Performance Of Photobioreactor Research Articles

Nutrient conservation achieved through mixing regime improves microalgal wastewater treatment and diminishes the net environmental impact

Operational mode of photobioreactor (PBR) play pivotal role in environmentally benign wastewater treatment. In this context, there is wider knowledge gap in decision making for sustainable microalgae PBR operation with least environmental impact. Therefore, the present work utilized two operational modes, aeration and mechanical mixing (non-aeration), for comparative evaluation of their impacts on nutrient removal, microalgae: bacteria (M:B) population dynamics, and performance along with environmental impact. The experiments initiated with dominant M:B inoculation ratio (60:40), demonstrated higher M:B ratio (78:21) with mixing regime, as essential nutrients (dissolved inorganic carbon and ammoniacal nitrogen) were conserved within the wastewater. On the other hand, lower M:B ratio (36:63) was obtained during aeration regime, as these nutrients were transformed into CO2 and NH3 and emitted to the environment. The nutrient conservation mechanism within mixing regime enhanced microalgal growth by 30 %, metal removal by 14–59 %, and exhibited carbon negative global warming potential (-0.0451 kgCO2 eqm−3), along with overall non-negative environmental impact. In contrast, aeration strategy showed net negative environmental impact with reduced contaminant removal potential. Overall, this study reveals a previously overlooked yet significant contribution of nutrient conservation achieved through mixing regime for holistic wastewater treatment.

Effect of pH Change on the Microalgae-Based Biogas Upgrading Process

An alternative way to remove CO2 from biogas is the use of photosynthetic microorganisms, such as microalgae. This can be achieved by the operation of an open photobioreactor, connected with a mass transfer column, such as a counterflow column. This technology provides up-graded biogas with high quality. The microalgal uptake of CO2 from the biogas in counterflow columns generates pH changes in microalgae culture. To clarify the potential effect of these dynamic pH conditions in the culture, the effect of pH change on the photosynthetic activity and PSII quantum yield was studied for microalgae Chlorella sorokiniana. Thus, assays were carried out, where the pH drop reported in the counterflow columns was replicated in batch microalgae culture through HCl addition and CO2 injection, moving the culture pH from 7.0 to 5.0 and from 7.0 to 5.8, respectively. Moreover, the effect of light/darkness on photosynthetic activity was tested when the pH decreased. The results obtained in this research showed that the photosynthetic activity decreased for the light conditions when the pH was shifted by HCl addition and CO2 injection. Despite this, the value of the PSII quantum yield remained at 0.6–0.7, which means that the microalgae culture did not suffer a negative effect on the photosynthetic system of cells because a high value of PSII efficiency remained. In the same way, the results indicated that when the pH change was corrected, the photosynthetic activity recovered. Moreover, the apparent affinity constant for dissolved inorganic carbon (KDIC) was 0.9 µM at pH 5 and 112.0 µM at pH 7, which suggests that the preferred carbon source for C.sorokniana is CO2. Finally, all the results obtained indicated that the pH drop in the counter-flow column for biogas upgrading did not cause permanent damage to the photosynthetic system, and the decrease in the photosynthetic activity as a result of the pH drop can be recovered when the pH is corrected.

Highly effective reduction of phosphate and harmful bacterial community in shrimp wastewater using short-term biological treatment with immobilized engineering microalgae

Shrimp farming wastewater includes high amounts of phosphate and microbiological contaminants, necessitating further treatment before release into receiving water bodies. After 24 h of shrimp wastewater treatment, alginate beads containing the blue-green algal Synechocystis strain lacking the phosphate regulator gene (mutant strain ΔSphU) at 150 mg L−1 reduced phosphate content from 17.5 mg L−1 to 5.0 mg L−1, representing 71.5% removal efficiency, with phosphate removal rate reaching 6.9 mg gDW−1 h−1 during photobioreactor operation. For short-term treatment, removal rates of nitrate, ammonium and nitrite were 42.7, 48.5 and 92.9%, respectively. Microalgal encapsulated beads also impacted the bacterial community composition dynamics in shrimp wastewater. Next-generation sequencing targeting the V3–V4 region of the 16S rDNA gene showed significant differences in bacterial community composition after 24 h of treatment. Proteobacteria are the most abundant phylum in shrimp wastewater. After 24 h of bioremediation, reductions of harmful bacteria in the Cellvibrionaceae and Pseudomonadaceae families were recorded at 5.85 and 3.18%, respectively. Engineered microalgal immobilization under optimal conditions can be applied as an alternative short-term bioremediation strategy to remove phosphate and other harmful microbial contamination from shrimp farming wastewater.

Obtaining Bioproducts from the Studies of Signals and Interactions between Microalgae and Bacteria.

The applications of microalgae biomass have been widely studied worldwide. The classical processes used in outdoor cultivations of microalgae, in closed or open photobioreactors, occur in the presence of bacteria. Understanding how communication between cells occurs through quorum sensing and evaluating co-cultures allows the production of microalgae and cyanobacteria to be positively impacted by bacteria, in order to guarantee safety and profitability in the production process. In addition, the definition of the effects that occur during an interaction, promotes insights to improve the production of biomolecules, and to develop innovative products. This review presents the interactions between microalgae and bacteria, including compounds exchanges and communication, and addresses the development of new pharmaceutical, cosmetic and food bioproducts from microalgae based on these evaluations, such as prebiotics, vegan skincare products, antimicrobial compounds, and culture media with animal free protein for producing vaccines and other biopharmaceutical products. The use of microalgae as raw biomass or in biotechnological platforms is in line with the fulfillment of the 2030 Agenda related to the Sustainable Development Goals (SDGs).

The Influence of Forward Osmosis Module Configuration on Nutrients Removal and Microalgae Harvesting in Osmotic Photobioreactor

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO4-P, NH3-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO4-P, NH3-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.

Current Concentrations of Zn, Cu, and As in Piggery Wastewater Compromise Nutrient Removals in Microalgae-Bacteria Photobioreactors Due to Altered Microbial Communities.

Simple SummaryPhotobioreactor systems based on consortia of microalgae and bacteria are a promising, efficient and sustainable alternative for treatment of wastewaters with high nitrogen content, such as piggery wastewater. In these biological systems, microorganisms play a key role in wastewater treatment by degradation of organic matter and accumulation of nutrients into the generated biomass. However, these wastewaters often contain high concentrations of zinc, copper and arsenic, which can severely affect the activity and growth of microorganisms, and so, the wastewater treatment performance. This article studies the effect of high concentrations of zinc, copper and arsenic on microbial communities, specifically microalgae and bacteria, in photobioreactors treating piggery wastewater, with the aim of elucidating their impact on wastewater treatment performance. For this purpose, the growth of microalgae and the composition and structure of bacterial communities exposed to these pollutants were studied. The performance of the reactors was also evaluated by determining the removal of nutrients, zinc, copper and arsenic. The results showed that high concentrations of zinc, copper and arsenic in piggery wastewater significantly affect the microbiome of the reactors without recovery after exposure to these contaminants, resulting in poorer performance of the reactors and compromising the environmental and health impact of treated effluents.The treatment of pig manure is a major environmental issue, and photobioreactors containing consortia of microalgae and bacteria have proven to be a promising and sustainable treatment alternative. This work studies the effect of Cu, Zn and As, three toxic elements frequently present in piggery wastewater, on the performance and microbiome of photobioreactors. After dopage with Zn (100 mg/L), Cu (100 mg/L), and As (500 µg/L), the high biomass uptake of Zn (69–81%) and Cu (81–83%) decreased the carbon removal in the photobioreactors, inhibited the growth of Chlorella sp., and affected heterotrophic bacterial populations. The biomass As uptake result was low (19%) and actually promoted microalgae growth. The presence of Cu and As decreased nitrogen removal, reducing the abundance of denitrifying bacterial populations. The results showed that metal(loid)s significantly affected 24 bacterial genera and that they did not recover after exposure. Therefore, this study makes an important contribution on the impact of the presence of metal(loid)s in piggery wastewater that compromises the overall performance of PBRs, and so, the environmental and health impact of treated effluents.

Novel 3D-printed buoyant structures for improvement in flue gas CO2-derived microalgal biomass production by enhancing anti-biofouling on vertical polymeric photobioreactor

Novel 3D-printed buoyant structures can be applied in various environmental processes because of their considerable advantages. Microalgae cultivation in photobioreactors, directly supplemented by industrial CO2, enables environmental pollution mitigation/cleanup and sustainable energy production. However, in photobioreactor systems, biofilm formation due to gas bubbling decreases microalgal productivity. Therefore, in this study, we aimed to develop a novel 3D-printed buoyant structure to suppress biofilm formation. The 10 mm-sized spherical buoyant structure reduced the height and area of the biofilm by 58.3% and 82.5%, respectively. The structure decreased space where bubble burst occurred and controlled the bubble size, reducing the overall biomass loss by 58.7%. It did not reduce photobioreactor performance noticeably during semi-continuous cultivation, indicating the possibility of long-term applicability. In large-scale outdoor microalgae cultivation using flue gas CO2, the buoyant structure improved the cell density and biodiesel production potential without contamination. This study provides a promising strategy to contribute to biological CO2 mitigation through the utilization of flue gas CO2 for enhanced microalgal production, paving the way for energy and environmental sustainability.

Pilot-scale annual production of Scenedesmus almeriensis using diluted pig slurry as the nutrient source: Reduction of water losses in thin-layer cascade reactors

The microalga Scenedesmus almeriensis was produced using diluted pig slurry as the sole nutrient source during one year using a 30 m2 thin-layer cascade photobioreactor located outdoors. Evaporation contributes significantly to the water requirements of microalgae production; approximately 1000 L of water are required to produce 1 kg of microalgal biomass. The aim of this study was to assess the potential of plastic covers to avoid or minimise water evaporation in open photobioreactors. The N–NH4+ concentrations at the inlets ranged from 40 to 100 mg L−1, depending on the experimental run. These values could not be increased because of the dark colour and turbidity of the pig slurry. The biomass productivity of the system was 17.6, 18.8, 23.4, and 17.3 g m−2·day−1 in winter, spring, summer, and autumn, respectively. Covering the reactors led to a decrease in biomass productivity that ranged from 8.5 to 16.9% depending on the season. However, water evaporation was reduced by 24.9–42.0% depending on the season. In summer, covering the reactors reduced the amount of water evaporated from 6.3 to 3.6 L m−2·day−1. In a theoretical 1 ha production facility, this would represent 2700 L of water saved per day. Overall, the processing of pig slurry using microalgae is challenging because of their variable nutrient concentration, colour and turbidity. Covering the reactors with inexpensive commercial plastics could significantly reduce the water requirements of the system.

Effect of plate distance on light conversion efficiency of a Synechocystis culture grown outdoors in a multiplate photobioreactor

In this work, the performance of a vertical multiplate photobioreactor is analyzed and presented. The photobioreactor consisted of 20 vertical plates (1 m2 each) connected by manifolds and a working volume of 1300 L. The total area occupied (footprint) was 10 m2, while the illuminated area was 40 m2, therefore the ratio of illuminated area to volume ratio was about 30 m−1. The performance of the photobioreactor was evaluated using a culture of Synechocystis PCC 6803, circulated by a centrifuge pump. The results showed that the amount of light captured by the photobioreactor at a plate spacing of 0.5 m was 90.2 % of the light incident on the horizontal surface, while at a plate spacing of 1.0 m, 50.3 % was captured. The corresponding biomass yield, calculated based on the ground area occupied by the reactor, was 26.0 g m−2 day−1 and 7.2 g m−2 day−1, when the plates were spaced at 0.5 m and 1.0 m respectively. Therefore, the light conversion efficiency calculated based on the ground area was significantly higher in the configuration with a plate spacing of 0.5 m, reaching 5.43 % based on PAR (photosynthetically active radiation), and 2.44 % based on solar radiation, giving a value 3.7 higher than when the plates were spaced 1.0 m apart. It was concluded that the light conversion efficiency might be further improved by reducing the plate spacing while also reducing the culture light path.

Employing newly developed plastic bubble wrap technique for biofuel production from diatoms cultivated in discarded plastic waste

Algal culturing in photobioreactors for biofuel and other value-added products is a challenge globally specifically due to expensive closed or open photobioreactors associated with the high cost, problems of water loss and contamination. Among the wide varieties of microalgae, diatoms have come out as potential source for crude oil in the form of Diafuel™ (biofuel from diatoms). However, culturing diatoms at large scale hypothesized as diatom solar panels for biofuel production is still facing a need for facile and economical production of value-added products. The aim of this work was to culture diatom (microalgae) in a closed system by sealing the reactor rim tightly with very cheap priced and used plastic bubble wrap material which is generally discarded in a lodging and transportation of goods. To optimize it, different plastic wraps discarded from a plastic industry were tested first for their permeability to gases and impermeability to water loss. It was found that among different varieties of plastic bubble wraps, low density polyethylene (LDPE) bubble wrap material which was used to seal glass containers as photobioreactors allowed harvest of maximum Diafuel™ (37%), lipid (35 μgmL−1), highest cell count (1152 × 102 cells mL−1), maximum CO2 absorbance (0.084) with almost no water loss and nutrient uptake for 40 days of experiments. This was due to its permeability to gases and impermeability to water. To check usability of such LDPE bubble wrap on other microalgae it was therefore tested on the red-green microalgae Haematococcus pluvialis, which showed scope to be scaled up for astaxanthin production using discarded bubble wrap packing material. This study thus would open up a new way for decreasing plastic disposal and with reuse for sustainable development and application of diatom in biofuel production which could find applications in environmental and industrial sectors.

Improving the photobioreactor operation efficiency in the technological scheme of wastewater treatment

Conventional process schemes of municipal sewage water treatment, advantages, and disadvantages of the methods applied when removing biogenic elements were considered. It was shown that the existing shortcomings cause additional explicit costs and difficulties when disposing of the resulting waste. Low efficiency of the removal processes themselves causing residual concentrations of biogenic elements in the treated sewage water was also shown. A process scheme for treating municipal sewage water was proposed. It includes the use of a photobioreactor of a proposed design for the removal of biogenic elements due to the metabolism of microalgae. It was experimentally shown that the use of Euglena gracilis strain for removal of phosphates in initial concentrations of 4, 7, and 14 mg/dm3 from sewage water is the most efficient way. It makes it possible to reduce these concentrations to residual 0…0.55 mg/dm3 in four days. A 3.75…5.58 times increment of microalgae biomass during this period was also shown. A mathematical model was constructed for calculating the time of staying the sewage water and microalgae mixture in a photobioreactor to achieve the required degree of removal of biogenic elements. Based on the proposed model and experimental studies, the required time of staying in the rector working area was calculated. It was shown that with the use of Euglena gracilis strain but without removal of biogenic elements at previous purification stages (process schemes including only mechanical purification), the time of mixture staying in the working zone was 37.81 hrs. With partial removal of biogenic elements at the stage of biological treatment (0.55 mg/dm3 total nitrogen, 0.91 mg/dm3 ammonium nitrogen, 0.44 mg/dm3 phosphates), this time was reduced to 26.66 hrs. It was found that the use of Euglena gracilis strain instead of Chlorella vulgaris (FC-16) in the removal of phosphates results in a 2-time increase in the process efficiency and a 50 % decrease in time of mixture staying in the working zone. Recommendations for calculating geometric parameters of photobioreactors of the proposed design were given for use in the process schemes

Biochar enhanced the performance of microalgae/bacteria consortium for insecticides removal from synthetic wastewater

The presence of pesticides in aquatic environments has threatened marine food resources, aquaculture, fisheries and human health; therefore, two most used insecticides were removed during this study. Two photobioreactors, including biochar and Chlorella vulgaris/activated sludge (reactor 1), and Chlorella vulgaris/activated sludge (reactor 2) were run to remove chlorpyrifos (CPF) and cypermethrin (CYP). Proteobacteria, Bacteroidetes and Chloroflexi were the dominant phyla of activated sludge. The optimization performance of both reactors was conducted by response surface methods. The performance of first photobioreactor was better than that in the second reactor, achieving abatement of 88.80% CPF and 93.12% CYP, at 69.7 h contact time and 0.32 mg/L initial concentration. The toxicity of CPF and CYP to Chlorella vulgaris was monitored under 0–4 mg/L of insecticide concentrations and 0–72 h contact time. The minimum chlorophyll content (2 mg/L) and protein (16.7%), and maximum growth inhibition (89.7%) were recorded at 4 mg/L insecticides concentration and 72 h contact time. Moreover, molecular docking simulation for catalytic enzyme degradation of Proteobacteria, Bacteroidetes and microalgae was carried out using individual hydrolase enzymes: carboxypeptidase in microalgae, isochorismatase hydrolase in Proteobacteria and alpha-L-arabinofuranosidase in Bacteroidetes. Ligand-binding energy, affinity and dimensions of ligands-binding sites in the enzyme cavity were calculated in each case. Hydrolase is an enzyme group that offers a promising practical application for the degradation of CYP and CPF due to its cavity features. This analysis demonstrated the mode of interaction of ligands with hydrolase enzymes in different species.

Characterization of communities in a microalgae-bacteria system treating domestic wastewater reveals dominance of phototrophic and pigmented bacteria

The consortia formed by microalgae and bacteria developed during semi-continuous operation of photobioreactors treating domestic wastewater was characterized by means of flow cytometry and DGGE techniques. While microalgae population was dominated by the inoculated wild strain Chlorella sorokiniana, the bacterial community included as activated sludge was totally replaced by microbial groups exhibiting adaptations to illuminated environments. The quantification conducted by flow cytometry evidenced bacterial population displacement favoring pigmented and photoheterotrophic groups. This fact was correlated with DGGE analysis that showed the dominance of Rhodobacteraceae family during steady state conditions and disappearance of Rhizobiaceae family present in the inoculum. This particular bacterial community composition was related with the limited organic matter consumption detected in the experimental reactors, estimated in removal rates of 64.2 ± 4.8% of biodegradable chemical oxygen demand present in primary treated wastewater. In conclusion, the dominance of photoheterotroph and pigmented bacteria reduced the metabolic capability of the photobioreactor resulting in insufficient wastewater treatment with regard to discharge regulations.

Multi-objective optimization of building-integrated microalgae photobioreactors for energy and daylighting performance

As a state-of-the-art green façade technology, building-integrated microalgae bioreactor has the potential to reduce buildings’ carbon footprint and energy consumption. The present study aims to address the knowledge gap in the energy and daylighting performance of algae photobioreactor façade. The paper first studies the effects of algae windows on building energy saving through simulation analysis of an office building in Mashhad, Iran, with a cold semi-arid climate. It also presents a multi-objective optimization framework for the optimization of the energy and daylighting performance of algae windows integrated with an office building facade. Two optimization metrics include maximum Useful Daylight Illuminance (UDI) (%), and minimum Energy Use Intensity (EUI) (kWh/m2/yr), representing optimal daylighting and energy performance metrics, respectively. The results demonstrate that a microalgae window significantly reduces building energy consumption comparing with single-glazed, double-glazed, and water windows. The extent of energy savings varies with window size, algae density, and façade orientation. The proposed optimization framework helps increase the average values of energy performance metrics by 21.37%, 33.25%, 36.22%, 39.67%, and daylighting metrics by 4.60%, 14.43%, 13.34%,14.33%, in the north, south, east, and west, respectively and sequentially. Sensitivity analysis demonstrates that window size has the highest effect on two studied performance metrics for all orientations, while algae density has minimal effect on energy consumption and no considerable effect on daylighting performance. Building energy performance simulation is validated by ASHRAE140-2017.

Membrane Fouling in Algal Separation Processes: A Review of Influencing Factors and Mechanisms

The use of algal biotechnologies in the production of biofuels, food, and valuable products has gained momentum in recent years, owing to its distinctive rapid growth and compatibility to be coupled to wastewater treatment in membrane photobioreactors. However, membrane fouling is considered a main drawback that offsets the benefits of algal applications by heavily impacting the operation cost. Several fouling control strategies have been proposed, addressing aspects related to characteristics in the feed water and membranes, operational conditions, and biomass properties. However, the lack of understanding of the mechanisms behind algal biofouling and control challenges the development of cost-effective strategies needed for the long-term operation of membrane photobioreactors. This paper reviews the progress on algal membrane fouling and control strategies. Herein, we summarize information in the composition and characteristics of algal foulants, namely algal organic matter, cells, and transparent exopolymer particles; and review their dynamic responses to modifications in the feedwater, membrane surface, hydrodynamics, and cleaning methods. This review comparatively analyzes (i) efficiency in fouling control or mitigation, (ii) advantages and drawbacks, (iii) technological performance, and (iv) challenges and knowledge gaps. Ultimately, the article provides a primary reference of algal biofouling in membrane-based applications.

Nutrient removal from hydroponic effluent by Nordic microalgae: From screening to a greenhouse photobioreactor operation

To guarantee year-round horticultural production, Nordic countries rely on greenhouses to cope with the harsh winter conditions. Despite substantial progress in greenhouse operation, greenhouse effluents are still overloaded with nutrients and are known to be a source of eutrophication that decreases the quality of natural waters worldwide. Here we investigate the possibility of recirculating hydroponic effluents from a commercial cucumber greenhouse to cultivate photoautotrophic microalgal biomass. A stepwise methodology was applied to scale-up procedures from laboratory to a pilot scale photobioreactor (PBR) which was operated inside a greenhouse. The screening results identified that 12 (of 13) strains were capable of proliferating in the hydroponic effluent without any adjustment or dilution. A Nordic microalga from the Scenedesmaceae family was selected for a PBR operation which lasted 36 days. This continuous cultivation was undertaken under four different test conditions and removal efficiencies between 18 and 35% for N-NO3− and 40–98% for P-PO43− were achieved. Over 1000 L of hydroponic effluent was recirculated, with a steady N-NO3− uptake of 86–92 mg g−1 and a P-PO43− uptake of 11–21 mg g−1 biomass. These results demonstrated that a hydroponic effluent N:P of 15–26 and pH of 7.5 were the most appropriate conditions for nutrient uptake, although increasing the pH to 9 may promote P-PO43− uptake. Overall, this work indicates the feasibility of microalgal bioremediation of greenhouse effluents in the Nordic countries.

Year-long performance assessment of an on-site pilot scale (100 L) photobioreactor on nutrient recovery and pathogen removal from urban wastewater using native microalgal consortium

The study was carried out as part of the Indo-Dutch collaboration project to ascertain the efficacy of the algal system for the treatment of urban wastewater. The study was done at Barapullah drain in New Delhi, using a pilot-scale (100 L) bubble column microalgae photobioreactor (PBR). The year-long study was intended to find the impact of seasonality coupled with varying hydraulic retention times (HRTs) on the PBR performance in terms of nutrient recovery, microbial contamination reduction, biomass productivity, and theoretical biomethane potential.To begin with, native microalgae consortium was enriched and cultivated in PBR directly on the Barapullah drain wastewater at the drain site. After achieving maximum recovery of nutrients in the batch mode, the PBR was operated in continuous mode at HRTs ranging from 1 to 3 days during summer, while 2–3 days during monsoon, autumn, and winter. The maximum and minimum biomass productivity obtained was 260 mg L−1 d−1 at the HRT of 1 day during summer and 77 mg L−1 d−1 at the HRT of 2 days during winter. At peak overall PBR performance at HRT of 2 days, the nutrient removal rate was 37.2 ± 6.2 mgCOD L−1 d−1, 39.3 ± 6 mgN L−1 d−1, and 4.7 ± 0.7 mgP L−1 d−1. Nearly 5 log removal of total and faecal coliform was obtained during summer and monsoon. However, the overall performance reduced during winters. The natural sedimentation of grown biomass achieved 81–95% of biomass settling at different HRTs. The areal footprint of the PBR is 1.42 m2 KLD−1, which was significantly lower than other pilot-scale microalgal wastewater treatment technologies. The obtained results at this lower HRT (2 days) even under non-optimized process parameters represent vital improvements over earlier reports with significantly higher HRTs. Results thus highlight the feasibility and scalability of the technology.

Modelling and pH Control in Raceway and Thin-Layer Photobioreactors for Wastewater Treatment

One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the microalgae/bacteria consortium already developing on these systems. For cost-saving reasons, the pH is usually controlled by classical On/Off control algorithms during the daytime period, typically with the dynamics of the system and disturbances not being considered in the design of the control system. This paper presents the modelling and pH control in open photobioreactors, both raceway and thin-layer, using advanced controllers. In both types of photobioreactors, a classic control was implemented and compared with a Proportional–Integral (PI) control, also the operation during only the daylight period and complete daily time was evaluated. Thus, three major variables already studied include (i) the type of reactors (thin-layers and raceways), (ii) the type of control algorithm (On/Off and PI), and (iii) the control period (during the daytime and throughout the daytime and nighttime). Results show that the pH was adequately controlled in both photobioreactors, although each type requires different control algorithms, the pH control being largely improved when using PI controllers, with the controllers allowing us to reduce the total costs of the process with the reduction of CO2 injections. Moreover, the control during the complete daily cycle (including night) not only not increases the amount of CO2 to be injected, otherwise reducing it, but also improves the overall performance of the production process. Optimal pH control systems here developed are highly useful to develop robust large-scale microalgae-related wastewater treatment processes.

Optimization of microalgal biomass and lipid productivities for bioenergy production using central composite design with desirability function

This study investigates the influences of light-dark cycles and NaNO3 dose on Chlorella kessleri microalgal-specific growth rate (SGR), biomass productivity (P), and intracellular lipid productivity (LP) by using central composite design with desirability function. A single-objective optimization showed that the maximum SGR, P, and LP can be achieved as 0.487 day−1, 58.718 g/L day−1, and 14.252 mg/L day−1, respectively. The corresponding optimized light-dark cycle and NaNO3 loading were determined as 11.6/8.4 (h/h) and 15.54 g/L, 12/12 (h/h) and 16.23 g/L, and 12/12 (h/h) and 6.63 g/L, respectively. The multi-response optimization showed that the highest SGR of 0.359 day−1, biomass productivity of 50.663 g/L day−1 and LP of 14.114 mg/L day−1 can be accomplished at culture environments of 12/12 (h/h) light-dark cycles and 10.38 g/L NaNO3. These results suggest that the central composite design with desirability function-based technique is useful for design and operation of photobioreactors to produce lipid from microalgae. Analysis of variance was employed to explore the significance of the factors affecting microalgal growth as well as biomass and lipid productivities. The predicted optimized culture conditions were experimentally confirmed (error < 6%) indicating the process is robust and reliable.

Effects of specific wavelengths of lights on performance of biofilm photobioreactor for treating septic tank effluent

Biofilm photobioreactors (BPBRs) employing algal-bacterial symbiotic reactions were designed as an on-site post-treatment system to treat septic tank effluent containing high concentrations of organic and nutrient matters. In this study, three BPBRs equipped with blue (peak wavelength ∼ 460 nm), red (peak wavelength ∼ 635) and mixed blue and red (50:50) lights for growing algal biomass (Chlorella sp.) were continuously operated at hydraulic retention times (HRT), light intensity and light/dark period of 6 days, 124 μmol/(m2.s) and 12/12 h, respectively. The experimental results illustrated that the chemical oxygen demand (COD) removal efficiency of 85 % and the highest total nitrogen (TN) and total phosphorus (TP) removal efficiencies of 87 and 84 %, respectively, were found in the BPBR with mixed blue and red lights, corresponding to the data of biomass productivity. Mass balance analyses of the BPBR performance indicated that TN (9.2 mg N/(L.d) or 74 %) and TP (0.73 mg P/(L.d) or 73 %) were mainly removed via biomass assimilation. Overall, the results of this study suggested that the mixed blue and red lights could enhance the biomass productivity and increase the treatment efficiencies of the BPBR system, resulting in the treated effluent meeting the discharge standards.