Removal of naphthalene and phenanthrene in synthetic solutions by electro-oxidation coupled with membrane bioreactor.

Naphthalene (NAPH) and phenanthrene (PHEN) are two of the most abundant polycyclic aromatic hydrocarbons (PAHs) found in nature, and they are considered in the list of US EPA priority pollutants. The contribution of this research lies in the comprehensive analysis of a strategy for the coupling of electro-oxidation (EO) and biodegradation in a submerged membrane bioreactor (SMBR) with the objective to remove PAHs, using NAPH and PHEN as model compounds. The electrochemical degradation of NAPH and PHEN in aqueous synthetic solution has been carried out using two different anodes: Ti/IrO2 and Ti/SnO2. The effects of EO operating parameters (current density, reaction time, and pH) on the NAPH and PHEN removals were investigated applying 23 factorial design with both electrodes. Additionally, the EO effluents were analyzed for COD, NH4-N, and biodegradability (respirometry tests). The highest removals of both compounds were reached with Ti/IrO2 anode, at acidic conditions (pH of 2), current density of 50 mA cm-2, and electrolysis time of 60 min. However, the Ti/SnO2 anode allowed greater reduction of the biomass inhibition, which means that the enhancement of the EO effluent biodegradability was reached; therefore, this electrode was selected for the coupled EO-SMBR system, applying the operating conditions that improved the biodegradability of the effluent. The EO process allowed NAPH and PHEN removal efficiencies of 96 ± 5% and 94 ± 3%, respectively. The membrane bioreactor was operated with organic load of 0.6 ± 0.1 gCOD gVSS-1 d-1, hydraulic retention time of 6 h, and solid retention time of 30 d, obtaining average COD, NH4-N, NAPH, and PHEN removals of 98±0.5%, 91±6.4%, 99.1±0.96%, and 99.7±0.4% respectively. The sorption of phenanthrene onto the biomass had a low contribution, 0.9±0.2%, concluding that biodegradation was the main removal mechanism in the bioreactor. The coupled system EO-SMBR allowed high NAPH and PHEN removal efficiencies of 99.99±0.01 and 99.99±0.02%, respectively.

Degradation of pharmaceutical compounds in water by oxygenated electrochemical oxidation: Parametric optimization, kinetic studies and toxicity assessment.

The pharmaceutical compounds sulfamethoxazole (SMX), propranolol (PRO) and carbamazepine (CBZ) are biorecalcitrant and frequently detected in waters causing negative impacts on human health and aquatic organisms. Electrochemical oxidation appears as an effective option for the removal of recalcitrant compounds and its enhancement is an important issue for the removal of emerging compounds in water. The contribution of this research lies in the comprehensive analysis of the oxygenated electro chemical oxidation of CBZ, SMX and PRO using Nb/BDD mesh anode. The effect of treatment time, current, pH and oxygen injection on the SMX, PRO and CBZ degradation was assessed using Na2SO4 as electrolyte, process optimization was performed, by-products were identified, kinetic and toxicity tests were carried out using different electrolytes. Finally, the process effectiveness was tested using real secondary effluent spiked with the mixture of the pharmaceutical compounds and the acute toxicity was determined. The obtained results indicated that the oxygenated electrochemical oxidation allows effective simultaneous SMX, PRO and CBZ degradation, which showed a significant dependence of treatment time, current and oxygen injection in Na2SO4 electrolyte. At 90 min of electrolysis the parent compounds were detected as well as eight by-products. At 150 min of treatment, further to the already determined by-products and the parent compounds, appeared phenol and p-benzoquinone. Based on the identified compounds, degradation pathways were explained as a result of two main mechanisms: transformation (hydroxylation, deamination, desulfunation) and bond rupture. The kinetic study indicated an increase of the first-order kinetic constant in the oxygenated electrochemical oxidation process using Na2SO4 and NaBr as electrolyte, nevertheless the constant decreased in the presence of NaCl. In the assays with secondary effluent spiked with SMX, PRO and CBZ, the oxygenation did not enhance the performance of the process, however; pharmaceuticals were degraded with a higher removal rates compared with the ones determined in the Na2SO4 synthetic solutions assays; the oxygenation enhanced the TOC and COD removal. The acute toxicity of spiked secondary effluent was reduced from the first few minutes of the electrochemical oxidation process.

Biodegradability of fluoxetine, mefenamic acid, and metoprolol using different microbial consortiums.

The biodegradation of fluoxetine, mefenamic acid, and metoprolol using ammonium-nitrite-oxidizing consortium, nitrite-oxidizing consortium, and heterotrophic biomass was evaluated in batch tests applying different retention times. The ammonium-nitrite-oxidizing consortium presented the highest biodegradation percentages for mefenamic acid and metoprolol, of 85 and 64% respectively. This consortium was also capable to biodegrade 79% of fluoxetine. The heterotrophic consortium showed the highest ability to biodegrade fluoxetine reaching 85%, and it also had a high potential for biodegrading mefenamic acid and metoprolol, of 66 and 58% respectively. The nitrite-oxidizing consortium presented the lowest biodegradation of the three pharmaceuticals, of less than 48%. The determination of the selected pharmaceuticals in the dissolved phase and in the biomass indicated that biodegradation was the major removal mechanism of the three compounds. Based on the obtained results, the biodegradation kinetics was adjusted to pseudo-first-order for the three pharmaceuticals. The values of k biol for fluoxetine, mefenamic acid, and metoprolol determined with the three consortiums indicated that ammonium-nitrite-oxidizing and heterotrophic biomass allow a partial biodegradation of the compounds, while no substantial biodegradation can be expected using nitrite-oxidizing consortium. Metoprolol was the less biodegradable compound. The sorption of fluoxetine and mefenamic acid onto biomass had a significant contribution for their removal (6-14%). The lowest sorption coefficients were obtained for metoprolol indicating that the sorption onto biomass is poor (3-4%), and the contribution of this process to the global removal can be neglected.

Clofibric acid and gemfibrozil removal in membrane bioreactors.

The removal of two blood lipid regulators, clofibric acid (CLA) and gemfibrozil (GFZ), was evaluated using two identical aerobic membrane bioreactors with 6.5 L effective volume each. Polysulfone ultrafiltration hollow fiber membranes were submerged in the reactors. Different operating conditions were tested varying the organic load (F/M), hydraulic residence time (HRT), biomass concentration measured as total suspended solids in the mixed liquor (MLTSS) and the sludge retention time (SRT). Complete GFZ removal was obtained with F/M of 0.21-0.48 kg COD kgTSS⁻¹ d⁻¹, HRT of 4-10 hours, SRT of 10-32 d and MLTSS of 6-10 g L⁻¹. The GFZ removal can be attributed to biodegradation and there was no accumulation of the compound in the biomass. The CLA removals improved with the SRT and HRT increase and F/M decrease. Average removals of 78-79% were obtained with SRT 16-32 d, F/M of 0.21-0.34 kgCOD kgTSS⁻¹ d⁻¹, HRT of 7-10 hours and MLTSS of 6-10 g L⁻¹. Biodegradation was found to be the main removal pathway.