Microalgal biomass and oil production using leachate

Landfill leachate leaking through compressed wastes in landfills overtime, is toxic to natural ecosystem and pose serious health issues for communities and surrounding environment. Since landfill continue to produce leachate (with high concentration of NH4+-N) through out its life span even after closure, this waste stream can be used as a nutrient resource for the growth of microalgae. The dual role of microalgae to remediate leachate (tertiary treatment) and simultaneously produce biomass make them one of the most sustainable renewable biological system to accumulate oils for future biodiesel conversion. For this purpose ultra-membrane treated landfill leachate TL was taken from Odayeri, Istanbul municipal landfill (Istanbul Büyükşehir Belediyesi) and evaluated in laboratory experiments and onsite pilot scale open raceway pond cultivation for the production of microalgal (Chlorella vulgaris and Chlamydomonas reinhardtii) biomass and simultaneous removal of nutrients (mainly NH4+-N-NO3) and intracellular oil accumulation. Firstly different dilutions of TL were screened in laboratory studies and then scaled up in onsite open raceway pond cultivation. Laboratory conditions were also altered to check its effect on growth, NH4+-N removal and oil production. Generated microalgal biomass was subjected to oil extraction process, oil content and productivity was then measured. From first set of lab screening, It was observed that increasing leachate concentration as in lower dilutions of TL (70-100%) had a negative effect on biomass growth and nutrient removal. Better biomass growth (~1.67 gL-1 dry biomass) was found in 50% TL (~242 mgL-1 NH4+-N) with 50% NH4+-N removal from the system. Growth in 10% TL (~50 mgL-1 NH4+-N) was minimum but NH4+-N removal efficiency was 100%. From second set of lab screening, again highest biomass 1.5 gL-1 was found from 50% TL (~ 380 mgL-1 NH4+-N) with 31.88% NH4+-N removal from the system. Onsite raceway pond cultivation had reduced biomass growth ~ 0.5 gm-2d-1 and nutrient removal. NH4+-N concentration kept on fluctuating in the open system. NO3-N removal was minimum from both the setups. From 3rd set of lab acreening, increased biomass 2.5 gL-1 was observed in 50% TL (~ 248 mgL-1 NH4+-N with phosphate addition (6 mgL-1 PO4-3-P) with a N:P ratio of 40:1. Biomass productivity achieved was 92.59 mgL-1d-1 with oil content as 51.38 mg g-1 (5.14 %) and a lipid productivity of 5.6 mgL-1d-1. In terms of oil content, although microalgal cultures grown in 50% TL produced highest biomass (2.5 gL-1 dry weight) but the intracellular accumulated oil content was the lowest as 5.14%. 10% TL grown biomass accumulated the highest oil content, 114.64 mg g-1 dry biomass, with oil content as 11.5 % and lipid productivity as 4.37 mgL-1d-1, which was still on the lowest scale according to literature survey (4 – 505 mgL-1 day-1). Overall treated landfill leachate with concentration of ~250 mgL-1 NH4+-N (50%TL) was found to support growth of microalgae with NH4+-N removal above 30% from the system. In terms of oil production, accumulated oil was not enough to be considered as a raw material for biodiesel. Futher optimization is required to increase the intracellular oil content of microalgal species grown in leachate. The issues discussed in the thesis can be a focus point for growing biomass and nutrient removal from landfill leachate which in turn can improve the microalgal oil production for future biodiesel energy generation.