Scholarly article on topic 'Effect of Hydraulic Retention Time on Hydrogen Production from the Dark Fermentation of Petrochemical Effluents Contaminated with Ethylene Glycol'

Effect of Hydraulic Retention Time on Hydrogen Production from the Dark Fermentation of Petrochemical Effluents Contaminated with Ethylene Glycol Academic research paper on "Chemical sciences"

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{"Anaerobic Baffled Reactor (ABR)" / "Petrochemical industries" / "Ethylene Glycol (EG)" / "EG removal" / "hydrogen yield"}

Abstract of research paper on Chemical sciences, author of scientific article — Ahmed Elreedy, Ahmed Tawfik

Abstract In this work, the performance of an Anaerobic Baffled Reactor system (ABR) was investigated for biohydrogen production from petrochemical industries’ effluents, which are contaminated with Ethylene Glycol (EG). Five different Hydraulic Retention Times (HRTs) were operated, at constant EG concentration of 1000 mgCOD/L, in order to study their effects on both hydrogen production and EG removal efficiency. Decreasing HRT gradually from 72 to 18hrs affected the hydrogen yield to be increased from 45.50 to 377.03ml HR2R/gCODRremoved especially, when the HRT was decreased to 36 and 18hrs. The results for Volatile Fatty Acids (VFAs) compositions showed that maximum H2 yield was observed at high Acetic-to-Butyric ratio. EG removal of 92.38±0.68%, in terms of COD, was achieved at HRT of 72hrs; however, this value was largely deteriorated to reach 13.74±4.46% at HRT of 18hrs. Strong effect of pH on hydrogen production was also observed. Thus, the pH values were dropped gradually to 5.23±0.19, with maximum corresponding hydrogen yield.

Academic research paper on topic "Effect of Hydraulic Retention Time on Hydrogen Production from the Dark Fermentation of Petrochemical Effluents Contaminated with Ethylene Glycol"

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Energy Procedia 74 (2015) 1071 - 1078

International Conference on Technologies and Materials for Renewable Energy, Environment and

Sustainability, TMREES15

Effect of Hydraulic Retention Time on hydrogen production from the dark fermentation of petrochemical effluents contaminated with

Ethylene Glycol

Ahmed Elreedy*; Ahmed Tawfik*

Egypt-Japan University of Science and Technology, (E-JUST), Environmental Engineering Department, P.O. Box 179, New Borg Al-Arab City,

Postal Code 21934, Alexandria, Egypt.

Abstract

In this work, the performance of an Anaerobic Baffled Reactor system (ABR) was investigated for biohydrogen production from petrochemical industries' effluents, which are contaminated with Ethylene Glycol (EG). Five different Hydraulic Retention Times (HRTs) were operated, at constant EG concentration of 1000 mgCOD/L, in order to study their effects on both hydrogen production and EG removal efficiency. Decreasing HRT gradually from 72 to 18 hrs affected the hydrogen yield to be increased from 45.50 to 377.03 ml H2/gCODTemoved especially, when the HRT was decreased to 36 and 18 hrs. The results for Volatile Fatty Acids (VFAs) compositions showed that maximum H2 yield was observed at high Acetic-to-Butyric ratio. EG removal of 92.38±0.68%, in terms of COD, was achieved at HRT of 72 hrs; however, this value was largely deteriorated to reach 13.74±4.46% at HRT of 18 hrs. Strong effect of pH on hydrogen production was also observed. Thus, the pH values were dropped gradually to 5.23±0.19, with maximum corresponding hydrogen yield.

© 2015TheAuthors.Publishedby ElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) Keywords: Anaerobic Baffled Reactor (ABR); Petrochemical industries; Ethylene Glycol (EG); EG removal; hydrogen yield

1. Introduction

Doubtless, at the last 50 years, there was a rapidly increase in energy demand, which was accompanied by heavy consumption of non-renewable energy produced by the combustion of the fossil fuel [1]. Accordingly, the excessive

* Corresponding author. Tel.: +2-03-4599520. E-mail address: Ahmed.elreedy@ejust.edu.eg

* Corresponding author. Tel.: +2-03-4599520. E-mail address: Ahmed.tawfik@ejust.edu.eg

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4 .0/).

Peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi: 10.1016/j.egypro.2015.07.746

produced emissions of greenhouse gases, especially CO2, were the main source of the global warming problem. Renewable resources for energy (e.g. wind, solar and biogas energy) must be considered as environmentally friendly and economic solutions. Hydrogen gas is considered as the cleanest burning fuel because of its combustion product, which is only water. Furthermore, hydrogen has high energy content per unit mass of 120.21 MJ/kg (while CH4 is only 50.2 MJ/kg), which can be directly used in fuel cells for generating electricity [2,3]. The applied Hydrogen production methods such as steam reforming of methane as well as other hydrocarbons and non-catalytic partial oxidation of fossil fuels are intensively energy consuming methods, which require extremely high temperatures (> 850»C) [4].

The anaerobic biological hydrogen production, or dark fermentation process, is the most effective way compared with photo fermentation process because it does not depend on the availability of light sources [5]. Moreover, the anaerobic process is one of the most effective technologies for the removal of organic compounds in both domestic and industrial effluents, due to its relatively low cost in addition to its byproducts [6,7]. Several studies have been recorded that both of mixed and pure culture inoculums are able to produce hydrogen [8,9].

Interestingly, one of the most polluting problems in Egypt is the disposal of industrial effluents especially; the petrochemical industries, which have the majority of their contaminated effluents and heavy discharges. Ethylene Glycol (EG), an organic solvent excessively used in several industries, such as antifreeze, synthetic fiber, textile, paper, Leather, resin, polyester, ink, print, wax, film and tape. Therefore, the removal of EG from the industrial effluents have become important to satisfy the allowable disposal limits. Various methods, such as nano-filtration, vacuum membrane distillation, wet oxidation, photo-catalytic oxidation, and biological treatment have been suggested for the treatment and removal of EG [10-14].

The Anaerobic Baffled Reactor (ABR) has been described as a series of Upflow Anaerobic Sludge Blanket (UASBs), which does not need granulation for its operation. Therefore, it has lower start-up period than the other high rate reactors. Interestingly, Weiland and Rozzi [15] reported that, the most significant benefit of using ABR is the separation of both acidogenesis and methanogenesis longitudinally down the reactor, which allows it to behave as a two-phase system. To date, there are many reports show that ABR are capable to be used to treat various wastewaters with satisfactory performance for both treatment and biogas production [16,17]. Nevertheless, overall assessment of the ABR for treatment of industrial wastewater has been concluded that there is no ideal system applicable to all conditions; each situation must be deal individually.

Regarding to previous studies, which have been reported for Ethylene Glycol or its derivatives, especially that used as aircraft de-icing fluid; Marin et al. [18] reported that 75 % COD removal with an average methane production of CH4./gCOD.removed at 33°C were achieved. Another study by Darlington et al. [19], using Upflow Anaerobic Sludge Blanket (UASB) reactors for treating dilute aircraft deicing fluid (ADF) wastewater (5, 10 and 20 gCOD/L), concluded that COD removal efficiencies between 85 and 98 % can be successfully achieved at OLRs as high as 10 gCOD/L/d. On the other hand, different aerobic configurations by Hassani et al. and Shakerkhatibi et al. [20,21] were studied for the treatment of EG effluents. Nevertheless, the aerobic treatment still faces economic challenges; the heavy energy consumption and the high solids production to be waste [22,23]. It is interested to point out that, no previous studies focused on the production of hydrogen from EG contaminated wastewaters.

Accordingly, this study aims to assess the feasibility of using the Anaerobic Baffled Reactor configuration for the biological degradation of EG contaminated effluents. In addition, changing the system operational conditions, in terms of HRTs, was investigated to get the optimum conditions for each of EG removal efficiency and producing biohydrogen as a source of energy. Moreover, low temperature conditions (23-27°C during the study period) were experimented to investigate the feasibility of both removal of EG and hydrogen production, which is easier and more economic to be applied for such large flows, produced by the petrochemical industries.

Nomenclature

ABR Anaerobic Baffled Reactor EG Ethylene Glycol HRT Hydraulic Retention Time VFAs Volatile Fatty Acids

2. Materials and method

2.1. Seed sludge and media compositions

The seed sludge, which had been collected from the aerobic treatment plant, for domestic wastewater, of Al-Agamy, Alexandria, Egypt, was inoculated uniformly inside the ABR compartments. Thus, it was kept to be concentrated under anaerobic conditions before the system inoculation. Analysis of the sludge sample showed that Total Suspended Solids (TSS), Volatile Suspended Solids and pH of the seed sludge were 37.64, 12.98 g/L and 7.23, respectively. The ABR was fed continuously with synthetic feed containing Ethylene Glycol (C.2H.6O.2.) as the main substrate. The initial concentration was kept constant with the variation of HRT during the study period, which was 775 mg/L, that was equivalent to a value of 1000 mgCOD/L. Ammonium Chloride (NH.4.CL) and potassium dihydrogen phosphate (KH.2PO.4.) were added according to a COD:N:P ratio of 400:7:1 [24,25], this nutrients supplementation is essential for enhancing the bacterial growth [5].

Table 1. The operational conditions for the ABR different scenarios.

HRT (hrs) OLR (mgCOD/L d) Flow rate (L/d) Feed Ethylene Glycol (mg/L) Feed COD (mg/L) COD:N:P Temperature (°C)

72 333.33 10.5

60 400 13

48 500 16 775 1000 400:7:1 23-27

36 666.67 21

18 1333.33 42.5

2.2. Anaerobic Baffled Reactor (ABR) setup and operation

Anaerobic Baffled Reactor consists of five stepped compartments was used in this study as shown in Fig. 1. The working volume of the reactor was 32 L. Intermediate baffles were supported to allow the substrate to get longer path, longer contact time, through the microbial consortium (down-up path) inside the reactor. The reactor was made using Perspex sheets with black covering, which can inhibit the activity of photosynthetic bacteria. Moreover, it was continuously fed by a peristaltic pump (Masterflex - USA, Cole-Parmer Instrument Company) with the prepared synthetic feed at variable flow rates for each operation conditions.

The designed operational conditions for the ABR system are shown in Table 1. Accordingly, steady state condition for each HRT was described to be reached when difference in effluent COD concentrations was found to be insignificant. The ABR system was operated at low temperature conditions, which were varying from 23 to 27°C during the study period.

Figure 1. A schematic diagram for the ABR system

2.3. Analytical methods

The gas production was measured using a wet gas meter. The composition of the biogas produced was analyzed by a gas chromatogram (GC, Agilent 4890D) with a thermal conductivity detector (TCD) and a 2.0 m stainless column packed with Porapak TDS201 (60/80 mesh). The Chemical oxygen demand (COD), ammonium nitrogen (NH4-N), Total Suspended Solids (TSS) and Volatile Suspended Solids (VSS) were analyzed according to standard methods [26]. The analysis of VFAs in terms of acetic (HAc), butyric (HBu) and propionic acid (HPr) were performed on a Shimadzu HPLC system (Kyoto, Japan). For each studied condition (HRT), the ABR system was operated to reach the steady state before taking data.

3. Results and Discussion

3.1. Organic removal performance

The results shown in Fig. 2 present the steady state COD removal efficiencies for the ABR, treating EG contaminated feed, at different HRTs. Five different HRTs (72, 60, 48, 36 and 18 hrs, respectively) were applied in order to investigate the effect of HRT, which is also accompanied by changing the OLR. In addition, the allowable HRT to be applied for optimum EG removal can be determined, according to the disposal regulations. The results obtained revealed that decreasing HRT from 72 to 18 hrs affected noticeably on the COD removal efficiency, which was decreased from 92.38±0.68 to 13.74±4.46 %. Furthermore, the removal efficiency was decreased gradually at the first three HRT, which was 72, 60 and 48 hrs, to reach 68.32±2.62 %. However, its value largely deteriorated by almost 50% to reach 68.32±2.62 % at HRT of 36 hrs.

Decreasing HRT and sequentially, increasing the OLR; intends to move the anaerobic process away from the methanogenesis to acidogenesis and thus, higher hydrogen content [18,27]. The certain drop of the system removal efficiency at the lowest HRT of 18 hrs, was due to the accumulation of the soluble microbial products (SMP) by the acidogenesis [28]. Likewise, it was reported that 96% COD removal (EG-based substrate) was achieved for 750 mg/L influent COD at HRT of 40 hrs. In addition, a noticeable COD removal depletion at HRT of 3 hrs was observed [18]. Moreover, applying low OLRs for EG biodegradation at low temperature conditions of 25°C or below, was also recommended by Schoenberg et al. [29].

3.2. Volatile Fatty Acids (VFAs) generation andpH values

The main indicators for biohydrogen production from the dark fermentation of organic substrates are the volatile

COD Removal

Inf. COD

Eff. COD

100 80 60 40 20

HRT 72 hrs

HRT 60 hrs

HRT 48 hrs

HRT 36 hrs

1-1-1-1-

-I-1-1-1-1-1-1-1—

HRT 18 hrs

1200 , D

1000 g

800 600 400 200 0

15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100105110115 Time, days

W m d m

na t n

Figure 2. COD removal efficiencies at the steady state of each scenario

fatty acids (VFAs) [30,31]. The measured VFAs' compositions were Acetic (HAc), Butyric (HBu) and Propionic acid (HPr) as shown in Fig. 3. The results show a strong effect of HRT on the generation of all metabolites especially, the acetic acid. Apparently, Decreasing HRT from 72 to 18 hrs increased significantly the concentrations of HAc from 22.21±2.72 to 247.00±11.29 mg/L. As well, it was noticed that no HBu was observed at HRT of 72 hrs; however, HBu concentrations started to be increased from 12.80±0.79 to 48.20±3.17 mg/L, when the HRT was changed from 60 to 18 hrs, respectively. It is noteworthy that the accumulation of HAc has a strong reflection of higher performance of the acidogenesis [32]. Likewise, Schoenberg et al. [29] reported that HAc is the main metabolic pathway for the anaerobic degradation of EG, which also be consumed later by methanogens.

■HRT

■HBu

300 250 200 150 100 50 0

DQa"" № Vance

oK//x>

i i i i i i i i i i i i

15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100105110115 Time, days

6.00 d

5.00 T,

4.00 3C

3.00 S

2.00 X ft

Figure 3. pH and VFAs compositions, in terms of acetic, butyric and propionic acid, variations with the different HRTs

On the other hand, the HPr concentrations have no significant variation, when the HRT was increased from 72 to 36 hrs (14.53±1.31 mg/L as average value), but there was a noticeable increase to 32.59±3.51 mg/L at HRT of 18 hrs. That's due to the higher volume of produced hydrogen to be converted to HPr [33].

The pH variation, during the ABR working days, is also mentioned in Fig. 2, as a result of the different concentrations of the generated metabolites, by the microbial consortium, along with changing the operational conditions. Clearly, pH values were dropped significantly, at HRT of 18 hrs, to 5.23±0.19. Accordingly, the ABR system achieved better environment for acidification (optimum pH for hydrogen production [4,32]) at the lowest HRT of 18 hrs. Nevertheless, the COD removal of 13.74 % was significantly not acceptable in order to meet the environmental regulations for direct disposal to streams.

3.3. Biohydrogen production results

Fig. 4 shows the both of hydrogen content (% of the total produced gas) and hydrogen yield (in terms of ml H2/gCOD.removed) in addition to their association with effluent pH values. Clearly, the results obtained show a gradual increase of hydrogen content from 16.70 to 32.26 % with the decreasing of HRT from 72 to 36 hrs. However, high amount of hydrogen was produced at HRT of 18 hrs, which increased the hydrogen content to be 57.44 %. Similar studies were conducted for hydrogen production, which proved that the hydrogen content increases with the increase of OLR, reaching 50-55% [4] and 44% [5]. Moreover, Hafez et al. [34] reported that, at initial COD concentrations of 1-25 g/L when hydrogen production peaked, acetic-to-butyric ratios were >1. Accordingly, the acetic-to-butyric acid ratios were compared to the corresponding hydrogen yield at the five scenarios, as shown in Fig. 5.

▲ H2 yield

7.00 -

6.00 -

5.00 -

4.00 -3.00

----- A

R2 = 0.917 - ✓ u *

A A -■--m- R2 = 0.9305 ■

^300 U ^

- 200 - 100 0

HRT, d

Figure 4. The dependency of pH, hydrogen yield and hydrogen content with the operated HRT.

As mentioned by Intanoo et al. [32] for the strong dependency of producing hydrogen with pH values, effluent pH was dropped significantly from 6.34 to 5.23 with the increasing of hydrogen yield and hydrogen content. Likewise, the hydrogen yield results show a steady increase from 45.5 to 79.85 ml H2R/gCODRremovel with the HRT variation from 72 to 48 hrs. Nevertheless, large increase of hydrogen yield from 141.54 and 377.03 ml HR2R/gCODRremovedR was observed at HRT of 36 d and 18 hrs, respectively.

0.00 100.00 200.00 300.00 400.00 Hydrogen yield, ml ^/gCODremoved

500.00

Figure 5. The relation between acetic-to-butyric acid ratio and hydrogen yield variation

As well, these results reveal that the optimum hydrogen production was occurred when the ABR was operated at HRT of 18 hrs; though, by stepwise increase of the HRT, the hydrogen content decreased as result of the conversion of hydrogen and acetic acid by methanogens to CH.4. and CO.2. [35]. Strong correlation between HRT and both of the hydrogen yield and hydrogen content (0.917 and 0.930, respectively) was represented using exponential regression relations, as shown in Fig. 4.

4. Conclusion

In this study, anaerobic dark fermentation for Ethylene Glycol (EG) contaminated effluents was operated using Anaerobic Baffled Reactor system under low temperature conditions (27-23°C). Changing of HRT and subsequently the OLR was operated to investigate their effects on the hydrogen production in addition to EG reduction (in terms

of COD). COD removal efficiencies were decreased significantly with the HRT reduction, from 92.38% at HRT of 72 hrs to 13.74% at HRT of 18 hrs. By contrast, maximum hydrogen yield and hydrogen content were observed at HRT of 18 hrs, which were 377.03 ml H^/gCOD^^ve^ and 57.44 %, respectively. Moreover, the hydrogen yield increasing was found to be accompanied by high acetic-to-butyric acid ratios. The results obtained showed that producing hydrogen was mainly occurred after substrate contact time of 18 hrs, and then the hydrogen content was decreased with the increase of HRT. Eventually, the ABR configuration can be effectively and economically applied for both EG reduction and hydrogen production from EG contaminated petrochemical wastewaters. However, post treatment process is recommended for better removal efficiency, when the HRT of 18 hrs was applied to maximize the hydrogen production.

Acknowledgements

The first author is very grateful for Ministry of Higher Education (MOHE) for giving him a PhD scholarship to study at Egypt-Japan University of Science and Technology (E-JUST). This study was financed by STDF project no. 3665.

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