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

Ammonia-oxidizing activity and microbial structure of ammonia-oxidizing bacteria, ammonia-oxidizing archaea and complete ammonia oxidizers in biofilm systems with different salinities

Ammonia-oxidizing activity of different ammonia-oxidizing microorganisms (AOMs), such as ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and complete ammonia oxidizers (comammoxs), were investigated by adding the inhibitors such as 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, octyne, and KCLO3 in biofilm systems with different salinities. It was found that the ammonia-oxidizing activity of all AOMs gradually decreased with increasing salinity. The ammonia-oxidizing activity of AOB was consistently higher than those of AOA and comammox at different salinities. Moreover, nitrite-oxidizing bacteria (NOB) were more sensitive to changes in salinity than AOMs. Metagenomic analysis revealed that nitrifiers were detected at high level, with the AOB Nitrosomonas sp. comprising 24.9 % and the NOB Nitrospira sp. comprising 47.2 % of all nitrifiers. The main functional genes involved in the nitrification reaction were amoABC, hao, and nxrAB. This study demonstrates that higher abundance of functional microorganisms and genes is related to the ammonia-oxidizing activity and ammonia removal contribution rate.

Advancements and hurdles in symbiotic microalgal co-cultivation strategies for wastewater treatment

Microalgae offer significant potential in various industrial applications, such as biofuel production and wastewater treatment, but the economic barriers to their cultivation and harvesting have been a major obstacle. However, a promising strategy involving co-cultivating microalgae in wastewater treatment could overcome the limitations of monocultivation and open the possibility for increased integration of microalgae into various industrial processes. This symbiotic relationship between microalgae and other microbes can enhance nutrient removal efficiency, increase value-added bioproduct production, promote carbon capture, and decrease energy consumption. However, unresolved challenges, such as the competition between microalgae and other microbes within the wastewater treatment system, may result in imbalances and reduced efficiency. The complexity of managing multiple microbes in a co-cultivation system poses difficulties in achieving stability and consistency in bioproduct production. In response to these challenges, strategies such as optimizing nutrient ratios, manipulating environmental conditions, understanding the dynamics of microbial relationships, and employing genetic modification to enhance the metabolic capabilities of microalgae and improve their competitiveness are critical in transitioning to a more sustainable path. Hence, this review will provide an in-depth analysis of recent advancements in symbiotic microalgal co-cultivation for applications in wastewater treatment and CO2 utilization, as well as discuss approaches for improving microalgal strains through genetic modification. Furthermore, the review will explore the use of efficient bioreactors, advanced control systems, and advancements in biorefinery processes.

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.

Stable isotope labeling and functional gene prediction elucidate the carbon metabolism in fermentative bacteria and microalgae coupling system

The application of the fermentative bacteria and microalgae coupling system in the wastewater treatment has been studied, but there remains few knowledge regarding the organic and inorganic carbon metabolism within this system. In this study, the carbon metabolism of microalgae and fermentative bacteria was elucidated by 13C stable isotope labeling and functional gene prediction, respectively. The 13C glucose and 13C NaHCO3 were used as stable isotope tracers to clarify the organic and inorganic carbon metabolism of microalgae, indicating that approximately 71.5 % of the Acetyl-CoA in microalgae was synthesized from organic carbon sources, while 26.8 % was synthesized through the utilization of inorganic carbon sources. Inorganic carbon sources can enhance the activity of photosynthetic system and facilitate the Calvin cycle. Considering the adequate organic carbon sources and insufficient inorganic carbon sources in the fermentative bacteria and microalgae coupling system, NaHCO3 was added to improve carbon utilization of microalgae. The maximum microalgal lipid yield reached 1130.37 mg/L with 1000 mg/L NaHCO3 supplementation. Functional gene prediction was used to analysis the effect of various carbon composition on the bacterial carbon metabolism. Notably, the additional inorganic carbon sources increased the abundance of bacterial functional genes associated with the fermentation and acetic acids synthesis, which was advantageous for VFAs production and further promoted microalgae growth. This study can gain a deeper understanding of microbial metabolic mechanisms during the operation of fermentative bacteria and microalgae system, and improve its sustained operational stability.

Microalgal-bacterial interactions: Research trend and updated review

Microalgae are being recognized as the key contributor to sustainability in many sectors, starting from energy up to food industries. The microorganism has also been utilized as environmental remediator, capable of converting organic compounds into economically valuable biomass. To optimize the use of microalgae in these sectors, researchers have explored various approaches, of which is the use of bacteria. The interaction between bacteria and microalgae can potentially be harnessed, but its complexity requires extensive research. Herein, we present the bibliometric analysis on microalgal-bacterial interactions. The metadata of published literature was collected through Scopus database on August 4, 2023. The downloaded.csv file was uploaded to VOSViewer and biblioshiny for network visualization. We found that the research has gained a lot of attention from researchers since 2012 with an exponential increase of the publication number. The United States and China are leading the research with a strong collaboration. Based on the research sub-topic clusters, the interaction is mostly studied for wastewater treatment, biomass production, and algal bloom control. Updated reviews on this topic reveal that researchers are now focus on optimizing the efficacy of microalgae-bacteria system, investigating the modes of actions, and identifying challenges in its real-world implementation. The microalgal-bacterial interaction is a promising approach for microalgae utilization in wastewater treatment, biomass production, and algal bloom control.

Effect of light intensity and photoperiod on high-value production and nutrient removal performance with bacterial-algal coupling system

Direct discharge of mariculture wastewater can lead to eutrophication, posing a threat to aquatic ecosystems. A novel Bacteria-Algae Coupled Reactor (BACR) offers advantages in treating mariculture wastewater, which can effectively remove pollutants while simultaneously obtaining microalgal products. However, there is limited information available on how illumination affects the cultivation of mixotrophic microalgae in this bacteria-algae coupling system. Therefore, a combined strategy of photoperiod and light intensity regulation was employed to improve the biological mariculture wastewater remediation, promote microalgae biomass accumulation, and increase the high-value product yield in this study. Optimal light conditions could effectively enhance microalgal carbohydrate, protein, lipid accumulation and photosynthetic activity, with the carbohydrate, protein and lipid contents reached 44.11, 428.57 and 399.68 mg/L, respectively. Moreover, excellent removal rates were achieved for SCOD, NH4+-N and TP, reaching 86.68%, 87.35% and 95.13% respectively. This study proposes a comprehension of BACR processes in mariculture wastewater under different light conditions.

Sustainable management and valorization of biomass wastes using synthetic microbial consortia

In response to the persistent expansion of global resource demands, considerable attention has been directed toward the synthetic microbial consortia (SMC) within the domain of microbial engineering, aiming to address the sustainable management and valorization of biomass wastes. This comprehensive review systematically encapsulates the most recent advancements in research and technological applications concerning the utilization of SMC for biomass waste treatment. The construction strategies of SMC are briefly outlined, and the diverse applications of SMC in biomass wastes treatment are explored, with particular emphasis on its potential advantages in waste degradation, hazardous substances control, and high value-added products conversion. Finally, recommendations for the future development of SMC technology are proposed, and prospects for its sustainable application are discussed.