Microalgal Biofilms Research Articles

A novel microalgal biofilm reactor using walnut shell as substratum for microalgae biofilm cultivation and lipid accumulation

Microalgae are a potential candidate for biofuels, but the high cost and low biomass yield hinder the scale-up application of microalgae. In this study, a novel walnut shell based self-permeating biofilm reactor (WSPBR) was proposed for cultivation of Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus). Major influencing factors such as walnut shell size, light intensity and CO2 concentration were studied in detail. The results showed that CO2 can enhance the storage of metabolic products in microalgal cells. Thermodynamics analysis indicated that C. vulgaris and S. obliquus were likely to adhere on the surface of walnut shells. S. obliquus and C. vulgaris biomass reached the maximum values of 97.43 and 70.49 g m−2, respectively, corresponding to the walnut shell size of 0.8–1.2 mm, light intensity of 150 μmol m−2 s−1 and CO2 concentration of 2%. The lipid contents of these microalgal cells were 34.32% and 28.94%, respectively. These results indicated that WSPBR was an efficient system for microalgae cultivation as feedstock for biofuels.

Modeling and improving arrayed microalgal biofilm attached culture system

A microalgal biofilm-attached-system is an alternative cultivation method, that offers potential advantages of improved biomass productivity, efficient harvesting, and water saving. These biofilm systems have been widely tested and utilized for microalgal biomass production and wastewater treatment. This research a microalgal growth model for the biofilm attached culture system has been developed and experimentally validated, both, in single and arrayed biofilm systems. It has been shown that the model has the capability to accurately describe microalgae growth. Moreover, via the model simulation, it was observed that system structural parameters, light dilution rate, and light intensity significantly affected the culture performance. The limitations, and improvement aspects of the model, are also discussed in this study. To our knowledge, this is the first time that a mathematical model for an arrayed-biofilm-attached-system has been developed and validated. This model will certainly be helpful in the design, improvement, optimization, and evaluation of the biofilm-attached-systems.

Enhanced tolerance and resistance characteristics of Scenedesmus obliquus FACHB-12 with K3 carrier in cadmium polluted water

Microalgae have been recognized as a cost-effective biosorbent for heavy metal pollutants in wastewater, while microalgal biofilms exhibit significant potential in microalgae–water separation post-treatment. In this study, cadmium (II) removal mechanisms of suspended Scenedesmus obliquus FACHB-12 (isolated from southern China) and Scenedesmus obliquus biofilm with K3 carriers were investigated based on their cadmium removal efficiency, pigment content, and antioxidant activity. Scenedesmus obliquus biofilm achieved the highest cadmium (II) removal of 91.27% under 20 mg/L of cadmium stress compared to 87.49% by suspended Scenedesmus obliquus after three days. Under 10 mg/L of cadmium stress, photosynthetic pigments, extracellular polymeric substances, total protein, and antioxidant responses including superoxide dismutase, catalase, and glutathione were measured for both suspended and biofilm forms of Scenedesmus obliquus. During the cultivation process with cadmium solution, temporary inhibition of pigments was observed within the first 24 h and then recovered after two days of exposure to cadmium. Extracellular polymeric substance concentration increased significantly in the biofilm at 34.91 mg/g on the third day of exposure to 10 mg/L of cadmium compared to 22.52 mg/g for suspended Scenedesmus obliquus. Protein levels in both groups increased over time at similar concentrations at the end of the experiment. Antioxidant activity was enhanced during the absorption process, with higher activity observed in the biofilm group. The results suggested that Scenedesmus obliquus biofilm could provide higher cadmium removal efficiency with increased tolerance to cadmium content. This study provides insightful information on the response mechanism of Scenedesmus biofilms under heavy metal oxidative stress.

Surface attached cultivation and filtration of microalgal biofilm in a ceramic substrate photobioreactaor

In this research, a capillary ceramic membrane was used as the substrate for surface attached cultivation of microalgae. A photobioreactor was constructed and tested for cultivation of Chlorella vulgaris adhered to this substrate. Optimum biomass productivity of 4.65 ± 0.42 g/m2/d was obtained during 8 days of cultivation by using the light intensity of 17,000 lx and BG-11 medium flow rate of 14 mL/d. The moisture content of the produced biofilm was around 80% which is comparable with the moisture content obtained from centrifugation of suspended algal cultures. It was shown that further dewatering is possible by applying vacuum to the ceramic membrane. According to these results, moisture content was reduced to 59% under the vacuum of 0.6 bar. It was also illustrated that after scrapping the biofilm, the remaining cells on the ceramic membrane can be used as an inoculum for the re-culture of the algal biofilm. According to the current results, the biomass productivity of the re-cultured biofilm was very close to the initially cultured biofilm, which indicates the applicability of the proposed system for long term cultivation of algal biofilm. Comparing the results obtained in this study with similar surface attached cultivation systems demonstrated the promissing performance of the designed photobioreactor with a lower culture medium consumption rate.

Biomass quantification and 3-D topography reconstruction of microalgal biofilms using digital image processing

An accurate and non-invasive technique for online biomass quantification of microbial attached growth is needed. In this research, image processing through Red-Green-Blue (RGB) analysis is used to assess biomass thickness from simple macroscopic images captured from microalgal biofilms by a digital camera. The results show that the green (G) vector in images of an Ettlia sp. biofilm can estimate the biomass concentration with R2 = 0.994 through an exponential correlation. Moreover, the R2 coefficient for the biofilm thickness measurement using the G vector is 0.973, which shows the high potential of this method. Furthermore, using the mathematical correlation between the G index and the biofilm thickness, it is possible to reconstruct the 3-D topography of a microalgal biofilm and to calculate the quantitative parameters, such as biomass yield and thickness, at every specific point of the biofilm. RGB analysis can easily determine the biofilm concentration and 3-D topography with satisfactory accuracy. This is promising technique for biofilm quantification and can be used in different applications, such as wastewater treatment by moving a bed biofilm reactor (MBBR), which was formerly possible only through sophisticated techniques.

Feasibility and comparative analysis of cadmium biosorption by living scenedesmus obliquus FACHB-12 biofilms

Microalgal biofilm has been recognized as a cost-effective biorsorbent for heavy metal and a promising method for microalgae-water separation. In this study, living suspended Scenedesmus obliquus FACHB-12 (isolated from southern China) and its biofilm with different carriers were investigated to remove cadmium from aqueous solution. S. obliquus FACHB-12 biofilm with luffa sponge carrier showed highest cadmium removal efficiency at 92.7% compared to biofilm with K3 carrier (75.3%) and significantly higher than suspended S. obliquus FACHB-12 (61.8%) in 2 h experiment with initial Cd2+ concentration at 3.0 mg/L at pH = 6.0 with 0.8 g/L of biomass under room temperature. S. obliquus FACHB-12 biofilm with K3 and luffa sponge carrier also demonstrated higher tolerance towards increased Cd2+ concentration with highest biosorption efficiency at 85.1% and 90.35% respectively under 20 mg/L of Cd2+, while suspended S. obliquus FACHB-12 biosorption efficiency achieved 81.4% under 10 mg/L of Cd2+ and started to decline over increased cadmium concentration. The adsorption kinetics for all experimental groups followed the pseudo-second-order adsorption model, with biosorption equilibrium favored in Langmuir isotherm. The maximum biosorption capacity estimated by Langmuir isotherm reached 133.14 mg/g biomass in S. obliquus FACHB-12 biofilm with luffa sponge carrier, followed by 78.76 mg/g with K3 carrier, and 60.03 mg/g with suspended S. obliquus FACHB-12. Results suggest an efficient, inexpensive microalgal biofilm with biological carrier system could enhance high cadmium removal for advanced wastewater treatment and provide a cost-effective method for microalgae harvesting process.

Selection of LED lighting systems for the reduction of the biodeterioration of speleothems induced by photosynthetic biofilms in the Nerja Cave (Malaga, Spain)

Electrical lighting favours the development of photosynthetic biofilms in caves which can induce biodeterioration in the colonized substrates. The use of specific lights as a limiting factor for biofilm growth could be effective in their control and represents an alternative to chemical methods since they can damage the substrate. However, studies about lighting and the photosynthetic activity of organisms in caves are scarce. In order to select the most effective LED light source in reducing photosynthesis and therefore, in reducing the growth rates of microalgae and cyanobacteria, four biofilms in the Nerja Cave were illuminated by several light emitted diodes (LEDs) with different spectral compositions and the photobiological responses were measured both by empirical and theoretical methodologies. The empirical approach was based on the photosynthetic efficiency, by measuring the in vivo chlorophyll a (Chl a) fluorescence and the theoretical approach was based on the photonic assimilation performance related to the proportion of the light quality used for photosynthesis, according to the action spectra for photosynthesis available in the literature. The photobiological responses showed differences between the empirical and theoretical approach mainly in biofilms dominated by cyanobacteria and red algae, probably because the available action spectra were not useful for monitoring these Nerja Cave biofilms. However, the expected spectral responses of photosynthesis were observed in green microalgal biofilms with maximum photosynthetic efficiency in red and blue light although the green light was also unexpectedly high. The high photosynthetic efficiency in green light could be explained by the predictable high chlorophyll content due to a very dark environment. The results were not conclusive enough for all the biofilm types to be able to recommend a specific lighting system for the photocontrol of biofilm expansion. Therefore, new action spectra for photosynthesis of the extremophile organisms of the Nerja Cave are required. This approach, based on theoretical and empirical methodologies, is a useful tool to obtain information to allow the design of the most adequate lighting systems to reduce photosynthetic activity and favour the conservation of the caves.

Effect of hydrodynamics on the formation and removal of microalgal biofilm in photobioreactors

To prevent the formation of biofilm or to remove already formed biofilm on the transparent walls of the closed cultivation systems, it is important to ensure that there are sufficient wall shear stresses to disrupt the stability of the biofilm. A pilot-scale flat-panel photobioreactor and laboratory tubular system were used to determine the critical value of the wall shear stress. The formation of biofilm on transparent walls of the cultivation systems reduces light penetration into the cultivation medium, which can subsequently reduce the production of microalgae, since light radiation a key parameter influencing the growth of microalgae. To study the influence of hydrodynamic conditions on the prevention of biofilm formation, a numerical model of a flat-panel photobioreactor was validated based on the experimental data. Using the validated model, a critical value of wall shear stress that above which avoids the formation of biofilm was defined to be 0.2 Pa. To refine the values from the numerical model, and to investigate the influence of hydrodynamic conditions on the process of disruption of the formed and stabilized biofilm, a simple experimental tubular system with the one-dimensional flow was developed. For one-dimensional flow, it is easier to describe the hydrodynamic behaviour and more precisely define the parameters influencing biofilm formation. The experiments in this simplified tubular system were focused on removing already formed biofilm. The formed biofilm on the transparent wall was completely removed from the surface when the wall shear stress reached a value of 53 Pa. However, the stability of the biofilm was already disturbed at a value of 6 Pa. The resulting values of critical wall shear stress could be used to select the operating conditions of the cultivation systems or to adjust their geometry affecting the hydrodynamic conditions. According to the velocity distribution based on the measured values, the thickness of the biofilm was less than the thickness of the viscous sublayer. Thus, the prevention of formation, disruption, or even removal of biofilm can be ensured by shear forces in the viscous sublayer.

The effect of surface properties on the formation of Scenedesmus rubescens biofilm

Microalgae are known for their ability to purify wastewater and at the same time to be able to produce biofuels. The development of microalgal biofilms has received attention in recent years, as the growth of microalgae on a substrate facilitates their separation from water. In the present study, we compared 6 different materials (cork, sponge towel, denim, plexiglass, stainless steel and silicone rubber) as substratum to examine their capability on the attachment of Scenedesmus rubescens. Biomass attachment on the various materials was monitored for 16 days of cultivation. Different physico-chemical surface properties such as contact angle, surface energy, point of zero charge (pzc) were examined in order to elucidate materials properties role on algal attachment. Plexiglass produced the greatest increase in biomass (up to 35.1 g/m2), while stainless steel and sponge towel came in second place both with 21 g/m2. Based on the results, the contact angle and pzc alone, are not sufficient for explaining the selectivity of algal cells to get attached on a surface.

Performance evaluation of anoxic–oxic–anoxic processes in illuminated biofilm reactor (AOA-IBR) treating septic tank effluent

Abstract This study was conducted to evaluate the treatment performance of the anoxic–oxic–anoxic processes in illuminated biofilm reactor (AOA-IBR) in removing organics and nitrogen contained in septic tank effluent. The 27 L of the AOA-IBR was illuminated with red light-emitting diode (LED) lamps (peak wavelength of 635 nm, intensity of 100 μmol/(m2s)). Three types of biofilm media, namely ball ring®, plastic sheets and zeolite beads, were placed in the anoxic, oxic and anoxic zones, respectively, of the reactor to support the growth of microalgal–bacterial biofilm. The AOA-IBR was continuously fed with septic tank effluent and operated at hydraulic retention times (HRTs) of 24, 48 and 72 h. The experimental results found the increases in chemical oxygen demand (COD), total nitrogen (TN) and ammonia nitrogen (NH4-N) removal efficiencies with increasing HRTs in which the HRT of 72 h resulted in 78.6, 72.8 and 90.6% removals of COD, TN and NH4-N, respectively. The effluent quality of the AOA-IBR could meet the ISO 30500 effluent standards for Non-Sewered Sanitation Systems. The predominant microalgal biofilm species was observed to be Oscillatoria sp., while Proteobacteria was the predominant bacterial phylum found in the biofilm growing in the reactor. The above results suggested the applicability of the AOA-IBR in improving septic tank treatment performance which should result in better water pollution control.

Enhanced microalgal biofilm formation and facilitated microalgae harvesting using a novel pH-responsive, crosslinked patterned and vibrating membrane

Harvesting efficiency is one of the key issues restricting the further commercialization of microalgae. Traditional biofilm studies only tend to focus on enhancing biofilm formation, while neglecting the subsequent harvesting of the biofilm. In this study, a win–win strategy for high-density microalgal cultivation and low-cost harvesting through biofilm cultivation on a pH-responsive, charge-switchable, patterned membrane was investigated using a polyethylenimine (PEI)-crosslinked polyvinylidene fluoride (PVDF) membrane. The patterned membranes were prepared by spray-modified non-solvent induced phase inversion, and the effect of pattern height on biofilm formation and microalgal harvesting was investigated. The PEI-crosslinked PVDF membrane surface was positively charged below pH 8 and negatively charged above pH 9, resulting in a higher attractive energy below pH 8 and a repulsive energy above pH 9 according to the extended Derjaguin, Landau, Verwey, Overbeek model. Patterning of these membranes increased the active area for microalgal attachment, and created a low-shear area in the valleys that prevents early detachment of microalgal cells. Membranes with a higher pattern height resulted in faster biofilm development and increased final biomass accumulation. Low-energy membrane vibration was applied to enhance cell detachment. pH = 7 was found to be the optimal pH for enhanced microalgal biofilm formation on PEI-crosslinked patterned membranes, and a switch to pH = 10 was best for microalgal harvesting.

Analyzing microalgal biofilm structures formed under different light conditions by evaluating cell–cell interactions

Biofilm structure plays an important role in microalgae biofilm-based culture. This work aims to understand microalgal biofilm structures formed under different light conditions. Here, Scenedesmus obliquus was biofilm cultured under the light spectra of white, blue, green, and red, and the photoperiods of 5:5 s, 30:30 min, and 12:12 h (light : dark period). Biofilms were observed with confocal laser scanning microscopes and profilometry, then the porosity and roughness of biofilm were determined. We found that cells under white light formed a heterogeneous biofilm with many voids, high porosity, and roughness. While under red and blue lights, cells formed homogeneous biofilms with low porosity. Biofilm structures formed under different photoperiods were different. The mechanism of forming different biofilm structures under different light conditions was interpreted from the aspect of cell–cell interactions. Moreover, the results revealed that biomass accumulation increased with the increasing biofilm porosity due to the high effective diffusion coefficient.

Phototrophic biofilms and microbial mats from the marine littoral of the central Mediterranean

Phototrophic biofilm and microbial mat communities grow along the rocky coastline of the Maltese islands. This research involved studying phototrophs from the mediolittoral and supralittoral zones over a two-year period and seasonal changes were observed. Attachment of pioneer microorganisms to the porous eroded limestone bedrock was facilitated via a gelatinous matrix composed of exopolymeric substances (EPS). In submerged areas, such as undisturbed rock pools, these progressively formed green or brown compact biofilms, some of which thickened over the spring to form microbial mats via the production of more extensive EPS layers. Microbial mats gradually attained a lighter colouration due to the presence of ultraviolet (UV) screening pigments. In full summer, they were observed to shrink, detach from the exposed substrate, harden and progressively calcify. Biofilm microorganisms survived the harsh summer months in sheltered areas. The major biofilm formers were filamentous non-heterocytous cyanobacteria belonging to the Leptolyngbyaceae, Pseudanabaenaceae and Oscillatoriaceae. Their sheaths were thick, lamellated and often confluent. A higher biodiversity of phototrophs was observed in late autumn and winter, when tufts of heterocytous Calothrix sp. grew on thin compact biofilms of Nodosilinea sp., Toxifilum sp. and Phormidesmis spp., while Lyngbya spp. trichomes were surrounded by thick brown sheaths. Germlings of green and brown macroalgal species belonging to Ulva, Cladophora and Sphacelaria were embedded in biofilms and microbial mats and gradually grew to form extensive macroalgal covers submerged in rock pools. Erythrotrichia sp. filaments colonised the mediolittoral zone and were confined to areas that were exposed to wave action and submerged intermittently. Over the summer, macroalgal coverage diminished and microalgal biofilms and microbial mats prevailed in rock pools.

Early colonization stages of fabric carriers by two Chlorella strains

Microalgal biofilms are increasingly attracting attention as a cultivation platform for different biotechnological purposes. The initial adhesion of algae to a surface, one of the key factors for the formation of a biofilm, was analyzed by coupling image analysis techniques and mathematical modeling. Two isolated microalgae, Chlorella vulgaris ACUF_809 and Chlorella sp. ACUF_802, were identified by molecular techniques. Their health condition and biomass growth were measured using pulse amplitude modulated (PAM) fluorometry; the carrier colonization was studied by imaging analysis (Weka Segmentation) and measuring the green tones of the biofilm through CIELAB colorimetry. Structural features and biofilm vertical distribution were determined by multichannel confocal laser scanning microscopy (CLSM), and some parameters were aligned to the Gompertz model. Chlorella vulgaris ACUF_809 showed good adaptation to form biofilm on cotton fabric measured as high biomass growth reflected in the high F0 (0.42) and biofilm colonization through the CIELAB colorimetry (a*− 9.3), coverage area 32.3%, and average biofilm thickness (106.37 ± 47 μm). This work demonstrated the feasibility of C. vulgaris ACUF_809 and Chlorella sp. ACUF_802 biofilm formation on cotton fabric which potentially provides an alternative for cultivating and producing microalgae biomass.

Perspectives on Microalgal Biofilm Systems with Respect to Integration into Wastewater Treatment Technologies and Phosphorus Scarcity

Phosphorus is one of the non-renewable natural resources. High concentration of phosphorus in surface water leads to undesirable eutrophication of the water ecosystem. It is therefore necessary to develop new technologies not only for capturing phosphorus from wastewater but also for phosphorus recovery. The aim of the study was to propose three different integration scenarios for a microalgal biofilm system for phosphorus removal in medium and small wastewater treatment plants, including a comparison of area requirements, a crucial factor in practical application of microalgal biofilm systems. The area requirements of a microalgal biofilm system range from 2.3 to 3.2 m2 per person equivalent. The total phosphorus uptake seems to be feasible for construction and integration of microalgal biofilm systems into small wastewater treatment plants. Application of a microalgal biofilm for phosphorus recovery can be considered one of the more promising technologies related to capturing CO2 and releasing of O2 into the atmosphere.

A Novel System for Real-Time, In Situ Monitoring of CO2 Sequestration in Photoautotrophic Biofilms.

Climate change brought about by anthropogenic CO2 emissions has created a critical need for effective CO2 management solutions. Microalgae are well suited to contribute to efforts aimed at addressing this challenge, given their ability to rapidly sequester CO2 coupled with the commercial value of their biomass. Recently, microalgal biofilms have garnered significant attention over the more conventional suspended algal growth systems, since they allow for easier and cheaper biomass harvesting, among other key benefits. However, the path to cost-effectiveness and scaling up is hindered by a need for new tools and methodologies which can help evaluate, and in turn optimize, algal biofilm growth. Presented here is a novel system which facilitates the real-time in situ monitoring of algal biofilm CO2 sequestration. Utilizing a CO2-permeable membrane and a tube-within-a-tube design, the CO2 sequestration monitoring system (CSMS) was able to reliably detect slight changes in algal biofilm CO2 uptake brought about by light–dark cycling, light intensity shifts, and varying amounts of phototrophic biomass. This work presents an approach to advance our understanding of carbon flux in algal biofilms, and a base for potentially useful innovations to optimize, and eventually realize, algae biofilm-based CO2 sequestration.

Effect of light spectra on microalgal biofilm: Cell growth, photosynthetic property, and main organic composition

The light spectrum is an important parameter that affects microalgae growth, but to date has not been thoroughly studied in microalgae biofilm-based systems. In this study, the effect of light spectra on biofilms of two microalgae (Chlorella sp. and Nannochloris oculata) was explored by investigating their growth, photosynthetic property, and main organic composition cultured under white, blue, green, and red light. The results indicated that blue light and red light were more efficient in enhancing cells’ growth than white light. Microalgae cultured under blue light had higher photosynthetic and photoprotective capability. The highest lipid accumulation was achieved for microalgae cultured under blue light, while the highest carbohydrate accumulation was obtained under red light. Protein accumulation in cells cultured under these four light conditions were almost the same. The results of this study may have important implications in selecting suitable light spectra for microalgae biofilm-based cultivation systems.

Cell Surface Energy Affects the Structure of Microalgal Biofilm.

Microalgae biofilm-based culture systems have wide applications in environmental engineering and biotechnology. Biofilm structure is critical for the transport of nutrients, gas, and signaling molecules in a microalgal biofilm. This work aims to understand the influence of cell surface energy (SE) on the microalgal biofilm structure. Three microalgae species were used as model cells in the study: Chlorella sp., Nannochloris oculata, and Chlorella pyrenoidosa. First, by mediating biofilm culture conditions, we obtained Chlorella sp. cells with SEs of 40.4 ± 1.5, 44.7 ± 1.0, and 62. 7 ± 1.2 mJ/m2, N. oculata cells with SEs of 47.7 ± 0.5, 41.1 ± 1.0, and 62.6 ± 1.2 mJ/m2, and C. pyrenoidosa cells with SEs of 64.0 ± 0.6, 62.1 ± 0.7, and 62.8 ± 0.6 mJ/m2. Then, based on the characterizations of biofilm structures, we found that cell SE can significantly affect the microalgae biofilm structure. When the cell SEs ranged from 40 to 50 mJ/m2, the microalgae cells formed heterogeneous biofilms with a large number of open voids, and the biofilm porosity was higher than 20%. Alternatively, when the cell SEs ranged from 50 to 65 mJ/m2, the cells formed a flat, homogeneous biofilm with the porosity lower than 20%. Finally, the influencing mechanism of cell SE on biofilm structure was interpreted based on the thermodynamic theory via analyzing the co-adhesion energy between cells. The study has important implications in understanding factors that influence the biofilm structures.

Dynamic changes in community composition of Scenedesmus-seeded artificial, engineered microalgal biofilms

Artificial, non-sterile, microalgal biofilms present a promising biotechnological avenue for the production of valuable biomass, biofuels and biochemicals while simultaneously engaging in photosynthetic carbon capture. Here we use a psbA amplicon library and high-throughput 16S and 18S rRNA gene sequencing to investigate the effects of time and CO2 concentration on the composition and community dynamics of photoautotrophically grown microalgal biofilms pre-conditioned with wastewater and heavily seeded with the green alga Scenedesmus obliquus. While biomass increased in a stable, linear manner, our analysis revealed that the photoautotrophic community dramatically changed over time. Photoautotrophs such as Chorella and the cyanobacterium Leptolyngbya, presumably seeded from the wastewater, rapidly established as constituents of the biofilm while the seed species was far less dominant than anticipated. With time, photoautotrophic diatoms and dinoflagellates also established themselves as constituents of the biofilm. Low CO2 (0.04% v/v) favoured the early proliferation of cyanobacteria while high CO2 (12%) delayed, but did not prevent the proliferation. In addition, a phylogenetically diverse array of heterotrophic α-, β- and γ-proteobacteria, Bacteriodetes along with a selection of eukaryotic microorganisms inhabited the biofilms. Principal coordinate analyses reveal unique clustering patterns indicating that the composition of the initial and the final microbial communities were distinctly different from one another. Alpha diversity measures indicated that the 16S (prokaryotic) community peaked around day 10 / 11 at both 0.04% and 12% CO2. However, unlike the 18S (eukaryotic) community where diversity was at a maximum at the end of the 26-day time-course, prokaryotic diversity achieved minimum values, particularly for biofilms grown at 0.04% CO2, where the cyanobacteria proliferated. In spite of the planned experimental design bias toward S. obliquus biofilm growth, the collective data suggest that selection against undesirable microorganism also needs to be incorporated as an essential feature of biofilm photobioreactor design and operation.

Replacement of feed by fresh microalgae as a novel technology to alleviate water deterioration in aquaculture.

The main aim of this work was to evaluate the feasibility of microalgae-assisted aquaculture and explore the relevant mechanisms. In this regard, our work explored the pollution problems in traditional aquaculture and studied the contribution of microalgae to eutrophication control, oxygen gas production and feed replacement. Besides, potential protection mechanisms of microalgae-assisted aquaculture were studied by bacterial community profile analysis and microscope observation. The results showed that microalgae performed well in nutrient assimilation and oxygen production, thus slowing down the eutrophication and preventing oxygen depletion in aquaculture. Study of the mechanisms revealed that microalgae-assisted aquaculture contained much fewer pathogens and a microalgal biofilm was formed to prevent the eutrophication caused by sludge degradation. It is expected that the findings in this work can support the further development of microalgae-assisted aquaculture and promote the industry upgrade.