1. Introduction

Nosy-be is the largest island in Madagascar, it is located north-west of Madagascar, it is between 13° 11’ and 13° 30’ south latitude and between 48° 22’and 48° 8’ longitude. It measures 30 km from north to south and 19 km from east to west. This lake is located in the district of DZAMANDZAR. The populations who live around the lake can use it as drinking water, which is why my research will be carried out to analyze the physico-chemical, microbiological and specific treatment parameters corresponding to the results found.

2. Objective of My Research

The first objective of my research is the determination of the concentration for the physical parameters compared with the international standards required for drinking water, respectively for the chemical parameters.

The second objective is to determine the levels of microbiological germs to know whether the water ismicrobial or not.

The third objective is the specific treatment corresponding to the disinfection of the germs that exist in the water, in order to make the water drinkable without risk of contamination.

3. Research Methods and Materials

For physical parameters: measure directly using a thermometer for temperature measurement, pH meter for pH, measure with turbidimeter for turbidity and measure with conductivity meter for conductivity.

For chemical parameters: measurement of total hardness is titrated with CaCO3, calcium, magnesium, sodium, potassium and chloride are measured with the spectrometer apparatus and total iron, lead and aluminum are measured using a PERKIN ELMER lamp and acetylene gas.

For the microbiological parameters, we use the colimetry techniques H. Vincent method and the recommended Buttiaux technique to determine the concentration of germs that exist in water using a Smallest Number (MPN).

4. Characteristics of the Lake

It is a sacred lake named FARIHY MIRAHAVAVY (lower and upper sister lake), so the study is done by the lower FARIHY MIRAHAVAVY.

Lake Mirahavavy inferior

5. Quality Standards

Table 1. Recommendation by the WHO

Table 2. Recommendation by the EU

Table 3. Recommendation by the E.M

6. Analysis Parameters

Physical parameters:

Temperature: determines the natural heat of water, it measures directly with the thermometer.

Turbidity: determination of the transparency of the water, possibly the presence of suspended particles.

pH: the potential of Hydrogen is the measure of the concentration of H + ions, the water being acidic, basic and neutral.

Conductivity: determination of the amount of dissolved matter and dissolved salt in water.

Chemical parameters:

Total hardness: determination of the calcium and magnesium content in the water.

Calcium, magnesium, sodium, chloride and potassium: are abundant and very important elements in water for human consumption.

Total iron: obligatory element that exists in water, but their excess in concentration results in the existence of toxicity in water.

Lead and Aluminum: Existence in sample indicates water is toxic.

Microbiological parameters:

The existence of one in the sample of five required for water intended for human consumption indicates the water is microbial.

7. Analysis Results

I - Physical parameters:

1 – temperature [3]

Table 4. Temperature measurement

Figure 1. Temperature measurement

2 – Conductivity

Table 5. Conductivity measurement

Figure 2. Conductivity measurement

3 – pH: [2], [3]

Table 6. pH measurement

Figure 3. pH measurement

4 – Turbidity [1]

Table 7. Turbidity measurement

Figure 4. Turbidity measurement

II - Chemical parameters

1 - Mineralization

Table 8. Mineralization concentration

Figure 5. Mineralization concentration

2 – Total hardness [4]

Table 9. Determination of the total hardness concentration

Figure 6. Total hardness concentration

3- Calcium [6]

Table 10. Determination of the calcium concentration

Figure 7. Calcium concentration

4 – Magnesium [6]

Table 11. Determination of the magnesium concentration

Figure 8. Magnesium concentration

5 - Potassium [9]

Table 12. Determination of the potassium concentration

Figure 9. Potassium concentration

6 – Sodium [9]

Table 13. Determination of the sodium concentration

Figure 10. Sodium concentration

7 – Chloride [7]

Table 14. Determination of the chloride concentration

Figure 11. Chloride concentration

8 – Total iron [8]

Table 15. Determination of the total iron content

Figure 12. Total iron concentration

9 –Lead

Table 16. Determination of the lead content

Figure 13. Lead concentration

10 – Aluminum [5]

Table 17. Determination of the aluminum content

Figure 14. Aluminum concentration

III - Microbiological parameters

Table 18. Determination of the concentration of microbiological parameters

Figure 15. Concentration of microbiological parameters

According to this analysis, the values found exceed international standards, therefore the lake water is microbial, it must be treated before use.

Treatment method [10]

The method used is disinfection by calcium hypochlorite by the "Break-Point" method, ie determining the optimal dose of chlorine for the disinfection of the water in FRIHY MIRAHAVY.

The result of the chlorine demand is given in the following table 19.

Table 19

Figure 16. Variation of the chlorine concentration after 30mn of contact

From 1 to 3 mg / L: chlorine in the form of amino compounds.

From 3 to 4 mg / L: progressive increase in Chlorine.

The optimum dose of calcium hypochlorite from the Break-point, the chlorine content of 3.5 mg / L is taken for disinfection.

Result immediately after disinfection

Table 20

8. Discussions

For the physical parameters, respectively temperature, pH, turbidity and conductivity, the values found are admissible to the standards required for water intended for human consumption.

For the chemical parameters: calcium, magnesium, sodium, potassium and chloride, the concentrations found are acceptable for the international standards required for drinking water, despite their insufficient concentrations such as calcium is 45 mg / L potassium 15 mg / L and sodium is 85 mg / L.

For heavy metals such as lead, aluminum and total iron, the concentrations found are very low, so the water is not a risk of contamination, but it is necessary to take the measurement every season and clean the border this lake.

For microbiological parameters: the results are very bad, ie the water is microbial, it must be treated before use.

I choose the “Break-Point” method for the treatment. According to this method we take the dose 3.5 mg / L of calcium hypochlorite can be taken for disinfection, finally the population uses the water of FARIHY MIRAHAVY without risk of contamination on everything during the rainy season.

9. Conclusions

The water of FARIHY MIRAHAVY is good according to the analysis of the physical parameters, that is to say, the value found is acceptable according to the international standards for drinking water.

For the chemical parameters, it is good, despite the insufficient concentration of calcium 45 mg / L, magnesium 15 mg / L and sodium 85 mg / L; The water is drinkable and without risk to health, but lacks the very important elements in water intended for human consumption.

Heavy metals Aluminum is 0.02 mg / L and lead is 0.04 mg / L, comparison to international standards require that the limit value less than 0.5 mg / L, for heavy metals; based on this concentration, water is found to be safe for toxicity.

For microbiological parameters, water is bad and very dangerous for health. It is necessary to treat by the method of chlorination with the optimal dose of 3.5 mg / L of calcium hypochlorite before being used, in the end the populations who live in the range of FARIHY MIRAHAVY drink this water in complete safety. especially during the rainy season.