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

Enhancing spontaneous biosurfactant production through water steeping of olive mill waste

This study offers novel and valuable insights into the spontaneous production of biosurfactant extracts from olive mill waste (OMW) through a steeping process with water at 37 °C for 15 days, followed by extraction with ethyl acetate or phosphate-buffered saline (PBS). The results showed that steeping process significantly improves the extraction efficiency and produces biosurfactant extracts with more favorable critical micellar concentration (CMC) and wettability properties than those from non-steeped OMW. Under best conditions, it yielded 104.6 g/Kg of OMW. Elemental analysis and comparative ATR-FTIR spectroscopy revealed that ethyl acetate biosurfactant extracts is compatible with biosurfactant extracts that contains phospholipids and lipopeptides. It reduced water surface tension to 46.7 mN/m and exhibited a CMC of 0.22 g/L. Conversely, the biosurfactant extract obtained through solid-liquid extraction with PBS was more compatible with glycopeptides biosurfactants, reducing the water surface tension to 50.4 mN/m, similarly to the surface tension values achieved by biosurfactants produced by lactic acid bacteria, but achieving reduced CMC value (0.19 g/L). Therefore, this approach presents a sustainable method for valorizing OMW, promoting sustainability, and circular economy principles. These extracts could have potential applications in various fields, such as soil bioremediation, surface cleaning, and in cosmetic and agrochemical formulations.

Exploring the impact of eco-enzyme diversity on the physicochemical characteristics of rice husk and sawdust compost

Management of agricultural waste generated by farm practices has emerged as a significant global problem. Also, handling raw animal manure in a hygienic and eco-friendly process appears to be tedious. The present lab scale study has been carried out to assess the effect of lab-synthesized eco-enzyme applications on the physio-chemical properties of compost prepared using rice husk and sawdust. The study portrays a maturation period of 150 days without eco-enzyme as compared to a maturation period of 120 days when using 10% eco-enzyme with water (V/V). The highest moisture content has been observed in compost from sawdust and rice husk with 20% eco-enzyme under the thermophilic stage. However, the highest organic carbon value of 36.75% was observed in rice husk compost with 10% eco-enzyme on the 15th day, whereas the minimum organic carbon value of 6.0% was observed in rice husk compost with 20% eco-enzyme on the 135th day. The minimum C/N ratio of 13% was observed in rice husk compost with 15% eco-enzyme. The data in the present study has been used for statistical analysis by applying one-way ANOVA, and the computed results in terms of F value for all eco-enzymes variations for sawdust and rice husk are less than the critical F value of 3.19 at a 5% level of significance for all analyzed parameters including pH, moisture content, organic, TKN, and C/N ratio. The current study's conclusions may inspire the creation of innovative and sustainable techniques for producing high-quality compost, promoting the more ecologically conscious and circular use of organic waste in horticultural and agricultural applications.

Bacterial community dynamics in a biofilm-based process after electro-assisted Fenton pre-treatment of real olive mill wastewater

In this work, the effect of the electro-assisted Fenton (EAF) process on the bacterial community of a moving bed biofilm reactor (MBBR) for olive mill wastewater (OMW) co-treatment with urban wastewater (UWW) was investigated. According to metagenomic analysis, pre-treatment by EAF, while removing total phenols (TPHs) up to 84 % ± 3 % and improving biodegradability of OMW from 0.38 to 0.62, led to the emergence of bacterial genera in the MBBR (R2) that were not detected under conditions without pre-treatment (R1). Indeed, in that condition, Candidatus Competibacter replaced Amaricoccus as dominant denitrifying bacteria. In both cases, the bacterial community composition matched with high simultaneous nitrification-denitrification efficiency (up to 98 %). Finally, Chlorobium (2.5-4.1 %), sulphate-reducing bacteria and Geobacter (up to 1.6 ± 0.4 %), anaerobic bacteria that utilise iron oxides, were observed exclusively with EAF application, suggesting potential for the development of new integrated microbial electrochemical systems.

Microbial intervention improves pollutant removal and semi-liquid organo-mineral fertilizer production from olive mill wastewater sludge and rock phosphate

Olive mill wastewater sludge (OMWS) represents a residual pollutant generated by the olive oil industry, often stored in exposed evaporation ponds, leading to contamination of nearby land and water resources. Despite its promising composition, the valorization of OMWS remains underexplored compared to olive mill wastewater (OMW). This study aims to identify potent native microbial species within OMWS suitable for bioremediation and its transformation into a high-value organic fertilizer. The microbial screening, based on assessing OMWS tolerance and phosphate solubilization properties in vitro, followed by a singular inoculation using a mixture of OMWS and rock phosphate (RP). Identification of FUN 06 (Galactomyces Geotrichum), a fungal species, employed as an inoculant in the treatment of sterile OMWS supplemented with RP. Results demonstrate that fungal inoculation notably diminished OMWS phytotoxicity while enhancing its physicochemical parameters, nutrient concentrations, and removal of toxic organic compounds by up to 90% compared to the control, and enhances plant growth, offering a sustainable approach to tackle environmental concerns. Additionally, metataxonomic analysis unveiled FUN 06's propensity to enhance the presence of microbial species engaged in pollutant degradation. However, higher RP dosage (10%) appeared to adversely affect bioprocess efficiency, suggesting a potential dose-related effect. Overall, FUN 06, isolated from OMWS evaporation ponds, shows promise for effective bioremediation and sustainable reuse. In fact, our results indicate that targeted microbial inoculation stands as an effective strategy for mitigating pollutants in OMWS, facilitating its conversion into a nutrient-rich organo-mineral fertilizer suitable for direct use, promoting its beneficial reuse in agriculture, thereby presenting a promising avenue for olive oil waste management.

Soil conditioners promote the formation of Fe-bound organic carbon and its stability

The close association of soil organic carbon (SOC) with Fe oxides is an important stabilization mechanism for soil organic matter (SOM) against biodegradation. Soil conditioners are of great importance in improving soil quality and soil health. Yet it remains unclear how different conditioners would affect the fractionation of SOC, particularly the Fe-bound organic carbon (Fe-OC). Field-based experiments were conducted in farmland to explore the fractionation of organic carbon (OC) and Fe oxides under the effects of three different soil conditioners (mineral, organic, and microbial conditioners). The results showed that all soil conditioners increased the total OC and Fe-OC contents, with the contribution of Fe-OC to total OC increasing from 1.57% to 2.99%. The low OC/Fe molar ratio indicated that surface adsorption played a crucial role in soil Fe-OC accumulation. Nuclear magnetic resonance (NMR) results suggested that soil conditioner altered the composition of SOM, accelerating O-alkyl C degradation and increasing recalcitrant alkyl C and aromatic C sequestration. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analysis indicated that all conditioners promoted the association of OC and Fe oxides. Furthermore, comprehensive analysis of 13C isotope and synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy showed that the mineral conditioner enhanced the association of microbial-derived OC and Fe oxides, whereas the organic conditioner increased the association of plant-derived OC with Fe oxides. These findings provide important insights into the potential mechanisms through which soil conditioners regulate the stability of OC and guide agricultural management.

Short-term evaluation of soil physical, chemical and biochemical properties in an abandoned cropland treated with different soil organic amendments under semiarid conditions

This study evaluate the effects of four organic soil amendments on soil. Physical, chemical and biochemical properties were compared to untreated and natural (not cultivated) soils in a semiarid region (Andalusia, Spain). A large set of physical, chemical biochemical properties and, the composition of bacterial communities; and overall soil quality index (SQI) were evaluated on soils treated with organic soil amendments of animal origin (compost from sheep and cow manure [CS] or chicken manure, [CK], vegetal origin (greenhouse crop residues [CC]), and vermicompost (CV). Immediately after application, the animal origin compost significantly increased pH, electrical conductivity (EC), and total nitrogen (TN) as well as the enzymatic activities associated with the carbon (C) cycle but decreased the richness and evenness of bacterial communities. After 3 months of treatment, all measured properties recovered except for EC, TN and dehydrogenase activity (whose increase was stable over time), as did bacterial richness, which remained lower. The vegetal-originating compost increased EC and pH whereas the other effects were not significant throughout the monitoring period. CV application did not affect soil properties. The SQI was the highest for soils treated with CK compost, both immediately after application and over time. The soil treatments with the other organic amendments did not result in a significantly different SQI over time compared to both untreated and natural sites.

Fungal community enhanced humification and influenced by heavy metals in industrial-scale hyperthermophilic composting of municipal sludge

The succession of fungal community and effects of heavy metals on fungi during industrial-scale hyperthermophilic composting of municipal sludge remain unclear. Results showed hyperthermophilic composting enhanced decomposition and humification of municipal sludge in the short terms, while heavy metal concentrations and speciation had no significant change with high copper and zinc levels (101-122 and 292-337 mg/kg, respectively) in compost samples. The fungal community and its ecological assembly displayed dynamic change during hyperthermophilic composting. Some thermophilic-resistant fungi, such as phylum Ascomycota and genera Candida, Aspergillus, Thermomyces and Petriella dominated in hyperthermophilic phase. Heavy metals served important effects on fungal community structure and functions during composting. Some fungal drivers (e.g., Thermomyces, Petriella and Schizophyllum) and keystone fungi (e.g., Candida and Pichia) might be thermophilic- and heavy metal-resistant fungi which played important roles in decomposition and humification of municipal sludge. This study reveals fungal community accelerating humification and its influencing factors during composting.