Biorecovery of nutrient waste as protein in freshwater macroalgae

Valorization of swine wastewater in a circular economy approach: Effects of hydraulic retention time on microalgae cultivation

To optimize the swine wastewater (SWW) treatment, this study investigated different hydraulic retention times (HRTs) for microalgae cultivation. For this purpose, five pilot-scale reactors operated in semi-continuous flow, with HRTs equal to 9, 12, 15, 18, 21 days were evaluated in terms of SWW polishing and biomass production. The effluent treatment was discussed accompanied by principal component analysis, which allowed identification of causes of variance in the data set, ideal for studies with real effluent and influenced by environmental conditions. All reactors show satisfactory removals of N-NH₄⁺ (91.6-95.3%), COD (15.8-39.9%), DO increment (in average 7.5 mg O₂/L) and, only the longest HRT (21 days) was able to remove Ps (21%). The results obtained indicated that a consortium of microalgae and bacteria was developed for all the tested HRTs. On the other hand, HRT = 12 days provided a healthier culture of photosynthesizing organisms (chl-a/VSS = 3.04%). Carbohydrates (20.8-31.3%) and proteins (2.7-16.2%) were the compounds of commercial interest in the highest proportion in the biomass of all reactors, with contents comparable to that of terrestrial crops. Thus, it was suggested a valorization route of these compounds of high added value to return to pig farming, where the nutrients were intended to supplement the swine feed and clarified water for cleaning the pig stalls. Thus, in the circular economy context, this research contributes to water footprint reduction and the sustainability of the pig farming production chain. The economic and environmental analysis of the route is suggested to enable its implementation on a large scale, as well as further technical feasibility research (reactor types, exposure to external environment, evaluation of pathogen removal and animal feed supplementation from SWW microalgae biomass).

Second-Generation Phosphorus: Recovery from Wastes towards the Sustainability of Production Chains

Phosphorus (P) is essential for life and has a fundamental role in industry and the world food production system. The present work describes different technologies adopted for what is called the second-generation P recovery framework, that encompass the P obtained from residues and wastes. The second-generation P has a high potential to substitute the first-generation P comprising that originally mined from rock phosphates for agricultural production. Several physical, chemical, and biological processes are available for use in second-generation P recovery. They include both concentrating and recovery technologies: (1) chemical extraction using magnesium and calcium precipitating compounds yielding struvite, newberyite and calcium phosphates; (2) thermal treatments like combustion, hydrothermal carbonization, and pyrolysis; (3) nanofiltration and ion exchange methods; (4) electrochemical processes; and (5) biological processes such as composting, algae uptake, and phosphate accumulating microorganisms (PAOs). However, the best technology to use depends on the characteristic of the waste, the purpose of the process, the cost, and the availability of land. The exhaustion of deposits (economic problem) and the accumulation of P (environmental problem) are the main drivers to incentivize the P’s recovery from various wastes. Besides promoting the resource’s safety, the recovery of P introduces the residues as raw materials, closing the productive systems loop and reducing their environmental damage.

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.

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.

A holistic zero waste biorefinery approach for macroalgal biomass utilization: A review

The growing concerns over the depleting fossil fuels and increase in the release of greenhouse gas emissions have necessitated the search for the potential biomass source for alternative energy generation. In this context, third generation biomass specifically maroalgae has gained a lot of research interest in the recent years for energy and products generation such as ethanol, butanol, alginates, agars, and carrageenans. There are a few reviews available in scientific domain on macroalgal biomass utilization for bioethanol production but none of them has addressed precisely from phenolic precursor compounds to the entire ethanol production process and its bottlenecks. Here, we explained critically the processes involved in bioethanol, value added products and chemicals production utilizing macroalgal biomass as a feedstock along with its zero waste feasibility approach. Apart from this, we have also summarized the major issues linked to the macroalgae based biofuels and bioproducts generation processes and their possible corrective measures. Biorefinery is a promising way to generate multiple products from a single source with short processing time. Thus, this review also focuses on the recent advancement in the macroalgal biomass scaling up and how this could help in the growth of macroalgal biorefinery industry in the near future.

Biological nutrient removal and recovery from solid and liquid livestock manure: Recent advance and perspective

Rapid development of livestock industry produces large amount of livestock manure rich in nutrients, organic matters, antibiotics, and heavy metals, thus imposes great harms to human and environment, if the manure is not suitably treated. Biological removal and recovery of nutrients from manure as agriculture fertilizer is attractive due to low cost and simple operation. This review offers an overview of recent development in biological nutrient removal and recovery from livestock manure. Livestock manure is divided into solid manure and liquid manure. Composting and anaerobic digestion of solid manure are fully discussed and important parameters are investigated. Then various processes of nutrient removal and recovery from liquid manure are summarized. Brief economic sustainability and eco-environmental effects are carried out. Finally, current challenges and future prospects in this field are analyzed.

Wastewater treatment using filamentous algae - A review

Wastewater treatment using algae is a promising approach for efficient removal of contaminating nutrients and their conversion into useful products. Monocultures of filamentous algae provide easier harvesting compared to microalgae, and better control of biomass quality than polyculture systems such as algal turf scrubbers. In this review, recent research into wastewater treatment using freshwater filamentous algae is compiled and critically analysed. Focus is given to filamentous algae monocultures, with key relevant findings from microalgae and polyculture systems discussed and compared. The application of monocultures of filamentous algae is an emerging area of research. Gaps are identified in our understanding of key aspects important to large-scale system design, including criteria for species selection, influence of nutrient type and loading, inorganic carbon supply, algae-bacteria interactions, and parameters such as pond depth, mixing and harvesting regimes. This technology has much promise, however future research is needed to maximise productivity and wastewater treatment efficiency.

Insights into the Regulation of Algal Proteins and Bioactive Peptides Using Proteomic and Transcriptomic Approaches

Oceans abound in resources of various kinds for R&D and for commercial applications. Monitoring and bioprospecting allow the identification of an increasing number of key natural resources. Macroalgae are essential elements of marine ecosystems as well as a natural resource influenced by dynamic environmental factors. They are not only nutritionally attractive but have also demonstrated potential health benefits such as antioxidant, antihypertensive, and anti-inflammatory activities. Several bioactive peptides have been observed following enzymatic hydrolysis of macroalgal proteins. In addition, significant differences in protein bioactivities and peptide extracts of wild and cultivated macroalgae have been highlighted, but the metabolic pathways giving rise to these bioactive molecules remain largely elusive. Surprisingly, the biochemistry that underlies the environmental stress tolerance of macroalgae has not been well investigated and remains poorly understood. Proteomic and functional genomic approaches based on identifying precursor proteins and bioactive peptides of macroalgae through integrated multi-omics analysis can give insights into their regulation as influenced by abiotic factors. These strategies allow evaluating the proteomics profile of regulation of macroalgae in response to different growth conditions as well as establishing a comparative transcriptome profiling targeting structural protein-coding genes. Elucidation of biochemical pathways in macroalgae could provide an innovative means of enhancing the protein quality of edible macroalgae. This could be ultimately viewed as a powerful way to drive the development of a tailored production and extraction of high value molecules. This review provides an overview of algal proteins and bioactive peptide characterization using proteomics and transcriptomic analyses.

Good for sewage treatment and good for agriculture: Algal based compost and biochar

In this study we test a novel approach to closing the anthropogenic nutrient cycle, by using the freshwater macroalga, Oedogonium intermedium, to recover dissolved nitrogen (N) and phosphorous (P) from municipal wastewater. We then convert this cultivated algae into two types of soil ameliorant; compost and biochar. To produce compost, algae was combined with sugarcane bagasse and left to mature for 10 weeks, and to produce biochar, algae was processed through slow pyrolysis at 450 °C. The mature compost had a total N and P content of 2.5% and 0.6%, which was 2- to 4-times lower than the algal biochar, which had a total N and P content of 5.5% and 2.5% respectively. Composting stabilized the N and P recovered from wastewater, with 80% of the initial N and >99% of the initial P retained in the mature compost. In contrast, only 29% of the initial N and 62% of the initial P was retained in the biochar. When the mature compost was added to a low fertility soil it significantly increased the production of sweet corn (Zea mays). Treatments receiving 50 and 100% compost produced 4-9 times more corn biomass than when synthetic fertilizer alone was added to the low fertility soil. When biochar was applied in conjunction with compost there was an additional 15% increase in corn productivity, most likely due to the ability of the biochar to bind labile N and P and prevent its loss from the soil. This study demonstrates a unique model for recovering N and P from municipal wastewater and recycling these nutrients into the agricultural industry. This could be an ideal model for regional areas where agriculture and water treatment facilities are co-located and could ultimately reduce the reliance of agriculture on finite mineral sources of P.