Heterogeneous Photocatalysis for Visible Light Degradation of Emerging Contaminants (ECs) in Pharmaceutical Wastewater from Twin Cities of Pakistan

Abstract

The annual growth rate of pharmaceutical industry in Pakistan is 10% and is continuously expanding to fulfill the increasing demand of the rapidly growing population. But inability of the pharmaceutical sector to comply with the existing environmental standards leads to the introduction of large quantities of various pollutants in the natural environment which presents serious ecological challenges. In this study, effluent wastewater samples from 14 manufacturing units of the pharmaceutical industries of the National Industrial Zone, Rawat, Pakistan, were collected and characterized for physicochemical parameters including color, odor, pH, electric conductivity, temperature, dissolved oxygen (DO), total suspended solids, chemical oxygen demand (COD), salinity, total dissolved solids, nitrates, sulfates, and phosphates according to the standard methods. The qualitative and quantitative analyses of commonly prescribed drugs in Pakistan like diclofenac (DCF) and ciprofloxacin (CIP) were carried out in the pharmaceutical wastewater samples (PWWSs) using HPLC-PAD. Exceptionally high concentration of the DCF was detected in one of the industrial disposals of MB-12 (311,495 μg L−1); while CIP concentrations were mostly detected in the concentration ranges reported previously. PWWSs were analyzed using multivariate analysis techniques including PFA and CA i.e., principal factor analysis and cluster analysis, respectively which were used to extract the latent information from the data set to assess the water quality. PFA explained almost 81.4% of the total variance by the newly extracted four components and complemented the strong Pearson’s correlation coefficient (r) of DCF concentrations to that of the levels of COD, r = 0.752, and DO, r = −0.609, in PWWSs. Six clusters were generated during similar wastewater characteristics-based CA dendrogram, in which reverse osmosis-treated PWWSs were observed to cluster with the untreated PWWSs, suggesting the need to adopt an advance and better wastewater treatment methods by the pharmaceutical industries. The current study is also the first attempt for the assessment of HMs in the wastewaters released from pharmaceutical industries of the National Industrial Zone, Rawat, Pakistan. The metal concentrations depicted the following trend: Fe » Zn > Ni > Pb > Mn > Cr6+ > Cd > Cu. Mn, Zn and Cu were recorded within the maximum PLs of Pakistan National Environmental Quality Standards (Pak-NEQS) and World Health Organization (WHO) in all the pharmaceutical wastewater samples; but Cd, Pb, Fe, Cr6+ and Ni surpassed one or both the admissible limits which can be the potential threat to the human health and aquatic life. Fe was detected with the xxi highest concentration (10.8 ± 0.01 mg L− 1) in the MB-12 wastewater sample, exceeding the upper NEQS limit (2 mg L− 1). Maximum number of significant correlations were observed for Cr with multiple water quality parameters, including DO, salinity, phosphates, and copper during Pearson’s correlation analysis. During PFA, three principal factors were extracted containing high positive factor loadings of Cd, Fe; Cu, Mn; and Pb in the principal factors 1, 2 and 3, respectively, indicating the contribution of the anthropogenic and industrial operations in the water contamination due to the discharge of improperly treated or untreated pharmaceutical wastewater. Heavy metals based CA also produced dendrogram with single cluster containing reverse osmosis treated PWWSs along with the untreated samples which strongly recommends the need to properly treat the pharmaceutical effluents before their disposal in the fresh waters, thus reducing the potential ecological hazards. The spherical titanium vanadium oxide deposited with varying concentrations of bismuth oxide was successfully synthesized via co-precipitation method and assessed for the visible light irradiated photocatalytic treatment of DCF and CIP. The synthesized photocatalysts were characterized using high resolution-transmission electron microscopy, field emission-scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Both DCF (81.4%) and CIP (88.5%) showed significant removal in 3h treatment time under optimized parameters of pollutant concentration, catalyst loading and pH. The improved electron-hole separation and contribution of powerful oxidative species contributed to the enhanced photocatalytic activity. The recyclability experiments indicate that 3%-BVT1 retained its efficiency up to 74.1% and 85.2% after 5 and 4 consecutive photocatalytic cycles for DCF and CIP, respectively. Gas chromatography–mass spectrometry analysis indicated formation of several transformation products during the degradation pathway. Thus, 3%-BVT1 has a potential to treat various organic pollutants including pharmaceuticals irrespective of the interfering ions encountered in the real aquatic environments.