Survey on taste and odor occurrence in Mahabad dam reservoir water and presenting mitigation and improving quality strategies

Abstract

Abstract Introduction Taste and odor in drinking water is one of the most important problems for consumers, because consumers are very sensitive to changes in water quality. One of the main reasons of taste and odor in water is growth of blue-green algae and Cyanobacteria that product toxins such as Microcystins, Geosimin, 2-Methylisoborneol and deadly toxic compounds called Cyanotoxins. With regard to the objection of water consumers in the Mahabad city to the taste and odor in drinking water and the importance of providing safe and sanitation drinking water for them, it was decided to achieve this study(It is explained that in this study the main producing taste and odor compounds are Geosimin and 2-Methylisoborneol that no clear guidance from international organizations such as the World Health Organization Therefore, Microcystins toxin that produced by cyanobacteria and has guidance one micrograms per liter from World Health organization was selected as representative of toxins.) Material and Methods In this cross-sectional study, in order to cover the different seasons, sampling was carried out monthly from input treatment plant that feeds directly into the pond dam for 10 months. Since the Mahabad dam has two pipes that feed treatment plant water, Therefore, a sample was taken from each pipes monthly and with the change of seasons was taken other samples from different parts of the water behind the dam to a better comparison between water treatment plant and other locations. Since chlorophyll a is representative for the presence of cyanobacteria then we measured chlorophyll a instead of cyanobacteria at this study. Other parameters studied include temperature, nitrate, nitrite, phosphate, pH, diatoms, Chlorophyte, BOD, COD, Microcystin and secchi disk test. Result The results of this study show that the maximum amount of nutrients such as nitrates and phosphorus is enter into Mahabad reservoir in spring. From May to September, the thermal stratification happens in the reservoir and Chlorophyll is appears in maximum concentration in June (88/1 mg per liter). And the secchi depth considering show that reservoir is in the eutrophic state in the months of March, April, May, June, September and October and it is appear in the mesotrophic state in the months of July, August and September. The maximum amount Microcystin toxin was determined in September to 3.21 micrograms per liter. Conculasion: Concurrent with the increase temperature in the spring and beginning of thermal stratification in May and reaches its maximum in July and August, Nutrients levels such as nitrate and phosphate in the Mahabad reservoir to increase and With increase nutrients, temperature, sunlight intensity and …, the growth of cyanobacteria and algae will increase in reservoirs and in the months of July, August and September to reach its maximum level As the amount of chlorophyll a in June reach to its maximum and the amount is 88/1 mg per liter. By increasing the amount of chlorophyll a, which represents the amount of algae and cyanobacteria the microsystin toxins also begins to increase and reach to maximum rate is 3.21 micrograms per liter in months of August and September. The thermal stratification in recent months is the most severe and microbial metabolism by increasing the temperature reached the highest level, which reduces the amount of dissolved oxygen in the bottom layer and increase the taste and odor in water. According to the results, as well as with regard to the proposed guidelines one micrograms per liter for microsystin toxin. The need for further measures to prevent the entry of nutrients into the Mahabad reservoir and apply advanced techniques such as activated carbon and ozonation seems to be necessary to remove microsystin toxin.