Molasses wastewater treatment and lipid production at low temperature conditions by a microalgal mutant Scenedesmus sp. Z-4

Abstract

BackgroundSimultaneous wastewater treatment and lipid production by oleaginous microalgae show great potential to alleviate energy shortage and environmental pollution, because they exhibit tremendous advantages over traditional activated sludge. Currently, most research on wastewater treatment by microalgal are carried out at optimized temperature conditions (25–35 °C), but no information about simultaneous wastewater treatment and lipid production by microalgae at low temperatures has been reported. Microalgal growth and metabolism will be inhibited at low temperature conditions, and satisfactory wastewater treatment performance will be not obtained. Therefore, it is critical to domesticate and screen superior microalgal strains with low temperature adaptability, which is of great importance for wastewater treatment and biodiesel production.ResultsIn this work, simultaneous wastewater treatment and lipid production were achieved by a microalgal mutant Scenedesmus sp. Z-4 at the low temperature conditions (4, 10, and 15 °C). The results showed that algal growth was inhibited at 4, 10, and 15 °C compared to that at the optimal temperature of 25 °C. However, decreased temperature had no significant effect on the total cellular lipid content of algae. Importantly, lipid productivity at 10 °C was compromised by more net energy output relevant to biodiesel production, which demonstrated that the low temperature of 10 °C was favorable to wastewater treatment and energy recovery by Scenedesmus sp. Z-4. When molasses wastewater with optimal COD concentration of 8000 mg L−1, initial inoculation ratio of 15%, and C/N ratio of 15 was used to cultivate microalgae, the maximum removal rate of COD, TN, and TP at 10 °C reached 87.2, 90.5, and 88.6%, respectively. In addition, lipid content of 28.9% and lipid productivity of 94.4 mg L−1 day−1 were obtained.Conclusions Scenedesmus sp. Z-4 had good adaptability to low temperature conditions, and showed great potential to realize simultaneous wastewater treatment and lipid production at low temperatures. The proposed approach in the study was simple compared to other wastewater treatment methods, and this potential novel process was still efficient to remove COD, N, and P at low temperatures. Thus, it had a vital significance for the wastewater treatment in low temperature regions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0797-x) contains supplementary material, which is available to authorized users.

Structural effects of microalgae additives on the starch gelatinisation process

“…Similarly, V-type crystallites have been reported to originate from the formation of complexes between the polar lipids found in native starches and the amylose fraction (Zobel, 1988 Figures 2B and 2D). These peaks could arise from crystalline components, such as fatty acids, which are known to be found in the microalgae (Ahlgren, Gustafsson, & Boberg, 1992;James, Al-Hinty, & Salman, 1989;Ma, et al, 2017;Matos, et al, 2016). In fact, as shown in Figure S1, interactions with amylose, leading to the formation of V-type crystallites.…”

“…The total lipidic contents have been reported as ca. 6% for Spirulina (Matos, et al, 2016), 8-16% for Nannochloropsis (Matos, et al, 2016) and up to 30% for Scenedesmus microalgae (Jiang, et al, 2017;Ma, et al, 2017). However, the Nannochloropsis microalgae have been shown to possess a tough cell wall, formed by a cellulosic inner layer and an outer layer rich in algaenans, which requires intense sonication treatments to be disrupted (Fabra, et al, 2017;Scholz, et al, 2014).…”

Effect of Hydraulic Retention Time on Anaerobic Baffled Reactor Operation: Enhanced Biohydrogen Production and Enrichment of Hydrogen-producing Acetogens

“…The total nitrogen of NMWW was 35 mg/L; thus, the corresponding C/N was 230. To maintain the bioactivity of the anaerobic activated sludge, NH 4 Cl and K 2 HPO 4 were added at a COD:N:P ratio of 200:5:1. NaHCO 3 was used to adjust the initial pH value of the wastewater to 7.5-8.0.…”

“…enrichment of biohydrogen-producing acetogens, the specific hydrogen and methane yields from COD removal increased by factors of 1.54 and 1.63 in normal molasses wastewater treatment [2]. In addition, lipid production through microalgae cultivation in normal molasses wastewater treatment presented its economic feasibility when a lipid content of 28.9% and lipid productivity of 94.4 mg·m −3 ·d −1 were finally obtained [3,4].…”

“…enrichment of biohydrogen-producing acetogens, the specific hydrogen and methane yields from COD removal increased by factors of 1.54 and 1.63 in normal molasses wastewater treatment [2]. In addition, lipid production through microalgae cultivation in normal molasses wastewater treatment presented its economic feasibility when a lipid content of 28.9% and lipid productivity of 94.4 mg·m −3 ·d −1 were finally obtained [3,4].The use of fermentation to produce biohydrogen is a process in which hydrogen-producing microorganisms metabolize organic matter to produce hydrogen under anaerobic conditions [5]. The mechanism of the fermentation to produce biohydrogen has three possible ways: pyruvate decarboxylation in the EMP(Embden-Meyerhof-Parnas) pathway, the oxidation and reduction balance adjustment of acetyl coenzyme I, and the bacteria producing hydrogen and acetic acid [6].…”