The article presents the results of an experimental study of the effect of high-temperature thermal pretreatment on the specific resistance to filtration (SRF) of the sewage sludge (SS) from the Lviv wastewater treatment plant (WWTP), which is a combination of primary sludge and excess-activated sludge collected in primary sedimentation tanks. The kinetics of SRF reduction over time at temperatures of 140 − 150 °С are described by simple exponents, while at temperatures of 160 − 170 °С, they are described by modified two-parameter exponents. The study analyzed the dimensionless optimization function, which is the product of the final relative SRF of the sludge and the dimensionless time of thermal pretreatment. An optimal dimensionless thermal pretreatment time of 4.1 tr.0/2 was determined, and an empirical exponential equation for the time of SRF reduction by twice tr.0/2 was derived. Based on the analysis, it was found that the highest efficiency in reducing the SRF of Lviv WWTP SS occurs at a temperature of 170 °C and an optimal duration of thermal pretreatment of 55 min.

  • Thermal pretreatment is an effective method for decreasing specific resistance to filtration (SRF) of sewage sludge (SS).

  • Two-parameter exponents are used as trendlines for SRF reduction during thermal pretreatment.

  • An optimization function is proposed for the thermal pretreatment of SS.

  • Optimal parameters for the thermal pretreatment of SS from the Lviv wastewater treatment plant are determined.

At typical municipal wastewater treatment plants (WWTPs), as a result of sewage treatment, a mixture of sewage sludge (SS) is formed in the amount of 1–1.5% of the volume of treated sewage. The disposal of SS is a complex and costly process; however, SS is a source of carbon, nutrients, and trace elements and can be effectively disposed of (Gahlot et al. 2022; Kelessidis & Stasinakis 2012; Liew et al. 2021). An important step in SS utilization is a dewatering process, which allows a significant reduction of the SS volumes (Wu et al. 2020; Cao et al. 2021). Depending on the susceptibility of the sludge to mechanical dewatering, the water content in the SS can range from 95–99 to 65–85% (Skinner et al. 2015; Wójcik & Stachowicz 2019).

One of the main quantitative parameters of SS dewatering properties is specific resistance to filtration (SRF). SRF varies within very wide limits for types of sludge and different WWTPs. Thus, the values of SRF for sludge from primary settling tanks at different WWTPs are in the range of (60–3,000) × 1011 m/kg (Smollen 1986; Wojciechowska 2005; Liu et al. 2012), which can be explained by differences in the composition of wastewater at the inlet of WWTP, primarily due to the influence of industrial wastewater. The activated sludge of typical WWTP has low dewatering properties, its SRF is in the range of (1,700–11,500) × 1011 m/kg, and it increases sharply with increasing the total solids (TS) content (Ng & Hermanowicz 2005; Xiao et al. 2022).

On the other hand, SS from primary clarifiers and activated sludge of WWTPs have less SRF compared to anaerobically digested sludge. The SRF of the digested SS depends not only on the type of sludge and the mode of its digestion but also on the accepted loading dosage and the method of SS mixing in the digester, and SRF decreases slightly with prolonged fermentation. Anaerobically digested activated sludge has higher SRF compared with the primary sludge fermented in the same conditions (Liu et al. 2021).

A key issue in the efficiency of sludge dewatering is the selection of an appropriate conditioning method according to the physicochemical properties of SS (Barber 2016; Wu et al. 2020). Zhang et al. (2022) analyzed the advantages and deficiencies of the different SS pretreatment methods, as well as their mechanisms. Most often, SS pretreatment is performed by adding the flocculants (Wójcik & Stachowicz 2019; Hu et al. 2021; Qi et al. 2011), by the sonochemical method (Pilli et al. 2011), and by thermal hydrolysis (Haug et al. 1978; Lin & Shien 2001; Feng et al. 2014; Wang & Li 2015). In order to reduce the consumption of chemical reagents, the sludge conditioning process is modified, and new methods of sludge pretreatment are proposed and studied, for example, different combined methods (Bień & Bień 2020, 2021; Ngo et al. 2021; Nguyen et al. 2021).

Thermal pretreatment of SS is a process of heating the sludge to 60–180 °C in a hermetic environment under appropriate excess pressure (Bougrier et al. 2008; Deng et al. 2019; Kim et al. 2020). The process of thermal hydrolysis of SS has been used since the 1930s and has reached its maximum spread in the last 2–3 decades (Gavala et al. 2003; Hidaka et al. 2022; Neyens & Baeyens 2003; Wang & Li 2015). Thermal pretreatment of SS is a simple and effective method of reducing its filtration resistance (Neyens & Baeyens 2003; Bonu et al. 2023). However, it is important to note that thermal treatment is associated with high specific energy consumption (Ruffino et al. 2015). Therefore, the cost-effectiveness of this method in each specific case must be carefully evaluated through the development of an appropriate feasibility study. This highlights the significance of optimizing thermal pretreatment techniques.

The process of thermal pretreatment before anaerobic digestion improves sludge dewatering, increases the biodegradability of excess-activated sludge, ensures sludge decontamination, and causes a positive energy balance compared to other sludge pretreatment methods (Haug et al. 1983; Pinnekamp 1989). In different studies of thermal pretreatment of activated sludge at temperatures of 160–180 °C and a duration of 30–60 min, a reduction in the time of SS anaerobic digestion, an increase in the specific yield of biogas, a higher degree of decomposition of organic substances and better dewaterability of the obtained digestate were obtained (Pilli et al. 2015).

Lab-scale thermal pretreatment of the activated sludge of the industrial WWTP of a cellulose manufacturing plant (Aanekoski, Finland) at the temperature of 180 °C and the duration of 30 min caused the SRF decrease from (200 − 800) × 1011 to 5 × 1011 m/kg (Kyllönen et al. 1988).

In previous studies, a lack of information was identified regarding the kinetics of SS SRF reduction based on the duration of high-temperature pretreatment. The experimental data provided by Everett (1972) only cover the temperature range of 180–220 °C, which raises concerns about energy efficiency. On the other hand, there is also a notable gap in optimizing the thermal pretreatment of SS, which is particularly relevant given the current rise in electricity and other energy costs.

The objective of this study is to elaborate on the method of optimizing the thermal pretreatment of SS, with a specific focus on the temperature and duration of the pretreatment process. This study hypothesizes that it is possible to determine the optimal temperature and duration for the thermal pretreatment of SS by analyzing the kinetics of SRF reduction using lab-scale experiments. The significance of this study lies in its potential to reduce energy costs associated with the thermal pretreatment of SS in other WWTPs by applying the developed method.

Tested SS

An experimental lab-scale study of the effect of high-temperature pretreatment on the dewatering properties of SS from the Lviv municipal WWTP was performed. In the city of Lviv (Ukraine), a combined sewerage system is used. The total nominal capacity of the Lviv WWTP is 490,000 m3/day. The SS of the Lviv WWTP is a mixture of primary sludge and excess-activated sludge that is collected from the primary settling tanks. Excess-activated sludge is added to primary clarifiers in order to increase the sedimentation efficiency of primary sludge, acting as a biocoagulant. The composition of SS from the Lviv WWTP exhibits consistent stability over time. This stability can be attributed to the diversion of stormwater runoff during periods of heavy rainfall. Rather than being directed to the WWTP, the stormwater is channeled through the overflow spillway into the Poltva River, which is part of the Baltic Sea basin. This practice is implemented to ensure compliance with permissible environmental impacts.

The dry matter (DM) content in the samples of SS from the Lviv WWTP was determined to be 40 g/L using standard laboratory techniques. Additionally, the volatile solids (VS) were found to account for 70% of the DM. Following the thermal pretreatment process and subsequent cooling to a temperature of 20 °C, the samples were diluted with tap water to achieve a lower DM content of 8 g/L. This dilution was done to enhance the accuracy of the filtration stage results.

Thermal pretreatment experimental unit

Experimental studies were performed on a special high-pressure lab-scale unit (Figure 1). After filling the high-pressure reactor 1 with sludge, air was pumped into reactor 1 through pipeline 3. The amount of air was regulated by control valve 4. The pressure in the reactor was controlled by manometer 6. After reaching the required pressure, valve 4 was closed. To heat the sludge in reactor 1, a heating device was used, which was connected to the 220 V alternating current network through electrical transformer 2.
Figure 1

Experimental lab-scale unit for SS thermal pretreatment: 1 – high-pressure reactor; 2 – electrical transformer; 3 – air supply pipeline; 4 – control valve; 5 – thermometer; 6 – manometer.

Figure 1

Experimental lab-scale unit for SS thermal pretreatment: 1 – high-pressure reactor; 2 – electrical transformer; 3 – air supply pipeline; 4 – control valve; 5 – thermometer; 6 – manometer.

Close modal

The sludge in reactor 1 was heated to a specified temperature, which was controlled by a thermometer 5. After some time of exposure at a given temperature, the heater was turned off, and reactor 1 was cooled to room temperature. Then the pretreated sludge was poured out of reactor 1 for the SRF measurement.

The high-pressure reactor (Figure 2) consists of body 6, heating device 5, cover 2, sleeve with oil for a thermometer 4, reduction valve 1, nozzle for connecting a pressure gauge 7, fitting for connecting an air supply pipeline 8, and gasket 3 between the body 6 and cover 2.
Figure 2

High-pressure reactor: 1 – reduction valve; 2 – cover; 3 – gasket; 4 – sleeve with oil for thermometer; 5 – heating device; 6 – body of reactor; 7 – nozzle for connecting a pressure gauge; 8 – fitting for connecting the air supply pipeline.

Figure 2

High-pressure reactor: 1 – reduction valve; 2 – cover; 3 – gasket; 4 – sleeve with oil for thermometer; 5 – heating device; 6 – body of reactor; 7 – nozzle for connecting a pressure gauge; 8 – fitting for connecting the air supply pipeline.

Close modal
Figure 3

SFR of Lviv WWTP SS after the thermal pretreatment at temperatures of 140 − 170 °С and the corresponding exponential trend lines (4), (5), (7) and (8) (indicated bars of relative errors ±10%).

Figure 3

SFR of Lviv WWTP SS after the thermal pretreatment at temperatures of 140 − 170 °С and the corresponding exponential trend lines (4), (5), (7) and (8) (indicated bars of relative errors ±10%).

Close modal

SRF of the SS

SRF is the main quantitative parameter of SS dewaterability. In this study, SRF was found according to the standard method (EN 14701-2:2013; Górka et al. 2018; To et al. 2016):
formula
(1)
where p is the filtration vacuum pressure; F is the area of the filtration surface; η is the dynamic viscosity of the filtrate; C is the TS content; b=t/V2 is the experimental parameter, t is the time of filtration; and V is the volume of the filtrate.

During the mechanical dewatering of SS, mainly free water is released, so Equation (1) for determining the SRF is fully applicable to the SS. The duration of filtration depends on the rate of sludge dewatering. To obtain a sufficient number of data, as usual, it does not exceed 20 min. The parameter b was defined as the coefficient of the linear trend of the experimental data in the axes Vt/V. Knowing the volumes of filtrate V1, V2, V3, … Vn, at the time t1, t2, t3, … tn, respectively, parameter b was found for each tested sludge.

Sludge SRF was determined at a vacuum pressure of 66.7 kPa (500 mmHg). Buchner funnel with a diameter of 80 mm and a filtration area of 50.24 cm2 was used. The viscosity of the filtrate was assumed equal to the viscosity of water at the temperature of 20 °C (η = 0.001 Pa·s). TS content was equal to C = 80 kg/m3. Thus, the SRF of the raw, untreated SS of the Lviv WWTP was equal to 686.5 × 1011 m/kg.

Kinetics of the decreasing of SS SRF

High-temperature pretreatment of samples of the SS from the Lviv WWTP was performed at four different temperatures, namely 140, 150, 160, and 170 °С. The control values for the duration of the thermal pretreatment were equal to 30, 60, and 90 min.

The kinetics of the decreasing the SRF of the SS of the Lviv WWTP (Figure 3) using the least-squares method is approximated by the different exponential trend lines. At temperatures of 140 and 150 °С, the decreasing of SFR over time is well described by a simple exponent
formula
(2)
which is the solution of the differential equation of the first-order reaction:
formula
(3)
where r and r0 are SRF of the sludge, respectively, at an arbitrary moment of time t and before the thermal pretreatment at t = 0, r0 = 686.5 × 1011 m/kg; k is the constant of the rate of SRF decreasing, min−1.
Figure 4

Experimental duration of Lviv WWTP SS SRF decreasing to (100–400) × 1011 m/kg depending on the temperature of the thermal pretreatment.

Figure 4

Experimental duration of Lviv WWTP SS SRF decreasing to (100–400) × 1011 m/kg depending on the temperature of the thermal pretreatment.

Close modal
In particular, for the temperature T1 = 140 °C, a simple exponent trend line is obtained:
formula
(4)
and for Т2 = 150 °С:
formula
(5)

Thus, an increase in the pretreatment temperature of the SS from T1 = 140 °C to T2 = 150 °C leads to an increase in the constant k from 0.0216 to 0.0252 min−1 or by 16.7%.

At temperatures T3 = 160 °C and T4 = 170 °C, a quantitatively different kinetics of the change in SRF over time was obtained, which is characterized by its sharp decrease in the first 30 min, followed by an asymptotic trend at large t to some limiting values rlim > 0. Such kinetics is best approximated by two-parameter exponents:
formula
(6)
At temperature T3 = 160 °C, limiting SRF rlim = 40 × 1011 m/kg is obtained, and at temperature Т4 = 170 °С, rlim = 52 × 1011 m/kg, and trend lines are, respectively,
formula
(7)
formula
(8)

The experimental duration of SRF decreasing to typical round values in the range of (100 − 400) × 1011m/kg for temperatures of 140 − 170 °С is shown in Figure 4.

The time of the corresponding SRF reduction is approximated by logarithmic and linear trends:
formula
(9)
formula
(10)
where С1, С2, k1, and k2 are empirical parameters, as presented in Table 1.
Table 1

Parameters of trend lines (9) and (10) for the thermal pretreatment of the SS of the Lviv WWTP at temperatures of 140–170 °С

SRF (×1011 m/kg)Logarithmic Equation (9)
Linear Equation (10)
C1k1R2C2k2R2
100 1397.8 264.1 0.9428 333.0 1.720 0.9543 
150 1107.6 209.4 0.9775 262.8 1.361 0.9852 
200 867.6 163.8 0.9897 206.8 1.062 0.994 
300 523.6 98.1 0.9953 127.65 0.636 0.9977 
400 287.8 53.1 0.9944 72.26 0.344 0.9968 
SRF (×1011 m/kg)Logarithmic Equation (9)
Linear Equation (10)
C1k1R2C2k2R2
100 1397.8 264.1 0.9428 333.0 1.720 0.9543 
150 1107.6 209.4 0.9775 262.8 1.361 0.9852 
200 867.6 163.8 0.9897 206.8 1.062 0.994 
300 523.6 98.1 0.9953 127.65 0.636 0.9977 
400 287.8 53.1 0.9944 72.26 0.344 0.9968 
The decreasing of the dimensionless SRF (r/r0) of the SS of the Lviv WWTP occurs intensively when it is treated for up to 30 min. At the same time, an increase in temperature in the range of 140 − 170 °С strengthens the effect of thermal pretreatment on the reduction of r/r0 (Figure 5). A further increase in processing time to 90 min leads to a less intense decrease of dimensionless SRF. A similar trend was obtained for the SRF of activated sludge at temperatures of 180–220 °С (Everett 1972).
Figure 5

Decreasing of the dimensionless SRF of the SS of the Lviv WWTP at temperatures of 140 − 170 °C (results of the authors' research) and of activated sludge at a temperature of 180 °C (Everett 1972).

Figure 5

Decreasing of the dimensionless SRF of the SS of the Lviv WWTP at temperatures of 140 − 170 °C (results of the authors' research) and of activated sludge at a temperature of 180 °C (Everett 1972).

Close modal
All four series of dimension SRF at different temperatures are reduced to a single generalized dimensionless dependence when dimensionless time is used, where t′ = t/tr.0/2, and tr.0/2 is the time of SRF reduction by twice (Figure 6).
Figure 6

Generalized dimensionless kinetics of the Lviv WWTP SS SRF decreasing after thermal pretreatment at temperatures of 140 − 170 °С depending on the dimensionless time t/tr.0/2 (deviations ±0.05 are specified).

Figure 6

Generalized dimensionless kinetics of the Lviv WWTP SS SRF decreasing after thermal pretreatment at temperatures of 140 − 170 °С depending on the dimensionless time t/tr.0/2 (deviations ±0.05 are specified).

Close modal
The dimensionless generalized kinetics of SRF reduction resulting from the thermal pretreatment of the Lviv WWTP SS:
formula
(11)
where r′=r/r0 is dimensionless SRF.
In general form, Equation (11) can be written as:
formula
(12)
where k′ is a dimensionless constant of the rate of SRF decreasing.
For the SS of the Lviv WWTP, the dimensionless constant k′ = 0.827 and the time for the SRF decreasing twice tr.0/2 can be found by the empirical equation:
formula
(13)
The obtained trend line (13) indicates the exponential nature of the temperature dependence of time tr.0/2 (Figure 7).
Figure 7

The duration of the SRF halving of the Lviv WWTP SS depending on the pretreatment temperature T (deviations ±10% are specified).

Figure 7

The duration of the SRF halving of the Lviv WWTP SS depending on the pretreatment temperature T (deviations ±10% are specified).

Close modal

Optimization of the high-temperature thermal pretreatment of SS

Since the generalized kinetics of the SRF decreasing of the Lviv WWTP SS can be well described by a two-parameter exponent, according to which the SRF decreases asymptotically with increasing time to a non-zero final value rlim, the optimization problem, which consists in determining the optimal time of high-temperature thermal pretreatment, is thus relevant.

Taking into account that the optimal results of high-temperature pretreatment correspond to the lowest possible value of the SS SRF in the shortest possible time, and assuming the weight of these two parameters to be the same, we use the dimensionless optimization function F(t′) as the product of the final dimensionless SRF r′ and the dimensionless pretreatment time t′ :
formula
(14)
Optimization function, taking into account Equation (12):
formula
(15)
The first derivative of the optimization function:
formula
(16)
Equation (16) is transcendental with respect to dimensionless time t′. The numerical solution of Equation (16) for the parameters of the Lviv WWTP SS (rlim = 0.075, k′ = 0.827) indicates the presence of two extremes, namely the local maximum F = 0.514 at t* = 1.57 and the local minimum F = 0.435 at t** = 4.09 (Figure 8) with the tendency of the following monotonic increase of the function F when t > t**. Thus, the duration of high-temperature pretreatment of the Lviv WWTP SS to increase the technical and economic parameters of the process should be taken equal to about topt = 4.1 tr.0/2, which corresponds to the local minimum of the optimization function F(t′). In order to determine the optimal temperature for the thermal pretreatment of the Lviv WWTP SS, the dimensional efficiency criterion topt × r/r0 for the temperature range of 140–170 °С was analyzed (Table 2).
Table 2

Optimum parameters of thermal pretreatment of the Lviv WWTP SS at temperatures of 140–170 °С

T (°C)tr.0/2 (min)topt (min)r (×1011 m/kg) at toptr/r0topt × r/r0 (min)
140 34.9 142.8a 31.4 0.046 6.53 
150 25.4 103.7a 50.3 0.073 7.60 
160 18.4 75.3 79.6 0.116 8.73 
170 13.4 54.7 71.4 0.104 5.69 
T (°C)tr.0/2 (min)topt (min)r (×1011 m/kg) at toptr/r0topt × r/r0 (min)
140 34.9 142.8a 31.4 0.046 6.53 
150 25.4 103.7a 50.3 0.073 7.60 
160 18.4 75.3 79.6 0.116 8.73 
170 13.4 54.7 71.4 0.104 5.69 

aExtrapolated values.

Figure 8

Optimization parameters of the Lviv WWTP SS SRF decreasing after the thermal pretreatment: F(t′) – optimization function; r′(t′) is a dimensionless curve of SRF decreasing; t*, t** are local extrema.

Figure 8

Optimization parameters of the Lviv WWTP SS SRF decreasing after the thermal pretreatment: F(t′) – optimization function; r′(t′) is a dimensionless curve of SRF decreasing; t*, t** are local extrema.

Close modal

Thus, the optimal technical and economic decreasing of the SRF of the Lviv WWTP SS corresponds to the temperature of 170 °C and the duration of the thermal pretreatment of about 55 min (Table 2). Concerning the wide variability of the composition and SRF values of SS at different WWTPs, it is advisable to carry out similar lab-scale studies to optimize thermal pretreatment for each individual type of SS using the method presented above.

High-temperature thermal pretreatment of SS is a reagent-free, simple, and effective method of decreasing the SRF of the SS at WWTP, while also ensuring the simultaneous disinfection of the sludge and improving the parameters of its anaerobic digestion.

An experimental study of the effect of high-temperature pretreatment on the SRF was performed for the Lviv WWTP SS, which is a mixture of primary sludge and excess-activated sludge deposited in primary sedimentation tanks. The main parameters of the studied SS before the thermal pretreatment are TS content – 8 g/L; VS – 70%, and the SRF – 686.5 × 1011 m/kg.

Dependences of SRF were obtained for the SS thermal pretreatment in the temperature range of 140 − 170 °С and the duration from 30 to 90 min. SRF kinetics at temperatures of 140 − 150 °С are described by simple exponential Equations (4) and (5), while at temperatures of 160 − 170 °С using the two-parameter exponents (7) − (8).

A dimensionless optimization function is introduced as a product of the exit dimensionless SRF of the SS and the dimensionless time of the thermal pretreatment. The optimal dimensionless thermal pretreatment time 4.1 × tr.0/2 is found, where the time of the SRF halving tr.0/2 is an empirical exponential function (13) of the temperature. According to the optimization function analysis, the highest efficiency in decreasing the SRF of the Lviv WWTP SS corresponds to the temperature of 170 °C and the thermal pretreatment duration of about 55 min.

The presented optimization method can be applied to determine the optimal time and temperature for thermal pretreatment of SS at various WWTPs. To achieve this, a comprehensive laboratory study should be conducted using 3–4 sludge samples collected under diverse weather and operational conditions over a minimum period of 6 months. For each SS sample, kinetic curves depicting the dependence of SRF on the duration of thermal hydrolysis should be obtained at a minimum of four temperature values within the range of 140–180 °C. A recommended approach is to conduct thermal hydrolysis for up to 120 min, with intermediate SRF measurements taken every 30 min to find the parameters of the maximum efficiency of the thermal pretreatment.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

Barber
W. P. F.
2016
Thermal hydrolysis for sewage treatment: a critical review
.
Water Research
104
,
53
71
.
https://doi.org/10.1016/j.watres.2016.07.069
.
Bień
B.
&
Bień
J.
2020
Dewatering of sewage sludge treated by the combination of ultrasonic field and chemical methods
.
Desalination and Water Treatment
199
,
72
78
.
https://doi.org/10.5004/dwt.2020.25740
.
Bień
B.
&
Bień
J. D.
2021
Conditioning of sewage sludge with physical, chemical and dual methods to improve sewage sludge dewatering
.
Energies
14
(
16
),
5079
.
https://doi.org/10.3390/en14165079
.
Bonu
R.
,
Anand
N.
&
Palani
S. G.
2023
Impact of thermal pre-treatment on anaerobic co-digestion of sewage sludge and landfill leachate
.
Materials Today: Proceedings
72
,
99
103
.
Bougrier
C.
,
Delgenès
J. P.
&
Carrère
H.
2008
Effects of thermal treatments on five different waste activated sludge samples solubilisation, physical properties and anaerobic digestion
.
Chemical Engineering Journal
139
(
2
),
236
244
.
https://doi.org/10.1016/j.cej.2007.07.099
.
Cao
B.
,
Zhang
T.
,
Zhang
W.
&
Wang
D.
2021
Enhanced technology based for sewage sludge deep dewatering: a critical review
.
Water Research
189
,
116650
.
https://doi.org/10.1016/j.watres.2020.116650
.
Deng
W.
,
Ma
J.
,
Xiao
J.
,
Wang
L.
&
Su
Y.
2019
Orthogonal experimental study on hydrothermal treatment of municipal sewage sludge for mechanical dewatering followed by thermal drying
.
Journal of Cleaner Production
209
,
236
249
.
https://doi.org/10.1016/j.jclepro.2018.10.261
.
EN 14701-2:2013
.
Characterisation of Sludges. Filtration Properties. Part 2: Determination of the Specific Resistance to Filtration
.
Everett
J. G.
1972
Dewatering of wastewater sludge by heat treatment
.
Journal – Water Pollution Control Federation
44
,
92
100
.
Feng
G.
,
Tan
W.
,
Zhong
N.
&
Liu
L.
2014
Effects of thermal treatment on physical and expression dewatering characteristics of municipal sludge
.
Chemical Engineering Journal
247
,
223
230
.
https://doi.org/10.1016/j.cej.2014.03.005
.
Gahlot
P.
,
Balasundaram
G.
,
Tyagi
V. K.
,
Atabani
A. E.
,
Suthar
S.
,
Kazmi
A. A.
,
Stepanec
L.
,
Juchelkova
D.
&
Kumar
A.
2022
Principles and potential of thermal hydrolysis of sewage sludge to enhance anaerobic digestion
.
Environmental Research
214
,
113856
.
https://doi.org/10.1016/j.envres.2022.113856
.
Gavala
H. N.
,
Yenal
U.
,
Skiadas
I. V.
,
Westermann
P.
&
Ahring
B. K.
2003
Mesophilic and thermophilic anaerobic digestion of primary and secondary sludge. Effect of pre-treatment at elevated temperature
.
Water Research
37
(
19
),
4561
4572
.
https://doi.org/10.1016/S0043-1354(03)00401-9
.
Górka
J.
,
Cimochowicz-Rybicka
M.
&
Kryłów
M.
2018
Use of a water treatment sludge in a sewage sludge dewatering process
.
E3S Web of Conferences
30
(
02006
),
1
7
.
https://doi.org/10.1051/e3sconf/20183002006
.
Haug
R. T.
,
Stuckey
D. C.
,
Gossett
J. M.
&
McCarty
P. L.
1978
Effect of thermal pretreatment on digestibility and dewaterability of organic sludges
.
Water Pollution Control Federation
50
(
1
),
73
85
.
Haug
R. T.
,
LeBrun
T. J.
&
Tortorici
L. D.
1983
Thermal pretreatment of sludges: a field demonstration
.
Journal (Water Pollution Control Federation)
55
(
1
),
23
34
.
Hidaka
T.
,
Nakamura
M.
,
Oritate
F.
&
Nishimura
F.
2022
Comparative anaerobic digestion of sewage sludge at different temperatures with and without heat pre-treatment
.
Chemosphere
307
,
135808
.
https://doi.org/10.1016/j.chemosphere.2022.135808
.
Hu
P.
,
Zhuang
S.
,
Shen
S.
,
Yang
Y.
&
Yang
H.
2021
Dewaterability of sewage sludge conditioned with a graft cationic starch-based flocculant: role of structural characteristics of flocculant
.
Water Research
189
,
116578
.
https://doi.org/10.1016/j.watres.2020.116578
.
Kelessidis
A.
&
Stasinakis
A. S.
2012
Comparative study of the methods used for treatment and final disposal of sewage sludge in European countries
.
Waste Management
32
(
6
),
1186
1195
.
https://doi.org/10.1016/j.wasman.2012.01.012
.
Kim
H. J.
,
Chon
K.
,
Lee
Y. G.
,
Kim
Y. K.
&
Jang
A.
2020
Enhanced mechanical deep dewatering of dewatered sludge by a thermal hydrolysis pre-treatment: effects of temperature and retention time
.
Environmental Research
188
,
109746
.
https://doi.org/10.1016/j.envres.2020.109746
.
Kyllönen
H. L.
,
Lappi
M. K.
,
Thun
R. T.
&
Mustranta
A. H.
1988
Treatment and characterization of biological sludges from the pulp and paper industry
.
Water Science and Technology
20
(
1
),
183
192
.
Liew
C. S.
,
Kiatkittipong
W.
,
Lim
J. W.
,
Lam
M. K.
,
Ho
Y. C.
,
Ho
C. D.
,
Ntwampe
S. K. O.
,
Mohamad
M.
&
Usman
A.
2021
Stabilization of heavy metals loaded sewage sludge: reviewing conventional to state-of-the-art thermal treatments in achieving energy sustainability
.
Chemosphere
277
,
130310
.
https://doi.org/10.1016/j.chemosphere.2021.130310
.
Lin
C. F.
&
Shien
Y.
2001
Sludge dewatering using centrifuge with thermal/polymer conditioning
.
Water Science and Technology
44
(
10
),
321
325
.
https://doi.org/10.2166/wst.2001.0652
.
Liu
F.
,
Zhou
J.
,
Wang
D.
&
Zhou
L.
2012
Enhancing sewage sludge dewaterability by bioleaching approach with comparison to other physical and chemical conditioning methods
.
Journal of Environmental Sciences
24
(
8
),
1403
1410
.
https://doi.org/10.1016/S1001-0742(11)60958-3
.
Liu
Q.
,
Li
Y.
,
Yang
F.
,
Liu
X.
,
Wang
D.
,
Xu
Q.
,
Zhang
Y.
&
Yang
Q.
2021
Understanding the mechanism of how anaerobic fermentation deteriorates sludge dewaterability
.
Chemical Engineering Journal
404
,
127026
.
https://doi.org/10.1016/j.cej.2020.127026
.
Neyens
E.
&
Baeyens
J.
2003
A review of thermal sludge pre-treatment processes to improve dewaterability
.
Journal of Hazardous Materials
98
(
1–3
),
51
67
.
https://doi.org/10.1016/S0304-3894(02)00320-5
.
Ngo
P. L.
,
Udugama
I. A.
,
Gernaey
K. V.
,
Young
B. R.
&
Baroutian
S.
2021
Mechanisms, status, and challenges of thermal hydrolysis and advanced thermal hydrolysis processes in sewage sludge treatment
.
Chemosphere
281
,
130890
.
https://doi.org/10.1016/j.chemosphere.2021.130890
.
Nguyen
V. K.
,
Chaudhary
D. K.
,
Dahal
R. H.
,
Trinh
N. H.
,
Kim
J.
,
Chang
S. W.
,
Hong
Y.
,
La
D. D.
,
Nguyen
X. C.
,
Ngo
H. H.
,
Chung
W. D.
&
Nguyen
D. D.
2021
Review on pretreatment techniques to improve anaerobic digestion of sewage sludge
.
Fuel
285
,
119105
.
https://doi.org/10.1016/j.fuel.2020.119105
.
Pilli
S.
,
Bhunia
P.
,
Yan
S.
,
LeBlanc
R. J.
,
Tyagi
R. D.
&
Surampalli
R. Y.
2011
Ultrasonic pretreatment of sludge: a review
.
Ultrasonics Sonochemistry
18
(
1
),
1
18
.
https://doi.org/10.1016/j.ultsonch.2010.02.014
.
Pilli
S.
,
Yan
S.
,
Tyagi
R. D.
&
Surampalli
R. Y.
2015
Thermal pretreatment of sewage sludge to enhance anaerobic digestion: a review
.
Critical Reviews in Environmental Science and Technology
45
(
6
),
669
702
.
https://doi.org/45.10.1080/10643389.2013.876527
.
Pinnekamp
J.
1989
Effects of thermal pretreatment of sewage sludge on anaerobic digestion
.
Water Pollution Research and Control Brighton
97
108
.
https://doi.org/10.1016/B978-1-4832-8439-2.50014-6
.
Qi
Y.
,
Thapa
K. B.
&
Hoadley
A. F.
2011
Application of filtration aids for improving sludge dewatering properties–a review
.
Chemical Engineering Journal
171
(
2
),
373
384
.
https://doi.org/10.1016/j.cej.2011.04.060
.
Ruffino
B.
,
Campo
G.
,
Genon
G.
,
Lorenzi
E.
,
Novarino
D.
,
Scibilia
G.
&
Zanetti
M.
2015
Improvement of anaerobic digestion of sewage sludge in a wastewater treatment plant by means of mechanical and thermal pre-treatments: performance, energy and economical assessment
.
Bioresource Technology
175
,
298
308
.
http://dx.doi.org/10.1016/j.biortech.2014.10.071
.
Skinner
S. J.
,
Studer
L. J.
,
Dixon
D. R.
,
Hillis
P.
,
Rees
C. A.
,
Wall
R. C.
,
Cavalida
R. G.
,
Usher
S. P.
,
Stickland
A. D.
&
Scales
P. J.
2015
Quantification of wastewater sludge dewatering
.
Water Research
82
,
2
13
.
https://doi.org/10.1016/j.watres.2015.04.045
.
Smollen
M.
1986
Dewaterability of municipal sludges 1: a comparative study of specific resistance to filtration and capillary suction time as dewaterability parameters
.
Water SA
12
(
3
),
127
132
.
To
V. H. P.
,
Nguyen
T. V.
,
Vigneswaran
S.
&
Ngo
H. H.
2016
A review on sludge dewatering indices
.
Water Science and Technology
74
(
1
),
1
16
.
https://doi.org/10.2166/wst.2016.102
.
Wojciechowska
E.
2005
Application of microwaves for sewage sludge conditioning
.
Water Research
39
(
19
),
4749
4754
.
https://doi.org/10.1016/j.watres.2005.09.032
.
Wójcik, M. & Stachowicz, F.
2019
Influence of physical, chemical and dual sewage sludge conditioning methods on the dewatering efficiency
.
Powder Technology
344
,
96102
.
Xiao
H.
,
Liu
H.
,
Jin
M.
,
Deng
H.
,
Wang
J.
&
Yao
H.
2022
Process control for improving dewatering performance of sewage sludge based on carbonaceous skeleton-assisted thermal hydrolysis
.
Chemosphere
296
,
134006
.
https://doi.org/10.1016/j.chemosphere.2022.134006
.
Zhang
X.
,
Ye
P.
&
Wu
Y.
2022
Enhanced technology for sewage sludge advanced dewatering from an engineering practice perspective: a review
.
Journal of Environmental Management
321
,
115938
.
https://doi.org/10.1016/j.jenvman.2022.115938
.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original work is properly cited (http://creativecommons.org/licenses/by-nc-nd/4.0/).