Batch mixed culture of Chlorella vulgaris using settled and diluted piggery waste

A study of the effect of the initial concentration of settled piggery wastewater in the range from 250 to 1100 mg COD/l on a mixed culture of Chlorella vulgaris and bacteria was carried out using 1-l batch culture bottles. COD removals and microorganisms concentrations increased with the time in a range of initial substrate concentrations from 250 to 800 mg COD/l. Nevertheless, when the initial substrate concentration increased to 1100 mg COD/l, the COD removal and microorganism concentrations decreased considerably, showing the occurrence of an inhibition phenomenon. The specific growth rates of the exponential phases obtained for each initial concentration of substrate were determined and verified by the utilization of a modified logistic model applied to total chlorophyll (∑C) and volatile suspended solids (VSS) concentrations, indirect measurements of the concentrations of microalgae and total microorganisms, respectively. A strong relationship between the ratio of the initial substrate concentration and the initial concentration of microorganisms S0/X0 (BX) and the specific growth rate expressed in ∑C and VSS was found. Process inhibition was observed for BX values of 100 mg COD/mg ∑C and 4.8 mg COD/mg VSS, respectively. The values of μmax were found to be 0.050 h−1 (1.20 d−1) for microalgae and 0.044 h−1 (1.06 d−1) for total microorganisms. The maximum value of the observed yield (Yobs. max.) was determined with respect to microalgae and was equal to 0.088 mg ∑C/mg COD.