A new framework proposal, towards a common EU agricultural policy, with the best sustainable practices for the re-use of olive mill wastewater

Methane production from anaerobic pre-treatment of municipal wastewater combined with olive mill wastewater: A demonstration study

The advanced anaerobic technology (AAT), developed based on an immobilized high-rate anaerobic reactor, was applied as a pretreatment of municipal wastewater (WW) at Karmiel's treatment plant in Israel. The demonstration-scale AAT (21 m3) system was operated at a flow rate of 100 m3day-1 municipal WW mixed with olive mill wastewater (OMW) (0.5 m3day-1) to simulate the scenario of illegal discharge of agro-industrial WW. The AAT provided a stable performance. Specifically, AAT enabled treating high organic loads (9.3 kg m-3day-1) resulting from OMW discharge by shaving the high peaks of organic content and protecting the subsequent activated sludge process. This system enabled the recovery of a significant part of the organic load by anaerobic biodegradation to produce biogas, shown to be highly dependent on temperature and partly on the organic loading rate. The outcomes indicate that the AAT could tolerate an addition of up to 0.5% OMW to municipal WW by removing more than 50% of the total chemical oxygen demand and 18-47% of polyphenols. This work shows that the AAT system has the potential of pretreating municipal WW, increasing the energy efficiency of the plant, and protecting small-medium WWTPs from sudden agro-industrial discharges.

Impact of olive mill wastewater on the operational efficiency of wastewater treatment plants in the Gaza Strip

The improper disposal of olive mill wastewater (OMW) presents a significant environmental challenge for wastewater treatment plants (WWTPs) in the Gaza Strip. This study aims to evaluate the impact of OMW discharge on the operational efficiency of WWTPs, particularly during the olive harvesting season. To achieve this, samples were collected from both olive mills and WWTPs across the region and analyzed for key parameters such as chemical oxygen demand (COD), biological oxygen demand (BOD5), phenols, oil and grease, and total suspended solids (TSS). The study also calculated the total pollutant load generated by the olive oil production process. The results revealed that olive oil production in the Gaza Strip generates substantial amounts of pollutants, including 3374.76 tons of COD, 797.55 tons of BOD5, 1.33 tons of phenols, 184.42 tons of oil and grease, and 1204.99 tons of TSS. During the olive harvesting season, influent pollutant levels at the Gaza Central WWTP spiked to 3040 mg/L for COD, 1382 mg/L for BOD5, and 1810 mg/L for TSS, which exceeded the plant's design capacity. In contrast, the North Gaza WWTP, which serves fewer olive mills, recorded lower pollutant values of 760 mg/L for BOD5 and 933 mg/L for TSS. These findings underscore the significant seasonal impact of OMW on the WWTPs, highlighting the need for improved management strategies to mitigate the environmental and operational challenges associated with OMW disposal.

Olive mill wastewater treatment using coagulation/flocculation and filtration processes

Olive mill wastewater (OMWW), a pollutant resulting from the olive oil industry, poses a serious ecological challenge due to its high pollution load. This effluent is highly concentrated in chemical oxygen demand (COD), which is 200 times higher than that of sewage wastewater. Moreover, OMWW is characterized by a strong acidity, high content of fatty matter, and high concentration of phenolic compounds. In this study, coagulation/flocculation and filtration processes were investigated in order to decrease the pollution load of OMWW for potential reuse in olive orchard irrigation. First, two successive coagulation/flocculation steps were applied to a centrifuged OMWW. Lime and aluminum sulfate (alum) were used as coagulants by testing different concentrations in order to select optimal conditions. Then, the efficiency of various filtration systems using activated carbon and/or natural materials (olive stones, olive leaves, sand, Celite, and gravel) was tested. pH, electrical conductivity (EC), total solid (TS), and COD were measured before and after each treatment step (coagulation or filtration). Five phenolic compounds were monitored before and after applying the selected treatment steps under optimal conditions. The quantification and valorization of the sludge derived from coagulation/flocculation were also performed. During the first coagulation/flocculation step, the results showed that the application of 8 g/L of lime combined with 7 g/L of alum allows the removal rates for EC, TS, and COD of approximately 10 %, 41 %, and 48 %, respectively. While the application of 5 g/L of lime and 4 g/L of alum during the second coagulation/flocculation step allows for lower reductions rates for TS (37 %) and higher reduction rates for COD (67 %). In addition, the resulting sludge showed its potential usage as a solid alternative fuel with a calorific value of 3295.79 cal/g. Moreover, filtration using activated carbon and gravel was found to be the optimum filtration system. The reduction rates were 51 %, 37 %, and 26 % for EC, TS, and COD, respectively. Finally, the combination of coagulation/flocculation and filtration allows the substantial elimination of the studied phenolic compounds with global reduction yields of 97 % for vanillyl alcohol, 92 % for tyrosol, and 91 % for vanillic acid and p-coumaric acid. Besides, Mediterranean countries are suffering from water shortages and the majority of olive mill trituration units are known for their artisanal types thus facing economic challenges. This research suggests a practical treatment process and the final effluent can be used to irrigate olive orchards at a rate of 170 m3 per hectare.

Biotechnological Innovations Unleashing the Potential of Olive Mill Wastewater in Added-Value Bioproducts

Byproducts and wastes from the food processing industry represent an important group of wastes generated annually in large quantities. It is important to note that the amount of this waste will increase with industrialization, and effective solutions must be found urgently. Many wastes that cause environmental pollution are evaluated by their low-tech conversion into products with little economic value, such as animal feed and fertilizer. Therefore, the evaluation of food processing waste using effective recycling techniques has become an interesting subject with increasing population, ongoing biotechnological studies, and advances in technology. The conversion of food waste into biotechnological products via fermentation is a sustainable, environmentally friendly, and economical method in line with the principles of green chemistry. This approach promotes the reuse of food waste by supporting the principles of a circular economy and offers sustainable alternatives to fossil fuels and synthetic chemicals. This contributes to reducing the carbon footprint, preserving soil and water quality, and providing economic sustainability through the production of high-value products. In this study, the properties of olive mill wastewater, an important and valuable waste in the olive oil industry, its environmental aspects, and its use in biotechnological applications that integrate green chemistry are evaluated.

Olive mill wastewater treatment strategies to obtain quality water for irrigation: A review

The olive mill industry is a relevant sector in the economy of Mediterranean countries, while it involves high consumption of water and the production of effluents with high environmental impact. The efficient treatment of olive mill wastewater (OMW) is of high relevance, particularly for these countries. Climate changes are leading to increasing periods of droughts, and water recovery from polluted streams is essential to ensure the sustainability of this scarce resource. A combination of various technologies involving physical, chemical, and biological processes has been developed for OMW treatment. However, the treatments studied have limitations such as the operation costs, difficulty of industrial scale-up, and the fact that the vast majority do not lead to suitable treated water for discharge/reuse. As such, it is urgent to develop a solution capable of efficiently treating this effluent, overcoming the disadvantages of existing processes to convert OMW from a serious environmental problem into a valuable source of water and nutrients. In this review, several studies based on the OMW treatment are critically discussed, from conventional approaches such as the physical (e.g. centrifugation, filtration, and adsorption) and biological (anaerobic digestion and anaerobic co-digestion) processes, to the most recent technologies such as advanced membrane filtration, advanced oxidation processes (AOPs) and sulfate radical based AOPs (SR-AOPs). Due to the complexity of the effluent, OMW cannot be efficiently treated by a single process, requiring a sequence of technologies before reaching the required characteristics for discharge into water courses or use in crop irrigation. Reviewing the published results in this matter, it seems that the sequence of processes encompassing ozonation, anaerobic digestion, and SR-AOPs could be the ideal combination for this purpose. However, membrane technologies may be necessary in the final stage of treatment so that the effluent meets legal discharge or irrigation limits.

Transcriptomic Analysis of Colorectal Cancer Cells Treated with Oil Production Waste Products (OPWPs) Reveals Enrichment of Pathways of Mitochondrial Functionality

Oil production waste products (OPWPs) derive from olive mill and represent a crucial environmental problem due to their high polyphenolic content able to pollute the ground. One option to reduce the OPWPs' environmental impact is to exploit polyphenols' biological properties. We sought to analyze the transcriptomic variations of colorectal cancer cells exposed to the OPWPs extracts and hydroxytyrosol, the major component, to recognize unknown and ill-defined characteristics. Among the top affected pathways identified by GSEA, we focused on oxidative phosphorylation in an in vitro system. Colorectal cancer HCT116 and LoVo cells treated with hydroxytyrosol or OPWPs extracts showed enhancement of the respiratory chain complexes' protein levels, ATP production and membrane potential, suggesting stimulation of mitochondrial functions. The major proteins involved in mitochondrial biogenesis and fusion events of mitochondrial dynamics were positively affected, as by Western blot, fostering increase of the mitochondrial mass organized in a network of elongated organelles. Mechanistically, we proved that PPARγ mediates the effects as they are mimicked by a specific ligand and impaired by a specific inhibitor. OPWP extracts and hydroxytyrosol, thus, promote mitochondrial functionality via a feed-forward regulatory loop involving the PPARγ/PGC-1α axis. These results support their use in functional foods and as adjuvants in cancer therapy.

Luminescent Carbon Dots from Wet Olive Pomace: Structural Insights, Photophysical Properties and Cytotoxicity

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles through a systematic search of the best reaction conditions to convert the waste biomass, mainly consisting in holocellulose, lignin and proteins, into carbon dots (CDs) by hydrothermal carbonization processes. Blue-emitting CDs with high fluorescence quantum yields were obtained. Using a comprehensive set of spectroscopic tools (FTIR, Raman, XPS, and ¹H/¹³C NMR) in combination with steady-state and time-resolved fluorescence spectroscopy, a rational depiction of WP-CDs structures and their PL properties was reached. WP-CDs show the up-conversion of PL capabilities and negligible cytotoxicity against two mammalian cell lines (L929 and HeLa). Both properties are excellent indicators for their prospective application in biological imaging, biosensing, and dynamic therapies driven by light.

Exploiting Olive Mill Wastewater via Thermal Conversion of the Organic Matter into Gaseous Biofuel—A Case Study

Olive oil is one excellence of the Italian food industry: around 300 kt yr−1 are produced, creating roughly the same amount of olive mill wastewater (OMW) to be disposed of. The present work describes a process to exploit OMW by converting its organic compounds to valuable gaseous biofuel. A sample OMW was characterized (COD, TOC, solids, and polyphenols) and submitted to membrane filtration tests to concentrate the organic compounds. Based on the results of the experiments, a treatment process was outlined: the retentate streams from microfiltration and ultrafiltration steps were fed to a cracking and a steam reforming reactor, respectively; the obtained syngas streams were then mixed and sent to a methanation reactor. The process was simulated with Aspen Plus (AspenTech©) software, assessing operating conditions and streams compositions: the final biofuel is around 81 mol.% methane, 4 mol.% hydrogen, and 11 mol.% carbon dioxide. The permeate stream cannot be directly disposed of, but both its amount and its polluting charge are greatly reduced. The heat needed by the process, mainly due to the endothermic reactions, can be obtained by burning an amount of olive pomaces, roughly corresponding to one-third of the amount left by olive treatments giving rise to the processed OMW feed.

Polyphenols Extracts from Oil Production Waste Products (OPWPs) Reduce Cell Viability and Exert Anti-Inflammatory Activity via PPARγ Induction in Colorectal Cancer Cells

Olive oil production is associated with the generation of oil production waste products (OPWPs) rich in water-soluble polyphenols that represent serious environmental problems. Yet OPWPs can offer new opportunities by exploiting their bioactive properties. In this study, we chemically characterized OPWPs polyphenolic extracts and investigated their biological activities in normal and colorectal cancer cells. Hydroxytyrosol (HTyr), the major constituent of these extracts, was used as the control. We show that both HTyr and the extracts affect cell viability by inducing apoptosis and cell cycle arrest. They downregulate inflammation by impairing NF-κB phosphorylation and expression of responsive cytokine genes, as TNF-α and IL-8, at both mRNA and protein levels, and prevent any further increase elicited by external challenges. Mechanistically, HTyr and the extracts activate PPARγ while hampering pro-inflammatory genes expression, acting as a specific agonist, likely through a trans-repression process. Altogether, OPWPs polyphenolic extracts show stronger effects than HTyr, conceivably due to additive or synergistic effects of all polyphenols contained. They display anti-inflammatory properties and these results may pave the way for improving OPWPs extraction and enrichment methods to reduce the environmental impact and support their use to ameliorate the inflammation associated with diseases and tumors.

Thermophilic Dark Fermentation of Olive Mill Wastewater in Batch Reactors: Effect of pH and Organic Loading

In recent decades, olive oil consumption has almost tripled worldwide. Olive oil production is linked with the production of enormous amounts of olive mill wastewater, the main by-product derived from three-phase olive mills. Due to the environmental risks of olive mill wastewater disposal, the management and valorization of the specific waste stream is of great importance. This work focuses on the thermophilic dark fermentation of olive mill wastewater in batch reactors, targeting pH optimization and the organic loading effect. A series of experiments were performed, during which the organic load of the substrate remained at 40 g/L after dilution with tap water, and the pH was tested in the range of 4.5 to 7.5. The maximum yield in terms of produced hydrogen was obtained at pH 6.0, and the yields were 0.7 mol H2/mol glucose or 0.5 L H2/Lreactor. At the same conditions, a reduction of 62% of the waste’s phenols was achieved. However, concerning the effect of organic loading at the optimized pH value (6.0), a further increase in the organic load minimized the hydrogen production, and the overall process was strongly inhibited.

A novel bioprocess combining anaerobic co-digestion followed by ultra-filtration and microalgae culture for optimal olive mill wastewater treatment

Treatment of olive mill wastewater (OMW) has received considerable research globally due to its influence on the technical, economic, and environmental sustainability of wastewater biogas production. This work presents a novel combined biological process for OMW treatment in terms to produce for the first time, treated OMW and a valuable microalgae biomass. The process involves anaerobic co-digestion (AD), a low cut-off membrane ultra-filtration (UF) and a subsequent Scenedesmus sp. culture. The AD of OMW was conducted at high initial COD ranging from 28 to 38 g/L using an up-flow anaerobic fixed bed bio-reactor (300 L). Results revealed that the maximum biogas production was about 0.507 L/g COD_introduced.day containing 73% of methane corresponding to a methane yield of 0.370 L/g COD_introduced.day obtained at an organic loading rate of 4.58 g COD/L.day. High removal levels of COD, total phenolic compounds, and total suspended solids in the anaerobic liquid digestate (ALD) were achieved after AD and UF. Scenedesmus sp. was then cultivated on the ultra-filtrated ALD. A maximum biomass productivity of 0.15 g/L.day was recorded when Scenedesmus sp. is grown on 25% of ultra-filtrated ALD with a maximum nitrogen removal rate of 15.18 mg/L.day and an almost total elimination of phosphorus and phenolic compounds.

Thermophilic anaerobic digestion of olive mill wastewater in an upflow packed bed reactor: Evaluation of 16S rRNA amplicon sequencing for microbial analysis

Olive mill wastewater, a by-product of olive oil production after the operation of three-phase decanters, was used in a thermophilic anaerobic digester targeting efficient bioconversion of its organic load into biogas. An active anaerobic inoculum originating from a mesophilic reactor, was acclimatized under thermophilic conditions and was filled into a high-rate upflow packed bed reactor. Its performance was tested towards the treatment efficacy of olive mill wastewater under thermophilic conditions reaching the minimum hydraulic retention time of 4.2 d with promising results. As analysis of the microbial communities is considered to be the key for the development of anaerobic digestion optimization techniques, the present work focused on characterizing the microbial community and its variation during the reactor's runs, via 16S rRNA amplicon sequencing. Identification of new microbial species and taxonomic groups determination is of paramount importance as these representatives determine the bioprocess outcome. The current study results may contribute to further olive mill wastewater exploitation as a potential source for efficient biogas production.

Olive Mill Wastewater as Renewable Raw Materials to Generate High Added-Value Ingredients for Agro-Food Industries

Olive oil production represents an agro-industrial activity of vital economic importance for many Mediterranean countries. However, it is associated with the generation of a huge amount of by-products, both in solid and liquid forms, mainly constituted by olive mill wastewater, olive pomace, wood, leaves, and stones. Although for many years olive by-products have only been considered as a relevant environmental issue, in the last decades, numerous studies have deeply described their antioxidant, anti-inflammatory, immunomodulatory, analgesic, antimicrobial, antihypertensive, anticancer, anti-hyperglycemic activities. Therefore, the increasing interest in natural bioactive compounds represents a new challenge for olive mills. Studies have focused on optimizing methods to extract phenols from olive oil by-products for pharmaceutical or cosmetic applications and attempts have been made to describe microorganisms and metabolic activity involved in the treatment of such complex and variable by-products. However, few studies have investigated olive oil by-products in order to produce added-value ingredients and/or preservatives for food industries. This review provides an overview of the prospective of liquid olive oil by-products as a source of high nutritional value compounds to produce new functional additives or ingredients and to explore potential and future research opportunities.

Progress on green table olive processing with KOH and wastewaters reuse for agricultural purposes

Table olive wastewaters are seriously polluting and a difficult to treat effluent worldwide, mainly due to their high content in sodium. An alternative approach could be the treatment of the olives with KOH instead of NaOH, in order to reuse the olive streams as biofertilizers. In this study, the debittering of olives with KOH was investigated at pilot plant scale in two olive seasons. The results indicated that a concentration between 1.7 and 2.0% of KOH (similar to that employed with NaOH) led to a fermented product with the same physicochemical and organoleptic characteristics than the traditional one. The spent lyes and washing waters from the KOH treatments were gathered and vacuum evaporated, giving rise to a concentrated solution rich in potassium (52 g/L) that was tested as biofertilizer in open tomato fields. Furthermore, the drip irrigation of the tomato plants with a combined olive solution and mineral fertilizer (NH₄NO₃) produced similar tomato yield and quality than the irrigation with only mineral fertilizer (NH₄NO₃ + KNO₃). Overall, it has been demonstrated that Spanish-style green olives can be processed with KOH and the effluents valorized to be used as biofertilizer.

Olive mill wastewater reuse to enable solar photo-Fenton-like processes for the elimination of priority substances in municipal wastewater treatment plant effluents

Olive mill wastewater (OMW) appears as an interesting and innovative natural alternative to synthetic chelating agents of iron in solar photo-Fenton processes at circumneutral pH due to its high polyphenol content, valorizing wastewater typically found in sunny countries. The aim of this work was the reuse of OMW for the elimination of other recalcitrant microcontaminants: terbutryn, chlorfenvinphos, diclofenac, and pentachlorophenol. Highly diluted OMW (1:1500) was employed to keep the iron in solution at circumneutral pH. Eighty percent degradation of microcontaminants was achieved, although the reaction rate was slow compared with conventional photo-Fenton process, due to Fe-polyphenol complex instability at neutral pH. At pH around 4 (considerable superior to the photo-Fenton optimal pH 2.8), Fe-polyphenol complex stability was promoted: solar UV energy required was 25 times lower to reach the objective of 80% microcontaminants degradation, which was attained in a single step, without coupling with other processes. Operating photo-Fenton at slightly acidic pH was proposed for the first time for possible reuse of treated wastewater in crop irrigation, requiring minimum pH adjustment by simply mixing it with natural wastewater. Graphical abstract.

Sustainable Environmental Management and Valorization Options for Olive Mill Byproducts in the Middle East and North Africa (MENA) Region

Cultivation of olive trees and olive oil production have been considered as a legacy for the Mediterranean region. This custom represents a very important benefit for many nations in terms of wealth and health. However, huge amounts of by-products and waste are generated during olive oil production. This represents a serious environmental impact on land and water bodies if not properly handled. Olive oil extraction generates two waste streams, a solid waste called pomace and olive mill wastewater (OMWW), which has been considered as highly pollutant and phytotoxic waste. These wastes have high disposal costs and predominantly generated from small-scale enterprises that have limited financial resources to treat them properly before discharge to the environment. Besides being a serious environmental problem, OMWW has potential economic value that remains to be utilized such as: fertilizers, valuable antioxidants agents and fatty acids needed in human diet. Also, Olive pomace is a valuable renewable energy source with an energy density of 23 MJ/kg and has become an inexpensive alternative for fossil fuels. Aiming at adding value to the olive production sectors and potential valorization options for byproducts in the MENA region, international practices applied in olive mills wastes management’s and treatment methods used in major oil producing countries are presented.

Fitting Biochars and Activated Carbons from Residues of the Olive Oil Industry as Supports of Fe- Catalysts for the Heterogeneous Fenton-Like Treatment of Simulated Olive Mill Wastewater

A series of biochars and activated carbons (ACs) was prepared combining carbonization and physical or chemical activation of cheap and abundant residues of the olive oil industry. These materials were used as Fe-support to develop low-cost catalysts for the heterogeneous Fenton-like oxidation of simulated olive mill wastewater (OMW), the highly pollutant effluent generated by this agroindustry. Commercial ACs were also used as reference. All catalysts prepared were extensively characterized and results related with their performances in the catalytic wet peroxide oxidation (CWPO). Results showed a linear relationship of the textural properties of the catalysts with the adsorptive and catalytic performance, as well as the preferential adsorption and degradation of some phenolic compounds (caffeic and gallic acids) by specific interactions with the catalysts’ surface. Despite the best performance of catalysts developed using commercial supports, those prepared from agro-industrial residues present some advantages, including a smaller catalyst deactivation by iron leaching. CWPO results show that catalysts from physically activated olive stones are the most promising materials, reaching total organic carbon and toxicity reductions of 35% and 60%, respectively, as well an efficient use of H₂O₂, comparable with those obtained using commercial supports. This approach showed that the optimized treatment of this type of residues will allow their integration in the circular economic process of the olive oil production.

Optimal conditions for olive mill wastewater treatment using ultrasound and advanced oxidation processes

The treatment of olive mill wastewater (OMW) in Jordan was investigated in this work using ultrasound oxidation (sonolysis) combined with other advanced oxidation processes such as ultraviolet radiation, hydrogen peroxide (H₂O₂) and titanium oxide (TiO₂) catalyst. The efficiency of the combined oxidation process was evaluated based on the changes in the chemical oxygen demand (COD). The results showed that 59% COD removal was achieved within 90 min in the ultrasound /UV/TiO₂ system. A more significant synergistic effect was observed on the COD removal efficiency when a combination of US/UV/TiO₂ (sonophotocatalytic) processes was used at low ultrasound frequency. The results were then compared with the COD values obtained when each of these processes was used individually. The effects of different operating conditions such as, ultrasound power, initial COD concentration, the concentration of TiO₂, frequency of ultrasound, and temperature on the OMW oxidation efficiency were studied and evaluated. The effect of adding a radical scavenger (sodium carbonate) on the OMW oxidation efficiency was investigated. The results showed that the sonophotocatalytic oxidation of OMW was affected by the initial COD, acoustic power, temperature and TiO₂ concentration. The sonophotocatalytic oxidation of OMW increased with increasing the ultrasound power, temperature and H₂O₂ concentration. Sonolysis at frequency of 40 kHz combined with photocatalysis was not observed to have a significant effect on the OMW oxidation compared to sonication at frequency of 20 kHz. It was also found that the OMW oxidation was suppressed by the presence of the radical scavenger. The COD removal efficiency increased slightly with the increase of TiO₂ concentration up to certain point due to the formation of oxidizing species. At ultrasound frequency of 20 kHz, considerable COD reduction of OMW was reported, indicating the effectiveness of the combined US/UV/TiO₂ process for the OMW treatment.

Calcium-modified clinoptilolite as a recovery medium of phosphate and potassium from anaerobically digested olive mill wastewater

Olive mill wastewater (OMW) is characterized as a high-strength effluent due to the high organic load, low biodegradability, and presence of phytotoxic compounds. Most of the OMW treatment methods proposed, including adsorption, focus mainly on the reduction of chemical oxygen demand and recovery of polyphenols. Adsorption studies aiming at nutrient removal from OMW are very limited. In the present work, Ca(OH)₂-treated zeolite (CaT-Z) in a granular form was used for simultaneous recovery of phosphate (PO₄^3-) and potassium (K⁺) ions from two samples of anaerobically digested OMW. Nutrient adsorption was investigated as a function of contact time, pH and dilution of OMW with deionized water. The lower removal efficiency of phosphorus (P) by CaT-Z was observed at higher dilution ratios consisted of 3.125-6.25% OMW-1 and 5% OMW-2. The maximum P removal was 73.9% in 25% OMW-1 and 85.9% in 10% OMW-2. Potassium removal, as the predominant cation of OMW samples, increased from 17.3 to 46.1% in OMW-1 and from 15.1 to 57.7% in OMW-2 with increasing dilution. The maximum experimental adsorption capacities were 15.8 mg K and 2.14 mg P per gram of CaT-Z. Five sequential treatments of 50% OMW-2 with fresh CaT-Z at each stage ensured a cumulative removal of 87.5% for P and 74.9% for K. Adsorption kinetics were faster for K than for P. The plant-available P was found to be the predominant fraction on the loaded CaT-Z. Electron Probe Micro-analysis confirmed the enhanced content of K and P on the loaded CaT-Z, whereas X-ray mapping revealed the co-distribution of Ca and P. This study demonstrates the potential usage of CaT-Z as an immobilization medium of P and K from anaerobically treated OMW.

Best management practices from agricultural economics: Mitigating air, soil and water pollution

Often the several stakeholders involved in the agricultural sector place a greater emphasis on the negative externalities from farming production rather than on the solutions and approaches to mitigate, namely impacts from pollution. The scientific literature, in certain circumstances, follows this tendency leaving a vast chasm of enormous potential left to be explored. It is important to contribute towards the reduction of this gap, highlighting the best management practices implemented across the agricultural sector around the world, specifically to make them more visible and give incentive to the several agents in adopting and spreading their use. In this way, the main objective is to stress the best management practices presented by the global scientific literature from the farming sector. To achieve this objective methodology based on bibliometric analysis-factor-analysis-literature survey approach was considered, applied to 150 documents obtained from the Web of Science (core collection) related with the following topics: best management practice; agricultural economics; air, soil and water pollution. As main insights, it is worth referring the best management practices to deal with problems from agricultural production, such as, for example, the use of agricultural residues as feedstock for renewable energies. With regard to sustainable development in the agricultural sector, concepts such as "sustainable remediation" have their place. On the other hand, the agricultural and environmental policies and the agricultural costs associated with the several farming practices also play a determinant role here. Finally, only fraction of the scientific documents analysed (16 papers) belong to the group of studies related to policies, showing that there are potential subjects to be addressed here in future studies related with these topics. The same happens for cost-benefit analyses (24 documents).

Processing of table olives with KOH and characterization of the wastewaters as potential fertilizer

In Mediterranean countries the table olive industry produces a huge volume of wastewaters that are phytotoxic due to their high sodium content. Olives intended for Spanish-style green olives are currently debittered with NaOH that generates lyes and washing waters that cannot be used for agronomic purposes. In this study, the substitution of NaOH with KOH during the debittering of Manzanilla and Hojiblanca cultivars was assessed as well as the vacuum evaporation of the olive wastewaters to comply with fertilizer requirements. Typical lactic acid fermentation occurred in brines of olives treated with KOH and a final product with similar color and flavor characteristics to those treated with NaOH was achieved. However, lower texture was found in olives debittered with KOH than those with NaOH, using them at the same molar concentration. Furthermore, the lyes and washing waters from the KOH treatment were concentrated up to 10% of their initial volume and they complied with Spanish requirements to be considered as organo-mineral fertilizers (C_organic > 4%, K₂O > 2%, N_total + K₂0 > 6%) although an external source of nitrogen would be needed. They also had a high content in phenolic compounds, particularly hydroxytyrosol. This research demonstrates that table olives can be processed with KOH and the generated waste streams could have potential applications in agriculture or being a source of bioactive substances.

How an environmental issue could turn into useful high-valued products: The olive mill wastewater case

Carbon-based nanomaterials have been directly synthesized from olive mill wastewaters (OMWWs) for the first time, using expedite and simple environmental-friendly procedures. The OMWWs collected from a mill operating by a two-phase centrifugation system, after being heated (150-300 °C) solely or in the presence of additives for 2-12 h, furnished nanostructured materials in high yields. Under an optimised set of reaction conditions here described, the resultant as-synthetized aqueous dispersions of carbon nanoparticles exhibit outstanding fluorescence emission properties, which encompass an astonishing quantum yield (Φ_F > 0.4). The as-prepared carbon nanomaterials show excitation-dependent emissions covering the whole visible spectrum, with a predominant high glow in the blue-green region, and a remarkable photostability. The relevant features attained by the nanomaterials here reported, allied to their easy synthesis and carbon source affordability, render them with unique capabilities to be used in several current and emerging technological applications, namely in bioimaging and nanomedicine, sensorial analysis, (photo)catalysis and optoelectronics. The as-synthesized nanoparticles show a remarkable high sensitivity and selectivity towards haemoglobin.

Biostimulant Potential of Humic Acids Extracted From an Amendment Obtained via Combination of Olive Mill Wastewaters (OMW) and a Pre-treated Organic Material Derived From Municipal Solid Waste (MSW)

Olive mill wastewaters (OMW) contain significant levels of phenolic compounds with antimicrobial/phytotoxic activity and high amounts of undecomposed organic matter that may exert negative effects on soil biology. Among OMW detoxification techniques, those focusing on oxidative degradation of phenolic compounds are relevant. The composting (bio-oxidation) process in particular, exploits exothermic oxidation reactions by microorganisms to transform the organic matrix of OMW into an amendment biologically stable and feasible to use in agriculture. This process consists of an active phase during which organic compounds are rapidly decomposed, and a curing phase characterized by a slow breakdown of the remaining materials with the formation of humic substances (HS) as by-products. In this study, bio-oxidation of OMW was performed using a pre-treated organic material derived from municipal solid waste (MSW). The obtained amendment (OMWF) was stable and in accordance with the legislative parameters of mixed organic amendments. HS were then extracted from OMWF and MSW (control amendment, Amd-C), and differences in structural properties of their humic acid (HA) fraction were highlighted via spectroscopy (Fourier Transform Infrared) and Dynamic Light Scattering. To assay a potential use of HA as biostimulants for crops, 12-day old Zea Mays L. plants were supplied with HA at 0.5 mg and 1 mg C L-1 for 2 days. HA from both amendments increased plant growth, but HA from OMWF was more effective at both dosages (plus 35-37%). Also, HA from OMWF enhanced both nitrogen assimilation and glycolysis by increasing the activity of nitrate reductase (∼1.8-1.9 fold), phosphoglucose isomerase (PGI) (∼1.8-2 fold) and pyruvate kinase (PK) (∼1.5-1.8 fold), while HA from Amd-C targeted glycolysis preferentially. HA from OMWF, however, significantly stimulated plant nutrition only at lower dosage, perhaps because certain undetermined compounds from detoxified OMW and incorporated in HA altered the root membrane permeability, thus preventing the increase of nutrient uptake. Conversely, HA from Amd-C increased nutrient accumulation in maize at both dosages. In conclusion, our results indicate that the amendment obtained via OMW composting using MSW had a reduced pollution load in terms of phenolic compounds, and HA extracted from OMWF could be used as valuable biostimulants during maize cultivation.

Mechanisms governing the leaching of soil metals as a result of disposal of olive mill wastewater on agricultural soils

Olive mill wastewater (OMWW) is an acidic, saline, and organic matter-rich aqueous byproduct of olive oil production that is usually disposed of by spreading on agricultural soils. This study tested whether spreading OMWW can release indigenous soil metals (Fe, Mn, Cu and Zn) through pH, redox, and DOM complexation-related mechanisms, using three agricultural soils having different textures and chemical properties, and controlled pH and redox conditions (pH5.6 or 8.4; ORP from -200 to +250mV). Comparison treatments included a solution having the same salt content and composition as OMWW but lacking OM, and deionized water (DW). In all three soils and under all pH and redox conditions, the model salt solution and DW treatments solubilized considerably fewer metal cations than did OMWW. Overall, the primary factor in metals release from the soils by OMWW was the DOM fraction. pH, redox and soil type played secondary but important roles in solubilization of the various metals. pH had a major impact on Mn leaching but no impact on Fe and Cu leaching. Conversely, redox did not affect Mn leaching, but lower redox conditions contributed to elevated release of both Fe and Cu. For the most part, released metals were sourced from water soluble, exchangeable, easily reducible, and moderately reducible soil metals pools. Fe, Mn and Cu released from the soils by OMWW featured mainly as metal-organic complexes, and OMWW generally caused Zn precipitation in the soils. Soils rich in clay and organic matter under reduced pH and low redox conditions released substantially more metal cations than did a sand-rich soil. Spreading OMWW may result in sequestration of essential micronutrients like Zn, and increased availability of other micronutrients such as Fe, Mn and Cu.