Municipal wastewater treatment via co-immobilized microalgal-bacterial symbiosis: Microorganism growth and nutrients removal

New insights into microalgal-bacterial immobilization systems for wastewater treatment: mechanisms, enhancement strategies, and application prospects

The wastewater treatment based on the symbiosis of microalgae and bacteria has attracted increasing attention for its excellent pollutant removal efficiency, energy savings, and resource recovery. Among them, the microalgae-bacteria immobilization (MABI) system stands out by enhancing the electron transfer efficiency through carrier domain confinement, thereby overcoming bottlenecks of low light energy utilization and challenging biomass recycling. MABI is considered a key breakthrough for advancing engineering applications. However, a comprehensive exploration of MABI systems remains lacking. This review systematically summarizes the latest advancements, covering major immobilization techniques and the intrinsic mechanisms underlying microalgae-bacteria interactions and electron transport. Additionally, it explores enhancement strategies aimed at balancing microbial light energy allocation, optimizing nutrient supply, and constructing complementary ecological niches. The advantages and application prospects of MABI systems are highlighted. The review contributes to structuring the knowledge framework of MABI research and identifies critical gaps for future investigation.

Removing high strength lincomycin in pharmaceutical wastewater by a bacteria microalgae consortium co-immobilized filter

Lincomycin (LIN) in pharmaceutical wastewater would enter municipal wastewater treatment plants and decrease their performance, leading to residual LIN enter the natural environment and pose serious eco-risk. In this study, a bacterium-microalgae consortium co-immobilized filter (BMCCF) was established and used to remove LIN in artificial pharmaceutical wastewater treatment plants effluents (PWWTPE). LIN removal mechanisms and degradation products' eco-toxicity was studied, and the abundance change of class 1 integrase gene (intI1) and antibiotic resistance genes (ARGs) was monitored. As a result, 98.54% of 82 mg L-1 LIN was removed within 7 days, LIN removal was mainly attributed to bio-degradation by the Bacillus subtilis strain, and LIN degradation products were less toxic than their substrate. Therefore, the BMCCF established in this study provides a promising alternative for the bio-treatment of pharmaceutical wastewater containing high concentration of LIN.

Performance, mechanism regulation and resource recycling of bacteria-algae symbiosis system for wastewater treatment: A review

The bacteria-algae synergistic wastewater treatment process not only efficiently eliminates nutrients and absorbs heavy metals, but also utilizes photosynthesis to convert light energy into chemical energy, generating valuable bioresource. The study systematically explores the formation, algal species, and regulatory strategies of the bacterial-algal symbiosis system. It provides a detailed analysis of various interaction mechanisms, with a particular focus on nutrient exchange, signal transduction, and gene transfer. Additionally, the efficacy of the system in removing nitrogen, phosphorus, and heavy metals, as well as its role in CO2 reduction and bioresource recycling, is thoroughly elaborated. Potential future research of bacteria-algae cell factory producing bioenergy production, feed or fertilizers are summarized. This paper clearly presents effective strategies for efficiently removing pollutants, reducing carbon emissions, and promoting resource recycling in the field of wastewater treatment. It also provides recommendations for further research on utilizing microbial-algal symbiotic systems to remove novel pollutants from wastewater and extract value-added products from the resulting biomass.

Microalgae growth-promoting bacteria for cultivation strategies: Recent updates and progress

Microalgae growth-promoting bacteria (MGPB), both actinobacteria and non-actinobacteria, have received considerable attention recently because of their potential to develop microalgae-bacteria co-culture strategies for improved efficiency and sustainability of the water-energy-environment nexus. Owing to their diverse metabolic pathways and ability to adapt to diverse conditions, microalgal-MGPB co-cultures could be promising biological systems under uncertain environmental and nutrient conditions. This review proposes the recent updates and progress on MGPB for microalgae cultivation through co-culture strategies. Firstly, potential MGPB strains for microalgae cultivation are introduced. Following, microalgal-MGPB interaction mechanisms and applications of their co-cultures for biomass production and wastewater treatment are reviewed. Moreover, state-of-the-art studies on synthetic biology and metabolic network analysis, along with the challenges and prospects of opting these approaches for microalgal-MGPB co-cultures are presented. It is anticipated that these strategies may significantly improve the sustainability of microalgal-MGPB co-cultures for wastewater treatment, biomass valorization, and bioproducts synthesis in a circular bioeconomy paradigm.

Global diversity of airborne pathogenic bacteria and fungi from wastewater treatment plants

Wastewater treatment plants (WWTPs) have been recognized as one of the major potential sources of the spread of airborne pathogenic microorganisms under the global pandemic of COVID-19. The differences in research regions, wastewater treatment processes, environmental conditions, and other aspects in the existing case studies have caused some confusion in the understanding of bioaerosol pollution characteristics. In this study, we integrated and analyzed data from field sampling and performed a systematic literature search to determine the abundance of airborne microorganisms in 13 countries and 37 cities across four continents (Asia, Europe, North America, and Africa). We analyzed the concentrations of bioaerosols, the core composition, global diversity, determinants, and potential risks of airborne pathogen communities in WWTPs. Our findings showed that the culturable bioaerosol concentrations of global WWTPs are 102-105 CFU/m3. Three core bacterial pathogens, namely Bacillus, Acinetobacter, and Pseudomonas, as well as two core fungal pathogens, Cladosporium and Aspergillus, were identified in the air across global WWTPs. WWTPs have unique core pathogenic communities and distinct continental divergence. The sources of airborne microorganisms (wastewater) and environmental variables (relative humidity and air contaminants) have impacts on the distribution of airborne pathogens. Potential health risks are associated with the core airborne pathogens in WWTPs. Our study showed the specificity, multifactorial influences, and potential pathogenicity of airborne pathogenic communities in WWTPs. Our findings can improve the understanding of the global diversity and biogeography of airborne pathogens in WWTPs, guiding risk assessment and control strategies for such pathogens. Furthermore, they provide a theoretical basis for safeguarding the health of WWTP workers and ensuring regional ecological security.

Microalgal-bacterial immobilized co-culture as living biofilters for nutrient recovery from synthetic wastewater and their potential as biofertilizers

This study investigates nutrient recovery from synthetic municipal wastewater using co-immobilized cultures of Chlorella vulgaris TISTR 8580 (CV) and plant growth-promoting bacteria, Bacillus subtilis TISTR 1415 (BS) as living biofilters for a subsequent biofertilizer activity. The optimal condition for nutrient recovery was at the 1:1 ratio of CV/BS using mixed guar gum/carrageenan (GG/CG) binders. After 7-day wastewater treatment, the living biofilters removed 86.7 ± 0.5% of ammonium and 99.3 ± 0.3% of phosphates and were tested subsequently as biofertilizers for 20 days to grow selected plants. The highest optimal biomass and chlorophyll a content was 2 ± 0.3 g (CV/BS 3:1) and 12.4 ± 0.7 µg/g (CV/BS 1:1) from cucumber respectively, however, the close-to-neutral pH (8.0 ± 0.3) was observed from sunflower using CV/BS 1:1 living biofilters. Conclusively, the designed living biofilters exhibit the potential to recover nutrients from wastewater and be used as biofertilizers for circular agriculture.

Immobilized microalgae: principles, processes and its applications in wastewater treatment

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Mechanism of enhanced microalgal biomass and lipid accumulation through symbiosis between a highly succinic acid-producing strain of Escherichia coli SUC and Aurantiochytrium sp. SW1

Microalgae, known for rapid growth and lipid richness, hold potential in biofuels and high-value biomolecules. The symbiotic link with bacteria is crucial in large-scale open cultures. This study explores algal-bacterial interactions using a symbiotic model, evaluating acid-resistant Lactic acid bacteria (LAB), stress-resilient Bacillus subtilis and Bacillus licheniformis, and various Escherichia coli strains in the Aurantiochytrium sp. SW1 system. It was observed that E. coli SUC significantly enhanced the growth and lipid production of Aurantiochytrium sp. SW1 by increasing enzyme activity (NAD-IDH, NAD-ME, G6PDH) while maintaining sustained succinic acid release. Optimal co-culture conditions included temperature 28 °C, a 1:10 algae-to-bacteria ratio, and pH 8. Under these conditions, Aurantiochytrium sp. SW1 biomass increased 3.17-fold to 27.83 g/L, and total lipid content increased 2.63-fold to 4.87 g/L. These findings have implications for more efficient microalgal lipid production and large-scale cultivation.

A microbial flora with superior pollutant removal efficiency and its fermentation process optimization

Microbial flora plays an important role in microorganism-enhanced technology. The pollutant degradation ability and viable counts of these agents are crucial to guarantee their practical application. In this study, an efficient pollutant-degrading microbial flora was screened, its medium components and culture conditions were optimized, and its effect was verified in zeolite trickling filter towers. After a 24 h culture under the optimal conditions, the viable count reached 4.76 × 109 cfu/mL, with the degradation rates of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) increased to 93.5%, 100%, 68.3%, 32.6%, and 85%, respectively. After optimizing the feeding strategy, the concentration of viable bacteria reached 5.80 × 109 cfu/mL. In the application effect verification experiment, the degradation rates of NH4+-N, TN, TP, and COD in the experimental group reached 96.69%, 75.18%, 73.82%, and 90.83%, respectively, showing a significant improvement compared to the results of the control group. The main components in the control group were Dokdonella, Brevundimonas, Alishewanella, Rhodobacter, Pseudoxanthomonas, and Thauera, whereas those in the experimental group were Dokdonella, Proteocatella, Rhodobacter, Dechlomonas, and Nitrospira. Proteocatella, Dechlomonas, and Nitrosra, which were unique to the experimental group, are common bacteria used for nitrogen and phosphorus removal. This explains the difference in the sewage treatment capacity between the two groups. This study provides an alternative sewage treatment microbial flora with a reasonable production cost and high degradation efficiency for NH4+-N, TN, TP, and COD.

A review on microalgal-bacterial co-culture: The multifaceted role of beneficial bacteria towards enhancement of microalgal metabolite production

Mass microalgal-bacterial co-cultures have come to the fore of applied physiological research, in particularly for the optimization of high-value metabolite from microalgae. These co-cultures rely on the existence of a phycosphere which harbors unique cross-kingdom associations that are a prerequisite for the cooperative interactions. However, detailed mechanisms underpinning the beneficial bacterial effects onto microalgal growth and metabolic production are rather limited at the moment. Hence, the main purpose of this review is to shed light on how bacteria fuels microalgal metabolism or vice versa during mutualistic interactions, building upon the phycosphere which is a hotspot for chemical exchange. Nutrients exchange and signal transduction between two not only increase the algal productivity, but also facilitate in the degradation of bio-products and elevate the host defense ability. Main chemical mediators such as photosynthetic oxygen, N-acyl-homoserine lactone, siderophore and vitamin B12 were identified to elucidate beneficial cascading effects from the bacteria towards microalgal metabolites. In terms of applications, the enhancement of soluble microalgal metabolites is often associated with bacteria-mediated cell autolysis while bacterial bio-flocculants can aid in microalgal biomass harvesting. In addition, this review goes in depth into the discussion on enzyme-based communication via metabolic engineering such as gene modification, cellular metabolic pathway fine-tuning, over expression of target enzymes, and diversion of flux toward key metabolites. Furthermore, possible challenges and recommendations aimed at stimulating microalgal metabolite production are outlined. As more evidence emerges regarding the multifaceted role of beneficial bacteria, it will be crucial to incorporate these findings into the development of algal biotechnology.

Quorum Sensing as a Trigger That Improves Characteristics of Microbial Biocatalysts

Quorum sensing (QS) of various microorganisms (bacteria, fungi, microalgae) today attracts the attention of researchers mainly from the point of view of clarifying the biochemical basics of this general biological phenomenon, establishing chemical compounds that regulate it, and studying the mechanisms of its realization. Such information is primarily aimed at its use in solving environmental problems and the development of effective antimicrobial agents. This review is oriented on other aspects of the application of such knowledge; in particular, it discusses the role of QS in the elaboration of various prospective biocatalytic systems for different biotechnological processes carried out under aerobic and anaerobic conditions (synthesis of enzymes, polysaccharides, organic acids, etc.). Particular attention is paid to the biotechnological aspects of QS application and the use of biocatalysts, which have a heterogeneous microbial composition. The priorities of how to trigger a quorum response in immobilized cells to maintain their long-term productive and stable metabolic functioning are also discussed. There are several approaches that can be realized: increase in cell concentration, introduction of inductors for synthesis of QS-molecules, addition of QS-molecules, and provoking competition between the participants of heterogeneous biocatalysts, etc.).

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Advancement on mixed microalgal-bacterial cultivation systems for nitrogen and phosphorus recoveries from wastewater to promote sustainable bioeconomy

Biological wastewater treatment is a promising and environmentally friendly method that utilises living microorganisms to remediate water and enable recovery or conversion of contaminants into valuable products. For many decades, microalgae and cyanobacteria, photosynthetic living microorganisms, have been explored extensively for wastewater bioremediation. They can be used for recovering valuable nutrients such as nitrogen and phosphorous from secondary effluents and capable of transforming those nutrients into marketable products such as biofuels, biofertilisers, nutraceutical, and pigments for promoting a Bio-Circular Green economy. In recent years, there has been a shift towards mixing compatible microalgae with bacteria, which is inspired by their natural symbiotic relationships to increase nitrogen and phosphorus recoveries. With this enhanced bioremediation, recovery of polluted wastes can be intensified and higher biomass quality (with high nutrient density) can be achieved. This review focuses on the state-of-the-art of mixed microalgal-bacterial cultivating systems. A comprehensive comparison of existing studies that used Chlorella species as microalgae in various mixed microalgal-bacterial cultivating systems (suspension, biofilm, and immobilisation) for nitrogen and phosphorus recoveries from wastewater is conducted. Key technical challenges such as balancing microalgae and bacteria species, pH regulation, light distribution, biomass harvesting, and biomass conversion are also discussed. From the data comparisons among different cultivation systems, it has been suggested that immobilisation appears to require less amount of operational light compared to the suspended and biofilm-based systems for similar nitrogen and phosphorus removal efficiencies.

Biotechnological Approaches for Biomass and Lipid Production Using Microalgae Chlorella and Its Future Perspectives

Heavy reliance on fossil fuels has been associated with increased climate disasters. As an alternative, microalgae have been proposed as an effective agent for biomass production. Several advantages of microalgae include faster growth, usage of non-arable land, recovery of nutrients from wastewater, efficient CO₂ capture, and high amount of biomolecules that are valuable for humans. Microalgae Chlorella spp. are a large group of eukaryotic, photosynthetic, unicellular microorganisms with high adaptability to environmental variations. Over the past decades, Chlorella has been used for the large-scale production of biomass. In addition, Chlorella has been actively used in various food industries for improving human health because of its antioxidant, antidiabetic, and immunomodulatory functions. However, the major restrictions in microalgal biofuel technology are the cost-consuming cultivation, processing, and lipid extraction processes. Therefore, various trials have been performed to enhance the biomass productivity and the lipid contents of Chlorella cells. This study provides a comprehensive review of lipid enhancement strategies mainly published in the last five years and aimed at regulating carbon sources, nutrients, stresses, and expression of exogenous genes to improve biomass production and lipid synthesis.

A review on algal-bacterial symbiosis system for aquaculture tail water treatment

Aquaculture is one of the fastest growing fields of global food production industry in recent years. To maintain the ecological health of aquaculture water body and the sustainable development of aquaculture industry, the treatment of aquaculture tail water (ATW) is becoming an indispensable task. This paper discussed the demand of environmentally friendly and cost-effective technologies for ATW treatment and the potential of algal-bacterial symbiosis system (ABSS) in ATW treatment. The characteristics of ABSS based technology for ATW treatment were analyzed, such as energy consumption, greenhouse gas emission, environmental adaptability and the possibility of removal or recovery of carbon, nitrogen and phosphorus as resource simultaneously. Based on the principle of ABSS, this paper introduced the key environmental factors that should be paid attention to in the establishment of ABSS, and then summarized the species of algae, bacteria and the proportion of algae and bacteria commonly used in the establishment of ABSS. Finally, the reactor technologies and the relevant research gaps in the establishment of ABSS were reviewed and discussed.

Corncob biocarriers with available carbon release for Chlamydopodium sp. microalgae towards enhanced nitrogen removal from low C/N rare earth element tailings (REEs) wastewater

Low nitrogen (N) removal efficiency limits the potential of microalgae technology for the treatment of high nitrogen and low carbon rare earth tailings (REEs) wastewater. In this study, waste corncob was utilized as a biocarrier immobilizing Chlamydopodium sp. microalgae to realize high-efficient treatment of the REEs wastewater. In only 2.5 d, corncob-immobilized microalgae allowed the residual concentrations of N lower than the emission standards, and ammonia nitrogen (NH4+-N) removal rate is 83.3 mg L-1·d-1, total inorganic nitrogen (TIN) removal rate is 86.7 mg L-1·d-1, which was 18.5 times that of the previously-reported microalgae (4.68 mg L-1·d-1). Compared with other microalgae immobilization carriers, corncob possesses the ability to release available carbon sources for microalgae. Composition analysis and sugar verification experiments showed that the main content of TOC released by corncob was monosaccharide, and in a certain range, the removal rate of N was positively correlated with the TOC concentration. The utilization of biomass wastes with dual functions as biological carriers has great potential to improve the performance of microalgae, and is conducive to the development of engineering applications.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

Biochemical pathways and associated microbial process of di-2-ethyl hexyl phthalate (DEHP) enhanced degradation by the immobilization technique in sequencing batch reactor

A bacterial strain ASLT-13 was successfully isolated from activated sludge and identified as Pseudomonas amygdali. Gas chromatograph-mass spectrometer (GC-MS) analysis indicated that strain ASLT-13 could completely mineralize di 2-ethyl hexyl phthalate (DEHP). DEHP was first metabolized from the longer side chain of the benzene ring into shorter branches (Phatlalic mono-esters) like Dibutyl phthalate (DBP) under the action of degrading genes. DBP was then converted into di-methyl phthalate (DMP), and then hydrolysed to phthalic acid (PA). PA was eventually converted to CO₂ and H₂O through the TCA cycle. The optimal conditions for immobilization were the sodium alginate (SA) concentration of 6%, CaCl₂ concentration of 5%, ratio of bacteria and SA of 1:1, crosslinking time of 6 h. Bacterial quantity and community structure in sequencing batch reactors (SBRs) was investigated by q-PCR and high-throughput sequencing. The results indicated that DEHP removal efficiency was significantly enhanced by immobilization. Arthrobacter, Acinetobacter, Bacillus and Rhodococcus were the predominant genera for DEHP degradation. This study suggested that the cell immobilization technology had a potential application in DEHP wastewater treatment.

Performance of an immobilized microalgae-based process for wastewater treatment and biomass production: Nutrients removal, lipid induction, microalgae harvesting and dewatering

Immobilized microalgae are good for wastewater treatment and biomass production. This study investigated treatment efficiency of a continuously operated system employing immobilized microalgae for secondary effluent of wastewater treatment plants, as well as the effectiveness on induction of valuable products, harvesting and dewatering of microalgae biomass. Under semi-continuous operation condition, microalgal dry weight increased 4.75 times within 2 d, associated with the highest removal rate of ammonia and phosphate at 28.95 mg/L·d and 4.83 mg/L·d, respectively. An immobilized microalgae membrane bioreactor (iMBR) was continuously operated for a month. The harvested immobilized microalgae beads were transferred to induction stage to obtain 4.5 times increase of lipid content per cell within 2 d. Immobilized microalgae performed 1.9 cm/s settling velocity and 97% water removal efficiency around 40 °C. A prospective integrated process on resource recovery and carbon neutrality was proposed for wastewater treatment, induction, harvesting and dewatering of immobilized microalgae cells.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.

Symbiotic treatment of ammonia-nitrogen wastewater by algae and activated sludge: effects of algae and sludge inoculation rates

A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. It was composed of microalgae and activated sludge and established in the SBR to explore the effect of different dosing ratios of algae and sludge on the removal of nitrogen and phosphorus from simulated wastewater containing ammonium. It can be seen from the result that varied algae-sludge dosing ratios had a higher removal effect on COD removal, but the difference was not significant. The algal-bacterial symbiosis system had a 100% removal rate for ammonium removal on the 8th day. Relatively speaking, the removal of nutrients and related mechanisms vary with environmental conditions (inoculation rate). In general, when the additive ratio was 5:1 (algae: AS), the removal rate of TN and TP was the highest, reaching 53.85% and 85.13% in the shortest time (14 days), among them, the removal rate of ammonium and COD was 100%, and the reduction rates of Nitrite nitrogen and Nitrate nitrogen were 362.99% and 73.42%, respectively. In addition, 16S rDNA gene analysis results demonstrated that the microbial community in the reactor with algal sludge inoculation ratio of 5:1 had differences in three stages of the initial reaction, the middle reaction and the end of the reaction. Comamonadaceae, Flavobacterium, Paenarthrobacter, Mesorhizobium, Nitrobacter were enriched during the reaction operation.

Volatile organic compounds involved in the communication of microalgae-bacterial association extracted through Headspace-Solid phase microextraction and confirmed using gas chromatography-mass spectrophotometry

In the present study, bacterial mixture (Rhizobium and Agrobacterium) and axenic Chlorella were cultivated individually, in a mixed (co-cultured) form, and through headspace connections to study volatile organic compounds (VOCs) profile and their effect on growth. Results indicated that VOCs produced by the axenic microalgae and microalgae co-cultured with bacteria were significantly different. Axenic Chlorella predominantly produced a flavouring organic compound 2-pentadecanone (69.54%), bacterial mixed culture produced 1-decanone, 1,2,3-butanetriol, and quinoline (15-20%), and direct co-culturing of Chlorella with bacteria predominantly produced 2-pentadecanone (32.4 %). When they were allowed to communicate distantly through headspace connection, highly diversified VOCs in large numbers but low quantities were noted, predominantly 1,2-propanediol (28.82 %). In addition, growth of the co-cultured Chlorella was 1.5 times higher, while Chlorella in headspace connection with bacterial mixture exhibited ∼ 3.2 times increase in growth compared to the axenic Chlorella, indicating the essential role of VOCs in growth and communication.

The performance of co-immobilized strains isolated from activated sludge combined with Scenedesmus quadricauda to remove nutrients and organics in black odorous water

In this study, three bacteria were isolated from activated sludge (Pseudomonas aeruginosa, Bacillus subtilis, and Dietzia maris). After that, isolated strains and Scenedesmus quadricauda that could degrade refractory organics, as co-immobilization species, were prepared gel beads to treat black odorous water. Under the optimized conditions, the removal rate of chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total nitrogen (TN) and total phosphorus (TP) reached 94.36%, 95.7%, 91.22% and 95.27%, respectively, and organics (including aromatic proteins and microbial-by-product-like compounds) were also significantly removed. Microbial analysis reveals that the community structure had a significant difference before and after treatment, and the main dominant at the genus level was transformed from Nitrospirillum (approximately 18.03%) to Flavobacterium (approximately 17.64%). This study also found that the immobilized gel beads have excellent stability and reusability, which provided a feasible and robust bioremediation strategy for the treatment of actual black-odor water.

Recent advances biodegradation and biosorption of organic compounds from wastewater: Microalgae-bacteria consortium - A review

The litter of persistent organic pollutants (POPs) into the water streams and soil bodies via industrial effluents led to several adverse effects on the environment, health, and ecosystem. For the past decades, scientists have been paying efforts in the innovation and development of POPs removal from wastewater treatment. However, the conventional methods used for the removal of POPs from wastewater are costly and could lead to secondary pollution including soil and water bodies pollution. In recent, the utilization of green mechanisms such as biosorption, bioaccumulation and biodegradation has drawn attention and prelude the potential of green technology globally. Microalgae-bacteria consortia have emerged to be one of the latent wastewater treatment systems. The synergistic interactions between microalgae and bacteria could proficiently enhance the existing biological wastewater treatment system. This paper will critically review the comparison of conventional and recent advanced wastewater treatment systems and the mechanisms of the microalgae-bacteria symbiosis system.

Microalgae Chlorella vulgaris and Scenedesmus dimorphus co-cultivation with landfill leachate for pollutant removal and lipid production

In this study, landfill leachate was pre-treated with NaClO, and then diluted to 5%, 10% and 15% for microalgae growth of Chlorella vulgaris and Scenedesmus dimorphus in the mono- and co-culture modes to investigate the nutrient removal and growth characteristics of microalgae. The results revealed that landfill leachate with the 10% dilution rate was conducive for microalgae growth and exhibited robust biomass growth and the highest nutrient removal efficiency. The co-culture biomass in 10% landfill leachate achieved 0.266 g/L within 10 days and demonstrated the improved nutrient utilisation efficiency of microalgae. In addition, the chemical oxygen demand, ammonia nitrogen, total nitrate and total phosphorus removal efficiencies accordingly reached 81.0%, 80.1%, 72.1% and 86.0% in 10% landfill leachate. Meanwhile, both the enzyme activity and fluorescence parameters proved that the cell activity of co-culture was higher than that of mono-culture.

Distribution patterns of microbial community and functional characteristics in full-scale wastewater treatment plants: Focusing on the influent types

The impacts of the influent type in wastewater treatment plants (WWTPs) on the distribution patterns of the microbial community and functional characteristics were investigated. The obtained results indicated that the influent types exhibited evident influences on the microbial distribution patterns. The diversity and richness of functional microbes in HI-WWTP (with a ratio of >30% industrial wastewater in influents) were evidently decreased compared with those in HM- (with 70-90% municipal wastewater in influents) and M-WWTPs (with >90% municipal wastewater in influents). The core functional bacteria included denitrifiers, anaerobic fermentation bacteria (AFB), organic degrading bacteria (ODB), phosphorus accumulating organisms (PAO) and nitrite oxidizing bacteria (NOB), but they exhibited distinct abundances in WWTPs receiving different categories of wastewater. The denitrifiers in HI-WWTPs was 15.6-32.5% higher than that in other WWTPs, while PAOs had higher abundances in M - and HI-WWTPs (28.9% and 39.3%, respectively) compared with HM-WWTPs. Clear co-occurrence relationships were found among the main functional microbes with similar metabolic characteristics. Moreover, information on functional genes related to carbon, nitrogen and phosphorus metabolism, which is closely associated with pollutant removal efficiency, was obtained. M-WWTPs had higher abundances of genetic expressions for organic matters degradation (i.e. amino acid (10.42%) and carbohydrate (9.86%) metabolisms). Nar, Nir and Nor showed lowest abundances in HM-WWTPs, causing the low nitrogen removal (63.04-65.79%). However, influent type had little effect on genetic expression related with phosphorus removal. This work provided new insights into the interrelationship among bacterial co-occurrence, microbial activity and pollutant removal in WWTPs with different influent types.

Ammonia Bioremediation from Aquaculture Wastewater Effluents Using Arthrospira platensis NIOF17/003: Impact of Biodiesel Residue and Potential of Ammonia-Loaded Biomass as Rotifer Feed

The present work evaluated the capability of Arthrospira platensis complete biomass (ACDW) and the lipid-free biomass (LFB) to remove ammonium ions (NH4+) from aquaculture wastewater discharge. Under controlled conditions in flasks filled with 100 mL of distilled water (synthetic aqueous solution), a batch process ion-exchange was conducted by changing the main parameters including contact times (15, 30, 45, 60, 120, and 180 min), initial ammonium ion concentrations (10, 20, 30, 40, 50, and 100 mg·L-1), and initial pH levels (2, 4, 6, 8, and 10) at various dosages of ACDW and LFB as adsorbents (0.02, 0.04, 0.06, 0.08, and 0.1 g). After lab optimization, ammonia removal from real aquaculture wastewater was also examined. The removal of ammonium using ACDW and LFB in the synthetic aqueous solution (64.24% and 89.68%, respectively) was higher than that of the real aquaculture effluents (25.70% and 37.80%, respectively). The data of IR and Raman spectroscopy confirmed the existence of various functional groups in the biomass of ACDW and LFB. The adsorption equilibrium isotherms were estimated using Freundlich, Langmuir, and Halsey models, providing an initial description of the ammonia elimination capacity of A. platensis. The experimental kinetic study was suitably fit by a pseudo-second-order equation. On the other hand, as a result of the treatment of real aquaculture wastewater (RAW) using LFB and ACDW, the bacterial counts of the LFB, ACDW, ACDW-RAW, and RAW groups were high (higher than 300 CFU), while the LFB-RAW group showed lower than 100 CFU. The current study is the first work reporting the potential of ammonia-loaded microalgae biomass as a feed source for the rotifer (Brachionus plicatilis). In general, our findings concluded that B. plicatilis was sensitive to A. platensis biomass loaded with ammonia concentrations. Overall, the results in this work showed that the biomass of A. platensis is a promising candidate for removing ammonia from aquaculture wastewater.

Start-up of a trickling photobioreactor for the treatment of domestic wastewater

A stand-alone trickling photobioreactor (TPBR) was seeded with activated sludge and microalgae to treat domestic wastewater. The TPBR was started-up at 12-h hydraulic retention time at room temperature with 12:12 h light:dark cycle. The light was provided by blue LED strips. The reactor has a total volume of 30 L and is divided into six segments. Each segment is 30 cm long and has a diameter of 15 cm. Each segment was packed with polyurethane foam sponge cubes (2.5 × 2.5 × 2.5 cm³ ) with 40% occupancy. The chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), and phosphorus (P) of domestic wastewater varied in the range of 164-256 mg/L, 84.4-133.8 mg/L, 34.2-55.6 mg/L, and 24.7-39.3 mg/L, respectively, during this period. The COD, TOC, TN, and P concentrations in the effluent after 45 days of operation were 30.24 ± 3.36 mg/L, 7.69 ± 0.09 mg/L, 16.67 ± 0.39 mg/L, and 17.48 ± 0.5 mg/L, respectively. The chlorophyll-to-biofilm biomass ratio increased during the experimental period. The above results indicate that the algal-bacterial symbiotic relationship is beneficial for carbon and nutrient removal from domestic wastewater. PRACTITIONER POINTS: Trickling photobioreactor works on natural ventilation and has low power requirements and a small footprint. The porous sponge media helped in immobilizing and subsequent harvesting of biomass. The reactor conditions favored the growth of diatoms (brown algae) over green algae.

A review on algal-bacterial symbiotic system for effective treatment of wastewater

Industrialization, urbanization and other anthropogenic activities releases different organic and inorganic toxic chemicals into the environment which prompted the water contamination in the environment. Different physical and chemical techniques have been employed to treat the contaminated wastewater, among them biological wastewater treatment using algae has been studied extensively to overwhelm the constraints related to the usually utilized wastewater treatment techniques. The presence of bacterial biota in the wastewater will form a bond with algae and act as a natural water purification system. The removal efficiency of single algae systems was very low in contrast with that of algal-bacterial systems. Heterotrophic microorganisms separate natural organic matter that is discharged by algae as dissolved organic carbon (DOC) and discharges CO₂ that the algae can take up for photosynthesis. Algae bacteria associations offer an exquisite answer for tertiary and scrape medicines because of the capacity of micro-algae to exploit inorganic compounds for their development. Furthermore, for their ability to evacuate noxious contaminants, in this way, it does not prompt optional contamination. The present review contribute the outline of algae-bacteria symbiotic relationship and their applications in the wastewater treatment. The role of algae and bacteria in the wastewater treatment have been elucidated in this review. Moreover, the efforts have been imparted the importance of alage-bacteria consortium and its applications for various pollutant removal from the environment.

Role of porous polymer carriers and iron-carbon bioreactor combined micro-electrolysis and biological denitrification in efficient removal of nitrate from wastewater under low carbon to nitrogen ratio

In the current research, a novel bioreactor composed of porous polymer carriers and iron-carbon (PPC@FeC) was established through bacterial immobilized technology. The influence of key factors was studied on the nitrate removal performance of the PPC@FeC bioreactor. The experimental results showed that the highest removal rate of nitrate (7.33 mg L^-1 h^-1) can be obtained with short hydraulic retention times (HRT = 2.0 h) and low carbon-to-nitrogen ratio (C/N = 2.0). The results of high-throughput sequencing revealed that Zoogloea sp. L2 was the dominant strain in bioreactor responsible for nitrate removal. Moreover, the SEM and XRD analyses elucidated that Fe₂O₃ was the final product produced by the interaction of FeC and strain L2. These findings showed that the PPC@FeC bioreactor successfully combined micro-electrolysis and biological denitrification, which exhibited great potential in removing nitrate effectively from wastewater under low C/N ratio and short HRT conditions.

Prospects and development of algal-bacterial biotechnology in environmental management and protection

The coexistence of algae and bacteria in nature dates back to the very early stages when life came into existence. The interaction between algae and bacteria plays an important role in the planet ecology, cycling nutrients, and feeding higher trophic levels, and have been evolving ever since. The emerging concept of algal-bacterial consortia is gaining attention, much towards environmental management and protection. Studies have shown that algal-bacterial synergy does not only promote carbon capture in wastewater bioremediation but also consequently produces biofuels from algal-bacterial biomass. This review has evaluated the optimistic prospects of algal-bacterial consortia in environmental remediation, biorefinery, carbon sequestration as well as its contribution to the production of high-value compounds. In addition, algal-bacterial consortia offer great potential in bloom control, dye removal, agricultural biofertilizers, and bioplastics production. This work also emphasizes the advancement of algal-bacterial biotechnology in environmental management through the incorporation of Industry Revolution 4.0 technologies. The challenges include its pathway to greener industry, competition with other food additive sources, societal acceptance, cost feasibility, environmental trade-off, safety and compatibility. Thus, there is a need for further in-depth research to ensure the environmental sustainability and feasibility of algal-bacterial consortia to meet numerous current and future needs of society in the long run.

Nighttime aeration mode enhanced the microalgae-bacteria symbiosis (ABS) system stability and pollutants removal efficiencies

Utilizing external aeration to enhance the performance of microalgae-bacteria symbiosis (ABS) system has been extensively studied. However, inappropriate aeration damaged ABS system stability. A nighttime aeration mode (NA-ABS) in different aeration intensities (20, 50, 100 mL/min) was adopted to compare to continuous aeration microalgae-bacteria symbiosis (CA-ABS) mode and no-aerated mode on pollutants removal efficiencies and system stability. Results showed that NA-ABS system performed better on total organic carbon (TOC), NH₄⁺-N, total nitrogen (TN) and PO₄^3- removal than CA-ABS system, especially under the aeration intensity of 20 mL/min (NAI20), with the removal efficiencies of 96.59%, 99.18%, 90.30% and 89.16%, respectively. These results were because NA-ABS system prevented CO₂ stripping and provided more dissolved inorganic carbon (DIC) for the microalgae growth. Furthermore, less CO₂ stripping released the competition between microalgae and autotrophic bacteria for the DIC, leading to a more stable ABS system during long-term operation. This paper suggested that NA-ABS system would provide some new insights into ABS system and be helpful for further study.

Kinetics of a fixed bed reactor with immobilized microorganisms for the removal of organic matter and phosphorous

The biodegradation of domestic wastewater contaminants has been carried out using microorganisms immobilized in sodium alginate gel (Alg-Na). A fixed bed reactor with immobilized microorganisms was used for the treatment of domestic wastewater. A wastewater pretreatment was carried out to remove the larger particulate matter, which consisted of a reactor packed with different materials (anthracite, zeolite, and activated carbon). Later, a second reactor packed with balls with immobilized microorganisms was used to eliminate organic matter and nutrients. 2.5% w/v of Alg-Na was used as a support to immobilize the microorganisms. According to the results, a total phosphorus (TP) and chemical oxygen demand (COD) removal of 94.26% and 78.25% was obtained, respectively. In addition, the degradation rate for both organic matter and phosphorous was studied by using the kinetic model for fix bed reactor. © 2020 Water Environment Federation PRACTITIONER POINTS: Phosphorous and organic matter removal by adsorption and immobilized microorganisms. High removal efficiency of phosphorous and organic matter was found. An innovative wastewater treatment alternative is proposed. Kinetic model for fixed bed reactor is also proposed for scaling-up purposes.

Simultaneous nitrification-denitrification by phosphate accumulating microorganisms

Nitrogen and phosphorous are important inorganic water pollutants that pose a major threat to the environment and health of both humans and animals. The physical and chemical ways to remove these pollutants from water and soil are expensive and harsh, so biological removal becomes the method of choice to alleviate the problem without any side effects. The identification of microorganisms capable of simultaneous heterotrophic nitrification and aerobic denitrification has greatly simplified the sequestration of nitrogen from ammonium (NH₄⁺) into dinitrogen (N₂). Further, the discovery of phosphorous accumulating organisms offers greater economic benefits because these organisms can favourably and simultaneously remove both nitrogen and phosphorous from wastewaters hence reducing the nutrient burden. The stability of the system and removal efficiency of inorganic pollutants can be enhanced by the use of immobilized organisms. However, limited work has been done so far in this direction and there is a need to further the efforts towards refining process efficiency by testing low-cost substrates and diverse microbial populations for the total eradication of these contaminants from wastewaters.

Modified PVA (polyvinyl alcohol) biomaterials as carriers for simultaneous removal of nitrate, Cd (II), and Mn (II): performance and microbial community

The ecological toxicity and potential risks of heavy metals that coexist with nitrates in wastewater have aroused public attention. This study developed an immobilized Fe₃O₄@Cu/PVA mixotrophic reactor (Fe₃O₄@Cu/PVA-IMR) to investigate the effect of different Mn (II) concentrations (10 mg L^-1, 50 mg L^-1, and 90 mg L^-1), Cd (II) concentrations (10 mg L^-1, 20 mg L^-1, and 30 mg L^-1), and hydraulic retention time (HRT) (6 h, 8 h, and 10 h) on simultaneous nitrate, Cd (II), and Mn (II) removal. Using the advanced modified biomaterial Fe₃O₄@Cu/PVA as carrier to embed bacteria, the performance of the reactor was further improved. The surface morphology of Fe₃O₄@Cu/PVA was characterized by SEM as a rough surface three-dimensional skeleton structure. When the HRT was 10 h, Mn (II) and Cd (II) concentrations were 40 mg L^-1 and 10 mg L^-1, respectively, indicating that the immobilized Pseudomonas sp. H117 with Fe₃O₄@Cu/PVA achieved the highest nitrate, Cd (II), and Mn (II) removal efficiencies of 100% (1.64 mg L^-1 h^-1), 98.90% (0.92 mg L^-1 h^-1), and 92.26% (3.58 mg L^-1 h^-1), respectively. Compared with a reactor without Fe₃O₄@Cu/PVA addition, the corresponding removal ratio increased by 22.63%, 7.09%, and 15.96%. Gas chromatography (GC) identified nitrogen as the main gaseous product. Moreover, high-throughput sequencing showed that Pseudomonas sp. H117 plays a primary role in the denitrification process.

Non-suspended microalgae cultivation for wastewater refinery and biomass production

Non-suspended microalgae cultivation technology coupled with wastewater purification has received more scientific attention in recent decades. Since the non-suspended microalgae cultivation is quite different from the suspended ones, the following issues are compared in this study such as advantages and disadvantages, pollutant removal mechanisms and regulations, influential factors, and microalgae biomass accumulation. The analysis aims to support the further application of this technology. The median removal rates of COD, TN, TP, NH₄⁺-N and NO₃^--N were 91.6%, 78.2%, 87.5%, 93.2% and 81.7%, respectively, by non-suspended microalgae under the TN & TP load rates up to 150 mg·L^-1·d^-1. The main pathway for TN & TP removal is microalgae cell absorbance. Light intensity, pollutant composition and microalgae metabolic types are the major factors that influence pollutant removal and the lipid content of microalgae. Meanwhile the mechanism concerning how macro-outer conditions influence the micro-environment and further growth of non-suspended microalgae requires more investigation.

Nitrogen and phosphorus removals by the agar-immobilized Chlorella sacchrarophila with long-term preservation at room temperature

Immobilized microalgae have great potential on the nutrient removal during wastewater treatment. However, their applications are challenged by how to cost-effectively maintain and preserve large number of viable and active microalgal cells. In this study, the cells of Chlorella sacchrarophila were immobilized in the agar containing with algal nutrient, encapsulated in a transparent package and preserved at room temperature. After the preservation for 200 days, microalgal cells with viability of 47-52% were maintained and could be quickly revived after the cultivation in fresh algal medium. Based on the agar-immobilized microalgae, the NH₄⁺-N and PO₄^3--P were efficiently removed from batch and continuous cultures, with the highest removal efficiencies ranging from 96% to 99% were observed. Even being recycled for eight times, the agar-immobilized microalgae were still able to remove 94% of NH₄⁺-N and 66% of PO₄^3--P. Moreover, more than 60% of the nutrient removal efficiency was determined even the agar-immobilized microalgae being preserved for 120 days at room temperature. This work provides a simple, cost-effective and practicable method for the long-term preservation of microalgae at room temperature, which makes the application of microalgal species on the nutrient removal during wastewater treatment more convenient and useful.

Simultaneous removal of nitrate, phosphorous and cadmium using a novel multifunctional biomaterial immobilized aerobic strain Proteobacteria Cupriavidus H29

A novel biomaterial FeCl₃/CaCl₂/KH₂PO₄ modified municipal sludge biochar (FCPC) was synthesized. And the impacts of critical factors such as HRT, temperature and C/N ratio on simultaneous denitrification, dephosphorization and Cd(II) removal were investigated. Results show that the highest nitrate removal efficiency reached 92.22% (8.49 mg·L^-1·h^-1) in test group A and approximately 100% (9.19 mg·L^-1·h^-1) in test group B. Very low phosphate concentrations (approximately 2.50 mg/L) were detected in the effluent. The average removal efficiency of Cd(II) reached 86.40% (4.42 mg·L^-1·h^-1) in experimental group A and 90.15% (4.61 mg·L^-1·h^-1) in experimental group B. Gas emissions and biological precipitation in the bioreactors were monitored, further to confirming contaminant removal mechanisms. Additionally, Cupriavidus H29 was found to contribute dominantly to the FCPC bioreactor activity.

Integration of sodium hypochlorite pretreatment with co-immobilized microalgae/bacteria treatment of meat processing wastewater

Wastewater with 0.2, 0.4, 0.8, 1.0 mg/L free chlorine was biologically treated using co-immobilized microalgae/bacteria. In contrast, non-pretreated wastewater was treated with beads (control) and blank beads (blank) under the same operating condition. Results showed that NaClO pretreatment removed 8-33% total nitrogen (TN), 31-45% true color and 0.7-2.5 log CFU/mL aerobic-bacteria. At the end of treatment, maximum algal biomass (2,027 dry weight mg/L) was achieved with 0.2 mg/L free chlorine. Bacterial growth in wastewater was decreased by NaClO pretreatment before reaching 7.2-7.7 log CFU/mL on the fifth day. Beads with microorganisms (control) removed 15% more chemical-oxygen-demand (COD), 16% more TN, and 13% more total phosphate (PO₄^3-) than blank. Pretreatment with 0.2 mg/L free chlorine increased TN removal from 75% to 80% while pollutants removal was substantially decreased with 0.4-1.0 mg/L free chlorine. Considering algal biomass growth and pollutants removal, 0.2 mg/L free chlorine pretreatment was recommended for microalgae/bacteria co-immobilized system.

Phycoremediation potential of microalgae species for ethidium bromide removal from aqueous media

Ethidium Bromide (EtBr) is an organic compound used in molecular biology investigations. EtBr ability of intercalating in the DNA molecule makes it a toxic substance. The objective was to evaluate the phycoremediation potentials of Chlorella vulgaris, Desmodesmus subspicatus and Raphidocelis subcapitata tested separately and in a mixture (Mix) for EtBr removal from the aqueous medium. Experiments were conducted using an initial algae biomass of 10⁶ cell/mL, exposed to 500 µg/L of EtBr. The removal efficiency (µg EtBr L^-1) after 3 h in each treatment were: Mix (72.8 µg.L^-1) >D. subspicatus (48.4 µg.L^-1) >R. subcapitata (24.6 µg.L^-1) >C. vulgaris (19.9 µg.L^-1). However, when EtBr mass reduction per microalgae density is considered (ng.algae^-1), the efficiency ranking changes to: D. subspicatus (1.9 × 10^-5ng.algae^-1) >C. vulgaris (1.4 × 10^-5ng.algae^-1) >Mix (9.8 × 10^-6ng.algae^-1) >R. subcapitata (2.8 × 10^-6ng.algae^-1). The results suggest that initial algal population density is a determinant factor for efficient EtBr removal by microalgae species in short term treatments. In order to obtain 100% of EtBr removal, it should be necessary 10¹⁰, 10¹⁰ and 10¹¹ algae.mL^-1 of C. vulgaris, D. subspicatus and R. subcapitata, respectively. The results strongly suggest phycoremediation can be explored as an alternative method for EtBr removal.

Investigating the potentiality of Scenedesmus obliquus and Acinetobacter pittii partnership system and their effects on nutrients removal from synthetic domestic wastewater

A lab-scale study of Scenedesmus obliquus: Acinetobacter pittii (S. obliquus: A. pitti) partnership cultured in synthetic domestic wastewater was conducted to evaluate the partnership performance for growth and removal of nutrients from wastewater. To draw out the functional dependencies of this partnership measured the ammonia-nitrogen (NH₄⁺-N), ortho-phosphate (PO₄^3--P), soluble total phosphorus (TP), chemical oxygen demand (COD) and have got the nutrient removal rate of 85.90%, 91.50%, 73.75% and 100% respectively. The results showed that their optimized partnership ratio is 2:1 for S. obliquus: A. pitti and, CO₂ & O₂ exchanges in between was the more crucial parameters to shifting the best nutrient removals performance and promoted biomass quantity.

Removal of Nutrients from Fertilizer Plant Wastewater Using Scenedesmus sp.: Formation of Bioflocculation and Enhancement of Removal Efficiency

Eutrophication of surface water has become an environmental concern in recent decades. High concentrations of nutrients, especially nitrogen- and phosphorus-rich species, have contributed to the process of eutrophication, highlighting a demand for effective and economical methods of removing nitrogen and phosphorus from wastewater. This study aimed to investigate the ability of a green microalga species, Scenedesmus sp., to remove nitrogen and phosphorus, as well as chemical oxygen demand (COD) and biochemical oxygen demand (BOD5), from fertilizer plant wastewater. Different microalgae concentrations from 10 mg/L to 60 mg/L were used to assess the growth rate, biomass production, and removal ability. The results indicated that Scenedesmus sp. grew well in the wastewater (with a growth rate from 0.3 to 0.38/day) and produced up to 70.2 mg/L of dry biomass. The algal species was able to remove ammonium (NH4+), nitrate (NO3−), phosphate (PO43−), total phosphorus (TP), COD, and BOD5 with removal rates up to 93%, 84%, 97%, 96%, 93%, and 84%, respectively. Autobioflocculation (AFL) was observed in all cultures with flocculation activity of up to 88.3% in the highest algal biomass treatment. The formation of bioflocculation enhanced the removal of nutrients, COD, and BOD5 from wastewater effluent. The results indicated that wastewater from a fertilizer plant could be used as a cost-effective growth medium for algal biomass. The autoflocculation of microalgae could be used as a more practical approach for wastewater treatment using microalgae to eliminate eutrophication.

Multifunctional modified polyvinyl alcohol: A powerful biomaterial for enhancing bioreactor performance in nitrate, Mn(II) and Cd(II) removal

The co-existence of multiple pollutants in wastewater such as nitrate and heavy metal, is of high concern due to the potential environmental impact. In this study, a novel biomaterial PPy@Fe₃O₄/PVA was synthesized as a multifunctional bacteria immobilized carrier, to enhance simultaneous denitrification, Cd(II) and Mn(II) removal efficiency in bioreactor environments. The morphology and main components of the PPy@Fe₃O₄/PVA material were characterized by SEM and XRD. Using PPy@Fe₃O₄/PVA as a carrier, the maximum removal efficiencies for nitrate (0.207 mg L^-1·h^-1), Mn(II) (90.98%) and Cd(II) (98.78%) were increased by 27.05%, 30.27%, and 16.48%, respectively, compared to in the absence of PPy@Fe₃O₄/PVA. Regeneration experiments were performed, demonstrating the excellent stability and reusability of the PPy@Fe₃O₄/PVA material. Furthermore, effects of key factors were investigated on the performance of the PPy@Fe₃O₄/PVA bioreactor in simultaneous denitrification, Mn(II) and Cd(II) removal. Experimental results indicate that the highest nitrate, Mn(II) and Cd(II) removal efficiencies were obtained under the conditions of HRT of 10 h, initial Mn(II) concentration of 40 mg/L and initial Cd(II) concentration of 10 mg/L. Gas chromatography analysis indicated that N₂ was the mainly final gaseous product. Moreover, the bioreactor community diversity was markedly influenced by the initial concentration of Cd(II) and Pseudomonas sp. H117 played a primary role in the process of simultaneous denitrification, Mn(II) and Cd(II) removal.