Impacts of operating conditions on nanofiltration of secondary-treated two-phase olive mill wastewater

On the modeling and optimization of two-phase olive-oil washing wastewater treatment and polyphenols recovery by ceramic tubular microfiltration membranes

This research is focused on modelling and optimization of the performance of a 'green procedure' based on microfiltration (MF) technology, for recovery of high added-value antioxidant compounds (TACs) from two-phase olive-oil washing wastewater (OOWW) and its treatment. Concern of olive oil industry to improve the production process in line with Circular Economy is vital to make it respectful with the environment including the management of the generated effluents. Key operational factors of the MF process were studied, modelled and optimized by multifactorial statistical analysis. Box-Behnken design was implemented and data analyzed by ANOVA and interpreted by RSM methodology. MF flux was ulteriorly modelled by a second-grade quadratic fitting equation comprising the significant operating variables, being them pressure and tangential velocity. Optimized flow achieved 10962.4 L/hm² at 8.5 bar, 4.2 L/min tangential velocity, ambient temperature (25 °C) and raw pH (5.13). Finally, multiple-response permitted to optimize up to 67% TSS rejection and minimum rejection of TACs of 22.9%, upon 3.57 bar, 4.2 m/s, 23.4 °C and effluent pH of 5.1, meaning the recovery of 77.1% of TACs from OOWW in the permeate stream, up to 1207.1 mg/L. Results show that the proposed process allows a reduction in energy consumption by using the raw effluent with unmodified pH and ambient temperature.

Application of nanofiltration and reverse osmosis for treatment and reuse of laundry wastewater

The aim of this study was to investigate the treatment and reuse of laundry wastewater with couple of nanofiltration (NF) and reverse osmosis (RO). In the NF process, optimal values of pH, temperature, transmembrane pressure (TMP) and cross-flow rate were determined using the Taguchi L₁₆ (4⁴) experimental design method. The smaller-the-better signal-to-noise (S/N) ratio was used to analyze the results of experiments. Flux decline caused by fouling was selected as response parameter. A pH of 8.5, temperature of 30 °C, TMP of 12 bar and cross-flow rate of 2 L/min were determined as optimum operating conditions in the NF process. According to analysis of variance (ANOVA), pH was the most effective factor while TMP and cross-flow rate had low effects on the fouling. Membrane fouling was also evaluated with scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), zeta potential and optical profilometer measurements. In the RO process, the quality of NF permeate obtained from optimum operating conditions was improved by an RO membrane. Although a NF membrane was not effective in reducing chemical oxygen demand (COD), Orto-P and NH₄ ⁺-N, these parameters were almost removed in the NF + RO system. These results showed that, the Taguchi method was successfully applied to determine the optimum operating conditions for the treatment of laundry wastewater with an NF process. Water treated with integrated membrane processes (NF + RO) is sufficient for use as laundry washing water.

Recovery of sulfuric acid aqueous solution from copper-refining sulfuric acid wastewater using nanofiltration membrane process

We used a nanofiltration (NF) membrane process to produce purified aqueous sulfuric acid from copper-refining sulfuric acid wastewater. Wastewater generated from a copper-refining process was used to explore the membrane performances and acid stabilities of six commercial NF membranes. A combination of permeate flux, sulfate permeation, and metal ion rejection clearly showed that two polyamide membranes and a polyacrylonitrile-based membrane achieved recovery of a purified sulfuric acid solution. Acid-stability and long-term performance tests showed that the polyamide membranes were unsuitable for copper-refining wastewater treatment because of their low acid stabilities. In contrast, the polyacrylonitrile-based composite membrane showed excellent acid stability, and gave greater than 90% metal ion rejection, with the exception of calcium ions, for 430 d. We also evaluated the recovery performance in 1 ton/d pilot-scale process using wastewater from copper-refining process; 90% metal ion rejection was achieved, with the exception of calcium ions, even at 95% recovery rate.

Pilot scale nanofiltration treatment of olive mill wastewater: a technical and economical evaluation

The treatment of large volumes of olive mill wastewater is presently a challenge. This study reports the technical and economical feasibility of a sequential treatment of olive mill wastewater comprising a dissolved air flotation pre-treatment and nanofiltration. Different pilot nanofiltration assays were conducted in a concentration mode up to different volume reduction factors (29, 45, 58, and 81). Data attained demonstrated that nanofiltration can be operated at considerably high volume reduction factors and still be effective towards the removal of several components. A flux decline of approximately 50% was observed at the highest volume reduction factor, mainly due to increase of the osmotic pressure. Considerably high rejections were obtained across all experiments for total suspended solids (83 to >99%), total organic carbon (64 to 99%), chemical oxygen demand (53 to 77%), and oil and grease (67 to >82%). Treated water was in compliance with European legal limits for discharge regarding total suspended solids and oil and grease. The potential recovery of phenolic compounds was evaluated and found not relevant. It was demonstrated that nanofiltration is economically feasible, involving operation costs of approximately 2.56-3.08 €/m³, depending on the working plan schedule and volume reduction factor, and requiring a footprint of approximately 52 m² to treat 1000 m³ of olive mill wastewater.