Simultaneous treatment and energy production from PIW using electro coagulation & microbial fuel cell

Accepted Manuscript Title: Simultaneous Treatment and Energy Production from PIW using Electro Coagulation and Microbial Fuel Cell Author: Ravi Shankar Anil Kumar Varma Prasenjit Mondal Shri Chand PII: DOI: Reference:

S2213-3437(16)30381-5 http://dx.doi.org/doi:10.1016/j.jece.2016.10.021 JECE 1301

To appear in: Received date: Revised date: Accepted date:

23-7-2016 27-9-2016 19-10-2016

Please cite this article as: Ravi Shankar, Anil Kumar Varma, Prasenjit Mondal, Shri Chand, Simultaneous Treatment and Energy Production from PIW using Electro Coagulation and Microbial Fuel Cell, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2016.10.021 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.

Simultaneous Treatment and Energy Production from PIW using Electro Coagulation& Microbial Fuel Cell

Ravi Shankar*, 1, Anil Kumar Varma2, Prasenjit Mondal3 and Shri Chand4

1

Department of Chemical Engineering, Madan Mohan Malviya University of Technology

Gorakhpur-273010, Uttar Pradesh, India 2-4

Department of Chemical Engineering, Indian Institute of Technology Roorkee

Roorkee-247667, Uttarakhand, India

*Corresponding author. Tel.: +91-1332- 285181; fax: +91-1332-276535, E-mail address: [email protected]

1

Highlights •

Organic content of the PIW can be converted in to useful energy.

•

EC process improves the BI (biodegradability index) of the treated wastewater.

•

MFC can be the better treatment option for EC treated wastewater for simultaneous treatment and energy production.

•

Sludge and scum generated during EC treatment process contain significant amount of energy.

Abstract The present work deals with the treatment and simultaneous energy generation from paper industries wastewater (PIW) using electro coagulation (EC) and microbial fuel cell (MFC). The PIW is first treated by EC, which improves the biodegradability index (BI) of PIW, which is then used as a raw material for the MFC process. It has been observed that the PIW with initial organic loadings of 2400 mg/L,750 mg/L, and 5600 mg/L can be treated using EC, MFC and EC followed by MFC respectively, to achieve the effluent under permissible limit. Under the experimental conditions, during the EC process, approximately 1.29 kJ/g and 8.62 kJ/g of energy can be generated from sludge and scum, respectively and approximately 56 mV voltage and 0.02 mA current can be generated from the continuous MFC process.

Keywords:

Electro

coagulation, Microbial Fuel

Biodegradability Index, Energy, COD

2

Cell, Paper

Industries

Wastewater,

1. Introduction Indian paper industries use agriculture/forest based raw materials and high amount of water for paper making. These industries thus generate huge amount of wastewaters, which contain complex chemical compounds formed during the processing [1]. Approximately 20 to 250 m3 of wastewater per ton of paper produced are generated, which contains high initial COD (100000 mg/L), BOD (30000-40000 mg/L) and color with alkaline nature and biodegradability index (BI) value < 0.4[2-5]. The organic and inorganic compounds present in PIW have potential to generate energy by using various techniques [6]. Several processes have been developed for the simultaneous treatment and energy production from wastewater by various researchers [7-9], such as, (a) biomethanation (b) aerobic treatment and bio-methanation (c) two stage aerobic treatments and biomethanation, etc [10]. The bio-methanation process depends on the BI of wastewater and this process may achieve to 70-80% of COD reduction [11, 12]. Therefore, high organic load and low BI of PIW after bio methanation process requires further secondary/tertiary treatment. Various secondary/tertiary treatment technologies such as adsorption, wet air oxidation, Fenton oxidation, electro coagulation etc., can be used. Among these treatment technologies electro coagulation (EC) can play an important role in treatment of low BI and high suspended particle containing wastewater because of various reasons such as (a) EC process can be used for the treatment of both organic and inorganic waste containing wastewater [13,14], (b) sludge and scum generated during EC process can be used as energy source [15], (c) during EC treatment process suspended particles are removed [16], and (d) it improves the BI of the wastewater [17, 18]. Therefore, EC treated PIW with considerable initial COD requires further treatment. As 3

MFC has potential to generate energy for the EC treated wastewater having considerable BI, MFC can be used as a subsequent treatment option. The Performance of EC process depends upon various factors such as, type of reactor used, electrodes material and surface area, charge loading/current density, NaCl concentration, solution pH, operating temperature, power supply, type of effluent etc. The anodic reaction (for aluminium material) during EC process is follows [19]. Al  Al3+ + 3eAl3+ +3OH- Al(OH)3(In alkaline solution) Al3+ + 3H2O  Al(OH)3 + 3H+

(In acidic solution)

During EC, Al is converted to hydrolysed Al ion by electrochemical changes. These ions form large number of Al-O-Al-OH networks, which have capability to absorb pollutants by the mechanism of chemical absorption [20]. Various other factors of advantage, such as high suspended particle removal capacity, comparatively low cost and small installation area attract the use of EC process in wastewater treatment. MFCs are based on the principle in which electricity/hydrogen can be generated/produced through the bacterial action. Various factors such as, type of MFC reactor, surface area and material of electrodes, types of inorganic and organic catalysts, microbes, operating conditions (solution pH, temperature, organic load etc) and type of membrane affect the process [21]. Use of low cost electrode material with continuous membrane less MFC can be the better and economical biological treatment option for the simultaneous treatment as well as energy production from the waste water. In this study individual and combined effect of EC and MFC for the simultaneous treatment and energy production from PIW has been investigated and its performance has been compared.

4

2. Material and Process All the chemicals used in this study were analytical grade (AR) of HiMedia Laboratories Private Limited and Fine-Chem Limited, India. PIW were collected from a local paper mill at Saharanpur, India. The characteristics of PIW are given in Table 1. Activated sludge from the treatment of municipal wastewater (MW-AS) required for anaerobic microbes was collected from sewage treatment unit, Jagjitpur, Haridwar, India. Two important bacterial strains such as, Pseudomonas stutzeri and Micrococcus species were identified in the MW-AS by the phenotypic characterization at IMTECH, Chandigarh, India. Fig.1 (a) shows the treatment procedure of PIW and Fig.1 (b) and (c) show the experimental setup of batch scale EC and continuous scale MFC. For electro-coagulation studies, a rectangular batch container made of Perspex glass of volume of 1.52 L was used. Aluminum metal sheets with an active surface area of 64 cm2 were used as electrodes. Multiple electrodes were placed parallel to each other at inter distance of 1 cm. Direct current (DC) was given in mono polar mode to the electrodes at the required current intensity and each experiment was carried out at constant current condition. Each experiments of EC were operated at initial pH of 7, initial electrode distance of 1 cm, electrolyte (NaCl) concentration of 1g/L, current density of 110 A/m2 and operation time of 75 minutes [15]. The PIW was diluted with distilled water. The final concentration was computed by Eq. (1). V1C1 = V2C2

(1)

Where, V1and V2 are the initial and final volume, C1 and C2 are initial and final concentration. The continuous MFC used in the present study consists of the bio-column reactor (MFC), a feed tank and sampling ports, all are made of Perspex [22, 23]. MFC column with total height of 100 cm and diameter of 10 cm was made in two parts. The lower part as anodic chamber with height

5

of 60 cm and upper part as cathodic chamber with height of 40 cm. The cathodic and anodic chambers were separated by a filter media placed above the anodic chamber. This consisted of glass wool supported on glass beads of 5 cm diameter. Anaerobic condition in the feed tank was maintained by flowing nitrogen. Single cathode and multiple anodes (3 numbers) of graphite with equal surface area of 78.5 cm2 were used. Anodes were fixed at 25, 40 and 55 cm from the bottom of the reactor. Feed was supplied from feed tank to anodic chamber at a volumetric flow rate of 1 mL/min from the bottom of the reactor using a peristaltic pump [23]. The MFC was operated at initial pH of 7 and temperature of 35 ± 1 oC [24]. All the connections were made with copper wire and electrodes were connected with 50 Ω external resistance and a multimeter, which was connected to a personal computer. The pH of the solution used in both EC and MFC were maintained by using 1 N NaOH and 1 N H2SO4 solution. 3. Results & Discussion The effect of initial COD on EC process and effect of initial COD of EC treated wastewater on MFC and combined effect of EC and MFC process as well as energy perspective of EC and MFC process are described below: 3.1.

Effect of initial COD on COD and color removal by EC process

Different values of initial COD such as 1000, 4000, 7000, 10000, 13000 and 16000 mg/L were taken for EC process. The effects of initial COD on the color and COD reduction are shown in Fig. 2 as a function of process parameters. From Fig. 2, it is evident that the percentage removals of COD, color and BI of treated effluent decrease continually with increase in initial COD. The above observation is obvious since, other parameters particularly current density, pH and run time, which influence significantly the release of coagulant, remain constant for all the cases.

6

Under constant values of these parameters fixed amount of in situ coagulant is generated. At lower initial COD almost complete removal of organics is possible giving high percentage removal of COD and color. However, in the present case it seems that initial organic load of 1000 mg/L gives residual COD in treated water at around 20 mg/L, which is under the acceptable limit as prescribed by CPCB. Residual color is also very less (15 Hazen). However, at the initial organic load of 4000, 7000 and 10000 mg/L the residual COD values are 390, 1680 and 3500 mg/L respectively. Also, it has been observed that the BI of the PIW is increased after the treatment but BI of treated effluent decreases with increase in initial COD concentration. During EC process the generated metallic cations interact with OH- to form hydroxides, which adsorb pollutants (bridge coagulation). In some cases, the hydroxides form larger lattice-like structures and sweep through the water (sweep coagulation). The cations or hydroxyl ions can also form a precipitate with the pollutants by neutralizing the charge of the colloidal particles. Further, the adhesion of bubbles to the flocks resulting and electro-flotation can also help the removal of pollutants [25, 26]. Also, during EC process the complex organic and inorganic pollutants break down in smaller compounds, which improve the BI of the wastewater in spite of decrease in initial COD. BI after treatment decreases with increase in initial COD as the rate of COD removal also decreases with increase in initial COD, decreasing the rate of formation of biodegradable compounds. So, PIW with organic load up to 2400 mg/L can be treated with the EC process to attain the effluent within permissible limit (250 mg/L for COD and 30 mg/L for BOD). 3.2.

Effect of initial COD on the reduction of COD and color removal by MFC process

The effects of initial COD on the voltage generation as well as COD and color removal are shown in Fig.3. From Fig.3, it is evident that with increase in initial COD value from 250 mg/L

7

to 1250 mg/L, the % removals of COD and color both decrease and voltage generation increase, However, the rate of increase in voltage generation after 750 mg/L decreases significantly. Further, as the flow rate is constant for all the wastewater samples, the residence time of the solution in the MFC column remains constant for all the cases. At the lower initial COD value most of the organics present in the wastewater may be degraded, however, with increase in COD value the residence time may not be sufficient for the degradation of all the organics. From Fig. 3, it is evident that more than 81.5 % of COD is removed when initial COD is 250 mg/L and around 77.5 % COD is removed when initial COD is 500 mg/L. The COD removal further decreases with the increase in initial COD. Another important fact is that for multi substrate system, pathway for each substrate is inducible and the presence of one substrate can influence the expression of the pathway of other substrate [27]. It may be possible that with increase in initial COD the consumption of organics in PIW becomes relatively slower due to substrate inhabitation being favored. Further, with increase in initial COD, the percentage removal of COD decreases and it is observed that at initial COD of 250, 500, 750, 1000 and 1250 mg/L, the residual COD are 46, 112.5, 237, 396 and 532.5 mg/L, respectively and corresponding voltage generations are 30, 48, 56, 62 and 64 mV, respectively. This implies that the initial COD of 750 mg/L or less can produce effluent as per CPCB norm. 3.3. Comparison of individual and combined EC and MFC process The results of individual EC and MFC process on PIW to meet the CPCB norms is shown in Fig. 4. From Fig. 4, it is clear that PIW with initial COD of 2400 mg/L can produce treated water containing COD and BOD within permissible limits of 250 mg/L for COD and 30 mg/L for BOD using a single step EC treatment process. Since, during EC treatment process BI of the wastewater increases which attracts the use of biological treatment technologies after EC

8

treatment. PIW after EC treatment is treated in MFC and the effect of initial COD (250, 500, 750, 1000 and 1250 mg/L) on performance of MFC is shown in Fig. 3. From Fig.5, it is clear that, initial COD of 750 mg/L can produce treated water containing COD value within the permissible limit using MFC process alone after 30 days. On the basis of the above facts the combined treatment options (EC followed by MFC) for the removal of organics from PIW is shown in Fig. 6. From Fig. 6, it is interesting to note that COD values in EC treated effluent are less than the MFC treated one. Since, the biodegradability index of the EC treated wastewater samples are high (0.31), COD value above 97 mg/L cannot meet the permissible limit of BOD (30 mg/L) in the treated water. From Fig. 6, it is also clearly evident that by the combination of EC and MFC process PIW having initial COD value of ~5600 mg/L can be treated effectively and the permissible limits of COD and BOD in treated effluent can be achieved. 3.4. Energy recovery The scanning electron micrograph (SEM) of the scum and sludge generated during EC of PIW is shown in Fig 7. Comparing the SEM of scum and sludge as shown in Figs.7 (a) and (b), it appears that the scum particles are more irregular and porous than the sludge particles. This may be due the floatation of these particles as scum during EC. The dense structure of sludge favors its settling. Atomic percentage of some important elements, obtained from the EDAX spectrum of the scum and sludge of PIW is shown in Table 2. Comparing the EDAX data of sludge and scum, it seems that the carbon content in scum (51.64 %) is more than that in sludge (35.6 %), where as aluminium content in sludge (25.51 %) is more than that in scum (13.47 %). FTIR spectra of scum and sludge generated during electro coagulation of PIW have similar types of functional groups in both scum and sludge [15].

9

Thermal stability of scum and sludge are directly dependent on the decomposition temperature of its various functional groups and oxides. The thermal gravimetric analysis (TGA), differential thermal analysis (DTA) and derivative thermal gravimetric analysis (DTG) of sludge and scum are shown in Figs. 8 (a) and (b) respectively. The TGA shows the loss in weight due to moisture and some low molecular weight compound from 25 to 200 oC. The rate of weight loss increases between 200 to 500 oC due to evolution of CO2 and CO for both sludge and scum. The weight loss due to the heating in the temperature range of 500-1000 oC is ~ 3% only for both scum and sludge. The maximum degradation rates are 0.29 mg/min at 360 oC for scum and 0.17 mg/min for sludge at 349 oC. From Figs.8 (a) and (b), it seems that the incineration of these materials may be carried out within the temperature range of 400- 500oC. The ash content in scum and sludge are found as ~ 40% and 60% respectively. From Figs. 8 (a) and (b), the calorific value of sludge seems to be lower than that of scum, which is also supported by the low carbon and high ash in sludge with respect to scum. A significant amount of heat (-8.62 kJ/mg) is released due to oxidation of scum where as it is around -1.29 kJ/g in case of oxidation of sludge. From the above discussion, it is clear that sludge and scum contain similar type of functional groups, however the scum is more porous than sludge. The average calorific value of scum and sludge is around -5 kJ/g, which is almost equivalent to the heating value of some municipal solid wastes [28]. Thus, mixture of scum and sludge can be used effectively for energy production through incineration. Further, both scum and sludge can be used to recover aluminum present in these [29]. Voltage production under the optimum conditions using EC treated PIW with initial COD of 750 mg/L is 56 mV, which is shown in Fig.9. Form Fig. 9, it is evident that the voltage generation initially decreases slightly, which starts to increase after around ~2 days and attains a steady value in 14-15 days, This is due to the adaptation of the microorganism in new environment as

10

well as the presence of variety of organics present in the wastewater. In the present case, the natures of the organic molecules present in wastewater sample are different. PIW contains lignin and its derivatives and phenols. These compounds are not equally susceptible to the microorganisms added into the wastewater samples and due to presence of these chemical compounds biological activity is also affected [30, 31]. However, with the use of suitable design as well as the material used (i.e. electrode, catalyst and microbes) the performance of MFC can be increased. 4. Conclusions The treatment of high organics containing wastewater requires significant efforts and cost. By the use of EC and MFC treatment processes together apart from reducing COD, energy can also be produced. Use of EC process requires less installation area and cost, whereas the use of bacterial source in MFC minimizes the use of chemical resources. During EC process the scum and sludge generated have significant calorific value, thus scum and sludge of PIW can be used for the production of energy through incineration. Also during EC treatment processes, BI of PIW increases from ~ 0.1 to 0.31, this attracts the suitability of biological treatment technology. The treatment of PIW with EC and MFC improves the wastewater treatment capacity. Under the experimental conditions, wastewater with initial COD value of ~5600 mg/L can be treated to generate 56 mV voltage and 0.02 mA current along with its treatment through the EC followed by MFC process. This process has also potential to produce approximately, 1.29 kJ/g and 8.62 kJ/g of energy from sludge and scum generated during EC under the conditions of investigation.

11

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List of Figures Pulp & Paper Industries wastewater Screening

Treatment with electro coagulation

Treatment with microbial fuel cell

Treated water

(a) Power source Al parallel cathodes

A

V

Al parallel anodes

Rheostat

Electro coagulation Cell

Synthetic wastewater

Magnetic bar

Magnetic stirrer

(b)

(c) Fig. 1. (a) Treatment procedure of PIW (b) Experimental setup of batch scale EC (c) Experimental setup of continuous MFC

16

120

0.5 0.45 0.4

80

0.35

60

0.3

BI

Percentage removal

100

0.25

40

Colour

0.2

COD

20

0.15

BI

0 0

3000

6000 9000 12000 Initial COD (mg/L)

15000

0.1 18000

Fig. 2. Effect of initial COD on color and COD removal, and Biodegradability Index (BI) (Conditions: current density 110 A/m2, initial pH 7, run time 75 min, NaCl concentration1g/L, electrode distance 1cm)

17

70

80

60

70 50 60 40 50

COD removal Colour removal Voltage

40

30

30 200

400

600 800 1000 Initial COD (mg/L)

Voltage (mV)

Percentage removal

90

1200

20 1400

Fig. 3.Effect of initial COD on voltage generation as well as color and COD removal (Conditions: substrate flow rate 1ml/min, temperature 35±1oC, anodic pH 7 ± 0.2, number of anodes3, distance between upper anode and cathode 20 cm)

18

Fig. 4. COD before and after treatment for treating various types of wastewater through EC and MFC process individually (under optimum conditions)

19

80

Percentage removal

70 60 50 40 30 COD removal colour removal

20

10 0 0

5

10

15

20 25 Time (days)

30

35

40

45

Fig.5.Effect of time (days) on COD and Colour removal from EC treated PIW in MFCcolumn (Conditions: anodic pH 7, temperature 35oC, microbes of (MW-AS), flow rate of anodic solution 1 mL/min, number of electrode 3, initial COD for PIW 750 mg/L)

20

Fig. 6. Initial and final COD after treating various types of wastewater through combined process (EC followed by MFC) (under optimum conditions)

21

(a)

(b)

Fig. 7. SEM of scum and sludge generated by EC of PIW, (a) scum,(b) sludge

22

Fig. 8. TGA, DTA and DTG pattern of scum and sludge generated during the EC of PIW, (a) scum, (b) sludge 23

80 70

Voltage(mV)

60 50 40 30 20 10 0 0

2000

4000

6000 8000 Time (1 unit = 5 minute)

10000

12000

Fig. 9.Voltage generation from EC treated PIW in column MFC (Conditions: anodic pH 7, temperature 35oC, microbes of (MW-AS), flow rate of anodic solution 1 mL/min, number of anodes 3, initial COD of PIW 750 mg/L)

24

List of Table Table 1 Characteristics of wastewater from PIW used in the present investigation Parameters

Values(original wastewater)

COD (mg/L)

185000

BOD5 (mg/L)

20100

Colour (Hazen)

272531

pH

11.68

TOC(mg/L)

74661

TC(mg/L)

76062

IOC(mg/L)

1401

Total solids (g/L)

259.2

Total dissolve solid

15.84

Total suspended solid

243.36

Cl-(mg/L)

800

SO42-

10202

Phenol

8330

25

Table 2. Atomic % of some important elements in scum and sludge of the PIW

Elements

Scum

Sludge

Atomic %

Atomic%

C

51.64

35.60

O

28.35

34.04

Na

3.20

2.28

Al

13.47

25.51

Si

1.01

0.79

S

0.98

0.87

Cl

1.36

0.91

26