Microbial inactivation using only Ultrasound (US) vibrations presents considerable advantages by applying green techniques with non-generation of greenhouse gases, eliminating chemicals, and operating conditions close to environmental conditions. However, industrial effluent treatment systems have been investigated as a microbial inactivation step, using isolated US associated with thermal (T) and manometric (P) microbial inactivation techniques. A stainless-steel bench prototype was built for the present study, operating in continuous mode, with a 2.5 L volume test chamber. The indicator microorganism detected in the effluent of a hospital laundry located in the Agreste region of the state of Pernambuco, Brazil, was the E. coli bacterium. In addition to the isolated US effect, US/T, US/P, and US/T/P combinations were obtained using a central composite design (CCD). The factors used for the CCD were frequency, hydraulic detention time, temperature, and pressure. The results showed that the lethality rate increased with the frequency and time of hydraulic detention but was reduced when increasing temperature from 30°C to 50°C and increasing pressure between 1.0 bar and 1.8 bar. Isolated ultrasonic vibrations, at 120 kHz and with 10-minute HRT, reached an inactivation efficiency of 98%. Such a value was found using the thermomannosonic condition around 40 min. The use of the isolated US vibration technique proved advantageous, mainly due to the efficient inactivation results and potential energy and chemical reductions.

In this work, an induced pre-saturation tower (IPST) for oil–water separation was built on a semi-industrial scale, based on experimental results obtained on a laboratory scale prototype. The main strategy for generating these criteria was to increase the efficiency of the bench scale prototype, which is limited by conditions of low levels of automation and control, with the use of a biosurfactant as an auxiliary collector. The validation of the developed criteria allowed the construction of an IPST with three stages, all fed with previously saturated effluents. The IPST was built in stainless steel, with multistage centrifugal pumps and adapted to generate microbubbles without the use of saturation tanks or compressors. The most relevant operational parameters were selected using a fractional factorial design, while a central composite rotatable design (CCRD) followed by the application of the desirability function allowed to optimize the conditions for partial and global variables, the latter with desirability of 95%. A nominal flow rate of approximately 1000 L·h−1, a recycle flow rate of 450 L·h−1, a scraper rotation speed of 80 rpm, an average pressure of the microbubble pumps of 11 bar, and an effluent temperature from IPST of about 38 °C ensured optimized operation for the proposed technological development.

At the end of this review on applications of ultrasonic waves in the inactivation of microorganisms in hospital laundry effluents, the fourth type of predictive model is proposed, based on the application characteristics of the experimental plans. The number of works for the disinfection of wastewater by ultrasound waves (US) associated with other techniques or individuals has been increasing. The use of ultrasound to produce lethal effects on microorganisms is attractive because it is considered a "green" technology in that it involves sound energy and does not require additional chemicals, or a very small amount. Also, the US as a tool for water reuse processes - operates at low pressure and temperature and does not produce toxic or greenhouse gases. Hospital laundry effluents are characterized by different microorganisms, a fact that can hinder the application of conventional physical-chemical technologies. To contribute to future developments in the application of ultrasound (US), this work uses some typical US applications in the disinfection of aqueous effluents. To propose strategies for carrying out new works, comments are made regarding an approach oriented towards new advances based on the need to interrelate the variables involved in the studies, at the same time that these variables are correlated with the rate of inactivation. For this, it is discussed the predictive models and their contributions, according to the number of factors that should be involved for a better understanding of the rate of microbial inactivation.