Attached cultivation of microalgae on rational carriers for swine wastewater treatment and biomass harvesting

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Indole-3-acetic acid regulating the initial adhesion of microalgae in biofilm formation

Regulating the microalgal initial adhesion in biofilm formation is a key approach to address the challenges of attached microalgae cultivation. As a type of phytohormone, Indole-3-acetic acid (IAA) can promote the growth and metabolism of microalgae. However, limited knowledge has been acquired of how IAA can change the initial adhesion of microalgae in biofilm formation. This study focused on investigating the initial adhesion of microalgae under different IAA concentrations exposure in biofilm formation. The results showed that IAA showed obvious hormesis-like effects on the initial adhesion ability of microalgae biofilm. Under exposure to the low concentration (0.1 mg/L) of IAA, the initial adhesion quantity of microalgae on the surface of the carrier reached the highest value of 7.2 g/m2. However, exposure to the excessively high concentration (10 mg/L) of IAA led to a decrease in the initial adhesion capability of microalgal biofilms. The enhanced adhesion of microalgal biofilms due to IAA was attributed to the upregulation of genes related to the Calvin Cycle, which promoted the synthesis of hydrophobic amino acids, leading to increased protein secretion and altering the surface electron donor characteristics of microalgal biofilms. This, in turn, reduced the energy barrier between the carriers and microalgae. The research findings would provide crucial support for the application of IAA in regulating the operation of microalgal biofilm systems.

Effects of dilution and pretreatment on nutrient removal and biomass production of Chlorella vulgaris in kitchen wastewater

This research investigated the effect of kitchen wastewater (KWW) concentrations and pretreatment methods on Chlorella vulgaris biomass production, lipid content and nutrient removal. This study was divided into two separate experiments. The first experiment determined the appropriate dilution rate of KWW for the growth of microalgae, sterilized KWW was varied between 25%, 50%, 75%, and 100%(v/v). The result indicated that 50%(v/v) showed the highest nutrient removal by 90.23%, 85.87%, and 80.64% of sCOD, TKN, and TP, respectively. The highest biomass and lipid content were obtained with 50%(v/v) (1.447 g/L, 37.9%). The second experiment was to find an effective physical pretreatment method, which separated the biotic contaminant, non-sterilized KWW was diluted 50%(v/v) and filtered with different mesh size filters (150 μm, 50 μm, and 30 μm) compared with sterilized KWW as a control sample. The result indicated that pretreatment with 50 μm filtration was found highest nutrient removal by 90.51%, 84.74%, and 77.50% of sCOD, TKN, and TP, respectively. The highest biomass and lipid content were obtained with 50 μm filtration (1.496 g/L, 39.4%). Our results support the hypothesis that the optimal dilution and proper filtration of KWW helps create more favorable environment for microalgal growth.

Strategies for livestock wastewater treatment and optimised nutrient recovery using microalgal-based technologies

Global sustainable development faces several challenges in addressing the needs of a growing population. Regarding food industries, the heightening pressure to meet these needs has resulted in increased waste generation. Thus, recognising these wastes as valuable resources is crucial to integrating sustainable models into current production systems. For instance, the current 24 billion tons of nutrient-rich livestock wastewater (LW) generated yearly could be recovered and valorised via biological uptake through microalgal biomass. Microalgae-based livestock wastewater treatment (MbLWT) has emerged as an effective technology for nutrient recovery, specifically targeting carbon, nitrogen, and phosphorus. However, the viability and efficacy of these systems rely on the characteristics of LW, including organic matter and ammonium concentration, content of suspended solids, and microbial load. Thus, this systematic literature review aims to provide guidance towards implementing an integral MbLWT system for nutrient control and recovery, discussing several pre-treatments used in literature to overcome the challenges regarding LW as a suitable media for microalgae cultivation.

Emerging revolving algae biofilm system for algal biomass production and nutrient recovery from wastewater

Toward the direction of zero‑carbon emission and green technologies for wastewater treatment, algae-based technologies are considered promising candidates to deal with the current situation of pollution and climate change. Recent developments of algae-based technologies have been introduced in previous studies in which their performances were optimized for wastewater treatment and biomass production. Among these, revolving algae biofilm (RAB) reactors have been proven to have a great potential in high biomass productivity, simple harvesting method, great CO2 transfer rate, high light-use efficiency, heavy metal capture, nutrient removal, and acid mine drainage treatment in previous studies. However, there were few articles detailing RAB performance, which concealed its enormous potential and diminished interest in the model. Hence, this review aims to reveal the major benefit of RAB reactors in simultaneous wastewater treatment and biomass cultivation. However, there is still a lack of research on aspects to upgrade this technology which requires further investigations to improve performance or fulfill the concept of circular economy.

Eco-friendly cultivation of microalgae using a horizontal twin layer system for treatment of real solid waste leachate

Solid waste leachate (SWL) requires dilution with water to offset the negative effects of high nutrient concentration and organic compounds for its microalgae-based treatment. Among attached cultivation systems, twin layer is a technology in which limited information is available on treatment of high strength wastewater using microalgae. Moreover, widespread application of twin layer technology is limited due to cost of substrate and source layer used. In the present study, potential of Scenedesmus sp. for the treatment of SWL was assessed on horizontal twin layer system (HTLS). Novel and cost-effective substrate layers were tested as attachment material. Wetland treated municipal wastewater (WMW) was used to prepare SWL dilutions viz, 5%, 10%, 15%, 20% and 25% SWL. Recycled printing paper showed maximum biomass productivity of 5.19 g m-2 d-1. Among all the SWL dilutions, Scenedesmus sp. achieved maximum growth of 103.05 g m-2 in 5% SWL which was 16% higher than WMW alone. The maximum removal rate of NH4+ -N, TKN, and PO43- P was obtained in 20% SWL which was 1371, 1588 and 153 mg m-2 d-1 respectively. Varying concentrations of nutrients in different SWL dilutions significantly affected lipid biosynthesis, with enhanced productivity of 2.28 g m-2 d-1 achieved in 5% SWL compared to 0.97 g m-2 d-1 in 20% SWL. Hence, it can be concluded that 5% SWL dilution was good for biomass and lipid production, while the highest nutrient removal rates were obtained at 20% SWL mainly attributed to biotic and abiotic processes. Based on these results HTLS can be a promising technology for pilot scale to explore industrialized application of wastewater treatment and algal production.

Insight into the roles of hematite iron oxide nanoparticles on microalgae growth, urban wastewater treatment and bioproducts generation: Gompertz simulation, nutrient mass balance and gene expression

In this study, the effect of α-Fe2O3 nanoparticles spiking in urban wastewater (UWW) on growth rate, wastewater treatment ability and bioproducts generation of C. vulgaris and Spirulina was investigated and compared with pure cultivation system. The biomass concentration of C. vulgaris and Spirulina improved by 20 % and 39 % at 10 and 15 mg/L α-Fe2O3, respectively while the both microalgae growth pattern fitted better with Gompertz simulation after treatment with α-Fe2O3. The nutrients mass balance revealed that 1 g of treated C. vulgaris and Spirulina could uptake more COD, TN and TP in comparison to the untreated cells. The lipid generation increased remarkably (C. vulgaris: 45 % and Spirulina: 72 %) after α-Fe2O3 treatment. While, the addition of α-Fe2O3 showed no significant impact on the protein and carbohydrate productivity. Overall, this study evangelize the role of nanoparticles on promoting microalgae applications as a sustainable approach for UWW treatment and promising feedstock for biofuel production.

Nitrogen and phosphorus removal performance of sequential batch operation for algal cultivation through suspended-solid phase photobioreactor

Nitrogen (N) and phosphorus (P) absorbed by algae in the suspended-solid phase photobioreactor (ssPBR) have emerged as an efficient pathway to purify the effluent of wastewater treatment plants (WWTPs). However, the key operational parameters of the ssPBR need to be optimized. In this study, the stability of the system after sequential batch operations and the efficiency under various influent P concentrations were evaluated. The results demonstrated that the ssPBR maintained a high N/P removal efficiency of 96 % and 98 %, respectively, after 5 cycles. When N was kept at 15 mg/L and P ranged from 1.5 to 3.0 mg/L, the system yielded plenty of algae products and guaranteed the effluent quality that met the discharge standards. Notably, the carriers were a key contributor to the high metabolism of algae and high performance. This work provided theoretical ideas and technical guidance for effluent quality improvement in WWTPs.

Microalgae cultivation with recycled harvesting water achieved economic and sustainable production of biomass and lipid: Feasibility assessment and inhibitory factors analysis

This study was conducted to achieve economic and sustainable production of biomass and lipids from Chlorella sorokiniana by recirculating cultivation with recycled harvesting water, to identify the major inhibitory factors in recirculating culture, and to analyze accordingly economic benefits. The results showed that recirculating microalgae cultivation (RMC) could obtain 0.20-0.32 g/L biomass and lipid content increased by 23.1 %-38.5 %. Correlation analysis showed that the extracellular polysaccharide (PSext), chemical oxygen demand (COD) and chromaticity of recirculating water inhibited photosynthesis and induced oxidative stress, thus inhibiting the growth of C. sorokiniana. In addition, the economic benefits analysis found that circulating the medium twice could save about 30 % of production cost, which is the most economical RMC solution. In conclusion, this study verified the feasibility and economy of RMC, and provided a better understanding of inhibitory factors identification in culture.

Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

A semi-continuous efficient strategy for removing phosphorus and nitrogen from eel aquaculture wastewater using the self-flocculating microalga Desmodesmus sp. PW1

The phosphorus content in eel aquaculture wastewater exceeds the discharge standard, and the amount of wastewater discharged is substantial. Therefore, there is an urgent need to explore an economical and efficient method of treating aquaculture wastewater. This study explored the use of Desmodesmus sp. PW1, a type of microalgae, to treat eel aquaculture wastewater. By optimizing the conditions, Desmodesmus sp. PW1 achieved a total phosphorus (TP) removal efficiency of 92.3%, as well as total nitrogen (TN) and ammonia nitrogen (NH4+-N) removal efficiency of 99%, using a photoperiod of 24:0, a temperature of 25 °C, and an inoculation amount of 15%. Furthermore, Desmodesmus sp. PW1 demonstrated a high self-flocculating efficiency (>90%) within 100 min of settling, which facilitated biomass recovery. Subsequently, a semi-continuous treatment process mode was established with a sewage renewal rate of 90%. The results showed that after four rounds of sewage renewal operations, the microalgae biomass in the sewage treatment system could be maintained between 160.0 and 220.0 mg/L, and the average removal rate of TP was 0.13 mg/(L * h). The lipid content of algae cells collected in the semi-continuous treatment system for eel aquaculture wastewater was as high as 36.5%, and the biodiesel properties met the biodiesel standards authorized by Europe and the United States. Overall, this study provides an economical and effective strategy for converting wastewater into high-value microalgae products.

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

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

Optimization of biochar production from greywater grown polyculture microalgae using microwave pyrolysis

Biochar was produced from polyculture microalgae cultivated in greywater using microwave pyrolysis. The highest biochar yield and fixed carbon content of 49.9% and 68.7% were obtained at microwave power (P) of 800 W and reaction time (T) of 8.6 min. The developed quadratic models, 166.96 - 0.23P - 3.87 T - 3.49 x10-3PT + 1.73 x10-4P2 + 0.13 T2 and - 73.79 + 0.29P + 1.86 T - 1.80 x10-4P2 could predict biochar yield and fixed carbon content respectively with errors of 6.2 and 7.9%. The volatile matter (VM), fixed carbon (FC), and high heating value (HHV) of the biomass were 69.2%. 23.4% and 17.6 MJ/Kg, respectively. VM, FC, and HHV for biochar obtained at optimum conditions were 20.2%, 68.7%, and 28.3 MJ/Kg, respectively. The process had a net positive energy balance of 11.32 MJ/Kg and energy efficiency of 1.76. This study paves the way for biochar production from greywater-grown microalgae, contributing to waste valorization and energy sustainability.

The effects of carbon nitrogen ratio and salinity on the treatment of swine digestion effluent simultaneously producing bioenergy by microalgae biofilm

In order to remove high concentrations of ammonia nitrogen (NH4+-N) and refractory sulfamethazine (SM2) from swine digestion effluent, different carbon/nitrogen (C/N) ratios and salinity were used to determine the effects of pollutants removal in the microalgae biofilm system. Microalgae biofilm treatment under optimal environmental conditions in synthetic swine digestion effluent were C/N ratio of 20 and salinity of 140 mM. In order to make the actual swine digestion effluent discharge up to the standard, three different two-cycle treatments (suspended microalgae, microalgae biofilm, microalgae biofilm under the optimal conditions) were studied. The results showed that after two-cycle treatment with microalgae biofilm under the optimal conditions, the actual swine digestion effluent levels of total nitrogen (TN), NH4+-N, total phosphorus (TP), chemical oxygen demand (COD), SM2 were 22.65, 9.32, 4.11, 367.28, and 0.99 mg L-1, respectively, which could satisfy the discharge standards for livestock and poultry wastewater in China. At the same time, first-order kinetic simulation equations suggested a degradation half-life of 4.85 d for SM2 under optimal conditions in microalgae biofilm, and microbial community analysis indicated that the dominant genus was Halomonas. Furthermore, 35.66% of lipid, 32.56% of protein and 18.44% of polysaccharides were harvested after two-cycle in microalgae biofilm treatment under optimal environmental conditions. These results indicated that the regulation of C/N and salinity in microalgae biofilm for the treatment of swine digestion effluent was a high-efficiency strategy to simultaneously achieve wastewater treatment and bioenergy production.

Enhancing algal growth and nutrient recovery from anaerobic digestion piggery effluent by an integrated pretreatment strategy of ammonia stripping and flocculation

Anaerobic digestion piggery effluent (ADPE) with a quite high ammonium (NH₄ ⁺) concentration and turbidity (dark brown color) generally requires high dilution before microalgae cultivation, owing to its NH₄ ⁺ toxicity and color inhibition to algal growth. An integrated pretreatment strategy of ammonia stripping and chemical flocculation may be a more practical pretreatment procedure for enhancing algae yield and nutrient recovery from anaerobic digestion piggery effluent. In this study, we determined the optimum pretreatment strategy of anaerobic digestion piggery effluent for subsequent microalgae cultivation and nutrient recovery. The results showed that the integrated anaerobic digestion piggery effluent pretreatment strategy of high-temperature ammonia stripping and chemical flocculation at a mixed dosage of 2 g L^-1 polyaluminum chloride (PAC) and 40 mg L^-1 cationic polyacrylamide (C-PAM), and 50 mg L^-1 ammonium nitrogen (NH₄ ⁺-N) enrichment provided maximum algal yield (optical density = 1.8) and nutrient removal (95.2%, 98.7%, 99.3%, and 78.5% for the removal efficiencies of total nitrogen, NH₄ ⁺-N, total phosphorus, and chemical oxygen demand, respectively) from anaerobic digestion piggery effluent. The integrated pretreatment strategy is expected to become a more practical pretreatment procedure for enhancing algae yield and nutrient recovery from anaerobic digestion piggery effluent.

Bioremediation of zinc and manganese in swine wastewater by living microalgae: Performance, mechanism, and algal biomass utilization

The remediation effects of living Chlorella sp. HL on zinc and manganese in swine wastewater was investigated, and the responses of algal cells and the mechanism were explored. In the wastewater with Zn(II) concentration of 1.85 mg/L and Mn(II) of 1 or 6 mg/L, the highest removal of Zn(II) by Chlorella reached 86.72% and 97.16%, respectively, and the Mn(II) removal were 42.74% and 30.33%, respectively. The antioxidant system of cells was activated by a significant increase in superoxide dismutase and catalase enzyme activities and a significant decrease in malondialdehyde in the mixed system compared to the single system. The presence of Mn(II) could positively regulate the differentially expressed genes related to catalytic activity and metabolic processes between the single Zn system and the mixed systems, reducing the stress of Zn(II) on Chlorella and more favorable to chlorophyll synthesis. The heavy metal-containing microalgal biomass obtained has the potential as feed additives.

The potential and sustainable strategy for swine wastewater treatment: Resource recovery

Swine wastewater is highly polluted with complex and harmful substances that require effective treatment to minimize environmental damage. There are three commonly used biological technologies for treating swine wastewater: conventional biological technology (CBT), microbial electrochemical technology (MET), and microalgae technology (MT). However, there is a lack of comparison among these technologies and a lack of understanding of their unique advantages and efficient operation strategies. This review aims to compare and contrast the characteristics, influencing factors, improvement methods, and microbial mechanisms of each technology. CBT is cost-effective but has low resource recovery efficiency, while MET and MT have the highest potential for resource recovery. However, all three technologies are affected by various factors and toxic substances such as heavy metals and antibiotics. Improved methods include exogenous/endogenous enhancement, series reactor operation, algal-bacterial symbiosis system construction, etc. Though MET is limited by construction costs, CBT and MT have practical applications. While swine wastewater treatment processes have developed automatic control systems, the application need further promotion. Furthermore, key functional microorganisms involved in CBT's pollutant removal or transformation have been detected, as have related genes. The unique electroactive microbial cooperation mode and symbiotic mode of MET and MT were also revealed, respectively. Importantly, the future research should focus on broadening the scope and scale of engineering applications, preventing and controlling emerging pollutants, improving automated management level, focusing on microbial synergistic metabolism, enhancing resource recovery performance, and building a circular economy based on low-cost and resource utilization.

Effects of fluidised carriers on the community composition, settleability and energy production of indigenous microalgal consortia cultivated in treated wastewater

Fluidised-bed systems are a promising approach to microalgal cultivation, but few studies have considered their application to indigenous microalgal consortia (IMCs), which have high adaptability to wastewater. In this study, IMCs were cultivated in treated wastewater with and without fluidised carriers, and the effects of operating parameters were considered. Microalgae in the culture were confirmed to originate from the carriers, and the IMC presence on the carriers was promoted by decreasing the carrier replacement number and increasing the culture replacement volume. The presence of carriers enabled greater nutrient removal from the treated wastewater by the cultivated IMCs. Without carriers, IMCs in the culture were scattered and showed poor settleability. With carriers, IMCs in the culture exhibited good settleability owing to floc formation. The improved settleability with carriers also increased the energy production from sedimented IMCs.

Integrated culture and harvest systems for improved microalgal biomass production and wastewater treatment

Microalgae cultivation in wastewater has received much attention as an environmentally sustainable approach. However, commercial application of this technique is challenging due to the low biomass output and high harvesting costs. Recently, integrated culture and harvest systems including microalgae biofilm, membrane photobioreactor, microalgae-fungi co-culture, microalgae-activated sludge co-culture, and microalgae auto-flocculation have been explored for efficiently coupling microalgal biomass production with wastewater purification. In such systems, the cultivation of microalgae and the separation of algal cells from wastewater are performed in the same reactor, enabling microalgae grown in the cultivation system to reach higher concentration, thus greatly improving the efficiency of biomass production and wastewater purification. Additionally, the design of such innovative systems also allows for microalgae cells to be harvested more efficiently. This review summarizes the mechanisms, characteristics, applications, and development trends of the various integrated systems and discusses their potential for broad applications, which worth further research.

Microalgal remediation and valorisation of polluted wastewaters for zero-carbon circular bioeconomy

Overexploitation of natural resources to meet human needs has considerably impacted CO₂ emissions, contributing to global warming and severe climatic change. This review furnishes an understanding of the sources, brutality, and effects of CO₂ emissions and compelling requirements for metamorphosis from a linear to a circular bioeconomy. A detailed emphasis on microalgae, its types, properties, and cultivation are explained with significance in attaining a zero-carbon circular bioeconomy. Microalgal treatment of a variety of wastewaters with the conversion of generated biomass into value-added products such as bio-energy and pharmaceuticals, along with agricultural products is elaborated. Challenges encountered in large-scale implementation of microalgal technologies for low-carbon circular bioeconomy are discussed along with solutions and future perceptions. Emphasis on the suitability of microalgae in wastewater treatment and its conversion into alternate low-carbon footprint bio-energies and value-added products enforcing a zero-carbon circular bioeconomy is the major focus of this review.

Biogasoline Obtained Using Catalytic Pyrolysis of Desmodesmus sp. Microalgae: Comparison between Dry Biomass and n-Hexane Extract

The present work deals with the production of hydrocarbons in the C5–C12 range obtained from the fast micropyrolysis of a laboratory-grown Desmodesmus sp. microalgae. It compares the properties of this specific fraction of hydrocarbons using or not using transition alumina catalysts during pyrolysis in experiments with both pure dried microalgae and its n-hexane extract. The microalgae were characterised using thermogravimetry (TG) and CHN analysis; the n-hexane extract was analysed through Fourier transform infrared spectroscopy (FTIR). The pyrolysis experiments were performed in a multi-shot pyrolyser connected online with a gas chromatograph coupled to a mass spectrometer (GC/MS). The composition of the C5–C12 fraction was compared to that of an industrial pyrolysis gasoline. The results of pyrolysis at 600 °C show that the alumina catalyst increases the quantity of C5–C12 hydrocarbon families when compared to purely thermal pyrolysis, representing about 40% of all the dry microalgae pyrolysis products. In the case of n-hexane extract, the C5–C12 area fraction corresponds to 33.5% of the whole products’ area when pyrolysis is conducted with an alumina catalyst. A detailed analysis shows that linear molecules, mainly unsaturated, are predominant in the products. Dry biomass formed more aromatic but less cyclic and alkylated molecules in relation to the n-hexane extract. Nitrogen products, essentially alkylated pyrroles, were produced in large quantities when dry biomass was used but were below the detection limit when pyrolysing the extracts. Thus, the extraction with hexane proved to be an effective way to remove nitrogen compounds, which are undesirable in fuels. The estimated low heating values of the present C5–C12 pyrolysis hydrocarbon fractions (between 43 and 44 MJ/kg) are quite comparable to the reported values for reformulated and conventional industrial gasolines (42 and 43 MJ/kg, respectively).

In-situ removal of aquaculture waste nutrient using floating permeable nutrient uptake system (FPNUS) under mixotrophic microalgal scheme

The current study investigated the in-situ aquaculture nutrient removal from fish tanks using mixotrophic Scenedesmus in a floating permeable nutrient uptake system (FPNUS) and compared with nutrient concentration in control, autotrophy, and bacterial nitrogen removal (BNR) treatments. In the first run, results were not as expected due to the missing PO₄^--P as the mixotrophic growth in flasks with PO₄^--P was 55.86% more than growth in aquaculture wastewater. With PO₄^--P addition in FPNUS, average and maximum removal rates under mixotrophy reached 2.53 and 10.96 mg/(L·d), respectively. The average mixotrophic removal rate was 40.31 and 81.42% higher than removal rates under autotrophy and BNR. Daily nutrient loading and removal were matched only in mixotrophy after fourth day of culture. These results show the great potential for nutrient removal using mixotrophic microalgae-based FPNUS due to its high efficiency, capability of in-situ treatment and nutrient recycling through biomass utilization.

Nitrogen recovery from wastewater by microbial assimilation - A review

The increased nitrogen (N) input with low utilization rate in artificial N management has led to massive reactive N (Nr) flows, putting the Earth in a high-risk state. It is essential to recover and recycle Nr during or after Nr removal from wastewater to reduce N input while simultaneously mitigate Nr pollution in addressing the N stress. However, mechanisms for efficient Nr recovery during or after Nr removal remain unclear. Here, the occurrence of N risk and progress in wastewater treatment in recent years as well as challenges of the current technologies for N recovery from wastewater were reviewed. Through analyzing N conversion fluxes in biogeochemical N-cycling networks, microbial N assimilation through photosynthetic and heterotrophic microorganisms was highlighted as promising alternative for synergistic N removal and recovery in wastewater treatment. In addition, the prospects and gaps of Nr recovery from wastewater through microbial assimilation are discussed.

Microalgae-driven swine wastewater biotreatment: Nutrient recovery, key microbial community and current challenges

As a promising technology, the microalgae-driven strategy can achieve environmentally sustainable and economically viable swine wastewater treatment. Currently, most microalgae-based research focuses on remediation improvement and biomass accumulation, while information on the removal mechanisms and dominant microorganisms is emerging but still limited. In this review, the major removal mechanisms of pollutants and pathogenic bacteria are systematically discussed. In addition, the bacterial and microalgal community during the swine wastewater treatment process are summarized. In general, Blastomonas, Flavobacterium, Skermanella, Calothrix and Sedimentibacter exhibit a high relative abundance. In contrast to the bacterial community, the microalgal community does not change much during swine wastewater treatment. Additionally, the effects of various parameters (characteristics of swine wastewater and cultivation conditions) on microalgal growth and current challenges in the microalgae-driven biotreatment process are comprehensively introduced. This review stresses the need to integrate bacterial and microalgal ecology information into the conventional design of full-scale swine wastewater treatment systems and operations. Herein, future research needs are also proposed, which will facilitate the development and operation of a more efficient microalgae-based swine wastewater treatment process.

A review on biodiesel production from microalgae: Influencing parameters and recent advanced technologies

Microalgae are the important part of carbon cycle in the nature, and they could utilize the carbon resource in water and soil efficiently. The abilities of microalgae to mitigate CO₂ emission and produce oil with a high productivity have been proven. Hence, this third-generation biodiesel should be popularized. This review firstly introduce the basic characteristics and application fields of microalgae. Then, the influencing parameters and recent advanced technologies for the microalgae biodiesel production have been discussed. In influencing parameters for biodiesel production section, the factors of microalgae cultivation, lipid accumulation, microalgae harvesting, and lipid extraction have been summarized. In recent advanced technologies for biodiesel production section, the microalgae cultivation systems, lipid induction technologies, microalgae harvesting technologies, and lipid extraction technologies have been reviewed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.