Semi-continuous Photobioreactor Research Articles

Production of phycobiliproteins, bioplastics and lipids by the cyanobacteria Synechocystis sp. treating secondary effluent in a biorefinery approach.

Cyanobacteria have been identified as promising organisms to reuse nutrients from waste effluents and produce valuable compounds such as lipids, polyhydroxyalkanoates (PHAs), and pigments. However, almost all studies on cyanobacterial biorefineries have been performed under lab scale and short cultivation periods. The present study evaluates the cultivation of the cyanobacterium Synechocystis sp. in a pilot scale 30 L semi-continuous photobioreactor fed with secondary effluent for a period of 120 days to produce phycobiliproteins, polyhydroxybutyrate (PHB) and lipids. To this end, the harvested biomass from the semi-continuous photobioreactor was transferred into 5 L vertical column batch photobioreactors to perform PHB and lipid accumulation under nutrient starvation. Three hydraulic retention times (HRT) (6, 8 and 10 days) were tested in the semi-continuous photobioreactor to evaluate its influence on biomass growth and microbial community. A maximum biomass concentration of 1.413 g L-1 and maximum productivity of 173 mg L-1 d-1 was reached under HRT of 8 days. Microscopy analysis revealed a shift from Synechocystis sp. to Leptolyngbya sp. and green algae when HRT of 6 days was used. Continuous, stable production of phycobiliproteins in the semi-continuous photobioreactor was obtained, reaching a maximum content of 7.4%dcw in the biomass. In the batch photobioreactors a PHB content of 4.8%dcw was reached under 7 days of nitrogen and phosphorus starvation, while a lipids content of 44.7%dcw was achieved under 30 days of nitrogen starvation. PHB and lipids production was strongly dependent on the amount of nutrients withdrawn from the grow phase. In the case of lipids, their production was stimulated when there was only phosphorus depletion. While Nitrogen and phosphorus limitation was needed to enhance the PHB production. In conclusion, this study demonstrates the feasibility of cultivating cyanobacteria in treated wastewater to produce bio-based valuable compounds within a circular bioeconomy approach.

Long-term semi-continuous production of carbohydrate-enriched microalgae biomass cultivated in low-loaded domestic wastewater

The production of carbohydrate-enriched biomass from waste streams as a sustainable biofuel precursor is a noteworthy endeavor. This study investigates the long-term microalgae cultivated under low domestic wastewater loads and different hydraulic retention times (HRT) in a semi-continuous photobioreactor. The influence of operational conditions, the microalgae interaction with carbon, nutrients availability, and microbial population in terms of carbohydrate content were elucidated. The results revealed that the operation at similar low nutrients and carbon loads maintained at three different hydraulic retention times (HRT) of 10, 8, and 6 days caused different patterns in nutrients uptake and biomass composition. Particularly, the carbohydrate accumulation was greatly influenced by the unbalance in the N:P ratios than complete depletion of the nutrients. Hence, during the period operated at HRT of 10 d, high nutrients removal efficiencies were observed while gradually increasing carbohydrate content up to 57% in dry cell weight (DCW). Afterward, the decrease to 8 and 6 d of HRT showed lower nutrient consumption with depleted alkalinity, reaching an appreciably high carbohydrate accumulation of up to 46%, and 56%, respectively. The biomass concentration decreased in the order of HRT of 10, 8, and 6 days. This study demonstrated that microalgae adapted to low carbon and nutrient loads could still accumulate high carbohydrate at shorter HRT using domestic wastewater as substrate.

Influence of light and flow on taxon composition and photosynthesis of marine phototrophic biofilm in photobioreactors

In this study, marine biofilms were cultured in a flow-lane, semi-continuous photobioreactor at different irradiances and flows to evaluate their combined effect on biofilms' phototrophic composition and photosynthetic activity. Taxon richness, evaluated by different microscopy techniques, including transmission and scanning electron microscopy, resulted to be heavily reduced from source communities to mature cultures. The strongest decrease was observed for diatoms, which were overcome by cyanobacteria and green algae over time. Photosynthetic performance was investigated by pulse amplitude modulated fluorescence. Irradiance was the main driver of data distribution of the photosynthetic parameters rel.ETRmax and Ik, while flow rate affected α and ΔF/Fm’. The combination of irradiance and flow rate affected ΔF/Fm’ reflecting the photosynthetic performance of the most relatively abundant taxa. Higher ΔF/Fm’ was attained when cyanobacteria and green algae were dominating, whilst lower ΔF/Fm’ when diatoms occurred in the initial phase of biofilm development.

Recycling industrial wastewater for improved carbohydrate-rich biomass production in a semi-continuous photobioreactor: Effect of hydraulic retention time

This study aimed to investigate a mixed microalgae culture's capacity to simultaneously remove nutrients and organic matter from industrial effluents while producing carbohydrate-rich biomass. A culture initially dominated by filamentous cyanobacteria Geitlerinema sp. was inoculated in a lab-scale stirred tank photobioreactor, operating at 10, 8, and 6 days hydraulic retention time (HRT). The results show that different HRT led to different inorganic carbon profiles and N:P ratios in the culture, influencing microbial changes, and carbohydrate content. Hence, higher N–NH4+ removal efficiencies were obtained at HRT of 10 d and decreased with decreasing HRT. Whereas, complete depletion of P-PO43- was achieved only at HRT of 8 d and 6 d. Also, the highest COD removal efficiency (60%) was achieved at 6 d of HRT. The maximum accumulation of carbohydrates was achieved at HRT of 8 d, which presented an N:P ratio of 22:1 and carbon availability, recording a constant carbohydrate content of 57% without any additional carbon source. Furthermore, this operational condition reached the best biomass production of 0.033 g L−1d−1 of easy-settling cyanobacteria dominated culture. According to the results, this process presents an alternative to recycling industrial effluents and, at the same time, grow valuable biomass, closing a loop for sustainable economy.

Semi-continuous desulfurization of natural gas in photobioreactor by green sulfur-oxidizing bacterial consortia isolated from hot spring

Anoxygenic phototrophic bacteria are able to oxidize and remove hydrogen sulfide from natural sources by using inorganic substrates and light. In the present study, anoxygenic phototrophic bacteria were isolated from Vartoon hot spring (east of Isfahan Province, Iran) and used for removal of sulfide compounds from natural gas in a semi-continuous photobioreactor. Mat samples that obtained from the depth of spring were introduced into Winogradsky columns and kept in the presence of sunlight for 3–4 months until green and purple layers were composed. The layers were then transferred into mineral medium and incubated under anaerobic condition. The sequence of amplified 16S rDNA in green bacteria and an amplified sequence among the gene encoding photosynthetic reaction center in purple bacteria were used for molecular identification of bacteria. The bacterial growth based on the contents of bacteriochlorophylls and the extent of elemental sulfur production by the cells were measured after ethanol extraction. Molecular identification validated the presence of Chlorobium phaeobacteroides and Prosthecochloris vibrioformis from green sulfur bacteria in the consortium. The results indicated the most increase in bacteriochlorophylls c, d, and e content of mineral medium after bacterial growth. In addition, by releasing 62.4 mmol elemental sulfur, 79.30% increase was detected in sulfur content of the medium during 3 weeks. The consortium of sulfur-oxidizing phototrophic bacteria was potentially used for natural gas desulfurization in the semi-closed photobioreactor. This system is suggested as a replacement for chemoautotrophic systems in areas where there is sufficient access to sunlight.

Nutrients and biomass dynamics in photo-sequencing batch reactors treating wastewater with high nutrients loadings

The present study investigates different strategies for the treatment of a mixture of digestate from an anaerobic digester diluted and secondary effluent from a high rate algal pond. To this aim, the performance of two photo-sequencing batch reactors (PSBRs) operated at high nutrients loading rates and different solids retention times (SRTs) were compared with a semi-continuous photobioreactor (SC). Performances were evaluated in terms of wastewater treatment, biomass composition and biopolymers accumulation during 30 days of operation. PSBRs were operated at a hydraulic retention time (HRT) of 2 days and SRTs of 10 and 5 days (PSBR2-10 and PSBR2-5, respectively), whereas the semi-continuous reactor was operated at a coupled HRT/SRT of 10 days (SC10-10). Results showed that PSBR2-5 achieved the highest removal rates in terms of TN (6.7 mg L−1 d−1), TP (0.31 mg L−1 d−1), TOC (29.32 mg L−1 d−1) and TIC (3.91 mg L−1 d−1). These results were in general 3–6 times higher than the removal rates obtained in the SC10-10 (TN 29.74 mg L−1 d−1, TP 0.96 mg L−1 d−1, TOC 29.32 mg L−1 d−1 and TIC 3.91 mg L−1 d−1). Furthermore, both PSBRs were able to produce biomass up to 0.09 g L−1 d−1, more than twofold the biomass produced by the semi-continuous reactor (0.04 g L−1 d−1), and achieved a biomass settleability of 86–92%. This study also demonstrated that the microbial composition could be controlled by the nutrients loads, since the three reactors were dominated by different species depending on the nutritional conditions. Concerning biopolymers accumulation, carbohydrates concentration achieved similar values in the three reactors (11%), whereas < 0.5% of polyhydrohybutyrates (PHB) was produced. These low values in biopolymers production could be related to the lack of microorganisms as cyanobacteria that are able to accumulate carbohydrates/PHB.

Semi-continuous operation and fouling characteristics of submerged membrane photobioreactor (SMPBR) for tertiary treatment of livestock wastewater

Abstract A submerged membrane photobioreactor was tested to provide a feasible means to conduct tertiary treatment of livestock wastewater. In this study, three phases of a semi-continuous photobioreactor were tested based on hydraulic retention time to evaluate biomass productivity, effluent quality, and fouling characteristics of the membrane module. The results show that the membrane module contributes to securing effluent quality with high nitrogen (36%) and phosphorus (25%) daily removal rates. Shorter hydraulic retention time resulted in better performance for removal of nitrogen and phosphorus; a 3 d hydraulic retention time resulted in 96% (nitrogen), and 85% (phosphorus) removal. Under the proposed condition, the biomass concentration simultaneously increased to 3500 mg/L (dry weight). Active photosynthesis in the photobioreactor was strongly associated with the average concentrations of soluble microbial products (carbohydrate: 84.5 mg/L, protein: 37.9 mg/L) and extracellular polymeric substances (carbohydrate: 44.1 mg/L, protein: 556.9 mg/L). Relatively high carbohydrate concentrations in the permeate provided evidence of a strong relationship between the effluent quality and carbohydrates in the soluble microbial products. Morphological and chemical analyses proved that micro-algal membrane fouling is attributable to soluble microbial products and/or extracellular polymeric substances. These occur in significant amounts after 10 d, indicating an unavoidable need for biomass harvesting. This study provides an understanding of the fouling trend according to varying hydraulic retention time and biomass harvesting, and offers a viable operation strategy for use of a submerged membrane photobioreactor to convert pollutants into useful bioresources and improve effluent quality.

Carbon-to-nitrogen and substrate-to-inoculum ratio adjustments can improve co-digestion performance of microalgal biomass obtained from domestic wastewater treatment

ABSTRACTThis study comparatively evaluated the effect of co-substrates on anaerobic digestion (AD) and biochemical methane potential of wastewater-derived microalgal biomass, with an emphasis on carbon-to-nitrogen (C:N) and substrate-to-inoculum (S:I) ratios. A semi-continuous photobioreactor was inoculated with Chlorella vulgaris and the nutrient recovery potential was investigated. Derived microalgal slurry was subjected to AD in the absence and presence of co-substrates; model kitchen waste (MKW) and waste activated sludge (WAS). The results revealed that up to 99.6% of nitrogen and 91.2% of phosphorus could be removed from municipal wastewater using C. vulgaris. Biomethane yields were improved by co-digestion with both MKW and WAS. The maximum biomethane yield was observed as 523 ± 25.6 ml CH4 g VSadded−1, by microalgal biomass and MKW co-digestion in 50:50 ratio, at an initial chemical oxygen demand (COD) concentration of 14.0 ± 0.1 g l−1, C:N ratio of 22.0, and S:I ratio of 2.2. The observed biomethane yield was 80.7% higher than that of the mono-digestion. The highest improvement achieved by 50:50 co-digestion of microalgal biomass and WAS was 15.5%, with biomethane yield of 272 ± 11.3 ml CH4 g VSadded−1 at an initial COD concentration of 14.0 ± 0.1 g l−1, C:N ratio of 13.0, and S:I of 2.3.

Biogas Production from Waste Microalgal Biomass Obtained from Nutrient Removal of Domestic Wastewater

In this study, a semi-continuous photobioreactor was operated for the investigation of nutrient removal efficiency of a unialgal culture, Chlorella vulgaris. Maximum nitrogen and phosphorous removal efficiencies of 99.6 and 91.2 % were achieved in the photobioreactor. The microalgal slurry obtained from the effluent of the photobioreactor was subjected to biochemical methane potential assay, after application of heat, autoclave, and thermochemical pretreatments to improve anaerobic digestibility and biogas production. Evaluation of pretreatment options indicated that heat pretreatment is the most efficient method in terms of enhancing anaerobic digestibility, at the chemical oxygen demand (COD) loading of 19 ± 0.5 g L−1. This method increased the methane yield by 83.0 %, from 223 to 408 mL CH4 g VS added −1 , compared to untreated microalgal slurry reactor with the same COD value. Among reactors with 35 ± 1.5 g L−1 initial COD concentration, autoclave-pretreated microalgal slurry was found to yield the highest methane value of 356 mL CH4 g VS added −1 , which was 43.0 % higher than the value observed in the reactor fed with untreated microalgal slurry. The thermochemical pretreatment caused production of inhibitory compounds and resulted in lower biomethane production and COD treatment values, compared to untreated microalgae. Outcomes of this study reveal that coupled micro-algal and anaerobic biotechnology could be a sustainable alternative for integrated nutrient removal and biofuel production applications.

Integrated nutrient removal and biogas production by Chlorella vulgaris cultures

Changes in global nutrient cycles as a result of industrialization affect both ecosystems and human well-being. A clear example of human manipulation on ecosystems is eutrophication; a phenomenon caused in receiving water bodies by discharge of urban sewage rich in nutrients such as nitrogen (N) and phosphorus (P). Microalgal nutrient removal is a viable alternative for biological wastewater treatment, considering high nutrient uptake capabilities of microalgae. These systems are also advantageous in terms of nutrient recycling and conversion into microalgal biomass, which, in turn, is a beneficial resource for biofuel production. In addition, microalgae can also aid reduction in atmospheric carbon dioxide levels, as a result of photosynthetic anabolism. In this study, a semi-continuous photobioreactor was operated for investigation of nutrient removal efficiency of unialgal culture, Chlorella vulgaris. Maximum N and P removal efficiencies of 99.6% and 91.2% were achieved in the photobioreactor. Biogas production from biomass obtained from semi-continuous photobioreactor was investigated via Biochemical Methane Potential assays. The results illustrated that maximum biogas yield of 442 ml/g Volatile Solids (VS) added could be achieved in anaerobic batch reactors fed with microalgal slurry.

Growth of an Indigenous Algal Consortium on Anaerobically Digested Municipal Sludge Centrate: Photobioreactor Performance and Modeling

Centrate from dewatering anaerobically digested municipal sludge is a particular concern in wastewater treatment, as it contains high ammonia concentrations and is often recycled to the head of the plant, reducing efficiency. Algae have the potential to remove ammonia from this wastewater, while producing biomass that can be used as an energy feedstock. In this research, an indigenous algal consortium was cultivated on municipal sludge centrate in a semi-continuous photobioreactor under natural light conditions. The goals of this research were to (1) enrich an algal consortium capable of growth on sludge centrate; (2) determine the main species of the consortium;(3) measure biomass, lipid production, and nutrient removal rates; and (4) develop a simple model to describe the system. The results suggested that Chlorella sp. was the dominant species (95 %) in the consortium. Mean biomass productivity was 5.2 g m−2 day−1, which was relatively high compared with other studies carried out with high ammonia strength wastewaters. Lipid production was low, comprising only 10 % of total biomass. The algal consortium effectively removed nutrients from the centrate, with observed mean removal efficiencies for total nitrogen, total phosphorus, and chemical oxygen demand of 65, 72, and 8 %, respectively. A simple irradiance-based model was developed from the fundamental Michaelis-Menten photosynthesis-irradiance (PI) response for photosynthetic organisms. A good fit to the experimental data was obtained with the irradiance-based model (R2 = 0.96), indicating that the system was light limited. The results show that biomass production can be predicted based on irradiance only.

Cultivation of &lt;i&gt;Isochrysis galbana&lt;/i&gt; in a Semicontinuous Photobioreactor

The cultivation of microalgae was studied experimentally in a glass semi-continuous photo-bioreactor. The effect of temperature, light intensity and light frequency on the growth rate of Isochrysis galbana was investigated in the work. The results showed that the optimum temperature and light intensity for the higher growth rate were 25°C and 18000 lux, respectively, the biomass productivity was 1.20×10-3g/(L•h). When the light frequency was 20hz,the the growth rate of I.galbana was the highest, which was 18.6% higher than that in continuous illumination..

Fed-batch cultivation and bioprocess modeling of Cyclotella sp. for enhanced fatty acid production by controlled silicon limitation

There is significant interest in utilizing microalgae as a source for biofuel and bioactive products such as polyunsaturated fatty acids. Diatoms are a class of single-celled microalgae which make silica cell walls and require silicic acid as a substrate for cell division. Therefore, manipulation of soluble silicon delivery to the culture offers a route to control the cell cycle and secondary or stress-induced metabolite production. A multi-stage, semi-continuous photobioreactor cultivation process was developed to produce lipid-rich algal biomass from the centric diatom Cyclotella sp. In the initial phase, algal cells were grown until the silicic acid in the medium was depleted. Next, fresh medium containing silicic acid was perfused for durations of 48, 72 or 96h. The silicic acid was rapidly consumed by the cells, which resulted in cell growth while silicon depleted conditions were maintained. Perfusions of 48 and 72h yielded high lipid concentrations (>45% of dry cell weight) while maintaining biomass generation, and showed higher lipid productivity than when silicon was added as a single pulse. Seven fatty acids were identified by GC–MS, including the three main fatty acids: palmitoleic acid, palmitic acid and eicosapentanoic acid. The lipid fatty acid distribution remained constant once silicon starvation was achieved, regardless of perfusion strategy. This study illustrates that controlled delivery of silicic acid to a cell culture of Cyclotella sp. can enhance lipid production. Additionally, a mechanistic model to predict biomass and lipid production of under silicon-stress conditions has been developed, which will aid in the development of future silicon-stress based bioprocesses for the production of fatty acids or high-valued metabolites.

Reduction of CO 2 by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor

The microalga incorporated photobioreactor is a highly efficient biological system for converting CO 2 into biomass. Using microalgal photobioreactor as CO 2 mitigation system is a practical approach for elimination of waste gas from the CO 2 emission. In this study, the marine microalga Chlorella sp. was cultured in a photobioreactor to assess biomass, lipid productivity and CO 2 reduction. We also determined the effects of cell density and CO 2 concentration on the growth of Chlorella sp. During an 8-day interval cultures in the semicontinuous cultivation, the specific growth rate and biomass of Chlorella sp. cultures in the conditions aerated 2–15% CO 2 were 0.58–0.66 d −1 and 0.76–0.87 g L −1, respectively. At CO 2 concentrations of 2%, 5%, 10% and 15%, the rate of CO 2 reduction was 0.261, 0.316, 0.466 and 0.573 g h −1, and efficiency of CO 2 removal was 58%, 27%, 20% and 16%, respectively. The efficiency of CO 2 removal was similar in the single photobioreactor and in the six-parallel photobioreactor. However, CO 2 reduction, production of biomass, and production of lipid were six times greater in the six-parallel photobioreactor than those in the single photobioreactor. In conclusion, inhibition of microalgal growth cultured in the system with high CO 2 (10–15%) aeration could be overcome via a high-density culture of microalgal inoculum that was adapted to 2% CO 2. Moreover, biological reduction of CO 2 in the established system could be parallely increased using the photobioreactor consisting of multiple units.