Potential of the cyanobacteria Anabaena sp. and Dolichospermum sp. for being produced using wastewater or pig slurry: Validation using pilot-scale raceway reactors

Integrating microalgae-based wastewater treatment, biostimulant production, and hydroponic cultivation: a sustainable approach to water management and crop production

A natural appearing microalgae-bacteria consortium was used to process urban wastewater. The process was done in an 80 m2 raceway reactor and the results were compared to an identical reactor operated using freshwater supplemented with commercial fertilisers. The biomass harvesting was done using commercial ultrafiltration membranes to reduce the volume of culture centrifuged. The membrane allowed achieving a biomass concentration of ∼9-10 g L-1. The process proposed avoids the use of centrifuges and the drying of the biomass, two of the most energy consuming steps of conventional processes. The specific growth rate in freshwater and the wastewater-based media was estimated as 0.30 ± 0.05 and 0.24 ± 0.02 days-1, respectively (p < 0.05). The maximum concentration reached at the end of the batch phase was 0.96 ± 0.03 and 0.83 ± 0.07 g L-1 when the biomass was produced using freshwater and wastewater, respectively (p < 0.05). The total nitrogen removal capacity of the system was on average 1.35 g m-2·day-1; nitrogen assimilation into biomass represented 60%-95% of this value. Furthermore, the P-PO4 3- removal capacity of the system varied from 0.15 to 0.68 g m-2·day-1. The outlet effluent of the reactor was used as a nutrient source in the hydroponic production of zucchini seedlings, leading to an increase in the root dry weight and the stem diameter compared to the water alone. The produced biomass showed potential for use as feedstock to produce plant biostimulants with positive effects on root development and chlorophyll retention.

Polyhydroxyalkanoates bioproduction from bench to industry: Thirty years of development towards sustainability

The pursuit of carbon neutrality goals has sparked considerable interest in expanding bioplastics production from microbial cell factories. One prominent class of bioplastics, polyhydroxyalkanoates (PHA), is generated by specific microorganisms, serving as carbon and energy storage materials. To begin with, a native PHA producer, Cupriavidus necator (formerly Ralstonia eutropha) is extensively studied, covering essential topics such as carbon source selection, cultivation techniques, and accumulation enhancement strategies. Recently, various hosts including archaea, bacteria, cyanobacteria, yeast, and plants have been explored, stretching the limit of microbial PHA production. This review provides a comprehensive overview of current advancements in PHA bioproduction, spanning from the native to diversified cell factories. Recovery and purification techniques are discussed, and the current status of industrial applications is assessed as a critical milestone for startups. Ultimately, it concludes by addressing contemporary challenges and future prospects, offering insights into the path towards reduced carbon emissions and sustainable development goals.

Effect of seawater on the biomass composition of Spirulina produced at a pilot-scale

The microalga Arthrospira platensis BEA 005B was produced in 11.4 m3 raceway photobioreactors and a culture medium based on commercial fertilisers and either freshwater or seawater. The biomass productivity of the reactors operated at a fixed dilution rate of 0.3 day-1 decreased from 22.9 g·m-2·day-1 when operated using freshwater to 16.3 g·m-2·day-1 when the biomass was produced using seawater. The protein content of the biomass produced in seawater was lower; however, the content of essential amino acids including valine, leucine and isoleucine was higher. Seawater also triggered the production of carotenoids and altered the synthesis and accumulation of fatty acids. For example, the biomass produced using seawater showed a 319% and 210% higher content of oleic and eicosenoic acid, respectively. The results demonstrate that it is possible to produce the selected microalga using seawater after an adaptation period and that the composition of the produced biomass is suitable for food applications.

Real-time response counterattack strategy of tolerant microalgae Chlorella vulgaris MBFJNU-1 in original swine wastewater and free ammonia

This work was the first time to systematically clarify the potential tolerance mechanism of an indigenous Chlorella vulgaris MBFJNU-1 towards the free ammonia (FA) during the original swine wastewater (OSW) treatment by transcriptome analysis using C. vulgaris UETX395 as the control group. The obtained results showed that C. vulgaris MBFJNU-1 was found to be more resistant to the high levels of FA (115 mg/L) and OSW in comparison to C. vulgaris UETX395 (38 mg/L). Moreover, the transcriptomic results stated that some key pathways from arginine biosynthesis, electron generation and transmission, ATP synthesis in chloroplasts, and glutathione synthesis of C. vulgaris MBFJNU-1 were greatly related with the OSW and FA. Additionally, C. vulgaris MBFJNU-1 in OSW and FA performed similar results in the common differentially expressed genes from these mentioned pathways. Overall, these obtained results deliver essential details in microalgal biotechnology to treat swine wastewater and high free ammonia wastewater.

Towards large scale biocrust restoration: Producing an efficient and low-cost inoculum of N-fixing cyanobacteria

Dryland soil degradation is increasing due to global change and traditional restoration methods are not successful due to water scarcity. Thus, an alternative technology based on inoculating biocrust-forming cyanobacteria on degraded soils has emerged. Biocrusts are communities of mosses, lichens, cyanobacteria or fungi that colonize soil surface forming a stable and fertile layer. Previous studies have shown the benefits of inoculating cyanobacteria to restore soils at a small scale. However, to face field restoration projects, it is necessary to produce high quantities of biomass at an affordable cost. In this work, we analyze if the previously tested cyanobacteria Scytonema hyalinum, Tolypothrix distorta (heterocystous strains) and Trichocoleus desertorum (a bundle-forming one) can be produced with agricultural fertilizers. Different culture media were used: two containing pure chemicals (BG11 and BG11₀, this N-free medium was used just for heterocystous strains) and two containing fertilizers (BG11-F and MM-F). The performance of the cultures was monitored by measuring the biomass concentration and photosynthetic stress. Afterwards, we analyzed their capacity to induce biocrusts and improve soil properties by inoculating the biomass on a mine substrate indoors and measuring, three months later, the albedo, chlorophyll a and organic carbon content. Results show that the bundle-forming cyanobacterium was unable to grow in the media tested, whereas both heterocystous cyanobacteria grew in all of them and induced the formation of biocrusts improving the organic carbon substrate content. The best results for S. hyalinum were found using the MM-F medium, and for T. distorta using a medium containing pure chemicals (BG11). However, results were also positive when using a medium containing fertilizers (BG11-F). Thus, agricultural fertilizers can be used to undertake the production of heterocystous cyanobacteria for large scale restoration in drylands. On the other hand, more research is needed to find sustainable techniques to produce biomass of bundle-forming cyanobacteria.

Pilot-scale outdoor trial of a cyanobacterial consortium at pH 11 in a photobioreactor at high latitude

The biomass of microalgae and cyanobacteria yields a variety of products. Outdoor pilot plant trials typically grow a single species at circumneutral pH and provide CO₂ by gas sparging. Here a cyanobacterial consortium was grown at high pH (beyond 11) and high dissolved carbonate concentrations (0.5 M) in an outdoor 1,150 L tubular photobioreactor for 130 days in Calgary, Canada. The aim was to assess the productivity and robustness of the consortium. Importantly, the system was designed to enable future integration of air capture of CO₂. Productivity was between 3.1 and 5.8 g ash-free dry weight per square metre per day, depending on biomass density and month. 16S rRNA amplicon sequencing showed that cyanobacterium Candidatus "Phormidium alkaliphilum" made up 80% of the consortium. The consortium displayed robust growth and adapted to environmental conditions. Bicarbonate uptake pushed medium pH past 11, demonstrating the ability to achieve CO₂ delivery by air capture.

Piggery wastewater treatment with algae-bacteria consortia: Pilot-scale validation and techno-economic evaluation at farm level

The efficiency of an outdoor pilot-scale raceway pond treating the wastewaters generated by a large-scale piggery farm in Northern Italy was evaluated. The biomass productivity over 208 days of experimentation was 10.7 ± 6.5 g TSS·m^-2·d^-1, and ammoniacal nitrogen, orthophosphate, and COD average removal efficiencies were 90%, 90%, and 59%, respectively. Results were used to perform a comprehensive techno-economic analysis for integrating algae-based processes in farms of different sizes (100-10000 pigs). The amount of N disposed of on agricultural land could be reduced from 91% to 21%, increasing the fraction returned to the atmosphere from 2.4% to 63%, and the fraction in the biomass from 6.2% to 16%. For intensive farming, the release of 110 t N·ha^-1·y^-1 contained in the digestate could be avoided by including algae-bacteria processes. The biomass production cost was as low as 1.9 €·kg^-1, while the cost for nitrogen removal was 4.3 €·kg N^-1.

Outflow from a Biogas Plant as a Medium for Microalgae Biomass Cultivation—Pilot Scale Study and Technical Concept of a Large-Scale Installation

Microalgae-based technologies have huge potential for application in the environment sector and the bio-energy industry. However, their cost-efficiency has to be improved by drawing on design and operation data for large-scale installations. This paper presents a technical concept of an installation for large-scale microalgae culture on digestate liquor, and the results of a pilot-scale study to test its performance. The quality of non-treated digestate has been shown to be insufficient for direct use as a growth medium due to excess suspended solids, turbidity, and organic matter content, which need to be reduced. To that end, this paper proposes a system based on mechanical separation, flotation, and pre-treatment on a biofilter. The culture medium fed into photobioreactors had the following parameters after the processing: COD—340 mgO2/dm3, BOD5—100 mgO2/dm3, TN—900 mg/dm3, and TP—70 mg/dm3. The installation can produce approx. 720 kgVS/day of microalgal biomass. A membrane unit and a thickening centrifuge (thickener) were incorporated into the design to separate and dehydrate the microalgal biomass, respectively. The total energy consumption approximated 1870 kWh/day.

Chlorella vulgaris cultivation in pilot-scale to treat real swine wastewater and mitigate carbon dioxide for sustainable biodiesel production by direct enzymatic transesterification

This study firstly addressed real swine wastewater (RSW) treatment by an indigenous Chlorella vulgaris MBFJNU-1 in 5-m³ outdoor open raceway ponds and then direct enzymatic transesterification of the resulting lipids from the wet biomass for sustainable biodiesel production. Compared to the control group, C. vulgaris MBFJNU-1 at 3% CO₂ achieved higher microalgal biomass (478.5 mg/L) and total fatty acids content (21.3%), higher CO₂ bio-fixation (63.2 mg/L/d) and lipid (9.1 mg/L/d) productivities, and greater nutrients removals (total nitrogen, 82.1%; total phosphorus, 28.4%; chemical oxygen demand, 37.1%). The highest biodiesel conversion (93.3%) was attained by enzymatic transesterification of wet disrupted Chlorella biomass with 5% lipase TL and 5% phospholipase PLA. Moreover, the enzymatic transesterification gave around 83% biodiesel conversion in a 15-L stirred tank bioreactor. Furthermore, the integrated process was a cost-effective approach to treat RSW and mitigate CO₂ for microalgal biodiesel production, based on the mass and energy balances analysis.

Microalgae based wastewater treatment coupled to the production of high value agricultural products: Current needs and challenges

One of the main social and economic challenges of the 21st century will be to overcome the worlds' water deficit expected by the end of this decade. Microalgae based wastewater treatment has been suggested as a strategy to recover nutrients from wastewater while simultaneously producing clean water. Consortia of microalgae and bacteria are responsible for recovering nutrients from wastewater. A better understanding of how environmental and operational conditions affect the composition of the microalgae-bacteria consortia would allow to maximise nutrient recoveries and biomass productivities. Most of the studies reported to date showed promising results, although up-scaling of these processes to reactors larger than 100 m² is needed to better predict their industrial relevance. The main advantage of microalgae based wastewater treatment is that valuable biomass with unlimited applications is produced as a co-product. The aim of the current paper was to review microalgae based wastewater treatment processes focusing on strategies that allow increasing both biomass productivities and nutrient recoveries. Moreover, the benefits of microalgae based agricultural products were also discussed.