The reuse of treated wastewaters could contribute to reducing water stress. In this research, ultrasound application on bacterial inactivation in municipal wastewater (MWW) was evaluated. Total and fecal coliforms were used as standard fecal indicators; volatile suspended solids (VSS) were analyzed too. Samples were taken from the effluent of secondary clarifiers. In addition, inactivation tests were carried out on pure cultures of E. coli (EC) and B. subtilis (BS). Sonication was performed at 20 kHz, 35% amplitude and 600 W/L for 15, 30 and 45 min. After 15 min of sonication, bacterial density was reduced by 1.85 Log 10 MPN/100 mL for EC and 3.16 Log 10 CFU/mL for BS. After 30 min, no CFU/mL of BS were observed in MWW and, after 45 min, the reduction of total and fecal coliforms was practically 6.45 Log 10 MPN/100mL. Inactivation mechanism was made by cavitation, which causes irreversible damage to the cell wall. Although high bacterial densities were employed, percentages of inactivation >99% were reached at 45 min. This research contributes to the implementation of ultrasound as a disinfection technique with high potential due to its high efficiency without producing byproducts. In fact, the water meets the guidelines for reuse in direct human contact services.
In this research, ultrasound (US; 26 kHz) application was evaluated as tertiary treatment of treated municipal wastewater coming from conventional activated sludge (AS) and constructed wetland (CW) systems. The degree of disinfection was evaluated through the total (TC) and faecal (FC) coliforms and by somatic coliphages (SCs) determinations. The experiments were carried out without temperature control at times of 200, 400 and 600 s and with temperature control (298.1 K) at 600, 1200 and 1800 s. Changes in the concentrations of C, N and P were also studied. The results shown that treatment without temperature control allowed 100% inactivation for TC, FC and SC at 600 s, while maximum with temperature was achieved at 1800 s. Temperature was an important factor influencing pathogens inactivation. In both cases, microorganism concentrations complied with different international guidelines for the reuse of treated wastewater. At 1800 s sonication concentrations of biochemical oxygen demand, chemical oxygen demand and total phosphorus were reduced 39.5, 39.4, 50.0 and 37.3% TN in the AS-treated water and 24.0, 49.8, 20.2 and 7.7% in the CW-treated water, respectively. In both cases, the formation of [Formula: see text] and [Formula: see text] radicals is most likely related to the observed pollutants removal. While energy consumption of ultrasound was higher than other advanced treatments such as electrocoagulation, its implementation allows the simultaneous removal of pathogens and organic pollutants without the generation of toxic by-products. In conclusion, ultrasound can be implemented as tertiary treatment of municipal wastewater for the removal of biological and organic pollution, according to reuse guidelines in terms of pathogens presence.
In the present work, an analysis is carried out to provide a relationship between the Molecular Weight (M w ) of degraded LDPE films (containing Mn stearate as pro oxidant (MnSt-LDPE) and changes in viscosity, elongation at break (EB %) and carbonyl index (CI) occurring during thermal degradation in the thermophilic phase of the compost process. The thermal treatment comprised various temperatures (508C, 608C, and 708C) and exposure times, and was characterized through a so-called Energy-Time Factor (the product of thermal energy and exposure time). Changes in viscosity, EB %, and CI were correlated to this factor. A modified Mark-Houwink equation was used to relate the zero shear-rate viscosity and M w of the degraded LDPE films. Results indicate that the EB %, M w and viscosity decrease simultaneously with an increase in the CI as the Energy-Time Factor augments, allowing the assessment of the variation of these properties with M w . Calculations of the percentage abiotic degradation (%D) of LDPE films indicate that a M w of 6 kg mol 21 corresponds to a maximum abiotic degradation degree of 91.85%, which is henceforth susceptible to biodegradation. The film treated with Energy-Time Factor of 2.79E109 J s mol 21 reached a 74% of biodegradation in 90 days (average time of the composting process). Results exhibit clearly the correlation between abiotic and biotic degradation. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42721.
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