1. The recommended time-weighted average air concentration for occupational exposure to water-soluble hexavalent chromium (chromium VI) is 0.05 mg/m³. This concentration is based on an assumption that the individuals is generally healthy and is exposed for 8 hours per day over a working life time (that is from age 18 to 65 years). Assuming the working day is 50 weeks per year and 5 days per week. Also assuming a body weight of 70 kg and an inhalation rate of 20 m³/day over the working life of the individual. 1-1. what is the lifetime (70 yr) CDI?

Please choose the correct answer: 1. In water cycle, ______ brings H2O from water in a lake to vapor at atmosphere. A. evaporation; B. evapotranspiration; C. precipitation;            D. infiltration 2. A drinking water well in NJ is seriously polluted due to saltwater intrusion. The major pollutant is _____. A. Oxygen demanding materials;     B.salts;           C. nutrients;                  D. toxic heavy metals 3. The real reason to cause saltwater intrusion is the different of _____ between freshwater and seawater. A. density;             B. temperature;   C. velocity;     D. all of the above 4. Which of the following represents a non-point pollution source? A. Leaking underground gas tanks;  B. CSO; C. urban runoff;            D. an outlet of untreated industrial wastewater into a river

vated sludge. 12.61 A step-aeration activated-sludge system at a loading of 40 lb of BOD/1000 ft³/day requires an air supply of 1200 ft/lb of BOD applied to maintain an adequate dissolved-oxygen level. The measured average oxygen utilization of the mixed liquor is 36 mg/1/hr. Calculate the oxygen transfer efficiency. (Assume 0.0174 lb of oxygen per cubic foot of air, which is the amount at 20°C and 760 mm pressure.) 12.62 An air sunnly

Total suspended particulate matter concentration in ambient air is to be measured using a high- volume sampler. The filter used for this purpose had an initial dry weight of 9.787 g. The filter was mounted in the sampler and the initial air flow rate through the filter was set at 1.5 m³/min. Sampling continued for 24 hours. The airflow after 24 hours was measured to be 1.4 m³/min. The dry weight of the filter paper after 24 hours sampling was 10.283 g. Assuming a linear decline in the air flow rate during sampling, what is the 24 hour average TSP concentration in the ambient air(in 10-6 g/m³?

A factory is discharging its wastewater into a slowly moving stream that has a mean velocity of 3 cm/s. The flow rate of the stream is 4 times as that of the wastewater. The ultimate BOD of stream and wastewater are 5 mg/L and 105 mg/L, respectively. And DO of the stream and wastewater are 6 mg/L and 1 mg/L, respectively. The temperatures of the stream and wastewater are 15oC. The deoxygenation rate at 15oC is 0.48 day-1, and the re-aeration rate at 15oC is 0.72 day-1.                   Draw a DO sag curve to show your clients using Microsoft Excel. Please insert your DO sag curve into your project report (30 points); Based on your DO sag curve, find the location of and travel time to the critical point, and determine the minimum D A type of local fish requires the minimum DO in the river above 2 mg/L. Please evaluate whether the actual minimum DO is acceptable. If not, please qualitatively and quantitatively select appropriate management strategies to allow water quality to reach…

In a BOD test, 5 ml of wastewater (with no dissolved oxygen) is diluted with 295 ml of water containing 8.5 mg/1 of dissolved oxygen. After 5 days incubation at 25°C, the dissolved oxygen content of the mixture is 5 mg/1. Temperature coefficient can be taken as 1.047 and BOD rate constant is 0.23 per day (base e) at 20°C. The ultimate biochemical oxygen demand of the wastewater is

14. Bench scale aeration test was performed on a sample of water evaluated for air stripping to remove VOCs. The target VOC is present in the water sample before aeration at 890 µg/L. The test data is given in the below table. Determine the order of the reaction. Show your work. Elapsed time of aeration (s) 15 30 45 65 90 120 Target VOC Effluent concentration (µg/L) 397 191 104 53 12 3