In the context of climate change and the circular economy, biochar agricultural and environmental applications have attracted a good deal of attention. Biochar has unique characteristics like surface area, porosity, water-holding capacity, pH, surface charge, and nutrients. This study reviews the biochar production from olive pomace (OP) and olive stone (OS) byproducts, its chemical and physical characterization, and its environmental application. The current review highlights the conditions for biochar production, the effects of pyrolysis temperature, and feedstock type on the physicochemical properties of biochar. High pyrolysis temperature (>500 °C) promotes a high specific surface area, high porosity (especially for OS biochars), and pH as well as the content of ash and fixed carbon, but generates low cation exchange capacity (CEC) and electrical conductivity (EC) and high values of O/C and H/C ratio. OP biochar also presents a high C amount, and ash content, i.e., rich in nutrients and high alkalizing capacity. OP biochar serves as an important source of plant nutrients, especially potassium. After adding both types of biochar, aggregate stability and the amount of water held in soil increase, and bulk density and bioavailability of trace elements decrease. Thus, biochar from olive mill wastes can be a potential plant nutrient reservoir, a good amendment to improve soil properties and long-term carbon sequestration. Results presented in this review can be used to build designer biochars from olive mill wastes to help solve environmental issues (water purification and pollutant remediation) and are suitable for improving soil physical chemistry characteristics and crop growth.

Olive mill wastewater (OMWW) is a major environmental stressor in Mediterranean regions, producing phytotoxic effluents that may threaten aquatic ecosystems. However, the ecological effects of OMWW discharges are rarely assessed, especially in filter feeders organisms such as freshwater bivalves. Given this gap, the present study evaluated the long-term effects of OMWW exposure (14 days) on four native (Unio delphinus, Unio tumidiformis, Anodonta anatina, and Potomida littoralis) and one non-native (Corbicula fluminea) freshwater bivalve species. Under controlled laboratory conditions specimens from the five species were exposed to three treatments: two OMWW concentrations (C1: 8.77 mg/L and C2: 21.31 mg/L of organic matter) and a control (CTL: 0 mg/L). At the end of the experiment, neurotoxicity (acetylcholinesterase- AChE) and oxidative stress (superoxide dismutase - SOD, Thiobarbituric acid reactive substances - TBARs) biomarkers were assessed in the gills and in the digestive gland. Results demonstrated higher sensitivity of native species-especially U. tumidiformis- showing an overall ineffectiveness of antioxidant mechanisms (SOD) to neutralize reactive oxygen species (ROS), leading to TBARs accumulation and neural inhibition (AChE). In contrast, the non-native species C. fluminea respond to the lower OMWW concentration used reducing basal activities such as SOD and AChE, which may be interpreted as a reduction in their metabolic rate, leading to minimal energy expenditure. Moreover, C. fluminea exhibited a biphasic response characterized by enzymatic downregulation at lower concentrations and enzymatic upregulation at higher levels, suggesting a higher physiological plasticity compared to native species. Overall, this study underscore the ecological importance of bivalves as sentinel species to assess OMWW pollution, supporting the objectives of the EU Water Framework Directive.