Comparative life cycle assessment of anaerobic digestion, lagoon evaporation, and direct land application of olive mill wastewater.

Olive mill wastewater is a prominent waste stream in the Mediterranean countries, with its uncontrolled disposal in water recipients causing significant environmental issues. Anaerobic digestion has been extensively studied for the treatment of various agricultural waste streams. The scope of the present study was the environmental evaluation of the anaerobic digestion of three-phase olive mill wastewater for energy production in an anaerobic bioreactor. Regarding the environmental assessment of the process, the results indicate a lead in the proposed process compared with the baseline scenarios. Moreover, several environmental issues in terrestrial acidification and water eutrophication midpoint categories were exhibited by the digestate utilization. The implementation of the anaerobic digestion method averts an overall environmental damage of 5 mPt per 1000 kg of waste treated. For this reason, the implementation of the proposed method could be a sustainable alternative for wastewater treatment in olive oil production regions, aiming to circular economy.

Cobalt oxide nanoparticles as a new strategy for enhancing methane production from anaerobic digestion of noxious aquatic weeds.

This study investigated the effect of cobalt oxide nanoparticles (Co3O4-NPs) supplementation on anaerobic microbial population changes and anaerobic digestion (AD) performance and production. Co3O4-NPs (3 mg/L) showed the maximum enhancement of biogas yield over the cow dung (CD) as control and the co-digestion process of CD with water hyacinth (WH) by 58.9 and 27.2 %, respectively. Furthermore, methane (CH4) yield was enhanced by 89.96 and 43.4 % over CD and co-digestion processes, respectively. Additionally, the microbiological assessment analysis using VIT® gene probe technology showed that Co3O4-NPs enhance the viability of total bacterial cells by 9 %. The techno-economic analysis reflects the revenue of this strategy on the highest net energy content of biogas, which was achieved with 3 mg/L Co3O4-NPs and was 428.05 kWh with a net profit of 67.66 USD/m3 of the substrate. Therefore, nanoparticle supplementation to the AD process can be considered a promising approach to enhance biogas and CH4.

Hydroxytyrosol Enrichment of Olive Leaf Extracts via Membrane Separation Processes.

Antioxidants isolated from plant materials, such as phenolics, have attracted a lot of attention because of their potential uses. This contributes to the idea of the biorefinery, which is a way to produce useful products from biomass waste. Olea europaea byproducts have been extensively investigated for their large contents in phenolics. Oleuropein is a phenolic compound abundant in olive leaves, with its molecule containing hydroxytyrosol, elenolic acid, and glucose. In this work, olive leaf extracts were treated using different combinations of ultrafiltration and nanofiltration membranes to assess their capacity of facilitating the production of hydroxytyrosol-enriched solutions, either by separating the initially extracted oleuropein or by separating the hydroxytyrosol produced after a hydrolysis step. The best performance was observed when an ultrafiltration membrane (UP010, 10,000 Da) was followed by a nanofiltration membrane (TS40, 200-300 Da) for the treatment of the hydrolyzed extract, increasing the purity of the final product from 25% w/w of the total extracted compounds being hydroxytyrosol when membrane processes were not used to 68% w/w.

High-rate in-vessel continuous composting of olive mill byproducts.

The increasing production of agro-industrial organic residues in modern society is extremely concerning. One of the most polluting procedures in the agricultural industry is the production of olive oil. This process creates a large amount of waste with high organic load and phytotoxic components. In this study, composting of two-phase olive pomace (OP), olive leaves (OL) and dewatered anaerobic sludge (DAS) from an olive mill wastewater anaerobic digestion process was conducted in a pilot-scale in-vessel high-rate continuous composter. Five different feed scenarios were studied with different OP/OL ratio in the feed material, while the effect of the addition of pine tree bark pieces (PB) and DAS was examined. The OP:OL 95:5 % w/w ratio exhibited the best results in terms of product quality, while OL proved capable of acting as a bulking agent for the better aeration of the material. The final product in the optimum feed ratio was free of Salmonella spp., was stable in terms of static respiratory index (lower than 0.5 g O2 kg-1 VS h-1) but contained elevated E. coli levels (3.5 × 104 CFU g-1 with a limit of 1 × 103 CFU g-1), which was the only EU proposed compost quality criteria not met. The addition of a more easily degradable material in the feed mixture is expected to lead to elevated composting temperature and amend the presence of pathogens.

Proposed protocol for rate-limiting step determination during anaerobic digestion of complex substrates.

Anaerobic digestion is a complex process, involving various microorganism groups and, consequently, several reactions. An easy-to-use protocol for the rate-limiting step determination of the process is proposed. The hydrogen production, acetate production, and acetate consumption rates can be calculated, according to a structured algorithm. During the rate limiting step determination, several compounds (biopolymer and monomer representatives, as well as sodium acetate) were used, combined or not with the substrate, to draw the corresponding conclusions. Three substrates were tested, characterized by specific organic compound groups (carbohydrates, proteins, and fats). All three substrates followed the acetate-consuming pathway for the organic matter conversion to methane. In this study, the rate-limiting step for the pathway of acetate consumption was acetate production. Determining the rate-limiting step through the proposed protocol can point to the appropriate actions needed to boost methane production, like substrate pretreatment, using an acidogenic reactor, or checking for the presence of inhibitors.

Biopolymers production from microalgae and cyanobacteria cultivated in wastewater: Recent advances.

Plastic materials are used to manufacture a broad variety of items with a short useful lifespan, resulting in significant amounts of waste material generation. This form of waste is often observed floating at sea, and different microplastics have been discovered in fish stomachs and women's placentas. Bioplastics are a more biodegradable substitute for fossil-based polymers. Microalgae are capable of producing poly (hydroxy alkanoate) esters (PHAs), aliphatic polyesters that are biodegradable. The most prevalent and well-characterized biopolymer is the poly (3-hydroxy butyrate) ester (PHB), which belongs to the short-chain PHAs. Under aerobic conditions, PHB compounds degrade fully to carbon dioxide and water. They are ecologically neutral, having thermal and mechanical qualities comparable to those of petrochemical polymers. Numerous microalgae species have been reported in the literature to be capable of making bioplastics under certain conditions (N-P restriction, light exposure, etc.), which may be exploited as a source of energy and carbon. To further ameliorate the environmental impact of microalgae culture for bioplastics production, a limited number of published studies have examined the accumulation of bioplastics, from microalgae grown in wastewater, at a concentration of 5.5-65% of dry biomass weight.

High-Yield Production of a Rich-in-Hydroxytyrosol Extract from Olive (Olea europaea) Leaves.

The aim of the present study was to explore the high-yield production of hydroxytyrosol, a phenolic compound with very high antioxidant capacity. Olea europaea leaves were chosen as feedstock as they contain significant amounts of oleuropein, which can be hydrolyzed to hydroxytyrosol. The chosen techniques are widely used in the industry and can be easily scaled up. Olive leaves underwent drying and mechanical pretreatment and extractives were transported to a solvent by solid-liquid extraction using water-ethanol mixtures. The use of approximately 60-80% ethanol showed an almost 2-fold increase in extracted phenolics compared to pure water, to approximately 45 g/kg of dry leaves. Extracted oleuropein was hydrolyzed with hydrochloric acid and the hydrolysate was extracted with ethyl acetate after pH adjustment. This step led to a hydroxytorosol content increase from less than 4% to approximately 60% w/w of dry extract, or 10-15 g of hydroxytyrosol recovery per kg of dry leaves.

Recovery of Water from Secondary Effluent through Pilot Scale Ultrafiltration Membranes: Implementation at Patras' Wastewater Treatment Plant.

Fresh water shortages affect larger areas each year due to the increased human population combined with climate change. Reuse of treated sewage water (mostly for nonpotable uses) can have a significant impact on reducing water scarcity. Ultrafiltration membranes are widely considered as a very good candidate for the remediation of this type of water. The case of Patras' sewage treatment plant was examined for the treatment of its secondary settling tank effluent using a pilot ultrafiltration unit to produce permeate water suitable for reuse according to Greek legislation. The physicochemical characteristics of the membrane permeate stream showed significant improvements in the quality of the produced water. Turbidity was reduced by 99%, total suspended solids were decreased by more than 94%, while COD was reduced by 37%. E. coli and Enterococcus were detected at high concentrations in the feed stream but were eliminated in the membrane permeate. The results presented herein indicate that the installed equipment is capable of producing improved quality water suitable for reuse even with the strictest limits imposed by Greek legislation.

Composting of anaerobic sludge from the co-digestion of used disposable nappies and expired food products.

Anaerobic sludge originating from the co-digestion of used disposable nappies and expired food products treated in a pilot two-stage system was examined as feed material for a continuous pilot-scale composter (capacity: 300 L feed per week). The feed materials and final compost products were analyzed and evaluated for their suitability as compost materials. Ιn terms of stability, the compost products were identified as stable through static respiratory index measurement (0.11-0.24 g O2/(kg Volatile Solids h)), heavy metals concentrations were within acceptable limits (i.e. concentration of Cu, Cd, Zn, Pb, Cr, As lower than 1 mg/kg dry mass) as well as polycyclic aromatic hydrocarbons (0.06-0.34 mg/kg dry mass lower than 6 mg/kg dry mass). During composting, significant losses of nitrogen from the digestate and the urea added for C/N correction were observed (51-75%), indicating that the adjustment of C/N ratio through the addition of chemicals is not efficient in composting processes with forced aeration and the pre-existing nitrogen in digestate was susceptible to air-stripping. The continuous composting process implemented proved capable of producing mature compost with a retention time of 14 d. The final products were within acceptable limits for all the parameters examined, except for the presence of pathogens (Salmonella and Enterococcus) which were not eliminated, even though the composter reached 56 °C for 3-4 days at the thermophilic stage. The characteristics of the anaerobic sludge samples examined indicate that direct land application of the anaerobic effluent should be considered as an option.

Isolation of organic compounds with high added values from agro-industrial solid wastes.

Phenols are organic compounds with high antioxidant activity. Occurring mainly in plants, where they act as pigments or even as part of defense mechanisms against insects and herbivores. Given the positive impact on on human health, their isolation and purification from agricultural products is of particular interest for the production of nutritional, pharmaceutical and cosmetics supplements. In our study different materials rich in phenolic compounds were used, in order to separate the phenolic content and maximum condensation using physicochemical methods such as solvent extraction, filtration through membranes, adsorption/desorption on resins and vacuum distillation. The materials tested were solid wastes from winery, cocoa residuals, olive leaves, etc. The first step for the treatment was the extraction of phenolic content using water-ethanol solutions which was initially optimized. Then, sequential membrane filtration of the extracts by Ultrafiltration membranes, Nanofiltration and Reverse Osmosis was performed to separate the contained compounds, based on their molecular weight. To remove non-polar compounds, with similar molecular weights with phenols, methods of adsorption/desorption on specific resins were developed, in order final ethanolic solutions rich in phenolic compounds to be obtained. Finally, the ethanol was removed by vacuum evaporation at low temperatures. The purification of olive leaf phenols is illustrated in details in the present work. The final obtained concentrate, was a rich phenolic concentrate and contained 98 g/L phenols in gallic acid equivalents. This technique, after modification, can be applied to a variety of phenol-rich byproducts, allowing the operation of phenol separation plant adjustable to local agricultural activities.

Purification of olive mill wastewater phenols through membrane filtration and resin adsorption/desorption.

Olive tree cultivation has a long history in the Mediterranean countries, and even today consists an important cultural, economic, and environmental aspect of the area. The production of olive oil through 3-phase extraction systems, leads to the co-production of large quantities of olive mill wastewater (OMW), with toxic compounds that inhibit its biodegradation. Membrane filtration has been used for the exploitation of this byproduct, through the isolation of valuable phenolic compounds. In the current work, a fraction of the waste occurring from a membrane process was used. More specifically the reverse osmosis concentrate, after a nanofiltration, containing the low-molecular-weight compounds, was further treated with resin adsorption/desorption. The non ionic XAD4, XAD16, and XAD7HP resins were implemented, for the recovery of phenols and their separation from carbohydrates. The recovered phenolic compounds were concentrated through vacuum evaporation reaching a final concentration of 378 g/L in gallic acid equivalents containing 84.8 g/L hydroxytyrosol.

Membrane filtration of agro-industrial wastewaters and isolation of organic compounds with high added values.

The aim of the current study was the exploitation of agro-industrial wastes or by-products such as olive mill wastewater (OMW) and defective wines. A cost-effective system for their maximum exploitation is suggested, using a combined process of membrane filtration and other physicochemical processes. Wastewaters are first treated in a membrane system (prefiltration, ultrafiltration, nanofiltration, and reverse osmosis) where pure water and other organic fractions (by-products) are obtained. Organic fractions, called hereafter byproducts and not wastes, are further treated for the separation of organic compounds and isolation of high added value products. Experiments were performed with OMW and defective wines as characteristic agro-industrial wastewaters. Profit from the exploitation of agro-industrial wastewaters can readily help the depreciation of the indeed high cost process of membrane filtration. The simple phenolic fraction of the OMW was successfully isolated from the rest of the waste, and problems occurring during winemaking, such as high volatile acidity and odours, were tackled.