Bioresource Technology 100 (2009) 5072–5078

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Bioresource Technology

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Development of a pilot scale anaerobic digester for biogas productionfrom cow manure and whey mix

Elena Comino a,*, Maurizio Rosso b, Vincenzo Riggio a

a Politecnico di Torino, Dipartimento di Ingegneria del Territorio dell’Ambiente e delle Geotecnologie, C.so Duca degli Abruzzi, 24, 10129 Turin, Italyb Politecnico di Torino, Dipartimento di Idraulica, Trasporti e Infrastrutture Civili, C.so Duca degli Abruzzi, 24, 10129 Turin, Italy

a r t i c l e i n f o

Article history:Received 10 March 2009Received in revised form 21 May 2009Accepted 22 May 2009Available online 25 June 2009

Keywords:Anaerobic digestionCow manureWheyEnergy production

0960-8524/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.biortech.2009.05.059

* Corresponding author. Tel.: +39 011 5647647; faxE-mail address: elena.comino@polito.it (E. Comino

a b s t r a c t

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaer-obic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. Theversatile and unique characteristics of the instrument allowed testing the methane production directly inthe farm. The digester performance was evaluated with two calibration tests, the main for a period of56 days. The study test was divided into three phases, one for each type of feeding operation (batch,fed-batch, batch). The initial phase of digestion resulted in 57 l-CH4/kg-VS, the second phase had a yieldof 86.6 l-CH4/kg-VS and the third one had a production of 67 l-CH4/kg-VS. The total methane yield wasequal to 211.4 l-CH4/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle,it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted testsdid show that there is a good potential to the use of a cow manure and whey biomass mix for biogasproduction.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

In the last decades, the use of anaerobic digestion has becomewidespread all across the European countries, thanks to the spe-cific legislative tools aimed to increase production of biogas inthe various economic sectors, such as from the agro industrial tozoo technical. The importance of this technology results in consid-erable environmental benefits (Chynoweth, 2004) and can be anadditional source of income for farmers. In Italy the biogas ismainly used to produce heat and electricity. Most of the biogas isobtained from organic waste present in landfills, for which, thanksto Legislative Decree No. 36 of 2003 (Decree 36/2003) assimilatedwith Directive 99/31/CE (Directive 99/31/CE) which is compulsoryto capture the gas emitted. A large quantity is also produced fromanaerobic digestion of crops and agro-industrial waste, and to alesser degree biogas is obtained from sludge and animal waste (Tri-case and Lombardi, 2008). In 2005 in Italy the total amount of elec-tricity generated from these substances has been, respectively, 3and 26 gwh. The trend of production of biogas from zoo technicalwaste from 1991 has been positive with an annual increase of1.36 gwh (ENEA, 2008). Anaerobic digestion of organic wastes toproduce energy, in the form of biogas, is the most likely optionto be of commercial interest, provided that the economics arefavorable. Economic efficiency depends on investment and operat-ing biogas plant costs, and on the optimum methane production

ll rights reserved.

: +39 011 5647699.).

(Walla and Schneeberger, 2005). The anaerobic digestion technol-ogy, properly implemented in a zoo technical reality, can also beused to control malodorous emissions. The stabilized biomasscan also be utilized as an excellent soil conditioner after appropri-ate treatment (Converti et al., 1999). The principle of a closed cir-cuit is strengthened because the nitrogen is being held strong bythe system (Möller, 2003). Protein, fat, fiber, cellulose, hemi-cellu-lose, starch and sugar markedly influence methane formation andare also the key factors for the methane yield from energy cropsand animal manure (Balsari et al., 1983). About 90% of the full scaleplants, currently in use in Europe, for the anaerobic digestion ofbiomass rely on continuous one-stage systems (Lissens et al.,2001). Another type of digestion operation is done in batch wheredigesters are filled once with fresh biomass, and allowed to gothrough all degradation steps sequentially. Other systems workin two steps, the first is the continuous digestion and the secondstep is batch digestion of the digested biomass. The hallmark ofbatch systems is the sharp separation between a first phase, whereacidification proceeds much faster than methanogenesis, and asecond phase, where acids are transformed into biogas (De Baere,2000). In terms of handling, this kind of process is easier but hasthe disadvantage of odors and gives some problems in emptyingthe cycle. In comparison to previous studies that have examinedthe methane yield of cattle manure or whey separately, the aimof the present research was to examine the methane yield fromcow manure and whey mix, considering that dairy farms of Pied-mont Region produce both wastes. For this purpose, an experimen-tal 128 l fed-batch anaerobic digester was developed. This volume

E. Comino et al. / Bioresource Technology 100 (2009) 5072–5078 5073

has been chosen in order to have data based on field-scale experi-ence and not on laboratory scale equipment. The reactor was useddirectly in a dairy farm. The test was conducted under three differ-ent feeding regimes: batch, fed-batch and batch. In this way, it waspossible to describe the evolution of total biomass, chemical oxy-gen demand (COD) behavior and methane production. Digestionof pig manure in batch condition was developed for the calibrationtest to assess the functionality and the efficiency of each part of thesystem during the co-digestion phases.

2. Methods

2.1. Experimental device

The designed digester can be loaded in both ways: a single loadfor each cycle, batch cycle or staged loads, with loading andunloading operations during the same cycle of work, batch orfed-batch. The experimental device realized and used in the tests(Fig. 1) was designed in a way to be easily transported and to as-sure the remote monitoring. The total surface occupied by the de-vice is 1.20 m2 with a height of 2.30 m.

The system can be divided into four different parts: control pa-nel, feeding system, digester and agitation system and gasometer.

(a) The control panel, located in a protective and closed box, con-tains all the electric system controls required for the func-tioning of the digester and collection of analytical data. Inthe upper part two LCD monitors are mounted, one is the‘‘Liquiline MCM42” connected to the pH probe (EndressHauser CPS-11D) and the other is the data logger (Endress

Fig. 1. Technical scheme of biogas anaerobic dige

Hauser Ecograph T RSG30). On the lower part of the panel,located on the electric board, are the mixer system speedregulator (Altivar ATV11) and the GSM modem, whichallows remote access to the analytical data collected in thedata logger. The regulation of the temperature and the pres-sure probes, in the digester and in the gasometer, is operatedby automatic switches.

(b) The feeding system is at the top of the reactor. For thebiomass loading a 76.19 mm diameter hole is present. Thesupply system is realized with a pipe controlled with threesubsequent valves. These valves allow the feeding of thereactor, avoiding air immersion into the digester. Thissystem is useful during the initial phase when it is importantto purge the air out of the reactor with nitrogen gas(Table 1).

(c) The digester is cylindrical and is made of 316 stainless steel,height in 94 cm and diameter in 40.3 cm, 128 l, of which102.8 l is the filling volume. The mixing system consists oftwo 316 stainless steel propellers, whose rotation is pro-vided by an electric three-phase motor (380 V) operated byan inverter through the control panel. The digester isequipped with temperature and pH probes. The pH sensoris manually inserted in the reactor, through a hole equippedwith a series of scaling valves. The T sensor is constantlyactive. The external surface of the digester is wrapped with15 m of electrical resistance, to maintain a constant temper-ature of 35 �C, and fully covered with insulating material toreduce the dispersion/loss of heat. A gauging valve of12.7 mm on one side of the digester permits the collectionof the samples for chemical analysis. A 76.19 mm valve

ster used by our group for the different tests.

Table 1Digester valves details and functions.

Valve Diameter(inch)

Diameter(mm)

Type Material Function

V1 3 76.19 Ball 316 SteelInox, coatingof Teflon

Reactor input

V2 3 76.19 Ball 316 SteelInox, coatingof Teflon

Reactor input

V3 7 12.7 Ball 316 SteelInox, coatingof Teflon

Allow the supply ofNitrogen in the system,allowing the initiation

V4 7 12.7 Ball 316 SteelInox, coatingof Teflon

Exit in case of overload

Table 2calibration test physical and chemical parameters, subdivided chronologically.

Parameter Inlet mix firstday

Biogassample

Outlet mix lastday

pH 7.68 8.03BOD5 (mgO2/l) 1600 680COD (mgO2/l) 8600 5200Density (g/cm3) 1.022 1014105� Residual (% p/p) 1.9 1.5505� Residual (% p/p) 1.1 1Total volatile solid (% p/p) 0.8 0.5NH4 (mg/l) 1000 900Volatile acid fat <10 <10Methane (CH4) (% v/v) 19.3Carbon dioxide (CO2) (% v/v) 10.9Oxygen (O2) (% v/v) 3Nitrogen (N) (% v/v) 66.4

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located at the bottom allows the unloading of digestedmaterial. The biogas produced by the digestion of biomassenters the gasometer through a 12.7 mm diameter pipe. Inthe lower part of this pipe the 1 l condensate catcher permitsthe discharge of condensate.

(d) The gasometer has two sections – a fixed and a mobile one,90 cm in height, 40.3 cm in diameter, with a total volumeof 122.8 l, and made of 316 stainless steel. The biogas col-lected inside the gasometer is allowed by a hydraulic closureformed by a saturated aqueous solution of sodium chlorideand 10% sulfuric acid (Garcia-Ochoa et al., 1999). A coupleof sensors enabling real-time monitoring of temperatureand pressure are located at the top. A water column to readof the level inside the gasometer and a valve to empty thewater is in the external part. In the bottom of the gasometeris placed a valve to empty the produced biogas. The measureof biogas yield is obtained with the movement of a slide-wired potentiometer, that is linked from one side with thetank upper part and with the chassis from the other.

2.2. Experimental procedure

The functionality of the different probes and the efficiency ofthe electric resistance that keeps the digester temperature at35 �C have been tested before starting the study experiment (Gav-ala et al., 2003). Next to the gasometer is located a nitrogen tank of5 l at 200 atm, with a pressure reducer. Before loading nitrogen gasis introduced inside the digester to displace the air out. The mixing

Fig. 2. Mix system relationship between inv

system is controlled by a knob that can change the inverter (Altivar11) frequency and so the propeller speed (Fig. 2).

2.2.1. Calibration testTwo calibration tests were performed to check the efficiency of

the digester. For both calibration tests 97 kg of pig manure from alivestock located in Turin district was used, mixed with 2 kg of bac-terial inoculum from a local wastewater treatment plant and 2 l ofwater. The substrate was stirred every two days at 22 rpm for aduration of 30–45 min. The first calibration test was carried outfor 19 days, the second one for 38 days. Effluent and biogas sam-ples were collected for analysis (Table 2 and 3). Meanwhile a workprocedure for the co-digestion test was created (Table 4). File-maker database was set up to collect, organize, store and auditthe experimental data.

2.2.2. Feed materialThe feed material was composed of cow manure, whey and

inoculum. Cow manure (200 l) was collected at the exit of thestable grid from the livestock farm ‘‘Fontanacervo” located in Vil-lastellone (Turin – Italy). Part of it was used to fill the digester,and part was stored at �4 �C for feeding the system. Freezinghas a measurable effect on the degradability of organic matter(Huntington and Givens, 1997; Hristov, 1998). The farm hasdiary activities that allowed the collection of 50 l of fresh whey,needed to complete the mix to be tested. Bacterial inoculum(32 l) was added to the mix in order to start the first phase. Inthe cow manure the VS was equal to 11.4%, in whey was

erter frequency and round per minute.

Table 3Second calibration test physical and chemical parameters, subdividedchronologically.

Parameter Inlet mix firstday

Biogassample

Outlet mix lastday

pH 7.43 7.96BOD5 (mg O2/l) 1900 430COD (mg O2/l) 11,000 7200Density (g/cm3) 1.019 1011105� Residual (% p/p) 2.4 0.7505� Residual (% p/p) 1.3 0.49Total volatile solid (% p/p) 1.1 0.21NH4 (mg/l) 900 1200Volatile acid fat <10 <10Alkalinity (mg CACO3/l) 8250Chrome (mg/l) <0.5Nickel (mg/l) 0.1Iron (mg/l) 13.8Cobalt (mg/l) <0.5Sulfides (mg/l) <0.1Methane (CH4) (% v/v) 26.5Carbon dioxide (CO2) (% v/v) 14.2Oxygen (O2) (% v/v) 2.3Nitrogen (N) (% v/v) 56.2

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5.48%; BOD5 values were, respectively, 82 g/l, 35 g/l, in cow man-ure and whey; COD values were equal to 152 g/l and 77.3 g/l,respectively. The influent and effluent details are presented inTable 5.

2.2.3. Co-digestion testThe digester was fed with 80 l of mix: 32 l cow manure, 32 l

whey and 16 l inoculum. The substrate was mixed for 15 min at28 rpm. After the mixing the nitrogen initiaion phase was per-formed and every valve was sealed. The mixer was set to work con-tinuously at a speed of 12 rpm. pH and temperature sensors wereinserted and the heating system was activated. The gas productionwas checked after 2, 7, 9, 15 and 16 days. The gasometer was reg-ularly emptied; the pH value and the temperature were monitored.During this period the condensate catcher was checked and emp-tied every 2 days. On the 16th day, the feed phase with the unload-ing and loading operation was started for three times a week untilthe 30th day. During this operation 4 l of substrate was unloadedand then 4 l of mix was (3.2 l of cow manure plus 0.8 l of wheystored in the refrigerator) loaded. Retention times of at least 3 daysare required to achieve 90% removal of influent BOD, giving loadingrates of between 1.5 and 2 kg BOD m�3 day�1 (Eckenfelder, 1980).After the last charge the system was let to work until stabilizationin the biogas production. The entire test was stopped on the 55thday when the reaction was stabilized. Eight samples for the chem-

Table 4Experimental device procedure for different operational situations.

Preliminary operations Loading procedures

� pH probe calibration (7–4 solution)� Digester visual check up and gasom-

eter water level check� Horizontal stabilization of the

gasometer� Biomass barrel weighing� Checkup of valves position� Control panel visual check up

� Propeller check up and speed set� pH probe position and valves visual chec� Visual checkup of gasometer height� Check the pipe link between the Nitrogen

inder and digester� Correct position of feeding valves V1 and� Feed the biomass inside the digester

desired level of substrate is reach� Close V1 valve� Start the propeller� Collect samples of mixed biomass for ana� Shut down the propeller� Calculate the free volumes inside� the digester and the gasometer

ical analysis were collected, six to characterize the substrate singlecomponents, and two for the biogas.

3. Analytical methods

For both calibration tests, the substrate samples were taken atthe beginning and at the end of the experiment, whereas for thebiogas analysis, a single sample was taken in the middle of the testperiod. BOD5 was analyzed with the ‘‘IRSA – CNR no. 5100 A/94”method, COD with the ‘‘IRSA – CNR no. 5110/94” method, pH with‘‘IRSA – CNR Quad 100 met. 2080/94” method, and from directly in-side the digester with the pH probe. Density was calculated withthe ‘‘EMRO/012/1999” method, 105 �C residual, and the 550 �Cresidual and Total Volatile Solids were obtained with the ‘‘IRSA –CNR Quad. 64 no. 2.4.2/84” method. Ammoniacal nitrogen (NHþ4 )was obtained following the IRSA/APAT guidelines 29/2003 met.no. 4030C, the Volatile Fatty Acids (C1–C6) were measured withthe ‘‘EMGC 003/1999” method. In the biogas samples were mea-sured methane, carbon dioxide, oxygen and nitrogen with the‘‘EMGC 032/2000 (GC/MS)” method. The metal values were con-trolled, so a sample at the end of the test was collected for analysisof chrome, cobalt, nickel (IRSA – CNR no. 3140 Q 100/94), iron(IRSA – CNR no. 3090 Q 100/94) and sulfides (I.L. no. 8). In this sam-ple the alkalinity with the ‘‘ARPA – CNR/IRSA 2010 met. B 2003”method was also evaluated. In the cow manure and whey mix testseveral samples both from single component and also from boththe mixed substrates were collected, two measurements of biogaswere done. The aim was to follow the three different phases of thetest: beginning (batch), stabilization (fed-batch) and end of theprocedure (batch). The analysis was conducted with the followingmethods: pH with ‘‘I.L. no. 124”, density with ‘‘ASTM no. D 1298”,alkalinity using ‘‘APAT – CNR/IRSA 2010 Met. B 2003,” suspendedsolids using ‘‘CNR IRSA 2050 Q 100/94,” BOD5 with ‘‘I.L. no. 55,”COD with ‘‘CNR IRSA 5110 Q 100/94,” ammoniacal nitrogen with‘‘I.L. no. 27” and hydrogen sulfide (H2S) with ‘‘I.L. no. 8”. The deter-mination of biogas parameters were obtained with ‘‘I.L. no. 704”method for methane, carbon dioxide, carbon monoxide, oxygenand nitrogen. Tables 5 and 6 show the analytical results for everysample.

4. Results and discussion

4.1. Calibration test

The first calibration test had a lifetime of 19 days, the digestionfollowed all the expected phases and had a yield of 104 l-CH4/kg-VS. The second calibration test was conducted for a period of38 days and a production yield of 123 l-CH4/kg-VS was obtained

Initiating procedures(Digester – Gasometer)

Unloading procedures

k up

gas cyl-

V3until the

lysis

� Open V9 valve� Open V4 valve� Open Nitrogen cylinder

knob� Check the inlet Nitrogen

volumes� Close all valves� Check the electric resis-

tance warming up� Start the propeller

� Control the closure of all valves� Agitate the digester and collect

the needed samples� Collect gasometer samples� Empty the gasometer� Open the fedding valves V1 and

V3� Open the digester unloading

valve� Shut down the electric panel� Empty the digester� Clean the digester� Visual control of the closure of all

valves

Table 5Inffluent–effluent analysis of each component of the mix in sample tested.

Parameter Whey 1st Day Cow manure 1st Day Inoculum 1st Day Cow manure 16th Day Digested 16th Day Digested 56th Day

pH 5.64 8.93 8.49 8.38 8.61 8.36Density (kg/dm3) 1.017 1.079 1.099 1.032 1.071 1.073Alkalinity (mgCaCO3/l) 4400 20,000 21,000 17,600 17,600 20,300Suspended materials (mg/l) 67,800 126,400 47,900 132,000 62,400 36,700BOD5 (mg/l) 35,000 82,000 27,200 65,000 23,100 11,700COD (mg/l) 77,300 152,000 50,400 140,000 58,600 26,600TVS (%) 5.48 11.4 3.49 10.8 4.65 2.31VFA (%) 0.39 0.6 0.37 0.21 0.06 0.25N (% ss) 0.21 2.13 3.55 0.97 3.02 3.13S (mg/l) 0.02 0.08 <10 <10 <10 <10

Table 6Biogas samples analysis of cow manure and whey mix test.

Parameter Biogas sample 16th day Biogas sample 56th day

Methane (CH4) (% v/v) 47.5 51.4Carbon dioxide (CO2) (% v/v) 46.2 46.8Carbon monoxide (CO) (% v/v) 0.08 0.1Oxygen (O2) (% v/v) 0.5 0.2Nitrogen (N) (% v/v) 5.0 1.1

5076 E. Comino et al. / Bioresource Technology 100 (2009) 5072–5078

(Fig. 3). These data are in agreement with those carried out byMÖller et al. (2004), even if they obtain a methane yield of 356 l/kg-VS. He obtained a higher biogas production due to higher valuesof VS. The effluent of the second calibration test had 13.8 mg/l ofiron. It is possible to assume that this anomalous high value isdue to the storage method of the pig manure at the farm.

4.2. Co-digestion test

The pH dropped rapidly at the beginning of each experiment, asthe easily digestible fraction of organic matter was hydrolyzed andconverted to fatty acids. After the initial drop, the pH began to risegradually as the fatty acids were consumed by methanogens bacte-ria. The fluctuation of pH during the second phase of the experi-ments was due to the periodic unloading/loading operations(Fig. 5). The value ranged between 8.4 and 7.7, due to the normalphases of anaerobic digestion and fully compatible with the opti-mal working range (Prasad et al., 2007; Macias-Corral et al.,2008). T was maintained at 35 �C in each phase of the digestion.

Fig. 3. Process performance during anaerobic digestion

The COD reduction was monitored, in order to verify efficiency.The values ranged between 45% and 47%. The lower value was ob-tained during the fed-batch phase where biodegradable fraction ofthe mixture was lowered by an addition of dairy manure in the mixcomposition. Similar range of values were obtained by Lo and Liao(1989) during their experiment for the anaerobic treatment of asimilar mix. The trend of biogas production is presented in Fig. 6.The cumulative curve represents the three phases of the experi-ment: the first part of the curve is characterized by a very rapidtrend, the intermediate is rather disjointed and shows a represen-tative production from fed-batch feeding, the last one is verysmooth and shows the beginning of the microorganism deathphase, with progressive reduction of production rate, typical ofbatch reactions (Gavala et al., 2003). From days 52 to 56, the curvebecomes almost horizontal, confirming the strong reduction inproduction that comes at the end of the treatment (Garcia-Ochoaet al., 1999). The test follows the three different loading phaseseach with its own characteristics and methane yield (Fig. 4).

From day 1 to day 16, using the data obtained from the labora-tory, the total quantity of produced biogas was equal to 694 l, thatconsidering a CH4 proportion around 50% was 347 l of methane.With VS (6.04 kg) calculated as the weighted sum of the threemix components, the methane yield was equal to 57 l-CH4/kg-VSfor 16-day test. In the second phase, from day 16 to day 30 the totalquantity of produced biogas was equal to 689.7 l, thus around344.85 l of methane. At 3.98 kg of VS (obtained from the analysisof the sample collected on the 16th day) the methane yield wasequal to 86.6 l-CH4/kg-VS for 14 test days. In the last phase, fromday 30 to day 56, a total quantity of produced biogas equal to536.6 l was obtained, with around 268.3 l of methane. With

of pig manure in the two calibration tests at 35 �C.

Fig. 5. pH values obtained by the digester pH probe during the cow manure and whey test.

Fig. 6. Cumulative biogas production curve for the cow manure and whey mix.

Fig. 4.

E. Comino et al. / Bioresource Technology 100 (2009) 5072–5078 5077

3.98 kg of VS (obtained from the sample collected on the 16th day)the production of methane was of 67 l-CH4/kg-VS for 14 test days.

Summing all the values, the obtained biogas production value wasequal to 1919.7 l and then about 959.85 l of CH4. The biogas pro-

5078 E. Comino et al. / Bioresource Technology 100 (2009) 5072–5078

duction was equal to 422.8 l/kg-VS, and consequently the methaneproduction was equal to 211.4 l-CH4/kg-VS during the 56 days oftest. Brachtl (2000) and Thomé-Kozmiensky (1995) digested cattlemanure and found biogas yields between 200 and 300 l biogas (kg-VS�1). Braun (1982), in his review paper on biogas production fromcattle manure, has reported a yield between 140 and 266 Nl biogas(kg-VS�1), whereas Amon et al. (2007) have obtained biogas frommaize and dairy cattle manure in a yield between 208 and267 Nl (kg-VS�1). Lo and Liao (1989) had tested a similar mix ofwhey and cow manure with 2:1 ratio, obtaining a methane yieldof 0.222 l g�1 VS for a 5-day HRT. This value is comparable withthat obtained in the performed test that gave methane yields of0.131 l g�1 VS with a mix of whey and cow manure of 1:1 for thesame HRT. Most of the biodegradable carbon in cattle feed is al-ready digested in the rumen and in the gut. Thus, cow manurehas a lower potential to produce biogas than pig or poultry manureand CH4 concentration in the biogas is lower (Weiland, 2001).

The efficiency of the reactor was confirmed in both three feed-ing phases. The first one fed with an influent mix containing awhey fraction of 30%, a manure fraction of 59% and an inoculumsfraction of 9.8% in terms of COD. COD in the feed was 102 g/l,HRT = 16 days and reactor temperature of 35 �C. The operated reac-tor reached stable conditions quite soon producing biogas for a to-tal value of 694 l and a reduction of COD equal to 42%. The secondphase started with a value of COD in the feed equal to 58.6 g/l,OLR = 255 g, COD/lR and HRT = 14 days. The operated reactor wasmaintaining stable condition and producing biogas for a total valueof 689.7 l (biogas production increases about 6%). In the thirdphase COD in the feed was equal to 58.6 g/l and HRT = 14 days.The anaerobic digester revealed an excellent functionality andreached a strong stabilization that led to a production of 536.6 lat the end of the test (biogas production decreases about 12.5%)and a COD reduction of 45.4%. In quantitative terms the usedexperimental mix substrate allowed to obtain a biogas productionin line with literature values, and in particular gave a total produc-tion of 211.4 l-CH4/kg-VS. Very high rates of BOD5 (78%) and COD(74%) removal can be achieved. In a regional territory where thepresence of cows is in over 837,000 units, the production of biogasfrom cow manure by anaerobic digestion is a good opportunity. In-deed in 2007, 22 biogas plants were scattered all around Piedmontand in the same year in the national territory 215 similar plantscould be counted (ARPA, 2008).

5. Conclusion

The developed pilot scale digester is quite innovative for itsdimensions and for its easy transportability in a farm, giving thepossibility to conduct the test directly in situ. The co-digestion isrelieved to be an extremely useful instrument for better calculationof the biogas productivity besides it being versatile and reliable.

This technology can solve two complex problems. On one side isthe methane production, on the other it allows a first efficientwastes treatment. It is clear that the utility better investigatesthe mix composition considering the workflow optimizing of theexisting biogas plant at the farm. Using the results of the pilot plantto a real scale diary production cycle, it is possible to obtain anelectricity production equal to 8.86 kwh per 1 t/d. The monitoringof the phenomena and the results of the analysis are done follow-ing an approach that gives the possibility to repeat the experimentin any moment and place. This is one of the fundamental aims ofthe scientific research: to give anyone and at any time the possibil-ity to repeat and verify the results starting from the sameconditions.

Acknowledgements

The authors particularly thank J.P. Schwithzguebel for his helpduring the manuscript revision. The research was funded by Regi-one Piemonte.

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