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The preliminary anaerobic fermentation of food wastes using anaerobic sludge.


Anaerobic Digestion (AD) is a biological process that takes place naturally when bacteria break down organic matter in the environment with or without oxygen [1]. Traditionally, AD processes were applied to wastewater and sewage sludge treatments. However, recently the focus of AD has switched relatively, from treatment of wastes such as BOD removal to energy production. A controlled anaerobic digestion of organic waste in an enclosed landfill will generate a bio-energy in the form of methane. Bio-energy production using AD technique comprised of around 60% of methane (C[H.sub.4]) and 40% of carbon dioxide (CO2) [2]. Therefore, AD has great potential for recovering bio-energy from organic waste such as food wastes.

Fodor and Klemes (in press) [3] described that anaerobic digestion offers the possibility of waste-to-energy by reducing the organic matter which would otherwise be land filled, burnt or treated other ways. In addition, AD will also produce a gaseous energy carrier with an additional end-product which can be used as biofertilizer. Several researchers also documented a bio-energy production from organic waste. Zhang [1] has reported that higher yields of up to 440 L CH4/kg volatile solid (VS). Research by Roati [4] showed that almost all of some food wastes exhibited bio-energy in term of biogas production that theoretically yield equal to about 0.7 to 1.6 [m.sup.3]/kg volatile solid and methane contents equal to about 40 to 60% v/v.

Besides that, anaerobic fermentation can reduce the total mass of waste, generates solid or liquid fertilizer and yields energy. Based on finding by Molino [2], anaerobic fermentation can be maintained at psychrophilic conditions (12 to 16[degrees]C, e.g. in the rumen and in anaerobic digester) or thermophilic conditions (55 to 60oC; e.g. in anaerobic digester or geothermally heated ecosystem) but the thermophilic anaerobic fermentation reduced digestion stability and dewatering properties of the fermented sludge and the thermal destruction of pathogenic bacteria at elevated temperatures. Slightly higher rates of hydrolysis and fermentation under thermophilic conditions have not led to a higher methane yield [2]. The mesophilic anaerobic fermentation is conventionally anaerobic fermentation that is carried out in temperatirres approximately 35 to 37[degrees] C [5].

The ability of microorganisms in producing bio-energy is one of the interests not as metabolic phenomenon, but also because bio-energy is a promising energy source. Consequently, elaboration of methods for ecologically sound in bio-energy synthesis can provide mankind with a cheap raw material or substrate and environmentally friendly source of energy. It is estimated that approximately 50% of all food produced is lost, converted or wasted [6]. According to the report by Joint Declaration Against Food Waste [6], 18 million tons of edible food is thrown away each year by households in Britain, resulting in an annual cost of 14 billion pounds. In Sweden, the average household is estimated to throw away 25% of all purchased food [6]. Approximately 20 million tons of food waste is generated eveiy year along the whole supply chain [6]. Gustavsson [7] reported that approximately one-third of the food produced for human consumption, which is approximately 1.3 billion tons total per year is lost or wasted globally. Thus, food waste is considered as raw material in producing bio-energy by using the AD technique.

A stable anaerobic digestion of food waste at high organic loading rates and with high throughput can be realized based on certain factors [8]. The factors include utilization of bioreactor systems with biomass retention, appropriate control processes as well as start-up procedures and adequate time for bio-film formation [8]. They also successfully demonstrated the efficient production of bio-energy from food waste using other different bioreactor system [8].


The aim of the paper was to study the anaerobic digestion at mesophilic temperatures (approximately 35[degrees]C) at three different parameters: temperature, pH, concentration of inoculums and concentration of substrate. The emphasis was to evaluate the biodegradation process and to evaluate the effects of pH, temperature, concentration of inocula and substrate in a anaerobic digestion process.


3.1 Inocula:

The anaerobic sludge used as inocula in this study was taken from a clarifier tank located in the Universiti Teknologi Mara (UiTM), Shah Alam, Selangor, Malaysia. The anaerobic sludge was used within a week and fresh inocula were collected again from the same location to ensure that their characteristics were consistent.

3.2 Substrate:

The food wastes were obtained from the University's Teknologi cafeteria. They consisted of equal parts by mass of post-consumer wastes from the kitchen, which consisted of unused food and food preparation wastes. These wastes included fruit peel and vegetable parts. Since the waste collected contained impurities such as plastic. These wastes were screened to remove the coarse contaminants before grinding process. A weekly sampling was done.

3.3 Analytical methods:

The parameters analyzed for the characterization were: Total Solids (TS), Volatile Solid (VS), Total Suspended Solid (TSS), Volatile Suspended Solid (TSS) and Chemical Oxygen Demand (COD) contents according to the standard methods of American Public Health Association [9]. Composition of carbon (C), Hydrogen (H), Nitrogen (N), Sulphur (S) and C/N ratio were analyzed using the Thermo Scientific Flash 2000 CHNS-O analyzer. Protein and carbohydrate contents were also analyzed by using Bradford Assay Method and High Performance Liquid Chromatography (HPLC) at mobile phase of 100% distilled water, temperature 85[degrees]C, the flow rate of 0.6 mL/min and glucose is use as standard.

3.4 Biomethane fermentation:

The study is programmed to evaluate the mesophilic anaerobic digestion (35[degrees]C) of three different parameters which are pH (8.2), substrate concentration (80% or 40% in volume of 5.3g VS/L) and inocula concentration (10% or 20% in volume of COD ranging 75-99 mg/l). The experiments were carried out in a 160 mL serum bottles containing 100 mL media. All serum bottles were loaded with a specific volume of substrate and inoculated with a specific volume of inocula and then adjusted to pH 8.2 before incubation for 24 hours in serum bottles to produce methane gas for 15 days of HRT. All bottles were flushed with nitrogen gas to ensure anaerobic conditions throughout the experiments and tightly capped with rubber septium (butyl rubber) before incubation at 35[degrees]C. The total gas volume is measured at 3 hours interval by releasing the pressure in the bottles using 10 mL syringes. The experiments are carried out in triplicates. Two blank digesters that contained 100% of inoculums and substrate were also incubated at the same temperature. Each blank digester contained 50 mL and was filled up to 100 mL with tap water. All digesters were mixed once a day for 15 minutes.

The biomethane yield production and methane production rate were analyzed using a gas chromatography equipped with a thermal conductivity detector and the column was packed with Porapack Q (80/100 mesh). The temperatures of injector and column were kept at 0[degrees]C and 50[degrees]C. Nitrogen was used as the carrier gas with a flow rate of 30 mL/min and 8% methane gas was used as standard.


Six lab-batch reactors were tested during a period of 15 days to evaluate the mesophilic anaerobic digestion of food waste. Each batch reactors were tested at mesophilic temperature (35[degrees]C and pH 8.2). All parameters tested in each batch are presented in table 1.

4.1 Substrate Characterization:

The substrate characterizations are presented in table 2. The food wastes contained a large amount of total solids (2.9 g/L) and volatile solids (5.3 g/L). The total suspended solid was 10,566.7 x [10.sup.6] g/L and volatile suspended solid was 9,610 x [10.sup.6] g/L. Food waste contained High range of Chemical Oxygen Demand which was between 43 to 105 Mg/L. The element in food wastes were 21.9% of carbon (C), 1.0% of Nitrogen (N), 4.2% of Hydrogen (H) and 22.2% of C/N ratio. It also contents contained various protein (4.8 g/L) and glucose (5.9 g/L).

4.2 Inocula characterization:

The inocula characterizations are presented in table 3. The anaerobic sludge contained a large amount of total solids (2.9 g/L) and volatile solids (5.4 g/L). The total suspended solid was 0.5 g/L and volatile suspended solid was 0.1 g/L. Inoculums contained High range of Chemical Oxygen Demand which is between 75 to 99 Mg/L. The inoculums also contents 29.1% of carbon (C), 3.5% of Nitrogen (N), 4.2% of Hydrogen (H), 0.9% of Sulfur (S) and 22.2% of C/N ratio.

4.3 Bioiethane production:

The methane production rate and biomethane yield production during digestion of food waste are shown in figures 1 and 2, respectively. Hydraulic Retention Time (HRT) also affected the biomethane production. The digestion processes were tested in a period of 15 days of HRT. Methane production increased at day 2 until day 5 and then remained constant at a low level until the end of the experiments. The experimental results showed that, the Batch 1 digester produced high methane production (1.9366 [m.sup.3]/kg VS and 4.3385 mL/hr) followed by 1.3573 [m.sup.3]/kg VS and 1.9710 mL/hr (Batch 2), 0.9916 [m.sup.3]/kg VS and 1.9123 mL/hr (Batch 4) and 0.9787 [m.sup.3]/kg VS and 1.1723 mL/hr (Batch 3).Whereas, methane production in blank digester increased at day 2 and later decreased until the end of experiments.


Experimental results showed important suitable parameters to produce biomethane. The final results suggest different patterns in these parameters. The experimental results showed that, the Batch 1 digester produce high methane production (1.9366 [m.sup.3]/kg VS and 4.3385 mL/hr) and batch 3 digester produce low methane production (0.9787 [m.sup.3]/kg VS and 1.1723 mL/hr).Whereas, methane production in blank digester increased at day 2 and later decreased until the end of experiments. Besides that, the digestion time also affected digestion process.


Article history:

Received 25 July 2015

Accepted 1 September 2015

Available online 19 September 2015


The authors like to acknowledge consistent help from main supervisor Assoc. Prof Dr Zainon Mohd Noor and co-supervisor Ms Zatilfarihiah Binti Rasdi. This research also has been received the financial support from Exploratoiy Research Grant Scheme (ERGS) Fund 600-RMI/ERGS 5/3 (11/2013).


[1] Zhang, R., H.M. El-Mashad, K. Hartman, F. Wang, G. Liu, C. Choate and P. Gamble, Characterization of Food Waste as Feedstock for Anaerobic Digestion (2007). Bioresource Technology, 98: 929-935.

[2] Molino, A., F. Nanna, Y. Ding, B. Bikson and G. Braccio, 2012. Biomethane Production by Anaerobic Digestion of Organic Waste. Fuel, Article in Press.

[3] Fodor, Z. and J.J. Klemes, "Waste as Alternative Fuel-Minimising Emisions and Effluents by Advanced Design", Process Safety and Environmental Protection, Article n Press.

[4] Roati, C., S. Ruffino, B. Marchese, F. Novarino and M.C. Zanetti, 2012. Preliminary Evaluation of the Potential Biogas Production of Food-Processing Industrial Wastes. American Journal of Environmental Sciences, 8(3): 291-296.

[5] Foster, T., M. Perez and L.I. Romero, 2008. Thermophilic Anaerobic Digestion of Source-Sorted Organic. Fraction of Municipal Solid Waste. Journal of Bioresource Technology, 99: 6763-6770.

[6] Joint Declaration Against Food Waste, 2010. EU- and UN- Declaration. (www.greencook.n/images/stories/joint_declaration_against_food_waste.pdf).

[7] Gustavsson, J., C. Cederberg, U. Sonessen, R. Otterdijk and A. Meybeck, 2011. Global Food Losses and Food Waste. Food and Agriculture Organization of the Untited Nation (FAO), Rome.

[8] Kastner, V., W. Somitsch and W. Schnitzhofer, 2012. The anaerobic Fermentation of Food Wast: A Comparison of Two Bioreactor Systems. Journal of Cleaner Production, 34: 82-90.

[9] AAHPA, 1998. Standard Methods for the Examination of Water and Wastewater, 18? ed. American Public Health Association, Washington, DC, USA.

(1) Nurul Shahida, O., (2) Zainon, M.N., (3) Zatilfarihiah, R.

(1,2) School of Biology, Faculty of Applied Sciences, Universiti Teknologi MARA Malaysia, 40450 Shah Alam, Selangor Darul Ehsan, Malaysia

(3) Health Sciences, Faculty of Dentistry Universiti Teknologi MARA Malaysia, 40450 Shah Alam, Selangor Darul Ehsan, Malaysia

Corresponding Author: Nurul Shahida, School of Biology, Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor Darul Ehsan, Malaysia.


Table 1: Parameters of lab-batch reactors.

Batch     Substrate Volume (Vo)   Inoculum Volume (Vo)

Batch 1            80                      10
Batch 2            80                      20
Batch 3            40                      10
Batch 4            40                      20
Batch 5            100                     0
Batch 6             0                     100

Table 2: Characteristics of food waste raw feed.

Parameter                        Unit    Food Waste Raw Feed

Total Solid (TS)                 g/L             2.9
Volatile Solid (VS)              g/L             5.3
Total Suspended Solid (TSS)      g/L    10,566.7 x [10.sup.6]
Volatile Suspended Solid (VSS)   g/L         9,610 x 106
Chemical Oxygen Demand (COD)     Mg/L          43-105
Glucose Content                  g/L             5.9
Protein Content                  g/L             4.8
Element Composition               %             21.9
Carbon (C)                        %               1
Nitrogen (N)                      %              4.2
Hydrogen (H)                      %               0
Sulfur (S)                        %             22.2
C/N ratio

Table 3: Characteristics of anaerobic sludge raw feed.

Parameter                        Unit         Sludge Feed

Total Solid (TS)                 g/L              1.9
Volatile Solid (VS)              g/L              5.4
Total Suspended Solid (TSS)      g/L              0.5
Volatile Suspended Solid (VSS)   g/L              0.1
Chemical Oxygen Demand (COD)     Mg/L   High range ranging 75-99

Element Composition
Carbon (C)                        %               29.1
Nitrogen (N)                      %               3.5
Hydrogen (H)                      %               4.2
Sulphur (S)                       %               0.9
C/N ratio                         %               8.4
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Article Details
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Author:Nurul Shahida, O.; Zainon, M.N.; Zatilfarihiah, R.
Publication:Advances in Environmental Biology
Article Type:Report
Date:Sep 1, 2015
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