River |POLVER05_0 d(DEOX)/d(T) = -k*La*exp(-k*(T)) #Deoxygenation d(D)/d(T) = k*La*exp(-k*(T))-r*(Cs-(C)) #Oxygen deficit [mg/L] d(C)/d(T) = r*(Cs-(C))-k*La*exp(-k*(T)) #Oxygen concentration [mg/L] d(REOX)/d(T) = r*(Cs-(C)) #Reoxygenation k20 = 0.3 #First order BOD degradation rate coefficient at 20 deg. C [1/d] r20 = 0.6 #Atmospheric oxygen dissolution rate coefficient at 20 deg C. [1/d] Cs = 14.126*exp(-0.0202*Temp) #Oxygen saturation concentration [mg/L] f = r/k # Qr = 20000 #River Flow rate [m3/d] Qsw = 1000 #Sewage (wastewater) flow rate [m3/d] Lr = 5 #Unpolluted river ultimate BOD [mg/L] Lsw = 300 #Raw sewage ultimate BOD [mg/L] Cr = 6.5 #Unpolluted river oxygen concentration [mg/L] Csw = 0 #Raw sewage oxygen concentration [mg/L] La = (Qr*Lr+Qsw*Lsw)/(Qr+Qsw) #Dilution point ultimate BOD [mg/L] Ca = (Qr*Cr+Qsw*Csw)/(Qr+Qsw) #Dilution point oxygen concentration [mg/L] Da = Cs-Ca #Dilution point initial oxygen deficit[mg/L] tcr = 1/k/(f-1)*ln(f*(1-(f-1)*Da/La)) #Critical time [d] Dcr = La*(exp(-k*tcr))/f #Critical oxygen deficit [mg/L] Ccr = Cs-Dcr #Critical oxygen concentration [mg/L] k = k20*1.047^(Temp-20) #First order BOD degradation rate coefficient [1/d] r = r20*1.024^(Temp-20) #Atmospheric oxygen dissolution rate coefficient [1/d] Temp = 40 # T(0)=0 DEOX(0)=6.667 D(0)=3.333 C(0)=6.667 REOX(0)=6.667 T(f)=20