Investigation of the agroecological applications of olive mill wastewater fractions from the ultrafiltration-nanofiltration process.

Agricultural applications of olive mill wastewater (OMW) represent a critical challenge, consistent with waste recycling and the trend towards a more sustainable pattern of agriculture. In this context, an integrated study on the agroecological applications of OMW from the ultrafiltration (UF) - nanofiltration (NF) process was carried out. This process generated three fractions: UF retentate and NF permeate, depleted in salts and phenolic compounds, were studied for their fertilization and irrigation potential, while NF retentate, enriched in these elements, was studied for its potential as a bioherbicide. The phytotoxicity of the NF retentate fraction on two crops (maize and flax) was evaluated on seedlings growth and chloroplast pigments content. In addition, the induced defense responses in maize and flax seedlings were investigated by measuring two parameters: the activity of the detoxification enzyme glutathione-S-transferase (GST) and the concentration of polyphenols, as a component of the antioxidant defense strategy in plants. Biomass, height, and chloroplast pigments content decreased progressively with increasing NF retentate concentration. Conversely, an increase in GST activity and polyphenol concentration was observed. These results highlighted the ability of OMW to induce an oxidative stress on maize and flax seedlings, triggering a defense response through GST and phenolic compounds. On the other hand, in vitro tests on the phytotoxicity of the NF retentate fraction on the common weed Sinapis arvensis were carried out. No germination was observed even with the lowest dilution applied, thus establishing the first data about the selectivity of potential OMW-derived bioherbicides. On the other hand, UF retentate and NF permeate treatments led to a significant increase in maize growth: these fractions could then be considered as a promising organic fertilizer for degraded agricultural soils, as well as an alternative water source for crops irrigation.

Agronomic application of olive mill wastewater: Effects on maize production and soil properties.

This study investigates the effect of direct amendment of olive mill wastewater (OMW) on the fertility of soil, described as poor in the area of Marrakech (semi-arid region) in Morocco. The treated plots were amended with untreated OMW generated by a traditional extraction process at the amount of 10 L/m(2)/year during two consecutive years. Results of these two years treatments with crude OMW at relatively high dose reveal an important increase in soil physicochemical characteristics, namely electric conductivity (EC), Na(+,) K(+), phosphorus, nitrogen, organic matter and soluble phenolic compounds. EC of treated soil was enhanced from 0.34 to 2.91 mS/cm as compared to the control soil. After spreading OMW in soil, the amounts of its nutritive elements increased by 81% for nitrogen, 66% for phosphorus and 88% for potassium. The accumulation of phenolic compounds and the increase of total peroxidase activity in plants provide evidence of their protective role against the physiological stress induced by OMW. However, this enrichment in mineral and nutritive elements decreased three months after OMW application, revealing OMW biodegradation in the studied calcareous soil. In parallel, an increase in the contents of the soluble phenolic compounds on the upper layer of soil was denoted and maize plants growth was efficiently raised. Significant amelioration was obtained notably in terms of fresh and dry weight of leaves, leaves area, spikes fresh and dry weight, 100 seeds weight and straw yield (37, 54, 27, 24, 14 and 9% respectively). Along with the correct choice of convenient soils notably calcareous ones and tolerant crops such as maize, this method could constitute an efficient approach for avoiding problems attributed to the uncontrolled disposal of these effluents and an effective strategy to regenerate degraded soils and represents an economical alternative that provides a local fertilizer.

Phytotoxicity assessment of olive mill wastewater treated by different technologies: effect on seed germination of maize and tomato.

The phytotoxicity effect of olive mill wastewater (OMWW) treated in a combined system regrouping pretreatment by filtration on olive stones and coagulation-flocculation, and anaerobic digestion (AD) on seed germination of maize and tomato was evaluated through germination tests in petri dishes and growth tests in pots. Three samples, referenced as AD-40, AD-60, and AD-80, were collected from the anaerobic reactor operating with an influent at 40, 60, and 80% OMWW/water (% v/v). Concentrations between 25 and 100% were used for maize and between 5 and 25% were used for tomato using raw and pretreated samples, while anaerobic samples were used without dilution. For maize, 100% and 75% OMWW were very phytotoxic and completely prohibited seed germination, while phytotoxicity was decreased following dilution at 25% and 50% OMWW. Maize germinability was found highly enhanced when watered with anaerobic samples. For tomato, high dilution was required to reduce the phytotoxicity of raw and pretreated OMWW and a high relative germination percentage was registered at 5, 10, and 15% OMWW, while for samples anaerobically treated, a high phytotoxicity is still observed. Growth tests, showed more favorable results for maize watered with raw and pretreated samples at 25% OMWW and with biological samples. For tomato and with the exception of 25% OMWW and AD-80, seeds respond positively to all samples. It was concluded that if the OMWW will be used for irrigating maize, it could be directly used after anaerobic digestion, while for tomato further dilution is required. The phenolic profile analysis of the tested samples coupled with the results of the germination tests showed that the OMWW phytotoxicity appears to be determined by not only the monomeric phenols but also by other toxic components unaffected by the applied treatments.

Assessment of the antioxidant and antibacterial activities of different olive processing wastewaters.

Olive processing wastewaters (OPW), namely olive mill wastewater (OMW) and table-olive wastewaters (TOW) were evaluated for their antibacterial activity against five Gram-positive and two Gram-negative bacteria using the standard disc diffusion and thin layer chromatography (TLC)-bioautography assays. Disc diffusion screening and bioautography of OMW were compared to the phenolic extracts of table-olive brines. Positive activity against S. aureus was demonstrated. The optimization of chromatographic separation revealed that hexane/acetone in the ratio of 4:6 was the most effective for phenolic compounds separation. A HPLC-MS analysis was performed showing that only two compounds, hydroxytyrosol and tyrosol, were the predominant phenolic compounds in all OPW. The phenolic extract of OMW generated by a semi-modern process showed the highest free radical-scavenging activity (DPPH assay) compared to the other phenolic extracts. It is apparent from the present study that OPW are a rich source of antioxidants suitable for use in food, cosmetic or pharmaceutical applications.