Operation of a vertical algal biofilm enhanced raceway pond for nutrient removal and microalgae-based byproducts production under different wastewater loadings

Effects of chemical oxygen demand and chloramphenicol on attached microalgae growth: Physicochemical properties and microscopic mass transfer in biofilm

During the wastewater treatment and resource recovery process by attached microalgae, the chemical oxygen demand (COD) can cause biotic contamination in algal culture systems, which can be mitigated by adding an appropriate dosage of antibiotics. The transport of COD and additive antibiotic (chloramphenicol, CAP) in algal biofilms and their influence on algal physiology were studied. The results showed that COD (60 mg/L) affected key metabolic pathways, such as photosystem II and oxidative phosphorylation, improved biofilm autotrophic and heterotrophic metabolic intensities, increased nutrient demand, and promoted biomass accumulation by 55.9 %, which was the most suitable COD concentration for attached microalgae. CAP (5-10 mg/L) effectively stimulated photosynthetic pigment accumulation and nutrient utilization in pelagic microalgal cells. In conclusion, controlling the COD concentration (approximately 60 mg/L) in the medium and adding the appropriate CAP concentration (5-10 mg/L) are conducive to improving attached microalgal biomass production and resource recovery potential from wastewater.

Enhancing biomass and lipid accumulation by a novel microalga for unsterilized piggery biogas slurry remediation

The cost and efficiency of an algal-BS treatment system are determined by the specific microalgal species and BS pretreatment method. This study examines the growth of a novel algae Chlorella sp. YSD-2 and the removal of nutrients from the BS using different pretreatment methods, including dilution ratio and sterilization. The highest biomass production (1.84 g L-1) was achieved in the 1:2 unsterilized biogas slurry, which was 2.03 times higher than that in the sterilized group, as well as higher lipid productivity (17.29 mg L-1 d-1). Nevertheless, the sterilized biogas slurry at a 1:1 dilution ratio exhibited the most notable nutrient-removal efficiency, with COD at 71.97%, TP at 91.32%, and TN at 88.80%. Additionally, the analysis of 16S rRNA sequencing revealed a significant alteration in the indigenous bacterial composition of the biogas slurry by microalgal treatment, with Proteobacteria and Cyanobacteria emerging as the predominant phyla, and unidentified_Cyanobacteria as the primary genus. These findings suggest that Chlorella sp. YSD-2 exhibits favorable tolerance and nutrient-removal capabilities in unsterilized, high-strength biogas slurry, along with high productivity of biomass and lipids. Consequently, these results offer a theoretical foundation for the development of an efficient and economically viable treatment method for algal-BS.

Enhancing microalgae biomass production: Exploring improved scraping frequency in a hybrid cultivation system

Recently, hybrid systems, such as those incorporating high-rate algal ponds (HRAPs) and biofilm reactors (BRs), have shown promise in treating domestic wastewater while cultivating microalgae. In this context, the objective of the present study was to determine an improved scraping frequency to maximize microalgae biomass productivity in a mix of industrial (fruit-based juice production) and domestic wastewater. The mix was set to balance the carbon/nitrogen ratio. The scraping strategy involved maintaining 1 cm wide stripes to retain an inoculum in the reactor. Three scraping frequencies (2, 4, and 6 days) were evaluated. The findings indicate that a scraping frequency of each 2 days provided the highest biomass productivity (18.75 g total volatile solids m-2 d-1). The species' behavior varied with frequency: Chlorella vulgaris was abundant at 6-day intervals, whereas Tetradesmus obliquus favored shorter intervals. Biomass from more frequent scraping demonstrated a higher lipid content (15.45%). Extrapolymeric substance production was also highest at the 2-day frequency. Concerning wastewater treatment, the system removed 93% of dissolved organic carbon and ∼100% of ammoniacal nitrogen. Combining industrial and domestic wastewater sources to balance the carbon/nitrogen ratio enhanced treatment efficiency and biomass yield. This study highlights the potential of adjusting scraping frequencies in hybrid systems for improved wastewater treatment and microalgae production.

Treatment of mixed wastewater by vertical rotating microalgae-bacteria symbiotic biofilm reactor

A novel vertical rotating microalgae-bacteria symbiotic biofilm reactor was built to treat the mixed wastewater containing municipal and soybean soaking wastewater. The reactor was operated in both sequential batch and semi-continuous modes. Under the sequential batch operation mode, the maximum removal rates for Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), and Ammonia Nitrogen (NH4+-N) of the mixed wastewater were 95.6 %, 96.1 %, 97.6 %, and 100 %, respectively. During the semi-continuous operation, the water discharge indices decreased gradually and eventually stabilized. At stabilization, the removal rates of COD, TN, and NH4+-N achieved 98 %, 95 %, and 99.9 %, respectively. The maximum biomass productivity of the biofilm was 2.69 g·m-2·d-1. Additionally, the carbohydrate, protein and lipid comprised approximately 22 %, 51 % and 10 % of the dry weight of Chlorella. This study demonstrates the great potential of the microalgae-bacteria symbiotic biofilm system to treat food and domestic wastewater while harvesting microalgal biomass.

The effects of carbon nitrogen ratio and salinity on the treatment of swine digestion effluent simultaneously producing bioenergy by microalgae biofilm

In order to remove high concentrations of ammonia nitrogen (NH4+-N) and refractory sulfamethazine (SM2) from swine digestion effluent, different carbon/nitrogen (C/N) ratios and salinity were used to determine the effects of pollutants removal in the microalgae biofilm system. Microalgae biofilm treatment under optimal environmental conditions in synthetic swine digestion effluent were C/N ratio of 20 and salinity of 140 mM. In order to make the actual swine digestion effluent discharge up to the standard, three different two-cycle treatments (suspended microalgae, microalgae biofilm, microalgae biofilm under the optimal conditions) were studied. The results showed that after two-cycle treatment with microalgae biofilm under the optimal conditions, the actual swine digestion effluent levels of total nitrogen (TN), NH4+-N, total phosphorus (TP), chemical oxygen demand (COD), SM2 were 22.65, 9.32, 4.11, 367.28, and 0.99 mg L-1, respectively, which could satisfy the discharge standards for livestock and poultry wastewater in China. At the same time, first-order kinetic simulation equations suggested a degradation half-life of 4.85 d for SM2 under optimal conditions in microalgae biofilm, and microbial community analysis indicated that the dominant genus was Halomonas. Furthermore, 35.66% of lipid, 32.56% of protein and 18.44% of polysaccharides were harvested after two-cycle in microalgae biofilm treatment under optimal environmental conditions. These results indicated that the regulation of C/N and salinity in microalgae biofilm for the treatment of swine digestion effluent was a high-efficiency strategy to simultaneously achieve wastewater treatment and bioenergy production.

Microalgal co-cultivation -recent methods, trends in omic-studies, applications, and future challenges

The burgeoning human population has resulted in an augmented demand for raw materials and energy sources, which in turn has led to a deleterious environmental impact marked by elevated greenhouse gas (GHG) emissions, acidification of water bodies, and escalating global temperatures. Therefore, it is imperative that modern society develop sustainable technologies to avert future environmental degradation and generate alternative bioproduct-producing technologies. A promising approach to tackling this challenge involves utilizing natural microbial consortia or designing synthetic communities of microorganisms as a foundation to develop diverse and sustainable applications for bioproduct production, wastewater treatment, GHG emission reduction, energy crisis alleviation, and soil fertility enhancement. Microalgae, which are photosynthetic microorganisms that inhabit aquatic environments and exhibit a high capacity for CO2 fixation, are particularly appealing in this context. They can convert light energy and atmospheric CO2 or industrial flue gases into valuable biomass and organic chemicals, thereby contributing to GHG emission reduction. To date, most microalgae cultivation studies have focused on monoculture systems. However, maintaining a microalgae monoculture system can be challenging due to contamination by other microorganisms (e.g., yeasts, fungi, bacteria, and other microalgae species), which can lead to low productivity, culture collapse, and low-quality biomass. Co-culture systems, which produce robust microorganism consortia or communities, present a compelling strategy for addressing contamination problems. In recent years, research and development of innovative co-cultivation techniques have substantially increased. Nevertheless, many microalgae co-culturing technologies remain in the developmental phase and have yet to be scaled and commercialized. Accordingly, this review presents a thorough literature review of research conducted in the last few decades, exploring the advantages and disadvantages of microalgae co-cultivation systems that involve microalgae-bacteria, microalgae-fungi, and microalgae-microalgae/algae systems. The manuscript also addresses diverse uses of co-culture systems, and growing methods, and includes one of the most exciting research areas in co-culturing systems, which are omic studies that elucidate different interaction mechanisms among microbial communities. Finally, the manuscript discusses the economic viability, future challenges, and prospects of microalgal co-cultivation methods.

Development of yeast and microalgae consortium biofilm growth system for biofuel production

Background

The current study aimed to develop a laboratory-scale biofilm photobioreactor system for biofuel production.

Scope & Approach

During the investigation, Jute was discovered to be the best, cheap, hairy, open-pored supporting material for biofilm formation. Microalgae & yeast consortium was used in this study for biofilm formation.

Conclusion

The study identified microalgae and yeast consortium as a promising choice and ideal partners for biofilm formation with the highest biomass yield (47.63 ± 0.93 g/m2), biomass productivity (4.39 ± 0.29 to 7.77 ± 0.05 g/m2/day) and lipid content (36%) over 28 days cultivation period, resulting in a more sustainable and environmentally benign fuel that could become a reality in the near future.

Trends in microalgal-based systems as a promising concept for emerging contaminants and mineral salt recovery from municipal wastewater

In the context of climate change leading to water scarcity for many people in the world, the treatment of municipal wastewater becomes a necessity. However, the reuse of this water requires secondary and tertiary treatment processes to reduce or eliminate a load of dissolved organic matter and various emerging contaminants. Microalgae have shown hitherto high potential applications of wastewater bioremediation thanks to their ecological plasticity and ability to remediate several pollutants and exhaust gases from industrial processes. However, this requires appropriate cultivation systems allowing their integration into wastewater treatment plants at appropriate insertion costs. This review aims to present different open and closed systems currently used in the treatment of municipal wastewater by microalgae. It provides an exhaustive approach to wastewater treatment systems using microalgae, integrating the most suitable used microalgae species and the main pollutants present in the treatment plants, with an emphasis on emerging contaminants. The remediation mechanisms as well as the capacity to sequester exhaust gases were also described. The review examines constraints and future perspectives of microalgae cultivation systems in this line of research.

Characterization and evaluation of substratum material selection for microalgal biofilm cultivation

Biofilm cultivation is considered a promising method to achieve higher microalgae biomass productivity with less water consumption and easier harvest compared to conventional suspended cultivation. However, studies focusing on the selection of substratum material and optimization of the growth of certain microalgae species on specific substratum are limited. This study investigated the selection of membranous and fabric fiber substrata for the attachment of unicellular microalgae Scenedesmus dimorphus and filamentous microalgae Tribonema minus in biofilm cultivation. The results indicated that both algal species preferred hydrophilic membranous substrata and nitrate cellulose/cellulose acetate membrane (CN-CA) was selected as a suitable candidate on which the obtained biomass yields were up to 10.24 and 7.81 g m^-2 day^-1 for S. dimorphus and T. minus, respectively. Furthermore, high-thread cotton fiber (HCF) and low-thread polyester fiber (LPEF) were verified as the potential fabric fiber substrata for S. dimorphus (5.42 g m^-2 day^-1) and T. minus (5.49 g m^-2 day^-1) attachment, respectively. The regrowth of microalgae biofilm cultivation strategy was applied to optimize the algae growth on the fabric fiber substrata, with higher biomass density and shear resistibility achieved for both algal species. The present data highlight the importance to establish the standards for selection the suitable substratum materials in ensuring the high efficiency and sustainability of the attached microalgal biomass production. KEY POINTS: • CN-CA was suitable membranous substratum candidate for algal biofilm cultivation. • HCF and LPEF were potential fabric fiber substrata for S. dimorphus and T. minus. • Regrowth biofilm cultivation was effective in improving algal biomass and attachment.

Impact of Various Visible Spectra on Attached Microalgal Growth on Palm Decanter Cake in Triggering Protein, Carbohydrate, and Lipid to Biodiesel Production

Attached microalgal growth of Chlorella vulgaris on palm decanter cake (PDC) under irradiation with various visible monochromatic and polychromatic spectra to produce biodiesel was studied in this work. The results demonstrated that the white spectrum cultivation exhibited the highest microalgal density of 1.13 g/g along with 1.213 g/L day of microalgal productivity. Correspondingly, the biodiesel obtained was comprised mainly of C16 and C18 fatty acids, possessing a high cetane number and oxidation stability from the high saturated fatty acid content (70.38%), which was appealing in terms of most biodiesel production requirements. Nevertheless, the highest lipid content (14.341%) and lipid productivity (93.428 mg/L per day) were discovered with green spectrum cultivation. Blue and white spectra led to similar protein contents (34%) as well as carbohydrate contents (61%), corroborating PDC as a feasible carbon and nutrient source for growing microalgae. Lastly, the energy feasibilities of growing the attached microalgae under visible spectra were investigated, with the highest net energy ratio (NER) of 0.302 found for the yellow spectrum. This value outweighed that in many other works which have used suspended growth systems to produce microalgal fuel feedstock. The microalgal growth attached to PDC is deemed to be a suitable alternative cultivation mode for producing sustainable microalgal feedstock for the biofuel industry.

Development of microalgae-bacteria symbiosis system for enhanced treatment of biogas slurry

In this study, microalgae-bacteria consortia were developed using bacteria and microalgae isolated from biogas slurry for enhanced nutrients recovery and promoted microalgae growth in wastewater. The enhancement rate was introduced to quantify the interaction between bacteria and microalgae. Co-culture of the indigenous microalgae and bacteria could significantly improve the tolerance of microorganisms to pollutants, increase value-added products' production, promote nutrients removal, and reduce carbon emissions compared to mono-culture. The co-culture of Chlorella sp. GZQ001 and Lysinibacillus sp. SJX05 performed best, with its biomass, lipid, protein and fatty acid methyl ester productivities achieved 113.3, 19.2, 40.9 and 3.7 mg·L^-1·d^-1, respectively. The corresponding nutrients removal efficiencies for ammonia nitrogen, total nitrogen, total organic carbon, and total phosphorus were 83.2%, 82.1%, 34.0% and 76.6%, respectively. These results indicated that co-culture of certain indigenous bacteria and microalgae is beneficial to biogas slurry treatment and microalgae growth.

Pollution prevention and waste phycoremediation by algal-based wastewater treatment technologies: The applications of high-rate algal ponds (HRAPs) and algal turf scrubber (ATS)

Following the escalating human population growth and rapid urbanization, the tremendous amount of urban and industrial waste released leads to a series of critical issues such as health issues, climate change, water crisis, and pollution problems. With the advantages of a favorable carbon life cycle, high photosynthetic efficiencies, and being adaptive to harsh environments, algae have attracted attention as an excellent agent for pollution prevention and waste phycoremediation. Following the concept of circular economy and biorefinery for sustainable production and waste minimization, this review discusses the role of four different algal-based wastewater treatment technologies, including high-rate algal ponds (HRAPs), HRAP-absorption column (HRAP-AC), hybrid algal biofilm-enhanced raceway pond (HABERP) and algal turf scrubber (ATS) in waste management and resource recovery. In addition to the nutrient removal mechanisms and operation parameters, recent advances and developments have been discussed for each technology, including (1) Innovative operation strategies and treatment of emerging contaminants (ECs) employing HRAPs, (2) Biogas upgrading utilizing HRAP-AC system and approaches of O₂ minimization in biomethane, (3) Operation of different HABERP systems, (4) Life-cycle and cost analysis of HRAPs-based wastewater treatment system, and (5) Value-upgrading for harvested algal biomass and life-cycle cost analysis of ATS system.

Potential of Microalgae in Bioremediation of Wastewater

The increase in global pollution, industrialization and fast economic progress are considered to inflict serious consequences to the quality and availability of water throughout the world. Wastewater is generated from three major sources, i.e. industrial, agricultural, and municipal which contain pollutants, such as: xenobiotics, microplastics, heavy metals and augmented by high amount of carbon, phosphorus, and nitrogen compounds. Wastewater treatment is one of the most pressing issues since it cannot be achieved by any specific technology because of the varying nature and concentrations of pollutants and efficiency of the treatment technologies. The degradation capacity of these conventional treatment technologies is limited, especially regarding heavy metals, nutrients, and xenobiotics, steering the researchers to bioremediation using microalgae (Phycoremediation). Bioremediation can be defined as use of microalgae  for removal or biotransformation of pollutants and CO2 from wastewater with concomitant biomass production. However, the usage of wastewaters for the bulk cultivation of microalgae is advantageous for reducing carbon, nutrients cost, minimizing the consumption of freshwater, nitrogen, phosphorus recovery, and removal of other pollutants from wastewater and producing sufficient biomass for value addition for either biofuels or other value-added compounds. Several types of microalgae like Chlorella and Dunaliella have proved their applicability in the treatment of wastewaters. The bottlenecks concerning the microalgal wastewater bioremediation need to be identified and elucidated to proceed in bioremediation using microalgae. This objective of this paper is to provide an insight about the treatment of different wastewaters using microalgae and microalgal potential in the treatment of wastewaters containing heavy metals and emerging contaminants, with the specialized cultivation systems. This review also summarizes the end use applications of microalgal biomass which makes the bioremediation aspect more environmentally sustainable. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Enhancement of nutrients removal and biomass accumulation of Chlorella vulgaris in pig manure anaerobic digestate effluent by the pretreatment of indigenous bacteria

High concentrations of pollutants in pig manure anaerobic digestate effluent (PMADE) can severely inhibit microalgal growth. In this study, two types of PMADE (PMADE-1, PMADE-2) were pretreated with indigenous bacteria which were selected from PMADE to alleviate their inhibition for the growth of Chlorella vulgaris. Indigenous bacteria could decrease 34.04% and 47.80% of total phosphorus (TP) and turbidity in PMADE-1, and 80.81%, 43.27%, and 57.51% of COD, TP, and turbidity in PMADE-2, respectively. And no significant reduction of NH₄⁺-N in both PMADE after 5 days pretreatment occurred. C. vulgaris failed to grow in unpretreated PMADE-2. Pretreatment of PMADE with indigenous bacteria could remarkably promote nutrients removal and cell growth of C. vulgaris compared to the unpretreated PMADE. The order of abiotic stress in the studied PMADE was COD > NH₄⁺-N > turbidity, and it is appropriate to pretreat the PMADE with indigenous bacteria for 2-3 days.

Immobilising Microalgae and Cyanobacteria as Biocomposites: New Opportunities to Intensify Algae Biotechnology and Bioprocessing

There is a groundswell of interest in applying phototrophic microorganisms, specifically microalgae and cyanobacteria, for biotechnology and ecosystem service applications. However, there are inherent challenges associated with conventional routes to their deployment (using ponds, raceways and photobioreactors) which are synonymous with suspension cultivation techniques. Cultivation as biofilms partly ameliorates these issues; however, based on the principles of process intensification, by taking a step beyond biofilms and exploiting nature inspired artificial cell immobilisation, new opportunities become available, particularly for applications requiring extensive deployment periods (e.g., carbon capture and wastewater bioremediation). We explore the rationale for, and approaches to immobilised cultivation, in particular the application of latex-based polymer immobilisation as living biocomposites. We discuss how biocomposites can be optimised at the design stage based on mass transfer limitations. Finally, we predict that biocomposites will have a defining role in realising the deployment of metabolically engineered organisms for real world applications that may tip the balance of risk towards their environmental deployment.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Innovative microalgae biomass harvesting methods: Technical feasibility and life cycle analysis

In order to ease one of the main challenges of biomass production in wastewater, the harvest stage, this study proposes as main innovations: the comparison of technical and environmental performance of different methods of harvesting biomass which have not been addressed in the literature and the projection of an optimal environmental scenario for biomass harvesting. For this, three harvesting methods were evaluated and compared, namely the gravitational sedimentation (GS) via settling tank, coagulation with tannin followed by gravitational sedimentation (TC/GS), and a biofilm reactor operated in parallel with a settling tank (BR/GS). TC/GS required less time to concentrate the biomass (121.13 g/day); however, the biomass had a higher moisture content (99.02%), which may compromise its direct application for production of most bioproducts and bioenergy, only a dewatering step is recommended. The harvesting methods interfered in biomass characterisation, mainly in carbohydrate content, which was higher in biomass concentrated over time (28-37%) than biomass concentrated in a single day by coagulation (13.8%). The results of the life cycle assessment revealed that in scenarios which included TC/GS methods and the BR/GS presented less environmental impact in relation to only GS. Additionally, the combination of these two methods comprises the best scenario and promises to optimise the harvest of biomass grown in wastewater.

The Perspective of Large-Scale Production of Algae Biodiesel

We have had high expectations for using algae biodiesel for many years, but the quantities of biodiesel currently produced from algae are tiny compared to the quantities of conventional diesel oil. Furthermore, no comprehensive analysis of the impact of all factors on the market production of algal biodiesel has been made so far. This paper aims to analyze the strengths, weaknesses, opportunities, and threats associated with algal biodiesel, to evaluate its production prospects for the biofuels market. The results of the analysis show that it is possible to increase the efficiency of algae biomass production further. However, because the production of this biodiesel is an energy-intensive process, the price of biodiesel is high. Opportunities for more economical production of algal biodiesel are seen in integration with other processes, such as wastewater treatment, but this does not ensure large-scale production. The impact of state policies and laws is significant in the future of algal biodiesel production. With increasingly stringent environmental requirements, electric cars are a significant threat to biodiesel production. By considering all the influencing factors, it is not expected that algal biodiesel will gain an essential place in the fuel market.

Innovative hybrid system for wastewater treatment: High-rate algal ponds for effluent treatment and biofilm reactor for biomass production and harvesting

The use of algal biomass still faces challenges associated with the harvesting stages. To address this issue, we propose an innovative hybrid system, in which a biofilm reactor (BR) operates as an algal biomass production and harvesting unit connected to a high-rate algal pond (HRAP), a wastewater treatment unit. BR did not interfered with the biomass chemical composition (protein = 32%, carbohydrates = 11% and total lipids = 18%), with the wastewater treatment (removals efficiency: chemical oxygen demand = 59%, ammonia nitrogen = 78%, total phosphorus = 16% and Escherichia coli = 1 log unit), and did not alter the sedimentation characteristics of the biomass (sludge volume index = 29 mg/L and humidity content = 92%) in the secondary settling tank of the hybrid system. On the other hand, the results showed that this technology achieved a biomass production about 2.6x greater than the conventional system without a BR, and the efficiency of harvesting of the hybrid system was 61%, against 22% obtained with the conventional system. In addition, the BR promoted an increase in the density (~1011 org/m²) and diversity of microalgae in the hybrid system. Chlorella vulgaris was the most abundant species (>60%) from the 4th week of operation until the end of the experiment. Hence, results confirm that the integration of BR into a wastewater treatment plant optimised the production and harvesting of biomass of the hybrid system, making it a promising technology. The importance of economic and environmental analysis studies of BR is highlighted in order to enable its implementation on a large scale.

Inclined algal biofilm photobioreactor (IABPBR) for cost-effective cultivation of lipid-rich microalgae and treatment of seawater-diluted anaerobically digested effluent from kitchen waste with the aid of phytohormones

Previous study has demonstrated that freshwater can be replaced with seawater for dilution of feed to algal production and wastewater treatment, but high harvest cost in suspended-growth systems is still a troublesome limitation for large-scale production. Therefore, a novel inclined algal biofilm photobioreactor (IABPBR) was constructed for algal bioproduct production and treatment of seawater-diluted anaerobically digested effluent (SA) in this study. Fluffy polyester was selected as the best carrier for the algal biofilm among ten discarded materials. With the help of phytohormones, the viability of SDEC-18 was clearly enhanced and an algal biomass productivity of 5.66 g/m²/d was achieved. The SDEC-18 biofilm provided removal capacities of 0.65, 0.25 and 3.31 g/m²/d for TN, TP and COD. Phytohormones clearly enhanced the lipid biosynthesis, with an extraordinary lipid productivity of 3.98 g/m²/d being achieved. Moreover, an automatic harvesting system was designed for the efficient harvesting process during large-scale production.

Integrating gravity settler with an algal membrane photobioreactor for in situ biomass concentration and harvesting

Gravity settler was integrated into an algal membrane photobioreactor (MPBR) for in situ biomass concentration and harvesting of Graesiella emersonii. By continuous circulation of suspended biomass between MPBR and settler, biomass was sedimented in the settler and harvested. MPBR-Settler operations at different recirculation rates (0.15-2.4 L/d) and settler volumes (250-1000 mL) affected both suspended (0.4-3.4 g/L) and settled (16.1-31.1 g/L) biomass concentrations. Maximum biomass productivity of 0.26 ± 0.06 g/L/d was achieved in the 1000 mL settler operating at 0.6 L/d recirculation rate, which also yielded 9-131 times concentrated biomass (31.1 g/L) compared to the baseline MPBR (0.2-3.4 g/L). This novel design also facilitated MPBR operation at low solids retention times (6-8 d) without incurring large outflow of unfiltered effluent, while alleviating light limitation via biomass dilution. These results demonstrated that the MPBR-Settler system can provide an excellent way to mitigate light limitation, enhance biomass productivity, and simplify biomass harvesting.

Non-suspended microalgae cultivation for wastewater refinery and biomass production

Non-suspended microalgae cultivation technology coupled with wastewater purification has received more scientific attention in recent decades. Since the non-suspended microalgae cultivation is quite different from the suspended ones, the following issues are compared in this study such as advantages and disadvantages, pollutant removal mechanisms and regulations, influential factors, and microalgae biomass accumulation. The analysis aims to support the further application of this technology. The median removal rates of COD, TN, TP, NH₄⁺-N and NO₃^--N were 91.6%, 78.2%, 87.5%, 93.2% and 81.7%, respectively, by non-suspended microalgae under the TN & TP load rates up to 150 mg·L^-1·d^-1. The main pathway for TN & TP removal is microalgae cell absorbance. Light intensity, pollutant composition and microalgae metabolic types are the major factors that influence pollutant removal and the lipid content of microalgae. Meanwhile the mechanism concerning how macro-outer conditions influence the micro-environment and further growth of non-suspended microalgae requires more investigation.

Bioremediation and biomass production of microalgae cultivation in river watercontaminated with pharmaceutical effluent

This work evaluated the potential of microalgae of Chlorella sp., SL7A, Chlorococcum sp., SL7B and Neochloris sp.,SK57 cultivated in river water contaminated with pharmaceutical effluent for biomass and lipid production. It has been observed that fast growing algae in this medium is Neochloris sp.SK57. Maximum biomass and lipid yield was obtained from Neochloris sp. SK57 (0.52 g/l) and Chlorococcum sp. SL7B (0.129 g/l)along with drycell weight of lipid was 28%.The increased in biomass and lipid in this media is could due to assimilation of organic nutrients and stress due to other components present in the river water. Fatty acid profile of algal biomass showed that saturated fatty acids production is enhanced in oils of Neochloris sp. SK57, and its suitability in food and fuel applications. Water quality of the river water was monitored before and after algal cultivation. Results showed that quality of river water was improved after algal cultivation.

Cultivation of Chlorella vulgaris in a Light-Receiving-Plate (LRP)-Enhanced Raceway Pond for Ammonium and Phosphorus Removal from Pretreated Pig Urine

Fresh pig urine is unsuitable for microalgae cultivation due to its high concentrations of NH4+-N, high pH and insufficient magnesium. In this study, fresh pig urine was pretreated by dilution, pH adjustment, and magnesium addition in order to polish wastewater and produce microalgae biomass. Chlorella vulgaris was cultured in an in-house-designed light-receiving-plate (LRP)-enhanced raceway pond to treat the pretreated pig urine in both batch and continuous mode under outdoor conditions. NH4+-N and TP in wastewater were detected, and the growth of C. vulgaris was evaluated by chlorophyll fluorescence activity as well as biomass production. Results indicated that an 8-fold dilution, pH adjusted to 6.0 and MgSO4·7H2O dosage of 0.1 mg·L−1 would be optimal for the pig urine pretreatment. C. vulgaris could stably accumulate biomass in the LRP-enhanced raceway pond when cultured by both BG11 medium and the pretreated pig urine. About 1.72 g·m−2·day−1 of microalgal biomass could be produced and 98.20% of NH4+-N and 68.48% of TP could be removed during batch treatment. Hydraulic retention time of 7-9d would be optimal for both efficient nutrient removal and microalgal biomass production during continuous treatment.

A comprehensive review on cultivation and harvesting of microalgae for biodiesel production: Environmental pollution control and future directions

Biodiesel is one of the best promising candidates in response to the energy crisis, since it has the capability to minimize most of the environmental problems. Microalgae, as the feedstock of third-generation biodiesel, are considered as one of the most sustainable resources. However, microalgae production for biodiesel feedstock on a large scale is still limited, because of the influences of lipid contents, biomass productivities, lipid extraction technologies, the water used in microalgae cultivation and processes of biomass harvesting. This paper firstly reviews the recent advances in microalgae cultivation and growth processes. Subsequently, current microalgae harvesting technologies are summarized and flocculation mechanisms are analyzed, while the characteristics that the ideal harvesting methods should have are summarized. This review also summarizes the environmental pollution control performances and the key challenges in future. The key suggestions and conclusions in the paper can offer a promising roadmap for the cost-effective biodiesel production.

Lignocellulosic residue as bio-carrier for algal biofilm growth: Effects of carrier physicochemical proprieties and toxicity on algal biomass production and composition

Five types of lignocellulosic materials were applied as the bio-carriers for low-cost algal biofilm cultivation of three algal strains. The effects of bio-carrier physicochemical properties and toxicity on algal cells growth and attachment were investigated. Rougher and hydrophilic bio-carrier could yield more algal biomass than smoother and hydrophobic bio-carrier. Pine sawdust (diameter: 0.420-0.595 mm) performed the best when cultured Diplosphaera sp. (9.61 g·m^-2·day^-1) biofilm. Meanwhile, bio-carriers could be leached by the culture medium during cultivation, and their energy conversion proprieties could be improved due to the reduced ash contents and the decreased crystallinities. In addition, Chlorella vulgaris growth tests indicated that pine sawdust (15.45%) leachate promoted cell growth, whereas rick husk (15.48%) and sugarcane bagasse (13.19%) leachate inhibited cell growth. And bio-carriers leachates also modified the chemical compositions (lipid, protein and carbohydrate) of algal cells and increased the corresponding saturated fatty acids methyl ester content (from 48.71 to 55.58-57.08%).

Wastewater Biofilm Photosynthesis in Photobioreactors

Photosynthetic performance of algal-bacterial biofilms from an Italian wastewater treatment plant was studied in a flow-lane photobioreactor at different irradiances, temperatures, and flow regime to evaluate the effects of these environmental parameters on biofilms’ functioning, in view of application of these communities in wastewater biological treatment. Pulse amplitude modulated fluorescence was used to estimate the effective quantum yield of PSII (ΔF/F_m’) of the light-acclimated biofilms and to perform rapid light curves (RLCs) for the determination of the photosynthetic parameters (rel.ETR_max, α, I_k). Chl a, ash free dry weight (AFDW), and dry weight (DW) were measured to assess phototrophic and whole biofilm biomass development over time. From the analysis of photosynthetic parameter variation with light intensity, temperature and flow rate, it was possible to identify the set of experimental values favoring biofilm photosynthetic activity. Biomass increased over time, especially at the highest irradiances, where substrata were fastly colonized and mature biofilms developed at all temperatures and flow conditions tested.

Microalgal biofilms: A further step over current microalgal cultivation techniques

The scientific community has turned its interest to microalgae lately, because of their countless applications such as wastewater treatment and pharmaceutical industry. Nevertheless, so far applied cultivation methods are still prohibitive. Ordinary cultivation techniques in which microalgae are suspended in liquid medium suffer from many bottlenecks, such as low biomass productivities, difficulty in biomass harvesting and recovery, high installation and operating cost, high water requirements etc. Although, microalgal biofilms are known to be a nuisance because of surfaces fouling, they have emerged as an innovative technology with which microalgae are developed attached to a solid surface. This technique seems to be advantageous as compared to conventional cultivation systems. Microalgal biofilm systems could resolve the problematic aspects of ordinary cultivation techniques such as low biomass productivities, water management and biomass recovery. A detailed description of this technique with respect to the parameters affecting them is reviewed in this work.

Optimizing culture conditions for heterotrophic-assisted photoautotrophic biofilm growth of Chlorella vulgaris to simultaneously improve microalgae biomass and lipid productivity

In order to solve the technical bottleneck that the biomass yield and lipid accumulation cannot be increased simultaneously during microalgae growth, a heterotrophic-assisted photoautotrophic biofilm (HAPB) growth mode of Chlorella vulgaris was constructed. The light penetration capability of the microalgae biofilm formed through heterotrophic-assisted photoautotrophic growth was 64% stronger than that formed by photoautotrophic growth. Due to the different demands of autotrophic and heterotrophic growth of microalgae, the nutrient environment and growth conditions were optimized to fully utilize the advantages and potentials of the HAPB culture model. An optimized molar ratio of total inorganic carbon (CO₂) to total organic carbon (glucose) (20:1) and a molar ratio of total carbon to total nitrogen (72:1) were obtained. The maximum specific growth rate of Chlorella vulgaris increased by 78% compared to that before optimization. Meanwhile, the lipid content and yield increased by 120% and 147%, respectively, up to 47.53% and 41.95 g m^-2.

An efficient Photobioreactors/Raceway circulating system combined with alkaline-CO2 capturing medium for microalgal cultivation

High efficiency of microalgal growth and CO₂ fixation in a Photobioreactors (PBRs)/Raceway circulating (PsRC) system combined with alkaline-CO₂ capturing medium and operation was established and investigated. Compared with a pH 6 medium, the average biomass productivity of Chlorella sp. AT1 cultured in a pH 11 medium at 2 L min^-1 circulation rate for 7 days increased by about 2-fold to 0.346 g L^-1 d^-1. The maximum amount of CO₂ fixation and CO₂ utilization efficiency of Chlorella sp. AT1 could be obtained at a PBRs to Raceway ratio of 1:10 in an indoor-simulated PsRC system. A similar result was also shown in an outdoor PsRC system with a 10-ton scale for microalgal cultivation. Under the appropriate circulation rate, the stable growth performance of Chlorella sp. AT1 cultured by long-term semi-continuous operation in the 10-ton outdoor PsRC system was observed, and the total amount of CO₂ fixation was approximately 1.2 kg d^-1 with 50% CO₂ utilization efficiency.

Vertical-algal-biofilm enhanced raceway pond for cost-effective wastewater treatment and value-added products production

A win-win strategy by the integration of wastewater treatment with value-added products production through a vertical-algal-biofilm enhanced raceway was investigated in the present study. Raceway pond was enhanced by vertically setting the biofilm in the system with a certain interval distance that could be adjusted for different light conditions and wastewater types. Two types of synthetic wastewater were treated with suitability-proven materials as biofilm carriers under four operation distances. Composition of the harvested algal biomass was analyzed. Coral velvet with 5-8 mm length villus was the optimal carrier, since it was durable and with high biomass productivity (6.95-8.11 g m^-2·day^-1). Nutrients in the wastewaters were efficiently removed with the COD, TN and TP reduction of over 86.61%, 73.68% and 89.85%, respectively. Wastewater with the low nutrients concentration experienced lower biomass and lipid productivity but larger biodiesel productivity and higher nutrient removal efficiency. In addition, as the operation distance increased, wastewater treatment efficiency was first increased but then decreased, while algal biomass footprint production was decreased. Differences in nutrients removal efficiencies were mainly due to the distance difference, which caused different biofilm culture surface areas and light regimes. The optimal operation distance as a function of the efficient nutrient removal and biodiesel production in this study was 6 cm.