Scholarly article on topic 'Continuous Biological Treatment of Paperboard Mill Wastewater along with Hydrogen Production'

Continuous Biological Treatment of Paperboard Mill Wastewater along with Hydrogen Production Academic research paper on "Chemical sciences"

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{"Paperboard mill wastewater" / "Anaerobic digestion" / "Organic loading rate" / "Anaerobic baffled reactor" / Hydrogen}

Abstract of research paper on Chemical sciences, author of scientific article — Ahmed Farghaly, Ahmed Tawfik, Mona Gamal Eldin

Abstract Continuous biological treatment of paperboard mill wastewater under changes of organic loading rate (OLR) along with hydrogen production was investigated. The continuous experiments were conducted at different OLRs from 1.2 to 18.6kg COD/L.d. The COD removal efficiency increased from 30.8±3.1 to 83.6±5.3% with decreasing OLR from 18.6 to 1.2kg COD/L.d, respectively. TSS, VSS, and carbohydrates removal efficiencies were 86.5±5.11%, 81.6±1.7%, and 63.5±19%, respectively. Meanwhile, the hydrogen production rate was amounted the highest value of 4.74±0.9 L/d at OLR of 9.3kg COD/L.d which coincided to the highest volatile fatty acids of 337±13.6mg/l and HAc/HBu of 2.13±0.4.

Academic research paper on topic "Continuous Biological Treatment of Paperboard Mill Wastewater along with Hydrogen Production"

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Energy Procedia 74 (2015) 926 - 932

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

Sustainability, TMREES15

Continuous Biological Treatment of Paperboard Mill Wastewater along with Hydrogen Production

Ahmed Farghaly*, Ahmed Tawfik*, Mona Gamal Eldin

Ahmed.abdelwahhab@ejust.edu.eg; ahmed. tawfik@ejust.edu.eg Egypt-Japan University of Science and Technology (E-JUST); Environmental Engineering Department; P.O. Box 179-New Borg El Arab City —

Postal Code 21934 - Alexandria — Egypt

Abstract

Continuous biological treatment of paperboard mill wastewater under changes of organic loading rate (OLR) along with hydrogen production was investigated. The continuous experiments were conducted at different OLRs from 1.2 to 18.6 kg COD/L.d. The COD removal efficiency increased from 30.8±3.1 to 83.6±5.3% with decreasing OLR from 18.6 to 1.2 kg COD/L.d, respectively. TSS, VSS, and carbohydrates removal efficiencies were 86.5±5.11%, 81.6±1.7%, and 63.5±19%, respectively. Meanwhile, the hydrogen production rate was amounted the highest value of 4.74±0.9 L/d at OLR of 9.3 kg COD/L.d which coincided to the highest volatile fatty acids of 337±13.6 mg/l and HAc/HBu of 2.13±0.4. © 2015TheAuthors. Published by 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: Paperboard mill wastewater, Anaerobic digestion, Organic loading rate, Anaerobic baffled reactor, Hydrogen

1. Introduction

Paperboard mill wastewater (PMW) treatment is of immense concern for the environment due to its after effects [1]. Especially, pollutants released from paperboard mills into the environment pose numerous problems and physiological impairment. Furthermore, some compounds in the effluents are resistant to biodegradation and can bio-accumulate in the aquatic food chain [2]. New environmental regulations and the increasing market preference for companies that respect the ecosystem have encouraged the industry to look after new methods of treatment for its effluents [3]. Many attempts have been used for the treatment of PMW such as coagulation, adsorption, chemical oxidation, aerobic and anaerobic treatment [4]. Among all, the anaerobic treatment methods seems to be attractive in terms of reduction of color, COD, BOD, and toxic low molecular weight chlorinated lignin derivatives present in PMW [1]. Also, anaerobic digestion methods are energy generating process, in contrast to aerobic systems that generally demand a high energy input for aeration purposes [5].

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.2015.07.828

On the other hand, the increasing cost of oil prices, depletion of fossil fuel investments, environmental degradation and climate change are driving factors for finding the alternative energy sources that are environmentally friendly and renewable [3]. Hydrogen (H2) is emerging as a strong candidate because it has the highest energy content per unit weight (122 kJ/g) and it produces water when combusted [6], [7]. Besides, H2 appears to be one of the best transportation fuels, more versatile, efficient, and the safest fuel [8]. In addition, H2 is widely used for the synthesis of ammonia, alcohols, and aldehydes, as well as for the hydrogenation of edible oils, petroleum, coal, and shale oil [9]. Accordingly, hydrogen production addresses three of today's major energy problems: rising energy demand, environmental pollution, and fossil fuel dependence [10].

Hydrogen production could be achieved by either photosynthetic or anaerobic microorganisms. The photofermentation process presents a number of disadvantages such as light dependence which requires large surface areas. In addition, during photo-fermentation, hydrogen production is catalyzed by nitrogenases which produce hydrogen at a lower rate than hydrogenases [11]. So, lower operational cost, more hydrogen production rate, wider range of substrates, and simplicity account for the superiority of dark fermentation over photo-fermentation [10]. In dark fermentation process, there are four stages: hydrolysis, acidogenesis, acetogenesis and methanogenesis. The main responsible bacterial cultures for acetate, hydrogen and carbon dioxide production are dominated in the first three stages. In the last stage, methanogenic bacteria produce methane from acetate, or alternatively from hydrogen and carbon dioxide [12].

In this approach, it is true indeed that the optimum values of the determinative parameters depend on several factors. Among these factors, the organic loading rate (OLR) is an important factor that affects the performance of the process. Specifically, the OLR affects the substrate conversion efficiency, the type of active microbial population as well as the metabolic pathways established in the system [13]. From literature, no significant trend was reported by varying OLR on both organic pollutants conversion efficiency as well as hydrogen production. In some studies, higher OLRs decreased the H2 yield (1.1 mol H2/mol glucose), whereas in some others, higher OLRs increased the H2 yield up to 2.8 mol H2/mol lactose [14]. Gomez at al. [15] observations revealed that agitation and reduction of OLR aided the stability of process performance. In another study, high OLR resulted in large concentrations of volatile fatty acids that could be accumulated in the fermentation system, leading to a decline of pH in the reactor and adversely affected the activity of the microorganisms [16].

Therefore, the main aim of the present research is to investigate the performance of anaerobic digestion process using anaerobic baffled reactor (ABR) for treating the paperboard mill wastewater and continuous H2 production in environmental friendly manner at different organic loading rates.

2. Material and Methods 2.1. Mill description and seed sludge

The mill selected for the study has a capacity of 60 ton/day of paperboard production, situated in Alexandria, Egypt. Printing paper and plastics wastes are used for manufacturing of paperboard. The mill generates 700 m3/d of wastewater that disposed to the sewage works without any treatment. The end of pipe effluent was sampled and transported within 1 hr. to the environmental lab for further experiments. The characteristics of PMW are presented in Table 1.

The seed sludge was collected from the thickener of the activated sludge treatment plant. The sludge was allowed to be settled for 24 h. where the supernatant was withdrawn. Volatile suspended solids and total suspended solids contents were 23 and 14.7 g/l, respectively. The sludge was pre-treated at 90 °C for 30 min. to harvest spore-forming bacteria and acclimatized with PMW under anaerobic conditions for a period of two weeks.

Table 1. Characteristics of paperboard mill wastewater

Parameter

Substrate

Total COD (mg/L) Soluble COD (mg/L) Particulate COD (mg/L) TSS (mg/L) VSS (mg/L) pH

Carbohydrates (mg/L) Total VFAs (mg/L) NH4-N (mg/L) TKj-N (mg/L) VSS/TSS %

2251 1074 1177 1000 440 7.5 56 243 3.4 56 44

2.2 Experimental set-up

The continuous experiments were conducted using anaerobic baffled reactor (ABR) with working volume of 14 L fabricated from Perspex materials. The reactor consists of five compartments with baffles to increase contact time between PMW and the inoculums. The fresh PMW was fed into the reactor with different OLRs of 1.2, 2.1, 9.3, and 18.6 kg COD/L.d using peristaltic pump. The biogas was collected via porthole in the top of ABR. In addition, the ABR was equipped with sampling ports that allowed biological solids and liquid samples to be withdrawn. The volume of evolved biogas was measured using the displacement method and corrected to the standard conditions (25 °C and 1 atm.) as described earlier [17].

3. Results and discussion

3.1 Organic pollutants conversion efficiency

The experimental results indicated that the OLR has a significant effect on organic pollutants conversion efficiency. As shown in Fig. 1, the operation of anaerobic digestion process at OLR of 1.2 kg COD/L.d results in the highest COD removal efficiency of 83.6±5.3%. Likewise, TSS and VSS removal (R%) were peaked at 86.9±4.8 and 78.83±12% at the same OLR, respectively as shown in Fig. 4. The obtained data indicates that anaerobic digestion process using ABR seems advantageous due to high treatment feasibility by generating separate environments for acidogenesis and methanogenesis. Moreover, It promotes favorable conditions for microbial populations which are involved in the degradation process [18]. Likely at higher OLRs, an increase in the yield of biomass that negatively affect conversion efficiency could be occurred [19]. Also, the lower removal efficiencies at higher OLRs may be attributed to the complex polymer structure of PMW [20].

^■PMW

-•-%R 18.6 3000

%R 9.3

I-19.3

—♦—%R 2.1

□ 2.1

-%R 1.2

I-11.2

33 37 40 44 52 59 67

Time (days)

Fig. 1. Effluent COD concentrations and removal efficiency % with time (days) 3.1 Hydrogen production rate and yield

Even more, the OLR effectively influences on the metabolic and kinetic characteristics of mixed culture bacteria and anaerobic fermentation process. The results in Fig. 2 show the effect of varying OLR values on fermentative hydrogen production from paperboard mill wastewater. It was found that the highest HPR of 4.74±0.9 was evolved at OLR of 9.3 kg COD/L.d. The lower HPR at OLR of 18.6 kg COD/L.d is likely due to that the ABR were operated under substrate limiting conditions resulted in lower H2 productivity [21]. Moreover, according to Tawfik et al. [22] findings; the excessive increase in OLR would result in higher concentrations of volatile fatty acids that inhibited the growth of hydrogen-producing bacteria. Conversely, at lower OLRs, the biomass accumulation has been increased which resulted in nutrients consumption and wastes production that in due course inhibit hydrogen production [23].

7 6 )5 d 4

a 2 1 0

33 37 40 44 52 59 67

Time (days)

Fig. 2. Hydrogen production rate with time at various OLR (kg COD/L.d)

The effect of organic loading rate on hydrogen yield (HY) can be used as a direct indicator of the vitality of the anaerobic process. As depicted in Fig. 3, as OLR increased from 1.2 to 9.3 kg COD/L.d, the HY increased form

1.03±0.54 to 3.37±0.89 L/gCOD.d, respectively. This result is in line with the highest HP at 9.3 kg COD/L.d. This observation indicates that ABR can provide high efficiency for recalcitrant substrates because of the phase separation [18]. In this sense, the highest HPR observed in ABR was not accompanied by the peak conversion efficiency which is comparable with Gomez et al. [15] results. The lower organic removal % at higher OLR may be attributed to the bacterial activity of releasing a significant amount of liquid intermediate products resulted from substrate metabolism and biomass decay which form the majority of the effluent COD [3], [24].

O 2 eg 2

Fig. 3. Hydrogen yield at different OLR (kg COD/L.d)

9.3 2.1

OLR (kg COD/L.d)

-TSS R%

-VSS R%

100 80 60 40 20 0

9.3 2.1

OLR (kg COD/L.d)

3 /d /(L

Fig. 4. The relationship between TSS and VSS removal efficiencies and hydrogen production rate at various OLR (kg COD/L.d)

3.2 Volatile fatty acids

The volatile fatty acids (VFAs) distributions are useful indicators for monitoring H2 production. The depicted data in Fig. 5 indicates that the highest VFAs concentration was coincided to the highest HPR and HY at OLR of 9.3 kg COD/L.d. In addition, the main soluble metabolite exerted during the process was acetate (HAc=85.87±7.5 mg/l) followed by butyrate (HBu=40.23±3.3 mg/l) at 9.3 kg COD/L.d indicates the HAc/HBu pathway occurred which is favorable for H2 production. That's due to the acidogenesis pathways for HAc and HBu are known for favor hydrogen production. Specifically, the hydrogen produced from HAc was the theoretical maximum of 4 mol H2/mol glucose and that produced from HBu was 2 mol H2/mol glucose as illustrated in Eqs. 1 and 2 [23].

Glucose + 2H2O —► 2CH3COOH + 2CO2 + 4H2 Glucose —► CH3CH2CH2COOH + 2CO2 + 2H2

■HPR

9.3 2.1

OLR (kg COD/L.d)

3 )/d 3 /(L ,

(1) (2)

Fig. 5. Volatile fatty acids concentrations and hydrogen production rate at different OLRs

4. Conclusions

The results obtained indicated that ABR has a great potential in treating paperboard mill wastewater (PMW) with stable operation and removal performance at OLR=18.6 kg COD/L.d. Where, ABR provided a considerable reduction of 86.5±5.11, 81.6±1.7, and 63.5±19% for TSS, VSS and carbohydrates, respectively. Moreover, the HPR achieved the highest value of 4.74±0.9 L/d at OLR=9.3 kg COD/L.d. This discrepancy about the optimum OLR between conversion efficiency (18.6 kg COD/L.d) and HPR and HY (9.3 kg COD/L.d) is mainly due to the significant concentrations of VFAs that was produced within hydrogen production and contribute to the effluent COD.

Acknowledgements

The 1st author is very grateful for Ministry of Higher Education (MOHE) of Egypt, for providing him financial support (PhD scholarship) for this research.

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