The level of environmental degradation has been on the increasing trend probably due to human activities on the environment and to lesser extent by natural phenomenon 12345. The degradation of the environment (e.g air, soil, sediment and water quality) often affect different life forms in such ecosystem. Authors have reported that human activities is having an impacts on the population status of biodiversity including mammals, amphibians, fisheries, reptiles, birds, vegetation/plants among others 6789.

Several human activities that impact on the soil including municipal solid wastes that are poorly managed in many developing countries 10, food processing effluents such as oil palm processing wastewater 1112 and cassava mill effluents 123, wastes emanating from markets 222324, slaughterhouse25etc. These wastes stream have the tendency to alter the characteristics of the receiving soil.

Basically Nigeria is the global leading cassava producing countries 1415161718192021. The cassava production in Nigeria has exceeded the combined production of second (Thailand) and third (Indonesia) largest cassava production countries in the world. In Nigeria, significant portion of the cassava tuber produced is used to produce gari and to lesser extent fufu, lafun, animal feeds and other industrial purposes such as adhesives, etc 26.

The cassava mill effluents generated during cassava processing in Nigeria are discharged into the environment with little or no treatment. Studies have shown that the effluents have some level of toxicity on the environment 231415161718192021 and its associated biota including some domestic animals, plants, fisheries, etc 2. Several biotechnological advances have shown the various means through which the effluents can be effectively managed 31. Among the various methods is the production of Saccharomyces cerevisiae biomass from the effluents 13. Studies have also indicated that when cassava mill effluents are treated some of its physicochemical and heavy metals characteristics are improved upon 1415. Therefore, this study aimed at assessing the fermentation dynamics of the Saccharomyces cerevisiae with regard to the microbial density.

The growth pattern of Saccharomyces cerevisiae in cassava mill effluents is presented in Figure 1. At the initial day (day 0) the population of Saccharomyces cerevisiae were 0.00 x 10⁶ cfu/ml, which rose to 2.88 x 10⁶ cfu/ml at day 3, 14.50 x 10⁶ cfu/ml at day 6, 23.0 x 10⁶ cfu/ml at day 9, 272.67 x 10⁶ cfu/ml at day 12 and decline slightly at day 15 (13.57 x 10⁶ cfu/ml). Typically, there was significant variations (P<0.05) among the various period of study. But Waller-Duncan statistics showed that day 12 had the highest density (272.67 x 10⁶ cfu/ml) which was significantly different among other days of study. This growth pattern showed that most of the nutrient in the cassava mill effluents has been utilized. Previous studies have indicated that Saccharomyces cerevisiae improves the physical and chemical characteristics of cassava mill effluents 1415. Izah et al. 14 reported a decline in total dissolved solid, conductivity, salinity, sulphate, phosphate, chemical oxygen demand, and increase in turbidity during treatment of cassava mill effluents with Saccharomyces cerevisiae. Izah et al. 15 also reported that Saccharomyces cerevisiae has the tendency to remove heavy metals (such as iron, zinc, copper, manganese) from cassava mill effluent through biosorption. Furthermore, Iwuagwu and Ugwuanyi 35 also reported that Saccharomyces cerevisiae could reduce the chemical oxygen demand and total dissolved solid concentration in palm oil mill effluents. Abioye et al. 39 reported that Saccharomyces cerevisiae aid in the degradation of pharmaceutical effluents. Okoduwa et al. 36 also reported the potentials of Saccharomyces cerevisiae in the treatment of tannery effluents. The nutrient uptake from the effluents suggests the possible increase in population of the Saccharomyces cerevisiae. A slight significant decline at day 15 suggest that most nutrients that are useful for the growth of Saccharomyces cerevisiae have been used up and therefore the cells requires addition nutrient for growth.

This study showed that during the treatment of cassava mill effluents using Saccharomyces cerevisiae the microbial cells increased from day 1 to 12 and then significantly declined at day 15. This suggest that at 12 days of fermentation of cassava mill effluents most of the nutrients that could enhance microbial growth have been used up and/ or the medium becomes toxic to the Saccharomyces cerevisiae cells. Therefore, there is the need for further study to focus on the implication of changing Saccharomyces cerevisiae population during the treatment of cassava mill effluents so as to prevent the attendant impacts associated with the untreated effluents in the environment particularly soil.