Synergistic microalgal co-cultivation for treatment of municipal wastewater using a two-stage cultivation system and biomass valorization

Abstract

The present study aimed to develop different microalgal co-cultivation Tetraselmis indica BDUG001 (TS) and Picochlorum sp. (PC) for the treatment and recycling of raw municipal wastewater (MWW). The nutrient removal and biomolecules production, 75 % raw MWW + 25 % ASN-III, 50 % secondary treated municipal wastewater (STMWW) + 50 % ASN-III, and 50 % TS-treated MWW (TSTMWW) + 50 % ASN-III was used. Among them, co-cultivation 2TS:1PC and 2PC:1TS exhibited maximum nutrient removal efficiency (NRE) and biomass and biomolecules production in 75 % raw MWW + 25 % ASN-III, and 50 % TSTMWW + 50 % ASN-III, respectively. Based on the above outcomes, two-stage cultivation systems (TSCSs) were developed to maximize the NRE and biomolecules production using the micro vertical glass photobioreactor (MVG-PBR). 2TS:1PC and 2PC:1TS co-cultivation ratio was used for first and second stage of cultivation and noted as 2TS:1PC (S1) and 2PC:TS (S2), respectively. The co-cultivation ratios were compared with monoculture TS (S1) and PC (S2), and the cost analysis was performed to assess the viability of the process. The obtained results showed that during the first stage of TSCSs, co-cultivation 2TS:1PC (S1) and TS (S1) exhibited NRE of COD (95 and 91.42 %), TN (93.06 and 89.54 %) and TP (100 and 93.87 %), and generated dry biomass (3.11 and 2.75 g/L), lipid content (46 and 42.17 %) having FAME content (82.25 and 32.01 %), astaxanthin (1.12 and 0.93 mg/g DCW) and β-carotene (7.01 and 3.30 mg/g DCW), respectively. During the second stage of TSCSs, co-cultivation 2PC:1TS (S2) and PC (S2) exhibited NRE of COD (95.50 and 93.28 %), TN (98.97 and 94.38 %) and TP (100 and 94.50 %), and generated biomass (3.24 and 2.78 g/L), lipid content (48.50 and 40.70 %) having FAME content (86.78 and 44.20 %), astaxanthin (1.15 and 0.71 mg/g DCW) and β-carotene (5.14 and 5.33 mg/g DCW), respectively. The cost analysis suggested that co-cultivation-assisted TSSCSs generated more revenue compared to monoculture-based TSCSs.