As a result of the growing global demand for energy, together with the depletion of resources and the growing emphasis on mitigating climate change and greenhouse gas emissions, an urgent need for an ...evolution of the renewable energy resources has emerged. On the architectural scene, we have become accustomed to seeing buildings incorporated with photovoltaics and wind turbines. Despite the great contribution of biomass as a clean energy producer, the integration of biomass into architecture is quite modest and still in its initial phases. Microalgae, as a plant-based biomass, can outperform other renewable resources with their potential to absorb CO2, recycle wastewater, and release O2. The limited experience regarding building-integrated microalgae photobioreactors (PBRs) requires shedding light on some issues. So, this paper aims to explore the following: 1) the proper types of PBRs for integration with buildings, 2) the overall bioprocess and the design considerations regarding PBRs and their technical requirements, 3) the environmental and energetic performance of PBRs, 4) their challenges, and 5) their prospects. Thus, the paper's methodology consists of 1) reviewing the promulgated literature concerning microalgae and PBRs, 2) reviewing and analyzing three building-integrated PBRs and three urban-integrated PBRs, and 3) reviewing the environmental and energetic performance of building-integrated PBRs. The paper has concluded that the symbiosis between PBRs and façades encounters some challenges, including 1) the biorefinery infrastructure, 2) the provision of a source of CO2, and 3) the high initial cost. On the other hand, the multifaceted environmental prospects of building-integrated PBRs are represented in 1) energy savings; 2) GHG emissions reduction; 3) oxygen and hydrogen release; 4) biofuel production; and 5) wastewater treatment. The unique benefits of the bio-façades through the combination of the technical and biological cycles within buildings inaugurate an innovative approach to sustainability by integrating environmental, energetic, and iconic values.
Depletion of fossil fuel sources and their emissions have triggered a vigorous research in finding alternative and renewable energy sources. In this regard, algae are being exploited as a third ...generation feedstock for the production of biofuels such as bioethanol, biodiesel, biogas, and biohydrogen. However, algal based biofuel does not reach successful peak due to the higher cost issues in cultivation, harvesting and extraction steps. Therefore, this review presents an extensive detail of deriving biofuels from algal biomass starting from various algae cultivation systems like raceway pond and photobioreactors and its bottlenecks. Evolution of biofuel feedstocks from edible oils to algae have been addressed in the initial section of the manuscript to provide insights on the different generation of biofuel. Different configuration of photobioreactor systems used to reduce contamination risk and improve biomass productivity were extensively discussed. Photobioreactor performance greatly relies on the conditions under which it is operated. Hence, the importance of such conditions alike temperature, light intensity, inoculum size, CO2, nutrient concentration, and mixing in bioreactor performance have been described. As the lipid is the main component in biodiesel production, several pretreatment methods such as physical, chemical and biological for disrupting cell membrane to extract lipid were comprehensively reviewed and presented. This review article had put forth the recent advancement in the pretreatment methods like hydrothermal processing of algal biomasses using acid or alkali. Eventually, challenges and future dimensions in algal cultivation and pretreatment process were discussed in detail for making an economically viable algal biofuel.
•Energy demand and the importance of bioenergy as alternative fuel was addressed.•Classification of biofuels and significance of microalgae was discussed.•Bioethanol, biodiesel, biogas, biohydrogen from algae was extensively described.•Open pond and photo bioreactor based cultivation and its development was reviewed.•Pretreatment processes, factors affecting algal fuel production was presented.
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•Portable outdoor cultivation system of A. platensis resulted to 2-fold biomass.•Safe harvesting using edible fungi from local food was developed.•R. microsporus was screened as the ...best bioflocculant.•Both cultivation and harvesting systems were practical and simple to be conducted.
In this study, the cultivation and harvesting of Arthrospira platensis biomass were proposed via simple, safe, and efficient techniques for direct consumption. Cultivation of microalgae in a covered macrobubble column under outdoor conditions resulted in significant differences (p < 0.05) with a maximum dry cell weight (Xm) of 0.959 ± 0.046 g/L. Notably, outdoor cultures resulted in approximately twofold biomass compared to indoor cultures. This outcome shows that the developed outdoor setup integrated with solar panels while utilising Malaysia's weather and atmospheric air as carbon sources is viable. Meanwhile, for harvesting, the screening showed that the fungus isolated from mould soybean cake (tempeh) starter indicated the highest harvesting efficiency, which was then further identified as Rhizopus microsporus, microscopically and molecularly. Overall, the economical and portable setup of outdoor cultivation coupled with safe harvesting via locally isolated fungus from tempeh as a bioflocculant would provide sustainability to produce A. platensis biomass.
In this study, a 1200L outdoor pilot scale microalgal photobioreactor (PBR) was used for toilet wastewater (WW) treatment and evaluate its ability to remove pharmaceutically active compounds (PhACs). ...The PBR was operated at two different hydraulic retention times (HRTs), which were 8 and 12days, during Period I (September–October) and Period II (October–December), respectively. Algal biomass concentrations varied by operating period because of seasonal changes. Nutrients (ammonia, nitrogen and total phosphorous) and chemical oxygen demand (COD) were monitored and efficiently removed in both periods (>80%), attaining the legislation limits. At the theoretical hydraulic steady state in both periods, pharmaceutical removal reached high levels (>48%). Two harvesting techniques were applied to the PBR microalgae effluent. Gravity sedimentation was efficient for biomass removal (>99% in 7min) in Period I when large particles, flocs and aggregates were present. In contrast, a longer sedimentation time was required when biomass was mainly composed of single cells (88% clarification in a 24h in Period II). The second harvesting technique investigated was the co-pelletization of algal biomass with the ligninolytic fungus Trametes versicolor, attaining >98% clarification for Period II biomass once pellets were formed. The novel technology of co-pelletization enabled the complete harvesting of single algae cells from the liquid medium in a sustainable way, which benefits the subsequent use of both biomass and the clarified effluent.
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•A pilot microalgal photobioreactor was successfully operated for wastewater treatment.•The microalgal system was able to operate under various regimes and seasonal periods.•The microalgal system could remove 30–80% of pharmaceutically active compounds.•Fungal co-pelletization was an efficient harvesting technique in effluent clarification.
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•Capillary photobiofilm reactors allow high density cultivation of cyanobacteria.•Continuous hydrogen production by diazotrophic cyanobacteria.•Environmental factors determine biofilm ...stability and hydrogen production.
Hydrogen (H2) is a promising fuel in the context of climate neutral energy carriers and photosynthesis-driven H2-production is an interesting option relying mainly on sunlight and water as resources. However, this approach depends on suitable biocatalysts and innovative photobioreactor designs to maximize cell performance and H2 titers. Cyanobacteria were used as biocatalysts in capillary biofilm photobioreactors (CBRs). We show that biofilm formation/stability depend on light and CO2 availabilityH2 production rates correlate with these parameters but differ between Anabaena and Nostoc. We demonstrate that high light and corresponding O2 levels influence biofilm stability in CBR. By adjusting these parameters, biofilm formation/stability could be enhanced, and H2 formation was stable for weeks. Final biocatalyst titers reached up to 100 g l−1 for N. punctiforme atcc 29133 NHM5 and Anabaena sp. pcc 7120 AMC 414. H2 production rates were up to 300 µmol H2 l-1h−1 and 3 µmol H2 gcdw-1h−1 in biofilms.
Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent ...years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.
Wastewater treatment dates back to the 1800s when the first municipal water treatment plant was built in Scotland, and since then the process has become established throughout the world for treatment of municipal and other sewage. In addition to any preceding physical and mechanical treatment operations, the process fundamentally relies on the biological breakdown of organic matter and pollutants, driven by bacterial consortia. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment. This review is intended to be a source of information and references for both experts and those who are new to this field, with the hope also that it will garner significant interest towards integrating micro-algae for the enhanced and cost-effective treatment of wastewater. Display omitted
•A critical overview of the role of micro-algae cultivation for wastewater treatment.•Efficient reduction of N, P, and COD by micro-algae in wastewater treatment discussed.•The energy demand of conventional biological treatment systems compared to micro-algae cultivation.•Economic challenges of microalgal cultivation in wastewater treatment reviewed.•Various abiotic and biotic factors influencing micro-algae discussed.
Phototrophic microorganisms that convert carbon dioxide are being explored for their capacity to solve different environmental issues and produce bioactive compounds for human therapeutics and as ...food additives. Full-scale phototrophic cultivation of microalgae and cyanobacteria can be done in open ponds or closed photobioreactor systems, which have a broad range of volumes. This review focuses on laboratory-scale photobioreactors and their different designs. Illuminated microtiter plates and microfluidic devices offer an option for automated high-throughput studies with microalgae. Illuminated shake flasks are used for simple uncontrolled batch studies. The application of illuminated bubble column reactors strongly emphasizes homogenous gas distribution, while illuminated flat plate bioreactors offer high and uniform light input. Illuminated stirred-tank bioreactors facilitate the application of very well-defined reaction conditions. Closed tubular photobioreactors as well as open photobioreactors like small-scale raceway ponds and thin-layer cascades are applied as scale-down models of the respective large-scale bioreactors. A few other less common designs such as illuminated plastic bags or aquarium tanks are also used mainly because of their relatively low cost, but up-scaling of these designs is challenging with additional light-driven issues. Finally, this review covers recommendations on the criteria for photobioreactor selection and operation while up-scaling of phototrophic bioprocesses with microalgae or cyanobacteria.
•Saline wastewater greatly improved microalgae sedimentation in PBR.•The mechanism of microalgae sedimentation changed with the influent salinity.•Microalgae achieved the highest lipid productivity ...at salinity of 1.0%.•Saturation of microalgae fatty acids increased with the increase of salinity.
Saline wastewater was used in this study to culture freshwater microalgae Chlorella pyrenoidosa in sequencing batch photobioreactor to improve the sedimentation and lipid production of algal cells. Influent salinity of 0.5% or above effectively promoted the sedimentation of microalgae in the settling stage of photobioreactor, and greatly reduced the algal biomass in effluent. The mechanism of the saline wastewater in improving the sedimentation of microalgae included decreasing zeta potential, increasing cell particle size and promoting extracellular polymeric substances synthesis, which varied with influent salinity. Saline wastewater also promoted the lipid accumulation in microalgae. Lipid content of microalgae increased with increasing influent salinity. However, the growth of microalgae was greatly inhibited at the influent salinity of 2.0% and 3.0%. Therefore, the PBR with influent salinity of 1.0% achieved the highest productivity of microalgae lipid. The saturation of fatty acids of microalgae gradually increased with increasing influent salinity.
In the present study, the design and fabrication of a micro-photobioreactor to produce the bio-hydrogen are aimed. Furthermore, the optimization of variables affecting hydrogen production was ...optimized using the response surface methodology (RSM). A quadratic model was used to predict the behavior of samples. The central composite design was applied using 20 treatments and 6 replications in the central points. Independent variables for evaluation included sulfur concentration (0.5–1%), run time (5–120 h) and algal biomass concentration (50–100 g/L). The results suggested that test length had a significant impact on hydrogen production and that sulfur content and biomass concentration had no significant effect on hydrogen production but did cause a little increase. The experimental values of response variable in these optimal conditions match the predicted values. Optimal conditions to produce bio-hydrogen were identified as the sulfur concentration of 0.75%, run time of 101.96 h, and biomass concentration of 53.31 g/L for maximum production of bio-hydrogen (66.32 mL g-VS−1). In conclusion, the response surface methodology can predict the production and extraction of bio-hydrogen in photobioreactors.
•The bio-hydrogen was produced by a micro-photobioreactor.•The running time has affected the hydrogen production.•The RSM was used to optimize the production condition.•The maximum production level of bio-hydrogen was 66.32 mL/g.VS.
•Four industrial wastewaters treated by microalgae-bacteria consortia were reviewed.•Photobioreactor design for wastewater treatment with microalgae were described.•Feasibility and potential of ...microalgae-based wastewater treatment was evaluated.
Although microalgae can serve as an appropriate alternative feedstock for biofuel production, the high microalgal cultivation cost has been a major obstacle for commercializing such attempts. One of the feasible solution for cost reduction is to couple microalgal biofuel production system with wastewater treatment, as microalgae are known to effectively eliminate a variety of nutrients/pollutants in wastewater, such as nitrogen/phosphate, organic carbons, VFAs, pharmaceutical compounds, textile dye compounds, and heavy metals. This review aims to critically discuss the feasibility of microalgae-based wastewater treatment, including the strategies for strain selection, the effect of wastewater types, photobioreactor design, economic feasibility assessment, and other key issues that influence the treatment performance. The potential of microalgae-bacteria consortium for treatment of industrial wastewaters is also discussed. This review provides useful information for developing an integrated wastewater treatment with microalgal biomass and biofuel production facilities and establishing efficient co-cultivation for microalgae and bacteria in such systems.
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