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Leachate production and disposal of kitchen food solid waste by dry fermentation for biogas generation
Renewable Energy 23 (2001) 673–684 www.elsevier.nl/locate/renene
Leachate production and disposal of kitchen food solid waste by dry fermentation for biogas generation I.I.I. Ghanem a
a,*
, Gu Guowei b, Zhu Jinfu
b
Agricultural and Engineering Research Institute (AEnRI), Agricultural Research Center (ARC), Nadi El Said St., P.O. Box 256, Dokki, Giza, Egypt b School of Environmental Engineering, Tongji University, Shanghai 200092, China
Abstract This laboratory research, which applies anaerobic digestion for a solid phase batch system using kitchen food solid waste (KFSW), is concerned with optimizing leachate production under different conditions. The solid-phase digestion process is expected to be superior to slurry-phase digestion and the so-called “dry fermentation” process. A batch system solid waste reactor was used in the present study. The performance of the reactor was tested under the conditions of constant temperature of 35°C and the reactor active volume was 12 l. On operation day 10, chemical oxygen demand (COD) for leachate extraction parameters such as COD rate, COD loading rate (LR) and COD concentration reached maximum values, and were 135 g COD/d, 11 g COD/1.d, and 214 g/l of COD, respectively. On day 25, accumulative leachate COD reached the top value of 1509.4 g. The pH value of leachate was kept around 4. However, volatile fatty acid (VFA) concentration of leachate fluctuated, especially in the initial period. A high concentration of VFA on day 5 inhibited gas production, but with the decrease of VFA concentration the gas production rate was increased gradually and the sludge acclimated to VFA gradually. The process can be operated at a profit and no unfavorable environmental impact is expected for this type of plant production of biogas using the leachate from dry fermentation. These considerations make it a viable alternative in most countries as a source of energy. 2001 Published by Elsevier Science Ltd. Keywords: KFSW; Dry fermentation; Solid phase; Anaerobic sludge; Wastewater; Leachate
* Corresponding author. 0960-1481/01/$ - see front matter 2001 Published by Elsevier Science Ltd. PII: S 0 9 6 0 - 1 4 8 1 ( 0 0 ) 0 0 1 5 2 - X
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1. Introduction The enormous production of municipal solid waste, especially in big cities, has concerned both authorities and researchers for many years. Within this situation, several ideas and processes that might be applied under different circumstances have arisen. However, an important fraction of the municipal solid waste stream can be defined as municipal solid biowaste (MSBW). This is food waste from the kitchen; animal, fruit and vegetable residues resulting from the handling, preparation, cooking and eating of food. It appears that not one of the processes considered up to now is ideal, or in other words, none can be considered an absolute solution for the KFSW problem. One of these possible solutions is anaerobic digestion of the organic fraction of the MSW. Anaerobic fermentation has been thought to be limited to wet organic waste, such as sewage sludge that contains greater than 90% water. The processing of drier biomass at these high water contents requires the addition of many tons of water for every dry ton of biomass. Solid biowaste is particularly troublesome since it not only requires large amounts of water, but is also extremely difficult to handle. One approach to fermentation of solid biowaste is to develop a method that could ferment the material without the addition of large quantities of water. “Dry fermentation” is the focus of this study [4].
2. Materials and methods 2.1. Kitchen food solid waste (KFSW) The cooking food solid waste used in this study was collected from the foreign student restaurant at Tongji University and separated from paper, bones and another material, then mixed and shredded to a diameter of 5 mm using a meat mincer. The cooking food solid waste was subjected to a centrifugal force to separate into: 1. a solid phase (semi-solid material) feed source for a Leachate-Bed, Solid Phase Anaerobic Reactor. This was used to produce a leachate feed solution source for the UBF Reactor to produce methane gas [3,4] and the residue can be used for animal nitration or agricultural fertilizer as a compost; 2. a liquid phase (kitchen food wastewater) was extracted from KFWS and also used as a feed solution source for a Biogas Reactor, treated by an anaerobic digestion process to produce methane gas as a source of energy.
2.2. Anaerobic sludge In this study, sludge was used for disposal by anaerobic digestion at the same time as an inoculum. The weight ratio of sludge to KFSW was 1:4 in this experiment.
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For the leach-bed anaerobic reactor the sludge was collected from a municipal wastewater treatment company in Shanghai (storage basin). 2.3. Leach-bed anaerobic reactor Bench-scale models of the leach-bed anaerobic reactor used in this study had the configuration shown in the sketch of the reactor given in Fig. 1. The reactor was constructed from cylindrical plexiglas columns with a diameter of 24 cm, a reactor height of 64.5 cm and a bed height of 44.5 cm corresponding to an active volume of 12 l. Three ports along the height of the fermentor allowed three thermometers to measure the temperature inside the reactor. The bed leachate flowed down through the bed and out of the system from the bottom port. The fermentation gas flowed up through the bed and out of the reactor from the upper port and the system was
Fig. 1. Sketch of leach-bed anaerobic reactor.
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placed in an incubator-like control chamber with a temperature of 35±1°C. The cooking food solid waste, seed sludge and support material (wood powder) were mixed together in proportion to meet the following criteria: 1. the weight of the kitchen food solid waste (KFSW) was 8.8 kg; 2. the weight of the seed sludge was 2.2 kg (20% of the weight of KFSW); 1 l of wood powder, used as support material, was 10% of the volume of the KFSW. 2.4. Shredding machine (meat mincer) Various types of shredders such as the hammer-mill drum pulverizer rasp mill, disk mill, and others are available. In this study we used a meat mincer [4]. 2.5. Centrifugation Dewatering of sludge and KFSW by centrifugation has been applied with increasing frequency in experiments on biowaste [4]. 2.6. Control chamber A wooden control chamber, with a polyurethane foam insulation layer to reduce the heat losses to the outside environment, was used in this study. The control room contained the following equipment: (1) a gas flow meter; (2) a feeding pump (peristaltic pump); (3) a heating source; (4) a thermostat: the temperature was held constant at 35°C [2]. 2.7. Chemical analysis Total suspended solids (TSS), VSS, chemical oxygen demand (COD) and volatile fatty acids (VFA) were determined according to the methods recommended by the American Public Health Association [1]. 2.8. Experimental procedure and operation conditions 앫 Cooking food solid waste (KFSW) was collected, recycled and sampled. 앫 The KFSW was shredded with the meat mincer and mixed directly, equal to 8.8 l⬇9 kg. 앫 Then 20% sludge by weight ratio was added to the KFSW. 앫 Centrifugation with 2750 rpm for 20 min with KFSW and sludge, equal to 2.2 kg. 앫 Add 10% support materials (wood powder) by the ratio of the total volume of biowaste (KFSW+Sludge), now equal to 11 l. 앫 The volume of KFSW+Sludge+support material is now 11+1=12 l. 앫 The weight of KFSW+Sludge is 11 kg.
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After obtaining KFSW, the support material and the sludge are mixed completely and put in the bed anaerobic reactor. 2.8.1. System operation and performance 앫 Analysis of the influents and effluents for volatile acids, pH, and chemical oxygen demand (COD) monitored system operation and performance. 앫 Gas production from the MSBW bed was measured daily. The temperature was kept constant at about 35±1°C. 2.8.2. Operation parameters The biogas operation parameters for KFSW by batch test anaerobic digestion reactor, with a temperature of 35±1°C [4], were as follows (these values are guidelines): 1. 2. 3. 4. 5. 6. 7. 8. 9.
use centrifugation with 2750/20 rpm/min; the moisture content was 26.61%; the support material used was wood powder; the quantity of support material in feed=10% by volume; the sludge added was from a municipal wastewater treatment company in Shanghai, storage basin; the sludge solid in feed=20% by weight; there was no shaking time or agitation; influent pH=8–8.3; median KFSW particle diameter=5 mm.
2.8.3. Operation conditions and performance of solid phase reactor The operation of the leach-bed, dry fermentation as detailed in Table 1, was divided into four stages. Tap water was added every day at each stage in the amounts shown below: 앫 앫 앫 앫
the the the the
first stage (5 days): 25 ml; second stage (6 days): 500 ml; third stage (6 days): 750 ml; and fourth stage (8 days): 1000 ml.
The aim of this function was to adapt the porosity at steady state by using different volume additions of UBF effluent of 25, 500, 750 and 1000 ml. As influent for solid phase reactor we chose the volume of influent that could allow the porosity to reach a steady state condition in the shortest operation period.
3. Results and discussion The significant liquefaction of biowaste (leachate) function is shown below.
COD COD rate of concentration of leachate leachate extraction (g/d) extraction (g/l)
First stage: addition of 25 ml UBF effluent every day 1 15 45.27 0.68 2 35 127.96 4.48 3 20 111.29 2.23 4 30 127.63 3.83 5 25 124.61 3.12 Second stage: addition of 500 ml UBF effluent every day 6 40 128.46 5.14 7 50 141.53 7.08 8 320 134.99 43.20 9 475 132.11 62.72 10 635 214.02 135.9 11 610 214.02 130.55 Third stage: addition of 750 ml UBF effluent every day 12 550 208.34 114.59 13 650 148.82 96.73 14 620 142.86 88.57 15 900 118.12 106.31 16 550 110.24 60.63 17 880 99.63 87.67 Fourth stage: addition of 1000 ml UBF effluent every day 18 800 93.02 74.42 19 950 83.07 78.92 20 970 76.92 74.61 21 1080 88.59 95.68 22 860 75.40 64.84 23 1100 63.49 69.84 24 860 57.54 49.48 25 900 53.57 48.21
Period (day) Leachate rate (ml/d)
2.71 3.50 4.76 6.76 15.61 10.81 9.39 10.41 11.58 8.36 8.51 7.93 9.34 9.32 7.60 7.89 6.56 7.33 8.56 9.71 10.37 11.11 12.01 12.68 11.47
0.68 5.16 7.39 11.22 14.34 19.48 26.56 69.76 132.51 268.41 398.96 513.55 610.28 698.85 805.16 865.79 953.46 1027.88 1106.0 1181.41 1277.09 1341.93 1411.77 1461.25 1509.46
7.8 8.0 5.9 6.0 5.6 8.1 6.5 6.4
1.6 12.1 8.0 14.8 11.4 8.9
0.5 0.2 0.3 0 0.6 4.2
0.1 13.8 11.5 4.1 0
COD cumulation VFA concentration Gas rate (l/d) of leachate of leachate extraction (g) extraction (g/l)
Table 1 Effect of addition of effluent of UBF or tap water reactor to the solid phase anaerobic reactor during the operation period
3.81 3.85 3.91 3.94 4.12 4.36 4.55 4.79
3.70 3.72 3.68 3.75 3.78 3.80
3.75 3.73 3.74 3.65 3.65 3.70
4.2 3.99 3.72 3.62 3.75
pH of leachate extraction
285.34
313.6
364
NH3–N concentration of leachate extraction (g/l)
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3.1. Effect of the different volume addition of tap water on the porosity of the biowaste during the operation period The solid phase anaerobic digester was a liquefaction reactor and in principle is an extracting apparatus. Increasing the porosity of the biowaste will increase the rate of extraction from the solids, carried away as a dilute solution, and will accelerate the extraction process and also solid waste treatment. Table 1 and Fig. 2 illustrate the effect that adding different volumes of UBF effluent or tap water will have on the porosity of the biowaste during the operation period using a solid anaerobic reactor. The results are as follows. 앫 In the first stage, 25 ml of influent was used and the increase in porosity ranged between 0.6 and 1. This was so because the biowaste contained free water and less influent was added. 앫 At the second stage, the porosity was 0.26 on the first day because there was no more free water and influent water was more than during the first stage. At the end of this stage the porosity had risen to 0.72. 앫 During the third stage, the porosity ranged between 0.72 and 0.84 approaching the steady state. 앫 At the fourth stage porosity increased from 0.84 to 0.89 (for the first day 0.84, second day 0.85, third day 0.86, fourth day 0.88, fifth day 0.88, sixth day 0.89, seventh day 0.89 and eighth day 0.89). The porosity of 0.89 was found to be steady state for the final 3 days. Therefore, for this type of reactor and this process the determining parameter was the volume of the influent to be used. Since the steady state was arrived at when
Fig. 2.
The porosity of the KFSW during the operation period.
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using 1000 ml of influent, it is recommended that an influent volume of 1000 ml be used from the first stage. The cumulative influent added was 15,625 ml; that is when using 1000 ml daily from the beginning a total of 15 days and 15 h is required. This is a reduction of 9 days and 9 h from the original duration of 25 days. These observations indicate that accelerated liquefaction of the organic bed can be achieved rapidly under fermentation conditions, with l000 ml of influent employed daily. 3.2. Effect of adding different volumes of tap water on COD concentration during the operation period The observations of the effluent (leachate) COD concentration during the operation period as a function of the influent volume during the four stages as indicted in Table 1 and Fig. 3 show that: 앫 at the first stage, the COD concentration increased from 45.27 to 124.61 g/l; 앫 at the second stage, the COD concentration was still increasing and ranged from 128.46 to 214.61, peaking over 2 days at the end of this stage, days 10 and 11; 앫 at the third and fourth stages, the COD concentration decreased until the end of the operation period down to 53.57 g/l.
Fig. 3.
COD concentration of leachate during the operation period.
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3.3. Effect of adding different volumes of tap water on COD rate during the operation period Table 1 and Fig. 4 show the effluent (leachate) COD rate during the operation period as a function of Up Flow Sludge Blanket Filter (UBF) reactor effluent with different volumes within the four stages, indicating that: 앫 at the first stage, the COD rate increased from 0.68 to 3.12 g/d; 앫 at the second stage, the COD rate increased very rapidly from 5.14 to 135.9 g/d, reaching the peak value near the end of this stage, at day 10; 앫 at the third and fourth stages, the COD rate decreased gradually, fluctuating until the end of the operation period when it reached 48.21 g/d.
3.4. Effect of adding different volumes of tap water on COD cumulative during the operation period The COD cumulative presented in Table 1 during the operation period (25 days), shows that the highly cumulative COD values can be attributed to the MSBW and the type of sludge used. 앫 At the end of the first stage, the COD cumulative was 14.34 g, equal to 1% of the total COD cumulative at the end of the operation period. 앫 At the end of the second stage, the COD cumulative was 384.62 g, equal to 25.48% of the total COD cumulative. 앫 At the end of the third stage, the COD cumulative was 554.5 g, equal to 36.73% of the total COD cumulative. 앫 At the end of the fourth stage, the COD cumulative was 556 g, equal to 36.83% by the total COD cumulative.
Fig. 4.
COD rate of leachate extraction during the operation period.
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Therefore for this type of reactor and this process the determining parameter was the volume of the influent to used. As the COD cumulative was almost the same when using 500 and 1000 ml, it is recommended that an influent volume of 500 or 1000 ml can be used from the beginning if the aim of this process is to arrive at the best COD cumulative with minimum or maximum influent. 3.5. Effect of adding different volumes of tap water on COD LR during the operation period In Table 1 the observations of the effluent (leachate) COD LR as a function of UBF reactor effluent with different volumes within the four stages show that: 앫 at the first stage, the COD LR increased from 0.06 to 0.26 g/l d; 앫 at the second stage, the COD LR was still increasing from 0.43 to 10.88 g/l d, peaking at the end of this stage on day 11; 앫 at the third and fourth stages, the COD LR decreased gradually, fluctuating until the end of the operation period, down to 4.02 g/l d.
3.6. Effect of adding different volumes of tap water on VFA concentration, pH of leachate and gas production during the operation period Table 1 and Fig. 5 show VFA concentration, pH of leachate and gas production during the operation period as a function of UBF reactor effluent, and indicate that:
Fig. 5. The relationship between VFA concentration with corresponding pH of leachate extraction and gas production during the operation period.
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앫 at the first stage, the concentration of VFA in leachate increased from 2.71 to 15.61 g/l at the end of this stage. There was a corresponding gas production decrease from 13.8 l/d at the second day down to 0 l/d at the end of this stage. However, pH slowly decreased from 4.2 to 3.5; 앫 during the second stage, the concentration of VFA in leachate fluctuated over the first 4 days between 9.39 and 11.40 g/l. There was also a corresponding gas production decrease from 0.5 l/d on the first day down to 0 l/d by the fourth day of this stage; the pH ranged from 3.75 to 3.65; 앫 at the third stage, VFA concentration on the second and third days was 9.34 and 9.32 g/l, while the gas production was 12.1 and 8.0 l/d. By the fourth and fifth days the VFA concentration was 7.60 and 7.89 g/l, while the gas production was 14.8 and 11.4 l/d. The pH ranged from 3.80 to 3.68; 앫 at the fourth stage, the concentration of VFA in leachate increased from 7.80 to 12.68 g/l. There was also a corresponding gas production decrease with a fluctuating rate from 8.1 down to 5.6 l/d. pH slowly increased from 3.81 to 4.79.
4. Conclusion The objective of this test was to study the leaching rate with operation time under the above-mentioned experimental conditions. The results can be concluded as follows. 1. The leaching rate reached a maximum on day 10. The COD of leachate extraction parameters such as COD rate, COD loading rate (LR) and COD concentration reached maximum values of 130 g COD/d, 11 g COD/l d, and 214 g/l of COD, respectively. 2. The leaching process increased accumulative COD gradually, especially after day 7. However, it appears that on day 25, accumulative leachate COD reached the maximum value, 1509.46 g. This is one of the reasons why the test was stopped on day 25. 3. The pH value of leachate remained at around 4. However, VFA concentration of leachate was fluctuating, especially in the initial period. High concentration of VFA on day 5 inhibited gas production. With a decrease in VFA concentration, the gas production rate increased gradually along with gradual change of sludge to VFA. 4. By increasing the amount of water added, the fermentation time can be decreased until the porosity is around 0.9. 5. According to the results of the leaching rate of a solid waste reactor using KFSW, the rational design for two-phase anaerobic digestion can be achieved.
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References [1] American Public Health Association. Standard methods for the examination of water and wastewater. 16th ed. Washington: American Public Health Association, 1985. [2] Ghanem III. A study on the possibility of using nontraditional energy in poultry farms. MSc thesis, Faculty of Agriculture, Al-Azhar University, Cairo, Egypt, 1992. [3] Ghanem III, Gu G, Zhu J, Tail SA, Khan-Y MFA, El-Shimi SA. Anaerobic digestion for waste water poultry manure by UBF reactor. J Environ Sci 1997;9(2):149–61. [4] Ghanem III. Study on biogas production technology and design for municipal solid biowaste. PhD dissertation, School of Environmental Engineering, Tongii University, Shanghai, China, 1998.
Leachate production and disposal of kitchen food solid waste by dry fermentation for biogas generation I.I.I. Ghanem a
a,*
, Gu Guowei b, Zhu Jinfu
b
Agricultural and Engineering Research Institute (AEnRI), Agricultural Research Center (ARC), Nadi El Said St., P.O. Box 256, Dokki, Giza, Egypt b School of Environmental Engineering, Tongji University, Shanghai 200092, China
Abstract This laboratory research, which applies anaerobic digestion for a solid phase batch system using kitchen food solid waste (KFSW), is concerned with optimizing leachate production under different conditions. The solid-phase digestion process is expected to be superior to slurry-phase digestion and the so-called “dry fermentation” process. A batch system solid waste reactor was used in the present study. The performance of the reactor was tested under the conditions of constant temperature of 35°C and the reactor active volume was 12 l. On operation day 10, chemical oxygen demand (COD) for leachate extraction parameters such as COD rate, COD loading rate (LR) and COD concentration reached maximum values, and were 135 g COD/d, 11 g COD/1.d, and 214 g/l of COD, respectively. On day 25, accumulative leachate COD reached the top value of 1509.4 g. The pH value of leachate was kept around 4. However, volatile fatty acid (VFA) concentration of leachate fluctuated, especially in the initial period. A high concentration of VFA on day 5 inhibited gas production, but with the decrease of VFA concentration the gas production rate was increased gradually and the sludge acclimated to VFA gradually. The process can be operated at a profit and no unfavorable environmental impact is expected for this type of plant production of biogas using the leachate from dry fermentation. These considerations make it a viable alternative in most countries as a source of energy. 2001 Published by Elsevier Science Ltd. Keywords: KFSW; Dry fermentation; Solid phase; Anaerobic sludge; Wastewater; Leachate
* Corresponding author. 0960-1481/01/$ - see front matter 2001 Published by Elsevier Science Ltd. PII: S 0 9 6 0 - 1 4 8 1 ( 0 0 ) 0 0 1 5 2 - X
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1. Introduction The enormous production of municipal solid waste, especially in big cities, has concerned both authorities and researchers for many years. Within this situation, several ideas and processes that might be applied under different circumstances have arisen. However, an important fraction of the municipal solid waste stream can be defined as municipal solid biowaste (MSBW). This is food waste from the kitchen; animal, fruit and vegetable residues resulting from the handling, preparation, cooking and eating of food. It appears that not one of the processes considered up to now is ideal, or in other words, none can be considered an absolute solution for the KFSW problem. One of these possible solutions is anaerobic digestion of the organic fraction of the MSW. Anaerobic fermentation has been thought to be limited to wet organic waste, such as sewage sludge that contains greater than 90% water. The processing of drier biomass at these high water contents requires the addition of many tons of water for every dry ton of biomass. Solid biowaste is particularly troublesome since it not only requires large amounts of water, but is also extremely difficult to handle. One approach to fermentation of solid biowaste is to develop a method that could ferment the material without the addition of large quantities of water. “Dry fermentation” is the focus of this study [4].
2. Materials and methods 2.1. Kitchen food solid waste (KFSW) The cooking food solid waste used in this study was collected from the foreign student restaurant at Tongji University and separated from paper, bones and another material, then mixed and shredded to a diameter of 5 mm using a meat mincer. The cooking food solid waste was subjected to a centrifugal force to separate into: 1. a solid phase (semi-solid material) feed source for a Leachate-Bed, Solid Phase Anaerobic Reactor. This was used to produce a leachate feed solution source for the UBF Reactor to produce methane gas [3,4] and the residue can be used for animal nitration or agricultural fertilizer as a compost; 2. a liquid phase (kitchen food wastewater) was extracted from KFWS and also used as a feed solution source for a Biogas Reactor, treated by an anaerobic digestion process to produce methane gas as a source of energy.
2.2. Anaerobic sludge In this study, sludge was used for disposal by anaerobic digestion at the same time as an inoculum. The weight ratio of sludge to KFSW was 1:4 in this experiment.
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For the leach-bed anaerobic reactor the sludge was collected from a municipal wastewater treatment company in Shanghai (storage basin). 2.3. Leach-bed anaerobic reactor Bench-scale models of the leach-bed anaerobic reactor used in this study had the configuration shown in the sketch of the reactor given in Fig. 1. The reactor was constructed from cylindrical plexiglas columns with a diameter of 24 cm, a reactor height of 64.5 cm and a bed height of 44.5 cm corresponding to an active volume of 12 l. Three ports along the height of the fermentor allowed three thermometers to measure the temperature inside the reactor. The bed leachate flowed down through the bed and out of the system from the bottom port. The fermentation gas flowed up through the bed and out of the reactor from the upper port and the system was
Fig. 1. Sketch of leach-bed anaerobic reactor.
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placed in an incubator-like control chamber with a temperature of 35±1°C. The cooking food solid waste, seed sludge and support material (wood powder) were mixed together in proportion to meet the following criteria: 1. the weight of the kitchen food solid waste (KFSW) was 8.8 kg; 2. the weight of the seed sludge was 2.2 kg (20% of the weight of KFSW); 1 l of wood powder, used as support material, was 10% of the volume of the KFSW. 2.4. Shredding machine (meat mincer) Various types of shredders such as the hammer-mill drum pulverizer rasp mill, disk mill, and others are available. In this study we used a meat mincer [4]. 2.5. Centrifugation Dewatering of sludge and KFSW by centrifugation has been applied with increasing frequency in experiments on biowaste [4]. 2.6. Control chamber A wooden control chamber, with a polyurethane foam insulation layer to reduce the heat losses to the outside environment, was used in this study. The control room contained the following equipment: (1) a gas flow meter; (2) a feeding pump (peristaltic pump); (3) a heating source; (4) a thermostat: the temperature was held constant at 35°C [2]. 2.7. Chemical analysis Total suspended solids (TSS), VSS, chemical oxygen demand (COD) and volatile fatty acids (VFA) were determined according to the methods recommended by the American Public Health Association [1]. 2.8. Experimental procedure and operation conditions 앫 Cooking food solid waste (KFSW) was collected, recycled and sampled. 앫 The KFSW was shredded with the meat mincer and mixed directly, equal to 8.8 l⬇9 kg. 앫 Then 20% sludge by weight ratio was added to the KFSW. 앫 Centrifugation with 2750 rpm for 20 min with KFSW and sludge, equal to 2.2 kg. 앫 Add 10% support materials (wood powder) by the ratio of the total volume of biowaste (KFSW+Sludge), now equal to 11 l. 앫 The volume of KFSW+Sludge+support material is now 11+1=12 l. 앫 The weight of KFSW+Sludge is 11 kg.
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After obtaining KFSW, the support material and the sludge are mixed completely and put in the bed anaerobic reactor. 2.8.1. System operation and performance 앫 Analysis of the influents and effluents for volatile acids, pH, and chemical oxygen demand (COD) monitored system operation and performance. 앫 Gas production from the MSBW bed was measured daily. The temperature was kept constant at about 35±1°C. 2.8.2. Operation parameters The biogas operation parameters for KFSW by batch test anaerobic digestion reactor, with a temperature of 35±1°C [4], were as follows (these values are guidelines): 1. 2. 3. 4. 5. 6. 7. 8. 9.
use centrifugation with 2750/20 rpm/min; the moisture content was 26.61%; the support material used was wood powder; the quantity of support material in feed=10% by volume; the sludge added was from a municipal wastewater treatment company in Shanghai, storage basin; the sludge solid in feed=20% by weight; there was no shaking time or agitation; influent pH=8–8.3; median KFSW particle diameter=5 mm.
2.8.3. Operation conditions and performance of solid phase reactor The operation of the leach-bed, dry fermentation as detailed in Table 1, was divided into four stages. Tap water was added every day at each stage in the amounts shown below: 앫 앫 앫 앫
the the the the
first stage (5 days): 25 ml; second stage (6 days): 500 ml; third stage (6 days): 750 ml; and fourth stage (8 days): 1000 ml.
The aim of this function was to adapt the porosity at steady state by using different volume additions of UBF effluent of 25, 500, 750 and 1000 ml. As influent for solid phase reactor we chose the volume of influent that could allow the porosity to reach a steady state condition in the shortest operation period.
3. Results and discussion The significant liquefaction of biowaste (leachate) function is shown below.
COD COD rate of concentration of leachate leachate extraction (g/d) extraction (g/l)
First stage: addition of 25 ml UBF effluent every day 1 15 45.27 0.68 2 35 127.96 4.48 3 20 111.29 2.23 4 30 127.63 3.83 5 25 124.61 3.12 Second stage: addition of 500 ml UBF effluent every day 6 40 128.46 5.14 7 50 141.53 7.08 8 320 134.99 43.20 9 475 132.11 62.72 10 635 214.02 135.9 11 610 214.02 130.55 Third stage: addition of 750 ml UBF effluent every day 12 550 208.34 114.59 13 650 148.82 96.73 14 620 142.86 88.57 15 900 118.12 106.31 16 550 110.24 60.63 17 880 99.63 87.67 Fourth stage: addition of 1000 ml UBF effluent every day 18 800 93.02 74.42 19 950 83.07 78.92 20 970 76.92 74.61 21 1080 88.59 95.68 22 860 75.40 64.84 23 1100 63.49 69.84 24 860 57.54 49.48 25 900 53.57 48.21
Period (day) Leachate rate (ml/d)
2.71 3.50 4.76 6.76 15.61 10.81 9.39 10.41 11.58 8.36 8.51 7.93 9.34 9.32 7.60 7.89 6.56 7.33 8.56 9.71 10.37 11.11 12.01 12.68 11.47
0.68 5.16 7.39 11.22 14.34 19.48 26.56 69.76 132.51 268.41 398.96 513.55 610.28 698.85 805.16 865.79 953.46 1027.88 1106.0 1181.41 1277.09 1341.93 1411.77 1461.25 1509.46
7.8 8.0 5.9 6.0 5.6 8.1 6.5 6.4
1.6 12.1 8.0 14.8 11.4 8.9
0.5 0.2 0.3 0 0.6 4.2
0.1 13.8 11.5 4.1 0
COD cumulation VFA concentration Gas rate (l/d) of leachate of leachate extraction (g) extraction (g/l)
Table 1 Effect of addition of effluent of UBF or tap water reactor to the solid phase anaerobic reactor during the operation period
3.81 3.85 3.91 3.94 4.12 4.36 4.55 4.79
3.70 3.72 3.68 3.75 3.78 3.80
3.75 3.73 3.74 3.65 3.65 3.70
4.2 3.99 3.72 3.62 3.75
pH of leachate extraction
285.34
313.6
364
NH3–N concentration of leachate extraction (g/l)
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3.1. Effect of the different volume addition of tap water on the porosity of the biowaste during the operation period The solid phase anaerobic digester was a liquefaction reactor and in principle is an extracting apparatus. Increasing the porosity of the biowaste will increase the rate of extraction from the solids, carried away as a dilute solution, and will accelerate the extraction process and also solid waste treatment. Table 1 and Fig. 2 illustrate the effect that adding different volumes of UBF effluent or tap water will have on the porosity of the biowaste during the operation period using a solid anaerobic reactor. The results are as follows. 앫 In the first stage, 25 ml of influent was used and the increase in porosity ranged between 0.6 and 1. This was so because the biowaste contained free water and less influent was added. 앫 At the second stage, the porosity was 0.26 on the first day because there was no more free water and influent water was more than during the first stage. At the end of this stage the porosity had risen to 0.72. 앫 During the third stage, the porosity ranged between 0.72 and 0.84 approaching the steady state. 앫 At the fourth stage porosity increased from 0.84 to 0.89 (for the first day 0.84, second day 0.85, third day 0.86, fourth day 0.88, fifth day 0.88, sixth day 0.89, seventh day 0.89 and eighth day 0.89). The porosity of 0.89 was found to be steady state for the final 3 days. Therefore, for this type of reactor and this process the determining parameter was the volume of the influent to be used. Since the steady state was arrived at when
Fig. 2.
The porosity of the KFSW during the operation period.
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using 1000 ml of influent, it is recommended that an influent volume of 1000 ml be used from the first stage. The cumulative influent added was 15,625 ml; that is when using 1000 ml daily from the beginning a total of 15 days and 15 h is required. This is a reduction of 9 days and 9 h from the original duration of 25 days. These observations indicate that accelerated liquefaction of the organic bed can be achieved rapidly under fermentation conditions, with l000 ml of influent employed daily. 3.2. Effect of adding different volumes of tap water on COD concentration during the operation period The observations of the effluent (leachate) COD concentration during the operation period as a function of the influent volume during the four stages as indicted in Table 1 and Fig. 3 show that: 앫 at the first stage, the COD concentration increased from 45.27 to 124.61 g/l; 앫 at the second stage, the COD concentration was still increasing and ranged from 128.46 to 214.61, peaking over 2 days at the end of this stage, days 10 and 11; 앫 at the third and fourth stages, the COD concentration decreased until the end of the operation period down to 53.57 g/l.
Fig. 3.
COD concentration of leachate during the operation period.
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3.3. Effect of adding different volumes of tap water on COD rate during the operation period Table 1 and Fig. 4 show the effluent (leachate) COD rate during the operation period as a function of Up Flow Sludge Blanket Filter (UBF) reactor effluent with different volumes within the four stages, indicating that: 앫 at the first stage, the COD rate increased from 0.68 to 3.12 g/d; 앫 at the second stage, the COD rate increased very rapidly from 5.14 to 135.9 g/d, reaching the peak value near the end of this stage, at day 10; 앫 at the third and fourth stages, the COD rate decreased gradually, fluctuating until the end of the operation period when it reached 48.21 g/d.
3.4. Effect of adding different volumes of tap water on COD cumulative during the operation period The COD cumulative presented in Table 1 during the operation period (25 days), shows that the highly cumulative COD values can be attributed to the MSBW and the type of sludge used. 앫 At the end of the first stage, the COD cumulative was 14.34 g, equal to 1% of the total COD cumulative at the end of the operation period. 앫 At the end of the second stage, the COD cumulative was 384.62 g, equal to 25.48% of the total COD cumulative. 앫 At the end of the third stage, the COD cumulative was 554.5 g, equal to 36.73% of the total COD cumulative. 앫 At the end of the fourth stage, the COD cumulative was 556 g, equal to 36.83% by the total COD cumulative.
Fig. 4.
COD rate of leachate extraction during the operation period.
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Therefore for this type of reactor and this process the determining parameter was the volume of the influent to used. As the COD cumulative was almost the same when using 500 and 1000 ml, it is recommended that an influent volume of 500 or 1000 ml can be used from the beginning if the aim of this process is to arrive at the best COD cumulative with minimum or maximum influent. 3.5. Effect of adding different volumes of tap water on COD LR during the operation period In Table 1 the observations of the effluent (leachate) COD LR as a function of UBF reactor effluent with different volumes within the four stages show that: 앫 at the first stage, the COD LR increased from 0.06 to 0.26 g/l d; 앫 at the second stage, the COD LR was still increasing from 0.43 to 10.88 g/l d, peaking at the end of this stage on day 11; 앫 at the third and fourth stages, the COD LR decreased gradually, fluctuating until the end of the operation period, down to 4.02 g/l d.
3.6. Effect of adding different volumes of tap water on VFA concentration, pH of leachate and gas production during the operation period Table 1 and Fig. 5 show VFA concentration, pH of leachate and gas production during the operation period as a function of UBF reactor effluent, and indicate that:
Fig. 5. The relationship between VFA concentration with corresponding pH of leachate extraction and gas production during the operation period.
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앫 at the first stage, the concentration of VFA in leachate increased from 2.71 to 15.61 g/l at the end of this stage. There was a corresponding gas production decrease from 13.8 l/d at the second day down to 0 l/d at the end of this stage. However, pH slowly decreased from 4.2 to 3.5; 앫 during the second stage, the concentration of VFA in leachate fluctuated over the first 4 days between 9.39 and 11.40 g/l. There was also a corresponding gas production decrease from 0.5 l/d on the first day down to 0 l/d by the fourth day of this stage; the pH ranged from 3.75 to 3.65; 앫 at the third stage, VFA concentration on the second and third days was 9.34 and 9.32 g/l, while the gas production was 12.1 and 8.0 l/d. By the fourth and fifth days the VFA concentration was 7.60 and 7.89 g/l, while the gas production was 14.8 and 11.4 l/d. The pH ranged from 3.80 to 3.68; 앫 at the fourth stage, the concentration of VFA in leachate increased from 7.80 to 12.68 g/l. There was also a corresponding gas production decrease with a fluctuating rate from 8.1 down to 5.6 l/d. pH slowly increased from 3.81 to 4.79.
4. Conclusion The objective of this test was to study the leaching rate with operation time under the above-mentioned experimental conditions. The results can be concluded as follows. 1. The leaching rate reached a maximum on day 10. The COD of leachate extraction parameters such as COD rate, COD loading rate (LR) and COD concentration reached maximum values of 130 g COD/d, 11 g COD/l d, and 214 g/l of COD, respectively. 2. The leaching process increased accumulative COD gradually, especially after day 7. However, it appears that on day 25, accumulative leachate COD reached the maximum value, 1509.46 g. This is one of the reasons why the test was stopped on day 25. 3. The pH value of leachate remained at around 4. However, VFA concentration of leachate was fluctuating, especially in the initial period. High concentration of VFA on day 5 inhibited gas production. With a decrease in VFA concentration, the gas production rate increased gradually along with gradual change of sludge to VFA. 4. By increasing the amount of water added, the fermentation time can be decreased until the porosity is around 0.9. 5. According to the results of the leaching rate of a solid waste reactor using KFSW, the rational design for two-phase anaerobic digestion can be achieved.
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References [1] American Public Health Association. Standard methods for the examination of water and wastewater. 16th ed. Washington: American Public Health Association, 1985. [2] Ghanem III. A study on the possibility of using nontraditional energy in poultry farms. MSc thesis, Faculty of Agriculture, Al-Azhar University, Cairo, Egypt, 1992. [3] Ghanem III, Gu G, Zhu J, Tail SA, Khan-Y MFA, El-Shimi SA. Anaerobic digestion for waste water poultry manure by UBF reactor. J Environ Sci 1997;9(2):149–61. [4] Ghanem III. Study on biogas production technology and design for municipal solid biowaste. PhD dissertation, School of Environmental Engineering, Tongii University, Shanghai, China, 1998.