مقاله قسمت 4(Volatile Solids Removal and Pathogens)
Results and Discussion
Kinetics
The rate of degradation of the sludge during the endogenous respiration has been widely
accepted to be a first order function of the concentration of the biodegradable biomass present,
known as biodegradable volatile suspended solids [14, 15]:
( ) k(bVSS)
dt
d bVSS = - (1)
Where
bVSS : biodegradable VSS remaining after batch aeration time (g/l)
k : digestion rate constant (day-1)
t : aeration time (day)
Eqn. 1. after integration takes the following form:
exp( )
0
kt
VSS nbVSS
VSSt nbVSS = -
-
-
(2)
Where nbVSS is non-biodegradable VSS and subscript “0” interprets initial concentration of
the variable VSS. The profiles of VSS concentrations during the course of the experiments
(aeration at 60 ºC) at various sludge initial concentrations are plotted in Fig.2. Each curve
finally ends in a horizontal line that represents the amount of nbVSS of the relevant sludge
sample. This amount will not be changed by aeration further with time. After 10 days of
thermophilic digestion, 16.5, 17.0, and 16.5 % of the initial VSSs will remain for three sludge
samples having initial TS of 60, 30, and 10 g/l respectively. Fig. 2 shows that during the last
days of the process, curves become horizontal and get almost parallel to each other. Therefore,
a fixed amount of 15% of initial VSS was assumed to be the amount of nbVSS part of the
sludge in the present work. Initial TS of 10 and 60 g/l were used to find the reaction constants
at different temperatures. Fig. 3 gives the results of the kinetic study in terms of the digestion
rate constant at temperatures ranging from 10 to 80 ºC (using Eqn.2). Highest kinetic rate
constants were observed at a temperature range of 55-60 ºC and had values between 0.40 to
0.45 d-1. The sludge with the highest concentration of TS (60 g/l), as Bhargava and Datar [15]
predicted, demonstrated a little lower constant at thermophilic conditions; however, as it has
been believed generally k is a strict function of temperature. As Fig. 3 shows, rate constants (k)
at temperatures between 55 to 60 ºC are close to each other and an average equal to 0.42 d-1
can be taken for this range. The kinetic rate constant, k, for endogenous decay which was
observed to increase with digestion temperature, follows an Arrhenius relationship k(T)=k20ºC .
θ(T – 20) , with θ varying from 1.02 to 1.07 in the mesophilic range. Matsch and Drnevich [16,
17]) showed this relationship to be applicable in the thermophilic range also. However, a value
of 1.04 for θ provides the least error from the kinetic rates below 55 ºC presented in this work
Kinetics
The rate of degradation of the sludge during the endogenous respiration has been widely
accepted to be a first order function of the concentration of the biodegradable biomass present,
known as biodegradable volatile suspended solids [14, 15]:
( ) k(bVSS)
dt
d bVSS = - (1)
Where
bVSS : biodegradable VSS remaining after batch aeration time (g/l)
k : digestion rate constant (day-1)
t : aeration time (day)
Eqn. 1. after integration takes the following form:
exp( )
0
kt
VSS nbVSS
VSSt nbVSS = -
-
-
(2)
Where nbVSS is non-biodegradable VSS and subscript “0” interprets initial concentration of
the variable VSS. The profiles of VSS concentrations during the course of the experiments
(aeration at 60 ºC) at various sludge initial concentrations are plotted in Fig.2. Each curve
finally ends in a horizontal line that represents the amount of nbVSS of the relevant sludge
sample. This amount will not be changed by aeration further with time. After 10 days of
thermophilic digestion, 16.5, 17.0, and 16.5 % of the initial VSSs will remain for three sludge
samples having initial TS of 60, 30, and 10 g/l respectively. Fig. 2 shows that during the last
days of the process, curves become horizontal and get almost parallel to each other. Therefore,
a fixed amount of 15% of initial VSS was assumed to be the amount of nbVSS part of the
sludge in the present work. Initial TS of 10 and 60 g/l were used to find the reaction constants
at different temperatures. Fig. 3 gives the results of the kinetic study in terms of the digestion
rate constant at temperatures ranging from 10 to 80 ºC (using Eqn.2). Highest kinetic rate
constants were observed at a temperature range of 55-60 ºC and had values between 0.40 to
0.45 d-1. The sludge with the highest concentration of TS (60 g/l), as Bhargava and Datar [15]
predicted, demonstrated a little lower constant at thermophilic conditions; however, as it has
been believed generally k is a strict function of temperature. As Fig. 3 shows, rate constants (k)
at temperatures between 55 to 60 ºC are close to each other and an average equal to 0.42 d-1
can be taken for this range. The kinetic rate constant, k, for endogenous decay which was
observed to increase with digestion temperature, follows an Arrhenius relationship k(T)=k20ºC .
θ(T – 20) , with θ varying from 1.02 to 1.07 in the mesophilic range. Matsch and Drnevich [16,
17]) showed this relationship to be applicable in the thermophilic range also. However, a value
of 1.04 for θ provides the least error from the kinetic rates below 55 ºC presented in this work
+ نوشته شده در دوشنبه 30 آذر1388ساعت 13:6 توسط مجتبی(مدیر وبلاگ)
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