Anaerobic Treatment Systems of Wastewater

Seasonal operation of olive oil mills is not a disadvantage for anaerobic treatment systems because anaerobic digesters can be easily restarted after several months of mill shutdown [51]. At present there are no large-scale plants. However, the anaerobic contact reactors and upflow sludge-blanket reactors have been mainly studied using several pilot tests (Fig. 7), besides other tested reactors such as anaerobic filters and fluidized-bed reactors.

Sludge retention is decisive for the load capacity and thus the field of application of an anaerobic reactor. In the UASB reactor, favorable sludge retention is realized in a simple way. Wastewater flows into the active space of the reactor, passing from the bottom to the top of the reactor. Owing to the favorable flocculation characteristics of the anaerobic-activated sludge, which in higher-loaded reactors normally leads to the development of activated sludge grains and to its favorable sedimentation capacity, a sludge bed is formed at the reactor bottom with a sludge blanket developing above it. To avoid sludge removal from the reactor and to collect the biogas, a gas-sludge separator (also called a three-phase separator) is fitted into the upper part of the reactor. Through openings in the bottom of this sedimentation unit, the separated sludge returns into the active space of the reactor. Because of this special construction, the UASB reactor has a very high load capacity. In contrast to the contact sludge process, no additional sedimentation tank is necessary, which would require return sludge flow for the anaerobic activated sludge, resulting in a reduction of the effective reactor volume. Several studies on anaerobic treatment of olive oil wastewaters have been carried out, and data from different publications are listed in Table 11.

Reactor Upflow Anaerobic Sludge Blanket
Figure 7 Anaerobic treatment processes: (a) Contact sludge reactor; (b) UASB reactor.

Table 11 Summary of the Data from Different Publications Related to Anaerobic Treatment of Olive Oil Wastewater

Aveni

Table 11 Summary of the Data from Different Publications Related to Anaerobic Treatment of Olive Oil Wastewater

Aveni

Fiestas

FIW38

(1984)44

FIW38

FIW38

FIW38

Steegmans Ubay

(1981)14

a

(1992)15

(1997)

Treatment

Contact

UASB

Contact

Conventional UASB

Packed-

UASB

UASB

process

process

reactor

process

reactor

reactor

bed reactor

reactor

reactor

Influent

33-42 g

4-6 g

20-65 g

5-15 g

45-50 g

26.7 g

5-22.6 g

bod5/l

COD/L

COD/L

COD/L

COD/L

COD/L

COD/L

Volumetric

1.2-1.5

15-20 kg

4 kg

20-65 kg

5-21 kg

1.59 kg

5-18 kg

loading

kg BOD/

COD/

COD/

COD/

COD/

COD/

COD/

(m3*day)

(m3*day)

(m3*day)

(m3*day)

(m3*day)

(m3*day)

(m3*day)

Purification

80-85%

70%

80-85%

80-85%

70-80%

45-55%

55.9%

70-75%

efficiency

BOD

COD

COD

COD

COD

COD

COD

COD

Gas

700 L/kg

550 L/kg

SOÛOL/

300-

50-100L

350 L

production

BODelim

CODelim

600

CH4/ kg

CH4/kg

L/kg

CODelim

CODelim

CODelim

Methane

70%

50-70%

70-80%

84%

70%

a Based on laboratory and pilot experimentation on diluted olive oil mill effluents. Source: Refs. 14, 15, 22, 38, 44.

a Based on laboratory and pilot experimentation on diluted olive oil mill effluents. Source: Refs. 14, 15, 22, 38, 44.

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