration of mirex in units of i ppbm ii pptm iii M b In the fish samples what is the concentration of mirex in fish in i ppmm ii ppbm Solution a i 0 002 g 1 mg 1 L 1000 million 0 002 ppb 1000 g 1 kg 1 billion L ii 0 002 g 1 mg 1 L 1 000 000 million 2 ppt 1000 g 1 kg L trillion iii 0 002 g 1 mole 3 7 10 6 M 540 g L b i 0 002 g 0 002 ppm g ii In solids ppb g kg 0 002 g 1000 million 2 ppb 1 billion g 8 2 8 Chlorophenols impart unpleasant taste and odor to drinking water at concentrations as low as 5 mg m3 They are formed when the chlorine disinfection process is applied to phenolcontaining waters What is the unpleasant taste and odor threshold in units of a mg L b g L c ppmm d ppbm Solution a in mg L 5 mg 1 m3 5 10 3 mg L 3 m 1000 L b in g L 5 mg 1 m3 1000 g 5 g L m3 1000 L 1 mg c in water mg L ppm 5 mg 1 m3 1L 5 10 3 ppm 3 1000 L 1 kg m d in water g L ppb 5 mg 1 m3 1 L 1000 million 5 ppb 3 1000 L 1 kg 1 billion m 9 2 9 The concentration of monochloroacetic acid in rain water collected in Zurich was 7 8 nanomoles L Given that the formula for monochloroacetic acid is CH2C1COOH calculate the concentration in g L Solution The molecular weight of monochloroacetic acid equals 94 5 g mole 7 8 nmoles 94 5 ng 1 g 0 74 g L L 1 nmole 1000 ng 10 2 10 Assume that concentrations of Pb Cu and Mn in rainwater collected in Minneapolis were found to be 9 5 2 0 and 8 6 g L respectively Express these concentrations as nmole L given that the atomic weights are 207 63 5 and 55 respectively Solution 9 5 g Pb 1 mole 1000 nmole 45 9 nmole L L 207 g Pb 1 mole 2 0 g Cu 1 mole 1000 nmole 31 5 nmole L L 63 5 g Cu 1 mole 8 6 g Mn 1 mole 1000 nmole 156 4 nmole L L 55 g Mn 1 mole 11 2 11 The dissolved oxygen DO concentration is measured as 0 5 mg L in the anoxic zone and 8 mg L near the …
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