Scholarly article on topic 'Anaerobic Co-Digestion Biomethanation of Cannery Seafood Wastewater with Microcystis SP; Blue Green Algae with/without Glycerol Waste'

Anaerobic Co-Digestion Biomethanation of Cannery Seafood Wastewater with Microcystis SP; Blue Green Algae with/without Glycerol Waste Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — Kiattisak Panpong, Kamchai Nuithitikul, Sompong O-thong, Prawit Kongjan

Abstract We investigated the feasibility of using Microcystis sp; blue green algae (MB) as a co-substrate to improve the mesophilic anaerobic digestion of cannery seafood wastewater (CSW) supplemented with 1% (v/v) glycerol waste (GW), to maximize bio-methane production. The MB content was set at 5, 10 and 15% (v/v) to find a near optimal methane yield. The maximum 291mL CH4/g VS-added methane yield, corresponding to 4.4 m3-CH4/m3 - mixed wastewater, was achieved with a CSW: GW: MB mixture at the volumetric 94:1:5 ratio. The methane yield of CSW digested alone was 278mL CH4/g VS-added (2.2 m3 CH4/ m3 of wastewater). The yields from our other experiments ranged within 81– 150 mLCH4/g VS-added. Ratios of MB: CSW exceeding 5% (v/v) gave lower than optimal methane yields. The energy content of methane from 1 m3 of mixed wastewater, with the near optimal mixture ratio 94:1:5, was 157MJ or equivalently 44 kWh.

Academic research paper on topic "Anaerobic Co-Digestion Biomethanation of Cannery Seafood Wastewater with Microcystis SP; Blue Green Algae with/without Glycerol Waste"

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Energy Procedía 79 (2015) 103 - 110

2015 International Conference on Alternative Energy in Developing Countries and Emerging

Economies

Anaerobic Co-Digestion Biomethanation of Cannery Seafood Wastewater with Microcystis SP; Blue Green Algae with/without

Glycerol Waste

Kiattisak Panponga*b, Kamchai Nuithitikulc, Sompong O-thongde,

Prawit Kongjanfg

aSongkhlaRajabhat University (Satun Campus) and bDepartment of Engineering, Faculty of Industrial Technology, SongkhlaRajabhat University,

Songkhla 90000, Thailand cSchool of Engineering and Resources, Walailak University, Nakhonsithammarat 80161, Thailand dDepartment of Biology, Faculty of Science, Thaksin University, Phatthalung 93110, Thailand eMicrobial Resource Management Research Unit, Faculty of Science, Thaksin University, Phatthalung 93110, Thailand fChemistry Division and gBio-Mass Conversion to Energy and Chemicals (Bio-MEC) Research Unit, Department of Science, Faculty of Science and Technology, Prince of Songkhla University (PSU), Muang, Pattani 94000, Thailand

Abstract

We investigated the feasibility of using Microcystis sp; blue green algae (MB) as a co-substrate to improve the mesophilic anaerobic digestion of cannery seafood wastewater (CSW) supplemented with 1% (v/v) glycerol waste (GW), to maximize bio-methane production. The MB content was set at 5, 10 and 15% (v/v) to find a near optimal methane yield. The maximum 291 mL CH4/g VS-added methane yield, corresponding to 4.4 m3-CH4/m3 - mixed wastewater, was achieved with a CSW: GW: MB mixture at the volumetric 94:1:5 ratio. The methane yield of CSW digested alone was 278 mL CH4/g VS-added (2.2 m3 CH4/ m3 of wastewater). The yields from our other experiments ranged within 81- 150 mLCH4/g VS-added. Ratios of MB: CSW exceeding 5 % (v/v) gave lower than optimal methane yields. The energy content of methane from 1 m3 of mixed wastewater, with the near optimal mixture ratio 94:1:5, was 157 MJ or equivalently 44 kWh.

© 2015 The Authors.PublishedbyElsevierLtd. 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 Organizing Committee of 2015 AEDCEE Keywords:Co-digestion; Biogas production; Cannery seafood wastewater; Glycerol waste; Blue green algae

1. Introduction

Seafood cannery processing requires large amounts of water and consequently, factories of tuna and sardine canning discharges about 14 to 22 m3-wastewater/ton -raw fish [1]. This kind of polluting wastewater has high concentration of organic matters in forms of BOD5, COD, and nitrogen content. Anaerobic treatment is suggested for cannery seafood wastewater due to high COD removal, less energy consumption, low sludge production and gaining energy carrier in a form of biogas [2, 3]. However, cannery seafood wastewater contains generally high content of protein and fat, which are the most difficult to be anaerobically degraded [4]. Protein-rich wastewater tends to be biodegraded rapidly to large amount of ammonium that directly inhibits methanogens in the methanogenesis stage of anaerobic digestion process [5]. Ammonia concentrations in the range 1.7 to 14 g-nitrogen/L could potentially inhibit

* Corresponding author. Tel.: +66 743 36392 (362); fax: +66 743 24221. E-mail address: panpong1@hotmail.com.

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 Organizing Committee of 2015 AEDCEE doi:10.1016/j.egypro.2015.11.487

methanogenic activity and may reduce methane production by a half [5, 6]. Additionally, wastewater salinity is one of the major concerns on treating cannery seafood wastewater. Methanogenesis is inhibited by sodium concentrations exceeding 10 g/L [2]. With those mentioned limitations, production yield of biogas produced from CSW cannery thus cannot justify an investment in a biogas system. However, the CH4 production from single anaerobic digestion process could be enhanced by a strategy of simultaneous digestion of two or more organic waste feedstock called co-digestion. Anaerobic co-digestion allows for increasing the external carbon source, COD concentration to feedstock by co-digesting nutrient-rich and improving the yields of methane production due to the positive synergisms in the anaerobic digestion [7, 8]. Thus, we consider the treatment of cannery wastewater as the environmental problem that needs to be mitigated, and the merging of other waste streams of glycerol waste and algal biomass as a means to make that treatment economically feasible.

Glycerol waste is a by-product of biodiesel production and is generated approximately 10% of oil material used [9]. Its global production is currently more than 3,000,000 tons and is expected to be around 4,600,000 tons by 2020 due to increasing in demand of using biodiesel [10]. The supply of glycerol waste already exceeds its demand [11]. Low price glycerol waste having high COD content is easily digested anaerobically and can be stored at room temperature over a long time [12]. Glycerol waste as a co-substrate could potentially improve the biogas production from various substrates such as pig manure, agri-food waste, and sewage sludge [13, 14, 15]. Furthermore, biogas production of pig manure could increase by about 400% due to co-digestion with 4% glycerol under mesophilic conditions [16]. Eutrophication usually promotes excessive cyanobacteria or blue green algae growth (algal bloom) and subsequent decay in natural lakes and reservoirs, which causes serious water toxicity problems, including N, P, and S pollution as well as bad smells. Energy recovery from the algal bloom biomass is potentially possible by anaerobic digestion (AD) that could produce in the form of methane rich biogas [17]. Algal compositions are highly varied for 6-52% proteins, 7-23% lipids, and 5-23% carbohydrates by weight, depending on algal species. These constituents can be converted into methane and carbon dioxide [17, 18]. Markou et al. [19] reported that algae can be used effectively to treat excessive nutrients consisted in agro-industrial and domestic wastewaters. The C/N ratio of the micro-algal biomass is rather low at less than 10, which is a serious problem in anaerobic digestion process [20]. A low C/N ratio feedstock causes high release of total ammonia nitrogen (TAN) and high accumulation of volatile fatty acids (VFAs) in the digester [21]. Adding other carbon rich substrates of waste paper and corn straw to be co-digested with algal biomass could improve significantly methane yield, due to having balanced C/N ratios of 18 and 20, respectively [21, 22]. The advantages of co-digestion include dilution of potentially toxic ammonia, increased loading rate, improved biogas yield, economic advantages derived from the sharing of equipment, easier handling of mixed wastes, and synergistic effects [22].

The aim of this research was to assess the feasibility of meso-philic anaerobic co-digestion of cannery seafood wastewater (CSW) and glycerol waste (GW) and Microcystis sp; blue green algae (MB) at different fraction to produce methane in batch mode operation and to evaluate adding GW and/or MB the effects on methane production and substrate biodegradability.

2. Materials and Methods

2.1 Granule sludge

The granule sludge samples were collected from the wastewater treatment plant of Kiang Huat Sea Gull Trading Frozen Food Public Company Limited (KST), in Hat-Yai district of Songkhla province, Thailand. The granule sizes ranged from 0.8 to 1 mm. The volatile suspended solid (VSS) of the granule sludge was 33.876 g VSS/L, determined for the samples collected by standard methods [23]. The sludge samples were stored at room temperature until use in experiments.

2.2 Cannery seafood wastewater, glycerol waste and microcystissp; blue green algae

Cannery sea food wastewater used in this investigation was collected from Kuang Pei San Food Products Public Co., Ltd. (in Muang, Trang, Thailand), and was stored in a refrigerator at 4 oC until use. The glycerol waste was obtained from a biodiesel plant (Prince of Songkla University, Hat-Yai, Songkhla, Thailand). The microcystis sp, blue green algae (MB) was collected from a microcystis refloating site in the wastewater ponds of Walailak University (Thasala, Nakhon Si Thammarat, Thailand). Prior to use as a co-substrate, the microcystis sp; blue green algae were centrifuged at 12,000 rpm for 15 minutes (Fig. 1A). The Microcystis spp. was the dominant species in these sample mixtures (>99%) as shown in Fig. 1B).

<4 »1

* - 5 "> v -5

Fig. 1. (A) The microcystissp; blue green algae (MB) was used as co-substrate (B) The dominant species of microalgae in the waste mixture was assessed by light microscopy

2.3 Experimental set-up

Batch biomethane production was performed in 1,000 ml serum bottles, with a 900 ml working volume. The volume of active granular sludge was held constant at 125 ml in all serum bottles. Each serum bottle was gassed with N2 for a few minutes, then immediately sealed with a rubber septum and an aluminum crimp cap. All filled bottles were incubated in the incubator controlled at 35 +1°C. The experimental tests were designed to assess the influence of the mixture ratio of CSW and 1%GW, and to select an MB concentration from 5, 10 and 15% (v/v), in order to maximize the methane production. The collected biogas quantities were determined daily by water displacement. The biogas composition was analyzed periodically by GC-TCD. The methane yield was defined as the total volume (STP reference conditions) of methane produced during the digestion period per amount of substrate initially added (mLCH4/g VS added). Thus as yield we use the observed conversion relative to what idealized reactions could possible produce from the feedstock.

2.4 Analytical methods

Total solids (VS), volatile solid (VS), volatile suspended solid (VSS), Total organic carbon (TOC), Total Kjeldahl Nitrogen (TKN), total phosphorus (TP), volatile fatty acid (VFA), alkalinity, proteins, carbohydrates and fats were measured by APHA standard methods [23]. The pH was measured with Sartorius Docu - pH meter. The methane content was analyzed by a gas chromatograph (GC) equipped with a thermal conductivity detector [24]. The synergistic effect was calculated using maximum methane production yield obtained from the batch co-digestion of CSW, GW and MB combined by linear weighing according to their fractions in co-digestion, compared with the methane productions of single digestion of CSW, GW and MB [25]. Theoretical methane yield was calculated according to Bushwell's formula which is derived by the stoichiometric conversion of compounds to CH4, CO2 and NH3 [26], and represent an idealized maximum yield from given feedstock.

The kinetics of methane formation under the mesophilic anaerobic process were parametrized by fitting with a modified Gompertz model shown as equation (1), where G(t) is the cumulative methane production (mLCH4/g VS-added); G0 is the maximum methane yield (mLCH4/g VS-added); Rmax is the maximum methane production rate (mLCH4/g VS-day); e = exp (1) = 2.7183; and 2 is the lag phase period (in days) (Kafle et al.,2013) [27].

3. Results and Discussion

3.1 Substrate characterization

The key characteristics of CSW, GW and MB, which were used at different volumetric mixing ratios for batch anaerobic co-digestion to determine biogas production and substrate biodegradability, are demonstrated in Table1. Both MB and CSW had quite low C/N ratios (7 and 11), while GW had rather high C/N ratio of 949. For anaerobic digestion a suitable C/N ratio is in the range 20 - 30 [28], which can only be reached by suitably mixing these feedstock components. As discussed earlier, the balancing of the C/N ratio helps avoid the formation of inhibitory

ammonium that happens at a low C/N, while the microorganisms require access to nitrogen and also too high C/N is expected to reduce the yield [29]. As very high buffering capacity GW had could help to protect the co-digestion process against failure due to pH drop caused by temporary VFA accumulation [30]. Furthermore, CSW has a comparatively low pH, while an optimum pH for mixed culture anaerobic digestion is in a range of 6.6-7.4 [31], so addition of GW and/or MB also can contribute by neutralizing the acidity of CSW.

Table 1. Physical-chemical characteristics of CSW, GW and MB

Parameter CSW GW MB

pH 6.3 8.8 7.8

Chemical Oxygen Demand: COD (g/L) 10.4 1,760 85.28

Volatile fatty acid: VFA (mg-acetate/L) 2,230 6,650 aND

Total alkalinity (mg-CaCO3/L) 2,560 35,050 aND

Total Kjeldahl Nitrogen: TKN (mg/L) 870 1,670 10,938

Total phosphorus: TP (mg/L) 53.6 71,500 aND

Total Solid: TS (g/L) 9.37 969 84.85

Volatile solid (VS: g/L) 7.76 910 69.55

Sulfate (g/L) aND. 15.58 aND

bProtein (g/L) 3.9 1.28 35.60

Carbohydrate (g/L) 1.91 845 21.20

Fat (g/L) 0.13 63.76 4.73

C/N ratio 11 949 7

a ND. = Not determined, bMultiplyingthe organic nitrogen (TKN minus TAN) by 6.25

3.2 Methane performance from co-digestion process

The BMP tests were run as 64-day batches. The results of cumulative methane production from various fractions of mixed substrate are shown in Fig 3. Table 2 summarizes the results of methane production achieved from batch experimental assay of different mixing ratios of individual substrate, including theoretical yield, experimental yield, methane content in biogas, and anaerobic biodegradability. The methane yield of CSW alone was 278 mL CH4/g VS-added, corresponding to 2.2 m3 CH4/ m3-wastewater with 95% biodegradability. Meanwhile, the maximum methane yield of CSW (99%) + GW (1%) was 577 mL CH4/g VS-added corresponding to 5.8 m3 CH4/ m3 of wastewater with 97% biodegradability. The yields of CSW (94%) + GW (1%) + MB (5%), CSW (89%) + GW (1%) + MB (10%), CSW (84%) + GW (1%) + MB (15%), CSW (95%) + MB (5%), CSW (90%) + MB (10%) and CSW (85%) + MB (15%) were 255, 190, 91, 192, 111 and 81 mL CH4/g VS-added, respectively (Table 2). The cumulative methane productions ranged from 1,655 to 3,431 mL CH4 at 64 days of co-digestion batches. CSW GW and MB co-digestion (94:1:5, V/V ) generated maximum methane yield of 291 mL CH4/g VS-added, corresponding to 4.4 m3 CH4/m3-mixed wastewater along with 88% biodegradability and an average methane content of 60.12%. For this near optimal mixture the theoretical methane yield was 690 mL CH4/g VS-added. Increasing the concentration of MB: CSW to more than 5 % (v/v) was decreased the yield. The high 10,938 mg/L nitrogen content of MB decreased the C/N ratio when it was used as a co-substrate. The C/N ratio of CSW (94%) + GW (1%) + MB (5%) at 18 was higher than that of CSW alone, which had C/N=11. As a result, the total ammonia nitrogen (TAN) decreased from 1,036 to 809 mg/L when C/N ratio increased from 11 to 18, while without the 1% GW the mixture of 94%CSW and 5%MB the concentration of TAN was higher at 1,434 mg/L (C/N ratio as 9) as seen in Table 2. Low C/N ratio feedstock could result in high TAN accumulated in the system and a decreased yield [21]. Zhong et al. [22] reported that the co-digestion of blue algae with corn straw at a C/N ratio of 20 increased methane yield by 61.69% to 325 mL CH4/g VS-added, which is similar to our co-digestion of 94% CSW, 1% GW and 5% MB with a methane yield of 291 mL CH4/g VS-added and a C/N ratio of 18. The appropriate C/N ratio for anaerobic digestion ranges from 20 to 30 [26]. Additionally, the methane content (%) increased with the C/N ratio. The initial pH was close to neutral with GW and MB added to CSW, which was more suitable for methanogenic digestions than the pH 6.3 of CSW alone. The final volatile fatty acids and alkalinity were in the ranges 700 - 4,200 mg/L and 2,650 - 4,650 mg/L, respectively. As a result, the VFA/Alk ratio was in the range 0.20 - 1.58, which relates to the efficiency of anaerobic digestion (Fig. 4). The VFA/Alk ratio should be less than 0.4 for effective anaerobic digestion [32].

A comparison of the experimental cumulative methane yields and the modified Gompertz models fitted to the 64 day batch runs is shown in Figure 5. Table 3 shows the identified parameters used in these models. The Gompertz model fit the experimental data well for the various co-substrate mixtures used. The Rmax values are in the range 3.24 -11.62 mL-CH4/g VS-day, and the highest value at 11.62 is for the co-digestion of 94%CSW, 1%GW and 5%MB. This is in agreement with Table 3 in Miao et al. [33]. The lag phase time (X) was in the range from 0.25 to 1.11, and the concentration of GW% (v/v) had a negligible effect on the lag phase. In summary, the experimental methane production from our co-digestion batches was well fit by the modified Gompertz model, as evidenced by Fig 5.

Table 2. Summary of BMP performance of co-digestion of CSW with GW and MB

Mixing ratio C/N ratio VS (g/L) CH4 Yield (mL CH4/g-VS added) Biodegradable (%) TAN (mg/L) CH4 content (%)

CSW (100%) 11 7.76 278 95 1,660 59.02

GW (1%) 576 4.50 211 70 ND. 59.38

MB (5%) 7 4.48 292 89 ND. 53.50

CSW (94%) + GW (1%) + MB (5%) 18 13.50 291 88 809 60.12

CSW (89%) + GW (1%) + MB (10%) ND. 19.94 150 56 ND. 46.03

CSW (84%) + GW (1%) + MB (15%) ND. 24.91 91 52 ND. 37.53

CSW (95%) + MB (5%) 9 12.74 192 56 1434 46.77

CSW (90%) + MB (10%) ND. 17.72 111 40 ND. 41.70

CSW (85%) + MB (15%) ND. 22.69 81 38 ND. 34.61

ND. = Not determined

Fig. 2. Cumulative methane production for each co-digested mixture of CSW, GW and MB

Fig. 3. Initial pH, final pH and VFA/Alkalinity ratios of the co-digested mixtures identified in the labels along the x-axis

Table 3. Summary of estimated parameters from Gompertz equation and experimental methane yields for co-digestion between CSW, GW and MB

Mixture ratio Go Rmax X Reference

(mL CH4/g VS-added) (mLCHj/g VS-day) (day)

CSW(100%) 278 18.56 0.25 In this study

GW(1%) 211 17.62 2.00 In this study

MS(5%) 292 19.46 2.00 In this study

CSW(94%) + GW(1%) + MB(5%) 291 11.62 0.65 In this study

CSW(89%) + GW(10%) + MB(10%) 150 6.01 0.75 In this study

CSW (84%) + GW(1%) + MB(15%) 91 3.65 0.93 In this study

CSW(95%) + MB(5%) 192 7.69 1.03 In this study

CSW(90%) + MB(10%) 111 4.43 1.24 In this study

CSW(85%) + MB(15%) 81 3.24 1.32 In this study

Blue algae (fresh algae) (100%) 209 19.22 3.40 [33]

Fig. 4. Comparison of experiments with fitted modified Gompertz models for 64-day cumulative methane yields

Fig. 5. The methane production potential of co-digesting CSW:MB:GW mixed in 94: 1: 5 ratio by volume; (A) cumulative methane production and (B) synergistic effect: T-MP(Total methane production), CSW-MP(Cannery seafood wastewater methane production), GW(1%) - MP (Glycerol waste (1%) methane production, MB(5%) - MP (Microcystissp; blue green algae (5%) methane production and Syn-MP (Synergistic methane production)

3.3 Synergistic effects

While the co-digestion of CSW (94%) + GW (1%) + MB (5%) increased the total methane production and methane yield, there was negative synergism. The total methane production was 3,431 mL CH4 while the mixture components (in the same order as above) produced 1,945, 951 and 1,307 mL CH4. The synergistic effect of MB addition was -772 mL CH4 (Fig. 6A). Total methane yield of co-digestion was 291 mLCH4/g VS-added when compared with the methane yield of single CSW, 1% GW and 5% MB were 278, 211 and 292 mL CH4/g VS-added. The synergistic effect on methane yield was - 490 mL CH4/g VS-added (Fig. 6B). Degradation efficiency decreased from 95% to 88% on adding 5% MB. The maximum methane production of co-digestion of CSW (94%) + GW (1%) + MB (5%) was 4.4 m3 CH4/m3 of mixed wastewater, while the components in the same order would give 2.2, 0.3 and 1.3 m3 CH4/m3 of wastewater. The approximate energy content 36 MJ/m3CH4 (about 10 kWh/m3 CH4) with a conversion efficiency of 40% in a gas motor [25] would correspond to 157 MJ or 44 kWh of electricity from 1 m3 of mixed wastewater.

4. Conclusions

The main conclusions from this experimental study of anaerobic batch digestion, to produce methane, are summarized as follows.

4.1 The anaerobic co-digestion of CSW, GW and MB improved both quality and quantity of biogas. A near optimal mixture of CSW (94%)+GW(1%)+ MB(5%) (v/v) gave a total 3,431 mLCH4 in methane production, and a 291 mL CH4 /g VS-added yield. Increasing the MB concentration past 5 % CSW (v/v) reduced the methane yield.

4.2 The co-digestion of the near optimal mixture increased the total methane production and methane yield relative to the CSW component, but relative to the totality of components there was negative synergism.

4.3 The near optimal mixture gave 4.4 m3 CH4/m3 of mixed wastewater, while the components had values about half of this or lower.

4.4 The experimental total methane production during a batch run was well fit by a modified Gompertz model, separately for each individual co-digestion experiment.

Acknowledgments

The authors would like to thank the Office of Higher Education Commission (OHEC) for funding this research. This research project would not have been possible without extensive assistance of the staff from the Microbial Management Research Unit (MRM-TSU), Faculty of Science, Thaksin University, Thailand.

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