Application of Ionizing Radiations in Conjunction with Biological Treatment for the Degradation of Pharmaceutical Effluents

Abstract

Due to rapid urbanization and steep population growth, the advancement in medical field has dramatically increased the consumption of pharmaceuticals in developing country like India. Pharmaceutical compounds are a group of man-made chemicals of utmost concern, as they may infuse into our environment. During pharmaceutical manufacturing, high volume of clean water is consumed with the generation of enormous volumes of complex and hazardous wastewater. In most of the existing pharmaceutical industry, the dilute aqueous streams from the plants are generally treated by conventional biological treatment. However, these treatment processes are ineffective in removal of the persistent and biological resistant pharmaceutical contaminants. In addition, evaporation technique is used to treat the refractory and high strength effluents which is energy and cost intensive process. Thus, there is stringent requirement to employ methods and technologies to treat wastewater in order to enhance its reuse or recyclability. In this regard, advanced oxidation processes (AOPs) are considered to be competent and effective approach, which is based on the generation of reactive radical species i.e., hydroxyl radical (HO•). Among various AOPs, Fenton and photo-assisted Fenton processes have been regarded as an efficient treatment for the degradation of pharmaceuticals and there is growing interest in the applications of heterogeneous Fenton-like processes using iron oxides and other naturally occurring minerals. Radiolytic degradation process using ionizing radiations i.e., gamma radiation and high electron beam (E-beam) have received much attention due to their ability to degrade recalcitrant organic contaminants without use of any additional oxidant and chemicals. Thus, the present study was aimed to explain the degradation of selected pharmaceuticals viz. amoxicillin (AMX), ofloxacin (OFX) and ornidazole (ORZ) as well as real pharmaceutical wastewater with independent Fenton/photo-Fenton, gamma and E-beam treatment. In addition, a coupled system involving gamma/E-beam irradiations along with biological treatment have been explored to study the feasibility of integrated approach on real pharmaceutical industrial wastewater. For the Fenton based treatment of model compounds, hematite (α-Fe2O3), graphene oxide-pyrite (GO-FeS2) nanocomposites and natural available soil were utilized as catalyst. Hematite particles of different shaped (rod, spherical and cubical) and graphene oxide-pyrite (GO-FeS2) nanocomposites were synthesized using sol-gel and hydrothermal procedure, respectively and were characterized for morphological properties. Complete removal (98%) of ORZ (0.22 mM) was achieved in solar-Fenton treatment with cubical hematite under the optimum operating conditions viz. 10 mM H2O2, 0.13 g L-1 α-Fe2O3 at pH 3 within 180 min. The highest concentration of leached iron in the aqueous solution confirms cubical hematite to be the most photoactive form among the various synthesized hematite particles. Highly dispersive iron oxide i.e., FeS2 fabricated on GO layer was utilized in solar-Fenton treatment of AMX (0.1 mM) and OFX (0.1 mM) leading to 97 and 80% degradation, respectively under the optimized conditions viz. 1 g L-1 GO-FeS2, 10 mM H2O2 at pH 5 within 180 min. The rate of H2O2 degradation and HO• concentration was investigated during the treatment process. The potential viability of soil as a cost-free catalyst was investigated in photo-Fenton degradation of ORZ (0.09 mM) and OFX (0.05 mM). Soil was found to be enriched with various iron oxides like hematite, magnetite, goethite, pyrite and wustite, which contributes toward enhanced dissolution of Fe3+ than Fe2+ in the aqueous solution. Elevated degradation efficiencies (95% ORZ and 92% OFX) were achieved due to Fe2+/Fe3+ cycling, producing more HO• leading to the co-existence of homogeneous and heterogeneous process simultaneously. Continuous scale studies conducted by employing soil in the form of soil beads and as a thin layer spread on the surface of baffled reactor lead to effective treatment of ORZ and OFX. Soil beads were found to have satisfactory reusability and stability. HPLC, mineralization and toxicity assessment confirmed the efficient removal of both the compounds. Gamma and E-beam radiolytic degradation of OFX (0.1 mM), AMX (0.1 mM) and ORZ (0.22 mM) was studied under different experimental conditions. The parameters viz. initial concentration, pH, dose and the concentrations of various additives were optimized and it was observed that degradation followed pseudo first-order reaction kinetics. Degradation rate of model compounds was significantly increased with increase in the absorbed dose and decrease with the initial concentration under acidic condition when compared to neutral or alkaline condition. Presence of different scavengers showed decrease in the dose constant, mainly owing to the competition reactions between model compounds and scavengers with the radiolytically generated reactive species. The addition of H2O2 had a synergistic effect on the degradation and mineralization extent of model compounds. Based on the LC-QTOF-MS analysis, it was inferred that OFX and ORZ radiolytic degradation was mainly attributed to oxidative HO• radicals and the direct cleavage of these molecules. Cytotoxicity assessment showed that the degradation products of OFX, AMX and ORZ did not exhibited any toxicity after irradiation treatment. The cost of energy consumed during gamma and E-beam irradiation treatment of model compounds was also evaluated. Overall, all the treatment technologies applied in the treatment of model compounds were effective in their degradation; however, the use of E-beam was effective in degradation of model compounds in term of treatment time. Moreover, the use of irradiation based treatment has eliminated the use of additional chemicals as well as sludge formation in comparison to photo-Fenton treatment. High strength wastewater (HSW) and low strength wastewater (LSW) collected from representative manufacturing unit were subjected to independent Fenton/photo-Fenton, gamma and E-beam treatment. For both the HSW and LSW, dark-Fenton (DF) and solar driven photo-Fenton (PF) were utilized as pre-treatment technologies to enhance the biodegradability and reduce the organic load of wastewater through simultaneous oxidation and coagulation. The operational parameters like pH, H2O2 dosage and Fe2+ concentration were optimized in case of DF and PF processes. Overall results indicated that treatment of wastewaters with PF lead to better COD and TOC removal efficiency with subsequent biological degradation when compared to DF treatment. For the effective treatment of LSW and HSW under gamma/E-beam irradiation, hybrid approach including coagulation, gamma/E-beam irradiation and biological treatment were employed individually and in sequence to determine the effective remediation of real wastewater. Effect of parameters like pH, irradiation dose and oxidants were investigated during gamma/E-beam irradiation treatment. To compare process performance, gamma-irradiation was employed as pre- and post-treatment to biological treatment. Use of H2O2 irradiation based treatment lead to enhanced COD and TOC removal efficiency when compared to K2S2O8 in independent gamma/E-beam irradiation. The sequential approach of coagulation, gamma and biological treatment accounts for the synergistic degradation and detoxification of wastewaters, and lead to overall 92 and 90% COD removal of LSW and HSW, respectively. Sequential coagulation, E-beam and biological treatment lead to overall COD removal of 94 and 89% for LSW and HSW, respectively. Cytotoxicity and cost assessment of the gamma/E-beam treatment process for LSW and HSW were examined. Considering the high dose rate of E-beam accelerators and capacity to treat large volume of wastewater, E-beam technology followed by existing aerobic biological treatment could be utilized as an effective technique for the degradation of real pharmaceutical industry wastewater in the common effluent treatment plant (CETP).