Producers in Greece Generate Electricity with Olive Mill Wastewater

Producers can save money and be more sustainable by shipping olive mill wastewater to local biogas production plants.
May. 4, 2021
Sofia Spirou - Agronews

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Following the pro­duc­tion of bio­gas from live­stock waste, anaer­o­bic diges­tion tech­nol­ogy is now emerg­ing as a solu­tion for man­ag­ing olive mill waste­water in Greece.

With the first bio­gas plants now pro­cess­ing liq­uid waste pro­duced through olive oil extrac­tion, a small group of olive oil pro­duc­ers in north­ern Greece can rid them­selves of the respon­si­bil­ity of dis­pos­ing of the toxic mate­r­ial while con­tribut­ing to the pro­duc­tion of green energy.

However, there are still some chal­lenges involved. The quan­ti­ties of olive mill waste­water cur­rently feed­ing bio­gas plants are extremely low in rela­tion to the total amount pro­duced across the coun­try.

However, experts point to Italy, sug­gest­ing there are sim­i­lar prospects for apply­ing the tech­nol­ogy to those of their neigh­bor.

No need for evap­o­ra­tion tanks

For the Kyklopas SA olive mill, in Evros, in north­east­ern Greece, the dis­posal of olive mill waste for bio­gas pro­duc­tion is a wel­come solu­tion in the man­age­ment of the toxic residues.

Our coop­er­a­tion with the pro­duc­tion unit of Biogas Komotini SA has taken a bur­den off our backs,” Niki Kelidou, of Kyklopas SA, said. Despite the fact that we have a license to dis­pose of the residue in our unit, the man­age­ment of waste­water is a job that requires sig­nif­i­cant effort and costs as the quan­ti­ties we pro­duce are high.”

The fam­ily-owned olive mill pro­duces 3.4 mil­lion liters of liq­uid waste­water annu­ally as a byprod­uct of its annual pro­duc­tion of 260 tons of olive oil.

See Also: Biomass from Olive Groves Fuels Heineken Factory in Southern Spain

The cost of build­ing the reser­voir where the liq­uid waste was deposited for evap­o­ra­tion was €40,000 and we built it just two years before we started col­lab­o­rat­ing with the bio­gas plant,” Kelidou said. Had we struck the deal ear­lier, we would not have built the tank.”

In addi­tion to con­struc­tion costs, the main­te­nance of the dis­charge basin incurs addi­tional expenses.

Every two to three years, the tank must be emp­tied and the thick sludge has to be scraped,” Kelidou said. Moreover, we incurred trans­port costs because the tank is located at a dis­tance of 20 kilo­me­ters from the olive mill.”

An addi­tional fac­tor that enabled the coop­er­a­tion with the bio­gas plant is the short dis­tance that sep­a­rates them, which keeps trans­porta­tion costs rel­a­tively low.

The Komotini bio­gas plant is only 50 kilo­me­ters from the mill,” Kelidou said. This is cru­cial because, dur­ing the oper­a­tion of the mill, about five tanks are loaded on a daily basis and trans­ported to the bio­gas plant.”

A great envi­ron­men­tal haz­ard

The prob­lem of olive mill waste­water man­age­ment is acute as the quan­ti­ties pro­duced amount to sev­eral hun­dred thou­sand tons.

In fact, the prob­lem con­cerns all olive oil-pro­duc­ing regions in the Mediterranean. The annual pro­duc­tion of olive mill waste­water across the basin is esti­mated to exceed 30 mil­lion cubic meters, of which 50 per­cent con­sists of liq­uid waste.

More than half of this amount is chan­neled into streams, which usu­ally end up in ground­wa­ter. The pol­lu­tion caused in ground­wa­ter by phe­nols cre­ates tox­i­c­ity prob­lems, while the con­t­a­m­i­na­tion of sur­face waters is also high.

The remain­ing vol­umes of the olive mill liq­uid waste are chan­neled to the ground (20 per­cent) and the sea and rivers (12 per­cent). Only 10 per­cent are directed to evap­o­ra­tion tanks and other infra­struc­ture which is appro­pri­ate for the dis­posal of this toxic liq­uid.

Green energy from olive oil waste

Thessaloniki-based Biogas Lagada SA, which has been in oper­a­tion since 2015, receives approx­i­mately 4,000 tons of olive mill liq­uid waste annu­ally. This cor­re­sponds to five per­cent of the total waste received by the unit.

We receive 80,000 tons of waste annu­ally, which con­sists mainly of live­stock waste mat­ter, pro­duc­ing 8,400 MWh of elec­tric­ity,” said Odysseas Koupatsiaris, the direc­tor of Biogas Lagadas SA. The pro­duc­tion of the unit cov­ers the elec­tric­ity needs of about 1,500 house­holds.

See Also: Olive Oil Waste Fuels Spanish Power Plant and Palestinian Startup

Utilizing the mil­l’s waste can also con­tribute towards the cir­cu­lar econ­omy in addi­tion to green energy pro­duc­tion.

At the Lagada bio­gas plant, we also pro­duce 75,000 tons of organic fer­til­izer, which is sup­plied to grow­ers at a com­pet­i­tive cost of €2.00 to €2.50 per ton and is mainly applied to wheat or corn­fields,” Koupatsiaris said.

A small-scale solu­tion

However, there are sig­nif­i­cant lim­i­ta­tions and the dis­posal of olive mill waste for bio­gas pro­duc­tion can­not be a large-scale solu­tion.

One dif­fi­culty con­cerns the sea­sonal flow of raw mate­r­ial dur­ing the period of olive oil pro­duc­tion, which only stretches across a few months a year,” Koupatsiaris said. The waste could poten­tially be stored in the premises of the bio­gas unit to feed sup­ply through the year, but this means that appro­pri­ate stor­age should have been planned dur­ing the design of the bio­gas plant facil­i­ties, which is not the case.”

Additionally, olive mill waste can­not account for the total amount of waste. It must be com­bined with large vol­umes of other types of waste, such as manure, to be digestible.

I esti­mate that olive mill waste can­not be more than 30 per­cent of the mate­ri­als processed in the unit,” Koupatsiaris said. This is because some of the waste com­po­nents cre­ate a prob­lem and can dis­rupt the chem­i­cal process of bio­gas pro­duc­tion.”

Thus, to cor­rect the prob­lem cre­ated by the lev­els of car­bon and fats, it is mixed with waste from pig farms, poul­try farms and mink units, as this cre­ates the nec­es­sary bal­ance of car­bon to nitro­gen,” he added.

Positive prospects

However, the lim­i­ta­tions fac­ing the dis­posal of olive mill liq­uid waste do not can­cel the fact that the tech­nol­ogy has promis­ing prospects, experts say.

In Greece, the liq­uid waste of olive mills is con­sid­ered as a sec­ondary source of bio­mass, but in Italy, there are bio­gas units that are designed to run on olive mill waste exclu­sively and belong to com­pa­nies in the olive oil sec­tor,” said Costas Alexandridis, mem­ber of the Board of the Hellenic Association of Biogas Producers.

The tech­nol­ogy is not well known in Greece, which per­haps explains the low lev­els of its appli­ca­tion,” he added.


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