Composting of Olive Mill Pomace, Agro-Industrial Sewage Sludge and Other Residues: Process Monitoring and Agronomic Use of the Resulting Composts

Abstract

The viability of co-composting of olive mill pomace added to sewage sludge with other organic residues was evaluated and the agronomic use of the final composts was investigated. Two composting piles at different carbon-nitrogen ratios were performed, in which olive mill pomace (OMP), sewage sludge from vegetable processing (SS), fresh residues from artichoke processing residues (AR), and wheat straw (WS) were used. The two composting piles were placed inside a specially built greenhouse and a turning machine pulled by a tractor was used for turning and shredding the organic matrix (every 6 days) during the process. The humidity and temperature of organic matrices have been monitored and controlled during the entire composting process, which lasted 90 days. The process was also monitored to evaluate the microbiological safety of the final compost. The humidity of both piles was always kept just above 50% until the end of the thermophilic phase and the maximum temperature was about 50 °C during the thermophilic phase. The carbon-nitrogen ratio decreased from 21.4 and 28.2, respectively (initial value at day 1 in Pile A and B), to values ranging from 12.9 to 15.1, both composts that originated from the two different piles were microbiologically safe. During a two-year period, the effects of different types of compost on the main qualitative parameters of processing tomato and durum wheat was evaluated. Five fertilization treatments were evaluated for tomato and durum wheat crops: unfertilized control (TR1); compost A (TR2); compost B (TR3); ½ mineral and ½ compost A (TR4); and mineral fertilizer commonly used for the two crops (TR5). Concerning the processing tomato yield, TR5 and TR4 showed the best results (2.73 and 2.51 kg, respectively). The same trend was observed considering the marketable yield per plant. The only difference was related to the treatments that included the compost (2.32, 1.77, and 1.73 kg/plant for TR4, TR3, and TR2, respectively). As regards the qualitative parameters of tomato, the highest average weight of the fruits was found in the TR5, TR4, and TR3 treatments (respectively, 73.67 g, 70.34 g, and 68.10 g). For durum wheat, only the protein component was differentiated between treatments. Furthermore, wheat grain yield parameters generally increased by combined application of mineral fertilizer and compost.

Application of Thermo-Malaxation Followed by Three-Phase Centrifugation to Enable the Biorefinery of Alperujo, the Main By-Product of Olive Oil

“…This fact has prevented the correct purification of olive oil by-products for several decades. Now, for the first time, the application of this system will make the use of microorganisms more feasible, for example, in the application of aerobic digestion in the production of bioethanol [30], or anaerobic digestion in the production of biomethane [31] or its composting for agricultural use [32], among many other bioprocess options, in order to achieve the true biorefinery of olive pomace.…”

Physicochemical Characterization of Pectic Polysaccharides from Rose Essential Oil Industry By-Products

“…However, the liquid part contains higher concentrations of polyphenols, which have a negative influence on the amount of available oxygen in aquatic systems. The solid residues, often used as a fertilizer when bio-certified roses are grown, could introduce unnecessary changes in the soil microbiota [14], and should be preliminary composted [15]. Additionally, the solid by-products are also rich sources of polyphenols, and polysaccharides, which could be further valorized [12].…”

Valorization of Olive By-Products: Innovative Strategies for Their Production, Treatment and Characterization

“…Regarding this prospective research, composting is a simple method to use, has few process requirements, has relatively low investment costs, and can be conveniently carried out using organic waste matrices from different agro-food chains. Considering the importance of valorizing organic waste from the food industry, minimizing the environmental impact of the sewage sludge, and, finally, the need to return mature organic substance to the soil as a soil improver for crops, a research paper of the SI [29] had the purpose of evaluating the technical feasibility of co-composting of four types of organic wastes, one of this represented by the olive mill pomace. In particular, the research has aimed to set up a composting plant equipped with a machine for turning and shredding the windrow.…”