Sustainable vs. Conventional Approach for Olive Oil Wastewater Management: A Review of the State of the Art

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.

The performance of pharmaceutical wastewater treatment system of electrocoagulation assisted adsorption using perforated electrodes to reduce passivation

The integrated electrocoagulation-assisted adsorption (ECA) system with a solar photovoltaic power supply has gained more attention as an effective approach for reduction chemical oxygen demand (COD) from pharmaceutical wastewater (PhWW). In this research, the ECA system was used for the treatment of PhWW. Several operating parameters were investigated, including electrode number, configuration, distance, operating time, current density, adsorption time, and temperature. A current density of 6.656 mA/cm2, six electrodes, a 20-min time, a 4 cm distance, an MP-P configuration, and a 45 °C temperature produced the maximum COD reductions, where the operating cost of conventional energy was 0.273 $/m3. The EC, adsorption, and combination of EC and adsorption processes achieved efficient COD reductions of 85.4, 69.1, and 95.5%, respectively. The pseudo-second-order kinetic model and the Freundlich isotherm fit the data of the endothermic adsorption process. Therefore, it was found that the combination processes were superior to the use of these processes in isolation to remove COD.

Application of halophiles in UMFC (upflow microbial fuel cell) for the treatment of saline olive oil industrial wastewater coupled with eco-energy yield

The olive oil industry faces a major problem of treating the wastewater with high organic content and safe disposal. Olive oil industrial wastewater (OOIWW) consists of highly toxic environmental pollutants with high salinity. Saline olive oil industrial wastewater was treated using halophilic consortium in UMFC (upflow microbial fuel cell) mobilized with carbon felt as electrode. Total and soluble COD (chemical oxygen demand), total suspended solids and phenol content removal were studied at different organic loads (0.56, 0.77, 1.05, 1.26, 1.52 and 1.8 gCOD/L). UMFC with OOIWW was optimized at 1.52 gCOD/L for high organic removal and corresponding electricity production. Total COD, soluble COD, TSS and phenol removal were 91%, 89%, 78%, and complete removal of phenol was accomplished at the optimized organic load (1.52 gCOD/L). Correspondingly, the maximum bioenergy yield was 784 mV with 439 mW/m2 (power density) and 560 mA/m2 (current density), respectively. The presence of prominent halophilic exo-electrogens such as Ochrobactrum, Marinobacter, Rhodococcus and Bacillus potently treated the OOIWW and exhibited high energy yield.

Towards effective recovery of humate as green fertilizer from landfill leachate concentrate by electro-neutral nanofiltration membrane

Under the environmental sustainability concept, landfill leachate concentrate can be up-cycled as a useful resource. Practical strategy for effective management of landfill leachate concentrate is to recover the existing humate as fertilizer purpose for plant growth. Herein, we designed an electro-neutral nanofiltration membrane to separate the humate and inorganic salts for achieving a sufficient humate recovery from leachate concentrate. The electro-neutral nanofiltration membrane yielded a high retention of humate (96.54 %) with an extremely low salt rejection (3.47 %), tremendously outperforming the state-of-the-art nanofiltration membranes and exhibiting superior promise in fractionation of humate and inorganic salts. With implementation of the pressure-driven concentration process, the electro-neutral nanofiltration membrane enriched the humate from 1756 to 51,466 mg∙L-1 at a fold of 32.6, enabling 90.0 % humate recovery and 96.4 % desalination efficiency from landfill leachate concentrate. Furthermore, the recovered humate not only exerted no phytotoxicity, but also significantly promoted the metabolism of red bean plants, serving as an effective green fertilizer. The study provides a conceptual and technical platform using high-performance electro-neutral nanofiltration membranes to extract the humate as a promising nutrient for fertilizer application, in view of sustainable landfill leachate concentrate treatment.

Dietary supplementation with olive oil co-products rich in polyphenols: a novel nutraceutical approach in monogastric animal nutrition

In recent years, the increased demand for agri-food products to feed livestock species has stimulated research to identify novel solutions for the valorization of natural waste, according to the modern concept of a circular economy. Numerous studies have shown the use of plant-derived and agro-industrial co-products that are sources of bioactive molecules for preparing animal feeds. Supplementation with co-products derived from the extraction of olive oil (i.e., olive pomace, olive mill wastewater, olive cake and olive leaf) in diet has been widely considered in recent decades, because these wastes are produced in high quantity and their re-use represents an innovative economic and environmental strategy. Olive oil co-products are characterized by various bioactive molecules such as polyphenols, carbohydrates, proteins, and lipids. Among them, polyphenols are the nutraceuticals most studied, showing to promote health effects in both humans and animals. Olive oil co-products and their phenolic extracts have shown many beneficial and promising effects when added to the diets of monogastric animals, by improving performance parameters and maintaining the oxidative status of meat and derived products. This review provides an update on the use of olive co-products in monogastric animal (swine, poultry and rabbit) diets and their effects on the productive performance, meat quality characteristics and gut health status.

Using circular economy principles in the optimisation of sludge-based activated carbon production for the removal of perfluoroalkyl substances

Massive sewage sludge (SS) production from municipal wastewater treatment plants and the presence of numerous pollutant types render the process of SS treatment and disposal costly and complex. Here, resource recovery from SS was maximised via the optimisation of sludge-based activated carbon (SBAC) production for the removal of poly- and perfluoroalkyl substances (PFASs), while considering economic factors and minimising environmental impacts. SBAC production optimisation was realised under different operating conditions (different ZnCl₂ impregnation ratios and different pyrolysis activation temperatures and durations). The sorption capacity of the optimised SBAC with respect to the removal of nine commonly detected PFASs, with environmentally relevant concentrations (∽50 μg/L), from simulated wastewater was evaluated. Economic analysis and life-cycle assessment (LCA) were also performed to determine the feasibility of the process and its potential role in the circular economy. Batch adsorption tests confirmed the high efficiency of the optimised SBACs for PFAS removal (93-100 %), highlighting the possibility of converting SS to SBAC. Economically speaking, the optimised SBAC at 1.5 M ZnCl₂, 500 °C, and 0.75 h reduced total production cost by 49 %. Further, the cost could be reduced to as little as 1087 US $/metric-ton compared with that corresponding to the original conditions (2.5 M ZnCl₂, 500 °C, 2 h; 2144 US $/metric-ton). LCA results also showed that freshwater ecotoxicity, marine ecotoxicity, and human non-carcinogenic toxicity were the most affected environmental impact indicators, showing a 49 % decrease when ZnCl₂ impregnation ratio was reduced from 2.5 to 1.5 M. These findings highlighted the optimal conditions for the production of SBAC with high sorption capacity at a reduced cost and with reduced environmental impacts. Thus, they can serve as valuable tools for decision making regarding the selection of the most sustainable and economically feasible process for PFAS removal.

Towards a circular economy in virgin olive oil production: Valorization of the olive mill waste (OMW) "alpeorujo" through polyphenol recovery with natural deep eutectic solvents (NADESs) and vermicomposting

Virgin olive oil (VOO) production generates large amounts of a harmful by-product, olive mill waste (OMW) or alpeorujo, which has a strong environmental impact and that must be recycled to adapt VOO production to a circular economy model. Here, the valorization of OMW was studied by considering three consecutive stages: Stage 1 involves the generation of OMW; Stage 2 the recovery of bioactive phenolic compounds from the fresh OMW using natural deep eutectic solvents (NADESs), generating a valuable phenolic extract and a new by-product, a dephenolized OMW named "alpeoNADES"; and Stage 3 involves vermicomposting alpeoNADES with Eisenia fetida earthworms. Six NADES were formulated and tested, selecting a NADES composed of citric acid and fructose (CF) derived from food grade and biodegradable substances. CF was the most effective solvent to obtain phenolic extracts for nutraceutical and agronomical purposes, extracting 3988.74 mg/kg of polyphenols from fresh OMW. This alpeoNADES is a non-palatable substrate for E. fetida earthworms, as the residual CF gives it an acidic pH (pH 2). Its palatability was improved by mixing it with horse manure and straw for vermicomposting, in a 1:1 and 3:1 dry weight ratio. When these substrates were precomposted for 3 weeks they reached pH 5.5-6 and they could then be vermicomposted for 23 weeks (using OMW as a control). The best substrate for vermicomposting was determined by the worm biomass, growth rate, carbon to nitrogen (C:N) ratio, and N and P content. AlpeoNADES and manure 3:1 produced the highest quality vermicompost in the shortest time, generating a product that complied with European standards for organic fertilizers. Hence, alpeoNADES was recycled to a low-cost, organic balanced fertilizer in Stage 3, enabling the olive oil industry to transition to sustainable production through this integrated circular economy design.