February 15, 2004 | General

Cocomposting Olive Residuals And Green Waste On Crete

T. Manios, K. Maniadakis, M. Kalogeraki, E. Mari, S. Terzakis, P. Magiatis, E. Mikros, A. Agalias, I. Spanos and V. Manios
BioCycle February 2004, Vol. 45, No. 2, p. 67
The olive tree is the main crop on the island of Crete in southern Greece. The 450,000 tons of olive oil – produced on an annual basis – contribute more than 70 percent of the total agricultural income of the island, where growing and harvesting the fruit occupies the majority of the farmer’s working time. For crushing the olives and production of the well-known Cretan oil, more than 650 olive oil mills operate on the island from late November to early March every year. Unfortunately, they also produce an equal amount of wastewater (more than 400,000 m3), characterized by a substantial organic load. Olive Mill Wastewater (OMW) values of BOD5 and COD range from 10,000 to 80,000 mg/L and 40,000 to 150,000 mg/L, respectively. It is also characterized by its low biodegradability and high polyphenol concentration. All of the above indicate why, for a number of years, a large number of researchers have been trying to establish a low-cost, low-technology treatment method, easily applicable in the mountainous terrain of the island where the olive mills are scattered.
Evaporation ponds are currently the dominant treatment method, mainly in Eastern Crete where limited rainfall increases their efficiency. Most ponds are 1.5 m deep with an effective volume of 500 — 700 m3, depending on the mill size. The wastewater produced evaporates during spring and summer, leaving a cake of suspended solid matter at the bottom. Evaporation ponds do manage to reduce the impact of OMW on the environment, with the unfortunate side effect of severe odor emission.
Olive tree leaves (OTL) accumulate as a waste at olive oil mills and are one of the most important organic waste residues on the island of Crete. Part of the fresh OTL is used as a feed for sheep and goats, but their abundance and availability on a cost-free basis make them a favorable organic material for compost production. Olive tree branches (OTB) are one of the most abundant agricultural organic residues on Crete and the majority are burned immediately after harvesting the olive fruit and tree pruning operations (between November and March). This material, due to its bulky character, is difficult and expensive to collect. Extracted Olive Press Cake (EOPC) is the major organic solid waste from the olive oil industry, and it has been used extensively as a fuel source. However, environmental problems associated with smoke emission from burning the waste have restricted this practice and, as a consequence, the price of the material has declined. Handling OTL, OTB and EOPC in an environmentally friendly and financially wise manner is a problem equally important to that of OMW.
Through a European Union funding program (LIFE-Environment), a process was set up aiming to tackle the problem of managing and treating OMW, OTL, OTB and EOPC. The objective of the proposed project was to establish a demonstration process for the integrated utilization of the wastes produced by olive tree cultivation. This process is composed of two parts: a) The produced OMW which contains chemical compounds with significant pharmacological, biological and chemical properties of high added value (natural antioxidants) is treated through a high-technology process for the recovery of these substances; and b) The above treated OMW (which still requires additional handling) and the OMW sludge from the stabilization ponds is cocomposted with OTL, OBT and EOPC (in secondary amounts), for the production of a natural organic fertilizer.
The objective of this paper is to present the realization of the second part of the process – into the first commercial (neither experimental or pilot) composting plant in Crete. All the following construction and equipment acquisition were funded by the EU through the LIFE-Environment program (Life 00 ENV/GR 000671 — MINOS) and the financial contributors to the program, the General Secretariat of the Crete Region, the Association Olive Oil Producers of Rouvas, and the Municipality of Rouvas, in the administrative limits of which the unit was established.
There were some important parameters which dictated the selection of the land where the plant was be constructed: 1) The land must be relatively flat and low cost. Municipality of Rouvas is located in the heart of the mountainous area of Crete, with an average altitude of 520 m; 2) The distance from the evaporation pond where the OMW ends up should be short allowing continuous pumping and use of the wastewater. Due to odor problems, the evaporation ponds are a considerable distance from inhabited areas, so the same applies for the composting site; 3) The distance from the olive mills should also be considerably short in order to have a small transportation cost of OTL and EOPC; and 4) The land must also be in the heart of the olive trees cultivated area in order to minimize the transportation cost for OTB.
The only available land which satisfied all the above requirements was the land next to the evaporation pond. The total available surface was approximately 1,200 m2, but some substantial excavation had to be done in order to flatten it. The cost for layering the pond’s bottom with a plastic 2 mm thick waterproof membrane and shaping the surrounding area was $14,877. An additional $5,677 were spent in constructing the composting and maturation surface of the plant (approximately 200 m2). Finally another $8,852 were used for constructing a shelter for the safekeeping of the plant’s machinery – a turner, a shredder and a pump.
The Technological Educational Institute of Crete (TEI of Crete) was responsible for determining the technical characteristics of the equipment which should be acquired for smooth operations of the plant. TEI of Crete has extensive experience in composting related issues, including operation of composting plants as demonstrated by a recent article in BioCycle (June 2003, pages 53-55). The following equipment was acquired, based on estimates of the raw material (OTB, OTL and OMW) volume as well as the limited available composting surface: A turner ST 250 (provided by Advensol Inc.,, able to shape windrows of 2.5 m wide and 1.3 m high; it weighs 1.500 kg, requires a tractor with a minimum provided power of 35 hp, and the turning shaft rotates with 200 — 400 rpm; A shredder Caravaggi Bio 300 operates with 40 rotating knifes able to shred wood of up to 10 cm diameter. A petrol engine of 20 hp powers the shredder which can also be powered by a tractor (35 hp requirement) .
A simple subsurface wastewater pump was also bought for pumping the OMW from the pond into the windrows. The required tractor for the turning of the piles was provided each time by the Municipality of Rouvas.
The composting plant was operational by late March, 2003 at the end of the olive harvesting season. This did not allow time to “exploit” the majority of the OTL, OTB and EOPC volume. OTL were almost completely absorbed by local farmers for animal feeding where OTB were burned with the exception of some quantities kept by the Municipality for the needs of the plant. These OTB quantities were transported in small volumes to the site where they were shredded and stored, before shaping windrows. The OMW was added in the piles before each turning until saturation and during the turning.
Despite the late start, it was possible to set up three piles:
Pile 1: OTL and OTB in 1:1 volume ratio. The total volume of the pile was approximately 10 m3. OMW was added 6 times in two weeks intervals and in 0.4 m3 each time (2.4 m3 in total). The temperature fluctuation with time is presented in Figure 1. Temperature monitoring and recording was the responsibility of the municipality’s workers, who unfortunately neglected to do so on a daily basis. Temperature failed to reach substantial values probably due to the nature of the materials involved (relatively low moisture, increased presence of woody parts). Efforts were made to support the decomposing process through the addition of OMW. However, OMW were added only just before and during the turning resulting in the absorption by the composting materials of a limited amount.
Pile 2: OTL, OTB and EOPC in 1:1:1 v/v. The total volume of the pile was 9 m3. OMW was added 6 times in two week intervals and in 0.4 m3 each time (2.4 m3 in total). The temperature fluctuation with time is presented also in Figure 1. The use of EOPC in this pile resulted in a substantial temperature increase, as it was expected. EOPC presents a unique ability of producing elevated amounts of energy during composting with either OTL or / and OTB.
Pile 3: OTL and OTB in 1:2 volume ratio. The total volume of the pile was 26 m3. OMW was added 5 times in approximately two weeks intervals and in 0.8 m3 each time (4.0 m3 in total). Again temperatures remained low, as in Pile 1. The addition of OMW followed the same practice with Pile 1. It is now obvious that if high temperatures in the windrows and increased use of OMW is the target, then addition of the settling wastewater should take place in more dense intervals (e.g. once every two days) not just once every two weeks (turning day).
The materials produced by the above windrows were piled in the maturation area and kept for a few weeks before taken by local farmers and used as organic soil amendments. The Municipality was thinking of distributing this material without any charge in order to publicize the plant among the farmers. However, a small charge might be imposed in an effort not to allow people to assume that this will be a standard practice in the future.
It is too soon to determine if this first of a kind plant will be able to meet the original expectations of providing substantial help in management and treatment of the olive oil production wastes in a feasible technical and economical manner. The plant is still subsidized by the “Minos” program and additional help is provided by the TEI of Crete staff. The real test for this plant is the coming winter where it will have to work at full capacity, if it is to provide some important help to the waste management problem. “MINOS” will be concluded in March 2004, and from this point onward no outside financial or other kind of help will be provided to the Municipality of Rouva, who will have to prove that all this effort and investment were not made in vain.
T. Manios, K. Maniadakis, M. Kalogeraki, E. Mari, S. Terzakis and V. Manios are in the Department of Agricultural Technology at the Technological Educational Institute of Crete, Heraklion, Greece, e-mail: P. Magiatis, E. Mikros and A. Agalias are with the Pharmaceutical School at the National and Kapodistrian University of Athens, Athens in Greece. I. Spanos is with Terra Nova, Environmental Consulting in Athens, Greece.

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