Degradation of carbamazepine (CBZ), a widely detected recalcitrant pharmaceutical in sewage treatment plant (STP) effluent, has been studied in the present work using combination of hydrodynamic cavitation (HC) and advanced oxidation processes (AOPs). Due to its recalcitrant nature, it cannot be removed effectively by the conventional wastewater treatment plants (WWTPs) which make CBZ a pharmaceutical of very high environmental relevance and impact as well as stressing the need for developing new treatment schemes. In the present study, the effect of inlet pressure (3-5bar) and operating pH (3-11) on the extent of degradation have been initially studied with an objective of maximizing the degradation using HC alone. The established optimum conditions as pressure of 4bar and pH of 4 resulted in maximum degradation of CBZ as 38.7%. The combined approaches of HC with ultraviolet irradiation (HC+UV), hydrogen peroxide (HC+HO), ozone (HC+O) as well as combination of HC, HO and O (HC+HO+O) have been investigated under optimized pressure and operating pH. It was observed that a significant increase in the extent of degradation is obtained for the combined operations of HC+HO+O, HC+O, HC+HO, and HC+UV with the actual extent of degradation being 100%, 91.4%, 58.3% and 52.9% respectively. Kinetic analysis revealed that degradation of CBZ fitted into first order kinetics model for all the approaches. The processes were also compared on the basis of cavitational yield and also in terms of total treatment cost. Overall, it has been demonstrated that combined process of HC, HO and O can be effectively used for treatment of wastewater containing CBZ.

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The concentration of hazardous pollutants in the wastewater streams has to keep below a certain level in order to comply with the stringent environmental laws. The conventional technologies for wastewater treatment have drawbacks in terms of limited applicability and efficiency. Utilization of hydrodynamic cavitation (HC) reactors for the degradation of pollutants at large scale has shown considerable promise over last few years, due to higher energy efficiencies and low cost operation based on lower consumption of chemicals for the treatment. The present work overviews the degradation of different pollutants, such as pharmaceuticals, pesticide, phenolic derivatives and dyes, as well as the treatment of real industrial effluents using hybrid methods based on HC viz. HC/H2O2, HC/Ozone, HC/Fenton, HC/Ultraviolet irradiations (UV), and HC coupled with biological oxidation. Furthermore, based on the literature reports, recommendations for the selection of optimum operating parameters, such as inlet pressure, solution temperature, initial pH and initial pollutant concentration have been discussed in order to maximize the process intensification benefits. Moreover, hybrid methods based on HC has been demonstrated to show good synergism as compared to individual treatment approach. Overall, high energy efficient wastewater treatment can be achieved using a combined treatment approach based on HC under optimized conditions.

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Removal of naproxen (NAP) present in wastewater has been studied using an improved approach based on hydrodynamic cavitation (HC), combined with ozone or hydrogen peroxide as pretreatment for biological oxidation. Initially, the operating conditions for pretreatment based on HC reactor has been optimized as an inlet pressure of 4 bar and pH 3, where the maximum extents of degradation of NAP (28.9%) and chemical oxygen demand (COD) reduction (11.3%) were achieved using the approach of HC operated individually. Combined approaches of HC with hydrogen peroxide (HC+ H 2 O 2 ) and ozone (HC + O 3 ) were also investigated for maximizing the removal of NAP from wastewater. Almost 100% NAP degradation with a COD reduction of 40% was obtained for the combined approach of HC + O 3 in 40 min, whereas HC + H 2 O 2 resulted in 80% degradation with COD reduction of 24% within 120 min of treatment. The effluent obtained from the best pretreatment approach of HC + O 3 was further treated using aerobic oxidation based on activated sludge, and it was observed that ∼89.5% COD reduction was achieved in the subsequent operation. Use of only aerobic oxidation resulted in 36.7% as the COD reduction and 20.4% as the biochemical oxygen demand (BOD) reduction. The biodegradability index (BI) was calculated for the raw effluent without any pretreatment, as well as for effluent subjected to HC + O 3 pretreatment. The increased value of biodegradability index, BI (from 0.35 to 0.70) and also the kinetic analysis of biological process revealed the improvement in biological oxidation using pretreatment based on HC and ozone. Also, the operational costs for different treatment approaches were calculated based on the power consumption. Overall, significant benefits using combination of ozone and hydrodynamic cavitation with aerobic oxidation have been demonstrated.

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