Selection of Wastewater UV Sterilizer and Calculation of Disinfection Dose and Lamp Count

Regardless of the choice of drinking water UV sterilizer, sewage UV sterilizer, or UV sterilizer selection, the selection of UV sterilizer first selects the UV sterilizer power, which is to choose the power of the UV germicidal lamp, choose the power of the UV lamp. The first thing to do is calculate the UV dose. UV dose calculation is usually based on the theoretical calculation dose method and biological verification dose method. In practical applications, the two methods need to be used in combination. No matter whether the drinking water UV sterilizer, the sewage UV sterilizer, or the water reuse UV sterilizer must be simultaneously Meet the standard requirements of the theoretical calculation dose method and biometric verification dose method.
1. Biological verification dose method. This method uses the biometric verification dose to determine the number of lamps. The steps are:
( 1 ) calculate the inactivation rate of microorganisms according to the requirements of the discharge standards;
( 2 ) Check the " microbial inactivation rate - UV dose " curve to determine the required UV dose;
( 3 ) Check the " Disinfection Reactor Flow Rate - UV Dose " curve to determine the amount of water handled by each UV lamp;
( 4 ) The total capacity of the UV disinfection system divided by the amount of water processed by each UV lamp to obtain the minimum number of UV lamps required for the entire system;
( 5 ) According to the requirements of modularization, the number of lamps is rounded up.
2. Calculate the dose theoretically. The United States Environmental Protection Agency described the design of the UV sterilizer system in detail in its "Urban Wastewater Disinfection Design Manual" published in 1986. The actual use of the UVDIS 3.1 software, which was released in 1992 , is widely used . The software can be used to calculate the average UV light intensity of the entire canal UV sterilizer system in the entire reactor, and then multiplied by the irradiation time received by the sewage, which is the theoretical calculation dose of the disinfection reactor.
When calculating the UV average intensity of the UV sterilizer reactor, the following parameters need to be entered: the UVC output intensity of the lamp; the arrangement of the lamps; the arc length of the lamp; the outer diameter of the quartz tube; the distance between the axes of the lamps; Tube transmittance; Quartz tube fouling coefficient; Sewage transmittance; Lamp aging coefficient and. Changes in any one parameter change the average intensity value.
In the design of sewage UV sterilizer equipment, determine the number of tubes according to the following steps:
( 1 ) Calculate the inactivation rate of microorganisms according to the import microbial concentration and emission standards of the disinfection system;
( 2 ) Check the " minimum microbial inactivation rate - UV theoretical dose calculation " curve to determine the minimum required UV theoretical dose;
( 3 ) Adopt the above technical parameters and calculation process to change the number of lamps and check the UV theoretical dose until it meets the requirements of the lowest UV theoretical dose calculation.
About the UV sterilizer lamp count calculation can refer to the following cases:
The number of ultraviolet germicidal lamps can be determined by theoretical calculations and theoretical calculations through some fixed parameters . For different fields, the following examples can be used as a reference for calculation.
1. Design requirements and related parameters of sewage UV sterilizer
Daily sewage flow : 1166m3/h
Peak sewage flow :?
CODCr: <60 mg/L
BOD5<20 mg/L
Total Solid Suspension (TSS): <20mg/L
Sewage 254 transmittance (T254): >65%
Before disinfection Number of fecal coliform: <1 × 107 th / L
The number of fecal coliform disinfection: 1 × 104 th / L
2. Calculate formula for fecal coliform residue
N=N0exp{ux[1-(1+4kE/u2)1/2)]/2E}-Np
Including : N = residual concentration of fecal coliforms after disinfection ( units /L)
N0 = fecal coliform concentration before disinfection ( units /L)
x= length of lamp (cm)
u = sewage flow rate (cm/s)
Calculated from u=x/(Vv/Q)
Vv = ultraviolet radiation area
Q = total flow
E = dispersion coefficient (cm2/s)
k = inactivation rate of fecal coliform (/s)
Np = Fecal Coliform Concentration Wrapped by Suspended Solids
Where : k=aIavgb
Np=c(SS)m
a=1.45×10-5
b=1.3
c=0.26
m=1.96 is derived from experiments, etc.
Design selected 260W UV lamp
1. Parameters and basic conditions
Lamp Model :
Power : 260W, UV maximum output : 100W
Lamp length : 157.5cm, arc length : 151.7cm
Outer quartz tube diameter : 4.0cm , UV transmittance = 90%
UV lamps arranged in a matrix in the direction of water flow
Lamp center distance : 7.5cm × 7.5cm
The energy loss factor is based on an international general rule, Fp ( lamp aging factor ) 0.7 , Ft ( quartz tube due to transmission errors caused by the calculation ) 0.7
2. Design process of sewage UV sterilizer
(1) System UV Density D
The average radiation volume of each lamp in sewage
Vv/ lamp = (S2z) - (Ï€dq2/4z)
S=7.5cm
z=157cm
Dq=4cm
Vv/ lamp = 6859cm3 (6.86 L)
UV density D
D=( ultraviolet power / lamp )/(Vv/ lamp )
D=100*0.9/6.86=13.1 W/L
2) Average UV intensity Iavg
Relationship between average UV intensity Iavg and UV density D
Corrected average UV intensity Iavg
Iavg= rated IavgFpFt
Iavg= rated Iavg×0.7×0.7
Adjusted Iavg see Table 1
Flow rate (m3) T254 (%) Rated Iavg (mw/cm2) Adjusted Iavg (w/cm2)
1166 65 23.5 11.5
(3) Deactivation rate k
Estimated by k=aIavgb
k=1.45*10-5*115001.3=2.75
(4) Determination of flow rate
N/N0=exp{[ux(1-(1+4kE/u2)1/2)]/2E}-Np
Np=0.26*201.96=92
Where: N = 10000 th / L, N0 = 107 th / L, Np = 92 th / L, k = 2.75 (/ s), x = 157 (cm), E = 100 cm2 / ss
Or -3=u*157/[2*100]*[(1-(1+4*2.75*100/u2))1/2]
That is u[1-(1+1100/u2)1/2]=-3.82
So u=150 cm/s
Residence time : t = x/u = 157/150 = 1 (s) , taking into account the reactor hydraulic characteristics and liquid distribution function, take t = 2 s
(5) Determine the number of lights
UV disinfection area volume : V=1166/3600*2=0.65 m3
Cross-section area : A=0.65/1.57=0.4 m2
Number of lamps : A/S=0.4/0.0752=71 ( root )
Based on the above analysis and calculations, the number of UV-disinfection lamps required for this UV sterilizer can be no less than 71 . Through the above example, the selection of sewage UV sterilizer and the calculation of disinfection dose and lamp count can be correctly performed.

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