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Thermophilic aerobic digestion of waste activated sludge

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Aerobic thermophilic stabilization and degradation of waste activated sludge from wastewater treatment plant was studied. The main parameter of research was the organic fraction reduction (expressed as VSS). The experimental part of the study was divided into two parts. In first, the goal was determination of the most beneficial operating temperature. Batch experiments were, performed at temperatures of 20, 37, 40, 45, 50 and 55 °C. The most beneficial temperature for aerobic digestion of waste activated sludge was found to be 50 °C. The second part of experiments studied the continuous process. Experiments were performed at 50 °C where VSS degradation was studied. It was found that VSS degradation was 29.7% at a retention time of 5 days, and 48.2% at a retention time of 10 days. A simple first order kinetic model was applied. From the batch experiments in the first part the model parameters were calculated. From the parameters calculated from the batch study, the behaviour of the continuous process was predicted. Comparison of model and experimental results showed a very good match for retention times up to 8 days. At retention times above 8 days the experimental data showed better results.
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Acta Chim. Slov. 2002, 49, 931943. 931
THERMOPHILIC AEROBIC DIGESTION OF
WASTE ACTIVATED SLUDGE
Milenko Roš, Gregor Drago Zupančič
National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia
Received 20-02-2002
Abstract
Aerobic thermophilic stabilization and degradation of waste activated sludge from
wastewater treatment plant was studied. The main parameter of research was the organic
fraction reduction (expressed as VSS). The experimental part of the study was divided into
two parts. In first, the goal was determination of the most beneficial operating temperature.
Batch experiments were, performed at temperatures of 20, 37, 40, 45, 50 and 55 °C. The
most beneficial temperature for aerobic digestion of waste activated sludge was found to be
50 °C. The second part of experiments studied the continuous process. Experiments were
performed at 50 °C where VSS degradation was studied. It was found that VSS degradation
was 29.7% at a retention time of 5 days, and 48.2% at a retention time of 10 days. A simple
first order kinetic model was applied. From the batch experiments in the first part the model
parameters were calculated. From the parameters calculated from the batch study, the
behaviour of the continuous process was predicted. Comparison of model and experimental
results showed a very good match for retention times up to 8 days. At retention times above
8 days the experimental data showed better results.
Introduction
Sludge digestion is the most common process for waste sludge treatment. The
anaerobic mesophilic process is that most widely used. Less common is the use aerobic
digestion. Generally, the anaerobic process is the subject of research, due to the biogas
evolved as a by-product of such a process. Degradation of volatile suspended solids in
the conventional mesophilic anaerobic process is about 40% at retention times between
30 an 40 days1-3. The aerobic process is generally used at smaller wastewater treatment
plant and mostly at ambient temperatures; its degradation rate is even smaller, about 30
40 % at 50 days retention time.1, 4, 5 In the thermophilic range sludge degrades at a
higher degradation rate. The aerobic digestion of biological sludge is a continuation of
the activated sludge process under endogenous conditions.6 When a culture of aerobic
heterotrophic microorganisms is placed in an environment containing a source of
organic material, the microorganisms will remove and utilize most of this material. A
fraction of the organic material removed is utilized for the synthesis of new
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
932
microorganisms, resulting in an increase of biomass. The remaining material will be
channelled into metabolic energy and oxidized to carbon dioxide, water and soluble
inert material, providing energy for both synthesis and maintenance (life support)
functions. Once the external source of organic material is exhausted, the microorganisms
will begin endogenous respiration where cellular material is oxidized to satisfy the
energy requirement for life support. If this condition is continued over an extended
period of time, the total quantity of biomass will be considerably reduced and the
remaining portion will exist at such a low energy state that it can be considered
biologically stable and suitable for disposal in the environment.
The aerobic digestion process, as stated above, consists of two steps; the direct
oxidation of biodegradable matter, and endogenous respiration where cellular material is
oxidized. These processes can be illustrated in the following equations:
42 22
organic matter NH O cellular material CO H O
+
++→ ++
23
Eq. 1
22
bacteria
cellular material O digested sludge CO H O NO
+ + + + Eq. 2
The first equation (Eq. 1) describes the oxidation of organic matter to cellular
material. This cellular material is subsequently oxidized to digested sludge. The process
described in the second equation (Eq. 2) is typical of the endogenous respiration process
and is the predominant reaction in aerobic systems. The inclusion of primary sludge in
the process can shift the overall reaction to Eq. 1, because primary sludge contains little
cellular material, so the final result may be an increase of total biomass. Therefore the
aerobic process is recommended for excess activated sludge only where longer retention
times are possible.
Using typical formula C5H7NO2 as representative of the cell mass of a
microorganism4, the stoichiometry of the aerobic process can be represented by the
following equations:
57 2 2 2 2 3
55 2CH NO O CO HO NH energy+→ + + + Eq. 3
57 2 2 2 2 3
75 3CHNO O CO H O NO H energy
−+
+→ + + ++ Eq. 4
Eq. 3 represents a system inhibiting nitrification; nitrogen appears in the form of
ammonia. A system in which nitrification occurs is represented by Eq. 4. These
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943. 933
equations indicate that theoretically 1.42 kg of oxygen is required per kg of active cell
mass in the non-nitrifying system, whereas 1.98 kg/kg is required when nitrification
occurs. The actual oxygen requirement for the aerobic digestion process depends on
factors such as the operating temperature, inclusion of primary sludge, and the solids
retention time.
The operating temperature of the aerobic digestion system is the main parameter in
the process. Because aerobic digestion is a biological process the effects of temperature
can be estimated by the following equation1, 4, 7, 8 in Figure 1:
0
0,05
0,1
0,15
0,2
0,25
0 102030405060
Temperature of liquid in aerobic digester (°C)
Reaction rate Kd (days-1)
Figure 1 – Aerobic digestion reaction rate as a function of temperature
(
)
(
)
20
20
θ
=o
T
dd
TC
KK Eq. 5
The reaction rate constant (Kd) represents the destruction rate of volatile suspended
solids during the digestion process. An increase in the reaction rate constant (Kd)
generally occurs with increase in the temperature of the system and implies an increase
in the digestion rate. Temperature coefficients (θ) ranging from 1.02 to 1.10 have been
reported, with 1.023 as the average1, 4, 7, 8. Although Figure 1 shows the function up to 60
°C its relevance is limited to the range between 10 °C and 40 °C.
The rate of biological processes generally increases with temperature (Figure 1).
Hartmann9 found a maximum volatile solids destruction rate at 30 °C, with a reduction
in rate at higher temperatures. This is in contrast with the data in Figure 1, and indicates
the importance of obtaining data applicable to the particular sludge with the system
operating at higher temperature, which is also the topic of this paper.
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
934
Another concern in aerobic digestion is aeration. When the COD loads are much
higher than in the conventional activated sludge process, aeration must be very
intensive. Another problem appears when digestion is moved to the thermophilic range.
For effective aerobic biological degradation the difference between solubility of
dissolved oxygen (DO) and the actual oxygen concentration in the reactor must be at
least 6 mg/l4, 9-11. If the difference is smaller the degradation of organic compounds
becomes slower or even partly inhibited. That is why temperatures over 50 °C are not
appropriate for aerobic treatment of waste sludge (Figure 2).
0
2
4
6
8
10
12
14
16
0 102030405060708090
Temperature (°C)
Saturated conc. of DO (mg/l)
Cs=14,6 - 0,3943 T + 0,007714 T2– 0,0000646 T3
Figure 2 – Oxygen solubility in water at normal pressure
Most aerobic digesters are operated as continuous flow, completely mixed aeration
reactors and are designed on the basis of volatile suspended solids (VSS) reduction. The
most often used model was presented by Adams11. In this model it is assumed that the
loss of degradable volatile solids (only a fraction of total VSS) through endogenous
respiration follows the first order relationship:

=⋅


d
dd
R
dX KX
dt e
Eq. 6
The continuous flow completely mixed digester is shown in Figure 3.
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943. 935
Xdi
Xde
Xde
Figure 3 – Flow chart for a completely mixed aerobic digester
The material balance expression for degradable VSS entering and leaving the
system is:


=−



rate at which
net rate of change rate at which degradable VSS
in degradable VSS degradable VSS are lost from
in digester enter the digester the digester
And in mathematical form:
  
⋅=⋅ − +


  
dd
di de
R
dX dX
VQX VQX
dt dt Eq. 7
Assuming steady state conditions, substituting (dX/dt)R from Eq. 6 and considering
that V/Q =
θ
c, the equation takes the following form:
θ
=
di de
c
dde
X
X
KX Eq. 8
Introducing relations:
=
de e n
X
XX Eq. 9
and
=
di i n
X
XX Eq. 10
and substituting for Xdi and Xde from Eq. 9 and Eq. 10, the final form of Eq. 8 is:
()
θ
=⋅−
ie
c
den
XX
KXX
Eq. 11
The terms Kd and Xn are determined for a particular sludge experimentally through
batch studies.
In the experimental work we studied aerobic thermophilic stabilization and
degradation of waste activated sludge from a wastewater treatment plant at different
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
936
temperatures (20, 37, 40, 45, 50 and 55 °C). The aim was to define the most appropriate
temperature and sludge retention time for aerobic digestion.
Experimental
Figure 4 shows a cube shaped Plexiglas aerobic reactor with pyramidal bottom
having a mixing device on top of the reactor, a temperature regulation device behind the
reactor and a dosage flask on a stand to the right of the reactor.
qq
ir inflow
S
ludge
out
f
low
S
lud
g
e in
f
low
Operating volume 18.2 l
Full volume
22.1
l
M
ixing device
Figure 4 – Aerobic reactor used for experiments.
The total volume of the reactor is 22.1, although only 18.2 l were used in practice
because of extensive foaming that appeared while operating under high loads. The
reactor inlet is on the top, and the outlet is at the side. Aeration is introduced in the
pyramidal bottom. The maximum flow rate of the air into the reactor is 550 l/h. The
reactor is heated by hot water.
The main parameters considered in the experiments were volatile suspended solids
(VSS), pH, oxygen concentration and temperature. The sample volume was 25 ml. VSS
were analysed by Standard Methods.12 For evaluation of suspended solids in the system
the following expression was used:
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943. 937
[]
[
]
[]
removal rate of all suspended solids supplied all suspended solids leaving the system
suspended solids all suspended solids supplied

=


The first series of experiments were performed in the batch mode. The goal was to
determine the best operating temperature and model parameters for Kd and for Xn. The
experiments were conducted at temperatures of 20 °C, 37 °C, 40 °C and every 5 °C until
inhibition occurred. From the data gathered the average Kd was calculated as
recommended in Metcalf and Eddy.7 Xn was determined from long term batch studies
with a 60 day retention time13, assuming that almost all of the degradable material was
consumed.
The second series of experiments were performed in the semi-continuous mode.
Retention time was set from 5 to 10 days and the results were compared to the
theoretical model.
The sludge used in the experiments was collected from a municipal wastewater
treatment plant of 200000 PE.
Results and discussion
The first series of experiments were conducted at temperatures of 20, 37, 40, 45, 50,
and 55 °C. The results are shown in Figure 5. The best VSS degradation was achieved at
50 °C (62.3% in 17 days). If the results are plotted as VSS degradation in 17 days as a
function of temperature, the relation to temperature becomes more obvious (Figure 6).
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0 102030405060
days
level of degradation
AE 20°C VSS
AE 37°C VSS
AE 45°C VSS
AE 50°C VSS
AE 55°C VSS
AE 40°C VSS
Figure 5 – Results of aerobic batch experiments
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
938
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
15 20 25 30 35 40 45 50 55 60
Temperature (oC)
degradation level of VSS
Figure 6 – Temperature dependence of aerobic degradation (cross-section of
Figure 5 at 17 days as a function of temperature)
Assuming that degradation follows the function in Eq. 6, parameter Kd can be
calculated from the results obtained and shown in Figure 5. The results are presented in
Table 1.
Table 1 – Kd of aerobic degradation at different temperatures
20 °C 37 °C 40 °C 45 °C 50 °C 55 °C
Kd (day-1) 0.038 0.066 0.062 0.084 0.125 0.116
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
15 20 25 30 35 40 45 50 55 60
temperature (°C)
Kd (days-1)
Figure 7 – Kd as a function of temperature
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943. 939
Figure 7 shows the temperature dependence of Kd. In the range between 10 °C and
40 °C it can be considered to follow an exponential function, as cited in the literature.4,
7-9 Also, the recommended values are about the same (0.04 to 0.06 day-1). At
temperatures in excess of 40 °C Kd increases rapidly to its maximum at 50 °C, which is
3 times the normal average value in the temperature range between 10 °C and 40 °C.
To fully define the model, the parameter Xn must also be determined. A study13 of
the total biodegradability of VSS in sludge showed that the degradable part of VSS
varies between 67 and 77 % of total influent VSS. The different fractions of VSS in TSS
cause variation of the total degradability. Usually the VSS content of sludge is from 75
to 85% of TSS. When the VSS content is higher then the degradable part is also higher.
Having determined all the parameters, a model for continuous digestion (Eq. 11)
with the following starting conditions can be established:
Kd =0.1318 day-1, Xn=0.23 Xi (0.77 is the degradable fraction), Xi=8.0 g/l.
The influent concentration is chosen to be the same as in all the continuous
experiments where the TSS concentration was 10 g/l and VSS was between 75 and 85%
of TSS. The results of the model are presented in Figure 8.
0
1
2
3
4
5
6
7
8
9
0 50 100 150 200 250 300 350 retention time (days)
Effluent VSS concentration
Xe (g/l)
0
10
20
30
40
50
60
70
80
90
% degradeability
Xe
% degradeability
Figure 8 – Model for continuous aerobic digestion
In the second part we conducted continuous experiments with retention times of 5,
6, 7, 8 and 10 days. The results obtained were better than expected from the model; at
lower retention times the model is quite accurate, while at higher retention times the
experiments show better degradation. The numbers are compared in Figure 9.
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
940
20
25
30
35
40
45
50
46810
retention time
(days)
% model
% experiment
Figure 9 - Degradation levels of aerobic digestion: model and experiment
Experiments were not conducted at higher retention times since the general rate of
removal had been achieved. Also, experiments could not be conducted at retention time
of under 5 days, because the problem mentioned above with aeration appeared. System
aeration was in sufficient, and the process was completely slowed down. It simply was
not possible to sustain the oxygen requirements at such high loads. The values of
dissolved oxygen were a very good indicator of process quality. If the value was above
0.5 mg/l, good process quality was assured (Figure 10)
0
0,2
0,4
0,6
0,8
1
1,2
1,4
4567891011
retention time (days)
dissolved oxygen (mg/l)
0
10
20
30
40
50
60
70
% of degradation
dissolved oxygen
% degradation
Figure 10 – dissolved oxygen and % of degradation in aerobic digestion as a
function of HRT
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943. 941
Considering the model parameters, the results showed that the influent degradable
VSS concentration had no impact on the level of degradation. The only parameters
influencing the result were the ratio of the degradable portion Xn/Xi (a lower ratio gave
better results) and of course Kd (a higher Kd gave better results). However, in the model
it is assumed that there is always enough oxygen present to sustain the process.
Experiments showed a high sensitivity to a lack of oxygen. Therefore, when dealing
with higher concentrations of sludge, more efficient aerators have to be provided,
because the operation biomass occupying the reactor volume is greater. Eventually a
limit is reached, no matter how good the aerators are, and the process is inhibited due to
lack of oxygen. Also, the effect of foaming has to be considered, which is proportional
to aeration, and at high loads and extensive aeration becomes a problem, because most
of the active biomass can be washed out. Therefore, the reactors must be closed vessels,
which is also desirable to preserve the heat necessary for the process and to prevent
evaporation of water (in open vessels 5 to 7 volume % of water had to be compensated
daily, due to evaporation).
Conclusions
The aerobic digestion of excess waste activated sludge was studied. The most
favourable temperature of digestion was established to be 50 °C in the thermophilic
range. In this range a general VSS removal rate of 40% was reached at low retention
times. At a retention time of 10 days the removal rate was 48.2%, which is more than
usually reported in conventional aerobic digestion.
A simple first order relationship kinetic model was introduced. After determining
the main model parameters in batch studies, the model was able to predict behaviour in
the continuous process. Model results and experiment matched very well at retention
times up to 8 days; above 8 days experimental data shows higher mineralization.
Although the difference increases with retention time, the practical value of the model is
in obtaining reasonably good results for aerobic digestion of various sludges just from
batch studies. The disadvantage of the model is that it does not account for the aeration
needs of such a process. Aeration has to be considered specially and carefully, because
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
942
aerobic digestion is very sensitive to lack of oxygen, especially in the thermophilic
range of temperature.
Nomenclature
HRT Hydraulic retention time
[
]
days ,
TSS Total suspended solids
[
]
mg/l ,
VSS Volatile suspended solids (organic solids)
[
]
mg/l ,



d
R
dX
dt The rate at which degradable solids are lost as a result of endogenous respiration,
VSS
mass / volume
unit time



,
Kd The decay rate constant for degradable fraction of VSS determined in a batch reactor,
-1
mass degraded VSS/unit time unit time
mass of active degradable VSS in the system

=


,
Xd The concentration of degradable VSS remaining at time t
[
]
mass volume ,
Q The volumetric flow rate
[
]
mass volume ,
Xdi The concentration of degradable VSS in influent
[
]
mass volume ,
Xde The concentration of degradable VSS in effluent
[
]
mass volume ,
V Digester volume
Xi The total VSS concentration in influent
[
]
mass volume ,
Xe The total VSS concentration in effluent,
[
]
mass volume ,
Xn The concentration of nondegradable portion of VSS that is assumed to stay inert and
constant throughout the digestion process
[
]
mass volume .
References and Notes
1. Borchardt, J. A., Sludge and its ultimate disposal. 1981, Collingwood, Michigan: Ann Arbour
Science.
2. Cook E. J., Anaerobic sludge digestion: Manual of practice No. 16. 1986, Alexandria VA: Water
pollution control federation: Task force on Sludge stabilization.
3. Gene F. Parkin, William F. Owen, Journal of Environmental Engineering, 1986, 112, 867-920.
4. Aasheim S. E., Sludge stabilization: Manual of practice No. FD-9. 1985, Washington D.C.: Water
pollution control federation: Task force on Sludge stabilization.
5. EPA, Autothermal Thermophillic Aerobic Digestion of Municipal Wastewater Sludge, 1990, Risk
Reduction Engineering Laboratory, Washington D.C.
6. Roš, M., Respirometry of Activated Sludge. 1993, Lancaster, Basel: Technomic Publishing Co., Inc.
151.
7. Metcalf and Eddy, Wastewater engineering: Treatment, disposal, and reuse, ed. G. Tchobanoglous,
1991, Boston Massachusetts: Irwin/McGraw-Hill.
8. Larry D. Benefield, C.W.R., Biological process design for wastewater treatment. 1980, Engelwood
Cliffs NJ, USA: Prentice Hall.
9. Hartman R. B., Sludge stabilizattion through aerobic digestion, Journal of Water pollution control
federation, 1979, 49 p2353.
10. Ramalho, R. S., Introduction to wastewater treatment processes. 1977, London, GB: Academic Press
Inc.
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
Acta Chim. Slov. 2002, 49, 931943.
M. Roš, G. D. Zupančič: Thermophilic aerobic digestion of waste activated sludge
943
11. Adams C. E., W. W. Eckenfelder, R. M. Stein, Modifications to aerobic digester design, Water
research, 1974. 8 p213.
12. APHA, AWWA, WEF, Standard methods for the examination of Water and wastewater. 20th edition
ed., 1998, Washington D.C.
13. Milenko Roš, Gregor Drago Zupančič. Dvostopenjska anaerobno - aerobna termofilna stabilizacija
blata. in Vodni dnevi 2001, 2001, Celje: Slovensko društvo za zaščito voda.
Povzetek
Preučevali smo aerobno termofilno stabilizacijo in razgradnjo odpadnega aktivnega blata.
Glavni parameter raziskav je bil organski delež blata (hlapne suspendirane snovi).
Eksperimentalni del raziskav je bil razdeljen na dva dela. V prvem delu je bil cilj raziskav
določiti najugodnejšo temperaturo razgradnje. Preskusi so bili šaržni, izvedeni pri
temperaturah 20, 37, 40, 45, 50 in 55 °C. Najugodnejša temperatura razgradnje je bila 50
°C. Drugi del raziskav so bili kontinuirani preskusi, ki so bili izvedeni pri temperaturi 50
°C. Preučevali smo razgradnjo organskega dela blata. Razgradnja organskega dela blata se
je gibala od 29,7% pri zadrževalnem času 5 dni, do 48,2% pri zadrževalnem času 10 dni.
Uporabili smo tudi enostavni model prvega reda za kinetiko razgradnje. Iz rezultatov
šaržnih preskusov smo izračunali parametre modela. Iz izračunanih parametrov šaržnega
preskusa smo določili obnašanje kontinuiranega procesa. Primerjava rezultatov modela in
preskusov je pokazala zelo dobro ujemanje pri zadrževalnih časih do 8 dni. Pri zadrževalnih
časih nad 8 dni so bili boljši rezultati dobljeni pri preskusih.
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The environmental aspects of municipal solid waste (MSW) is a main concern in the management of urban services. There are many approaches for the determination of different emissions in different industries and MSW is not exempted from them. Among different methods, life cycle assessment (LCA) is an environmental impact assessment that has been carried out as an action of a comprehensive method in recent years. Therein this chapter, the application of LCA technique is surveyed in MSW. For this purpose, MSW and related scenarios including incineration, landfill, anaerobic digestion, compost and recycle are investigated at the first step. Then the concept of LCA and the pertinent processes comprising goals and scopes definition, life cycle inventory, impacts of life cycle and life cycle interpretation together with application in MSW scenarios point of view, are explained. Key LCA methods including CML 2 baseline and Impact 2002+ are investigated for determination of environmental impacts in MSW. Besides, several sample studies are surveyed about LCA utilization in MSW. Hence, comparison is performed amongst MSW scenarios. Results reveal Impact 2002+ is the better method for using LCA in MSW and recycle scenario is more environmental friendly scenario among all scenarios. Generally, in this chapter, LCA of MSW and comparison of scenarios are outlined step by step.
... Current study was consistent with previous trend on the operation of aerobic digestion. Ros et al. studied aerobic degradation and stabilization of waste activated sludge under thermophilic condition in a WWTP [71]. The major measured parameters determined for reduction of organic fraction was volatile solids. ...
Article
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In this research, feasibility of using a continuous flow integrated suspended growth bioreactor (i-SGBR) pilot plant was explored to treat beverage industry wastewater. The bioreactor treatment units comprise of three sequentially arranged suspended growth bioreactors with anoxic (ANX-C), aerobic (AER-C), and aerobic digester chambers (AD-C). Clarifier (CLR) was installed as last chamber to settle sludge. Parameters such as total chemical oxygen demand (TCOD) were monitored and validated with biochemical oxygen demand (BOD5). Other parameters measured include soluble COD (sCOD), mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), total suspended solids (TSS), and pH. Transformational behavior of aerobic metabolic performance for extended aeration process was investigated by operating regimes of variable aerobic hydraulic retention time (HRT) and organic loading rate (OLR) between 20 and 30 h and 0.49–0.79 kg COD/m³ day, respectively. Solids retention time (SRT) between 20 and 40 days was operated. The aim was to generate data for bacterial growth and substrate utilization kinetics from modified Monod’s model. Removal of TCOD, BOD5, and TSS were achieved in the range of 95.2–97.9% (Influent 995 ± 21–1028 ± 25 mg/L and Effluent 21 ± 2–4.9 ± 3 mg/L), 98–98.7% (Influent 489 ± 19–507 ± 7 mg/L and Effluent 27 ± 2–41 ± 1.8 mg/L), and 91.2–94.6% (Influent 500 ± 23–653 ± 11 mg/L and Effluent 6.3 ± 7–41 ± 1.8 mg/L), respectively. The maximum substrate utilization rate (k), half velocity constant (Ks), growth yield co-efficient (Y), and decay coefficients (kd) were determined as 2.81 days⁻¹, 979 mg sCOD/L, 0.72 mg VSS/mg sCOD, and − 0.0172 day⁻¹, respectively. Maximum specific growth rate (μmax) was found as 2.03 days⁻¹. Treatment efficiencies declined with reduction of HRT and with increased OLR applied to the bioreactor. The aerobic digester (AD) achieved between 9.8% (Influent 15,021 mg/L) and 18.6% (10,893 mg/L) MLVSS reduction, where performance decreased with additional solids concentration from influent aerobic digester (IAD). i-SGBR has accomplished effective removal of pollutants and simultaneous sludge degradation of beverage industry wastewater. Kinetic parameters obtained could be useful for design and modeling of aerobic treatment unit to improve effluent quality.
... The aerobic digestion process consists of two reaction steps (Ros and Zupancic, 2002) and these equations can be illustrated as follows: ...
Chapter
Pharmaceutical compounds are used for many beneficial purposes in the modern society, but they also contaminate surrounding environment during their exposure. They may enter the environment through numerous routes e.g. treated wastewater discharge, sewage from landfills, sewer lines, runoff from animal wastes and land application of manure fertilizers. The pharmaceutical wastewater consists of high concentration of organic matter, microbial toxicants, high salt concentration and non-biodegradable compounds. Due to limited water resources, it is essential to understand and develop the methodologies for treatment of pharmaceutical wastewater. Trace amounts of suspended solids and dissolved organic matter still persist even after secondary treatment, therefore, advanced treatment is prerequisite in order to improve the quality of pharmaceutical wastewater. In this chapter, the emphasis is mostly on best available technologies to remove and recycle the pharmaceutical wastewater. Effluents arising from different sectors of active pharmaceutical ingredients (API), bulk drugs and related pharmaceutics, consuming a bulk amount of water are evaluated and the strategies are destined to recover valuable compounds upto a larger extent, and finally wastewater treatment is discussed. The complete removal of pharmaceutics from wastewater is not feasible with a single technology. The hybrid wastewater treatment appears to be the best comprising conventional treatment plans in conjunction with biological and advanced post-treatment methods. The recommendations provided in this analysis will be useful for the treatment of wastewater resulting from the pharmaceutical industry.
Chapter
Both aerobic and anaerobic digestion processes are being used in new designs for treating biological sludges; there are advantages and disadvantages to both systems. Before a specific choice can be made, waste characteristics, general climatic conditions, type of sludge handling equipment, and the capacity of the facility must be considered. In a large facility, it may be feasible or desirable to digest primary sludge anaerobically, and secondary sludge aerobically. Aerobic digestion is the biochemical oxidative stabilization of wastewater sludge in open or closed tanks that are separate from the liquid process system. This method of digestion is capable of handling waste activated, trickling filter, or primary sludges as well as mixtures of the same. The aerobic digester operates on the same principles as the activated sludge process. As food is depleted, the microbes enter the endogenous phase and the cell tissue is aerobically oxidized to CO2, H2O, NH 4+, NO 2−, and NO 3−(1).
Article
Generally, aerobic digestion of biological sludges is conducted in completely-mixed aeration basins. Although first-order kinetics have classically been used to predict and design aerobic digestors, it is shown that these models will result in underdesign and that a model based on a mass balance around the digestor more accurately predicts digestor performance. The experimental work discussed herein demonstrates that a first-order rate coefficient, determined under batch conditions, can be employed in the completely-mixed model for design purposes. Certain design constraints are discussed, such as laboratory scale-up, temperature, etc. A design example is illustrated using the approach presented herein.
Article
The aerobic digestion process with certain modifications is evaluated as an alternative for sludge processing capable of developing a product with characteristics required for land application. Environmental conditions, including temperature, solids concentration, and digestion time, that affect the aerobic digestion of a mixed primary sludge-trickling filter humus are investigated. Variations in these parameters that influence the characteristics of digested sludge are determined, and the parameters are optimized to: provide the maximum rate of volatile solids reduction; develop a stable, nonodorous product sludge; and provide the maximum rate of oxidation of the nitrogenous material present in the feed sludge. (3 diagrams, 9 graphs, 15 references, 3 tables)
Article
A practical treatise on the design of biological effluent treatment plant which bases the calculations employed on an understanding of the theoretical principles involved. The first two chapters are concerned with the fundamentals of process kinetics and microbiology (including growth kinetics) respectively, and are followed by a section on waste water characteristics and flows. Thereafter a series of chapters on specific treatment applications is presented, including activated sludge and its various modifications, aeration system design, treatment ponds and aerated lagoons; attached-growth biological treatment methods, and sludge digestion. The problems and processes of nitrification and denitrification are considered where appropriate, in addition to the oxidation of organic matter.
Anaerobic sludge digestion: Manual of practice No
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Respirometry of Activated Sludge
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V prvem delu je bil cilj raziskav določiti najugodnejšo temperaturo razgradnje. Preskusi so bili šaržni, izvedeni pri temperaturah 20
  • Eksperimentalni Del Raziskav Je Bil Razdeljen Na Dva Dela
Eksperimentalni del raziskav je bil razdeljen na dva dela. V prvem delu je bil cilj raziskav določiti najugodnejšo temperaturo razgradnje. Preskusi so bili šaržni, izvedeni pri temperaturah 20, 37, 40, 45, 50 in 55 °C. Najugodnejša temperatura razgradnje je bila 50
Sludge and its ultimate disposal
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Borchardt, J. A., Sludge and its ultimate disposal. 1981, Collingwood, Michigan: Ann Arbour Science.