Environmental Engineering Dr Jawad Al-rifai Lecture no. Reactor Philadelphia University Faculty of Engineering Department of Civil Engineering

Definition: The tanks in which physical, chemical and biochemical. Ex Water softening & Wastewater treatment

Reactor Types 1- Batch reactor Fill & draw types; materials are added to the tank, mixed for sufficient time to allow reaction to occur and then drained. Ex. Laboratory experiment. – Size < 150m 3 /d – Inexpensive – Easy to operate & build – No influent or effluent –step increase or pulse; Mass balance C t /C o =e- kt C o : concentration at time zero C t : concentration at time t K: rate of reaction T: time

Continuous flow stirred tank reactor (CSTR) (Completely mixed flow reactor (CMFR)) Material flows into, through and out of the reactor at all times uniform throughout the tank Ex rapid mix or flash mix tank for Water treatment, wastewater treatment Ex natural system; lake, mixing of two streams, air in the room Water flow > 150m 3 /d The composition of the effluent is the same as the composition in the tank Mass balance express as Q in = Q out at no reaction

C t =C o exp (-t/t o )

Plug flow reactors (PFR) Fluid particles pass through the tank in sequence. Those that inter first leave first. Assuming no mixing occur in the lateral direction. As long as the flow conditions remain steady, the composition of the effluent remains constant. Ex. Pipes, long narrow rivers, biological treatment in WWTp MB eq: In (C out /C in )=-K L/U= -k V/Q L: length of plug-flow segment u: Linear velocity, m/s