Reduction of hospital wastewater through ozone-air micro-nanobubbles

The reduction of the organic matter concentration of hospital wastewater is expressed in BOD5 and COD. The treatment was developed using a micro-nanobubble generator with continuous system. Micro-nanobubbles of 0.024μm average diameter were obtained. For the treatment, two samples were taken; Sample 1 (at 8:00 a.m.) and show 2 (at 11:00 a.m.). After applying the treatment with ozone-air micro-nanobubbles, it was possible to reduce the initial concentrations of sample 1: BOD5 from 132mg/L to 14mg/L, COD from 374mg/L to 30mg/L and from sample 2: BOD5 from 127mg/L to 21mg/L and COD from 297mg/L to 36mg/L. The efficiency obtained at 15 minutes of sample 1 of BOD5 was 90.2% and of COD was 92.51% and of sample 2 of BOD5 was 83.5% and of COD was 87.9%.


Introduction
In Peru, only 32% of wastewater sent to the sewerage system receives some type of treatment, and several treatment plants are added, which are not adequate.(OEFA, 2014).The discharge of effluents without treatment is one of the main causes of the loss of water quality.Hospital effluents represent a particular problem, encompassing a mixture of medicines, detergents, antiseptics, solvents and organic matter, to which are added excreta and secretions from patients contaminated by different pathogens.It is also known that large quantities of disinfectant solutions are used in hospitals for the elimination of pathogens on surfaces (floors, walls, etc.), equipment and biomedical instruments and on the skin.Having alcohol, aldehydes and different chlorinated compounds as active ingredients of the solutions mentioned (Núñez, 2006).The use of ozone (dose of 187mg O3/h) in hospital wastewater at pH = 10, increases biodegradability by 70% and acute toxicity is reduced by 62% (Grisales et al., 2012).The Micro-Nano bubbles are sub-micronic cavities containing gas in aqueous solution.The Microbubbles (MBs) have a diameter of more than 100 μm, the micro-nano bubbles (MNBs) have a diameter between 1 to 100 μm and the nano-bubbles (NBs) have a diameter less than 1 μm inside the fluid.The micro-nanobubbles generation technology in water is applied in: sea water, water bodies, groundwater, domestic wastewater and industrial wastewater (Valverde, 2017).There are reductions of thermotolelant coliforms presents in marine water from 1400 CFU /100 mL, until 56 CFU/100 mL, (96%) after applying the air-ozone micro-nanobubbles (Abate and Valverde, 2017).The best treatment reduction Efficiency of BOD in river's water was applying ozone micro-nanobubbles (Salguero and Valverde, 2017).The chemical oxygen demand of 0.5 g Amoxicillin per Liter of water were reduced until 76.9%, organic matter until 65.8% and turbidity until 19.35% in 45 minutes applying air micro-nanobubbles (Mendez and Valverde, 2017).Total coliforms presents in domestic wastewater were reduced from 14500 CFU /100 mL, until 4900 CFU / 100 mL.applying air micro-nanobubbles (Reyes and Valverde, 2017).Sanguaza treated applying air micro-nanobubbles in 60 minutes achieved an average turbidity of 81.5 NTU (79.61%), average BOD5 of 134 mg/L (69.65%) and COD of 150.43 mg/L.(69.24%) (Ventura and Valverde, 2017).

Materials and Methods
A sample of 40 liters of hospital wastewater was used to develop the experimental process and 4L of residual water for the initial analysis.For the development of this research, four stages were considered:

Collection and initial analysis of the residual water sample
In this stage, 40 liters of hospital wastewater were collected.Sample 1 was taken at 8:00 a.m. when there was little activity and sample 2 was taken at 11:00 a.m. when the activities increased.Subsequently, the field parameters (temperature, pH, electrical conductivity and Turbidity) and physical-chemical parameters (TSS, BOD5, and COD) were determined.

Treatment with Ozone-air MNBs
In this stage, the continuous-system ozone-air micro-nanobubble generator was conditioned

A
To treat both sample 1 and sample 2, time intervals of 5, 10 and 15 minutes were used.

Analysis after treatment
The field parameters (T, pH, electrical conductivity and Turbidity) and the physical-chemical parameters (BOD5, COD and TSS) of the samples were analyzed.

Treatment efficiency on parameters.
To measure the MNBs treatment's efficiency on EC will be used the equation 1: Also this equation is used to measure treatment's efficiency on: Turbidity, TSS, BOD5 and COD.

Collection of the residual water sample
40 Liters of hospital wastewater were collected at the main drainage point, which were filled in plastic containers for later treatment.Initial samples required 1 L of wastewater for BOD5, 0.5 L for TSS and 0.25 L for COD preserved with 10 drops of H2SO4.

Initial analysis of the sample
For the initial analysis of the field parameters, the HQ40d multiparameter and the OAKTON T-100 turbidimeter were used.The results are shown below.The initial analysis of the field parameters for sample 1 was carried out: temperature (21.4 °C), pH (7.48), electrical conductivity (743 μS/cm) and turbidity (44.9 NTU) of the wastewater.In addition, the initial analysis was carried out for sample 2: temperature (21.5 °C), pH (7.65), electrical conductivity (775 μS/cm) and turbidity (79.5 NTU) of waste water.The initial analysis of the physical-chemical parameters for sample 1 was carried out: BOD5 (132 mg/L), COD (374 mg/L) and TSS (43 mg/L).In addition, the initial analysis of the physicalchemical parameters for sample 2 was carried out: BOD5 (127 mg/L), COD (297 mg/L) and TSS (110 mg/L) of waste water.

Treatment with Ozone-air MNBs
The micro-nano bubbles were generated at an air pressure of 30 PSI, water flow of 8L/min and 1000mg of O3/h.
The micro-nanobubbles were characterized through a trinocular microscope MOD BM-120T-LED light with a 5 MP camera obtaining as a result micro-nano bubbles of 0.024 μm average diameter.

Internal pressure
The internal pressure was determined from the Young's equation -Laplace Therefore, it is concluded that the internal pressure of the micro-nanobubbles is 22.01 atm.

Ascent speed pf air micro-nanobubbles.
Ascent speed of the micro-nanobubble was obtained by replacing equation (3).
V = pgd 2 /18 ᶯ (3) Where: V: ascending speed = X p: density of the liquid = 998.2g/L = 998.2kg/m 3 g: gravitational acceleration = 9.8 m/s 2 d: diameter of the bubble= 0.024x10 -6 m n: viscosity of the liquid = 1.003 x 10 -3 m 2 /s 18( 1.003x10 −3   )  = 3.12 x 10 −10 / Therefore, it is concluded that the ascent speed of the air micro-nanobubbles is 3.12 x 10 -10 m/s.Both for the treatment of sample 1 (8:00 a.m.) and sample 2 (11:00 a.m.), 12 L of residual water were used in a period of 5, 10 and 15 minutes.The results obtained from the analysis of the field parameters of sample 1 (8:00 a.m.) and sample 2 (11:00 a.m.) at 0, 5, 10 and 15 minutes with the ozone-air micro-nanobubbles are observed.The results obtained from the analysis of the physical-chemical parameters of sample 1 (8:00 a.m.) and sample 2 (11:00 a.m.) at 0, 5, 10 and 15 minutes with the ozone-air micro-nanobubbles are observed.The results obtained before and after the treatment of the field and physicalchemical parameters are detailed below.It is observed that Turbidity was decreasing with longer treatment time.Turbidity in sample 1 achieved 4 NTU, and in sample 2 achieved 5.9 NTU in 15 minutes.It is observed that BOD5 was decreasing with longer treatment time.BOD5 in sample 1 achieved 13 mg/L, and in sample 2 achieved 21 mg/L in 15 minutes.It is observed that COD was decreasing with longer treatment time.COD in sample 1 achieved 28 mg/L, and in sample 2 achieved 36 mg/L in 15 minutes.

Treatment's efficiency
To calculate treatment's efficiency with ozone-air MNBs on Electrical conductivity in Sample 1 as % Remotion was used the equation 3: Then was calculated to the rest of Sample 1 and Sample 2. As a resume the efficiency is seen in figure 9. To calculate treatment's efficiency with ozone-air MNBs on Turbidity in Sample 1 as % Remotion was used the equation 1: % remotion (Sample1)15 = (44.9-4)*100/ 44.9 = 91.1 % Then was calculated to the rest of Sample 1 and Sample 2. As a resume the efficiency is seen in figure 10.Then was calculated to the rest of Sample 1 and Sample 2. As a resume the efficiency is seen in figure 11.
Figure 11.TSS removal efficiency of sample 1 and sample 2.
To calculate treatment's efficiency with ozone-air MNBs on BOD5 in Sample 1 as % Remotion was used the equation 1: % remotion (Sample1)15 = (132 -13)*100/ 132 = 90.2% Then was calculated to the rest of Sample 1 and Sample 2. As a resume the efficiency is seen in figure 12.To calculate treatment's efficiency with ozone-air MNBs on COD in Sample 1 as % Remotion was used the equation 1: % remotion (Sample1)15 = (374 -28)*100/ 374 = 92.51% Then was calculated to the rest of Sample 1 and Sample 2. As a resume the efficiency is seen in figure 13.
Figure 13.Efficiency of COD removal from sample 1 and sample 2

Conclusions
• It is concluded that the initial concentrations of the field parameters of the wastewater in sample 1 as: EC (743 μS/cm), and Turbidity (44.9 NTU) applying ozone-air micronanobubbles in 15 minutes decreased their concentrations at 405 μS/cm EC, and 4 NTU Turbidity.In addition, the initial concentrations of the field parameters of the wastewater in sample 2 as: EC (775 μS/cm), and Turbidity (79.5 NTU) applying ozone-air micronanobubbles in 15 minutes decreased their concentrations to 530 μS/cm of EC, and 5.9 NTU of Turbidity.
• It is concluded that the initial concentrations of the physical-chemical parameters of the wastewater in sample 1 such as: BOD5 (132mg/L), COD (374mg/L) and TSS (43mg/L) applying ozone-air micro-nanobubbles in 15 minutes decreased their concentrations to 13mg/L of BOD5, 28mg/L of COD and 9 mg/L of TSS.In addition, the initial concentrations of the parameters of wastewater in sample 2 such as: BOD5 (127mg/L), COD (297mg/L) and TSS (110mg/L) applying ozone-air micro-nanobubbles in 15 minutes decreased its concentrations at 21mg/L of BOD5, 36mg/L of COD and 13 mg/L of TSS.
• According to the results obtained, the percentage of the removal efficiency of the electrical conductivity was 45.5% for sample 1, turbidity was 92.6 for sample 2, Total Suspended Solids (TSS) was 88.2% for sample 2, BOD5 was 90.2% for sample 1 and COD was 92.51% for sample 1.

Figure 8 .
Figure 8. COD vs Time of Sample 1 and Sample 2.

Figure 9 .
Figure 9. Efficiency of removal of the electrical conductivity of sample 1 and sample 2

Figure 10 .
Figure 10.Efficiency of turbidity removal of sample 1 and sample 2

Figure 12 .
Figure 12.Efficiency of removal of BOD5 from sample 1 and sample 2

Table 1 .
Results of the initial measurement of the field parameters.

Table 2 .
Results of the initial measurement of the physical-chemical parameters

Table 3 .
Results of the characterization of the micro-nano bubbles

Table 4 .
Results of the field parameters of Sample 1 and sample 2.

Table 5 .
Results of the physical-chemical parameters of Sample 1 and sample 2.