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Anaerobic Fermentation of Organic Municipal Solid Wastes for the Production of Soluble Organic Compounds David Bolzonella,*,† Francesco Fatone,† Paolo Pavan,‡ and Franco Cecchi† Department of Science and Technology, University of Verona, Strada Le Grazie, 15, I-37134 Verona, Italy, and Department of Environmental Sciences, University of Venice, Dorsoduro 2137, I-30123 Venice, Italy
After investigating the application of the mesophilic and thermophilic processes in completely stirred, batch, and plug-flow reactors, in this study the authors consider the anaerobic fermentation of source-sorted organic municipal solid wastes in psychrophilic conditions (1422 °C) without pH control. The pilot-scale reactor was operated in a batch mode, with a hydraulic retention time of 4-4.5 d. The production of soluble COD from the particulate matter was (on average) 0.27 gCOD per gram of total volatile solids fed to the reactor when operating with a total solids content of 20-35 g/L. The volatile fatty acids (VFA) were 15% of the soluble COD produced after 4 d of reaction. These values are far lower than those found in mesophilic and thermophilic conditions, where the production of soluble COD ranged from 0.5 up to 0.9 gCOD/ gTVSfed and volatile fatty acids could reach 90% of soluble COD. Further, the first-order reaction constant for the hydrolysis process, Kh, for the psychrophilic conditions was found equal to 0.11 d-1 at 20 °C, while it was in the range 0.2-0.4 d-1 when operating in mesophilic or thermophilic conditions. Conclusively, the study of the psychrophilic fermentation process allowed for completing the scenario of different options of anaerobic solid-state fermentation of organic waste. Though mesophilic and thermophilic processes resulted in being more effective in dissolution of particulate matter, psychrophilic processes can be of some interest because they are simpler and energy saving. In particular, psychrophilic processes can be useful for the production of rough soluble COD to be used, e.g., for sustaining the biological nutrients removal processes in wastewater treatment. 1. Introduction The organic fraction of municipal solid wastes and other easily biodegradable solid substrates (e.g., agrowaste) have to be conveniently treated to reduce their environmental impact and to recover energy and material while massive disposal treatments (e.g., landfill or incineration) should be avoided. An obvious choice to achieve this goal is given by the anaerobic digestion and co-digestion processes for methane production.1 However, anaerobic solid-state biofermentative processes can be used for the production of valuable products:2 in fact, anaerobic fermentation is an effective bioprocess for the production of volatile fatty acids and other low weight organic compounds such as alcohols or lactic acid.3-7 These can then be used for the production of methyland ethyl-esters to be added to gasoline8 because of their high octane number (between 103 and 118), as a low cost external carbon source for the production of biopolymers, like poly-hydroxyl-alkanoates,9-11 for sustainment of the biological processes for nutrients removal in wastewater treatment plants,12-19 or, still, for anaerobic fermentation with a high hydrolysis rate being the first step of the anaerobic digestion process for biogas production when treating organic wastes with a high biodegradability (e.g., refs 20-22). The authors have been studying the anaerobic fermentation process for the treatment of organic solid wastes since the early 1990s:3-5,12 both mesophilic and * To whom correspondence should be addressed. Phone and fax: +39 045 8027965. E-mail:
[email protected]. † University of Verona. ‡ University of Venice.
thermophilic conditions had been previously investigated, while this study deals with the psychrophilic anaerobic fermentation without pH control of sourcesorted organic wastes for the production of soluble organic compounds. The choice of a psychrophilic environment enables one to verify the process yields also for processes with low energy input, to generalize the observed yields of the process, and to define the figures for reactors design at different reactor temperatures. 2. Materials and Methods Organic municipal solid wastes from source-sorting collection (some 500 kg/d) were pretreated in a specifically designed pilot-scale machine with a treatment capacity of 1 ton/h (see Figure 1). The characteristics of
Figure 1. Schematic representation of the pilot-scale rigs for the wastes selection and treatment, anaerobic fermentation, and pressing for phase separation (Italian Patent Bugnion rn2004a000038).
the source-sorted organic wastes treated in the experimentation are reported in Table 1 and compared with
10.1021/ie048937m CCC: $30.25 © 2005 American Chemical Society Published on Web 03/29/2005
Ind. Eng. Chem. Res., Vol. 44, No. 10, 2005 3413 Table 1. Characteristics of the Source-Sorted Organic Wastes Used in This Experimentation and Comparison with Similar Substratesa type of waste
TS g kg-1
TVS g kg-1
TVS/TS %
COD g kg-1
COD/TS
COD/TVS
TN g kg-1
TP g kg-1
SS-OFMSW this study
average min max
288 221 337
228 194 252
80 63 89
347 299 398
1.2 0.9 1.6
1.5 1.2 1.9
28 23 43
2.4 19 93
SC-OFMSW Traverso et al., 20007
average min max
88 54 133
80 47 106
91 71 94
102 55 151
1.0 0.7 1.5
1.3 1.0 1.6
23 14 33
3.7 1.3 4.3
MS-MSW Sans et al., 19954,5
average min max
647 472 832
301 212 488
45 36 62
510 230 760
0.8 0.5 1.0
1.5 1.1 1.7
14 10 18
14 10 18
a SS-OFMSW: source-sorted organic fraction of municipal solid wastes; SC-OFMSW: separately collected organic fraction of municipal solid wastes; MS-OFMSW: mechanically selected organic fraction of municipal solid wastes.
Table 2. Reactor Operational Conditions and Yields Operational Conditions HRT, d temperature, °C pH TS content, g L-1 TVS content, g L-1
4-4.5 14-22 4-5 20-35 15-25
Process Yields soluble COD, gSCOD gVSfed-1 volatile fatty acids, gVFA gVSfed-1
0.27 0.04
characteristics of similar wastes used in previous studies of the authors. The organic wastes were discharged in a receiving hopper and then shredded. The resulting material was treated for the removal of metals and then passed through a drum sieve (trommel) for the removal of plastics and cardboard or wood pieces before a second shredding in a 5 mm cutter. The fine material originated from the pretreatment line was then fed to the pilotscale reactor and added with water to match up a final total solid concentration of about 2-3%. The 3 m3 bioreactor operated in the psychrophilic range of temperature (14-22 °C) without pH control and in a pure batch mode with a hydraulic retention time of 4-4.5 d (Table 2). The reactor content was monitored daily for the following parameters: temperature, pH, and concentration of total solids, total volatile solids, soluble COD, volatile fatty acids (VFA), total and ammonia-nitrogen, and total and soluble phosphorus. Analyses were carried out according to the protocols reported in the Standard Methods. After the reaction time, the bioreactor content was drawn and treated in a screw-press for the separation of the liquid and solid streams. These were monitored for the same parameters mentioned above to close the mass balances of the process. 3. Results and Discussion 3.1. Psychrophilic Anaerobic Fermentation. The process operational conditions applied to the bioreactor and the process yields, in terms of soluble COD and VFA production, are reported in Table 2. The typical profiles for VFA, soluble COD, and ammonia-nitrogen in the reactor are reported in Figures 2a-c, respectively. According to the reported profiles, the hydrolytic process can be described as a first-order reaction. During the first day the pH dropped down from 6 to 4-4.5 because of the production of volatile fatty acids which increased from 500 mg L-1 up to 1000 mg L-1 in the first 24 h of reaction (see Figure 3). Then, pH generally increased again on the fourth day of reaction, when the fatty acids
Figure 2. VFA (a), SCOD (b), and ammonia-nitrogen (c) profiles with time within the reactor.
showed a slight decrease because of their bioconversion into biogas. Figure 3 shows the comparison between the profile of pH and VFA concentration in the reactor. Acetic acid was the most important product (some 80% of the total acids production) and propionic and butyric acids were the other two main components of the organic acids mixture. The acids production generally stopped after the fourth day of reaction and the VFA concentration remained constant or slightly decreased (see Figure 2a). However, the VFAs were just 10-15%, on average,
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Figure 5. Relationship between the reactor temperature and the VFA/SCOD ratio in the reactor after 4 d of reaction.
Figure 3. Relationship between the VFA concentration and pH profile in the reactor.
Table 3. Characteristics of the Liquid Effluent from the Screw-Press after the Anaerobic Fermentation (TS and TVS, COD, TKN, and P on Wet Weight) TS g TVS TVS/ CODpart TN TP SCOD NH4+-N PO4-P date kg-1 g kg-1 TS % g L-1 g L-1 g L-1 mg L-1 mg L-1 mg L-1 avg 28 min 8 max 38
22 6 29
77 67 83
28 8 38
0.9 0.5 1.2
0.08 11050 0.07 5300 0.09 12700
71 23 74
70 49 104
Table 4. Characteristics of the Solid Stream after Screw-Pressing (TS and TVS, COD, TN, and TP on Wet Weight)
Figure 4. Relationship between the total solids content in the feed and the soluble COD concentration in the reactor after 4 d of reaction.
of the soluble COD in the reactor (Figure 2b): in psychrophilic conditions other organic compounds, like lactic acid, alcohols, and simple sugars, were predominant, as shown in previous studies of the authors.7,23 These results are in contrast with previous findings obtained in mesophilic experiments: in fact, in that case, the VFAs were the most important products or nearly the only compounds in the soluble COD fraction when working with hydraulic retention times (HRTs) in the range of 2-4 d.4,5,7,14,23 This is because the acidogenic step, which transforms the soluble organic compounds produced in the hydrolytic phase into shortchain volatile fatty acids, was only partially developed. Moreover, the uncontrolled pH plays an important role in VFA formation: low pH, thus the presence of undissociated organic acids, may determine the inhibition of the fermentative anaerobic biomass.24 Specific studies showed that the pH control in acidogenic anaerobic fermentation may improve the VFA production in anaerobic reactors treating organic solid wastes.25,26 Figure 2c shows the typical trend of free ammonia (as nitrogen): this increased with time, passing from some 40 to 70 mg N L-1, because of the hydrolysis of proteins. In particular, some 15% of the fed organic nitrogen became free ammonia. The strict relation between the produced soluble COD (after 4 d of reaction) and the total solids fed to the reactor is shown in Figure 4: it is clear, as expected, that when the substrate concentration increases, the product increases as well. On the other hand, the relationship between temperature and the VFA/SCOD ratio was quite clear: Figure 5 shows this situation, which is typical for fermentative processes.25 The increase in the reaction temperature generally determines
date
TS g kg-1
TVS g kg-1
TVS/TS %
COD g kg-1
TN g kg-1
TP g kg-1
avg min max
155 104 214
129 91 196
87 78 92
377 319 442
22 10 31
5.7 1.0 6.5
an increase in VFA production. The high dispersion of VFA concentrations reported in Figure 2a can be ascribed to the difference of temperature among the different tests: Figure 5 shows the relation between VFA presence and temperature. 3.2. Mass Balances and Yields of the Psychrophilic Process. The reactor content was completely drawn after some 4 d of retention time (pure stirred batch system) and then pressed into a screw-press equipped with a screen with 1 cm wholes. Characteristics of liquid and solid streams obtained are reported in Tables 3 and 4, respectively. The global mass balance, calculated on the basis of 1000 kg of treated waste, is reported in Figure 6. The balances closed perfectly considering the experimental tolerance ((10-15%) of the analytical methods used in this study. The treated organic wastes from source-sorting collection were particularly clean so the amount of metals and inert materials was very little (some 7.5% of the treated wastes, on wet weight). Globally, the removal of total solids and total volatile solids was some 25% for both the parameters. It is important to note that some 60% of the total solids and 70% of the total COD entering the bioreactor passed then into the liquid stream (average concentration of 28 g/L for both the parameters). This determined a fermentation product characterized by a high content of carbon (COD/N ≈ 30) and biodegradability (TVS/TS ≈ 77%). This stream can be conveniently added to the anaerobic and/or anoxic processes of wastewater treatment plants for biological nutrients removal19 or can be used directly in the anaerobic digesters to be co-digested with wasteactivated sludge as in the AF-BNR-SCP process.12-15 With reference to the solid phase originating from the screw-press, this was characterized by a solid content of some 16%, a TVS/TS ratio of some 87%, and a 38% COD content (Table 4). Therefore, this material can be
Ind. Eng. Chem. Res., Vol. 44, No. 10, 2005 3415
Figure 6. Mass balance of the process.
reasonably considered a good substrate for the following process of anaerobic co-digestion for energy recovery or aerobic composting with other substrates. 3.3. Kinetic Study and Modeling of the Psychrophilic Fermentation Process. To better understand the hydrolytic process of particulate fermentable matter, i.e., the volatile fraction of total solids, a kinetic study was carried out. The batch hydrolysis process is described by a first-order kinetic model (see Figure 2),
rh ) -Kh‚X
(1)
where rh (g L-1 d-1) is the reaction rate for the hydrolysis process, X is the concentration of the fermentable particulate matter, the total volatile solids (g L-1), and Kh (d-1) is the first-order reaction constant. Separating variables and integrating with time from 0 (initial condition) to the hydraulic retention time of the batch system, we obtain
X ) X0‚exp-Kh‚t
(2)
Then, considering the soluble COD, SCOD, as the hydrolysis product of the biodegraded volatile solids, the following is obtained,
SCODt ) X0 - (X0 - SCOD0)‚exp-Kh‚t
(3)
where SCODt is the concentration of soluble COD (g L-1) after a hydraulic retention time of t d, SCOD0 is the initial concentration of soluble COD (g L-1), X0 (g L-1) is the concentration of fermentable organic matter (expressed as the COD equivalent of the total volatile solids concentration), Kh (d-1) is the first-order reaction constant, and t is the reaction time. Equation 3 gives the production of soluble COD due to the hydrolysis of the total volatile solids if the reactor is modeled as a completely stirred batch reactor. Moreover, if we consider the temperature dependence of the hydrolysis constant, according to Moser-Engeler et al.,27 we can write Kh,T ) Kh,T0‚exp-φ(T0-T). Here, Kh,T (d-1) is the first-order reaction constant at a given temperature, T, while Kh,T0 (d-1) is the first-order reaction constant at the reference temperature, T0, experimentally determined as equal to 0.11 d-1 (at 20 °C) and φ (°C-1) is the exponential temperature coef-
Figure 7. Comparison of measured and calculated SCOD concentrations (T ) 14-22 °C).
ficient, determined to be equal to 0.06 °C-1. These values are similar to those reported for the fermentation of primary sludge in psychrophilic conditions.27 Therefore, eq 3 becomes
SCODt ) X0 - (X0 - SCOD0)‚exp-Kh‚exp-φ(T0-T)‚t (4) The expected concentrations of soluble COD after reaction time t (with 1 < t < 4 d) at a given temperature T were calculated according to eq 4 and compared to experimental data: Figure 7 shows the comparison between experimental and calculated data; the proposed model can describe quite properly the behavior of the batch reactor (r2 ∼ 0.82). Equation 4 was solved considering the experimental data related to the initial concentration of soluble COD (SCOD0), fermentable organic matter, X0 (expressed as the COD equivalent of the total volatile solids concentration), and temperature. 3.4. Anaerobic Fermentation of Organic Municipal Solid Waste: A Generalization. The results obtained in this experimentation, in terms of soluble COD yields and VFA/SCOD ratio, have been compared with those obtained in mesophilic and thermophilic conditions in previous works: Table 5 summarizes the results of referenced studies. From reported data, it can be seen that the mesophilic and thermophilic fermentation processes, either in batch, plug-flow, or completely stirred configuration, allows for a hydrolysis efficiency that is clearly greater than the one observed in the psychrophilic environment (0.5-0.9 versus 0.27 gSCOD/ gTVSfed) and that VFAs were 50-90% of the soluble
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Table 5. Comparison of the Experimental Results with Literature Data of Anaerobic Fermentation of OFMSWa process
T °C
HRT d
OLR kg V S m-3 d-1
yields gSCOD gVSfed-1
VFA/SCOD %
BATCH BATCH CSTR CSTR PFR CSTR CSTR
15-20 35 35 35 37 37 55
4.5 1 1.5-6 1.5-6 2-6 1.5-8.5 1-5
40 92 82-85 4.5-18 38-85 2-25 19-78
0.27 0.54 0.48-0.55 0.43-0.56 0.5 0.4-0.5 0.50-0.90
13 50 55-90
a
30-60 38-73 50-65
ref this study Traverso et al.7 Traverso et al. 7 Andreottola et al. 17 Sans et al.4 Argelier et al.6 Pavan et al.23
PFR ) plug-flow reactor, CSTR ) continuously stirred tank reactor.
Table 6. Values of the First-Order Kinetic Constant for Hydrolysis of Solid Organic Wastes or Sludge
Table 7. Required Reactor Volume at Different Temperatures for a Population of 100000 Inhabitants process temperature
value of Kh d-1
T °C
ref
0.11 0.11-0.15 0.03-0.15 0.081-0.139 0.25 0.24-0.47 0.01-0.2 0.1-2 0.1-0.25
20 20 20 35 35 40 55 n.a. n.a.
this study Moser-Engeler et al.27 Veeken and Hamelers28 Zeeman et al.29 Traverso et al.7 Veeken and Hamelers28 Christ et al.30 Garcia-Heras31 Vavilin et al.32
COD (on average), while at lower temperatures the acidogenic step was hindered and large organic molecules (e.g., proteins and complex sugars) rather than short-chain organic acids accumulated in the reactor. However, it is not worth emphasizing the psychrophilic reaction need for simpler facilities and lower energy supply and is then cheaper so it should be considered when the VFA content of the soluble phase is not the most important product. Moreover, previous studies4,23,33 showed that the thermophilic reaction can present some limitations related to the process stability and that the recycling of part of the biomass is necessary. The determination of the value of the first-order reaction constant, Kh, for a psychrophilic fermentation process and the comparison with results of previous studies allows for the generalization and complete understanding of the kinetics of the anaerobic fermentation processes for the treatment of organic solid wastes. Table 6 illustrates typical values of Kh reported in previous studies of the authors and in recent literature. These are dispersed in a broad range: the value of Kh ranges between 0.01 and 0.4 d-1; however, a trend can be individuated. In particular, one can say that the value of the first-order reaction constant, Kh, is some 0.1 d-1 in psychrophilic conditions and goes up to some 0.2-0.3 when operating in a mesophilic or thermophilic environment. Clearly, one should always keep in mind that the determination of the first-order reaction constant, Kh, is valid for a certain substrate in certain conditions, and some factors such as specific surface area, particle shape, and particle size distribution all strongly affect the hydrolysis process, thus, the Kh value. Therefore, the determined values should always be considered as “indicative” rather than as “universal”; nevertheless, these can be conveniently used for reactor designing. 3.5. Consideration of the Design of Reactors for the Anaerobic Fermentation of Organic Solid Waste. The results of this and previous studies allows for some fundamental considerations dealing with the design of anaerobic reactors for the fermentation of solid organic wastes.
psychrophilic mesophilic thermophilic
population served, people reactor volume required, m3 construction costs, Euros
100000 65 75000
100000 40 49000
100000 30 39000
In particular, the reported results confirmed that the optimal hydraulic retention time for the production of soluble organic compounds in anaerobic fermentation processes of organic solid waste is in the range of 1-3 d as the hydrolysis step is particularly fast (see data reported in Table 5). Moreover, the applied organic loading rates seemed to be not very important; tested OLR were in a broad range (2-92 kg VS m-3 d-1) and results were only partially affected by that operational parameter: generally, the higher the applied OLR, the higher the concentration of soluble COD in the effluent (e.g., Figure 4) and very high OLRs did not affect the process stability.6,7 However, when very biodegradable organic wastes are fed to the reactor, the use of a recycle or a cascade of reactors can be a valuable indication to preserve the process stability.3-6 Considering the application of a completely stirred continuously fed reactor, the most used configuration for hydrolysis processes,3,6,7,14,16-18,23,26,30 and the mass balance for the substrate in steady-state conditions, the requested hydraulic retention time (HRT) to achieve a given final concentration of fed substrate is
HRT )
S0 - S 1 ‚ S Kh
(5)
where S0 is the concentration of the influent substrate (as COD), S is the concentration of the effluent substrate (as COD), and Kh is the first-order reaction constant (d-1). For a 25% conversion of the influent particulate COD into soluble COD, a typical yield for this process (see Table 5), the term (S0 - S)/S is equal to 0.33 and the required HRT is some 0.33/Kh. Assuming a collection basin for the organic municipal solid wastes of a population of some 100000 inhabitants and a collection capacity of the produced organic wastes of some 200 g/inhabitant/d, a typical figure in Europe,34 the minimum volumes required for the reactor for different temperatures of the process are those shown in Table 7. With reference to the costs, while building costs are strictly related to the volume of the reactor, managing costs depend on the specific situation: if the fermentation reactor is part of a plant for anaerobic digestion with energy recovery, heating costs will be negligible as part of the warming energy is recovered from the biogas combustion. Costs for reactor building were
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determined according to Vallini et al.,35 by means of the following formulas
EC ) 0.426‚V0.85
(6)
CC ) 0.235‚V0.916
(7)
where EC is the capital cost for electro-mechanical equipment (thousands Euros), CC is the cost of civil works (thousands Euros), and V is the reactor volume (cubic meters). Calculated costs were then actualized. Costs for mesophilic and thermophilic reactors were then increased a further 20% to consider the major costs for heat exchangers. Resulting costs are reported in Table 7: costs for electro-mechanical equipment are always higher than costs for civil works. In fact, an important issue when considering mixed reactors treating solid waste is the adoption of properly designed mixers and sufficiently high power applied (some 0.2 kW per cubic meter of reactor). However, besides costs strictly related to the reactor, the costs for the receiving and treatment line should also be considered: for a complete line treating some 15 tons of organic waste per day costs are some 1.5 million Euros, while typical managing costs are some 50 Euros per ton of treated waste.36 4. Conclusions The study of the psychrophilic anaerobic fermentation of organic municipal solid wastes enabled completion of the information related to the effect of temperature on anaerobic processes for the production of soluble organic compounds. According to the results of this and previous studies, the following conclusions can be summarized: (a) Anaerobic fermentation of organic solid wastes is a reliable process for the production of soluble organic compounds to be used as a substrate in methane production processes, as an external carbon source in biological nutrients removal processes for wastewater treatment, or as a source for further production of valuable organic compounds. (b) The highest concentration of soluble COD in the effluent is generally observed for a hydraulic retention time of 1-3 d; typical conversion rates ranged between 0.2 and 0.9 g of soluble COD per gram of total volatile solid fed to the reactor, passing from the psychrophilic to the mesophilic/thermophilic environment. After 4 d of reaction the soluble COD tends to decrease because of its conversion into biogas or to the inhibition due to fatty acids accumulation. Volatile fatty acids were some 10-15% of the soluble COD in psychrophilic conditions, while they reached values up to 50-75% in mesophilic and thermophilic conditions. Reported yields are strongly dependent on the kind of treated waste (i.e., source sorted, separately collected, or mechanically selected). Psychrophilic processes can be considered for the production of raw soluble COD to be used in nutrient removal processes because of their low managing costs. (c) Kinetic studies showed that the first-order reaction constant for hydrolysis, Kh, was 0.11 d-1 for the psychrophilic process and reached values in the range 0.20.4 d-1 in mesophilic and thermophilic conditions. However, thermophilic processes showed some problems of stability when treating highly biodegradable wastes and a partial recycle of the biomass was necessary.4,5
Acknowledgment The Italian Ministry for University and Scientific Research (FAR projects) and SETA SpA, Vigonza (Padova), are acknowledged for their financial support and hospitality. Literature Cited (1) Mata-Alvarez, J. Biomethanisation of the organic fraction of municipal solid wastes; International Water Association Publishing: London, UK, 2002. (2) Pandey, A.; Soccol, C. R.; Mitchell, D. New developments in solid-state fermentation: I - bioprocesses and products. Process Biochem. 2000, 35, 1153. (3) Viturtia, Mtz. A.; Mata-Alvarez, J.; Sans, C.; Costa, J.; Cecchi, F. Chemicals production from wastes. Environ. Technol. 1992, 13, 1033. (4) Sans, C.; Mata-Alvarez, J.; Cecchi, F.; Pavan, P.; Bassetti, A. Acidogenic fermentation of organic urban wastes in a plug-flow reactor under thermophilic conditions. Bioresour. Technol. 1995, 54, 105. (5) Sans, C.; Mata-Alvarez, J.; Cecchi, F.; Pavan, P.; Bassetti, A. Volatile fatty acids production by mesophilic fermentation of mechanically sorted urban organic wastes in a plug-flow reactor. Bioresour. Technol. 1995, 51, 89. (6) Argelier, S.; Delgenes, J. Ph.; Moletta, R. Design of acidogenic reactors for the anaerobic treatment of the organic fraction of solid food waste. Bioprocess Eng. 1998, 18, 309. (7) Traverso, P. G.; Pavan, P.; Bolzonella, D.; Innocenti, L.; Cecchi, F.; Mata-Alvarez, J. Acidogenic fermentation of source separated mixtures of vegetables and fruits wasted from supermarkets. Biodegradation 2000, 11, 407. (8) D’Addario, E.; Pappa, R.; Pietrangeli, B.; Valdiserri, M. The acidogenic digestion of the organic fraction of municipal solid-waste for the production of liquid fuels. Water Sci. Technol. 1993, 27, 183. (9) Chua, H.; Yu, P. H. F.; Ho, L. Y. Coupling of waste water treatment with storage polymer production. Appl. Biochem. Biotechnol. 1997, 63, 627. (10) Dionisi, D.; Majone, M.; Papa, V.; Beccari, M. Biodegradable polymers from organic acids by using activated sludge enriched by aerobic periodic feeding. Biotechnol. Bioeng. 2004, 85, 569. (11) Dionisi, D.; Renzi, V.; Majone, M.; Beccari, M.; Ramadori, R. Storage of substrate mixtures by activated sludges under dynamic conditions in anoxic or aerobic environments. Water Res. 2004, 38, 2196. (12) Cecchi, F.; Battistoni, P.; Pavan, P.; Fava, G.; MataAlvarez, J. Anaerobic digestion of OFMSW and BNR processes: a possible integration. Preliminary results. Water Sci. Technol. 1994, 30, 65. (13) Pavan, P.; Battistoni, P.; Traverso, P.; Musacco, A.; Cecchi, F. Effect of addition of anaerobic fermented OFMSW on BNR process: preliminary results. Water Sci. Technol. 1998, 38, 327. (14) Pavan, P.; Battistoni, P.; Bolzonella, D.; Innocenti, L.; Traverso, P.; Cecchi, F. Integration of wastewater and OFMSW treatment cycles: from the pilot scale experiment to the industrial realisation. The new full scale plant of Treviso (Italy). Water Sci. Technol. 2000, 41, 165. (15) Battistoni, P.; Pezzoli, S.; Bolzonella, D.; Pavan, P. The AF-BNR-SCP process as a way to reduce global sludge production: comparison with classical approaches on a full scale basis. Water Sci Technol. 2002, 46, 89. (16) Llabres, P.; Pavan, P.; Battistioni, P.; Cecchi, F.; MataAlvarez, J. The use of organic fraction of municipal solid waste hydrolysis products for biological nutrient removal in wastewater treatment plants. Water Res. 1999, 33, 214. (17) Andreottola, G.; Canziani, R.; Foladori, P.; Ragazzi, M.; Tatano, F. Laboratory scale experimentation for RBCOD production from OFMSW for BNR systems: results and kinetics. Environ. Technol. 2000, 21, 1413. (18) Lim, S. J.; Choi, D. W.; Lee, W. G.; Kwon, S.; Chang, H. N. Volatile fatty acids production from food wastes and its application to biological nutrient removal. Bioprocess Eng. 2000, 22, 543.
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(19) Bolzonella, D.; Innocenti, L.; Pavan, P.; Cecchi, F. Denitrification potential enhancement by addition of the anaerobic fermented of the organic fraction of municipal solid waste. Water Sci. Technol. 2001, 44, 187. (20) Vieitez, M.; Ghosh, S. Biogasification of solid waste by twophase anaerobic fermentation. Biomass Bioenergy 1999, 16, 299. (21) Pavan, P.; Battistoni, P.; Mata-Alvarez, J.; Cecchi, F. Performance of thermophilic semi-dry anaerobic digestion process changing the feed biodegradability. Water Sci. Technol. 2000, 41, 75. (22) Dinamarca, S.; Aroca, G.; Chamy, R.; Guerrero, L. The influence of pH in the hydrolytic stage of anaerobic digestion of the organic fraction of urban solid waste. Water Sci. Technol. 2003, 48, 249. (23) Pavan, P.; Veglio`, F.; Traverso, P.; Battistoni, P.; Cecchi, F. Acidogenic fermentation of the organic fraction of MSW. In Proceedings of ECCE 1, Florence, Italy, May 4-7, 1997. (24) Borzacconi, L.; Lopez, I.; Anido, C. Hydrolysis constant and VFA inhibition in acidogenic phase of MSW anaerobic degradation. Water Sci. Technol. 1997, 36, 479. (25) Yu, H. Q.; Fang, H. Acidogenesis of gelatin-rich wastewater in an upflow anaerobic reactor: influence of pH and temperature. Water Res. 2003, 37, 55. (26) Babel, S.; Fukushi, K.; Sitanrassamee, B. Effect of acid speciation on solid waste liquefaction in an anaerobic acid digester. Water Res. 2004, 38, 2417. (27) Moser-Engeler, R.; Kuhni, M.; Bernhard, C.; Siegrist, H. Fermentation of raw sludge on an industrial scale and applications for elutriating its dissolved products and non sedimentable solids. Water Res. 1999, 33, 3503. (28) Veeken, A. H. M.; Hamelers, B. V. M. Effect of temperature on hydrolysis rates of selected biowaste componenets. Bioresour. Technol. 1999, 69, 249. (29) Zeeman, G.; Palenzuela, A. R.; Sanders, W.; Miron, Y.; Lettinga, G. Anaerobic hydrolysis and acidification of lipids proteins and carbohydrates under methanogenic and acidogenic
conditions. In Proceeedings of the 2nd ISAD-SW, Barcelona, June 15th-18th, 1999; Mata-Alvarez, J., Cecchi, F., Tilche, A., Eds.; pp 21-24. (30) Christ, O.; Wilderer, P. A.; Angerhofer, R.; Faulstich, M. Mathematical modelling of the hydrolysis of anaerobic processes. Water Sci. Technol. 2000, 41, 61. (31) Garcia-Heras, J. L. Reactor sizing, process kinetics and modelling of anaerobic digestion of complex wastes. In Biomethanisation of the organic fraction of municipal solid wastes; MataAlvarez, J., Ed.; International Water Association Publishing: London, UK, 2002. (32) Vavilin, V. A.; Rytov, S. V.; Lokshina, L. Ya. A balance between hydrolysis and methanogenesis during the anaerobic digestion of organic matter. Microbiology 1999, 66, 712. (33) Viturtia Mtz, A.; Llabres, P.; Cecchi, F.; Mata Alvarez, J. 2-Phase kinetic-model fitting in a 2-phase anaerobic-digestion of highly biodegradable organic-matter. Environ. Technol. 1995, 16, 379. (34) European Environment Agency. Review of selected waste streams. Technical Report 69, 2002. (35) Vallini, G.; Cecchi, F.; Pavan, P.; Pera, A.; Mata-Alvarez, J.; Bassetti, A. Recovery and disposal of the organic fraction of municipal solid-waste (MSW) by means of combined anaerobic and aerobic bio-treatments. Water Sci. Technol. 1993, 27, 121. (36) Pavan, P.; Bolzonella, D.; Innocenti, L.; Cecchi, F. The AFBNR-SCP process: focusing on the anaerobic codigestion step of sewage sludge and OFMSW in the full scale experience of an OFMSW/wastewater integrate treatment. Proceedings of the ISWA World Congress, Rome, Italy, October 2004.
Received for review November 2, 2004 Revised manuscript received February 28, 2005 Accepted March 2, 2005 IE048937M
