CET 96

DOI: 10.3303/CET2296035

Paper Received: 22 January 2022; Revised: 31 July 2022; Accepted: 7 September 2022
Please cite this article as: Benites-Alfaro E., Olivera Lopez A., Rengifo Pereyra M., Castaneda Olivera C., 2022, Energy Efficiency in Bacterial
Treatment of Wastewater by Hydrodynamic Cavitation, Chemical Engineering Transactions, 96, 205-210 DOI:10.3303/CET2296035

CHEMICAL ENGINEERING TRANSACTIONS

VOL. 96, 2022

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The Italian Association

of Chemical Engineering
Online at www.cetjournal.it

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ISBN 978-88-95608-95-2; ISSN 2283-9216

Energy Efficiency in Bacterial Treatment of Wastewater by
Hydrodynamic Cavitation

Elmer Benites-Alfaroa,c*, Arantza Olivera Lópezb, Mery Rengifo Pereyraa, Carlos
Castañeda Oliveraa
aUniversidad César Vallejo, AV. Alfredo Mwendiola 6232, Los Olivos, C.P. Lima 15314, Perú
bBenemérita Universidad Autónoma de Puebla, 4 Sur 104 Centro Histórico C.P. 72000, México
ebenitesa@ucv.edu.pe

Helping energy consumers to make the best decision in the use of energy is essential to save it, as well as to
take advantage of it conveniently. There are many wastewaters treatment processes that generate negative
impacts on the environment and it is necessary to require new forms of treatment, seeking to mitigate said
impacts; Thus, in recent years, a physical phenomenon considered harmful has been taken into account, but
now it is sought to take advantage of it positively to decontaminate and improve the quality of surface and waste
water, we refer to hydrodynamic cavitation. Hydrodynamic cavitation in water treatment is a technology that is
on the rise due to its environmental advantages as it does not use chemical products as is done with some
traditional methods. Given the question about the energy consumption necessary to generate hydrodynamic
cavitation in the bacterial disinfection of wastewater, the research aimed to determine the energy efficiency for
each unit of energy in the reduction of the "microbiological load" parameter presented by domestic wastewater,
during the treatment time. The result, after 80 minutes, using cavitation equipment that operated with a 3.37
kWh pump, the energy efficiency was found to be the elimination of 2,344 MPN of bacteria for each joule
consumed; In addition, the value of the microbiological parameter was within the maximum permissible limits
established by the Peruvian environmental authority. Therefore, hydrodynamic cavitation turns out to be a
possibility for the treatment of bacteria in domestic effluents, it does not generate polluting residues, it has low
energy consumption and probably low economic cost; In parallel, other physicochemical parameters also
improved

1. Introduction

Water scarcity worldwide, as well as the increase of contamination in water resources are an issue of great
importance, these have been causing many social conflicts and damage to health. (Távares and Álamo, C.,
2020). Currently, a trend has been generated in research and projects that seek new ways of performing
domestic and industrial wastewater treatment, with the aim of increasing its efficiency, effectiveness, viability
and sustainability (Arcila and Peralta, 2015); however, few research works consider energy consumption, losses
and energy efficiency of the processes as a relevant variable to take into account in the treatment results. There
are different methods of wastewater treatment, and three classes can be distinguished: physical methods,
chemical methods and biological methods, and there are also certain combinations of these, such as
electrochemical and physical-chemical methods and others (Torres G., 2014).
Hydrodynamic cavitation is a physical process that requires energy to propel the fluid at high pressure into the
cavitating system to achieve the formation and intense implosion of vapor bubbles that occurs when liquids are
subjected to a pressure drop due to an increase in velocity when passing through a constriction. Hydrodynamic
cavitation is indicated is a non-conventional technology for the treatment of different products, by-products and
agro-industrial waste, in hydrodynamic technology the flow velocity of the liquid stream is considerably increased
at the expense of pressure and it was established that it is much more efficient, from the energy and operational
point of view, in contrast to the use of traditional techniques for the processing and transformation of raw
materials, products and waste from the agricultural sector (Gutiérrez-Mosquera et al., 2019)

205

This technology has been tested for the treatment of slaughterhouse water with the purpose of reducing the
organic and nitrogen load (Cadenas and Santos, 2020), to decontaminate the microbial load (Gashchin and
Viten'ko, 2008). It has also been used to eliminate cyanobacteria and microalgae in water with good results
(Matevž D., et al., 2016). Karamah E. and Sunarko I., (2013) carried out a study on the inactivation of
Escherichia coli using a hydrodynamic cavitation reactor using a Venturi tube and an orifice plate, decreasing
from the initial concentration of 104 CFU/mL to zero CFU/mL after 30 and 20 minutes respectively for said
cavitating devices; Another study demonstrated the efficient bacterial disinfection of contaminated water from
the Santa Clara River, Ecuador, concluding that when the discharge pressure increases, the degree of
disinfection efficiency also increases (La Fuente E., and López H, 2018). It has been established that
hydrodynamic cavitation offers an immediate and realistic offer in wastewater treatment (Gogate P.R. and Pandit
A. B., 2005).
In recent years, this technology has been taken up again to solve problems in the treatment of wastewater
contaminated with harmful elements, despite the fact that it probably still cannot compete economically with the
chemical method of chlorination (very common), if it has been shown to be effective in cavitation that by itself
(without the addition of chemical agents), compensates for the energy expenditure that this demands; Likewise,
in some cases it was shown that the use of the venturi is better in terms of energy efficiency, because it requires
a less permanent pressure drop (Carpenter et al., 2016). In this context, the objective of the research was to
determine the energy efficiency of hydrodynamic cavitation to minimize the bacterial load in domestic
wastewater.

2. Methodology

2.1 Cavitation phenomenon

It is a phenomenon that occurs when there is a change of state from liquid to vapor due to the sudden variation
in pressure, produced by effects of deposition of hydrodynamic, acoustic or optical energy. The bubbles or
cavities of vapor that form within the liquid grow until the pressure and velocity of the fluid are restored within
the passage through which they pass, after which they implode and release energy in the form of shock waves
(García, J.A. y Calvo Esteban, 2013, p. 184), release large amounts of energy at a certain pressure and
temperature (up to 1,000 bar and 10,000°k) in a small region and in multiple places at the same time, see figure
1. Hydrodynamic cavitation has a destructive erosive effect on metal walls; its beneficial use is very varied,
among it to destroy microorganisms in contaminated liquids (Domínguez, 2018).

Figure 1. Growth and collapse of a bubble by hydrodynamic cavitation (García and Calvo, 2013)

2.2 Research design

In order to identify the energy consumption of the cavitation process, domestic wastewater treatment was
performed in a hydrodynamic cavitation equipment at pilot level.
The process carried out can be seen in Figure 2.

Figure 2: Phases of the research process

Final implosion: high
temperature and
pressure, shock waves

Decreasing pressure:
bubbles grow

Rising pressure:
bubbles collapse

206

2.3 Bacterium removal

The mechanism of bacterial removal is presented by the combined processes of mechanical (physical),
chemical and heat effects. The mechanical effect is given by cell rupture in the presence of eddies, vortices and
reentrant flows that cause pressure differences in the cell walls (Save S., Pandit A. and Jshi B., 1997) and the
chemical one is due to the presence of hydroxyl radical (OH) and physical disruption of cell membranes taking
into account the high reactive and toxic power of OH for microorganisms that attacks the DNA chain (Medina I.
and Valencia L., 2008). All this also occurs with the generation of heat and high pressure as a consequence of
hydrodynamic cavitation (Mezule L, et al., 2009). Energy efficiency.

2.4 Energy efficiency

The energy efficiency calculation was calculated following the method used by Lafuente and Lopez (2018). This
procedure takes into account only the consumption of electrical energy. As follows:
• Treatment time (s)
• Volume used (mL)
• Power consumption (W)
• Initial CFU/mL
• CFU eliminated in the treatment time
• CFU removed/W of electrical consumption (CFU/mL)/W
• CFU removed/J power consumption (CFU/J).

2.5 Hydrodynamic cavitation equipment

The hydrodynamic cavitation equipment used was designed and manufactured by Promec Ingenieros as part
of the Innovate Project of the Peruvian Ministry of Production. This equipment used a pump with the following
characteristics in terms of the energy used in its operation:

TYPE P 9SL-450/6T
Q (L/MIN) 60-280
H(m) 95.5-66.6
Hmin 33.3
H max 103.1
P2(HP) 4.5-(KW) 3.37
p1 (kW) 4.56
MEI >= 0.4
IP 55
V 3 220/380
T max liquid 110 °C
A 13.8-8
Hz 60

Other operating parameters of the cavitator system were: Inlet pressure 8.2 bar. With an initial temperature of
34.5 °C which increased to 55.2, 59.9 and 62.1 °C at 80, 120 and 160 minutes of treatment respectively. The
pH of the sample ranged from 7.71 to 8.56.

3. 3. Results and discussions

3.1 Time, treatment volume and power consumption

Table 1 shows that the total time of treatment of domestic wastewater was 160 minutes, for a volume of 52,000
millilitres, the power of the motor was 3,370 W, appreciating that until the end of the time used, 32,352,000 W
were consumed of energy.

Table 1 Energy consumption in the cavitation treatment process

Time of treatment
Volume used (mL)

Engine power

(W)
consume electric

(W) (min) (s)

0 0 52,000 3370 0

80 4,800 52,000 3370 16 176,000

120 7,200 52,000 3370 24 264,000

160 9,600 52,000 3370 3 252,000

207

3.2 Characterization of domestic wastewater before treatment.

The wastewater from a housing complex presented the physicochemical and microbiological parameters shown
in Table 2. The level of microbiological load is emphasized, since it was based on this parameter that the energy
efficiency was evaluated

Table 2: Parameters of untreated wastewater

Parameter Units Value

Oils and Fats mg/L 16.40

Total Organic Carbon mg COT/L 98.94

Fecal Coliforms (Thermotolerant) (MPN) MPN/100mL 3 500 000 000.0

Biochemical Oxygen Demand mg BOD5/L 180.00

Chemical Oxygen Demand (mg O2/L) 395.80

Ammonia Nitrogen (mg N-NH3/L) 53514.00

Dissolved Oxygen mg DO/L 0.48

Total Suspended Solids mg/L 39.00

3.3 Microbiological load removal from domestic wastewater up to 160 minutes of treatment by

hydrodynamic cavitation

Table 3 shows the decrease of thermotolerant coliforms present in the domestic wastewater throughout the
hydrodynamic cavitation process. It can be seen that as the treatment process goes on, the coliforms decrease
progressively so that after 80 minutes of treatment, 99.99 % reduction of thermotolerant coliforms has been
reached and at 160 minutes the level of their presence is minimal (49 MPN). This is due to the presence of
hoxydryl radicals, the implosion of the cavities (bubbles) and the high temperature in the hydrodynamic
cavitation process (Mezule L, et al., 2009)

Table 3: Reduction of fecal coliforms in water during hydrodynamic cavitation treatment

Time (min)
Fecal coliform
(thermotolerant) (MPN/100mL)

Reduction (%)

0 3500000000 0
80 17000 99.9995143
120 70 99.999998
160 49 99.9999986

As can be seen in Figure 3, the percentage decrease of fecal coliforms reached almost 100 % (99.99 %) after
80 minutes of treatment, so this method is very efficient for recovering wastewater from this pollutant, and no
further treatment time is necessary

Figure 3: Fecal coliform reduction process (thermotolerant)

99.99951429 99.999998 99.9999986

100

120

0 50 100 150 200

C
o

li
fo

rm
r

e
d

u
ct

io
n

)

Time (min)

208

3.4 Energy efficiency in the reduction of fecal coliforms (thermotolerant)

Table 4 shows the energy efficiency measured as the amount of fecal (thermotolerant) coliforms that are
removed by the hydrodynamic cavitation process per unit of energy in Joules. It can be seen that the best
efficiency is after 80 minutes of treatment, eliminating 2,344 NMP of coliforms for each Joule consumed. It is
highlighted that the method used in the calculation of energy efficiency is based solely on the consumption of
electrical energy for a specific case of fecal coliform disinfection.

Table 4: Energy efficiency in the reduction of fecal coliforms

Time of
treatment
(min)

MPN/100mL
(initial)

MPN/100mL in
treatment times

MPN /mL in
wastewater removed
in the process

MPN /mL removed per
Watt of electrical
consumption

MPN removed per
Joule of electricity
consumption

0 3500000000 3500000000 0

80 3500000000 17000 3499983000 216.37 2344.00

120 3500000000 70 3499999930 144.25 1041.78

160 3500000000 49 3499999951 108.18 586.00

The operating pressure on the liquid in the cavitation process must be taken into account, according to the
research carried out by Lafuente E. and López H. (2018), they used 65 liters of water for a time of 65 minutes
and decreased 115.77 CFU per each joule of energy, equivalent to 72.8 % of the microbial load when working
at 2 bar pressure and 99.5 % when working at 3 bar pressure. In the present investigation, an energy efficiency
of 2,344 MPN per joule was obtained in 80 minutes, with a working pressure of 8.2 bar at the inlet of the cavitator
(Venturi), with a decrease of 99.99 % (close to 100 %); Therefore, it can be established that it is an efficient
method of eliminating thermotolerant coliforms and that the time to achieve an efficient result depends on the
type of wastewater, also on the cavitator system to be used, among other parameters; therefore, it is required
to establish specific conditions for each case, due to the presence of other contaminants such as benzene and
dyes (Bokhari A., Klemes J., Asif S., 2021; Orizano S., Benites E., 2020)

4. Conclusions

It was determined that the hydrodynamic cavitation process is efficient in the removal of fecal coliforms
(thermotolerant) from wastewater. In the investigation, for 52 liters of domestic wastewater, 2,344 MPN of fecal
coliforms were eliminated for each joule of energy consumed after 80 minutes of treatment, which meant a
reduction of 99.9999% of thermotolerant coliforms. On the other hand, it is highlighted that the physical method
did not generate dangerous or toxic by-products like the traditional ones (chlorination) for human health.
Although it can be said that there is an energy efficiency to reduce a load of fecal coliforms in wastewater, more
research is required to standardize optimal models for the use of cavitation, also taking into account the
economic value when it comes to being scaled to an industrial level.

Acknowledgments

The authors express their gratitude to Universidad César Vallejo for the financial support for the dissemination
of this research within the "Research UCV" program to the “GITA” Group.

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