Olive mill wastewater (OMW) resulting from the olive oil extraction process is usually disposed of in evaporation ponds where it concentrates generating a sludge that pollutes the ponds nearby area. In this study, four bio-treatments were applied for the in-situ bioremediation and valorization of OMW sludge: Landfarming, phytoremediation, composting and vermicomposting. In all cases, the OMW sludge was added with organic residues (mushroom compost, rabbit manure, and chicken manure). The bio-treatments were carried out in duplicate, inoculated and non-inoculated, to determine the effect of a specialized fungal consortium (Aspergillus ochraceus H2 and Scedosporium apiospermum H16) on the efficacy of the bio-treatments. The evaluation of chemical parameters, toxicity, and functional microbial biodiversity revealed that the four techniques depleted the toxicity and favored the stimulation of functional microbiota. Landfarming and phytoremediation allowed the decontamination and improvement of soils. Composting and vermicomposting also offered high-quality products of agronomic interest. Inoculation improved the bioremediation effectiveness. Biological treatments are effective for the safe recovery of contaminated OMW sludge into high-quality services and products.

Composting is considered an efficient and environmentally friendly alternative for plant waste management, resulting in compost, a high value-added product. During the process, microorganisms play a crucial role as organic matter-degrading agents. However, the highly recalcitrant nature of the lignocellulose present in plant residues sets a challenge to the microorganisms involved in the process. Therefore, the objective of this study was to evaluate the effect of a lignocellulolytic microbial consortium, previously selected in composting processes, to promote and improve the biodegradability of plant residues. For this purpose, a laboratory-scale inoculation strategy was optimized by applying different strains and doses of Bacillus spp., as well as different incubation times. Subsequently, the impact of the application of the consortium on the waste material as a pretreatment of a real composting process was evaluated. Samples from both experiments were subjected to the evaluation of parameters related to the biodegradation of the lignocellulosic fraction, in addition to those related to the stability and maturity of a compost. The inoculum proved to be effective in promoting the bioactivation of the material, favoring a higher respirometric rate and biodegradability during laboratory-scale pretreatment. In this case, inoculation with B. safensis at high doses resulted in AT₄ values higher than those observed for the rest of the treatments after ten days of incubation, while B. licheniformis inoculated at lower doses was able to maintain higher AT₄ values after ten days, compared to those observed in the rest of the samples analyzed. Additionally, inoculation with both strains resulted in a continuous decrease in the percentage of hemicellulose that could be detected until the end of the incubation period (thirty days), reaching biodegradation rates close to 40%. On the other hand, although the inoculation did not significantly affect the basic conditioning parameters at the beginning of the composting process (organic matter, C/N ratio, and moisture), a change in the dynamics of the lignocellulosic fractions was observed during the process, as well as in the evolution of other stability and maturity parameters, in particular the AT₄ index and the lignin/holocellulose ratio, revealing an acceleration of the bio-oxidative phase during the full-scale composting process. Therefore, the treatment of plant waste with lignocellulolytic microorganisms is proposed as an effective alternative to activate the biodegradability of organic waste at the beginning of a composting process, resulting in better-quality products.

Olive mill wastewater (OMW), a by-product of olive oil extraction, poses significant environmental challenges due to its toxicity and heterogeneity. This study evaluates the phenolic and mineral composition of OMW and alpechin sludges from abandoned ponds in Spain, and establishes a standardized conventional method to recover phenolic fractions and promote their safe valorization as bioactive ingredients. Phenolic compounds were identified by triple-TOF-LC-MS/MS, and minerals and heavy metals were quantified by ICP-MS. Across thirteen ponds analyzed, samples from Cordoba, Tarragona, Alicante and Toledo showed higher phenolic levels, ranging from 7.2 g GAE/kg to 18.9 g GAE/kg, with methanolic extracts reaching 10.98–15.67 mg GAE/mL. Thirty-one phenolic compounds were identified, predominantly luteolin, apigenin, quercetin, and secoiridoid derivatives, notably hydroxytyrosol and tyrosol, supporting their functional potential as natural antioxidants. The mineral profile was dominated by K and Ca and showed negligible carryover to the phenolic organic fraction (<1%). Heavy metal concentrations in fresh OMW were 0.32–1.06 µg/kg for Cd and Hg and 9–43.9 µg/kg for As and Pb. In OMW sludge, they ranged between 0.033 and 0.19 mg/kg for Cd, 0.01 and 0.12 mg/kg for Hg, 5.45 and 8.06 mg/kg for As, and 4.45 and 23.70 mg/kg for Pb, whereas phenolic extracts contained only 0.15–21.50 µg/kg, remaining below EU food safety limits. This work presents one of the first integrated approaches to risk-benefit mapping of abandoned ponds in Spanish soils and advances extraction standardization by jointly considering functional potential, contaminant profiles, and matrix location.