Characterization of stress tolerant microalgae strains for biogas production
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Date
2019
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Punjab Agricultural University, Ludhiana
Abstract
The present research work was aimed at characterization of stress tolerant microalgae strains for
biogas production. A total of six strains, five stress tolerant microalgae strains viz. BGLR4,
BGLR7, BGLR10, BGLR18, BGLRS and one standard strain Spirulina sp. NCIM 5143 were used
in the present study. These strains were screened for maximum biomass production, chlorophyll
content, protein, carbohydrate and lipids on four different media viz. Blue green-11(BG-11),
Bold’s basal medium (BBM), Algal culture medium (ACM) and Zarrouk’s medium (ZM) and on
different concentrations of unsterilized dairy wastewater (20%, 40%, 60%, 80% and 100%).
Among all the six strains, BGLR18 and BGLRS were found to produce maximum biomass BBM
and ACM respectively while Spirulina sp. NCIM 5143 produced maximum biomass on ZM.
BGLR18 and BGLRS showed maximum growth on 60% concentration of dairy wastewater
whereas Spirulina sp. NCIM 5143 on 100% concentration of dairy wastewater. Maximum percent
reduction in various physico-chemical parameters of dairy wastewater was shown by BGLR18
and BGLRS at 60% dairy wastewater while Spirulina sp. NCIM 5143 at 100%. Further, studies
were carried out with strains BGLR18 and BGLRS and compared with standard strain Spirulina
sp. NCIM 5143. Cultural conditions of BGLR18, BGLRS and Spirulina sp. NCIM 5143 were
optimized using response surface methodology (RSM) based on central composite design. The
optimized and most desirable cultural conditions of pH, temperature, light intensity, growth period
and inoculum concentration for BGRL18 were 10.02, 20.00°C, 7599.41 Lux, 21.75 days and
1.00% ; for BGLRS were 11.17, 26.03 °C, 4000.02 Lux, 39.37 days and 10.00% and for Spirulina
sp. NCIM 5143 were 10.35, 24.38 °C, 8000.00 Lux, 25.13 days and 1.00% respectively. On
molecular identification, BGLR18 showed 96% resemblance to Chlorosarcinopsis eremi and
BGLRS showed 99% resemblance with Scenedesmus sp. MKB. These three strains showed wide
variation in their total nitrogen, total protein,total phenols, antioxidant activity, DPPH radical
scavenging activity. ICP-AES analysis showed that heavy metals were negligible in all the three
strains while essential elements like Ca, Fe, P and Mg were present in higher concentrations than
Spirulina sp. NCIM 5143. GC-MS analysis of methanolic extract showed that many bioactive
compounds were present in all the strains. These strains were evaluated for their biogas production
potential alone and in co-digestion with paddy straw. The highest biogas was produced by BGLRS
(Scenedesmus sp. MKB) (28.80 Litres) with highest biogas production potential (P) of 30.85 mLg-1
VS showing maximum biogas production rate (Rm) of 0.58 mLg-1d -1 with a lag phase (λ) of 1.30
days. While in co-digestion experiment, the highest biogas production was recorded by BGLR18
(Chlorosarcinopsis eremi) (168.46 Litres) with maximum biogas production potential (P) of
214.30 mLg-1 VS showing maximum biogas production rate (Rm) of 8.76 mLg-1 d -1 with a lag
phase (λ) of 12.10 days. Hence, the stress tolerant microalgae strains can be co-digested with
paddy straw for enhancing biogas production.
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