Mariculture wastewater treatment with Bacterial-Algal Coupling System (BACS): Effect of light intensity on microalgal biomass production and nutrient removal

Employing Chlorella pyrenoidosa in eco-friendly acetylsalicylic acid degradation: Insights from physiology and transcriptomics

Emerging contaminants, often present at low concentrations, are of increasing concern due to their persistence and potential hazards. Chlorella pyrenoidosa has shown significant potential for removing these emerging contaminants from aquatic environments. In this study, C. pyrenoidosa effectively removed and degraded acetylsalicylic acid (ASA) at concentrations ranging from 2.2 to 22.1 mg/L, achieving a removal efficiency of 98.8 %, with 89.0 % of this removal attributed to biodegradation. ASA treatment also significantly promoted cellular growth, enhanced protein and soluble sugar accumulation, and improved both photosynthetic and respiratory activities. At 22.1 mg/L ASA, protein content increased by 51.9 %, and soluble sugar content rose by 34.8 %. Transcriptomic analysis revealed that ASA promoted carbon metabolism and nitrogen metabolism. These results highlight C. pyrenoidosa as a promising, eco-friendly solution for the removal of ASA, offering potential applications in sustainable wastewater treatment and resource recovery.

Innovative microalgae technologies for mariculture wastewater treatment: Single and combined microalgae treatment mechanisms, challenges and future prospects

The discharge of aquaculture wastewater, comprising nitrogen, phosphorus, heavy metals, and antibiotics from large-scale aquaculture, poses a significant threat to marine ecosystems and human health. Consequently, addressing the treatment of marine aquaculture wastewater is imperative. Conventional physicochemical treatment methods have various limitations, whereas microalgae-based biological treatment technologies have gained increasing attention in the field of water purification due to their ability to efficiently absorb organic matter from mariculture wastewater and convert CO₂ into biomass products. Microalgae offer potential for highly efficient and cost-effective mariculture wastewater treatment, with particularly noteworthy advancements in the application of combined microalgae technologies. This paper explores the research hotspots in this field through bibliometric analysis and systematically discusses the following aspects: (1) summarizing the current pollution status of mariculture wastewater, including the types and sources of pollutants in various forms of mariculture wastewater, treatment methods, and associated treatment efficiencies; (2) analyzing the factors contributing to the gradual replacement of single microalgae technology with combined microalgae technology, highlighting its synergistic effects, enhanced pollutant removal efficiencies, resource recovery potential, and alignment with sustainable development goals; (3) exploring the mechanisms of pollutant removal by combined microalgae technologies, focusing on their technical advantages in bacterial-algal coupling, immobilized microalgae systems, and microalgal biofilm technologies; (4) discussing the challenges faced by the three main categories of combined microalgae technologies and proposing future improvement strategies to further enhance their application effectiveness. In conclusion, this paper offers a detailed analysis of these emerging technologies, providing a forward-looking perspective on the future development of microalgae-based mariculture wastewater treatment solutions.

Tertiary treatment of dairy wastewater applying a microalga-fungus consortium

This paper aimed to apply filamentous fungi (Penicillium oxalicum and Cunninghamella echinulata), the microalga Tetradesmus obliquus and their co-culture in advanced treatment (tertiary treatment) of cheese whey. The bioremediation process was carried out in agitated flasks and bubble column bioreactors with different concentrations of chemical oxygen demand (COD) (223-1663 mg L-1), total nitrogen (TN) (13-61 mg L-1), and total phosphorus (TP) (3-26 mg L-1). The results obtained in shaken flasks showed a superiority of the consortium compared to the systems with separated species. In this sense, the treatment was carried out in a bubble column reactor, and the consortium formed by the microalga and the fungus C. echinulata showed a greater efficiency (at a light intensity of 100 µmol m-2 s-1), promoting by the symbiosis to reach removal efficiencies of up to 93.7, 78.8 and 93.4% for COD, TN and TP, respectively; meeting Brazilian and European standards for discharge into water bodies. In addition, no pH adjustment was required during the co-culture treatment, demonstrating the buffering effect of using these two types of microorganisms. Therefore, the use of the consortium formed by T. obliquus and C. echinulata as a remediator was highly promising to promote the advanced treatment of cheese whey.

Light intensity effects on bioproduct recovery from fuel synthesis wastewater using purple phototrophic bacteria in a hybrid biofilm-suspended growth system

This research looked at how three different light intensities (1600, 4300, and 7200 lx) affect the biomass development, treatment of fuel synthesis wastewater and the recovery of valuable bioproducts between biofilm and suspended growth in a purple-bacteria enriched photobioreactor. Each condition was run in duplicate using an agricultural shade cloth as the biofilm support media in a continuously mixed batch reactor. The results showed that the highest chemical oxygen demand (COD) removal rate (56.8 ± 0.9 %) was found under the highest light intensity (7200 lx), which also led to the most biofilm formation and highest biofilm biomass production (1225 ± 95.7 mg). The maximum carotenoids (Crts) and bacteriochlorophylls (BChls) content occurred in the suspended growth of the 7200 lx reactor. BChls decreased with light intensity in suspended growth, while in biofilm both Crts and BChls were relatively stable between light conditions, likely due to an averaging effect as biofilm thickened at higher light intensity. Light intensity did not affect protein content of the biomass, however, biofilm showed a lower average (41.2 % to 43.7 %) than suspended biomass (45.4 % to 47.7 %). For polyhydroxybutyrate (PHB) the highest cell concentration in biofilm occurred at 1600 lx (11.4 ± 2.4 %), while for suspended growth it occurred at 7200 lx (22.7 ± 0.3 %), though total PHB productivity remained similar between reactors. Shading effects from the externally located biofilm could explain most variations in bioproduct distribution. Overall, these findings suggest that controlling light intensity can effectively influence the treatment of fuel synthesis wastewater and the recovery of valuable bioproducts in a biofilm photobioreactor.

An assessment of the autotrophic/heterotrophic synergism in microalgae under mixotrophic mode and its contribution in high-rate phosphate recovery from wastewater

Dual carbon metabolisms and the synergism contribute to improving nutrient recovery under mixotrophy. However, how synergism influences nutrient recovery has yet to be understood, which is revealed in the current study. Due to dual carbon metabolisms and synergism,the PO4--P recovery rate under mixotrophy reached 0.34 mg L-1 h-1. Due to the internal cycling of respiratory CO2, the mutualistic index (MI) in terms of synergism helped Scenedesmus accumulate 27.49 % more biomass under mixotrophy than sum of the two controls. In contrast, MI contributed 0.26 g L-1 d-1 to the total modeled mixotrophic productivity of 1.15 g L-1 d-1. To total modeled PO4--P recovery, mixotrophic-auto, and mixotrophic-hetero shares were 42 % and 58 %. The synergism under mixotrophy contributed 20 % in total PO4--P recovery. The PO4--P recovery rate under mixotrophywas comparable to other biological P removal methods. These findings emphasize the potential of synergism in improving productivityand promoting resource recovery for sustainable wastewater treatment.

Re-vitalizing wastewater: Nutrient recovery and carbon capture through microbe-algae synergy using omics-biology

Increasing amounts of wastewater is the most pervasive and challenging environmental problem globally. Conventional treatment methods are costly and entail huge energy, carbon consumption and greenhouse gas emissions. Owing to their unique ability of carbon capturing and resource recovery, microalgae-microbiome based treatment is a potential approach and is widely used for carbon-neutral wastewater treatment. Microalgae-bacteria synergy (i.e., the functionally beneficial microbial synthetic communities) performs better and enhances carbon-sequestration and nutrient recovery from wastewater treatment plants. This review presents a comprehensive information regarding the potential of microalgae-microbiome as a sustainable agent for wastewater and discusses synergistic approaches for effective nutrient removal. Moreover, this review discusses, the role of omics-biology and Insilco approaches in unravelling and understanding the algae-microbe synergism and their response toward wastewater treatment. Finally, it discusses various microbiome engineering approaches for developing the effective microalgae-bacteria partners for carbon sequestration and nutrient recovery from wastewater, and summarizes future research perspectives on microalgae-microbiome based bioremediation.

Sustainable aquaculture and seafood production using microalgal technology - A circular bioeconomy perspective

The aquaculture industry is under the framework of the food-water-energy nexus due to the extensive use of water and energy. Sustainable practices are required to support the tremendous growth of this sector. Currently, the aquaculture industry is challenged by its reliance on capture fisheries for feed, increased use of pharmaceuticals, infectious outbreaks, and solid/liquid waste management. This review posits microalgal technology as a comprehensive solution for the current predicaments in aquaculture in a sustainable way. Microalgae are microscopic, freshwater and marine photosynthetic organisms, capable of carbon mitigation and bioremediation. They are indispensable in aquaculture due to their key role in marine productivity and their position in the marine food chain. Microalgae are nutritious and are currently used as feed in specific sectors of aquaculture. Due to their bioremediation potential, direct application of microalgae in shellfish ponds and in recirculating systems have been adopted to improve water quality and aquatic animal health. The potential of microalgae for integration into various aspects of aquaculture processes, namely hatcheries, feed, and waste management has been critically analyzed. Seamless integration of microalgal technology in aquaculture is feasible, and this review will provide new insights into using microalgal technology for sustainable aquaculture.

Simultaneous removal of sulfide and bicarbonate from synthetic wastewater using an algae-assisted microbial fuel cell

The anaerobic digestion (AD) process is one of the most practiced technologies for the remediation of organic waste and maximization of energy recovery in terms of biogas or biomethane. The presence of other gaseous components in biogas, e.g. CO2 and H2S, often makes its direct application in engines and electricity production unsuitable. This work aimed to develop and utilize an algae-assisted microbial fuel cell (AMFC) for the purification of biogas by removing both CO2 and H2S and simultaneous bioelectricity generation. In addition to biogas clean-up, elemental sulfur recovery and CO2 utilization for algae cultivation add value to the proposed AMFC process. Experiments were performed with both sulfide and bicarbonate in their dissolved form, in the respective anodic and cathodic chambers of the AMFC. The sulfide concentration was varied from 100 to 800 mg/l and the AMFC exhibited a sulfide removal efficiency exceeding 97% at all concentrations tested. The process efficiency dropped, however, at sulfide concentrations above 300 mg/l in terms of both sulfide removal and power output. The AMFC performed best at 400 mg/l sulfide by exhibiting a power density of 24.99 mW/m3 and sulfide removal efficiency of 98.87%. The system exhibited columbic efficiency (CE %) in the range of 7.85-80%. The total alkalinity representing CO2, carbonate and bicarbonate levels in the algae-based system was reduced by 49.54%. The electrical energy recovered from the AMFC was 0.1 kWh/m3 and the total energy recovery, which is the sum of the electrical and algal lipid energy, amounted to 7.25 kWh/m3.

Microalgae-mediated bioremediation: current trends and opportunities-a review

Environmental pollution poses a critical global challenge, and traditional wastewater treatment methods often prove inadequate in addressing the complexity and scale of this issue. On the other hand, microalgae exhibit diverse metabolic capabilities that enable them to remediate a wide range of pollutants, including heavy metals, organic contaminants, and excess nutrients. By leveraging the unique metabolic pathways of microalgae, innovative strategies can be developed to effectively remediate polluted environments. Therefore, this review paper highlights the potential of microalgae-mediated bioremediation as a sustainable and cost-effective alternative to conventional methods. It also highlights the advantages of utilizing microalgae and algae-bacteria co-cultures for large-scale bioremediation applications, demonstrating impressive biomass production rates and enhanced pollutant removal efficiency. The promising potential of microalgae-mediated bioremediation is emphasized, presenting a viable and innovative alternative to traditional treatment methods in addressing the global challenge of environmental pollution. This review identifies the opportunities and challenges for microalgae-based technology and proposed suggestions for future studies to tackle challenges. The findings of this review advance our understanding of the potential of microalgae-based technology wastewater treatment.

A systematic review of antibiotics and antibiotic resistance genes (ARGs) in mariculture wastewater: Antibiotics removal by microalgal-bacterial symbiotic system (MBSS), ARGs characterization on the metagenomic

Antibiotic residues in mariculture wastewater seriously affect the aquatic environment. Antibiotic Resistance Genes (ARGs) produced under antibiotic stress flow through the environment and eventually enter the human body, seriously affecting human health. Microalgal-bacterial symbiotic system (MBSS) can remove antibiotics from mariculture and reduce the flow of ARGs into the environment. This review encapsulates the present scenario of mariculture wastewater, the removal mechanism of MBSS for antibiotics, and the biomolecular information under metagenomic assay. When confronted with antibiotics, there was a notable augmentation in the extracellular polymeric substances (EPS) content within MBSS, along with a concurrent elevation in the proportion of protein (PN) constituents within the EPS, which limits the entry of antibiotics into the cellular interior. Quorum sensing stimulates the microorganisms to produce biological responses (DNA synthesis - for adhesion) through signaling. Oxidative stress promotes gene expression (coupling, conjugation) to enhance horizontal gene transfer (HGT) in MBSS. The microbial community under metagenomic detection is dominated by aerobic bacteria in the bacterial-microalgal system. Compared to aerobic bacteria, anaerobic bacteria had the significant advantage of decreasing the distribution of ARGs. Overall, MBSS exhibits remarkable efficacy in mitigating the challenges posed by antibiotics and resistant genes from mariculture wastewater.

Treatment of agricultural wastewater using microalgae: A review

The rapid development of agriculture has led to a large amount of wastewater, which poses a great threat to environmental safety. Microalgae, with diverse species, nutritional modes and cellular status, can adapt well in agricultural wastewater and absorb nutrients and remove pollutants effectively. Besides, after treatment of agricultural wastewater, the accumulated biomass of microalgae has broad applications, such as fertilizer and animal feed. This paper reviewed the current progresses and further perspectives of microalgae-based agricultural wastewater treatment. The characteristics of agricultural wastewater have been firstly introduced; Then the microalgal strains, cultivation modes, cellular status, contaminant metabolism, cultivation systems and biomass applications of microalgae for wastewater treatment have been summarized; At last, the bottlenecks in the development of the microalgae treatment methods, as well as recommendations for optimizing the adaptability of microalgae to wastewater in terms of wastewater pretreatment, microalgae breeding, and microalgae-bacterial symbiosis systems were discussed. This review would provide references for the future developments of microalgae-based agricultural wastewater treatment.

A vertical-flow constructed wetland-microalgal membrane photobioreactor integrated system for treating high-pollution-load marine aquaculture wastewater: A lab-scale study

Individual biological water treatment techniques often prove ineffective in removing accumulated high concentrations of nitrogen and phosphorus in the late stages of biofloc aquaculture. To address this issue, we integrated a previously developed autotrophic denitrification and nitrification integrated constructed wetland (ADNI-CW) with a microalgal membrane photobioreactor (MPBR). Under high nitrogen and phosphorus pollution loads in the influent, the standalone ADNI-CW system achieved removal rates of only 24.17 % ± 2.82 % for total nitrogen (TN) and 25.30 % ± 2.59 % for total phosphorus (TP). The optimal conditions for TN and TP degradation and microalgal biomass production in the Chlorella MPBR, determined using response surface methodology, were an inoculum OD680 of 0.394, light intensity of 161.583 μmol/m2/s, and photoperiod of 16.302 h light:7.698 h dark. Under the optimal operating conditions, the integrated ADNI-CW-MPBR system achieved remarkable TN and TP removal rates of 92.63 % ± 2.8 % and 77.46 % ± 8.41 %, respectively, and a substantial microalgal biomass yield of 54.58 ± 6.8 mg/L/day. This accomplishment signifies the successful achievement of efficient nitrogen and phosphorus removal from high-pollution-load marine aquaculture wastewater along with the acquisition of valuable microalgal biomass. A preliminary investigation of the microbial community composition and algal-bacterial interactions in different operational stages of the MPBR system revealed that unclassified_d__Bacteria, Chlorophyta, and Planctomycetes were predominant phyla. The collaborative relationships between bacteria and Chlorella surpassed competition, ensuring highly efficient nitrogen and phosphorus removal in the MPBR system. This study laid the foundation for the green and sustainable development of the aquaculture industry.

Mixotrophy, a more promising culture mode: Multi-faceted elaboration of carbon and energy metabolism mechanisms to optimize microalgae culture

Some mixotrophic microalgae appear to exceed the sum of photoautotrophy and heterotrophy in terms of biomass production. This paper mainly reviews the carbon and energy metabolism of microalgae to reveal the synergistic mechanisms of the mixotrophic mode from multiple aspects. It explains the shortcomings of photoautotrophic and heterotrophic growth, highlighting that the mixotrophic mode is not simply the sum of photoautotrophy and heterotrophy. Specifically, microalgae in mixotrophic mode can be divided into separate parts of photoautotrophic and heterotrophic cultures, and the synergistic parts of photoautotrophic culture enhance aerobic respiration and heterotrophic culture enhance the Calvin cycle. Additionally, this review argues that current deficiencies in mixotrophic culture can be improved by uncovering the synergistic mechanism of the mixotrophic mode, aiming to increase biomass growth and improve quality. This approach will enable the full utilization of advantagesin various fields, and provide research directions for future microalgal culture.

Effect of mariculture wastewater concentrations on high-value production and pollutants removal with bacterial-algal coupling reactor (BACR)

To achieve the goal of cost-effective mariculture wastewater treatment, a novel Bacteria-Algae Coupling Reactor (BACR) integrating acidogenic fermentation with microalgae cultivation was applied for the mariculture wastewater treatment. Currently, there is limited research on the impact of different concentrations of mariculture wastewater on the pollutant removal and the high-value products recovery. In this study, different concentrations (4, 6, 8, and 10 g/L) of mariculture wastewater were treated with BACR. The results showed thatoptimalMW concentrations of 8 g/L improved the growth viability and biochemical components synthetic of Chlorella vulgaris, which increased the potential for high-value products recovery. The BACR exhibited the excellent removal efficiency of chemical oxygen demand, ammonia-nitrogen and total phosphorus with 82.30%, 81.12% and 96.40%, respectively. This study offers an ecological and economic approach to improve the MW treatment through the utilization of a novel bacterial-algal coupling system.

Unexpected growth promotion of Chlorella sacchrarophila triggered by herbicides DCMU

The ecotoxicological effects of herbicide contamination on the autotrophic growth of microalgae in aquatic environments have been major concerns. However, little is known about the influence of herbicides on the mixotrophic growth of microalgae. This study investigated the ecotoxicological effect of 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (DCMU) on the mixotrophic growth of Chlorella sacchrarophila FACHB 4. Results showed that C. sacchrarophila in mixotrophy was more resistant to DCMU than in photoautotrophy. Moreover, a low content of DCMU (20-80 μg·L^-1) promoted the mixotrophic growth of C. sacchrarophila, and the promotion effect was obviously enhanced with the increase in light intensity. The chlorophyll content and glucose absorption rate of C. sacchrarophila were found to increase after incubation with DCMU for 24 h. Transcriptome analyses revealed that the mechanism of DCMU to promote the mixotrophic growth of C. sacchrarophila was probably through accelerating glucose uptake and utilization, which was accomplished by reducing photodamage and increasing the chlorophyll content of C. sacchrarophila. This study not only revealed an unexpected bloom of mixotrophic microalgae triggered by herbicides, but it also shed new light on an effective and low-cost strategy to improve the microalgae productivity for utilization.

Elucidating microalgae-mediated metabolism for sulfadiazine removal mechanism and transformation pathways

Sulfadiazine (SDZ) as a typical sulfonamide antibiotic is commonly detected in wastewater, and its removal mechanism and transformation pathways in microalgae-mediated system remain unclear. In this study, the SDZ removal through hydrolysis, photodegradation, and biodegradation by Chlorella pyrenoidosa was investigated. Higher superoxide dismutase activity and biochemical components accumulation were obtained under SDZ stress. The SDZ removal efficiencies at different initial concentrations were 65.9-67.6%, and the removal rate followed pseudo first-order kinetic model. Batch tests and HPLC-MS/MS analyses suggested that biodegradation and photodegradation through the reactions of amine group oxidation, ring opening, hydroxylation, and the cleavage of S-N, C-N, C-S bond were dominant removal mechanisms and pathways. Characteristics of transformation products were evaluated to analyze their environmental impacts. High-value products of lipid, carbohydrate, and protein in microalgae biomass presented economic potential of microalgae-mediated metabolism for SDZ removal. The findings of this study broadened the knowledge for the microalgae self-protection from SDZ stress and provided a deep insight into SDZ removal mechanism and transformation pathways.

Enhanced alginate-like exopolymers recovery from algal-bacterial aerobic granular sludge: Optimal cultivation condition and contribution of bacteria and microalgae during the transport/storage period

Extracting alginate-like exopolymers (ALE) is a promising approach for valuable resources recovery from excess algal-bacterial aerobic granular sludge (AGS) to achieve circular bioeconomy and environmental sustainability in wastewater treatment plants (WWTPs). In this study, six batch cultivation tests were conducted to investigate the optimal cultivation duration or transport/storage period, light intensity, and temperature for algal-bacterial AGS after sampling and before further processing or ALE extraction. At a light intensity of 5 klux, the highest ALE content (36.33 mg/g-VSS) was detected at a low temperature of 10°C, which increased by 300% from its original level after 6-h cultivation. Results from levofloxacin (LVX) exposure and dark condition imply that microalgae contributed more to ALE synthesis in the algal-bacterial granules. This work not only provides a better understanding of the mechanisms involved in ALE biosynthesis but also offers useful guidance for maintaining or improving ALE recovery after algal-bacterial biomass sampling.

Potential interactive effect on biomass and bio-polymeric substances of microalgal-bacterial aerobic granular sludge as a valuable resource for sustainable development

The algal/bacterial biomass and extracellular polymeric substances (EPSs) existing in microalgal-bacterial aerobic granular sludge (MB-AGS) offer a promising bioresource. The current review-based paper presents a systematic overview of the compositions and interactions (gene transfer, signal transduction, and nutrient exchange) of microalgal and bacteria consortia, the role of cooperative or competitive partnerships of MB-AGS in the treatment of wastewater and recovery of resource, and the environmental/operational factors affecting their interactions and EPS production. Moreover, a brief notes is given on the opportunities and major challenges of utilizing the microalgal-bacterial biomass and EPS for phosphorus and polysaccharides chemical recovery, renewable energy (i.e. biodiesel, hydrogen, electricity) production. Overall, this compact review will pave the way for developing MB-AGS future biotechnology.

Mixotrophic cultivation of Chlorella pyrenoidosa under sulfadiazine stress: High-value product recovery and toxicity tolerance evaluation

Sulfadiazine (SDZ) as a common sulfonamide antibiotic is frequently detected in wastewater, but there is little information on the high-value product recovery and toxicity tolerance evaluation of mixotrophic microalgae under SDZ stress. In this study, effects of SDZ on growth, photosynthesis, cellular damage, antioxidant capacity and intracellular biochemical components of Chlorella pyrenoidosa were investigated. Results showed that the growth of C. pyrenoidosa was inhibited by about 20% under high SDZ stress, but there was little impact on photosynthesis. Cellular damage and antioxidant capacity were evaluated using malondialdehyde (MDA) content and superoxide dismutase (SOD) activity to further explain the toxicity tolerance of mixotrophic microalgae. The SDZ stress not only increased lipid and carbohydrate content, respectively attaining to the maximum of 390.0 and 65.4 mg/L, but also improved the biodiesel quality of C. pyrenoidosa. The findings show the potential of mixotrophic microalgae for biodiesel production and wastewater treatment.

Adsorption of sulfamethoxazole via biochar: The key role of characteristic components derived from different growth stage of microalgae

Converting microalgal biomass residues into biochar (BC) after microalgal wastewater treatment is a popular approach that can produce an adsorbent to treat refractory organic pollutants. Moreover, the adsorption efficiency via BC is closely associated with the surface morphology, which may be determined by the composition of the microalgal biomass. However, the intrinsic relationship and advanced mechanism between the adsorption efficiency and microalgal composition have not been thoroughly investigated. In this work, four microalgal BCs were prepared from Chlamydomonas sp. QWY37 (CBC) after collection from four different growth stages of microalgal biomass during wastewater treatment. The adsorption performance for sulfamethoxazole indicates that the CBC collected in the mid-log phase (CBC_L-M) possessed the best adsorption capacity (287.89 mg/g) owing to the higher decomposition of the microalgal cellular protein concentration (70%). Meanwhile, a higher protein content contributed to the largest specific surface area (42.16 m²/g), maximum pore volume (0.037 cm³/g) and abundant surface functional groups of the CBC_L-M. Furthermore, based on the theoretical calculation of the structural analysis, the adsorption mechanism was a multilayer adsorption process in accordance with the Freundlich isotherm. Additionally, the strong hydrogen bond, electron donor-acceptor interaction and electrostatic attraction were the main adsorption mechanisms due to the carboxyl/ester functional groups. The results of this research provide a novel perspective on the reasonable harvest of microalgal biomass for BC fabrication and large-scale implementation of microalgal BC in future applications.

Metagenomics and network analysis elucidating the coordination between fermentative bacteria and microalgae in a novel bacterial-algal coupling reactor (BACR) for mariculture wastewater treatment

To achieve the goal of treating mariculture wastewater economically and efficiently, a novel bacterial-algal coupling reactor (BACR) integrating acidogenic fermentation and microalgae cultivation was firstly investigated for mariculture wastewater treatment. Volatile fatty acids (VFAs) generated in the dark chamber migrated into the photo chamber for microalgal utilization, which alleviated the pH drop and feedback inhibition of the acidogenic fermentation. The maximum dry cell weight (DCW) of microalgae was 1.46 g/L, and pollutants such as chemical oxygen demand (COD), ammonium (NH₄⁺-N) and total phosphorus (TP) in the BACR were effectively removed under the mixotrophic culture condition. Furthermore, bacterial community profiles and functional genes in the BACR and single acidogenic fermentation reactor were identified. Compared with the single acidogenic fermentation reactor, most of the fermentative bacteria (e.g., Ruminococcus, Christensenellaceae R-7 group, Exiguobacterium, Pseudomonas and Levilinea) were enriched by the BACR. From the genetic perspective, the abundances of dominant genes (ackA, acs and atoD) associated with acetic, propionic and butyric acid production were greatly enhanced in the BACR. In the fatty acid biosynthesis pathway (ko00061), three kinds of high-abundance acetyl-CoA carboxylase genes and eight kinds of downstream functional genes were up-regulated in the BACR. Finally, based on co-occurrence network analysis, the coordination between fermentative bacteria and microalgae in the BACR was revealed. This study provided a deep insight into the advantage and potential of the BACR in mariculture wastewater treatment.

Calcium ions-effect on performance, growth and extracellular nature of microalgal-bacterial symbiosis system treating wastewater

Microalgal-bacterial symbiosis (MABS) system treating wastewater has attracted great concern because of its advantages of carbon dioxide reduction and biomass energy production. However, due to the low density and negative surface charge of microalgae cells, the sedimentation and harvesting performance of microalgae biomass has been one limitation for the application of MABS system on wastewater treatment. This study investigated the performance enhancement of microalgae harvesting and wastewater treatment contributed by calcium ions (i.e., Ca²⁺) in the MABS system. Results showed that a low Ca²⁺ loading (i.e., 0.1 mM) promoted both COD and nutrients removal, with growth rates of 11.95, 6.53 and 1.21% for COD, TN and TP compared to control, and chlorophyll a was increased by 64.15%. Differently, a high Ca²⁺ loading (i.e., 10 mM) caused removal reductions by improving the aggregation of microalgae, with reduction rates of 34.82, 3.50 and 10.30% for COD, NH₄⁺-N and TP. Mechanism analysis indicated that redundant Ca²⁺ adsorbed on MABS aggregates and dissolved in wastewater decreased the dispersibility of microalgae cells by electrical neutralization and compressed double electric layer. Moreover, the presence of Ca²⁺ could improve extracellular secretions and promoted flocculation performance, with particle size increasing by 336.22%. The findings of this study may provide some solutions for the enhanced microalgae biomass harvest and nutrients removal from wastewater.

Pollution Control of Industrial Mariculture Wastewater: A Mini-Review

With the rapid development of intensive mariculture, lots of mariculture wastewaters containing residual feed and excrements are discharged into marinelands, leading to coastal pollution. Recently, the environmental problems caused by the discharge of mariculture wastewater have been paid much attention, as have other breeding industries in China. In fact, organic solid waste accounts for most of the pollutants and can be reduced by precipitation or filtration technologies, after which the supernatant can be easily treated by ecological methods. Some national guidelines and relevant local standards have been issued to strictly control the mariculture wastewater, but there are still few effective technologies for mariculture wastewater treatment due to its high salinity and extremely low pollutant concentration. This paper aims to propose feasible pollution control methods of mariculture wastewater according to the wastewater characteristics from different mariculture modes. For raw ammonia-based wastewater, it should be sequentially treated by precipitation, nitrification and denitrification and ecological methods, which would target solid waste, organic carbon/nitrogen and phosphorus removal, respectively. For the nitrate-based wastewater, this just needs denitrification filters and ecological methods for nitrate and phosphorus removal. After an overview of pollution control strategies for different types and scales of industrial mariculture wastewater treatment, some challenges are also mentioned.

Evaluation of the effects of input variables on the growth of two microalgae classes during wastewater treatment

Wastewater treatment carried out by microalgae is usually affected by the type of algal strain and the combination of cultivation parameters provided during the process. Every microalga strain has a different tolerance level towards cultivation parameters, including temperature, pH, light intensity, CO2 content, initial inoculum level, pretreatment method, reactor type and nutrient concentration in wastewater. Therefore, it is vital to supply the right combination of cultivation parameters to increase the wastewater treatment efficiency and biomass productivity of different microalgae classes. In the current investigation, the decision tree was used to analyse the dataset of class Trebouxiophyceae and Chlorophyceae. Various combinations of cultivation parameters were determined to enhance their performance in wastewater treatment. Nine combinations of cultivation parameters leading to high biomass production and eleven combinations each for high nitrogen removal efficiency and high phosphorus removal efficiency for class Trebouxiophyceae were detected by decision tree models. Similarly, eleven combinations for high biomass production, nine for high nitrogen removal efficiency, and eight for high phosphorus removal efficiency were detected for class Chlorophyceae. The results obtained through decision tree analysis can provide the optimum conditions of cultivation parameters, saving time in designing new experiments for treating wastewater at a large scale.