Using polyethylene sleeves with forced aeration for composting olive mill wastewater pre-absorbed by vegetative waste.

Composting in closed polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. The present study demonstrates the use of this system for composting olive mill wastewater (OMW), the undesired stream associated with the olive milling industry. A polyethylene sleeve of 1.5-m diameter and ca. 20-m long was packed with shredded municipal green waste which was pre-soaked in OMW for 72 h. Process conditions were controlled by means of a programmable logic controller (PLC) equipped with temperature and oxygen sensors. Thermophilic temperatures (>45 °C) were maintained for one month followed by temperatures in the range of 30-40 °C, ca. 20 °C above ambient temperature, for a period of 3.5 months. Oxygen levels were controlled and the system was kept aerobic. Water content gradually decreased with sufficient levels for efficient composting. The finished compost was non-phytotoxic to Cress (Lepidium sativum L.) in a lab bioassay. It was also found suitable as an ingredient in peat, tuff, and coir based growing media, evaluated by plant growth tests with basil and ornamental plants. The viability of this approach for disposing off OMW is much dependent on the liquid absorption capacity of the vegetative waste.

Composting municipal biosolids in polyethylene sleeves with forced aeration: Process control, air emissions, sanitary and agronomic aspects.

Composting in polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. A disadvantage of this technology is the lack of mixing during composting, potentially leading to non-uniform products. In two pilot experiments using biosolids and green waste (1:1; v:v), thermophilic conditions (>45°C) were maintained for two months, with successful control of oxygen levels and sufficient moisture. Emitted odors declined from 1.5-3.8×105 to 5.9×103-2.3×104 odor units m-3-air in the first 3weeks of the process, emphasizing the need of odor control primarily during this period. Therefore, composting might be managed in two phases: (i) a closed sleeve for 6-8weeks during which the odor is treated; (ii) an open pile (odor control is not necessary). Reduction of salmonella, E. coli and coliforms was effective initially, meeting the standards of "Class A" biosolids; however, total and fecal coliforms density increased after opening the second sleeve and exceeded the standard of 1000 most probable number (MPN) per g dry matter. Compost maturity was achieved in the open piles following the two sleeves and the final compost was non-phytotoxic and beneficial as a soil additive.

Co-composting of solid and liquid olive mill wastes: management aspects and the horticultural value of the resulting composts.

Successful co-composting of solid and liquid olive mill wastes (OMW) and obtaining a product of horticultural value may increase the viability of this recycling approach. Two composting cycles were performed, in which olive mill solid wastes (OMSW) were used to form five mixtures, wetted either with fresh water or with olive mill wastewater (OMWW). Up to approximately 0.3m(3) of OMWW could be applied to each m(3) of the raw materials without negatively affecting the chemical, physical and horticultural properties of the resulted composts. A growing media composed of perlite amended with 25-33% OMW-composts showed higher suppressiveness against Fusarium oxysporum f. sp. melonis as compared to equivalent perlite:peat moss mixtures. The yields of tomato plants grown in peat moss amended with 20% (v:v) of OMW-composts were not significantly different than plants grown in unamended peat. The viability of co-composting as a treatment approach for OMWW is discussed in the context of management aspects and the horticultural value of the final product.