Biogas from anaerobic digestion of fruit and vegetable wastes: Experimental results on pilot-scale and preliminary performance evaluation of a full-scale power plant

Published Date
Energy Conversion and Management
January 2014, Vol.77:22–30, doi:10.1016/j.enconman.2013.09.004

Author 

• Efisio Antonio Scano ^a,b
• Carla Asquer ^a
• Agata Pistis ^a
• Luca Ortu ^a
• Valeria Demontis ^a
• Daniele Cocco ^b,,

• aBiofuels and Biomass Laboratory, Sardegna Ricerche, Z.I. Macchiareddu, 09010 Uta, CA, Italy
• bDepartment of Mechanical, Chemical and Materials Engineering, University of Cagliari, Via Marengo, 2 09123 Cagliari, Italy

Received 29 June 2013. Accepted 5 September 2013. Available online 8 October 2013. 

Highlights

• •
  Biogas production from anaerobic digestion of fruit and vegetable wastes was studied.
• •
  A pilot scale tubular reactor fed by single waste substrates was used.
• •
  The optimum organic loading rate ranged from 2.5 to 3.0 kg_VS/m³ d.
• •
  Biogas production was about 0.78 Nm³/kg_VS, with a methane content of 55%.
• •
  Preliminary design of a full-scale anaerobic digestion system was carried out.

Abstract

This paper presents the experimental results obtained through an anaerobic digestion pilot plant by using fruit and vegetable wastes as single substrate. The substrate materials were sampled from the wastes produced by the Fruit and Vegetable Wholesale Market of Sardinia (Italy).

The experimental study was carried out over a period of about 6 months to evaluate the most suitable operating parameters of the process depending on the availability of different kinds of fruit and vegetable wastes over the different periods of the year. Overall, the optimum daily loading rate of wastes was 35 kg/d, with a corresponding hydraulic residence time of 27 days. The optimum organic loading rate ranged from 2.5 to 3.0 kg_VS/m³ d and the average specific biogas production was about 0.78 Nm³/kg_VS, with a specific methane yield of about 0.43 Nm³/kg_VS.

The results of the experimental investigation were used for a preliminary performance evaluation of a full-scale anaerobic digestion power plant for treating all the fruit and vegetable wastes produced by the Wholesale Market of Sardinia (9 t/d). The estimate of daily methane production (290 Nm³/d) leads to a CHP unit with a power output of about 42 kW and an annual electrical production of about 300 MW h/year (about 25% of the wholesale market electrical consumption). The AD power plant also shows interesting economic features, since its energy production cost (about 150 €/MW h) is slightly lower than the energy purchase cost of the wholesale market (about 200 €/MW h) and a Pay-Back Time of about 7.25 years can be achieved in the case of dispatching the electrical energy to the national grid. The PBT decreases to about 5.4 years if 50% of the available thermal energy is used to substitute heat production from fossil fuel boilers.

Keywords

Anaerobic digestion

Fruit and vegetable waste

Biogas production

Mesophilic digestion

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Nomenclature

C_p

specific heat (J/kg K)

C_O&M

operation and maintenance cost (€)

C_T

total annual costs (€)

E_AUX

auxiliary consumption energy (kW h)

E_N

net energy production (kW h)

h

specific enthalpy (J/kg)

H

utilization factor (–)

m

mass (kg)

P_M

mechanical power (W)

Q_F

substrate feeding heat (J)

Q_H

reactor electrical heat (J)

Q_L

reactor heat losses (J)

Q_R

biochemical reaction heat (J)

S

reactor outer surface (m²)

t

time (s)

T_A

ambient temperature (°C)

T_R

reactor temperature (°C)

U

overall heat transfer coefficient (W/m² K)

η_M

mechanical efficiency (–)

Subscripts

B

biogas

D

digestate

F

feedstock

Acronyms

AD

anaerobic digestion

CCR

Capital Charge Rate

CHP

Combined Heat and Power

CoE

Cost of Energy

FOS/TAC

ratio of volatile organic acid to alkaline buffer capacity

FVWs

fruit and vegetable wastes

GPR

Gas Production Rate

HHV

Higher Heating Value

HRT

Hydraulic Residence Time

LHV

Lower Heating Value

OLR

Organic Loading Rate

TCI

Total Capital Investment

TS

Total Solid

VS

Volatile Solid

Fig. 1.

 Table 1

Table 1.

 Table 2

Table 2.

 Table 3

Table 3.

Fig. 2.

 Table 4

Table 4.

 Table 5

Table 5.

 Table 6

Table 6.

Fig. 3.

 Table 7

Table 7.

 Table 8

Table 8.

• ⁎ 
  Corresponding author. Tel.: +39 070 6755720; fax: +39 070 6755717.

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