Microbial Community Succession and Organic Pollutants Removal During Olive Mill Waste Sludge and Green Waste Co-composting

Abstract

Olive mill wastewater sludge (OMWS) is the main by-product of the olive industry. OMWS is usually dumped in landfills without prior treatment and may cause several eco-environmental hazards due to its high toxicity, which is mainly attributed to polyphenols and lipids. OMWS is rich in valuable biocompounds, which makes it highly desirable for valorization by composting. However, there is a need to understand how microbial communities evolve during OMWS composting with respect to physicochemical changes and the dynamics of pollutant degradation. In this study, we addressed the relationship between microbial community, physicochemical variations and pollutants degradation during the co-composting of OMWS and green wastes using metagenomic- and culture-dependent approaches. The results showed that in raw OMWS, Pichia was the most represented genus with almost 53% of the total identified fungal population. Moreover, the bacteria that dominated were Zymobacter palmae (20%) and Pseudomonas sp. (19%). The addition of green waste to OMWS improved the actinobacterial diversity of the mixture and enhanced the degradation of lipids (81.3%) and polyphenols (84.54%). Correlation analysis revealed that Actinobacteria and fungi (Candida sp., Galactomyces sp., and Pichia manshurica) were the microorganisms that had the greatest influence on the composting process. Overall, these findings provide for the first time some novel insights into the microbial dynamics during OMWS composting and may contribute to the development of tailored inoculum for process optimization.

Organo-Mineral Fertilization Based on Olive Waste Sludge Compost and Various Phosphate Sources Improves Phosphorus Agronomic Efficiency, Zea mays Agro-Physiological Traits, and Water Availability

“…following the biodegradation of organic matter [49,50]. This effect was identified in our study (Table 5), with a high content of Ca 2+ in the soil when using OMF formulations.…”

Short-term effects of olive-mill-wastes-derived biochars amendment and arbuscular mycorrhizal fungi inoculation on growth of maize (Zea mays) and mycorrhizal colonization

“…A study by Hammad et al [77] showed a significant decrease in maize yield and quality without nitrogen application. Since chlorophyll contents (measured SPAD values) are proportional to the amount of nitrogen present in the leaves [78,79], the decrease in SPAD values over time can be due to nitrogen deficiency in plants. When maize is cultivated in optimal conditions, the plant tends to take up nitrogen (N) during vegetative growth, and this N is later remobilized from leaves to reproductive organs to support kernel formation [80,81].…”

“…However, AMF treatments provided new propagules and enhance maize root colonization. It is important to underline that biochar made from woody biomass addition to agricultural soils could increase the AMF spore number in the soil [78,79]. Indeed, when studying the effects of olive waste-based compost, a woodbased biochar, and their combination on soil fertility and maize growth, these authors found that a single application of biochar had a negative impact on mycorrhizal symbiosis after 3 months while the compost gave the best results in terms of mycorrhizal frequency (F%) and intensity of mycorrhizal colonization (M%) and F%.…”