Traditional Photobioreactors Research Articles

Dialysis bag-microalgae photobioreactor: Novel strategy for enhanced bioresource production and wastewater purification

Cultivating microalgae in wastewater offers various advantages, but it still faces limitations such as bacteria and other impurities in wastewater affecting the growth and purity of microalgae, difficulty in microalgae harvesting, and extracellular products of microalgae affecting effluent quality. In this study, a novel dialysis bag-microalgae photobioreactor (Db-PBR) was developed to achieve wastewater purification and purer bioresource recovery by culturing microalgae in a dialysis bag. The dialysis bag in the Db-PBR effectively captured the microalgae cells and promoted their lipid accumulation, leading to higher biomass (1.53 times of the control) and lipid production (2.50 times of the control). During the stable operation stage of Db-PBR, the average soluble microbial products (SMP) content outside the dialysis bag was 25.83 mg L−1, which was significantly lower than that inside the dialysis bag (185.63 mg L−1), indicating that the dialysis bag effectively intercepted the SMP secreted by microalgae. As a result, the concentration of dissolved organic carbon (DOC) in Db-PBR effluent was significantly lower than that of traditional photobioreactor. Furthermore, benefiting from the dialysis bag in the reactor effectively intercepted the microorganisms in wastewater, significantly improving the purity of the cultured microalgae biomass, which is beneficial for the development of high-value microalgae products.

Evaluation of microalgae biodiesel for carbon neutrality based on the waste treatment by the autotrophic and heterotrophic combination

Microalgae aid in addressing environmental pollution and climate change by enabling carbon sequestration as part of CCUS, which offers a promising solution to reduce fossil fuel dependence and mitigate emissions. This study uses the combination of autotrophic and heterotrophic methods to enhance the benefits of biodiesel based on waste treatment. The study demonstrates that by integrating autotrophic and heterotrophic biodiesel production, it is feasible to attain substantial economic advantages while maximizing carbon sequestration and reducing emissions. It shows a 62.73 % cost reduction for 1 ton of biodiesel produced using the coupled heterotrophic method over traditional photobioreactors. Additionally, compared with the corresponding heterotrophic proliferation, the carbon emissions of biodiesel under autotrophic coupled heterotrophic proliferation were reduced by 21.16 % and 24.08 %, respectively. The total economic benefits of biodiesel under autotrophic coupled heterotrophic proliferation increased by 2.12 % and 3.10 % compared to heterotrophic proliferation. However, it should be noted that due to the high carbon emissions caused by the heterotrophic proliferation of microalgae, biodiesel does not achieve negative carbon emissions. This study provides a new development strategy for waste resource utilization and microalgae bioenergy production phase. It will provide a theoretical and practical framework for utilizing microalgae biodiesel to achieve worldwide carbon neutrality.

CO2 capture and lipid production performance of microalgae in the S-shaped photobioreactor under different culture modes

An S-shaped photobioreactor was designed by adding grooves and baffles in the traditional photobioreactor to improve the culture efficiency of microalgae. After that, the parameters of the characterization of the S-shaped photobioreactor, such as the mixing time, gas holdup, and gas-liquid mass transfer coefficient, were determined. The biomass, lipid production rate, and average CO2 capture rate of microalgae were then analyzed under different culture modes. Finally, the feasibility of using digested piggery wastewater combined with simulated flue gas was explored as a culture mode for the microalgae and the lipid properties of the microalgae were analyzed. The results revealed that, at a flow rate of 0.08 vvm, the mixing time was reduced by 8.5 s, the gas hold-up increased by 44.6% and the gas–liquid mass transfer ability was also improved. Improvements were also observed in the biomass values, lipid production rate, and average CO2 capture rate of the microalgae under different culture conditions, with respective values reaching 0.23 g·(L·d)–1, 70.28 mg·(L·d)–1, and 0.43 g·(L·d)–1 under the mixotrophic mode. Additionally, digested piggery wastewater combined with the simulated microalgae flue gas culture was determined to be feasible. The biomass, lipid production rate, and the average CO2 capture rate of microalgae, the values of which were 0.22 g·(L·d)–1, 52.55 mg·(L·d)–1, and 0.41 g·(L·d)–1, respectively. Lipid was observed to have the potential to produce high-quality biofuel.

High-efficiency nutrients reclamation from landfill leachate by microalgae Chlorella vulgaris in membrane photobioreactor for bio-lipid production

Using microalgae to treat landfill leachate is a promising approach due to the effective nutrients reclamation ability and additional profit of bio-lipid production. To offset the negative effect of landfill leachate on microalgae cells, a membrane photobioreactor (m-PBR) was adopted in the study, in which microalgae biomass concentration was improved from 0.66 in traditional photobioreactor (T-PBR) to 0.95 g/L. Nutrients reclamation efficiencies of leachate were analyzed according to elemental balance, and the results showed that nitrogen reclamation efficiency was generally lower than 50% while phosphorus reclamation efficiency was higher than 70% due to elemental availability. The nitrogen and phosphorus reclamation efficiencies in the m-PBR were much higher than that in the T-PBR. Besides, lipid produced from the m-PBR had a high cetane number of 60.96% and low linolenic acid content of 8.32%, which demonstrated good combustion properties of the microalgae-based lipid when using landfill leachate as nutrients source.

Improvement of microalgae lipid productivity and quality in an ion-exchange-membrane photobioreactor using real municipal wastewater

To improve the productivity and quality of microalgae-based biodiesel when using municipal wastewater (MW) as nutrients source, an ion-exchange-membrane photobioreactor (IEM-PBR) was used in this study to eliminate the negative effects of pollutants in MW on microalgae Chlorella vulgaris and Scenedesmus obliquus. In the IEM-PBR, the real MW and microalgae cultures were separated in two chambers by the ion-exchange-membranes (IEMs). Nutrients (N, P, etc.) in the MW permeated into microalgae cultures through the IEMs, while pollutants (suspended solids, competitors, etc.) in the MW could hardly permeate into microalgae cultures. As a result, the lipid productivity in the IEM-PBR was improved to 85.7 mg/(L•d) for C. vulgaris and 111.8 mg/(L•d) for S. obliquus, which was slightly higher than that in the traditional photobioreactor (T-PBR) with real MW after centrifugation (82.5 mg/(L•d) for C. vulgaris and 105.8 mg/(L•d) for S. obliquus), but much higher than that in the T-PBR with untreated MW and primary MW (with lipid productivity of 20-30 mg/(L•d)). Besides, the lipid quality obtained in the IEM-PBR had higher proportion of cetane number (ca. 60%) and lower linolenic acid content (ca. 8%), which showed a superior quality in the IEM-PBR to that in the T-PBR. It demonstrated that the IEM-PBR is an effective approach to improve the productivity and quality of microalgae biodiesel. Keywords: microalgae, photobioreactor, lipid productivity, real municipal wastewater, ion-exchange-membrane DOI: 10.3965/j.ijabe.20171001.2706 Citation: Chang H X, Fu Q, Huang Y, Xia A, Liao Q, Zhu X. Improvement of microalgae lipid productivity and quality in an ion-exchange-membrane photobioreactor using real municipal wastewater. Int J Agric & Biol Eng, 2017; 10(1): 97－106.

Stacked optical waveguide photobioreactor for high density algal cultures

In this work, an ultracompact algal photobioreactor that alleviates the problem of non-optimal light distribution in current algae photobioreactor systems, by incorporating stacked layers of slab waveguides with embedded light scatterers, is presented. Poor light distribution in traditional photobioreactor systems, due to self-shading effects, is responsible for relatively low volumetric productivity. The optimal conditions for operating a 10-layer bioreactor are outlined. The bioreactor exhibits the ability to sustain uniform biomass growth throughout the bioreactor for 3weeks, and demonstrates an 8-fold increase in biomass productivity. Using a genetically engineered algal strain, constant secreted ethylene production for over 45days is also demonstrated. Since the stacked architecture leads to improved light distribution throughout the volume of the bioreactor, it reduces the need for culture mixing for optimum light distribution, and thereby potentially reducing operational costs.

Slab waveguide photobioreactors for microalgae based biofuel production

Microalgae are a promising feedstock for sustainable biofuel production. At present, however, there are a number of challenges that limit the economic viability of the process. Two of the major challenges are the non-uniform distribution of light in photobioreactors and the inefficiencies associated with traditional biomass processing. To address the latter limitation, a number of studies have demonstrated organisms that directly secrete fuels without requiring organism harvesting. In this paper, we demonstrate a novel optofluidic photobioreactor that can help address the light distribution challenge while being compatible with these chemical secreting organisms. Our approach is based on light delivery to surface bound photosynthetic organisms through the evanescent field of an optically excited slab waveguide. In addition to characterizing organism growth-rates in the system, we also show here, for the first time, that the photon usage efficiency of evanescent field illumination is comparable to the direct illumination used in traditional photobioreactors. We also show that the stackable nature of the slab waveguide approach could yield a 12-fold improvement in the volumetric productivity.