Using acidic-modified bentonite for anaerobically digested sludge conditioning and dewatering

Journal Pre-proof Using acidic-modified bentonite for anaerobically digested sludge conditioning and dewatering Hamidreza Masihi, Gagik Badalians Gholikandi PII:

S0045-6535(19)32335-5

DOI:

https://doi.org/10.1016/j.chemosphere.2019.125096

Reference:

CHEM 125096

To appear in:

ECSN

Received Date: 29 June 2019 Revised Date:

9 September 2019

Accepted Date: 9 October 2019

Please cite this article as: Masihi, H., Gholikandi, G.B., Using acidic-modified bentonite for anaerobically digested sludge conditioning and dewatering, Chemosphere (2019), doi: https://doi.org/10.1016/ j.chemosphere.2019.125096. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Graphical abstract

Sludge

AMB SiO2 + Al3+

Floc

LB-EPS

TB-EPS

Soluble-EPS

Microorganisms Free water

Bound water Negative charge

Using acidic-modified bentonite for anaerobically digested sludge conditioning and dewatering

1 2

Hamidreza Masihia, Gagik Badalians Gholikandib,1

3 4 5

a

Ph.D. cand., Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, A.C., Tehran, Iran, E-mail: [email protected]

6 7

b

Assoc.Prof, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, A.C., Tehran, Iran, E-mail: [email protected], [email protected]

8 9

Abstract

10

In this study, the acidic-modified bentonite (AMB) was developed to enhance conditioning and dewatering

11

processes of anaerobically digested sludge (ADS) for the first time and its performance was compared with

12

inorganic salts, e.g. FeCl3, AlCl3, Al2(SO4)3 and Fe2(SO4)3. AMB structural changes were investigated employing

13

XRD, XRF, FT-IR and specific surface area tests. AMB reduced the specific resistance to filterability (SRF),

14

capillary suction time (CST) and time to filter (TTF) of the sludge by 95.8%, 90.4% and 80.8%, respectively.

15

Moreover, it reduced the sludge compressibility and increased filtration yield significantly. Also, sludge

16

conditioning with the AMB resulted in a significant increase in the sludge particles size and formation of denser and

17

stronger flocs. In order to evaluate the related sludge conditioning mechanism, zeta potential, bound water,

18

extracellular polymeric substances (EPS) and XRF tests were conducted. It was determined that AMB acts as

19

physical and chemical conditioner. Dewatering of conditioned sludge with AMB utilizing a filter press resulted in

20

the sludge with 41% dry solids (DS). In addition, the economic survey showed that the cost of conditioning by using

21

AMB is $ 33.79 USD/t DS. In general, it can be concluded that AMB has an effective performance in conditioning

22

and dewatering of anaerobically digested sludge and is economically affordable in comparison to common

23

polymers.

24 25

Keywords: Sludge conditioning and dewatering, acidic-modified bentonite, anaerobically digested sludge, inorganic salts.

26 27 28 1

Corresponding author: Tel: +989121430209.

1

29

1. Introduction

30

The most important challenge in municipal wastewater treatment plants is excess sludge management

31

(Zhang et al., 2019; Gholikandi et al., 2017) since the cost of treatment, transfer and disposal is very high.

32

The most important processes in sludge management of municipal wastewater treatment plants are

33

conditioning and dewatering of sludge (Wei et al., 2018). Efficient conditioning and dewatering can lead to

34

reduced sludge volume and costs of sludge transport and depositing dramatically. Researches on materials

35

and methods for sludge conditioning are in processing to achieve lower moisture content and more solid

36

dry sludge cake. For example, materials such as inorganic polymer flocculant (Yang et al., 2019), iron and

37

aluminum salts (Liang et al., 2019), inorganic coagulants (Niu et al., 2013), modified phosphogypsum (Dai et

38

al., 2018), modified starch (Peng et al., 2017) and modified rice husk (Wu et al., 2016) were used for sludge

39

conditioning and dewatering. The new materials for sludge conditioning should be natural, inexpensive,

40

available and not harmful to the environment. Bentonite is a natural material that has the characteristics

41

listed above and is widely used in water and wastewater treatment (Pandey, 2017). It was used to remove

42

phosphorus (El-Bouraie and Masoud, 2017), heavy metals (El-Korashy et al., 2016), nitrates (Wasse Bekele and

43

Fernandez, 2014) and organic compounds (Hank et al., 2014) from water. Raw bentonite was used as a

44

coagulant and coagulant aid for dewatering the petrochemical and anaerobically digested sludge,

45

respectively, which results of both studies confirmed SRF (specific resistance to filtration) reduction of

46

sludge (Buyukkamaci and Kucukselek, 2007; Alvarenga et al., 2015). In this study, acidic-modified bentonite

47

(AMB) was used for sludge conditioning and dewatering. The bentonite main elements are SiO2 and

48

Al2O3. Acidic method was chosen for bentonite modification, because it converts Al2O3 to Al3+ ions and

49

increases SiO2 content and porosity of bentonite (Noyan et al., 2007; Bendou and Amrani, 2014). The Al3+

50

ions have coagulation property. The SiO2 of bentonite act as a skeleton builder in sludge dewatering

51

(Buyukkamaci and Kucukselek, 2007) and increasing porosity enhances sludge dewatering (Thapa et al.,

52

2009).

2

53

In the present study, the effect of acidic-modified bentonite (AMB) on conditioning and dewatering of

54

anaerobically digested sludge is investigated for the first time. The purposes of this study are at first the

55

proof of AMB ability in sludge conditioning and dewatering, the second one is to determine the

56

functional mechanism of the AMB in sludge conditioning and dewatering and the third is investigation of

57

economic costs of AMB use in sludge management. In this research, effective parameters including acid

58

to bentonite ratio, temperature, contact time and mixing speed were investigated to modify bentonite and

59

optimum conditions were determined by using the Taguchi method. Then XRF, XRD, FTIR and specific

60

surface area tests are done to investigate the structural changes of AMB. The effect of AMB on SRF, TTF,

61

CST, compressibility, floc morphological properties and filtration yield of anaerobically digested sludge

62

was investigated and compared with inorganic salts include FeCl3, ALCl3, Al2(SO4)3 and Fe2(SO4)3.

63

Performance of AMB was compared with mineral polymers due to the fact that it is an inorganic material

64

that is modified with mineral acids, and its functional mechanism is seen to be similar to that of mineral

65

polymers. Also, Zeta potential, bound water, XRF and EPS (extracellular polymeric substances) tests

66

were performed to determine the mechanism of AMB performance on anaerobically digested sludge

67

conditioning. Finally, AMB usage in sludge conditioning and dewatering was investigated economically.

68

2. Materials and methods

69

2.1 Materials

70

2.1.1 Anaerobically digested sludge (ADS)

71

In this study, the anaerobically digested sludge sample, supplied from mesophilic digester of the

72

traditional wastewater treatment plant (WWTP) in South of Tehran-Iran that fed with 50% of waste

73

activated sludge and 50% of primary sludge. The temperature of digester operating was 38 ± 1 ºC and the

74

time of hydraulic retention of the digester was 20±2 days. The digested sludge characteristics are shown

75

in Table 1.

76 3

77 78 79 80 81 82

Table 1. The characteristics of the anaerobically digested sludge sample Parameter Unit Value pH 6.95 ± 0.1 VS (volatile solid) g/L 12.63 ± 0.5 DS (dry solid) g/L 22.01 ± 1 VS/DS % 57 ± 2 COD (chemical oxygen demand) g/L 23.85 ± 3 SCOD (Soluble COD) mg/L 1367 ± 200 WC (water content) % 97.8 ± 0.1 Bound water g/g DS 4.73 ± 0.3 SRF (specific resistance to filtration) m/kg (265±20)× 1012 TTF (time to filter) Sec 600 ± 100 Zeta potential mV – (44.7 ± 3) Average diameter of sludge particles µm 47.5 ± 5

83 84 85

2.1.2 Chemical agents

86

Raw bentonite was prepared from the Kanisazejam Company in Iran. Bentonite has a surface area of 38

87

(m2/g) and average particles size of 78 (µm). The raw bentonite was washed twice with distilled water and

88

dried at 105 ° C for 24 hours and powdered using a crusher and passed through a sieve No. 200. 32%

89

Chloridric Acid (HCl) industrial grade from the Kimia Tehran Acid Company was used to modify

90

bentonite. Inorganic coagulants Al2(SO4)3.18H2O, FeCl3.6H2O, AlCl3.6H2O, and Fe2(SO4)3 were used by

91

Sigma Aldrich Company.

92

2.2 Methods

93

2.2.1 AMB preparation

94

To modify raw bentonite by using hydrochloric acid, effective parameters including the ratio of acid to

95

bentonite, reaction time, reaction temperature and mixing rate were investigated. Taguchi experiments

96

design model were used to determine the optimal amounts of parameters (Gholikandi et al., 2015). Each

97

parameter was defined in four levels (Table S1) and the orthogonal L16 array was selected to design the

98

experiments. Details of the use of the Taguchi method are presented in the supplementary information file

99

completely (section S1). The process was that of the bentonite was modified according to the design of

100

the experiments by the Taguchi method, and then 200 mg/g of AMB added to the sludge, and the SRF

101

reduction percentage was given as a result to the Taguchi model and analysis was performed. The greatest

4

102

effect on sludge dewatering was observed in the ratio of acid to bentonite = 0.8 (gram/gram), 90 °C

103

temperature, 4-hour reaction time and 300 rpm mixing speed. The error and reliability level of the

104

Taguchi model was 2.44% and 95%, respectively. The Taguchi model also determined that the ratio of

105

acid to bentonite with 59% participation was the most important parameter and mixing rate with 4.2%

106

participation was the least important parameter in bentonite modification (Table S5). Henceforth, the

107

AMB in this article, is bentonite prepared on the basis of optimum condition that ratio of acid to bentonite

108

= 0.8, 90 °C temperature, reaction time of 4 hours and mixing speed of 300 rpm and then dried at 105 ° C

109

for 24 hours and powdered using a crusher and passed through a sieve No. 200. The steps are accurately

110

described in the supplementary information, section S2.

111

2.2.2 Raw bentonite and AMB analysis

112

The detection of structure and phase analysis of raw bentonite and AMB sample was carried out by X-ray

113

diffraction (a Philips PW1710 XRD Spectrometer employing goniometers using Ni-filtered-Cu). The

114

scans were performed at 2θ=5–40°. X-ray fluorescence (XRF) of various bentonites was measured by

115

SPECTRO XEPOS operated at 50 W and 60 kV. The specific surface area, pore size and porosity of raw

116

bentonite and AMB were determined by N2 adsorption-desorption isotherm using a Bruner-Emmet-Teller

117

(BET, BELSORP-mini). FT-IR (Fourier transform infrared spectroscopy) analysis was carried out by

118

ABB Bomem- MB160D over the wave number of 4000–250 cm−1.

119

2.2.3 EPS extraction and analysis

120

A heat extraction procedure was utilized to extract various EPS components from the anaerobically

121

digested sludge (Li and Yang, 2007). The digested sludge sample was centrifuged (Centrifuge model:

122

BIOFUGE PRIMO-R) at 6000 rpm for 5 min in a 50mL tube and the supernatant was separated as

123

Soluble-EPS (S-EPS). The residual digested sludge at the end of the tube was re-suspended in 50 mL

124

NaCl 0.05% (w/v) which was heated at 70 °C. This suspension was blended by a vortex mixer for 10 min

125

and then was centrifuged at 6000 rpm for 10 min. The supernatant was taken as loosely bound-EPS (LB5

126

EPS). The remaining sludge was re-suspended again in 50 mL NaCl 0.05% (w/v) and was heated at 80°C

127

for 30 min then centrifuged at 6000 rpm for 15 min at the bottom of the tube. The supernatant was taken

128

as tightly bound-EPS (TB-EPS) (Dai et al., 2017). The extracted S-EPS, LB-EPS and TB-EPS were

129

analyzed for TOC (Total organic carbon), protein (PN), SiO2 (Silicon dioxide), Al3+ (Aluminum) and

130

polysaccharide (PS). The TOC was measured by a TOC analyzer (Shimadzu TOCV- CPH). The PN was

131

specified by the Lowry method using bovine serum albumin as the standard (Bollag et al., 1996) and PS

132

was determined by the phenol-sulfuric acid method with glucose as the standard (DuBois et al., 1956). The

133

SiO2 and Al3+ were detected by the 4500-SiO2.C and 3500-Al procedure of the standard method (APHA,

134

1999).

135

2.2.4 Bound water

136

A centrifugation method described by Jin et al. (2004) was employed for measuring bound water. 35 mL of

137

digested sludge sample at 3072 rpm (or 1057 g) for 600 sec was centrifuged and the supernatant was

138

sequester. The water content of residual sludge at the end of the tube was considered as bound water that

139

was measured at 105 ºC by an oven overnight (Xiao et al., 2017).

140

2.2.5 Aggregation, breakage, and re-growth of sludge floc (morphological properties)

141

Floc size, strength factor and recovery factor were used to evaluate the characteristics of sludge floc.

142

Increasing floc diameter after conditioning indicates a reduction in the repulsive forces between the

143

sludge particles and the formation of large particles with sedimentation property. Generally, increasing

144

the diameter of the sludge particles leads to improved sludge dewatering (Gholikandi et al., 2018). The

145

strength factor shows the floc power against shear force. The higher the power factor, the greater the floc

146

resistance to the shear force (Cao et al., 2016). The recovery factor shows how much the floc is able to

147

grow again and increase the diameter after the shear force brought on the floc. The higher the recovery

148

factor is, the greater the performance of used coagulant is (Jarvis et al., 2005). The experiments were

149

carried out in three steps. First, the coagulant was added to the sludge and mixed at a speed of 200 rpm 6

150

for 1.5 minutes, and then flocculation is performed for 15 minutes at a gentle speed of 30rpm. This step

151

was considered as aggregation. In the following, the sludge suspension is mixed for 30 seconds at

152

200rpm. This step is considered as a breakage. In the third step, the sludge suspension is mixed for 15

153

minutes at a gentle speed of 30 rpm, which is considered as a re-growth step (Jarvis et al., 2005). At the end

154

of each step, the size distribution of sludge particles was measured by using Malvern Mastersizer 2000

155

Malvern, UK, and the strength factor and recovery factor were measured by the Eq. 1 and Eq. 2 (Francois,

156

1987).

Strength factor (Sf ) =

d2 × 100% d1

Recovery factor (R f ) = (

(1)

d3 − d 2 ) × 100% d1 − d 2

(2)

157

d1 is the average diameter of sludge flocs in the aggregation step (µm). d2 is the average diameter of

158

sludge flocs in breakage step (µm). d3 is the average diameter of sludge flocs in re-growth step (µm).

159

2.2.6 Sludge compressibility testing

160

The sludge cake compressibility shows the sludge compactability when normal pressure is applied (Zhang

161

et al., 2017b). In practice, sludge compressibility is measured as the slope of a log-log plot of SRF against

162

the applied differential pressure. The coefficient of compressibility (s) is got by Eq. 3.

SRF1 P = ( 1 )S SRF2 P2

(3)

163

P2 and P1 are two distinct filtration pressures (Pa), SRF2 and SRF1 are specific resistance to filtration at P2

164

and P1, respectively. If s = 1, the pressure variations do not affect the sludge compressibility and sludge is

165

incompressible. If s < 1, sludge compressibility reduce and sludge permeability will improve so

166

dewatering will enhanced. If s > 1, sludge compressibility increase and sludge permeability decrease

167

because by increasing the pressure, sludge particles are deformed and sludge porosity is reduced (Coackley

168

and Jones, 1956).

7

169

2.2.7 Evaluation of sludge filtration yield

170

In order to appraise a conditioned digested sludge filtration process, the net yield of digested sludge

171

filtration (YN (kg/m2.h)) is determined. YN is the rate of total solids filtered per unit area per unit time.

172

The exact YN value is obtained when the filtrate volume is 90%. YN90 is calculated from the following

173

formula (Qi et al., 2011a).

YN 90 =

VS 90 × RS T90 × A

(4)

174

Where VS90 is the volume of conditioned digested sludge filtered at 90% of completion (m3), RS is the

175

concentration of digested sludge solids (kg/m3). T90 is the time to filter (h) at 90% of completion and A is

176

surface area of filtration (m2). The higher the YN90 value, the better the performance of the conditioned

177

sludge filtration process.

178

2.2.8 Correction coefficient (k)

179

k is a correction coefficient that is applied to consider the effect of the added conditioner. Correction

180

coefficient (k) is calculated by relation 5. In this study, the coefficient k was considered in SRF, YN90,

181

compressibility, bound water and EPS of sludge which was conditioned and dewatered by AMB.

k=

Original sludge solids mass Original sludge solids mass + Conditioner solids mass

(5)

182 183

2.2.9 Other method

184

In order to measure solids (VSS, VS, TSS, and TS), COD, TTF, CST and Fe, the following methods were

185

used respectively: 2540, 5220D, 2710H, 2710G and 3500-Fe standard methods (APHA, 1999). Also,

186

HANNA pH meter-211 was used to measure pH. Zetasizer Nano from Malvern Company was used to

187

measure the zeta potential. SRF was measured by using a Buchner Funnel with a Whatman® No. 1 filter

8

188

paper and exerting vacuum suction (To et al., 2016). The water content of sludge was measured based on

189

U.S. EPA standard (U.S. EPA, 1989). Also, a filter press (Nabtec laboratory equipment LFP-150, IR) was

190

used for sludge dewatering. Mercury porosimetry tests (section S4 in supplementary information) are

191

performed on the compressed sludge cakes to determine the cake porosity.

192

3. Result and discussion

193

3.1 Characterization of raw bentonite and AMB

194

The XRD pattern, XRF, FT-IR, specific surface area, porosity of raw bentonite and AMB samples are

195

shown and described in section S3 of supplementary information. The XRD pattern (Fig. S1) showed that

196

the bentonite structure is slightly altered from crystal to amorphous after acidic modification (Vuković et

197

al., 2005). In the first peak of XRD pattern (Fig S1), the basal spacing is reduced from d(001)=12.6Å to

198

d(001)=12.1Å because of Ca2+ and Al3+ cations exchange with H+ (Bieseki et al., 2013). The XRF analysis

199

showed that SiO2 and Al2O3 were the main components of raw bentonite and AMB. The relative SiO2

200

amount increased by acid activation whereas, other elements (Al2O3, Fe2O3, TiO2, MnO, CaO, MgO,

201

Na2O and K2O) decreased due to the inter-layer exchangeable cations (Na+, K+ Ca2+, Mg2+, Fe3+ and Al3+)

202

dissolved easily by gentle acid treatment (Bendou and Amrani, 2014). N2 adsorption-desorption analysis

203

(Fig. S2) show that specific surface area of bentonite is increased from 37.9 m2/g to 58 m2/g by acid

204

treatment. Replacement of the inter-layer cations with H+ ions of acid, and dissolution of constructional

205

cations (Si4+, Al3+) in the following lead to increase the bentonite specific surface area (Rabie et al., 2018).

206

Also after acidification, increasing total pore volume (from 0.09 cm3/g to 0.13 cm3/g) and average

207

porosity (from 21.6% to 31.2%) are observed. The dissolution of the exchangeable cations (Na+, Ca2+,

208

Al3+, Fe3+ and Mg2+) from smectite mineral layers leads to increase total pore volume and porosity (Noyan

209

et al., 2007; Bieseki et al., 2013). Generally, modification of bentonite by acid enhances its adsorption (Pawar

210

et al., 2016). The FT-IR spectra of the raw bentonite and AMB are displayed in Fig. S3. The acid treatment

211

of bentonite leads to decrease intensity or disappearance of OH-bending bands such as Al-Al-OH kinds,

9

212

Fe-Fe-OH, Al-Fe-OH and Si-O-Al (Luna et al., 2018; Javed et al., 2018; Li et al., 2018). This shows that the

213

release of aluminum was happened by acid treatment. Of course, color changing of bentonite from white

214

to yellow proves this claim (Fig. S4) that the aluminum contained in the bentonite structure has been

215

released after acidic modification and the reaction 6 has probably occurred. In general, one of the reasons

216

that can be concluded if AMB is suitable for sludge conditioning or not, is the presence of aluminum ion

217

in the bentonite structure and its release after acidic modification. The second reason is the probability of

218

increasing sludge porosity through the AMB addition. Raw bentonite is a porous material, which its

219

porosity increases with acidic modification. Increaseing sludge porosity by AMB, leads to reduce sludge

220

compressibility and improve dewatering.

Al2O3 + HCl → 2 AlCl3 + 3H 2O

(6)

221

3.2 The influence of AMB on sludge SRF and its properties

222

The effect of conditioning by using raw bentonite and AMB on SRF of anaerobic digest sludge was

223

evaluated in Fig. 1 (The correction coefficient (k) is considered in the SRF results of AMB conditioner)

224

and compared with the performance of FeCl3, AlCl3, Fe2(SO4)3 and Al2(SO4)3 salts. By increasing the

225

amount of raw bentonite from 0 to 500 mg/g DS, sludge SRF reduced by 16.6%, showing that raw

226

bentonite had no significant effect on reducing the SRF of anaerobic digest sludge and dewatering

227

improvement. Alvarenga et al reported the same results about the effect of raw bentonite on sludge

228

conditioning and dewatering (Alvarenga et al., 2015). The study of AMB effect on sludge SRF showed that

229

the best performance of AMB on anaerobic digest sludge conditioning is at a concentration of 300 mg/g

230

DS and leads to a 95.8% reduction of sludge SRF. Also, FeCl3 and AlCl3 salts resulted in 95% and 93.1%

231

SRF reduction at an optimal concentration of 150 mg/g DS, respectively, and salts of Fe2(SO4)3 and

232

Al2(SO4)3 resulted in a decrease of 83.4 and 80.4% SRF at an optimal concentration of 300 mg/g DS,

233

respectively. Liang et al have also reported similar results in the effect of inorganic salts on excess sludge

234

(Liang et al., 2019). The effect of conditioning on the sludge properties was also studied and the results are

235

presented in Table 2. AMB resulted in a decrease in sludge pH from 6.95 ± 0.1 to 6.63 ± 0.1, but 10

236

inorganic salts reduced pH to less than 5.5, which required neutralization PH and lime consumption. Also,

237

sludge CST, TTF and WC are studied and it was determined that AMB has the best performance in

238

sludge conditioning. The turbidity conditions, COD of sludge supernatant and its alkalinity were

239

investigated and AMB had the best performance in removing turbidity and COD from the supernatant.

240

The reason for the better performance of AMB is the presence of SiO2 in it (the 60.94% of AMB content

241

is SiO2). SiO2 (as coagulant aid) increases the coagulation and flocculation performance of positive metal

242

ions, thereby improving sludge conditioning and dewatering (Zhang et al., 2017a). The SiO2 act as a center

243

or a core for the formation of larger, denser, stronger and settable floc (Hay, 1944; Baylis et al., 1937). To

244

confirm this claim, the effect of AMB on morphological characteristics of floc was investigated (section

245

3-3). Also, the amount of SiO2 in different layers of EPS was measured to confirm the SiO2 presence in

246

floc structure. 280

SRF×(1012 m/kg)

240 200

Bentonite AMB Al₂(SO₄)₃ Fe₂(SO₄)₃ AlCl₃ FeCl₃

160 120 80 40 0 0

247 248 249

50

100

150

200 250 300 350 Dosage (mg/g DS)

400

450

500

Fig. 1. The effect of AMB and inorganic salts dosage on SRF. The correction coefficient (k) is considered in the SRF results of AMB conditioner.

250 251 252 253

11

254 conditioner AMB Al2(SO4)3 Fe2(SO4)3 AlCl3 FeCl3

Optimum dosage (mg/g DS) 300 ± 20 300 ± 10 300 ± 10 150 ± 10 150 ± 10

Table 2. Effect of conditioning on the sludge features Supernata pH after Supernatant nt b c conditioni TTF (sec) WC (%) COD Turbidity (mg/L)e ng a d (NTU) 6.63 ± 0.1 115 ± 20 86.7 ± 0.1 123 ± 10 792 ± 50 5.38 ± 0.1 140 ± 30 89.1 ± 0.1 364 ± 50 1085 ± 60 5.23 ± 0.1 137 ± 50 88.3 ± 0.1 411 ± 50 1103 ± 60 5.45 ± 0.1 118 ± 20 87.2 ± 0.1 198 ± 50 907 ± 50 5.41 ± 0.1 129 ± 20 86.8 ± 0.1 226 ± 50 884 ± 50

Alkalinity as CaCO3 (mg/g DS)f

CST (sec)g

83 ± 10 75 ± 10 69 ± 10 71 ± 10 73 ± 10

27 ± 10 57 ± 10 51 ± 10 35 ± 10 32 ± 10

a: Anaerobic digested sludge pH before conditioning = 6.95±0.1 b: Anaerobic digested sludge TTF before conditioning = 600 ± 100 sec c: Anaerobic digested sludge WC (water content) before conditioning = 97.8±0.1 d: Anaerobic digested sludge supernatant turbidity before conditioning = 2185 ± 50 NTU e: Anaerobic digested sludge supernatant COD before conditioning = 1367 ± 200 f: Anaerobic digested sludge alkalinity as CaCO3 before conditioning = 168 ± 50 mg/g DS = 3700 ± 1000 mg/L g: Anaerobic digested sludge CST before conditioning = 283 ± 50 sec

255 256

3.3 The influence of coagulants on aggregation, breakage, and re-growth of sludge floc (morphological

257

properties)

258

The effect of coagulants on aggregation, breakage, and re-growth of sludge floc (morphological

259

properties) was investigated in Fig. 2. The results showed that the average size of anaerobically digested

260

sludge particles increased from 47.5µm to 410µm, 385µm, 371µm, 321.5µm and 311.5µm by using FeCl3,

261

AMB, AlCl3, Fe2(SO4)3 and Al2(SO4)3 respectively (the aggregation step). The best performance in

262

increasing particle diameter or sludge flocs was associated with FeCl3 and AMB. In the following, the

263

effect of shear force on the sludge floc was investigated by using the Sf parameter (breakage step). The Sf

264

parameter represents the floc resistance potential against shear force, and the larger it is, the floc structure

265

is stronger and denser. The amount of Sf for conditioned sludge with AMB, AlCl3, FeCl3, Al2(SO4)3 and

266

Fe2(SO4)3 was 23.7%, 21.1%, 18.9%, 17.7% and 15.1%, respectively. The best performance against shear

267

force was related to the conditioned sludge floc with AMB. The Rf parameter was also studied (Re-

268

growth step). This parameter shows the ability of the sludge particles after applying the shear force to

269

reform the floc. The greater this parameter is, the better the performance of flocculation. The amount of

270

Rf for conditioned sludge with AMB, AlCl3, FeCl3, Al2(SO4)3 and Fe2(SO4)3 was 26.1%, 22.8%, 19.8%,

271

14% and 13.2%, respectively. The best performance in re-growth of sludge floc is related to the sludge

272

that is conditioned with the AMB. Investigating the particle size, Sf and Rf showed that AMB, in addition

273

to improve sedimentation and sludge dewatering by increasing the size of sludge particles, also provides 12

274

denser and stronger flocs rather than typical inorganic salts. The increase in sludge particle diameter and

275

the formation of large sludge flocs is due to the presence of Al3+ ions in the AMB. Also, the resistance

276

increase of conditioned sludge flocs with AMB against shear force and re-flocculation improvement are

277

due to SiO2 in AMB. Previous studies reported similar results on SiO2 performance in water purification

278

sludge floc stabilization (Hay, 1944; Baylis et al., 1937).

279 9

Aggregation Breakage Re-growth

8

Volume (%)

7 6 5 4

d₁ = 385 (µm) d₂ =91.5 (µm) d₃ =168 (µm) Sf =23.7 (%) Rf =26.1 (%)

3 2 1 0

0.3 (a): AMB

3

8

Volume (%)

5 4

300

3000

Aggregation Breakage Re-growth

7 6

30 Particle size (µm)

d₁ = 311.5 (µm) d₂ =55.07 (µm) d₃ =91 (µm) Sf =17.7 (%) Rf =14 (%)

3 2 1 0

0.2 (b): Al₂(SO₄)₃

2

20 Particle size (µm)

13

200

2000

8 Aggregation Breakage Re-growth

7

Volume (%)

6 5 4

d₁ = 321.5 (µm) d₂ =48.7 (µm) d₃ =84.6 (µm) Sf =15.1 (%) Rf =13.2 (%)

3 2 1 0

0.2 (c): Fe₂(SO₄)₃ 8 7

Volume (%)

6 5 4

2

20 Particle size (µm)

200

2000

30 Particle size (µm)

300

3000

Aggregation Breakage Re-growth d₁ = 371 (µm) d₂ =78.2 (µm) d₃ =145 (µm) Sf =21.1 (%) Rf =22.8 (%)

3 2 1 0

0.3 (d): AlCl₃

3

14

8 7

Volume (%)

6 5 4

Aggregation Breakage Re-growth d₁ = 410 (µm) d₂ =77.4 (µm) d₃ =143 (µm) Sf =18.9 (%) Rf =19.8 (%)

3 2 1 0

0.3 (e): FeCl₃

280 281

3

30 Particle size (µm)

300

3000

Fig. 2. The influence of coagulants on aggregation, breakage, and re-growth of sludge floc (under optimal dosages presented in Table 2)

282 283

3.4 The effect of AMB on compressibility (s) and filtration yield (YN) of sludge

284

The s and YN was used to evaluate physical conditioner. In this section, it becomes clear that if AMB acts

285

as a physical conditioner or not? Reducing s coefficient shows sludge compressibility reduction and

286

dewatering process improvement. For an anaerobic unconditioned sludge, s=1, means that variation of

287

pressure doesn’t affect the sludge dewatering. Compressibility of conditioned sludge with AMB (dosage

288

= 300 mg/g DS) was reduced from 1 to 0.8. This result indicates that AMB acts as a skeleton builder

289

(physical conditioner). Due to the distribution of the stiff AMB particles (especially SiO2), a sludge cake

290

with a reduced compressibility was produced. The second parameter is the filtration yield (YN90). For

291

unconditioned digested sludge YN90 is 0.2 kg/m2.h. The amount of YN90 for conditioned digest sludge with

292

AMB (dosage = 300 mg/g DS) is 1.82. The AMB increased sludge filtration yield (YN90) by 810%.

293

AMB particles help to construct a rigid and porous structure of sludge that leads to decrease s and

294

increase YN. To prove this event, the sludge porosity was investigated with and without AMB conditioner

295

(Fig. S5 in supplementary information). Increasing porosity of sludge reduces the sludge compressibility

296

and increases filtration yield (Thapa et al., 2009, Ning et al., 2013). Fig S5 showed that the porosity of 15

297

conditioned sludge with AMB was increased significantly compared to unconditioned sludge. These

298

results indicate that AMB conditioner acts as a skeletal builder (physical conditioner) in sludge

299

conditioning and dewatering. Also, Performance of AMB was compared with performance of physical

300

conditioner in previous studies (Table 3). Table 3 shows that performance of AMB as physical

301

conditioner is acceptable according to conditioner dosage.

302 Physical conditioner AMB Fly ash Rice husk biochar Lignite Gypsum Slag

Table 3. Review of performance of physical conditioner in previous studies Percentage of reducing Percentage of increasing Kind of sludge compressibility (s) filtration yield (YN) Anaerobicly digested sludge 20% 800 % Oily sludge 88 % 1100 % Waste activated sludge 42.6% 2800 % Anaerobicly digested sludge …….. 550 % Alum sludge 19.7% 400% Excess activated sludge 58.3% 551.3%

Conditioner dosage 0.3 g/g DS 5.8 g/g DS 0.6 g/g DS 1 g/g DS 0.6 g/g DS 1.5 g/g DS

reference This study Zall et al., 1987 Wu et al., 2016 Qi et al., 2011b Zhao et al., 2001 Ning et al., 2013

303 304

3.5 Impact of AMB on zeta potential and bound water

305

Reduction of negative zeta potential in sludge particles surface leads to form larger particles of sludge

306

with sedimentation. Also, one of the important parameters in a conditioner performance is its effect on

307

reducing the bound water of the sludge particles. In Fig. 3a (The correction coefficient (k) is considered in

308

the bound water results of AMB conditioner), the effect of coagulants on zeta potential and bound water

309

is investigated. AMB reduced zeta potential and bound water to 96.4% and 60.8%, respectively, and had

310

the best performance among coagulants. The negative zeta potential of raw bentonite particles was -27

311

mV, but when raw bentonite was modified with acid, the zeta potential of the particles became positive

312

(+14 mV). In 2017, Shokri et al reported similar results and stated that the acidic modification of bentonite

313

produced a positive zeta potential in the particles (Shokri et al., 2017). In acidic treatment, H+ ions are

314

replaced with the Na+, K+ Ca2+, Mg2+, Fe3+ and Al3+ ions (section S3-2) in the bentonite (Bendou and

315

Amrani, 2014) and these released ions lead to positive zeta potential in the modified bentonite particles

316

(Şans et al., 2017). Inorganic salts (FeCl3 and etc.) have Fe

317

potential of sludge, while AMB has Na+, K+ Ca2+, Mg2+, Fe3+ and Al3+ ions that they reduce negative zeta

318

potential of sludge better than inorganic salts.

16

3+

or Al3+ ions for reduction of negative zeta

319

Main reason of bound water reduction and increasing zeta potential of the sludge particles is existence of

320

Al3+ ions in the AMB. After adding AMB to the sludge, Al3+ ions were released in the sludge

321

environment and resulting in negative zeta potential decrease and bound water reduction. To prove this

322

claim, AMB powder was dissolved in distilled water and the amount of Al3+ ion was measured. The

323

results showed that after adding 1 gram of AMB to 1 liter of distilled water, the amount of Al3+ ion

324

increased from 0 to 51 ± 5 mg/L. Previous studies reported that Al3+ ions were adsorbed at the sludge

325

particles surface that resulting in a negative zeta potential reduction and decreasing bound water of the

326

sludge (Katsiris et al., 1987; Yang et al., 2019). Also, changing in raw bentonite structure from crystalline to

327

amorphous (Section S3-1) and increasing surface of bentonite particles (Section S3-3) after acidic

328

modification leads to a significant increase in AMB absorption (Vuković et al., 2005), which cause to

329

absorb and reduce bound water at the surface of sludge particles. These results indicate that AMB acts as

330

a chemical conditioner.

331

3.6 The influence of AMB and inorganic salts on sludge EPS

332

EPS plays a key role in sludge dewatering and its reduction leads to improved sludge dewatering (Zhou et

333

al., 2015). EPS has three components: S-EPS, LB-EPS and TB-EPS particles and also the closest layer to

334

the center of sludge particles is the TB-EPS, and the next layer is LB-EPS. The negative Zeta potential of

335

the sludge and bound water are formed in the TB-EPS and LB-EPS layers, respectively (Gholikandi et al.,

336

2018). This means that the reduction of negative Zeta potential and bound water represents a failure of the

337

structure of the TB-EPS and LB-EPS, respectively (Masihi and Gholikandi, 2018). The three parameters

338

TOC, PN and PS were measured at the extracted EPS (Fig. 3 (The correction coefficient (k) is considered

339

in the EPS results of AMB conditioner)). Sludge conditioning with inorganic salts and AMB increased

340

the amount of TOC in S-EPS (Fig. 3b), which is due to the destruction of the EPS structure by the Al3+

341

and Fe3+ ions and entering it into the sludge supernatant (Niu et al., 2013). The concentration of TOC was

342

207±4 mg/g DS in the S-EPS of anaerobically digested sludge that increased to 234.7±5 mg/g DS after

343

conditioning with AMB. Also, increasing the concentration of TOC in other inorganic salts is as follow: 17

344

FeCl₃=233.5±5 mg/g DS> AlCl₃> Fe₂(SO₄)₃> Al₂(SO₄)₃. Sludge conditioning by using AMB, FeCl₃,

345

AlCl₃, Fe₂(SO₄)₃ and Al₂(SO₄)₃ decrease the TOC of the LB-EPS layer 50.7%, 43.6%, 39.1%, 52.9%

346

and 48.9% respectively. The results of LB-EPS reduction correlate with the reduction of the bound water

347

(Fig. 3a) and showed that the reduction of LB-EPS leads to a reduction of the bound water. Also, sludge

348

conditioning by using AMB, FeCl₃, AlCl₃, Fe₂(SO₄)₃ and Al₂(SO₄)₃ reduced TOC of the TB-EPS layer

349

75.2%, 75%, 71.5%, 58.7% and 50.2% respectively. The results of TB-EPS reduction are also consistent

350

with the negative Zeta potential (Fig. 3a), showing that the destruction of the TB-EPS layer results in a

351

decrease in the negative Zeta potential. Also, changes in the concentration of PN (Fig. 3c) and PS (Fig.

352

3d) in the EPS are similar to changes in the concentration of TOC. In general, it can be concluded that

353

AMB has a better performance than other inorganic salts and has the ability to reduce TB-EPS and LB-

354

EPS simultaneously. To determine the functional mechanism of AMB, the XRF test was measured before

355

and after the sludge conditioning, and the results are presented in Table S9 of supplementary information.

356

This table shows that the amount of SiO2 and Al2O3 in the conditioned sludge with AMB has increased by

357

9.07% and 1.86% respectively. Increasing the concentrations of SiO2 and Al2O3 in sludge shows that Si

358

and Al Elements have affected on sludge dewatering. The concentration of Al and SiO2 of the EPS

359

components are presented in Table S10 of supplementary information (The correction coefficient (k) is

360

considered in the Al and SiO2 results of AMB conditioner). The results show that Al ions and SiO2 are

361

more absorbed in the TB-EPS and LB-EPS, respectively, and AMB through Al ions and SiO2 decreases

362

sludge EPS and improves dewatering. Also, previous studies reported that Al ions had the greatest impact

363

on the structure of the TB-EPS (Li et al., 2012). Presence of SiO2 in LB-EPS layer indicates that SiO2 act as

364

a center or a core for the formation of suitable floc.

18

0

4

-10 Bound water Zeta potential

3

-20

2

-30

1

-40

0

-50 ADS

AMB

Al₂(SO₄)₃ Fe₂(SO₄)₃

AlCl₃

FeCl₃

(a)

S-EPS

250

LB-EPS

TB-EPS

TOC (mg/g DS)

200

150

100

50

(b)

0 ADS

AMB

Al₂(SO₄)₃

19

Fe₂(SO₄)₃

AlCl₃

FeCl₃

Zeta potential (mV)

Bound water (g/g DS)

5

140

Soluble EPS

LB-EPS

TB-EPS

120

PN (mg/g DS)

100 80 60 40 20

(c)

0 ADS

AMB

30

Al₂(SO₄)₃

Soluble EPS

Fe₂(SO₄)₃

AlCl₃

LB-EPS

FeCl₃

TB-EPS

25

PS (mg/g DS)

20

15

10

5

(d) 0

365 366 367

ADS

AMB

Al₂(SO₄)₃

Fe₂(SO₄)₃

AlCl₃

FeCl₃

Fig. 3. (a): The effect of conditioner on zeta potential and bound water of digested sludge (under optimal dosages presented in Table 2). (b), (c) and (d): The effect of conditioner on EPS of digested sludge (under optimal dosages presented in Table 2). The correction coefficient (k) is considered in the bound water and EPS results of AMB conditioner.

368 369

3.7 Economic aspects of using AMB for sludge conditioning and dewatering

370

The cost of using AMB and common inorganic coagulants for anaerobically digested sludge conditioning

371

was investigated in Table 4. Making the cost of one ton of AMB is described in section S5 of

372

supplementary information. The cost of sludge conditioning by using AMB is 33.79 $/t DS, which is 20

373

much lower than common inorganic coagulants (Table 4). For the case of 450,000 m3/day Municipal

374

WWTP in South of Tehran with a sludge generation of 80 t/day, the total annual production of sludge is

375

29200 t DS/y. The annual costs of the conditioners including AMB, FeCl3, AlCl3, Fe2(SO4)3 and

376

Al2(SO4)3 are presented in table 4.

377

The dosage of AMB was 300 mg/g DS. It may be thought that this dosage will increase the amount of

378

sludge volume, but the volume of conditioned sludge by the AMB is less than other conditioned sludges

379

after dewatering. The volume of 1 ton sludge DS after conditioning and dewatering by AMB is 3.17 m3.

380

The volume of 1 ton sludge DS after conditioning and dewatering by FeCl3, AlCl3, Fe2(SO4)3 and

381

Al2(SO4)3, is 3.3, 3.55, 3.87 and 4.05 m3, respectively. The calculations of determining the volume of

382

dewatered sludge are described in Section S6 completely. Therefore, it can be concluded that conditioning

383

and dewatering sludge by AMB has a lower volume and less sludge transport cost than other coagulants.

384

Also, in terms of sludge volume, AMB can be compared to cationic polyelectrolytes (see section S7 in

385

supplementary information).

386

Table 4. The cost of using AMB and common inorganic coagulants for sludge conditioning DS percentage of volume of 1 ton annual costs of Dosage Unit price Agent cost sludge after sludge DS after the conditioners conditioner (t/t DS) (USD$/t) (USD$/t DS) conditioning and conditioning and in case study dewatering (%) f dewatering (m3) h (USD$/y) AMB 0.30 112.625 d 33.79 41 ± 0.5 3.17 986,668 Al2(SO4)3 0.584 a 150 e 87.65 26 ± 0.5 4.03 2,559,380 Fe2(SO4)3 0.30 280 e 84 28 ± 0.5 3.87 2,452,800 b AlCl3 0.272 300 e 81.5 29 ± 0.5 3.55 2,379,800 FeCl3 0.250 c 300 e 75 32 ± 0.5 3.3 2,190,000 a: Al2(SO4)3 .18H2O was used as hydrous salt of Al2(SO4)3 for sludge conditioning. Optimum dosage is 300 kg of Al2(SO4)3 that is equal to 584.34 kg Al2(SO4)3 .18H2O. b: AlCl3 .6H2O was used as hydrous salt of AlCl3 for sludge conditioning. Optimum dosage is 150 kg of AlCl3 that is equal to 271.6 kg AlCl3 .6H2O. c: FeCl3 .6H2O was used as hydrous salt of FeCl3 for sludge conditioning. Optimum dosage is 150 kg of FeCl3 that is equal to 250 kg FeCl3 .6H2O. d: unit price of AMB was calculated in section S5 of supplementary information. e: The chemical agents price was collected from http://www.alibaba.com f: dewatering of conditioned sludge was performed by a filter press at a pressure of 9±1 bars for 30 min. DS of sludge before conditioning and dewatering was (2.2 ± 0.2) % h: calculations of sludge volume is completely described in section S6 of supplementary information.

387 388

4. Conclusion

389

Sludge conditioning and dewatering are two important processes in sludge handling and disposal .There

390

are a lot of studies about chemical sludge conditioning that have been done in recent years. The aim of

21

391

these researches is reducing the sludge volume and cost of conditioning and dewatering. In this study, the

392

use of AMB for sludge conditioning and dewatering was investigated. Compressibility and filtration yield

393

results indicated that AMB acts as a physical conditioner or a skeleton builder. Also, the results of

394

negative zeta potential, the bound water and the EPS showed that AMB acts as a chemical conditioner

395

too. So it can be said that functionally the AMB is a physically-chemical conditioner. Conditioned and

396

dewatered sludge by AMB has a lower volume and less sludge transport cost than other coagulants. Also,

397

AMB is an effective and inexpensive option for sludge conditioning that reduces sludge volume

398

significantly. It is also easy to prepare that and can be industrialized. This study showed that AMB is a

399

new and applicable option for sludge conditioning and dewatering.

400 401

References

402

Alvarenga, E., Hayrapetyan, S., Govasmark, E., Hayrapetyan, L. and Salbu, B., 2015. Study of the flocculation of

403

anaerobically digested residue and filtration properties of bentonite based mineral conditioners. Journal of

404

Environmental Chemical Engineering, 3(2), 1399-1407.

405

American Public Health Association (APHA), 1999. In: Standard Methods for Examination of Water and

406

Wastewaters, twentieth ed. U.S. Environmental Protection Agency, Washington D.C.

407

Baylis, J.R., Powell, S.T. and Black, A.P., 1937. Silicates as aids to coagulation [with discussion]. Journal

408

(American Water Works Association), 29(9), 1355-1396.

409

Bendou, S. and Amrani, M., 2014. Effect of hydrochloric acid on the structural of sodic-bentonite clay. Journal of

410

Minerals and Materials Characterization and Engineering, 2(05), 404.

411

Bieseki, L., Treichel, H., Araujo, A.S. and Pergher, S.B.C., 2013. Porous materials obtained by acid treatment

412

processing followed by pillaring of montmorillonite clays. Applied Clay Science, 85, 46-52.

413

Bollag, D.M.E., Rozycki, S.J., Bollag, M.D., Rozycki, M.D., Edelstein, S.J., 1996. Proteins Methods (No. 547.96

414

BOL).

22

415

Buyukkamaci, N. and Kucukselek, E., 2007. Improvement of dewatering capacity of a petrochemical sludge. Journal

416

of hazardous materials, 144(1-2), 323-327.

417

Cao, B., Zhang, W., Wang, Q., Huang, Y., Meng, C. and Wang, D., 2016. Wastewater sludge dewaterability

418

enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation. Water Research, 105, 615-624.

419

Coackley, P. and Jones, B.R.S., 1956. Vacuum sludge filtration: I. Interpretation of results by the concept of specific

420

resistance. Sewage and Industrial Wastes, 28(8), 963-976.

421

Dai, Q., Ma, L., Ren, N., Ning, P., Guo, Z., Xie, L. and Gao, H., 2018. Investigation on extracellular polymeric

422

substances, sludge flocs morphology, bound water release and dewatering performance of sewage sludge under

423

pretreatment with modified phosphogypsum. Water research, 142, 337-346.

424

Dai, Y., Huang, S., Liang, J., Zhang, S., Sun, S., Tang, B. and Xu, Q., 2017. Role of organic compounds from

425

different EPS fractions and their effect on sludge dewaterability by combining anaerobically mesophilic digestion

426

pre-treatment and Fenton’s reagent/lime. Chemical Engineering Journal, 321, 123-138.

427

Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.T. and Smith, F., 1956. Colorimetric method for determination

428

of sugars and related substances. Analytical chemistry, 28(3), 350-356.

429

El Bouraie, M. and Masoud, A.A., 2017. Adsorption of phosphate ions from aqueous solution by modified bentonite

430

with magnesium hydroxide Mg (OH) 2. Applied Clay Science, 140, 157-164.

431

El-Korashy, S.A., Elwakeel, K.Z. and El-Hafeiz, A.A., 2016. Fabrication of bentonite/thiourea-formaldehyde

432

composite material for Pb (II), Mn (VII) and Cr (VI) sorption: A combined basic study and industrial application.

433

Journal of Cleaner Production, 137, 40-50.

434

Francois, R.J., 1987. Strength of aluminium hydroxide flocs. Water Research, 21(9), 1023-1030.

435

Gholikandi, G.B., Azimipour, M., Masihi, H., 2015. Sludge stabilization and reuse employing Fered-Fenton

436

technology (chapter book): an investigation view to applications of artificial neural networks modeling and taguchi

437

method. In: Golikandi, G.B. (Ed.), Enhanced Electrochemical Advanced Oxidation Processes for Wastewater

438

Sludge Stabilization and Reuse. E-Publishing Nova Science Publishers., New York, pp. 126-150.

23

439

Gholikandi, G.B., Sadabad, H.R., Karami, S. and Masihi, H., 2017. Heavy metal ions removal from waste-activated

440

sludge by Fered-Fenton electrochemical advanced oxidation process (EAOP) with the aim of agricultural land

441

application. Desalination and Water treatment, 93, 250-256.

442

Gholikandi, G.B., Zakizadeh, N. and Masihi, H., 2018. Application of peroxymonosulfate-ozone advanced oxidation

443

process for simultaneous waste-activated sludge stabilization and dewatering purposes: a comparative study. Journal

444

of environmental management, 206, 523-531.

445

Hank, D., Azi, Z., Hocine, S.A., Chaalal, O. and Hellal, A., 2014. Optimization of phenol adsorption onto bentonite

446

by factorial design methodology. Journal of Industrial and Engineering Chemistry, 20(4), 2256-2263.

447

Hay, H.R., 1944. Water Purification Methods involving Sodium Silicates. Journal of the American Water Works

448

Association, 36(6), 626-36.

449

Jarvis, P., Jefferson, B. and Parsons, S.A., 2005. Breakage, regrowth, and fractal nature of natural organic matter

450

flocs. Environmental science & technology, 39(7), 2307-2314.

451

Javed, S.H., Zahir, A., Khan, A., Afzal, S. and Mansha, M., 2018. Adsorption of Mordant Red 73 dye on acid

452

activated bentonite: kinetics and thermodynamic study. Journal of Molecular Liquids, 254, 398-405.

453

Jin, B., Wilén, B.M. and Lant, P., 2004. Impacts of morphological, physical and chemical properties of sludge flocs

454

on dewaterability of activated sludge. Chemical Engineering Journal, 98(1-2), 115-126.

455

Katsiris, N. and Kouzeli-Katsiri, A., 1987. Bound water content of biological sludges in relation to filtration and

456

dewatering. Water Research, 21(11), 1319-1327.

457

Li, H., Wen, Y., Cao, A., Huang, J., Zhou, Q. and Somasundaran, P., 2012. The influence of additives (Ca2+, Al3+,

458

and Fe3+) on the interaction energy and loosely bound extracellular polymeric substances (EPS) of activated sludge

459

and their flocculation mechanisms. Bioresource Technology, 114, 188-194.

460

Li, W., Bai, Y., Ma, Q., Chen, W., Wu, M. and Ma, H., 2018. Polyacrylic acid/CTAB-bentonite coated filter paper:

461

Efficient and rapid removal of anionic and cationic dyes. Applied Surface Science, 458, 903-909.

24

462

Li, X.Y. and Yang, S.F., 2007. Influence of loosely bound extracellular polymeric substances (EPS) on the

463

flocculation, sedimentation and dewaterability of activated sludge. Water research, 41(5), 1022-1030.

464

Liang, J., Zhang, S., Huang, J., Huang, S., Zheng, L., Sun, S., Zhong, Z., Zhang, X. and Yu, X., 2019.

465

Comprehensive insights into the inorganic coagulants on sludge dewatering: comparing aluminium and iron salts.

466

Journal of Chemical Technology & Biotechnology, 94(5), 1534-1550.

467

Lin, Y.F., Jing, S.R. and Lee, D.Y., 2001. Recycling of wood chips and wheat dregs for sludge processing.

468

Bioresource Technology, 76(2), 161-163.

469

Luna, F., Cecilia, J., Saboya, R., Barrera, D., Sapag, K., Rodríguez-Castellón, E. and Cavalcante, C., 2018. Natural

470

and Modified Montmorillonite Clays as Catalysts for Synthesis of Biolubricants. Materials, 11(9), 1764.

471

Masihi, H., & Gholikandi, G. B., 2018. Employing Electrochemical-Fenton process for conditioning and dewatering

472

of anaerobically digested sludge: A novel approach. Water Research., 144, 373-382.

473

Ning, X.A., Luo, H., Liang, X., Lin, M. and Liang, X., 2013. Effects of tannery sludge incineration slag

474

pretreatment on sludge dewaterability. Chemical Engineering Journal, 221, 1-7.

475

Niu, M., Zhang, W., Wang, D., Chen, Y., & Chen, R., 2013. Correlation of physicochemical properties and sludge

476

dewaterability under chemical conditioning using inorganic coagulants. Bioresource Technology, 144, 337-343.

477

Noyan, H., Önal, M. and Sarıkaya, Y., 2007. The effect of sulphuric acid activation on the crystallinity, surface area,

478

porosity, surface acidity, and bleaching power of a bentonite. Food chemistry, 105(1), 156-163.

479

Ottewill, R. H., and Rowell, R. L., 1981. Zeta potential in colloid science: principles and applications (Vol. 2).

480

Academic press.

481

Pandey, S., 2017. A comprehensive review on recent developments in bentonite-based materials used as adsorbents

482

for wastewater treatment. Journal of Molecular Liquids, 241, 1091-1113.

483

Pawar, R.R., Gupta, P., Bajaj, H.C. and Lee, S.M., 2016. Al-intercalated acid activated bentonite beads for the

484

removal of aqueous phosphate. Science of the Total Environment, 572, 1222-1230.

25

485

Peng, H., Zhong, S., Xiang, J., Lin, Q., Yao, C., Dong, J., Yin, G., Yao, K., Zeng, S. and Zhong, J., 2017.

486

Characterization and secondary sludge dewatering performance of a novel combined aluminum-ferrous-starch

487

flocculant (CAFS). Chemical Engineering Science, 173, 335-345.

488

Qi, Y., Thapa, K.B. and Hoadley, A.F., 2011b. Benefit of lignite as a filter aid for dewatering of digested sewage

489

sludge demonstrated in pilot scale trials. Chemical Engineering Journal, 166(2), 504-510.

490

Qi, Y., Thapa, K.B., Hoadley, A.F.A., 2011a. Application of filtration aids for improving sludge dewatering

491

properties e a review. Chemical Engineering Journal, 171 (2), 373-384.

492

Rabie, A.M., Mohammed, E.A. and Negm, N.A., 2018. Feasibility of modified bentonite as acidic heterogeneous

493

catalyst in low temperature catalytic cracking process of biofuel production from nonedible vegetable oils. Journal

494

of Molecular Liquids, 254, 260-266.

495

Şans, B.E., Güven, O., Esenli, F. and Çelik, M.S., 2017. Contribution of cations and layer charges in the smectite

496

structure on zeta potential of Ca-bentonites. Applied Clay Science, 143, 415-421.

497

Shokri, E., Yegani, R. and Ghofrani, B., 2017, Preparation of a new modified clay with amino acid for anionic

498

pollutant removal from water. Bulletin de la Société Royale des Sciences de Liège, 86, 157-164.

499

Thapa, K.B., Qi, Y., Clayton, S.A. and Hoadley, A.F.A., 2009. Lignite aided dewatering of digested sewage

500

sludge. Water Research, 43(3), 623-634.

501

To, V.H.P., Nguyen, T.V., Vigneswaran, S. and Ngo, H.H., 2016. A review on sludge dewatering indices. Water

502

Science and Technology, 74(1), 1-16.

503

U.S. EPA, 1989. POTW Sludge Sampling and Analysis Guidance Document. EPA 833-B-89-100.

504

Vuković, Z., Milutinović-Nikolić, A., Krstić, J., Abu-Rabi, A., Novaković, T. and Jovanović, D., 2005. The

505

influence of acid treatment on the nanostructure and textural properties of bentonite clays. In Materials Science

506

Forum, 494, 339-344.

507

Wasse Bekele, G.F. and Fernandez, N., 2014. Removal of nitrate ion from aqueous solution by modified Ethiopian

508

bentonite clay. International Journal of Research in Pharmacy and Chemistry, 4(1), 192-201.

26

509

Wei, H., Gao, B., Ren, J., Li, A., Yang, H., 2018. Coagulation/flocculation in dewatering of sludge: A review. Water

510

Research, 143, 608–631.

511

Wu, Y., Zhang, P., Zhang, H., Zeng, G., Liu, J., Ye, J., Fang, W. and Gou, X., 2016. Possibility of sludge

512

conditioning and dewatering with rice husk biochar modified by ferric chloride. Bioresource Technology, 205, 258-

513

263.

514

Wu, Y., Zhang, P., Zhang, H., Zeng, G., Liu, J., Ye, J., Fang, W. and Gou, X., 2016. Possibility of sludge

515

conditioning and dewatering with rice husk biochar modified by ferric chloride. Bioresource technology, 205, 258-

516

263.

517

Xiao, K., Chen, Y., Jiang, X., Yang, Q., Seow, W.Y., Zhu, W., Zhou, Y., 2017. Variations in physical, chemical and

518

biological properties in relation to sludge dewaterability under Fe (II)-Oxone conditioning. Water Research. 109, 13-

519

23.

520

Yang, P., Li, D., Zhang, W., Wang, N., Yang, Z., Wang, D., & Ma, T., 2019. Flocculation-dewatering behavior of

521

waste activated sludge particles under chemical conditioning with inorganic polymer flocculant: Effects of typical

522

sludge properties. Chemosphere, 218, 930-940.

523

Zall, J., Galil, N. and Rehbun, M., 1987. Skeleton builders for conditioning oily sludge. Journal (Water Pollution

524

Control Federation), 699-706.

525

Zhang, D., Wang, Y., Gao, H., Fan, X., Guo, Y., Wang, H. and Zheng, H., 2019. Variations in macro and micro

526

physicochemical properties of activated sludge under a moderate oxidation-in situ coagulation conditioning:

527

relationship between molecular structure and dewaterability. Water Research, 155, 245-254.

528

Zhang, J., Yue, Q., Xia, C., Yang, K., Zhao, P., Gao, B. and Yu, H., 2017. The study of Na2SiO3 as conditioner

529

used to deep dewater the urban sewage dewatered sludge by filter press. Separation and Purification Technology,

530

174, 331-337.

531

Zhang, W., Chen, Z., Cao, B., Du, Y., Wang, C., Wang, D., Ma, T. and Xia, H., 2017b. Improvement of wastewater

532

sludge dewatering performance using titanium salt coagulants (TSCs) in combination with magnetic nano-particles:

533

Significance of titanium speciation. Water Research, 110, 102-111.

27

534

Zhao, Y.Q. and Bache, D.H., 2001. Conditioning of alum sludge with polymer and gypsum. Colloids and Surfaces

535

A: Physicochemical and Engineering Aspects, 194(1-3), 213-220.

536

Zhou, X., Jiang, G., Zhang, T., Wang, Q., Xie, G.J., Yuan, Z., 2015. Role of extracellular polymeric substances in

537

improvement of sludge dewaterability through peroxidation. Bioresource technology, 192, 817-820.

28

Highlights • • • •

Acidic-modified bentonite (AMB) decreased sludge compressibility by 20%. AMB increased sludge filtration yield by 810%. AMB acts as a physical-chemical conditioner. AMB is an efficient and low-cost inorganic conditioner for sludge handling.