Reduction of the Biochemical Oxygen Demand of the water samples from the lower basin of the Chillon River by means of Air-Ozone MicroNanobubbles , Ventanilla-Callao

The dumping of domestic and industrial wastewater is one of the major problems facing rivers, the high level of pollution directly affects aquatic and plant life. Producers living near to the Chillon River use these waters to irrigate their farms, many of the food products are taken to shopping centers in the city and then consumed by the population. Due to this reason, this research aims to reduce or eliminate pollutants by measuring the Biochemical Oxygen Demand (BOD); since it is considered as a test of great value in the analysis of sewage effluent or highly contaminated. The results show that the mean initial sample was 173 mg/L. after treatment at 15 minutes with air Micro Nanobubbles was obtained 53 mg/L and with ozone Micro Nanobubbles was obtained 53 mg/L. The best obtained efficiency was 69.36%


Introduction
Water is one of the most important natural resources for life whose extraction and use has effects on the ecosystem; whereas human activity directly and indirectly influences the water cycle through waste water discharges, solid wastes and other wastes; which generate their pollution.The Chillon River is affected by discharging product of human activity such as pig farms, garbage dumps, washing of sacks, etc .; which present elements and substances with physical, chemical and bacteriological characteristics that affect the conditions of the receiving body.From the above, it is determined that the low basin of the Chillon River is contaminated and presents values of BOD5 that surpass the National Standard of Environmental Quality for Waters.The high level of BOD5 affects the water quality, aquatic-flora and fauna, as well as the soil if it is used for irrigation.It is necessary manage the water in order to grantee life in Peru (ANA, 2013) In order to reduce the level of Biochemical Oxygen Demand of wastewater, the species Eichhornia Crassipes (SOCLA, 2014), coliforms in domestic sewage, marine waters (Valverde, 2017;Agalwal et al., 2011) industrial sewage (Valverde, 2017), oils and fats (Valverde, 2017), by micro-nanobubbles (MNBs).
The Venturi type generator consists of three main parts of inlet flow, tubules and conical outlet.Cavitation occurs due to the decrease in static pressure of the pressurized fluid entering the tubular part.In the tubule part, the velocity of the fluid increases at the cost of the decrease of the static pressure.Then the gas entering the inside of tubule develops a phase between the gas flow and the liquid.When the fluid is high, a pressure in wall with a shock wave is created in the tubule.This mode MBs are generated through the gas collision with the pressure in wall developed with a shock wave.(AGARWAL et al, 2011;Valverde, 2016) The Microbubbles (MBs) have diameter more than 100 μm, the micro-nanobubbles (MNBs) have diameter between 1 to 100 μm and the nanobubbles (NBs) have diameter less than 1 μm within the fluid field (Valverde, 2016).Microbubbles have the ability to change the normal characteristic of water (Tsuge, 2014).Microbubbles (MBs) possess special properties such as the capacity for generating free radicals (Sadatomi et al., 2007), self-pressurization, and carrying a negative charge.MNBs have now attracted attention for applications in engineering areas such as the sewage treatment of wastewater by air flotation (Choung et al 1993, Fan et al. 2010).Ozone (O3) is a strong oxidizing agent commonly used for sterilization, virus inactivation, deodorization, bleaching (decoloration), and decomposition of organic matter (Takahashi and others 2007a).
The micro-bubble generation technology in water is applied in Health, especially when person has cardiovascular problems (Valverde, 2016).
Biochemical Oxygen Demand (BOD) is used as an indicator of the amount of oxygen that is required for the oxidation of biodegradable organic matter present in the water sample as a result of the aerobic oxidation action (Raffo, 2014;Ramalho, 2003).

i) Collection of water sample
The river's water samples were collected at the intersection of the Nestor Gambeta Km.50 Highway and the Rio Chillón basin in the Ventanilla district -Callao Province, following the indications of the Quality Monitoring National Protocol of Water from Peru.

ii) Sample analysis in laboratory
The total volume of water used for the experiment was 120 liters.The BDO was analyzed by an accredited laboratory.Also other parameters as Temperature, pH, Turbidity, Electrical Conductivity (EC), and Dissolved Oxygen (DO) were measured.The obtained average diameter of a MNB was 24 nm, the water flow was 4 L/min, the air pressure was 20 PSI.

v) Treatment's efficiency in laboratory
Results of the samples in different concentrations were analyzed after of using air micro-nanobubbles.
To measure the MNBs treatment's efficiency on BOD was used the equation 1:

Figure 1 .
Figure 1.Collection of samples from Chillon River iii) Fabrication of air-ozone micro-nanobubbles (MNBs) The research was carried out ex-situ, in laboratory, where the whole system was first assembled to generate and to use the air and ozone micro-nanobubbles in river's water.The patent obtained by Dr. Eng.Jhonny Valverde Flores was used to generate air MNBs.The schematic diagram of experimental apparatus for preparation of MNBs solutions is shown in Figure 2.

Figure 3 .
Figure 3. Average diameter of a MNB size is 24 nm iv) Treatment of the sample Four samples (One initial sample and three samples after treatment).Each sample was treated with air and ozone separately.The letter "A" represent Air and letter "O" represent Ozone.For example, TA1 represent treatment 1 with air and TO1 represent treatment 1 with ozone.