Abstract
The treatment of pharmaceutical wastewater was performed at the lab scale using UV/H₂O₂, process granular activated carbon (GAC) adsorption and their combination to investigate the total organic carbon (TOC) removal efficiency for different inlet TOC loadings and treatment times. Experimental study revealed that GAC adsorption alone had 81% efficiency in TOC removal in 10 min breakthrough time for flow rate of 0.6 L/min with granular activated carbon dosage of 333.33 mgActivated Carbon/L whereas UV/H₂O₂ process alone showed 26 and 29% TOC reduction at with 21.7 g/LH₂O₂ concentration with 254 and 185 nm wavelength lamps a 6 h hydraulic retention time, respectively, with average feed concentration (TOC) of 1,7555.75 mgC/L and COD of 5,214.6 mg/L at 25 ± 5°C. Experimental results showed that the optimum H₂O₂ dosage for the UV/H₂O₂ process was 1:2 stoichiometric COD: H₂O₂ molar ratio to achieve up to 26 and 29% TOC reduction efficiency than that at pH 12.01 which resulted 15-20% TOC reduction efficiency. The Bohart-Adams rate constants (K) and maximum adsorption capacity of carbon (N) from column breakthrough studies for synthetic pharmaceutical wastewater at 81% were found to be 7.10 x 10⁻³ L/(min.mgC) and 1.06 x 10³ mgC/L, respectively. In combined processes, it was found that GAC adsorption followed by desorption of contaminants from GAC by steam and UV₂₅₄/H₂O₂ treatment of the condensed steam let to 81% of TOC removal from the wastewater. Out of 358.73 mgC/L of TOC desorbed 88.1% of TOC was degraded in the UV₂₅₄/H₂O₂ treatment was degradation. Total operating cost of GAC adsortpion followed by desorption of contaminants from GAC by steam and UV₂₅₄/H₂O₂ treatment of condensed steam were found to be $11/L. While the pre-treated wastewater by UV₂₅₄H₂O₂ treatment followed by GAC adsorption, along the desorption of contaminants from GAC using steam and UV₂₅₄/H₂O₂ treatment of the condensed steam, let to an overall 81% TOC removal and 75.1% of TOC degradation using UV₂₅₄/H₂O₂ process. The cost of this combined treatment was found to be $6/L of wastewater treated which led to an economical saving of $5/L with respect to the combined TOC removal and degradation efficiency achieved. The savings predictions were achieved due to the less carbon dosage requirement and ability of UV/H₂O₂ process to degrade the TOC present in the wastewater. Based on single and combined treatments, the minimum total cost and time for 81% TOC removal were determined for the combination of UV₂₅₄/H₂O₂ treatment followed by GAC adsorption, along with desorption of contaminants from GAC using steam and UV₂₅₄/H₂O₂ treatment of the condensed steam. The overall minimum cost and minimum time were found to be $6/L of wastewater treated and 114.5 h, respectively. The treatment parameters and conditions for treating 30 L of the synthetic pharmaceutical wastewater were at an average feed concentration of TOC = 1,755.75 mgC/L and COD = 5,214.6 mg/L leading to TOC = 333.5 mgC/L of the effluent concentration which was near to the industrial effluent disposal level in Canada.
Highlights
Pharmaceutical drugs are vital substances due to their therapeutic effects
Bohart -Adams model is based on the surface reaction theory (Reynolds and Richards, 1995) and it assumes that equilibrium is not instantaneous; the rate of sorption is proportional to the fraction of sorption capacity still remaining on the adsorbent (Muraleedharan et al, 1994)
It was concluded that the adsorption is a viable process for the pharmaceutical wastewater and the monolayer adsorption on granular activated carbon (GAC) follows the Langmuir adsorption isotherm
Summary
Pharmaceutical drugs are vital substances due to their therapeutic effects. Their use is increasing ever since they were discovered. Since wastewaters or process waters generated by the pharmaceutical industries cannot be minimized because of the existing production technologies, effective end-of-pipe methods should be taken into consideration (Mizsey, 1994). Among various physical separation processes, the granular activated carbon (GAC) adsorption is widely used for the removal of volatile and bioresistant organic materials present in wastewater. The aim of this research work is to investigate the reduction and degradation of TOC found in high strength industrial pharmaceutical wastewater at a predefined TOC removal efficiency of 81% (based on the efficiency obtained when combined experiments were done so as to have a common platform to compare the results), by using GAC adsorption alone, UV/H2O2 alone, and their combination. Based on the results obtained, optimum carbon and H2O2 dosage, treatment time, and regenerant (in this case steam) requirement were determined. Cost analysis for all the treatment processes, was done based on the results obtained by conducting the above set of experiments
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