Effects of limiting nutrients on growth of spirulina on digested cattle waste
Pulluoglu, Melih Ahmet
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The primary objective of this study was: ( 1 ) to develop a more thorough understanding of the growth characteristics of Spirulina platensis, a filamentous cyanobacterium cultivated commercially as a source of human food, animal feed, and fme chemicals, ( 2 ) to predict overall inorganic nutrient uptake, and ( 3 ) to determine the optimum concentrations of inorganic nutrients at which biomass production as well as growth rate reaches maximum levels. Digested cattle waste was supplied to Spirulina platensis as the sole source of macro-and micro-nutrients. An experiment was conducted to measure the growth of algae under the influence of nitrate-N, ammonia-N, orthophosphateP, and inorganic carbon at various concentrations. In each division of the experiment, the concentration of one of the four nutrients was expanded and growth response of algae was monitored to identify the acceleratory effect of this single nutrient. The results of the experimental study showed that the addition of nitrate-N to digested cattle waste media produces the highest rate of growth as well as the biomass yield of algae. In every experimental period, it is observed that the addition of any one kind of the inorganic nutrient above a certain level does not create a corresponding increase in biomass yield. This action might be caused by toxicity due to the excess concentration of one type of inorganic nutrient but more likely indicates some other nutrient is limiting. While measuring the effect of inorganic carbon on growth of Spirulina platen sis, the variation in pH due to the addition of sodium bicarbonate ( NaHC03) was investigated and found that 4 g NaHC03fL was sufficient to balance the media's pH to approximately 9.2. The developed model predicted measured data with an R2 value greater than 0.97 in all cases with a high significance level ( 99.9% or a=O.OOI ).