Outdoor cultivation of the green microalga Chlorella minutissima in mini pond system under batch and fed-batch modes integrating low-dose sequential phosphate addition (LDSPA) strategy for biodiesel production

Abstract

Microalgae are appraised as the renewable feedstock for biodiesel production. With this view, the current study examines the possibility of a locally isolated microalga, Chlorella minutissima for production of biodiesel, under batch and fed-batch cultivation modes, being subjected to seasonal variations. Effects of different culture depths (5, 10, 15, and 20 cm) on the biomass yield and lipid accumulation were investigated using the mini pond system, and alterations in different physicochemical factors were documented. Both the batch as well as the fed-batch cultivations recorded the 15 cm culture depth to be optimum for obtaining the maximum biomass and lipid production. Consequently, this optimal depth was chosen for further experimentation integrating low-dose sequential phosphate addition (LDSPA) under both batch and fed-batch modes. For batch cultivation under LDSPA mode, the estimated annual biomass productivity was 10.04 ton hectare−1 year−1, with the lipid productivity of 1.37 ton hectare−1 year−1, considering 11 cycles of cultivation per year. On the other hand, the fed-batch cultivation under LDSPA mode projected the annual biomass productivity of 15.4 ton hectare−1 year−1 and lipid productivity of 2.29 ton hectare−1 year−1, even with 10 cycles of cultivation yearly, thus, certifying the supremacy of the fed-batch cultivation with LDSPA for obtaining a higher productivity of lipid. The biodiesel generated from the produced biomass demonstrated a greater prevalence of monounsaturated and saturated fatty acid methyl esters. Additionally, the fuel characteristics of the biodiesel samples were analyzed and recorded to be at par with the national (Indian) as well as international (European and American) biodiesel standards, hence, indicating its suitability as an alternative to petroleum-based fuel.