Anaerobic digestate as substrate for microalgae culture: the role of ammonium concentration on the microalgae productivity

Biological effects of culture medium on Tetraselmis chuii and Dunaliella tertiolecta: Implications for emerging pollutants degradation

In this study, laboratory-scale cultivation of T. chuii and D. tertiolecta was conducted using Conway, F/2, and TMRL media to evaluate their biochemical composition and economic costs. The highest cell density (30.36 × 106 cells/mL) and dry weight (0.65 g/L) for T. chuii were achieved with Conway medium. This medium also produced biomass with maximum lipid content (25.65%), proteins (27.84%), and total carbohydrates (8.45%) compared with F/2 and TMRL media. D. tertiolecta reached a maximum cell density of 17.50 × 106 cells/mL in F/2 medium, which was notably lower than that of T. chuii. Furthermore, the media cost varied from US$0.23 to US$0.74 for each 1 L of media, primarily due to the addition of Na3PO4, KNO3, and cyanocobalamin. Thus, biomass production rates varied between US$38.81 and US$128.80 per kg on a dry weight basis. These findings comprehensively compare laboratory conditions and the costs associated with biomass production in different media. Additionally, this study explored the potential of T. chuii and D. tertiolecta strains, as well as their consortia with bacteria, for the degradation of various emerging pollutants (EPs), including caffeine, salicylic acid, DEET, imidacloprid, MBT, cimetidine, venlafaxine, methylparaben, thiabendazole, and paracetamol. Both microalgal strains demonstrated effective degradation of EPs, with enhanced degradation observed in microalgae-bacterial consortia. These results suggest that the symbiotic relationship between microalgae and bacteria can be harnessed for the bioremediation of EPs, thereby offering valuable insights into the environmental applications of microalgal cultivation.

Comprehensive review of technologies for separate digestate treatment and agricultural valorisation within circular and green economy

Anaerobic digestion (AD) has the potential to catalyse the shift from a linear to a circular economy. However, effective treatment and management of both solid (DSF) and liquid (DLF) digestate fraction treatment and management require adopting sustainable technologies to recover valuable by-products like energy, biofuels, biochar, and nutrients. This study reviews state-of-the-art advanced technologies for DSF and DLF treatment and valorisation, using life cycle assessment (LCA) and techno-economic analysis (TEA) in integrated digestate management (IDM). Key findings highlight these technologies' potential in mitigating environmental impacts from digestate management, but there's a need to improve process efficiency, especially at larger scales. Future research should prioritize cost-effective and eco-friendly IDM technologies. This review emphasizes how LCA and TEA can guide decision-making and promote sustainable agricultural practices. Ultimately, sustainable IDM technologies can boost resource recovery and advance circular economy principles, enhancing the environmental and economic sustainability of AD processes.

Mini critical review: Membrane fouling control in membrane bioreactors by microalgae

Membrane bioreactors (MBRs) hold significant promise for wastewater treatment, yet the persistent challenge of membrane fouling impedes their practical application. One promising solution lies in the synergy between microalgae and bacteria, offering efficient nutrient removal, reduced energy consumption, and potential mitigation of extracellular polymeric substances (EPS) concentrations. Inoculating microalgae presents a promising avenue to address membrane fouling in MBRs. This review marks the first exploration of utilizing microalgae for membrane fouling control in MBR systems. The review begins with a comprehensive overview of the evolution and distinctive traits of microalgae-MBRs. It goes further insight into the performance and underlying mechanisms facilitating the reduction of membrane fouling through microalgae intervention. Moreover, the review not only identifies the challenges inherent in employing microalgae for membrane fouling control in MBRs but also illuminates prospective pathways for future advancement in this burgeoning field.

Integrating electro-Fenton and microalgae for the sustainable management of real food processing wastewater

The present study demonstrates, for the first time, the feasibility of a two-step process consisting of Electro-Fenton (EF) followed by microalgae to treat highly loaded real food processing wastewater along with resource recovery. In the first step, EF with a carbon felt cathode and Ti/RuO2-IrO2 anode was applied at different current densities (3.16 mA cm-2, 4.74 mA cm-2 and 6.32 mA cm-2) to decrease the amount of organic matter and turbidity and enhance biodegradability. In the second step, the EF effluents were submitted to microalgal treatment for 15 days using a mixed culture dominated by Scenedesmus sp., Chlorosarcinopsis sp., and Coelastrum sp. Results showed that current density impacted the amount of COD removed by EF, achieving the highest COD removal of 77.5% at 6.32 mA cm-2 with >95% and 74.3% of TSS and PO43- removal, respectively. With respect to microalgae, the highest COD removal of 85% was obtained by the culture in the EF effluent treated at 6.32 mA cm-2. Remarkably, not only 85% of the remaining organic matter was removed by microalgae, but also the totality of inorganic N and P compounds, as well as 65% of the Fe catalyst that was left after EF. The removal of inorganic species also demonstrates the high complementarity of both processes, since EF does not have the capacity to remove such compounds, while microalgae do not grow in the raw wastewater. Furthermore, a maximum of 0.8 g L-1 of biomass was produced after cultivation, with an accumulation of 32.2% of carbohydrates and 25.9% of lipids. The implementation of the two processes represents a promising sustainable approach for the management of industrial effluents, incorporating EF in a water and nutrient recycling system to produce biomass that could be valorized into clean fuels.

Lutein Production by Halophilic Microalgae Using Anaerobic Digestate as the Substrate and Its Potential Application as a Biopesticide

Production of value-added products from waste anaerobic digestate is economically and environmentally important for sustainable development of industrial process and products. In this study halophilic microalgae, Chlorella vulgaris 92001, Chlorella vulgaris 50291, Chlorella vulgaris 10241 and Tetraselmis indica, were initially screened for lutein production using synthetic dairy digestate (DD), municipal digestate (MD) and poultry digestate (PD) as no-cost substrates. Screening and optimization of parameters, such as dilution, pH, MgCl2, NaCl, NaHCO3 and inoculum concentration for maximum lutein production were further performed employing statistically designed Plackett-Burman and response surface methodology. Cultivation of C. vulgaris 92001 in a split column photobioreactor under optimum culture condition showed increase in lutein production by 2.36-fold in batch mode. The influence of different hydraulic retention time (HRT) values of 150, 130, 100 and 90 h on lutein production was evaluated in continuous mode with the split column photobioreactor. Lutein produced using the synthetic poultry digestate showed good potential biopesticide activity against Spodoptera litura (fall armyworm). Overall, this study demonstrated bioprocess development to produce lutein using synthetic anaerobic digestate from marine algae and its potential application as a biopesticide.

Engineered algal systems for the treatment of anaerobic digestate: A meta-analysis

The objective of this review was to provide quantitative insights into algal growth and nutrient removal in anaerobic digestate. To synthesize the relevant literature, a meta-analysis was conducted using data from 58 articles to elucidate key factors that impact algal biomass productivity and nutrient removal from anaerobic digestate. On average, algal biomass productivity in anaerobic digestate was significantly lower than that in synthetic control media (p < 0.05) but large variation in productivity was observed. A mixed-effects multiple regression model across study revealed that biological or chemical pretreatment of digestate significantly increase productivity (p < 0.001). In contrast, the commonly used practice of digestate dilution was not a significant factor in the model. High initial total ammonia nitrogen suppressed algal growth (p = 0.036) whereas initial total phosphorus concentration, digestate sterilization, CO2 supplementation, and temperature were not statistically significant factors. Higher growth corresponded with significantly higher NH4-N and phosphorus removal with a linear relationship of 6.4 mg NH4-N and 0.73 mg P removed per 100 mg of algal biomass growth (p < 0.001). The literature suggests that suboptimal algal growth in anaerobic digestate could be due to factors such as turbidity, high free ammonia, and residual organic compounds. This analysis shows that non-dilution approaches, such as biological or chemical pretreatment, for alleviating algal inhibition are recommended for algal digestate treatment systems.

Coupling anaerobic co-digestion of winery waste and waste activated sludge with a microalgae process: Optimization of a semi-continuous system

Wine production represents one of the most important agro-industrial sectors in Italy. Wine lees are the most significant waste in the winery industry and have high disposal and storage costs and few applications within the circular economy. In this study, anaerobic digestion and a microalgae coupled process was studied in order to treat wine lees and waste activated sludge produced within the same facility, with the aim of producing energy and valuable microalgae biomass that could be processed to recover biofuel or biostimulant. Chlorella vulgaris was cultivated on liquid digestate in a semi-continuous system without biomass recirculation. The best growth and phytoremediation performance were achieved applying a hydraulic retention time (HRT) of 20 days with a stable dry weight, lipid and protein storage of 1.85 ± 0.02 g l-1, 33.48 ± 7.54 % and 57.85 ± 10.14 % respectively. Lipid characterization highlighted the potential use in high quality biodiesel production, according to EN14214 (<12 % v/v linolenic acid). The microalgae reactor's liquid output showed high removal of ammonia (95.72 ± 2.10 %), but low organic soluble matter reduction. Further semi-continuous process optimization was carried out by increasing the time between digestate feeding and biomass recovery at HRT 10. These operative changes avoided biomass wash-out and provided a stable phytoremediation of the digestate with 84.58 ± 4.02 % ammonia removal, 33.01 ± 1.44 % sCOD removal, 38.06 ± 2.65 % of polyphenols removal.

Insight into the mechanism of nitrogen sufficiency conversion strategy for microalgae-based ammonium-rich wastewater treatment

The strategy of nitrogen sufficiency conversion can improve ammonium nitrogen (NH4+-N) removal with microalgal cells from ammonium-rich wastewater. We selected and identified one promising isolated algal strain, NCU-7, Chlorella sorokiniana, which showed a high algal yield and tolerance to ammonium in wastewater, as well as strong adaptability to N deprivation. The transition from N deprivation through mixotrophy (DN, M) to N sufficiency through autotrophy (SN, P) achieved the highest algal yields (optical density = 1.18 and 1.59) and NH4+-N removal rates (2.5 and 4.2 mg L-1 d-1) from synthetic wastewaters at two NH4+-N concentrations (160 and 320 mg L-1, respectively). Algal cells in DN, M culture obtained the lowest protein content (20.6%) but the highest lipid content (34.0%) among all cultures at the end of the stage 2. After transferring to stage 3, the lowest protein content gradually recovered to almost the same level as SN, P culture on the final day. Transmission electron microscopy and proteomics analysis demonstrated that algal cells had reduced intracellular protein content but accumulated lipids under N deprivation by regulating the reduction in synthesis of protein, carbohydrate, and chloroplast, while enhancing lipid synthesis. After transferring to N sufficiency, algal cells accelerated their growth by recovering protein synthesis, leading to excessive uptake of NH4+-N from wastewater. This study provides specific insights into a nitrogen sufficiency conversion strategy to enhance algal growth and NH4+-N removal/uptake during microalgae-based ammonium-rich wastewater treatment.

Abiotic stress as a dynamic strategy for enhancing high value phytochemicals in microalgae: Critical insights, challenges and future prospects

Microalgae showcase an extraordinary capacity for synthesizing high-value phytochemicals (HVPCs), offering substantial potential for diverse applications across various industries. Emerging research suggests that subjecting microalgae to abiotic stress during cultivation and the harvesting stages can further enhance the accumulation of valuable metabolites within their cells, including carotenoids, antioxidants, and vitamins. This study delves into the pivotal impacts of manipulating abiotic stress on microalgae yields, with a particular focus on biomass and selected HVPCs that have received limited attention in the existing literature. Moreover, approaches to utilising abiotic stress to increase HVPCs production while minimising adverse effects on biomass productivity were discussed. The present study also encompasses a techno-economic assessment (TEA) aimed at pinpointing significant bottlenecks in the conversion of microalgae biomass into high-value products and evaluating the desirability of various conversion pathways. The TEA methodology serves as a valuable tool for both researchers and practitioners in the quest to identify sustainable strategies for transforming microalgae biomass into high-value products and goods. Overall, this comprehensive review sheds light on the pivotal role of abiotic stress in microalgae cultivation, promising insights that could lead to more efficient and sustainable approaches for HVPCs 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.

Copper multifaceted interferences during swine wastewater treatment in high-rate algal ponds: alterations on nutrient removal, biomass composition and resource recovery

Microalgae cultivation in swine wastewater (SW) allows the removal of nutrients and biomass production. However, SW is known for its Cu contamination, and its effects on algae cultivation systems such as high-rate algal ponds (HRAPs) are poorly understood. This gap in the literature limits the proposition of adequate concentrations of Cu to optimise SW treatment and resource recovery in HRAPs. For this assessment, 12 HRAPs installed outdoors were operated with 800 L of SW with different Cu concentrations (0.1-4.0 mg/L). Cu's interferences on the growth and composition of biomass and nutrient removal from SW were investigated through mass balance and experimental modelling. The results showed that the concentration of 1.0 mg Cu/L stimulated microalgae growth, and above 3.0 mg Cu/L caused inhibition accompanied by an accumulation of H₂O₂. Furthermore, Cu affected the contents of lipids and carotenoids observed in the biomass; the highest concentration was observed in the control (16%) and 0.5 mg Cu/L (1.6 mg/g), respectively. An innovative result was verified for nutrient removal, in which increased Cu concentration reduced the N-NH₄⁺ removal rate. In contrast, the soluble P removal rate was enhanced by 2.0 mg Cu/L. Removal of soluble Cu in treated SW reached 91%. However, the action of microalgae in this process was not associated with assimilation but with a pH increase resulting from photosynthesis. A preliminary evaluation of economic viability showed that the commercialisation of biomass considering the concentration of carotenoids obtained in HRAPs with 0.5 mg Cu/L could be economically attractive. In conclusion, Cu affected the different parameters evaluated in this study in a complex way. This can help managers consort nutrient removal, biomass production, and resource recovery, providing information for possible industrial exploitation of the generated bioproducts.

Immobilization of Diatom Phaeodactylum tricornutum with Filamentous Fungi and Its Kinetics

Immobilizing microalgae cells in a hyphal matrix can simplify harvest while producing novel mycoalgae products with potential food, feed, biomaterial, and renewable energy applications; however, limited quantitative information to describe the process and its applicability under various conditions leads to difficulties in comparing across studies and scaling-up. Here, we demonstrate the immobilization of both active and heat-deactivated marine diatom Phaeodactylum tricornutum (UTEX 466) using different loadings of fungal pellets (Aspergillus sp.) and model the process through kinetics and equilibrium models. Active P. tricornutum cells were not required for the fungal-assisted immobilization process and the fungal isolate was able to immobilize more than its original mass of microalgae. The Freundlich isotherm model adequately described the equilibrium immobilization characteristics and indicated increased normalized algae immobilization (g algae removed/g fungi loaded) under low fungal pellet loadings. The kinetics of algae immobilization by the fungal pellets were found to be adequately modeled using both a pseudo-second order model and a model previously developed for fungal-assisted algae immobilization. These results provide new insights into the behavior and potential applications of fungal-assisted algae immobilization.

Life cycle assessment and techno-economic analysis of nitrogen recovery by ammonia air-stripping from wastewater treatment

Wastewater treatment plants (WWTPs) with anaerobic digestion of biosolids produce an ammonia-rich sidestream out of which nitrogen can be recovered through air stripping. Recovered ammonia can be used to produce ammonium sulfate (AS) for agricultural use, enabling the circular return of nitrogen as fertilizer to the food system. We investigate the cost and life cycle environmental impact of recovering ammonia from the sidestream of WWTPs for conversion to AS and compare it to AS production from the Haber Bosch process. We perform life cycle assessment (LCA) to investigate the environmental impact of AS fertilizer production by air-stripping ammonia from WWTP sidestreams at varying sidestream nitrogen concentrations. Techno-economic analysis (TEA) is performed to assess the break-even selling price of sidestream AS production at a WWTP in the City of Philadelphia. Greenhouse gas emissions for air-stripping technology range between 0.2 and 0.5 kg CO₂e/kg AS, about six times lower than the hydrocarbon-based Haber-Bosch process, estimated at 2.5 kg CO₂e/kg AS. Further reduction of greenhouse gas emissions is feasible by replacing fossil-based energy use in air-stripping process (82-98 % of net energy demand) with renewable sources. Also, a significant reduction in mineral depletion and improvement in human and ecosystem health are observed for the air-stripping approach. Furthermore, the break-even selling price for installing sidestream-based AS production at the Philadelphia's WWTP, considering capital and operating costs, is estimated at $0.046/kg AS (100 %), which is 92 % lower than the 2014 estimate of AS's average selling price at farms in the United States. We conclude that even with varying ammonia concentrations and high sidestream volume, air-stripping technology offers an environmentally and economically favorable option for implementing nitrogen recovery and simultaneous production of AS at WWTPs.

Selenium recovery from wastewater by the green microalgae Chlorella vulgaris and Scenedesmus sp

Selenium (Se) is an important element for many living organisms and its supplementation may be needed in food, feed, and soil to make up for its deficiency. At the same time, high selenium concentrations can harm the environment, thus its management in sewage and the study of its removal from waste streams are important. Microalgae-based systems may be used for wastewater treatment and nutrients recovery, while producing biomass for bioproducts or bioenergy. In this study, Chlorella vulgaris and Scenedesmus sp. grown in urban wastewater with different selenium concentrations (50-1000 μg Se/L) were evaluated for their resistance and selenium removal/recovery efficiency. Chlorella vulgaris and Scenedesmus sp. were able to remove up to 43 and 52 % of Se from wastewater, respectively. Chlorella vulgaris accumulated up to 323 mgSe/kg DW (in urban wastewater with 1000 μg Se/L). The Se-rich biomass produced may be applied to the supplementation of animal feed or used for biofortification of crops.

Treatment of Liquid Digestate by Green Algal Isolates from Artificial Eutrophic Pond

The ability of aquatic microalgae to treat the liquid digestate obtained from the anaerobic digestion of plant waste was investigated. Microalgae were isolated from natural environment for a laboratory-scale cultivation and were then used to remove nutrients and organic contaminants from the liquid digestate. It was shown that the microalgae consortia (Tetradesmus obliquus, Microglena sp., Desmodesmus subspicatus) could reduce nitrogen, phosphates, and total COD by up to 70%, 57%, and 95%, respectively. A new algae genus Microglena was isolated, which in a consortium with Tetradesmus obliquus and Desmodesmus subspicatus exhibited a high efficiency in the removal of both organic contaminants and nutrients from the liquid fraction of digestate.

A new cutting-edge review on the bioremediation of anaerobic digestate for environmental applications and cleaner bioenergy

Circular agriculture and economy systems have recently emerged around the world. It is a long-term environmental strategy that promotes economic growth and food security while reducing negative environmental consequences. Anaerobic digestion (AD) process has a high contribution and effective biodegradation route for bio-wastes valorization and reducing greenhouse gases (GHGs) emissions. However, the remaining massive digestate by-product contains non-fermented organic fractions, macro and/or micro-nutrients, heavy metals, and metalloids. Direct application of digestate in agriculture negatively affected the properties of the soil due to the high load of nutrients as well as the residuals of GHGs are emitted to the environment. Recycling and valorizing of anaerobic digestate is the main challenge for the sustainable biogas industry and nutrients recovery. To date, there is no global standard process for the safe digestate handling. This review described the biochemical composition and separation processes of anaerobic digestate. Further, advanced physical, chemical, and biological remediation's of the diverse digestate are comprehensively discussed. Moreover, recycling technologies such as phyco-remediation, bio-floc, and entomoremediation were reviewed as promising solutions to enhance energy and nutrient recovery, making the AD technology more sustainable with additional profits. Finally, this review gives an in-depth discussion of current biorefinery technologies, key roles of process parameters, and identifies challenges of nutrient recovery from digestate and prospects for future studies at large scale.

A review of advances in valorization and post-treatment of anaerobic digestion liquid fraction effluent

Traditionally, digestate is considered a waste, which is used as fertiliser in the agriculture industry. Recent studies focus on increasing the profitability of digestate by extracting reusable nutrients to promote biogas plants cost-effectiveness, sustainable management and circular economy. This review focuses on the post-treatment and valorization of liquor which is produced by solid-liquid fractioning of digestate. Nutrient recovery and removal from liquor are possible through mechanical, physicochemical and biological procedures. The processes discussed involve complex procedures that differ in economic value, feasibility, legislative restrictions and performance. The parameters that should be considered to employ these techniques are influenced by liquor characteristics, topography, climate conditions and available resources. These are key parameters to keep in mind during designing and manufacturing a biogas plant. In the following chapters, a discussion on available liquor treatment methods takes place. The present study examines the critical aspects of the available liquor treatment methods.

Effect of high ammonia on granular stability and phosphorus recovery of algal-bacterial granules in treatment of synthetic biogas slurry

The aim of the study was to investigate the application of algal-bacterial granules in treatment of high ammonia wastewater. Two identical cylindrical reactors, i.e., Rc and Rs was used to develop granular sludge system with synthetic biogas slurry. Rs was run under an artificial solar lamp controlled at 12 h power on and 12 h power off (∼10,000 lux); Rc was operated as control (no light). Results showed that algal-bacterial granules (ABGS) developed in Rs exhibited better structural stability in the face of high ammonia influent. Compared with aerobic granules (AGS), ABGS possessed high proteins (PN) content (145.3 mg/g-VSS) in extracellular polymeric substances (EPS) and better O₂ mass transfer inner granules. Higher phosphorus (P) removal capacity was obtained in Rs even under 400 mg/L NH₃–N which resulted in higher P content in ABGS biomass (56.4 mg/g-TSS). Bioavailable P in ABGS was 44 mg P/g-SS on day 160, approximately 1.53-times higher than that in AGS.

Microalgae Cultivation on Nutrient Rich Digestate: The Importance of Strain and Digestate Tailoring under PH Control

The bioremediation of digestate using microalgae presents a solution to the current eutrophication issue in Northwest Europe, where the use of digestate as soil fertiliser is limited, thus resulting in an excess of digestate. Ammonium is the main nutrient of interest in digestate for microalgal cultivation, and improving its availability and consequent uptake is crucial for optimal bioremediation. This work aimed to determine the influence of pH on ammonium availability in cultures of two green microalgae, additionally screened for their growth performances on three digestates produced from different feedstocks, demonstrating the importance of tailoring a microalgal strain and digestate for bioremediation purposes. Results showed that an acidic pH of 6–6.5 resulted in a better ammonium availability in the digestate media, translated into better growth yields for both S. obliquus (GR: 0.099 ± 0.001 day−1; DW: 0.23 ± 0.02 g L−1) and C. vulgaris (GR: 0.09 ± 0.001 day−1; DW: 0.49 ± 0.012 g L−1). This result was especially true when considering larger-scale applications where ammonium loss via evaporation should be avoided. The results also demonstrated that digestates from different feedstocks resulted in different growth yields and biomass composition, especially fatty acids, for which, a digestate produced from pig manure resulted in acid contents of 6.94 ± 0.033% DW and 4.91 ± 0.3% DW in S. obliquus and C. vulgaris, respectively. Finally, this work demonstrated that the acclimation of microalgae to novel nutrient sources should be carefully considered, as it could convey significant advantages in terms of biomass composition, especially fatty acids and carbohydrate, for which, this study also demonstrated the importance of harvesting time.

Enhancing Algal Yield and Nutrient Removal from Anaerobic Digestion Piggery Effluent by an Integrated Process-Optimization Strategy of Fungal Decolorization and Microalgae Cultivation

The dark brown anaerobic digestion piggery effluent (ADPE) with a large amount of ammonium generally needs high dilution before microalgae cultivation due to its inhibiting effects on algal growth. Due to the strong decolorization of fungi by degrading organic compounds in wastewater, the process-optimization integrated strategy of fungal decolorization of ADPE and subsequent microalgae cultivation with ammonium-tolerant strain may be a more reliable procedure to reduce the dilution ratio and enhance algal biomass production, and nutrient removal from ADPE. This study determined a suitable fungal strain for ADPE decolorization, which was isolated and screened from a local biogas plant, and identified using 26s rRNA gene sequence analysis. Subsequently, ADPE was pretreated by fungal decolorization to make low-diluted ADPE suitable for the algal growth, and conditions of microalgae cultivation were optimized to achieve maximum algal yield and nutrient removal from the pretreated ADPE. The results showed one promising locally isolated fungal strain, Nanchang University-27, which was selected out of three candidates and identified as Lichtheimia ornata, presenting a high decolorization to ADPE through fungal pretreatment. Five-fold low-diluted ADPE pretreated by L. ornata was the most suitable medium for the algal growth at an initial concentration of ammonium nitrogen of 380 mg L−1 in all dilution treatments. Initial optical density of 0.3 and pH of 9.0 were optimal culture conditions for the algal strain to provide the maximum algal yield (optical density = 2.1) and nutrient removal (88%, 58%, 65%, and 77% for the removal rates of ammonium nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand, respectively) from the pretreated ADPE. This study demonstrated that fungal decolorization and subsequent microalgae cultivation could be a promising approach to algal biomass production and nutrient removal from ADPE.

Revealing the synergistic effects of cells, pigments, and light spectra on light transfer during microalgae growth: A comprehensive light attenuation model

As the sole energy for photosynthesis, light decrease rapidly with path due to absorption by pigments and scattering by cells in microalgal suspensions. By comprehensively considering cell concentrations, pigment components, and light spectra, a modified Cornet model for light transmission in microalgal suspensions is established. The developed model better fits experimental data with a higher adjusted R², which is 5% higher than the model that is based only on cell concentration. The attenuation of blue light is the most severe, followed by red and green light. Among the three main pigments, total carotenoids contribute the most to the absorption of blue and green light (with contribution coefficients of 89.26 ± 4.53% and 46.04 ± 3.77%, respectively), and chlorophyll a contributes the most to the absorption of red light (with a contribution coefficient of 75.33 ± 5.08%). This study provides a better understanding and prediction of light transmission during microalgal cultivation.

Microalgae cultivation in wastewater from agricultural industries to benefit next generation of bioremediation: a bibliometric analysis

The aim of this study was to provide a bibliometric analysis and mapping of existing scientific papers, focusing on microalgae cultivation coupled with biomass production and bioremediation of wastewater from agricultural industries, including cassava, dairy, and coffee. Using the Web of Science (WoS) database for the period 1996-2021, a search was performed using a keyword strategy, aiming at segregating the papers in groups. For the first search step, the keywords "wastewater treatment", AND "microalgae", AND "cassava" OR "dairy" OR "coffee" were used, resulting in 59 papers. For the second step, the keywords "wastewater treatment" AND "biomass productivity" AND "microalgae" AND "economic viability" OR "environmental impacts" were used, which resulted in 34 articles. In these papers, keywords such as "carbon dioxide biofixation" and "removal of nutrients by the production of biomass by microalgae" followed by "environmental and economic impacts" were highlighted. Some of these papers presented an analysis of the economic feasibility of the process, which reveal the state-of-the-art setup required to make the cultivation of microalgae economically viable. Researches focusing on the efficiency of microalgae biomass harvesting are needed to improve the integration of microalgae production in industrial eco-parks using wastewater to achieve the global goal of bioremediation and clean alternatives for renewable energy generation.

Maximizing nutrient recycling from digestate for production of protein-rich microalgae for animal feed application

The integration of phototrophic microalgal production and anaerobic digestion can recycle excess nutrients across European surplus hotspots to produce protein-rich biomass for nutritional applications. However, the challenging physico-chemical properties of raw digestate constrain microalgal growth and limit digestate valorization potential. This study focused on the pre-treatment of food waste-based digestate using paper-filtration to improve its properties for cultivating Desmodesmus sp. and Chlorella vulgaris. The microalgal growth performance in paper-filtered digestate (PFD, 10 μm-pore size) was then compared to growth in membrane-filtered digestate (MFD, 0.2 μm-pore size). A microplate-based screening coupled with Cytation device assessment of PFD and MFD samples after dilution and with/without phosphorus supplementation showed that PFD was the best substrate. Moreover, phosphorus supplementation resulted in improved growth at higher digestate concentrations (5-10% v/v PFD), indicating the importance of using a balanced growth medium to increase the volumetric usage of digestate. Results were validated in a 3-L bioreactor at 10% PFD with phosphorus supplementation, reaching a biomass concentration of 2.4 g L^-1 with a protein and carbohydrate content of 67% and 13% w/w respectively. This trial indicates that paper-filtration is a promising pre-treatment technique to maximize digestate recycling and deliver a sustainable animal feed-grade protein alternative.

Microalgae production for nitrogen recovery of high-strength dry anaerobic digestion effluent

Dry anaerobic digestion (D-AD) generates nitrogen-rich effluents that are normally neglected in the circular bioeconomy. The high turbidity and ammonium content hamper nitrogen recovery from these effluents via biological processes, such as microalgae culture. The goal of this study was to demonstrate microalgae growth viability in high-strength D-AD effluents in order to recover nitrogen (N) as microalgae biomass. According to the experimental factorial design conducted in batch reactors, ammonium was identified as the critical inhibitory compound for microalgae growth while turbidity did not exhibit a significantly negative effect. Instead, turbidity resulted advantageous since it promoted high nitrogen uptake rates and biomass production. The presence of organic turbidity resulted in a positive effect that boosted Chlorella growth in a stream with higher ammonium (350 mg NH₄⁺-N L^-1) and turbidity (175 NTU) than the inhibition thresholds reported in the literature, reaching 98.7% of N recovery as microalgae biomass. When microalgae culture was scaled up in a photobioreactor operated in continuous mode, microalgae biomass was effectively produced while recovering 100% of N at a hydraulic retention time of 10 days. By imposing long exposure times and high turbidity, Chlorella adaptation to high-strength D-AD effluent resulted in high N uptake and biomass production. This study demonstrated not only the most influencing factor and the optimal NH₄⁺-N and turbidity combination, but also the viability of using D-AD effluents as culture media for microalgae biomass production.

Attempts to alleviate inhibitory factors of anaerobic digestate for enhanced microalgae cultivation and nutrients removal: A review

Anaerobic digestion is a well-established process that is applied to treat organic wastes and convert the carbon to valuable methane gas as a source of energy. The digestate that comes out as a by-product is of a great challenge due to its high nutrient content that can be toxic in case of improper disposal to the environment. Several attempts have been done to valorize this digestate. Digestate has been considered as an interesting medium to cultivate microalgae. The nutrients available in the digestate, mainly nitrogen and phosphorus, can be an interesting supplement for microalgae growth requirement. The main obstacles of using digestate as a medium to cultivate microalgae are the dark color and the high ammonium-nitrogen concentration. The focus of this review is to discuss in detail the major attempts in research to overcome inhibition and enhance microalgae cultivation in digestate. This review initially discussed the obstacles of digestate as a medium for microalgae cultivation. Different processes to overcome inhibition were discussed including dilution, supplying additional carbon source, favoring mixotrophic cultivation and pretreatment. More emphasis in this review was given to digestate pretreatment. Among the pretreatment methods, filtration, and centrifugation were of the most applied ones. These strategies were found to be effective for turbidity and chromaticity reduction. For ammonium nitrogen removal, ammonia stripping and biological pretreatment methods were found to play a vital role. Adsorption could work both ways depending on the material used. Combining different pretreatment methods as well as including selected microalgae stains were found interesting strategies to facilitate microalgae cultivation with no dilution. This study recommend that more study should investigate the optimization of microalgae cultivation in anaerobic digestate without the need for dilution.

Anaerobic digestate as a low-cost nutrient source for sustainable microalgae cultivation: A way forward through waste valorization approach

To suffice the escalating global energy demand, microalgae are deemed as high potential surrogate feedstocks for liquid fuels. The major encumbrance for the commercialization of microalgae cultivation is due to the high costs of nutrients such as carbon, phosphorous, and nitrogen. Meanwhile, the organic-rich anaerobic digestate which is difficult to be purified by conventional techniques is appropriate to be used as a low-cost nutrient source for the economic viability and sustainability of microalgae production. This option is also beneficial in terms of reutilize the organic fraction of solid waste instead of discarded as zero-value waste. Anaerobic digestate is the side product of biogas production during anaerobic digestion process, where optimum nutrients are needed to satisfy the physiological needs to grow microalgae. Besides, the turbidity, competing biological contaminants, ammonia and metal toxicity of the digestate are also potentially contributing to the inhibition of microalgae growth. Thus, this review is aimed to explicate the feasibility of utilizing the anaerobic digestate to cultivate microalgae by evaluating their potential challenges and solutions. The proposed potential solutions (digestate dilution and pre-treatment, microalgae strain selection, extra organics addition, nitrification and desulfurization) corresponding to the state-of-the-art challenges are applicable as future directions of the research.

Treatment and resource utilization of dairy liquid digestate by nitrification of biological aerated filter coupled with assimilation of Chlorella pyrenoidosa

Ammonia inhibition is considered a key issue when using liquid digestate for microalgae cultivation. To study the effect of pretreatment with a biological aerated filter (BAF) on microalgae culture with dairy liquid digestate, nitrification characteristics of BAFs under different hydraulic retention time (HRT) and the growth characteristics of Chlorella pyrenoidosa in effluents of BAFs were investigated. Results showed that the BAFs can rapidly nitrify ammonia nitrogen and significantly improve the light transmittance of liquid digestate (the maximum promotion rate was ~260%), and the effect improved as the HRT increased. Pretreatment of liquid digestate with BAFs can eliminate ammonia inhibition for C. pyrenoidosa. Furthermore, lipid, crude protein, and higher heating value (HHV) output were also not affected by HRT. The similar removal of nitrate nitrogen in microalgae culture systems using effluents with 6-h and 12-h HRT (21.59% and 21.07%, respectively) were recorded. The results suggested that BAF coupled with microalgae culture is a novel option on the resource utilization of dairy liquid digestate.

Swine wastewater treatment in high rate algal ponds: Effects of Cu and Zn on nutrient removal, productivity and biomass composition

This study aimed to evaluate the simultaneous interferences of Cu and Zn found in swine wastewater (SW) in the development of microalgae considering real conditions of cultivation in high rate algal ponds (HRAPs). Ten HRAPs on a pilot scale were fed with SW with different mixtures of Cu (0.5-3.0 mg/L) and Zn (5.0-25.0 mg/L). The interferences of these metals in removing nutrients (N-NH₄⁺ and soluble phosphorus (Ps)) from the SW were determined. In addition, this study evaluated the effects on biomass growth and biochemical composition. Chlorella sp. was dominant in all HRAPs and the condition that potentiated its growth occurred in medium containing 1.8 mg Cu/L + 15.0 mg Zn/L, while higher concentrations conferred inhibition. Only Cu compromised the removal rates of N-NH₄⁺ while the effects of Zn were not significant. Contrary, Zn interfered with Ps removal rates, but the impact of Cu was not significant. The greatest Cu applications increased the protein levels by biomass (50.5-55.2 %). Carbohydrate accumulation was favored by conditions that inhibited the development of microalgae due to either limitation or excess of metals. Copper and Zn compromised the levels of lipids, and the control treatment had the highest content (24.5 %). The presence of Cu and Zn changed the dynamics of HRAPs regarding nutrient removal, productivity, and biochemical composition of the biomass.

Integrated microalgal biorefinery for the production and application of biostimulants in circular bioeconomy

Adverse detrimental impacts of environmental pollution over the health regimen of people has driven a shift in lifestyle towards cleaner and natural resources, especially in the aspects of food production and consumption. Microalgae are considered a rich source of high value metabolites to be utilized as plant growth biostimulants. These organisms however, are underrated compared to other microbial counterparts, due to inappropriate knowledge on the technical, enviro-economical constrains leading to low market credibility. Thus, to avert these issues, the present review comprehensively discusses the biostimulatory potential of microalgae interactively combined with circular bio-economy perspectives. The biochemical content and intracellular action mechanism of microalgal biostimulants were described. Furthermore, detailed country-wise market trends along with the description of the existing regulatory policies are included. Enviro-techno-economic challenges are discussed, and the consensus need for shift to biorefinery and circular bio-economy concept are emphasized to achieve sustainable impacts during the commercialization of microalgal biostimulants.

Effect of nano-TiO2 on humic acid utilization from piggery biogas slurry by microalgae

Resource recovery from piggery biogas slurry has become an inevitable demand for sustainable development of pig industry. Microalgae show great potential in recovering nitrogen and phosphorus from piggery slurry, but struggle to utilize organic pollutants, as most of them are inert components (e.g., humic acids, HAs). In this study, nano-TiO₂ was used to enhance the utilization of HAs by microalgae from piggery biogas slurry. Results showed that the optimal conditions for microalgal growth and HAs removal by the microalgae-TiO₂ coupling system were TiO₂ dosage of 0.30 g/L, microalgal inoculation concentration of 0.40 g/L, light intensity of 360 µmol photon/(m²·s) and temperature of 30 °C, with the microalgal chlorophyll concentration of 6.51 mg/L and HAs removal efficiency of 50.14%. Analysis of HAs composition variations in the piggery biogas slurry indicated that the decrease of HAs was caused by their decomposition into small molecules under the photocatalytic reactions of TiO₂.

Heterotrophic cultivation of Galdieria sulphuraria under non-sterile conditions in digestate and hydrolyzed straw

Non-sterile heterotrophic cultivation of Galdieria sulphuraria in presence of digestate as well as straw after hydrolysis was investigated. G. sulphuraria can be grown in pure digestate at rates of 0.9 day^-1 with glucose. However, a proteolytic treatment of digestate resulted in increased growth rates (1.2 day^-1) and doubled cell concentrations. Furthermore, G. sulphuraria can utilize glucose obtained after straw hydrolysis. Biomass yields in glucose limited cultures were around 0.9 g per g glucose, while only 0.2 g biomass was formed per g glucose in glucose sufficient cultures. Biomass composition (w/w) of G. sulphuraria grown in digestate supplemented with straw hydrolysate consisted of 20% carbohydrates, 37% proteins and 3% lipids. This study revealed the potential to utilize agricultural waste streams to form algal biomass rich in proteins and may pave the way to novel utilization strategies to be implemented in rural areas.

Valorization of swine wastewater in a circular economy approach: Effects of hydraulic retention time on microalgae cultivation

To optimize the swine wastewater (SWW) treatment, this study investigated different hydraulic retention times (HRTs) for microalgae cultivation. For this purpose, five pilot-scale reactors operated in semi-continuous flow, with HRTs equal to 9, 12, 15, 18, 21 days were evaluated in terms of SWW polishing and biomass production. The effluent treatment was discussed accompanied by principal component analysis, which allowed identification of causes of variance in the data set, ideal for studies with real effluent and influenced by environmental conditions. All reactors show satisfactory removals of N-NH₄⁺ (91.6-95.3%), COD (15.8-39.9%), DO increment (in average 7.5 mg O₂/L) and, only the longest HRT (21 days) was able to remove Ps (21%). The results obtained indicated that a consortium of microalgae and bacteria was developed for all the tested HRTs. On the other hand, HRT = 12 days provided a healthier culture of photosynthesizing organisms (chl-a/VSS = 3.04%). Carbohydrates (20.8-31.3%) and proteins (2.7-16.2%) were the compounds of commercial interest in the highest proportion in the biomass of all reactors, with contents comparable to that of terrestrial crops. Thus, it was suggested a valorization route of these compounds of high added value to return to pig farming, where the nutrients were intended to supplement the swine feed and clarified water for cleaning the pig stalls. Thus, in the circular economy context, this research contributes to water footprint reduction and the sustainability of the pig farming production chain. The economic and environmental analysis of the route is suggested to enable its implementation on a large scale, as well as further technical feasibility research (reactor types, exposure to external environment, evaluation of pathogen removal and animal feed supplementation from SWW microalgae biomass).

Simultaneous biogas upgrading, CO2 sequestration, and biogas slurry decrement using biomass ash

A novel system for simultaneous biogas upgrading, CO₂ sequestration, and biogas slurry decrement was established by adding biomass ash into biogas slurry to form a renewable CO₂ mixture absorbent. After CO₂ saturation, the CO₂-rich mixture absorbent could be applied for plant growth. When the mass ratio of liquid to solid was 4:1, CO₂ absorption capacity of this mixture absorbent reached up to 97.33 g-CO₂/kg-biomass-ash, which was about 135% higher than that of the biomass ash-water mixture. The highest value of 129.94 g-CO₂/kg-biomass-ash was obtained at a liquid-solid ratio of 99:1. When the TS concentration of anaerobic digestion feedstock was higher than 16 wt% and the water content of CO₂-rich absorbent was about 50 wt%, more than 80% of biogas slurry can be adsorbed by the biomass ash. If the biomass ash with a CO₂ absorption capacity of 100 g-CO₂/kg was adopted and its transportation distance was less than 45 km, the biogas upgrading cost could be lower than the global average level (about RMB¥ 0.7/Nm³-biogas) when using the novel system proposed in this study.

Terrestrial anaerobic digestate composite for fertilization of oligotrophic coastal seas

To promote primary production in oligotrophic seas, we developed a fertilization composite consisting of blast furnace cement and anaerobic digestate with a high nutrient content derived from biogas power plant byproducts. In this study, we investigated the dissolution behavior of nutrients from the fertilization composite and evaluated the effects of the fertilization composite on the growth of marine primary producers. Batch experiments and tank experiments to simulate oligotrophic coastal seas revealed that the nutrients dissolved from the fertilization composite were taken up by marine microalgae and seaweed. The fertilization composite promoted the growth of both planktonic and benthic micro algae. The total amounts of chlorophyll a in the fertilization composite tank increased by 1.4 times compared to control (p < 0.01). The flow of dissolved inorganic nitrogen uptake by marine microalgae increased 3-5 times when the fertilization composite was applied. In Wakame seaweed culture experiments, the nitrogen contents of Wakame from the fertilization composite tank were 1.2 times higher than those cultured in the control tank (p < 0.01). As a result, Wakame leaves cultured in the fertilization composite tank were 1.4 times longer than those cultured in the control tank. Approximately 44% of dissolved inorganic nitrogen from the fertilization composite was taken up by the seaweed. Hence, the fertilization composite was demonstrated to enhance the growth of marine microalgae and seaweed, which are primary producers in marine ecosystems. The fertilization composite proposed in this study can create novel nutrient mass flow by connecting terrigenous anaerobic digestate from biogas power plants to oligotrophic seas and thus stimulate the recovery of fishery production.

Microalgal growth, nitrogen uptake and storage, and dissolved oxygen production in a polyculture based-open pond fed with municipal wastewater in northern Sweden

Microalgal-based wastewater treatment and CO₂ sequestration from flue gases with subsequent biomass production represent a low-cost, eco-friendly, and effective procedure of removing nutrients and other pollutants from wastewater and assists in the decrease of greenhouse gas emissions. Thus, it supports a circular economy model. This is based on the ability of microalgae to utilise inorganic nutrients, mainly nitrogen and phosphorous, as well as organic and inorganic carbon, for their growth, and simultaneously reduce these substances in the water. However, the production of microalgae biomass under outdoor cultivation is dependent on several abiotic and biotic factors, which impact its profitability and sustainability. Thus, this study's goal was to evaluate the factors affecting the production of microalgae biomass on pilot-scale open raceway ponds under Northern Sweden's summer conditions with the help of a mathematical model. For this purpose, a microalgae consortium and a monoculture of Chlorella vulgaris were used to inoculate outdoor open raceway ponds. In line with the literature, higher biomass concentrations and nutrient removals were observed in ponds inoculated with the microalgae consortium. Our model, based on Droop's concept of macronutrient quotas inside the cell, corresponded well to the experimental data and, thus, can successfully be applied to predict biomass production, nitrogen uptake and storage, and dissolved oxygen production in microalgae consortia.

Phycoremediation and biomass production from high strong swine wastewater for biogas generation improvement: An integrated bioprocess

This study investigated the phycoremediation process from swine digestate integrated with photosynthetic biomass and biogas production in the context of circular economy. Effects of total ammonia nitrogen (TAN) and pH on biomass productivity and nutrients removal, using a central rotational composite design, were evaluated. pH showed a significant effect on biomass productivity and phosphate removal. The strain Chlorella sorokiniana (LBA#39) was able to tolerate up to 1300 mg TAN L^-1 at neutral pH, with maximum biomass productivity of 198 mg DW L^-1 d^-1 and removal of 90 and 70 (%) of phosphate and nitrogen, respectively. The biomass harvested after phycoremediation from digestate showed high content of volatile solids (95.4%) and proteins (59.5%). Biochemical methane potential (BMP) from microalgae monodigestion was 292 ± 10 mL_NCH4 g_VSadd^-1. The use microalgae biomass addition in the biodigestion process increased up to 32.1% in biogas production. It is an attractive approach to integrating raw materials into existing agro-industrial facilities and improving biogas production, adopting the concept of circular economy and mitigating greenhouse gas emissions.

Towards high-quality biodiesel production from microalgae using original and anaerobically-digested livestock wastewater

In this study, we conducted proof-of-concept research towards the simultaneous treatment of livestock wastewater and the generation of high-quality biodiesel, through microalgae technology. Both original (OPE) and anaerobically-digested (DPE) piggery effluents were investigated for the culture of the microalgae, Desmodesmus sp. EJ8-10. After 14 days' cultivation, the dry biomass from microalgae cultivated in OPE increased from an initial value of 0.01 g/L to 0.33-0.39 g/L, while those growing in DPE only achieved a final dried mass of 0.15-0.35 g/L, under similar initial ammonium nitrogen (NH₄⁺-N) concentrations. The significantly higher microalgal biomass production achieved in the OPE medium may have been supported by the abundance of both macronutrient, such as phosphorus (P), and of micronutrients, such as trace elements, present in the OPE, which may not been present in similar quantities in the DPE. However, a higher lipid content was observed (19.4-28%) in microalgal cells from DPE cultures than those (18.7-22.3%) from OPE cultures. Moreover, the fatty acid compositions in the microalgae cultured in DPE contained high levels of monounsaturated fatty acids (MUFAs) and total C16-C18 acids, which would afford a superior potential for high-quality biodiesel production. The N/P ratio (15.4:1) in OPE was much closer to that indicated by previous studies to be the most suitable (16:1) for microalgae growth, when compared with that determined from the DPE culture medium. This may facilitate protein synthesis in the algal cells and induce a lower accumulation of lipids. Based on these findings, we proposed a new flowsheet for sustainable livestock waste management.

Year-Round Cultivation of Tetraselmis sp. for Essential Lipid Production in a Semi-Open Raceway System

There is increasing demand for essential fatty acids (EFAs) from non-fish sources such as microalgae, which are considered a renewable and sustainable biomass. The open raceway system (ORS) is an affordable system for microalgae biomass cultivation for industrial applications. However, seasonal variations in weather can affect biomass productivity and the quality of microalgal biomass. The aim of this study was to determine the feasibility of year-round Tetraselmis sp. cultivation in a semi-ORS in Korea for biomass and bioactive lipid production. To maximize biomass productivity of Tetraselmis sp., f medium was selected because it resulted in a significantly higher biomass productivity (1.64 ± 0.03 g/L) and lower omega-6/omega-3 ratio (0.52/1) under laboratory conditions than f/2 medium (0.70/1). Then, we used climatic data-based building information modeling technology to construct a pilot plant of six semi-ORSs for controlling culture conditions, each with a culture volume of 40,000 L. Over 1 year, there were no significant variations in monthly biomass productivity, fatty acid composition, or the omega-6/omega-3 ratio; however, the lipid content correlated significantly with photosynthetic photon flux density. During year-round cultivation from November 2014 to October 2017, areal productivity was gradually increased by increasing medium salinity and injecting CO₂ gas into the culture medium. Productivity peaked at 44.01 g/m²/d in October 2017. Throughout the trials, there were no significant differences in average lipid content, which was 14.88 ± 1.26%, 14.73 ± 2.44%, 12.81 ± 2.82%, and 13.63 ± 3.42% in 2014, 2015, 2016, and 2017, respectively. Our results demonstrated that high biomass productivity and constant lipid content can be sustainably maintained under Korean climate conditions.

Enhancement of nutrients removal and biomass accumulation of Chlorella vulgaris in pig manure anaerobic digestate effluent by the pretreatment of indigenous bacteria

High concentrations of pollutants in pig manure anaerobic digestate effluent (PMADE) can severely inhibit microalgal growth. In this study, two types of PMADE (PMADE-1, PMADE-2) were pretreated with indigenous bacteria which were selected from PMADE to alleviate their inhibition for the growth of Chlorella vulgaris. Indigenous bacteria could decrease 34.04% and 47.80% of total phosphorus (TP) and turbidity in PMADE-1, and 80.81%, 43.27%, and 57.51% of COD, TP, and turbidity in PMADE-2, respectively. And no significant reduction of NH₄⁺-N in both PMADE after 5 days pretreatment occurred. C. vulgaris failed to grow in unpretreated PMADE-2. Pretreatment of PMADE with indigenous bacteria could remarkably promote nutrients removal and cell growth of C. vulgaris compared to the unpretreated PMADE. The order of abiotic stress in the studied PMADE was COD > NH₄⁺-N > turbidity, and it is appropriate to pretreat the PMADE with indigenous bacteria for 2-3 days.