Macroalgae culture to treat anaerobic digestion piggery effluent (ADPE)

Effect of light intensity on Chlorella sp. biofilm growth on anaerobically digested food effluents (ADFE)

Optimizing light conditions in any culture design for effluent treatment is crucial for maximizing microalgae growth and nutrient uptake. We investigated the impact of low (53 ± 1 μmol m-2 s-1), medium (208 ± 12 μmol m-2 s-1), and high (518 ± 22 μmol m-2 s-1) light intensities on the diffused biofilm-based growth of Chlorella sp. for treating anaerobically digested food effluent (ADFE). The alga grew well across all treatments, irrespective of light intensity. However, biomass yields, and productivity positively correlated with light intensity, with the highest biomass yield (120 g m-2) and productivity (11.6 g m-2 d-1) occurring at high light intensity. Notably, specific growth rates peaked uniformly on day 2 across all treatments, indicating an initial surge in growth. A relatively stable photosynthetic performance occurred under medium light treatment, while stress evidence was noticed particularly after day 4 at high and low light treatments, with higher magnitude seen under low light treatments. Total ammonia nitrogen (TAN) and phosphate removal efficiencies increased with light intensities, reaching 100 % removal at high light after 10 days. Intriguingly, there was a notable enhancement in chemical oxygen demand (COD) removal under low light conditions, being 2.9- and 1.64-fold higher compared to medium and high light intensities, respectively. Despite the superior performance of Chlorella sp. biofilm under high-light conditions in biomass yield and uptake of nutrients, the low-light treatment also achieved remarkable results, indicating that this biofilm design offers enhanced exposure to light. Therefore, this biofilm configuration presents an enticing opportunity for treating ADFE at lower light intensities, potentially minimizing energy consumption while maximizing profitability.

Sulfamethoxazole removal and ammonium conversion in microalgae consortium: Physiological responses and microbial community changes

Microalgae (Mychonastes sp.) consortium was investigated for nutrient and antibiotics removal and its responses to varying sulfamethoxazole (SMX) concentrations (0-1000 μg/L) in ammonia-rich wastewater. The results showed that the introduction of SMX (100-1000 μg/L) slightly improved ammonium nitrogen removal efficiency instead of inhibition. Swift SMX degradation was observed across all SMX-treated systems, with the highest SMX removal efficiency (96 %) at an SMX concentration of 100 μg/L. Biodegradation remained the dominant SMX removal mechanism, contributing 78 % of SMX removal at an SMX concentration of 800 μg/L, while adsorption and photolysis played minor roles. Addition of SMX augmented biomass and lipid productivity, but decreased chlorophyll contents in the microalgae consortium. Furthermore, extracellular polymeric substance (EPS) production correlated positively with SMX input concentration, with the microalgae consortium exposed to 800 μg/L SMX displaying the most pronounced stimulation of protein production (51.5 ± 2.0 mg/g DCW) and polysaccharides production (74.8 ± 3.9 mg/g DCW). In response to an increase in SMX concentrations, enzyme activities associated with antioxidant defense, such as superoxide dismutase (SOD), peroxidase (POD) and malondialdehyde (MDA) increased, the catalase (CAT) decreased, indicating an initial defense mechanism. Concurrently, the relative abundance of Mychonastes sp. within the consortium rose from 87 % at 300 μg/L SMX to 99.9 % at 800 μg/L SMX. while Shannon indices of the bacterial community increased from 1.415 to 2.867. This shift inhibited the initially dominant Saprospiraceae bacteria, facilitating the profound increase of adapted Aquimonas. These findings demonstrate the feasibility of the simultaneous removal of antibiotics and nutrients from wastewater with a microalgae consortium system.

Ensuring carbon neutrality via algae-based wastewater treatment systems: Progress and future perspectives

The emergence of algal biorefineries has garnered considerable attention to researchers owing to their potential to ensure carbon neutrality via mitigation of atmospheric greenhouse gases. Algae-derived biofuels, characterized by their carbon-neutral nature, stand poised to play a pivotal role in advancing sustainable development initiatives aimed at enhancing environmental and societal well-being. In this context, algae-based wastewater treatment systems are greatly appreciated for their efficacy in nutrient removal and simultaneous bioenergy generation. These systems leverage the growth of algae species on wastewater nutrients-including carbon, nitrogen, and phosphorus-alongside carbon dioxide, thus facilitating a multifaceted approach to pollution remediation. This review seeks to delve into the realization of carbon neutrality through algae-mediated wastewater treatment approaches. Through a comprehensive analysis, this review scrutinizes the trajectory of algae-based wastewater treatment via bibliometric analysis. It subsequently examines the case studies and empirical insights pertaining to algae cultivation, treatment performance analysis, cost and life cycle analyses, and the implementation of optimization methodologies rooted in artificial intelligence and machine learning algorithms for algae-based wastewater treatment systems. By synthesizing these diverse perspectives, this study aims to offer valuable insights for the development of future engineering applications predicated on an in-depth understanding of carbon neutrality within the framework of circular economy paradigms.

Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m-2) than Scenedesmus sp. biofilm (9.39 g m-2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L-1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L-1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L-1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L-1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L-1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68-81 % of removed nitrogen in biomass, while in suspension, only 55-71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

Commercial paper as a promising carrier for biofilm cultivation of Chlorella sp. for the treatment of anaerobic digestate food effluent (ADFE): Effect on the photosynthetic efficiency

Microalgal technology is still economically unattractive due to the high cost associated with microalgal cultivation and biomass recovery from conventional suspension cultures. Biofilm-based cultivation is a promising alternative for higher biomass yield and cheap/easy biomass harvesting opportunities. Additionally, using anaerobic digestate food effluent (ADFE) as a nutrient source reduces the cultivation cost and achieves ADFE treatment as an added value. However, the search for locally available, inexpensive, and efficient support materials is still open to research. This study evaluates the potential of commercially available, low-cost papers as support material for biofilm cultivation of Chlorella sp. and treatment of ADFE. Among the four papers screened for microalgal attachment, quill board paper performed better in higher biomass yield and stability throughout the study period. The attached growth study was done in a modular food container vessel, using anaerobic digestate food effluent (ADFE) as a nutrient source and a basal medium as a control. The microalgae grew well on the support material with higher biomass yield and productivity of 108.64 g(DW) m-2 and 9.96 g (DW) m-2 d-1, respectively, in the ADFE medium compared with 85.87 g (DW) m-2 and 4.99 g (DW) m-2 d-1, respectively in the basal medium. Chlorophyll, a fluorescence (ChlF) probe, showed that cell density in the biofilm significantly changes the photosynthetic apparatus of the algae, with evidence of stress observed as the culture progressed. Also, efficient nutrient removal from the ADFE medium was achieved in the 100 %, 85 %, and 40.2 % ratios for ammoniacal nitrogen, phosphate, and chemical oxygen demand (COD). Therefore, using quill board paper as carrier material for microalgal cultivation offers promising advantages, including high biomass production, easy biomass harvesting (by scrapping or rolling the biomass with the paper), and efficient effluent treatment.

Global seaweed farming and processing in the past 20 years

Seaweed has emerged as one of the most promising resources due to its remarkable adaptability, short development period, and resource sustainability. It is an effective breakthrough to alleviate future resource crises. Algal resources have reached a high stage of growth in the past years due to the increased output and demand for seaweed worldwide. Several aspects global seaweed farming production and processing over the last 20 years are reviewed, such as the latest situation and approaches of seaweed farming. Research progress and production trend of various seaweed application are discussed. Besides, the challenges faced by seaweed farming and processing are also analyzed, and the related countermeasures are proposed, which can provide advice for seaweed farming and processing. The primary products, extraction and application, or waste utilization of seaweed would bring greater benefits with the continuous development and improvement of applications in various fields.

Graphical Abstract

Exploratory analysis of Spirulina platensis LB 2340 growth in varied concentrations of anaerobically digested pig effluent (ADPE)

There is a significant interest in novel waste management solutions to treat wastewater from swine operations. Anaerobic digestion is a rising and prominent solution, but this technology still generates highly concentrated effluent that requires further remediation. Therefore, the aim of this study was to explore the feasibility of cultivating the cyanobacterium Spirulina platensis in swine effluent for future applications in biological waste treatment and value-added fermentation. To accomplish this goal, growth of S. platensis was characterized in varying proportions of ideal, synthetic Zarrouk medium and anaerobically digested pig effluent (ADPE) to obtain growth rate models. Results yielded a positive correlation between S. platensis growth rate and Zarrouk medium proportion, with the highest growth rate in 100% Zarrouk media but comparable growth in the 50/50% Zarrouk/ADPE mixture. This study demonstrates the potential for S. platensis to further improve the treatment efficacy of anaerobic digestion systems, and the exploratory analysis also highlights that further testing is required to investigate possible carbon availability, chemical inhibition, and overall nutrient reduction in ADPE. This research contributes important data toward the feasibility of producing value-added cyanobacterial biomass while simultaneously consuming excess nutrients to aid in agricultural wastewater management efforts and generate cost-effective products in a more sustainable manner.

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.

Wastes to profit: a circular economy approach to value-addition in livestock industries

The livestock sector is a fundamental part of the modern global economy and provides food, clothing, furnishings, and various other products. So as to ensure its resilience to changes in consumer expectations, cost of production, and environmental sustainability, the sector must shift to a circular economy model. Current strategies to recover value from wastes and low-value co-products from livestock industries yield limited value; hence, new technologies are required to upgrade wastes and co-products, and generate high-value products that can feed into the livestock value chain. Anaerobic digestion can convert high organic-content waste to biogas for energy and a stable nutrient-rich digestate that can be used as fertiliser. Microbial technologies can transform wastes to produce nutritionally advanced feeds. New materials from waste can also be produced for livestock industry-specific applications. While aiming to add commercial value, the successful implementation of these technologies will also address the environmental and productivity issues that are increasingly valued by producers and consumers.

Viability of combining microalgae and macroalgae cultures for treating anaerobically digested piggery effluent

Algal phytoremediation represents a practical green solution for treating anaerobically digested piggery effluent (ADPE). The potential and viability of combining microalgae and macroalgae cultivation for the efficient treatment of ADPE were evaluated in this study. Bioprospecting the ability of different locally isolated macroalgae species illustrated the potential of Cladophora sp. to successfully grow and treat ADPE with up to 150 mg/L NH₄⁺ with a biomass productivity of (0.13 ± 0.02) g/(L·day) and ammonium removal rate of (10.23 ± 0.18) mg/(L·day) NH₄⁺. When grown by itself, the microalgae consortium used in this study consisting of Chlorella sp. and Scenedesmus sp. was found to grow and treat undiluted ADPE (up to 525 mg/L NH₄⁺) with an average ammonium removal rate of 25 mg/(L·day) NH₄⁺ and biomass productivity of (0.012 ± 0.0001) g/(L·day). Nevertheless, when combined together, despite the different cultivation systems (attached and non-attached) evaluated, microalgae and macroalgae were unable to co-exist together and treat ADPE as their respective growth were inversely related to each other due to direct competition for nutrients and available resources as well as the negative physical interaction between both algal groups.

Enhancing methane production from U. lactuca using combined anaerobically digested sludge (ADS) and rumen fluid pre-treatment and the effect on the solubilization of microbial community structures

Methane production by the anaerobic digestion of seaweed is restricted by the slow degradation caused by the influence of the rigid algal cell wall. At the present time, there has been no study focusing on the anaerobic digestion of U. lactuca by co-fermentation and pre-treatment with rumen fluid. Rumen fluid can favor methane production from algal biomass by utilizing the diversity and quantity of bacterial and archaeal communities in the rumen fluid. This research presents a novel method based on combined ADS and rumen fluid pre-treatment to improve the production of methane from seaweed. Biochemical methane potential (BMP) tests were performed to investigate the biogas production using combined ADS and rumen fluid pre-treatment at varied inoculum ratios on the performance of methane production from U. lactuca biomass. Compared to the control (no rumen fluid pre-treatment), the highest BMP yields of U. lactuca increased from 3%, 27.5% and 39.5% to 31.1%, 73% and 85.6%, respectively, for three different types of treatment. Microbial community analysis revealed that the Methanobrevibacter species, known to accept electrons to form methane, were only detected when rumen fluid was added. Together with the significant increase in species of Methanoculleus, Methanospirillum and Methanosaeta, rumen fluid improved the fermentation and degradation of the microalgae biomass not only by pre-treatment to foster cell-wall degradation but also by relying on methane production within itself during anaerobic processes. Batch experiments further indicated that rumen fluid applied to the co-fermentation and pre-treatment could increase the economic value and hold promise for enhancing biogas production from different seaweed species.