WITHDRAWN: Experimental Study of Waste Activated Sludge Treatment Using a Rotational Hydrodynamic Cavitation Generator and Ultrasonication

Accepted Manuscript Experimental Study of Waste Activated Sludge Treatment Using a Rotational Hydrodynamic Cavitation Generator and Ultrasonication Hyun Soo Kim, Seung ho Lee, Xun Sun, Joon Yong Yoon PII: DOI: Reference:

S1350-4177(18)31120-9 https://doi.org/10.1016/j.ultsonch.2018.12.005 ULTSON 4402

To appear in:

Ultrasonics Sonochemistry

Received Date: Revised Date: Accepted Date:

24 July 2018 13 September 2018 4 December 2018

Please cite this article as: H.S. Kim, S.h. Lee, X. Sun, J.Y. Yoon, Experimental Study of Waste Activated Sludge Treatment Using a Rotational Hydrodynamic Cavitation Generator and Ultrasonication, Ultrasonics Sonochemistry (2018), doi: https://doi.org/10.1016/j.ultsonch.2018.12.005

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

1

Experimental Study of Waste Activated Sludge Treatment Using

2

a Rotational Hydrodynamic Cavitation Generator and

3

Ultrasonication

4 5

Hyun Soo Kima, Seung ho Lee a, Xun Sunb, Joon Yong Yoonc*

6 a

7

Graduate Student, B.S.

8

Department of Mechanical design Engineering, University of Hanyang,

9

55, Hanyangdaehak-ro, Sangrok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea

10

Kim, H.S. E-mail: [email protected]

11

Lee, S.H. E-mail: [email protected]

12 13

b

Post-Doctoral Research, Ph.D.

14

Department of Mechanical design Engineering, University of Hanyang,

15

55, Hanyangdaehak-ro, Sangrok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea

16

Sun, X. E-mail: [email protected]

17 18

c Professor,

Ph.D.

19

Department of Mechanical Engineering, University of Hanyang,

20

55, Hanyangdaehak-ro, Sangrok-gu, Ansan, Gyeonggi-do, 15588, Republic of Korea

21

*Corresponding author, Tel.: +82-31-400-5282, Fax: +82-31-400-4707

22

Yoon, J. Y. E-mail: [email protected]

23 24

Word Count: 5,845

1

1

Abstract

2

In the present work, the performance of a waste-activated sludge (WAS) treatment using a

3

novel rotational hydrodynamic cavitation generator (RHCG) was investigated. To verify the

4

performance, a comparison with an ultrasonic device was conducted in four experimental

5

cases at the same specific energy input using three assessment factors. The RHCG consisted

6

of a rotor and three covers with inserted dimples. Ultrasonication was performed using a

7

general ultrasonic bath. The experimental parameters were established to calculate the

8

specific energy input of the sludge passing through the RHCG for a total of 5, 10, 15, and 20

9

times. Disintegration performance using particle size distribution and SVI, solubilization rate

10

using soluble COD, and oxidation performance using total COD and VSS reduction rate were

11

analyzed as assessment factors. For oxidation and particle disintegration, the RHCG showed

12

overwhelming performance and was superior to the ultrasonic device at low energy input. The

13

tCOD and VSS of the sludge treated five times in the RHCG were reduced by 52.9 and

14

66.0 %, respectively, and the median particle size of the sludge treated 10 times in the RHGG

15

was reduced by 92.7 %. Otherwise, at comparable specific energy inputs, sludge treated by

16

the ultrasonic device were reduced by 0, 26.4, and 67.6 %, respectively. However, due to the

17

contradictory interactions of particle disintegration and oxidation, the two treatment methods

18

showed similar performance in terms of solubilization rate and reached up to 42.3 and 41.4 %

19

in the RHCG and ultrasonic device, respectively. In the present work, the RHCG is proposed

20

as a new novel WAS treatment technique.

21

Key words: Rotational hydrodynamic cavitation generator, Ultrasonication, Waste-activated

22

sludge treatment, Performance comparison

23

2

1

1. Introduction

2

Environmental pollution has become a serious global problem due to continuous

3

industrialization. Along with air pollution, water pollution is a major problem, and regulations

4

for waste water treatment are being reinforced globally to solve this problem. Consequently,

5

treatment methods that are both environmentally friendly and effective have become critical

6

needs [1-4]. The general process of waste water treatment comprises sludge disintegration,

7

anaerobic digestion, dewatering, and disinfection. Various techniques have been used to treat

8

waste water for decades. However, traditional methods generally involve a high processing cost,

9

long treatment time, low treatment capability, or generation of chemical by-products [5]. To

10

overcome these drawbacks, new methods have been proposed in the literature [6-9], one of

11

which is waste water treatment using cavitation.

12

Cavitation refers to the process of bubble generation, growth, and collapse in a liquid due to

13

decreasing pressure. The bubbles generated in the liquid grow until the internal pressure equals

14

the surrounding liquid pressure through heat transfer from the liquid. At maximum size, the

15

bubble collapses and releases tremendous energy in the form of heat and a shockwave that

16

imparts the three following effects [10, 11]. The first is the physical effect. When the bubble

17

collapses, a shock wave of 550 MPa is emitted at a speed of 2,000 m/s, a micro jet generates a

18

450 MPa water hammer at 100 m/s, and shear stress reaches 3.5 kPa. The second is a thermal

19

effect. The collapse of the bubble generates a local hot spot of 2000-6000 K and induces 1010

20

K/s heat transfer within one microsecond. The third is a chemical effect. Due to the energy

21

generated by bubble collapse, water molecules are decomposed into H• and OH•, the later are

22

highly oxidizing agent. These three effects can be used in waste water treatment. The physical

23

effect of cavitation leads to disintegration of particles and lysis of microorganisms. These effects

24

could enhance biogas production during anaerobic digestion of biomass [12]. The thermal effect

25

improves the dewaterability of the sludge by causing cell lysis and destroying the cell walls,

26

resulting in easily accessible proteins for biological degradation. Also, the thermal effects reduce

27

the sludge’s viscosity, resulting in easier handling [13]. In terms of the chemical effect, the free

28

radicals generated by cavitation accelerate chemical reactions and inactivate and remove

29

microorganisms through decomposition of hydrogen bonds [14, 15].

30

Cavitation can be classified as a method inducing pressure perturbation in liquid. Ultrasonic

31

cavitation induces pressure perturbation using ultrasound. When ultrasound waves propagate in

32

liquid medium, the liquid molecules repeatedly contract and expand. In the contracting cycle, the

33

liquid pressure is positive, while that in the expanding cycle is negative due to molecular

3

1

separation [16]. This type of cavitation has a simple structure and easily generates bubbles; hence,

2

it has been used for waste water treatment [17]. Ultrasonic cavitation, however, has much low

3

energy transfer efficiencies (10-40 %), due to the generation mechanism, and the cavitation

4

intensity rapidly decreases with distance from the ultrasonic device [18, 19]. Hence, ultrasonic

5

cavitation has poor scalability and is unable to treat uniformly. Hydrodynamic cavitation occurs

6

via pressure perturbation a using cross-sectional area change. For an incompressible fluid, the

7

flow rate is calculated as the product of cross-sectional area and velocity. When cross-sectional

8

area decreases at constant flow rate, fluid velocity increases, by Bernoulli’s equation, the

9

pressure will be decreased. Hydrodynamic cavitation generates bubbles using this phenomenon,

10

and due to the generation mechanism, all fluids pass through the cavitation generation region and

11

could be treated uniformly [19, 20]. The hydrodynamic cavitation generator can be classified by

12

the manner changing cross-sectional area. The non-rotation type of hydrodynamic cavitation

13

generator lets liquid pass through fixed narrow cross-sectional area regions, e.g., the venturi tube

14

and orifice plate. The rotational type of hydrodynamic cavitation generator changes cross-

15

sectional area using rotation, e.g., a shockwave power reactor [21-23]. In most previous studies

16

on waste water treatment, non-rotation type of hydrodynamic cavitation generators was utilized

17

because of their simple design. However, to induce considerable pressure drop, a high-power

18

pump is required, resulting in a substantial cost. In addition, the cavitation intensity is poor,

19

resulting in long treatment times and low treatment performance [24-26]. The rotational

20

hydrodynamic cavitation generator (RHCG) could overcome such limitations. Since the RHCG

21

generates bubbles using variation in cross-sectional area, uniform treatment is possible. Also, the

22

RHCG incurs cavitation using rotation rather than a circulation pump, the cavitation region and

23

cavitation intensity are much larger than with the non-rotation type, and additional energy

24

consumption is low. Some research groups have studied the potential for utilizing this technique

25

for water treatment [19, 21-23, 27-34].

26

Waste water treatment performance depends on the characteristics of the substance requiring

27

treatment [35, 36]. In light of this, to evaluate the waste water treatment capabilities of the

28

RHCG, comparisons of performance with existing techniques should use the same substance. In

29

the present work, the WAS collected at a sewage treatment plant was treated using the RHCG

30

and an ultrasonication device used in industry. The treatment performance was compared by

31

analyzing particle disintegration, oxidation, and solubilization. The aim of this study was to

32

verify WAS treatment performance of the RHCG and to demonstrate its viability as a real water

33

treatment device.

4

1

2. Experimental methods

2

2.1 Rotational hydrodynamic cavitation generator

3

The RHCG was constructed using the knowledge and results from a previously designed

4

cavitation generator [37]. Since hydrodynamic cavitation generates bubbles using pressure

5

perturbation induced by variations in cross-sectional area in flow path, 32 dimples were located

6

on each surface of a rotor and three covers. The rotor and rear cover were made of stainless steel,

7

while the front and side cover were made of transparent polycarbonate to observe generation of

8

cavitation. The shapes of the rotor and covers are shown in figure 1. To allow all fluids to

9

uniformly pass through the cavitation generation region, the inlet is located at the center of the

10

front cover, and the outlet is located at the rear cover. Due to the flow path, all liquids pass

11

through three cavitation generation regions and are treated uniformly.

12

To turn the rotor, a 15 kW (20HP), three-phase, 380V electrical motor (Hyosung Co., TE-F

13

series) with a standard efficiency of 90.2 % was used. To measure the electric power

14

consumption of the motor, a clamp-on power meter (Yokogawa Co., CW240) was utilized. The

15

flow rate was measured by an electromagnetic flow meter (Ientek Co., EMFF) with an accuracy

16

of ± 0.5 % and a range of 0.2-10 m3/h. All flow rate signals were collected and transformed to

17

digital signals using a National Instruments PCI-6299 board as the data acquisition (DAQ)

18

device. Signals were saved in a computer using LabVIEW. The WAS treatment system was

19

assembled as a circuit system without temperature regulation using 15A pipes and a 100 L

20

reservoir, a single-phase 220 V inverter pump (Wilo SE Co., PBI-L405MA), and involving the

21

RHCG. A schematic of the RHCG treatment system is shown in figure 2.

22 23

2.2 Ultrasonic bath

24

The general ultrasonic bath, which has 8 ultrasonic terminals on the bottom, was used to

25

provide ultrasonic sludge treatment and is shown in figure 3. Since maximum floc size reduction

26

and increase in solubilization rate are obtained at low frequencies [38, 39], the operating

27

frequency was set to 28 kHz. The power supplied to the ultrasonic bath was 400 W, and a control

28

box was used to regulate ultrasonic intensity and operating time. Two liters of sludge were

29

treated using maximum ultrasonic intensity, and only operating time was regulated in order to

30

produce the same specific energy input [40] as imparted with the RHCG treatment.

31 32

2.3 Waste Activated Sludge

5

1

In this study, secondary sewage sludge was obtained from a bioreactor from the Gulpo River

2

Waste Water Treatment Plant (Bucheon, Republic of Korea). The sludge was stored at 4 ℃ for

3

24 hours prior to experimentation to avoid changes in physicochemical properties and to stabilize

4

the sludge. The properties of the WAS used in the work are shown in table 1.

5 6

2.4 Establishment of experimental cases

7

To compare the sludge treatment performance of the RHCG with that of an ultrasonic bath,

8

four experimental cases were established at the same specific energy input. The specific energy

9

input of the four experimental cases was calculated using consumed energy every time the

10

sludge passed through the RHCG, which occurred five times. The number of passes was

11

calculated using total sludge amount and flow rate. To exclude other parameters affecting

12

cavitation intensity, the rational speed and pressure setting of the inverter pump were fixed at

13

3000 rpm and 0.1 bar, respectively. The experimental cases are shown in table 2.

14 15 16

6

1

3. Results and discussion

2

3.1 Decomposition performance

3

To evaluate the sludge particle disintegration performance of the RHCG, the particle size

4

distribution was analyzed. The particle size of the sludge is closely related to anaerobic digestion

5

performance and dewaterability. Smaller sludge particle size improved anaerobic digestion

6

performance and dewaterability by transforming the bound water to free water [13, 35, 41-43].

7

Disintegration of the particles via cavitation proceeds physically by shear stress and chemically

8

due to the OH• [44-46]. In this section, using a comparison of particle size distribution with

9

ultrasonication, the disintegration performance of the RHCG was evaluated. The particle size

10

distribution was analyzed using a particle size analyzer (Malvern Co., Mastersizer 2000). In each

11

experimental case, the particle size distributions of sludge treated with the three methods, non-

12

treated (NT.), treated by ultrasonic bath (U.C), and treated by, RHCG (H.C), are shown in figure

13

4.

14

In figure 4, for all experimental cases, U.C and H.C graphs shifted to the left compared to the

15

NT graph. These results show that particle sizes of the sludge treated by both treatment devices

16

were reduced, i.e., both treatment devices decomposed the sludge particles. Comparing the

17

particle size distributions of the experimental cases, the typical particle sizes of the sludge treated

18

by U.C were slightly smaller in case 1, however, the portion of sludge which in the range of 100-

19

1000 μm treated by the RHCG was lesser. This result shows that, for the lowest specific energy

20

input, the particle disintegration performance of the ultrasonication bath was generally superior

21

to that of the RHCG. A limitation of ultrasonic cavitation came to light wherein uniform

22

treatment was unattainable due to the mechanism of bubble generation. In case 2, the graph of

23

H.C was significantly shifted to the left compared to the graph of U.C. This result shows that the

24

particle disintegration performance of the RHCG was superior to that of the ultrasonic bath. In

25

case 3, the graph of U.C significantly shifted to the left compared to case 2, while the graph of

26

H.C hardly changed. Finally, in case 4, for both graphs, most particles are in the range of 1-10μm.

27

For quantitative comparison, the particle size distributions as a percentile size (diameter of

28

particle with a 10 % volume fraction: d(0.1), 50 %: d(0.5) and 90 %: d(0.9)) are compared in

29

table 3. The results show that d(0.1) and d(0.5) of U.C and H.C were lower than those of N.T. In

30

case 1, d(0.1) and d(0.5) of U.C were smaller than the those of H.C. However, in case 2, the

31

median size (result of d(0.5)) of H.C was 4.029 μm, which had decreased by 92.7 % compared to

32

N.T. In contrast, the median size of U.C was 17.804 μm, which represented a 67.6 % reduction at

33

the same specific energy input. The maximum size reduction achieved was 82.3 % in case 4, 7

1

which had the highest specific energy input. As reference, a particle size reduction of 68 % was

2

achieved in a previous investigation using AOPs [47]. This result shows overwhelming particle

3

decomposition performance of the RHCG. Also, in all cases, the d(0.9) values of H.C were much

4

smaller than those of U.C, i.e., the RHCG decomposed the sludge particles much more

5

uniformly than the ultrasonic bath.

6

The particle size distribution obtained from the sludge treated by the RHCG indicated that

7

there was no significant change after 10 treatments. This is thought to be due to the sludge

8

decomposition reaching the final by the RHCG in case 2. However, for the sludge treated by the

9

ultrasonic bath, the particle size distribution continued to change through case 3 and even

10

changed slightly in case 4. Consequently, the final stage of particle decomposition was similar in

11

the two devices; however, the RHCG reached the final stage at a much lower specific energy

12

input. Also, the final particle size of the sludge treated by the RHCG was generally smaller. To

13

support this result, sludge volume index (SVI) results are shown in figure 5.

14

Figure 5(a) shows the SVI result of sludge treated by the ultrasonic bath, and figure 5(b)

15

shows the SVI result of sludge treated by the RHCG. The SVI was visualized for 100 ml sludge

16

stored for 30 minutes. For ultrasonication (Figure 5(a)), visibly settled sludge was present in all

17

experimental cases. Otherwise, for hydrodynamic cavitation (Figure 5(b)), only in cases 1 and 2

18

was there visibly settled sludge. Additionally, in case 1, the sedimentation amount of sludge

19

treated by the RHCG was about 3 times less than that treated by the ultrasonic bath. Since the

20

settling occurs on particles over a certain size, it is confirmed that the RHCG decomposed sludge

21

particle more evenly than did the ultrasonic bath.

22 23

3.2 Oxidation performance

24

As mentioned earlier, it is obvious that OH• is generated when cavitation occurs. Often,

25

cavitation intensity is expressed using the amount of generated OH•, e.g., the Weissler reaction

26

[48]. In this section, the total chemical oxygen demand (tCOD) and volatile suspended solid

27

(VSS) reduction rates were calculated to evaluate the oxidation performance of the RHCG. Both

28

parameters are reduced by oxidation. The tCOD was measured based on the HACH COD

29

measurement with 8000 using a DR 3900 (HACH Co.), and VSS was measured based on the

30

Standard Methods for the Examination of Water and Wastewater. The reduction rates were

31

calculated as follows:

32

8

1

tCOD r (%)=

tCOD m - tCOD0 VSSm - VSS0  100, VSSr (%)=  100 tCOD0 VSS0

(1)

2 3 4

Here, the subscript r represents the reduction rate, m represents the measured value, and 0 represents the initial value. The tCOD and VSS reduction rates are shown in figure 6.

5

As shown in figure 6(a), the tCOD reduction rate of sludge treated by the RHCG increased

6

steadily. The tCOD is a parameter representing the amount of organic matter in sludge. Thus, a

7

reduction of tCOD means that the amount of organic matter is reduced in the sludge. Since

8

organic matter is reduced by oxidation, tCOD can serve as an indicator of oxidation. Namely,

9

increased specific energy input via RHCG increased oxidation. However, in case 1, the tCOD of

10

the sludge treated by the ultrasonic bath was not reduced, i.e., oxidation did not occur. Otherwise,

11

in case 2, the tCOD reduction rate suddenly increased and was equal to that of sludge treated by

12

the RHCG. This result could be interpreted as follows. There is a certain level of threshold

13

required to oxidize organic matter, and sudden oxidation occurs when that level is exceeded.

14

This threshold could be determined by amount of generated OH• or energy needed for

15

generating OH•. In any case, the oxidation performance of the RHCG is remarkable superior to

16

that of the ultrasonic bath.

17

In cases 3 and 4, the tCOD reduction rate of sludge treated by the RHCG converged, while the

18

tCOD reduction rate of sludge treated by the ultrasonic bath decreased. The oxidation of organic

19

matter did not occur at more than a certain threshold level. The oxidation of organic matter

20

proceeds due to a reaction of OH• during cavitation. The OH• is a highly reactive oxidant and

21

quickly disappears when there are no substances to oxidize. Therefore, when oxidation of

22

organic matter in the sludge reached a particular level, the concentration of organic matter

23

decreased, and the oxidation reaction did not actively occur even if OH  was generated by the

24

cavitation. This type of circumstance was pronounced in ultrasonic cavitation. As mentioned in

25

the Introduction, ultrasonic cavitation occurs most intensely near ultrasonic devices, and this

26

intensity decreases with distance. As a result, the organic matter far from the ultrasonic device

27

can not react with the OH• generated by cavitation.

28

In figure 6(b), the VSS reduction rate shows a trend similar to the tCOD reduction rate. The

29

VSS reduction rate of sludge treated by the RHCG increased with specific energy input.

30

However, in case 1, the VSS reduction rate of sludge treated the by ultrasonic bath was about

31

25 %, demonstrating that oxidation occurred differently than the trend in tCOD reduction rate.

32

Otherwise, in case 2, the VSS reduction rate of sludge treated by the ultrasonic bath was similar

33

to that of the sludge treated by the RHCG, and cases 3 and 4 also showed similar patterns. The 9

1

VSS and tCOD are parameters indicating the amount of organic matter contained in sludge;

2

however, the two parameters are not the same. Hence, these results should not be considered as

3

conflicting but should be considered simultaneously to assess oxidation performance. In

4

summary, in case 1, the oxidation of organic matter occurred only slightly within the sludge

5

treated by the ultrasonic bath. The tCOD and VSS of sludge treated by both devices are

6

quantitatively compared in table 4.

7

Table 4 shows that the tCOD of the sludge by treated both devices were only similar in case 2.

8

On the other hand, the VSS of sludge treated by both devices displayed a clear difference only in

9

case 1. Consequently, the sludge was oxidized by both devices, and potent oxidation

10

performances were confirmed. However, in a low specific energy input condition, the oxidation

11

performance of the RHCG was overwhelmingly superior to that of the ultrasonic bath. Also,

12

oxidation of the sludge converged when the applied energy was beyond a specific threshold.

13 14

3.3 Solubilization performance

15

The solubilization rate of the sludge was analyzed to evaluate the sludge treatment

16

performance of the RHCG. Solubilization of sludge is the rate of soluble chemical oxygen

17

demand (SCOD) among the tCOD. Solubilization is conducted by disintegration of organic

18

matter contained in the sludge. The disintegration of organic matter entails cell lysis, resulting in

19

increased hydrolysis and, consequently, an improvement in anaerobic digestion performance

20

[49-51]. The solubilization rate is expressed as the ratio of tCOD and an increment of SCOD and

21

is calculated as follows [52]:

22 23

Solubilization rate (%)=

SCOD - SCOD0  100 . tCOD0 - SCOD0

(2)

24 25

Generally, when sludge is disintegrated, SCOD and solubilization rate increase. However, as

26

discussed earlier, tCOD decreased due to oxidation in this study. Thus, to compare the

27

solubilization rate according to sludge decomposition, the SCOD was normalized, and the

28

solubilization was calculated as follows:

29 30

SCOD n =

tCOD0  SCOD m , tCOD m

(3)

31

10

1

where the subscript n indicates the normalized value. The measured SCOD, normalized SCOD,

2

and solubilization rate are shown in figure 7.

3

In figure 7, the SCODm of the sludge treated by RHCG gradually increased with specific

4

energy input. Otherwise, the SCODm of the sludge treated by the ultrasonic bath was

5

particularly high in case 1 and decreased in case 2, after which it then linearly increased with

6

specific energy input. This is because, as discussed in the above section, oxidation of sludge

7

treated by the ultrasonic bath does not occur in case 1. Namely, the organic matter contained in

8

the sludge treated by the ultrasonic bath was only disintegrated and not oxidized in case 1; thus,

9

the SCOD of the sludge sharply increased. Otherwise, the organic matter in the sludge treated by

10

the RHCG was disintegrated as well as actively oxidized in case 1; thus, the SCOD of the sludge

11

slightly increased. As a result, the SCOD of the sludge treated by the ultrasonic bath was much

12

greater than the SCOD of the sludge treated by the RHCG in case 1. In case 2, the sludge treated

13

by the ultrasonic bath was also oxidized, and the SCOD was reduced compared to that of case 1.

14

To avoid this circumstance, a normalized SCOD and solubilization rate were compared in figure

15

7(b). Unlike the SCODm, the SCODn and solubilization rate of sludge treated by both devices

16

showed reasonable trends without abnormal values. In figure 7(b), the SCODn and the

17

solubilization rate of sludge treated by the ultrasonic bath were higher than those of sludge

18

treated by the RHCG under a low specific energy input (case 1 and case 2); on the other hand,

19

the SCODn and solubilization rate of the sludge treated by the RHCG were higher under a high

20

specific energy input (case 3 and case 4). To compare quantitative results, the values of SCODm,

21

SCODn, and solubilization rate are shown in table 5.

22

Except in case 1, the SCODm of sludge treated by the ultrasonic bath was 10-20 % higher

23

than that of sludge treated by the RHCG. However, when examining the results for SCODn, the

24

SCODn for the ultrasonic bath treatment and the RHCG showed similar values for all specific

25

energy inputs. The solubilization rate also showed a similar trend, with that of sludge treated by

26

the RHCG reaching 42.3 % at the highest specific energy input.

27

Solubilization of the sludge is accompanied by simultaneous particle decomposition and

28

oxidation of organic matter. Consequently, although the particle decomposition and oxidation of

29

the RHCG were superior to those of the ultrasonic bath, due to contradictory interactions, the

30

solubilization performance was similar in the two devices.

11

1

4. Conclusions

2

In the present work, to evaluate the waste water treatment performance of RHCG,

3

comparisons of WAS treatment performance were conducted with an ultrasonic bath already

4

used in industry using three assessment factors. The following conclusions were established from

5

the present work.

6

‧

Particle decomposition of the RHCG is superior to that of the ultrasonic bath using

7

particle size distribution and SVI analysis. After 10 treatments, the median particle size

8

decreased by 92.7 % in the RHCG, compared to a median particle size reduction of

9

67.6 % at the same specific energy input in an ultrasonic bath. Also, through the results

10

of SVI, it was discovered that the RHCG decomposed the sludge much more uniformly

11

compared to the ultrasonic bath.

12

‧

A comparison of the tCOD and VSS reduction rates revealed that the RHCG had

13

superior oxidation performance over the ultrasonic bath. In case 1, which had the lowest

14

specific energy input, the RHCG reduced the tCOD and VSS by 53 and 66 %,

15

respectively. On the other hand, the ultrasonic bath reduced the tCOD and VSS by 0 and

16

26 %, respectively. In case 4, which had the highest specific energy input, the RHCG

17

showed outstanding oxidation performance through a reduction of tCOD and VSS by 67

18

and 74 %, respectively.

19

‧

As shown through SCODn and solubilization rate, the two devices showed similar

20

solubilization performance. Since particle disintegration and oxidation counteract each

21

other, in case 1 and case 2, the ultrasonic bath exhibited only a slightly higher

22

solubilization rate. In contrast, the RHCG in case 3 and case 4 showed a slightly higher

23

solubilization rate. In case 1, which shows significant different oxidation performances,

24

the SCODm values were considerably different.

25

In the present paper, superior WAS treatment performance of the RHCG was revealed,

26

especially at a low specific energy input. This result shows that RHCG could be utilized as a

27

more efficient WAS treatment device and may be of use even though the operation conditions in

28

the present work were not optimized. Studies into the optimal conditions for RHCG operation

29

should be conducted. In the meantime, the RHCG can be utilized as an effective,

30

environmentally friendly, economical, and novel WAS treatment technique.

31

12

1

Acknowledgements

2

This work was supported by the Small & Medium Business Administration in Korea, project

3

number 1425114753: Development of equipment to reduce moisture content of dehydrated

4

cake using ultrasonic and catalyst.

5

13

1

References

2

[1] M.V. Bagal, P.R. Gogate, Wastewater treatment using hybrid treatment schemes based on

3

cavitation and Fenton chemistry: A review, Ultrasonics sonochemistry, 21 (2014) 1-14.

4

[2] M. Cvetković, B. Kompare, A.K. Klemenčič, Application of hydrodynamic cavitation in

5

ballast water treatment, Environmental Science and Pollution Research, 22 (2015) 7422-7438.

6

[3] C.R. Holkar, A.J. Jadhav, D.V. Pinjari, N.M. Mahamuni, A.B. Pandit, A critical review on

7

textile wastewater treatments: Possible approaches, Journal of Environmental Management,

8

182 (2016) 351-366.

9

[4] P. Xu, G.M. Zeng, D.L. Huang, C.L. Feng, S. Hu, M.H. Zhao, C. Lai, Z. Wei, C. Huang,

10

G.X. Xie, Z.F. Liu, Use of iron oxide nanomaterials in wastewater treatment: A review,

11

Science of The Total Environment, 424 (2012) 1-10.

12

[5] P.R. Gogate, A.B. Pandit, A review of imperative technologies for wastewater treatment I:

13

oxidation technologies at ambient conditions, Advances in Environmental Research, 8 (2004)

14

501-551.

15

[6] S. Ai, H. Liu, M. Wu, G. Zeng, C. Yang, Roles of acid-producing bacteria in anaerobic

16

digestion of waste activated sludge, Frontiers of Environmental Science & Engineering, 12

17

(2018) 3.

18

[7] G. Zhen, X. Lu, L. Su, T. Kobayashi, G. Kumar, T. Zhou, K. Xu, Y.-Y. Li, X. Zhu, Y.

19

Zhao, Unraveling the catalyzing behaviors of different iron species (Fe2+ vs. Fe0) in

20

activating persulfate-based oxidation process with implications to waste activated sludge

21

dewaterability, Water Research, 134 (2018) 101-114.

22

[8] P.R. Gogate, Treatment of wastewater streams containing phenolic compounds using

23

hybrid techniques based on cavitation: a review of the current status and the way forward,

24

Ultrasonics sonochemistry, 15 (2008) 1-15.

25

[9] P.N. Patil, P.R. Gogate, L. Csoka, A. Dregelyi-Kiss, M. Horvath, Intensification of biogas

26

production using pretreatment based on hydrodynamic cavitation, Ultrasonics sonochemistry,

27

30 (2016) 79-86.

28

[10] L. Rayleigh, VIII. On the pressure developed in a liquid during the collapse of a

29

spherical cavity, The London, Edinburgh, and Dublin Philosophical Magazine and Journal of

30

Science, 34 (1917) 94-98.

31

[11] K.S. Suslick, Sonochemistry, Science, 247 (1990) 1439-1445.

32

[12] M. Zieliński, M. Dębowski, M. Kisielewska, A. Nowicka, M. Rokicka, K. Szwarc,

33

Comparison of Ultrasonic and Hydrothermal Cavitation Pretreatments of Cattle Manure

14

1

Mixed with Straw Wheat on Fermentative Biogas Production, Waste and Biomass

2

Valorization, (2017) 1-8.

3

[13] M. Ruiz-Hernando, G. Martinez-Elorza, J. Labanda, J. Llorens, Dewaterability of sewage

4

sludge by ultrasonic, thermal and chemical treatments, Chemical Engineering Journal, 230

5

(2013) 102-110.

6

[14] S.K. Pawar, A.V. Mahulkar, A.B. Pandit, K. Roy, V.S. Moholkar, Sonochemical effect

7

induced by hydrodynamic cavitation: Comparison of venturi/orifice flow geometries, AIChE

8

Journal, 63 (2017) 4705-4716.

9

[15] Y. Tao, J. Cai, X. Huai, B. Liu, A novel antibiotic wastewater degradation technique

10

combining cavitating jets impingement with multiple synergetic methods, Ultrasonics

11

sonochemistry, 44 (2018) 36-44.

12

[16] S. Pilli, P. Bhunia, S. Yan, R.J. LeBlanc, R.D. Tyagi, R.Y. Surampalli, Ultrasonic

13

pretreatment of sludge: A review, Ultrasonics sonochemistry, 18 (2011) 1-18.

14

[17] F. Jorand, F. Zartarian, F. Thomas, J.C. Block, J.Y. Bottero, G. Villemin, V. Urbain, J.

15

Manem, Chemical and structural (2D) linkage between bacteria within activated sludge flocs,

16

Water Research, 29 (1995) 1639-1647.

17

[18] M. Sivakumar, A.B. Pandit, Wastewater treatment: a novel energy efficient

18

hydrodynamic cavitational technique, Ultrasonics sonochemistry, 9 (2002) 123-131.

19

[19] M. Badve, P. Gogate, A. Pandit, L. Csoka, Hydrodynamic cavitation as a novel approach

20

for wastewater treatment in wood finishing industry, Separation and Purification Technology,

21

106 (2013) 15-21.

22

[20] M. Gągol, A. Przyjazny, G. Boczkaj, Highly effective degradation of selected groups of

23

organic compounds by cavitation based AOPs under basic pH conditions, Ultrasonics

24

sonochemistry, 45 (2018) 257-266.

25

[21] P.J. Milly, R.T. Toledo, M.A. Harrison, D. Armstead, Inactivation of food spoilage

26

microorganisms by hydrodynamic cavitation to achieve pasteurization and sterilization of

27

fluid foods, Journal of food science, 72 (2007) M414-422.

28

[22] P.J. Milly, R.T. Toledo, J. Chen, B. Kazem, Hydrodynamic cavitation to improve bulk

29

fluid to surface mass transfer in a nonimmersed ultraviolet system for minimal processing of

30

opaque and transparent fluid foods, Journal of food science, 72 (2007) M407-413.

31

[23] P.J. Milly, R.T. Toledo, W.L. Kerr, D. Armstead, Hydrodynamic Cavitation:

32

Characterization of a Novel Design with Energy Considerations for the Inactivation

33

ofSaccharomyces cerevisiaein Apple Juice, Journal of food science, 73 (2008) M298-M303.

15

1

[24] S. Arrojo, Y. Benito, A. Martínez Tarifa, A parametrical study of disinfection with

2

hydrodynamic cavitation, Ultrasonics sonochemistry, 15 (2008) 903-908.

3

[25] L. Patil, P.R. Gogate, Large scale emulsification of turmeric oil in skimmed milk using

4

different cavitational reactors: A comparative analysis, Chemical Engineering and Processing:

5

Process Intensification, 126 (2018) 90-99.

6

[26] C. Yi, Q. Lu, Y. Wang, Y. Wang, B. Yang, Degradation of organic wastewater by

7

hydrodynamic cavitation combined with acoustic cavitation, Ultrasonics sonochemistry, 43

8

(2018) 156-165.

9

[27] M. Petkovšek, M. Zupanc, M. Dular, T. Kosjek, E. Heath, B. Kompare, B. Širok,

10

Rotation generator of hydrodynamic cavitation for water treatment, Separation and

11

Purification Technology, 118 (2013) 415-423.

12

[28] M.P. Badve, P.R. Gogate, A.B. Pandit, L. Csoka, Hydrodynamic cavitation as a novel

13

approach for delignification of wheat straw for paper manufacturing, Ultrasonics

14

sonochemistry, 21 (2014) 162-168.

15

[29] M. Zupanc, T. Kosjek, M. Petkovsek, M. Dular, B. Kompare, B. Sirok, M. Strazar, E.

16

Heath, Shear-induced hydrodynamic cavitation as a tool for pharmaceutical micropollutants

17

removal from urban wastewater, Ultrasonics sonochemistry, 21 (2014) 1213-1221.

18

[30] M. Petkovsek, M. Mlakar, M. Levstek, M. Strazar, B. Sirok, M. Dular, A novel rotation

19

generator of hydrodynamic cavitation for waste-activated sludge disintegration, Ultrasonics

20

sonochemistry, 26 (2015) 408-414.

21

[31] A. Sarc, J. Kosel, D. Stopar, M. Oder, M. Dular, Removal of bacteria Legionella

22

pneumophila, Escherichia coli, and Bacillus subtilis by (super)cavitation, Ultrasonics

23

sonochemistry, 42 (2018) 228-236.

24

[32] X. Sun, J.J. Park, H.S. Kim, S.H. Lee, S.J. Seong, A.S. Om, J.Y. Yoon, Experimental

25

Investigation of the Thermal and Disinfection Performances of a Novel Hydrodynamic

26

Cavitation Reactor, Ultrasonics sonochemistry, (2018).

27

[33] X. Sun, C. Hyeok Kang, J. Jin Park, H. Soo Kim, A. Son Om, J. Yong Yoon, An

28

Experimental Study on the Thermal Performance of a Novel Hydrodynamic Cavitation

29

Reactor, Experimental Thermal and Fluid Science, (2018).

30

[34] L.M. Cerecedo, C. Dopazo, R. Gomez-Lus, Water disinfection by hydrodynamic

31

cavitation in a rotor-stator device, Ultrasonics sonochemistry, 48 (2018) 71-78.

32

[35] P.W. Harris, B.K. McCabe, Review of pre-treatments used in anaerobic digestion and

33

their potential application in high-fat cattle slaughterhouse wastewater, Applied Energy, 155

34

(2015) 560-575. 16

1

[36] J. Bandelin, T. Lippert, J.E. Drewes, K. Koch, Cavitation field analysis for an increased

2

efficiency of ultrasonic sludge pre-treatment using a novel hydrophone system, Ultrasonics

3

sonochemistry, 42 (2018) 672-678.

4

[37] W.C. Kwon, J.Y. Yoon, Experimental study of a cavitation heat generator, Proceedings

5

of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical

6

Engineering, 227 (2012) 67-73.

7

[38] R. Dewil, J. Baeyens, R. Goutvrind, Ultrasonic treatment of waste activated sludge,

8

Environmental Progress, 25 (2006) 121-128.

9

[39] A. Tiehm, K. Nickel, M. Zellhorn, U. Neis, Ultrasonic waste activated sludge

10

disintegration for improving anaerobic stabilization, Water Research, 35 (2001) 2003-2009.

11

[40] X. Feng, H. Lei, J. Deng, Q. Yu, H. Li, Physical and chemical characteristics of waste

12

activated sludge treated ultrasonically, Chemical Engineering and Processing: Process

13

Intensification, 48 (2009) 187-194.

14

[41] N. Mahmoud, G. Zeeman, H. Gijzen, G. Lettinga, Solids removal in upflow anaerobic

15

reactors, a review, Bioresource technology, 90 (2003) 1-9.

16

[42] L. Huan, J. Yiying, R.B. Mahar, W. Zhiyu, N. Yongfeng, Effects of ultrasonic

17

disintegration on sludge microbial activity and dewaterability, Journal of Hazardous Materials,

18

161 (2009) 1421-1426.

19

[43] Y. Liu, H.L. Wang, Y.X. Xu, Y.Y. Fang, X.R. Chen, Sludge disintegration using a

20

hydrocyclone to improve biological nutrient removal and reduce excess sludge, Separation

21

and Purification Technology, 177 (2017) 192-199.

22

[44] Z. Wu, F.J. Yuste-Córdoba, P. Cintas, Z. Wu, L. Boffa, S. Mantegna, G. Cravotto,

23

Effects of ultrasonic and hydrodynamic cavitation on the treatment of cork wastewater by

24

flocculation and Fenton processes, Ultrasonics sonochemistry, 40 (2018) 3-8.

25

[45] K.S. Suslick, Y. Didenko, M.M. Fang, T. Hyeon, K.J. Kolbeck, W.B. McNamara, M.M.

26

Mdleleni, M. Wong, Acoustic cavitation and its chemical consequences, Philosophical

27

Transactions of the Royal Society of London. Series A:

28

Mathematical, Physical and Engineering Sciences, 357 (1999) 335.

29

[46] T. Zorba Gozde, F.D. Sanin, Disintegration of Sludge by Sonication and Improvement of

30

Methane Production Rates in Batch Anaerobic Digesters, CLEAN – Soil, Air, Water, 41

31

(2012) 396-402.

32

[47] T.H. Kim, S.R. Lee, Y.K. Nam, J. Yang, C. Park, M. Lee, Disintegration of excess

33

activated sludge by hydrogen peroxide oxidation, Desalination, 246 (2009) 275-284.

17

1

[48] A. Weissler, H.W. Cooper, S. Snyder, Chemical Effect of Ultrasonic Waves: Oxidation

2

of Potassium Iodide Solution by Carbon Tetrachloride, Journal of the American Chemical

3

Society, 72 (1950) 1769-1775.

4

[49] C. Bougrier, C. Albasi, J.P. Delgenès, H. Carrère, Effect of ultrasonic, thermal and ozone

5

pre-treatments on waste activated sludge solubilisation and anaerobic biodegradability,

6

Chemical Engineering and Processing: Process Intensification, 45 (2006) 711-718.

7

[50] Y. Wu, P. Zhang, G. Zeng, J. Liu, J. Ye, H. Zhang, W. Fang, Y. Li, Y. Fang, Combined

8

sludge conditioning of micro-disintegration, floc reconstruction and skeleton building

9

(KMnO4/FeCl3/Biochar) for enhancement of waste activated sludge dewaterability, Journal

10

of the Taiwan Institute of Chemical Engineers, 74 (2017) 121-128.

11

[51] R. Wang, J. Liu, Y. Hu, J. Zhou, K. Cen, Ultrasonic sludge disintegration for improving

12

the co-slurrying properties of municipal waste sludge and coal, Fuel Processing Technology,

13

125 (2014) 94-105.

14

[52] K.W. Jung, M.J. Hwang, Y.M. Yun, M.J. Cha, K.H. Ahn, Development of a novel

15

electric field-assisted modified hydrodynamic cavitation system for disintegration of waste

16

activated sludge, Ultrasonics sonochemistry, 21 (2014) 1635-1640.

17 18

List of Figures

19 20

Figure 1 Sketch of the rotor and three covers........................................................................2

21

Figure 2 Schematic of the hydrodynamic cavitation treatment system.................................3

22

Figure 3 Sketch of the ultrasonic bath ...................................................................................4

23

Figure 4 Particle size distributions for the experimental cases .............................................5

24 25

Figure 5 SVI results for each of the experimental cases: (a) SVI using ultrasonic bath and (b) SVI using the RHCG..........................................................................................6

26

Figure 6 (a) The tCOD reduction rate and (b) the VSS reduction rate..................................7

27 28

Figure 7 The solubilization rate for (a) measured SCOD and (b) nomalized SCOD for both RHCG and ultrasonic bath .....................................................................................8

29

18

1 2

Figure 1 Sketch of the rotor and three covers

19

1 2

Figure 2 Schematic of the hydrodynamic cavitation treatment system

20

1 2

Figure 3 Sketch of the ultrasonic bath

21

1 2

Figure 4 Particle size distributions for the experimental cases

22

1 2 3

Figure 5 SVI results for each of the experimental cases: (a) SVI using ultrasonic bath and (b) SVI using the RHCG

23

1 2

Figure 6 (a) The tCOD reduction rate and (b) the VSS reduction rate

24

1 2 3

Figure 7 The solubilization rate for (a) measured SCOD and (b) nomalized SCOD for both RHCG and ultrasonic bath

4 5

List of Tables

6 7

Table 1 Waste activated sludge properties .............................................................................2

8

Table 2 Operational conditions of experimental cases...........................................................3

9

Table 3 Percentile particle sizes of the raw and treated sludge ..............................................4

10

Table 4 Oxidization performance of the two treatment devices.............................................5

11

Table 5 Solubilization results of the two treatment devices...................................................6

12

25

1

Table 1 Waste activated sludge properties Item

Unit

Value

pH

-

6.48

tCOD

mg/L

4480

SCOD

mg/L

34

VSS

mg/L

2120

TS

mg/L

3726.5

2

26

1

Table 2 Operational conditions of experimental cases Specific energy input

Number of passes

Ultrasonication time

(kJ/kgTS) Case 1

84530

5

26m 15s

Case 2

167718

10

52m 5s

Case 3

248491

15

1h 17m 10s

Case 4

329800

20

1h 42m 25s

2

27

1

Table 3 Percentile particle sizes of the raw and treated sludge Item

d(0.1)

d(0.5)

d(0.9)

17.286

54.921

127.023

H.C

6.116

34.737

101.324

U.C

4.558

30.647

257.734

H.C

0.778

4.029

142.733

U.C

1.820

17.804

227.587

H.C

0.865

5.719

161.269

U.C

0.941

13.999

682.707

H.C

0.778

4.053

153.402

U.C

0.992

9.685

389.672

N.T Case 1 Case 2 Case 3 Case 4

Percentile size (μm)

2

28

1

Table 4 Oxidization performance of the two treatment devices N.T

Item tCOD(mg/L)

VSS (mg/L)

U.C H.C U.C H.C

4480

2120

Case1

Case2

Case3

Case4

4482.5

1665

1800

1830

2110

1650

1505

1480

1560

620

600

520

720

640

540

540

2 3

29

1

Table 5 Solubilization results of the two treatment devices Item

Case1

Case2

Case3

Case4

U.C

855

532.5

639

766.5

H.C

369.5

483.5

562

633

U.C

854.5

1432.8

1590.4

1876.5

H.C

784.5

1312.8

1672.9

1916.1

Solubilization

U.C

18.5

31.5

35.0

41.4

rate (%)

H.C

16.9

28.8

36.9

42.3

SCODm (mg/L) SCODn (mg/L)

2 3 4 5

Highlight

6 7

‧

The comparison of WAS treatment performance of RHCG and ultrasonication device was conducted

8 9

‧

10 treatment shows most efficient performance of RHCG in all aspect

10

‧

Decomposition performance of RHCG was overwhelmingly superior to ultrasonic bath

11 12

‧

In low energy density oxidation occurred only at RHCG

13

30