Lecture 7 Introduction to Environmental Engineering

M.B. with Multiple Materials Multiple compounds into and out of our “black box” Remember: you must have strong fundamentals and organizational skills to keep track of all components

M.B. with Multiple Materials Great Examples in this section Allegheny and Monongahela Rivers form the Ohio River in Pittsburgh, PA Allegheny, 340 cfs, 250 mg/L Monongahela, 460 cfs, 1500 mg/L Ohio River, ?, ?

M.B. with Multiple Materials Accum. = In – Out + Prod. – Consum. 0 = [(340 cfs)(250 mg/L) + (460 cfs)(1500 mg/L)] – (800 cfs)(C) C = 969 mg/L

M.B. with Multiple Materials Sometimes the “black box” Is an actual box, like a rectangular reactor in WWTP’s or WTP Is a theoretical representation of space, like the “box model” in air pollution –Width, length, and a theoretical mixing depth over a city –Wind blows through mixing with the pollutants –Example 3.7 is a good example of SO2 pollution of the air –Donora, PA, 27 deaths, “Donora Episode”

Materials Separator Goal To split a mixed feed material into the individual components by exploiting some difference in the material properties Example: clarifiers in wastewater treatment

Materials Separator Recovery and Purity x o y o x 2 y 2 x 1 y

Materials Separator Recovery and Purity If R x and R y equal 100%, then the separator is perfect Purity We want to make sure only a small portion of y 1 is ending up in product stream 1

Materials Separator Example 3.9 – Sedimentation Q i =40m 3 /hr, C i = 5000 mg/L Q o =30m 3 /hr, C o = 25 mg/L Q u =?, C u = ?

Materials Separator Qu = 40 m 3 /hr –30 m 3 /hr = 10 m 3 /hr 0 = C i Q i – (C u Q u + Q o C o ) + 0 – 0 0 = (5000 mg/L)(40 m 3 /hr) – [(C u (10 m 3 /hr)+ (30 m 3 /hr)(25 mg/L) C u = 19,900 mg/L

Materials Separator In some situations, purity and recovery will not give you the information you need to choose between two alternatives Worrell-Stessel Effectiveness Rietema Effectiveness

Complex Processes with Multiple Materials Most Env. Eng. Processes involve a series of unit operations, with different individual functions M.B.’s can solve internal processes M.B.’s can help determine the order of unit processes

Complex Processes with Multiple Materials General Rules for process train Placement 1.Decide what material property to exploit, this becomes the code. 2.Decide how the code is to activate the switch. 3.Try to separate easiest materials first. 4.Try to separate the highest quantity material first. 5.If possible do not add anything to promote separation.

Complex Processes Activated Sludge System Waste Activated Sludge Anaerobic Digestion Volatile Solids Digested sludge Secondary digester Supernatant Gases