Nutrient Removal Efficiency Research Articles

Carbon-efficient Nutrients removal from real municipal wastewater under conditions of highly variable influent quality and low temperature

In order to maximize carbon efficient nutrient removal of real primary effluent under the conditions of highly variable influent quality and low temperature, this study integrated four advanced bioprocesses, namely partial nitrification, endogenous denitrification, partial denitrification-anammox, enhanced biological phosphorus removal, into one advanced pilot design. The pilot system has been on-site operated for 212 days and was able to handle highly variable conditions with the aid of automatic feedback and feedforward controllers nested in secondary and tertiary treatment. Comparing to the case when full nitrification and full dentification technologies had to be used to meet the effluent requirement of total inorganic nitrogen (TIN) ≤ 3 mg/L and orthophosphate phosphorus ≤ 0.1 mg/L, the pilot results showed that 100 wt% carbon and 55.5 wt% oxygen could be saved in the secondary process and another 45.2 wt% carbon could be saved in the tertiary process. 44.5 wt% influent TIN was removed through endogenous denitrification in the secondary treatment with another 39.5 wt% TIN polished by partial denitrification-anammox in tertiary treatment. Because post-anoxic endogenous denitrification has removed majority of the NOX-N, it was concluded that the energy intensive mixed liquor recirculation that has been popular in traditional design for pre-anoxic zone denitrification can be eliminated.

Wastewater treatment process using immobilized microalgae.

Microalgae biomass products are gaining popularity due to their diverse applications in various sectors. However, the costs associated with media ingredients and cell harvesting pose challenges to the scale-up of microalgae cultivation. This study evaluated the growth and nutrient removal efficiency (RE) of immobilized microalgae Tetradesmus obliquus in sodium alginate beads cultivated in swine manure-based wastewater compared to free cells. The main findings of this research include (i) immobilized cells outperformed free cells, showing approximately 2.3 times higher biomass production, especially at 10% effluent concentration; (ii) enhanced organic carbon removal was observed, with a significant 62% reduction in chemical oxygen demand (383.46-144.84 mg L-1) within 48 h for immobilized cells compared to 6% in free culture; (iii) both immobilized and free cells exhibited efficient removal of total nitrogen and total phosphorus, with high REs exceeding 99% for phosphorus. In addition, microscopic analysis confirmed successful cell dispersion within the alginate beads, ensuring efficient light and substrate transfer. Overall, the results highlight the potential of immobilization techniques and alternative media, such as biodigested swine manure, to enhance microalgal growth and nutrient RE, offering promising prospects for sustainable wastewater treatment processes.

Enhanced Performance of Membrane Bioreactor in Sewage Treatment through Integrated Control Strategy

<p>Wastewater includes sewage water, which presents serious environmental problems that necessitate effective treatment techniques. Membrane Bioreactors (MBRs) have emerged as promising solutions, albeit plagued by membrane fouling and computational loading issues. To resolve these issues, this research article presents an innovative control strategy combining both artificial bee colony optimization (ABC) and recurrent neural network (RNN) to regulate the performance of MBR in sewage treatment. Initially, the influent wastewater data was collected and pre-processed using the regression imputation approach. RNN architecture was designed and trained using the pre-processed data to forecast the performance of the MBN system. Further, the ABC algorithm was applied to optimize the function of MBR by adjusting the control variables. The developed model was validated with the publically available wastewater treatment plan dataset and the effectiveness of the developed model was validated by performing intensive performance and comparative assessment. The performance evaluation demonstrates that the proposed methodology attained greater results of 98.59% effluent quality, 98.70% of nutrient removal efficiency, less computational time of 2.87s, and a low membrane fouling index of 1.23%. The comparative analysis illustrates that the presented approach achieved improved performances than the existing methodologies.</p>

Investigating the application of the aquaponic paradigm to Litopenaeus vannamei farming

Abstract Aquaponics, a sustainable farming system combining aquaculture and hydroponics, has been widely adopted, used, particularly in freshwater. This study explores the feasibility of adapting the aquaponic model to saltwater conditions, specifically for wastewater treatment from Litopenaeus vannamei farming using the salt-tolerant plant species Rhizophora apiculata Blume. It focuses on plant development and calculates the water treatment effectiveness in terms of nutrient removal in mg of NH4 +, NO2 −, NO3 −, and total phosphorus per gram of plant mass. The first phase involved seedling production, model creation, and testing the plant’s wastewater treatment capabilities. After three months of growth, the plants are subjected to shrimp wastewater, and their nutrient removal efficiency is determined. The obtained data provides essential parameters for the operation of the model during Phase 2. In Phase 1, R. apiculata Blume removed NH4 +, NO2 −, NO3 −, and total phosphorus at 95%, 97%, 59%, and 57% efficiency after seven days, respectively. It focuses on plant development and quantifies the efficiency of water treatment by measuring the removal of nutrients such as NH4 +, NO2 −, NO3 −, and total phosphorus per gram of plant mass.The calculated nutrient removal coefficients per gram of plant mass are NH4 +: 0.007, NO2 −: 0.005, NO3 −: 0.031 and total phosphorus: 0.121. In Phase 2, the designed aquaponic model was developed, which included a shrimp tank with 300 individuals per 1 m3, a fish tank with 50 individuals per 0.5 m3, and a plant growing system. The experimental aquaponic model demonstrates the technical feasibility of using R. apiculata Blume to recycle water in shrimp farming. The model shows potential for scaling up and offers additional benefits, as the leaves R. apiculata of can serve as an herbal source for aquatic species.

Efficient nutrient and antibiotics removal from aquaculture wastewater using different microalgae-based systems by agricultural multi-phytohormone induction

The present study innovatively explores the impact of adding agricultural mixed plant hormones (gibberellin acid-indole-3-acetic acid-brassinolide, GIB) on simultaneously removing nutrients and antibiotics out of aquaculture wastewater within different four microalgae-bacteria-fungus symbionts. The results indicated that under the optimal symbiotic technology (Chlorella vulgaris+S395-2+Clonostachys rosea) and the best hormone GIB (20 mg L−1) addition, both growth characteristics and photosynthetic performance of microalgae-bacteria-fungus symbionts were optimal. Under optimal treatment conditions, the average nutrient removal efficiency (TN and TP) reached 93.71 ± 5.02 % and 93.56 ± 4.07 %, separately, whereas the average removal efficiency of antibiotics (oxytetracycline, ciprofloxacin and sulfadiazine) were 99.46 ± 0.17 %, 89.53 ± 5.41 %, and 85.68 ± 6.82 %, respectively. This study offers a promising new direction for algal treatment technology, particularly in the concurrent removal of antibiotics and nutrients.

Novel overlapping constructed wetlands with water drops reoxygenation and lightweight fillers for decentralized wastewater treatment

Constructed wetlands (CWs), crucial for the rural decentralized wastewater treatment, have encountered limitations in nutrient removal efficiency and require extensive land area. This study has constructed a novel overlapping horizontal subsurface flow CWs (OLCWs). Remarkably, OLCWs with mixed lightweight fillers (M-OLCWs) exhibited a significant enhancement in total nitrogen (TN) removal efficiency (88–91 %) in different hydraulic loading rates compared to single filler OLCWs (48–62 %). This significant enhancement can be attributed to the lightweight fillers, which have higher abundances and diversity of nitrogen related microorganisms. The treatment dynamics revealed that the second stage exhibited an excellent TN removal efficiency (73–75 %) attributed to sufficient dissolved oxygen concentration by water drops reoxygenation. The research reveals that M-OLCWs, by utilizing water drops reoxygenation and lightweight fillers, not only enhance pollutant treatment efficiency but also reduce required land area, thereby offering a sustainable solution for rural decentralized wastewater treatment.

Green Roof Systems for Rainwater and Sewage Treatment

Green roof systems are regarded as a viable solution for mitigating urban environmental challenges and offering a multitude of environmental benefits. Currently, green roofs are increasingly being utilized for the management of rainwater runoff and wastewater. The integration of decentralized rainwater and sewage on-site treatment technology with urban green buildings is being gradually promoted. Green roofs can also be considered as a form of decentralized rainwater and sewage on-site technology, which holds great potential for widespread adoption in the future. Several studies have suggested that green roofs may serve as a potential source of pollutants; however, there are also studies that clearly demonstrate the efficient removal of nutrients and organic pollutants by green roofs. This article critically examines the existing literature on water treatment aspects associated with green roofs and elucidates their classification and operational mechanisms. Through an analysis of previous research cases, it becomes evident that both substrate and vegetation play a significant role in influencing the treatment performance of green roofs. By designing and configuring appropriate substrate and vegetation, green roofs can play a pivotal role in the purification of water quality. Finally, a brief outlook is presented for the future research directions of green roofs, with the anticipation that green roofs will feature more innovative and environmentally friendly designs, as well as expanded prospects for application.

Multi-criteria analysis of the continuous operation of a membrane photobioreactor to treat sewage: Modeling and sensitivity analysis

Microalgae-based wastewater remediation is aligned with circular economy principals but successful large-scale facilities are scarce due to the limited knowledge of the interactions between all relevant variables and the scarce development of control and automation systems. Machine learning (ML) methods have the potential predict performance in microalgae photobioreactors, with the aim to optimize it. Some attempts have been performed under controlled lab conditions which prevents the direct application of their results to industrial scale. This study aims to develop ML models for the prediction of nutrient removal, biomass production and photosynthetic efficiency using a database obtained from 1.5-y operation of a pilot-scale membrane photobioreactor (MPBR) that treated sewage. A total of 14 inputs and 6 outputs were selected. Random forests (RF), boosted trees (BT), multilayer perceptron (MLP), support vector machine methods (SVM) were tested. The lowest prediction errors were obtained with the MLP model, allowing the developed tool to be used as an alternative to mechanistic models. Large ranges of data were used, considering the variability of factors in the diurnal cycle whose influence on the variability of the data is usually neglected. Using global sensitivity analysis (GSA), input-output relationships were verified, reflecting relevant number of variables showing significant values of Shapley Indices. Additionaly, partial dependence plots showed both linear and nonlinear depending on the selected inputs and outputs. Finally, using ML models, multi-criteria optimization of operating parameters was performed for two variants: a) optimization of operating parameters (HRT, SRT, and air flowrate (Fair)); and b) optimization of operating parameters and influent nutrient loads (HRT, SRT, Fair, nitrogen and phosphorus loading rates).

Sequential two-stage cultivation system using novel microalga consortia for treatment of municipal wastewater and simultaneous biomass production: Sustainable environmental management

Monoculture-based microalgae cultivation systems to treat wastewater are well-reported. Despite that, this method has some limitations in terms of nutrient removal potential, environment adaptation, and low biomass productivity. Conversely, microalgae co-cultivation and a two-stage sequential cultivation system (TSSCS) recently emerged as a promising approach to improve the treatment process and biomass productivity through better adaptation to the environment. However, no outdoor large-scale experiments were reported using this approach which hinders the viability of the process. Thus, in the present study, a sequential two-stage large-scale outdoor novel microalgae consortia experiment was developed. In first stage consortia-assisted sequential cultivation, two ratios of Tetraselmis indica (TS) and one ratio of Picochlorum sp. (PC) (2 TS:1 PC) were cultivated in a 1000-L pond containing 75%-municipal wastewater (MWW) + 25%-ASN-III, while in the second stage, 2 PC:1 TS was cultivated in two different ponds, and each containing 375-L 2 TS:1 PC-treated water + 375-L ASN-III. Outdoor parameters and nutrient removal efficiency (NRE), biomass, and biomolecule productivity such as lipid, photosynthetic pigments, astaxanthin, and β-carotene were quantified, and cost analysis was performed. At the end of the first and second stages, 2 TS:1 PC and 2 PC:1 TS showed maximum NRE of COD (68.71 and 86.40%), TN (66.98 and 94.73%), and TP (82.70 and 94.36%), respectively. Moreover, 2 TS:1 PC and 2 PC:1 TS Pond 1 and 2 produced maximum dry biomass production; 2.41 and ∼2.54 g/L contained lipid content; 36.89 and 34.90% that have 86.50 and 55.79% FAME content respectively. Similarly, 2 TS:1 PC and 2 PC:1 TS biomass exhibited valuable pigments production of astaxanthin i.e., 0.56 and 0.35 mg/g, and β-carotene; 4.65 and 2.82 mg/g, respectively. The cost analysis suggested that only microalgal-based MWW treatment was unfeasible, while valorization of produced biomass into co-products could offset the operation costs and could allow the option for the microalgal-based sustainable approach for the treatment of MWW and recovery of valuable resources.

Microbial nutrient recovery cell as an efficient and sustainable nutrient recovery option in sewage treatment

Globally, nutrient pollution is a serious and challenging concern. Wastewater treatment plants (WWTPs) are designed to prevent the discharge of contaminants resulting from anthropogenic sources to the receiving water bodies. In this study, seasonal nutrient pollution load, and biological nutrient removal efficiency of an anoxic aerobic unit based WWTP were investigated. Seasonal assessment revealed that the average total nitrogen removal efficiency and total phosphorus removal efficiency of the WWTP do not meet the discharge standard of 10 mg/L and 1 mg/L, respectively. Furthermore, the WWTP does not utilize the energy contained in the wastewater. In this regard, dual chamber MFC (D-MFC) has emerged as a promising solution that can not only treat wastewater but can also convert chemical energy present in the wastewater into electrical energy. However, higher N O3− (57 ± 4 mg/L) and P–P O43− (6 ± 0.52 mg/L) concentration in cathodic effluent is a major drawback in D-MFC. Therefore, to solve this issue, D-MFC was transformed into a microbial nutrient recovery cell (MNRC) which demonstrated a final N H4+-N and P–P O43− concentration of nearly 1 mg/L with N H4+-N and P–P O43− recovery up to 74 % and 69 %, respectively in the recovery chamber. Besides, MNRC attained a maximum power density of 307 mW/m3 and a current density of 1614 mA/m3, thus indicating MNRC is an eco-friendly, energy-neutral, and promising technology for electricity generation and recovering nutrients.

Impact of abiotic stressors on nutrient removal and rhizomicrobiome composition in floating treatment wetland with Equisetum hyemale

Floating treatment wetlands (FTW) are receiving growing interest as a phyto-technology. However, there are significant research gaps regarding the actual role of plant species and plant-microbiome interactions. In this study, the nutrient uptake of Equisetum hyemale was examined in FTW microcosms under the influence of abiotic stressors: As (3 mg/L) and Pb (3 mg/L) as well as Cl− (300 and 800 mg/L) in reference to a control during a short screening experiment. High removal efficiency of nutrients in water solutions, up to 88 % for TN and 93 % for PO4-P, was observed. However, PO4-P removal was inhibited in the As reactor, with a maximum efficiency of only 11 %. Lead and As were removed with high efficiency, reaching 98 % and 79 % respectively. At the same time only Pb was effectively bound to root biomass, reaching up to 51 %. Limited As accumulation of 0.5 % in plant roots suggests that microbial processes play a major role in its reduction. The development and structure of microbiome in the microcosms was analysed by means of 16S rRNA gene amplicon sequencing, proving that Pb was the most influential factor in terms of selection pressure on specified bacterial groups. In the As treatment, the emergence of a Serratia subpopulation was observed, while the Cl− treatment preserved a rhizobiome composition most closely resembling the control. This study indicates that E. hyemale is a suitable species for use in FTWs treating Pb polluted water that at the same time is capable to withstand periodic increases in salinity. E. hyemale exhibits low As binding in biomass; however, extended exposure might amplify this effect because of the slow-acting, but beneficial, mechanism of As uptake by roots and shoots. Microbiome analysis complements insights into mechanisms of FTW performance and impact of stress factors on bacterial structure and functions.

Assessment of Nutrient Removal Efficiency of Marine Microalgae Dunaliella salina in Saline Food Industry Wastewater

Industrial wastewater release into the environment is a critical global challenge leading to severe water pollution, adversely impacting terrestrial and aquatic ecosystems requiring effective solutions. The treatment, disposal, and recirculation of saline wastewater from food containing nitrate and phosphate poses significant health and environmental risks. This research aims to address the challenge by investigating the potential of using the marine microalgae Dunaliella salina for treating saline food industry wastewater, both in laboratory and pilot-scale settings using raceway tanks. In the laboratory study, a mixture of wastewater and F/2 medium was inoculated with Dunaliella salina to assess its potential for growth in saline wastewater, rich in nitrate and phosphate. The study observed a cell density of 5.5 x 105 cells/ml. Subsequently, a pilot-scale study was conducted, where the maximum cell density of 6.2 x 105 cells/ml was achieved. The efficacy of Dunaliella salina in removing nitrate and phosphorus from the culture was evaluated by measuring the levels of these compounds. A significant reduction in nitrate concentration from 146 to 22.16 mg/l was observed, with a removal efficiency of 84.82%; similarly, the phosphate concentration decreased from 55.3 to 10.79 mg/l, with a removal efficiency of 80.49 %. The reductions in nitrate and phosphate concentrations, along with the demonstrated growth of Dunaliella salina in saline industrial wastewater, confirmed the feasibility of employing these microalgae for bioremediation treatment in a sustainable way.

Freshwater microalgae Nannochloropsis limnetica for the production of β-galactosidase from whey powder

This study investigated the first-ever reported use of freshwater Nannochloropsis for the bioremediation of dairy processing side streams and co-generation of valuable products, such as β-galactosidase enzyme. In this study, N. limnetica was found to grow rapidly on both autoclaved and non-autoclaved whey-powder media (referred to dairy processing by-product or DPBP) without the need of salinity adjustment or nutrient additions, achieving a biomass concentration of 1.05–1.36 g L−1 after 8 days. The species secreted extracellular β-galactosidase (up to 40.84 ± 0.23 U L−1) in order to hydrolyse lactose in DPBP media into monosaccharides prior to absorption into biomass, demonstrating a mixotrophic pathway for lactose assimilation. The species was highly effective as a bioremediation agent, being able to remove > 80% of total nitrogen and phosphate in the DPBP medium within two days across all cultures. Population analysis using flow cytometry and multi-channel/multi-staining methods revealed that the culture grown on non-autoclaved medium contained a high initial bacterial load, comprising both contaminating bacteria in the medium and phycosphere bacteria associated with the microalgae. In both autoclaved and non-autoclaved DPBP media, Nannochloropsis cells were able to establish a stable microalgae–bacteria interaction, suppressing bacterial takeover and emerging as dominant population (53–80% of total cells) in the cultures. The extent of microalgal dominance, however, was less prominent in the non-autoclaved media. High initial bacterial loads in these cultures had mixed effects on microalgal performance, promoting β-galactosidase synthesis on the one hand while competing for nutrients and retarding microalgal growth on the other. These results alluded to the need of effective pre-treatment step to manage bacterial population in microalgal cultures on DPBP. Overall, N. limnetica cultures displayed competitive β-galactosidase productivity and propensity for efficient nutrient removal on DPBP medium, demonstrating their promising nature for use in the valorisation of dairy side streams.

Acclimated green microalgae consortium to treat sewage in an alternative urban WWTP in a coastal area of Central Italy

This study exposed a microalgal consortium formed by Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas reinhardtii to six mixed wastewater media containing different proportions of primary (P) or secondary (S) effluents diluted in centrate (C). Algae could grow at centrate concentrations up to 50 %, showing no significant differences between effluents. After acclimation, microalgae cultivated in 50%P-50%C and 50%S-50%C grew at a rate similar to that of control cultures (0.59–0.66 d−1). These results suggest that the consortium acclimated to both sewage streams by modulating the proportion of the species and their metabolism. Acclimation also altered the photosynthetic activity of wastewater-grown samples compared to the control, probably due to partial photoinhibition, changes in consortium composition, and changes in metabolic activity. No major differences were observed between the two streams with respect to biochemical composition, biomass yield, or bioremediation capacity of the cultivated algae but algae grown in the secondary effluent showed qualitatively higher exopolysaccharides (EPS) production than algae grown in primary. Regarding wastewater remediation, microalgae grown in both WW media showed proficient nutrient removal efficiencies (close to 100 %); however, the final pH value (close to 11) would be controversial if the system were upscaled as it is over the legal limit and would cause phosphorus precipitation, so that CO2 addition would be required. The theoretical scale-up of the microalgae system could achieve water treatment costs of 0.109 €·m−3, which was significantly lower than the costs of typical activated sludge systems.

Influence of the oxidative phosphorylation uncoupler m-chlorophenol on activated sludge production, nutrients removal efficiency and bacterial community structure of a membrane reactor system

In this work, the effects of the metabolic uncoupler meta-chlorophenol (m-CP) on excess sludge production and performance of an MBR system, as well as on activated sludge communities, were investigated. MLVSS were significantly reduced from 8410 mg/L to 5175 mg/L during the first week of the addition of 125 mg/L m-CP, while, thereafter, biosolids were restored to the level prior to uncoupler’s addition. Adding m-CP resulted in more severe effects on nitrifiers rather than organoheterotrophs. Both alkalinity, dissolved oxygen (DO), electrical conductivity (EC) and pH data evidenced the adverse effect of m-CP on the nitrification process. PO43--P concentration drastically raised immediately after m-CP addition from 2.48 ± 0.35 mg/L to 11.84 mg/L, possibly due to the uncoupling of P-release and the hydrolysis of phosphorus reserves. Diversity was highly affected by the addition of m-CP, resulting in the significant decrease of Chao1, Shannon and Fisher indices. By establishing stable operating conditions after m-CP addition, Pseudomonas, Arcanobacterium, Trichococcus, Kocuria and Actinobaculum raised from almost undetectable levels (0.12 % of the total relative abundance) to 35.9 %, 17.8 %, 15.1 %, 11.5 % and 5.7 %, respectively, indicating a massive shift in bacterial community structure, while no nitrifying taxa were detected after m-CP addition.

Performance evaluation of integrating Vertical Garden Constructed Wetlands (VGCWs) with diverse plant species and modified media for treating septic tank effluent

Vertical Garden Constructed Wetland (VGCW) system has been used as a secondary treatment system to improve effluent quality of septic tanks and cesspools by enhancing nutrients, organic and solid removal according to the guidelines of effluent discharge. This study aimed to investigate the treatment performance of the VGCWs by integrating with diverse plant species and modified media used as secondary treatment for conventional or solar septic tanks. In the study, laboratory-scale VGCW utilizing soil as the media and planted with Water Pennywort were operated at hydraulic retention times (HRT) of 6, 12, and 24 h, while modified planted vertical garden constructed wetlands (mpVGCW) operated at an HRT of 36 h, was fed with effluent collected from a septic tank. The treatment performance of VGCWs treating effluent from the septic tank and operating at an HRT of 24 h was found to achieve the highest removal efficiencies for organic matter, nutrients, and solids (up to over 90%), compared to an HRT of 6 or 12 h. Moreover, the highest log reduction of E.coli of 2.8 was also observed at the 24 h HRT, in comparison to HRTs of 6 or 12 h. The Spider Ivy, Coleus, and Selaginella frosty could be planted in the mpVGCW system to enhance the overall treatment efficiencies with consistently showed high removal efficiencies for TCOD (91.37–93.39%), TKN (97.1–97.8%), and TP (87.18–88.58%). These results suggested the potential of the VGCWs as a secondary treatment system for polishing septic tank effluent and improving environmental quality.

Nutrient Removal Efficiencies in a Bioretention Cell Using Pre-Treated Coconut By-Product as Carbon Source

Abstract In this research, the appropriateness of alkali pre-treatment on coconut by-products was managed by exposing coconut husk and shell to 2M NaOH. The powdered samples were analysed for morphology observation, Fourier Transform Infrared (FTIR), Particle Size Analyzer (PSA), and water quality tests. Weakening the hemicellulose structure resulted from subjecting the coconut shell to alkali pre-treatment shown in the morphology observation. Furthermore, the FTIR analysis exhibited the presence of O-H stretch in all pre-treated samples representing an indication for occurring the lignin breakdown, while an absence of the C=O functional group was shown in both additive samples after their subjection to alkali pre-treatment. In PSA analysis, the particles of all samples were found finer than the particle size distribution standards, in which the smallest D50 was obtained for the treated coconut shell (TCS), followed by untreated coconut shell (UCS), untreated coconut husk (UCH), and treated coconut husk (TCH). Among all the powdered samples (TCS, UCS, UCH, and TCH) analysed in this study, only TCH values met the ranges provided and recommended by the Urban Stormwater Management Manual for Malaysia (MSMA) and the Australian Department of Sustainability, Environment, Water, Population, and Communities (DSEWPC). Meanwhile, a poor removal rate for total suspended solids (TSS) was attained due to the contribution of TSS by the filter media which caused the TSS rates to surpass the inlet values. Additionally, the presence of a high concentration of total phosphorous (TP) in all the tested samples indicated their capabilities to provide PO43 in the bioretention cell, which is a vital nutrient for the plant’s growth. In contrast, Ammoniacal Nitrogen (AN) with a concentration rate as low as 4 mg/L was observed throughout the test periods which showed a significant reduction compared to the rate of AN at the inlet samples ranged between 5.2 and 11.4 mg/L. The findings indicated that coconut by-products, when subjected to an alkali pre-treatment process, are appropriate for incorporation as additives in bioretention filter media.

Cultivation of yeasts on liquid digestate to remove organic pollutants and nutrients and for potential application as co-culture with microalgae

In this study, the growth of yeast and yeast-like fungi in the liquid digestate from vegetable wastes was investigated in order to remove nutrients and organic pollutants, and for their application as co-culture members with green microalgae. The studied yeast strains were characterized for their assimilative and enzymatic profiles as well as temperature requirements. In the first experimental stage, the growth dynamics of each strain were determined, allowing to select the best yeasts for further studies. In the subsequent stage, the ability of selectants to remove organic pollutants was assessed. Different cultivation media containing respectively 1:3, 1:1, 3:1 vol ratio of liquid digestate and the basal minimal medium were used. Among all tested yeast strains, Rhodotorula mucilaginosa DSM 70825 showed the most promising results, demonstrating the highest potential for removing organic substrates and nutrients. Depending on the medium, this strain achieved 50–80% sCOD, 45–60% tVFAs, 21–45% TN, 33–52% PO43− reduction rates. Similar results were obtained for the strain Candida sp. OR687571. The high nutrient and organics removal efficiency by these yeasts could likely be linked to their ability to assimilate xylose (being the main source of carbon in the liquid digestate). In culture media containing liquid digestate, both yeast strains achieved good viability and proliferation potential. In the liquid digestate medium, R. mucilaginosa and Candida sp. showed vitality at the level of 51.5% and 45.0%, respectively. These strains seem to be a good starting material for developing effective digestate treatment strategies involving monocultures and/or consortia with other yeasts or green microalgae.

Utilization of tofu wastewater and Nannochloropsis oceanica for eutrophication mitigation and eicosapentaenoic acid valorization: Advancing carbon neutrality and resource recycling

Seeking environmentally-friendly and resource-recycling strategies for tofu wastewater (TFW) treatment could effectively mitigate harsh ecological impacts and resource wastage caused by direct discharge. This study investigated the feasibility on the utilization of Nannochloropsis oceanica (N. oceanica) for TFW eutrophication mitigation and eicosapentaenoic acid valorization. The findings demonstrated that employing N. oceanica resulted in significant removal rates for total phosphorus, total nitrogen, ammonia nitrogen, and chemical oxygen demand by 88.60 %, 97.02 %, 94.22 %, and 98.02 % under fed-batch treatment mode. Such nutrients removal efficiency met discharge permit standards while accomplished a superior biomass at 26.37 g/L and EPA yield at 43.5 mg/g by N. oceanica, representing 2.61- and 2.52-fold more than that of batch treatment mode. Furthermore, TFW feeding enhanced the cytomembrane fluidity of N. oceanica and promoted TFW nutrients uptake into cells consequently boosted the nutrients removal efficiency. Simultaneously, TFW feeding upregulated enzymes such as antioxidases, desaturases and elongases responsible for EPA biosynthesis in N. oceanica to collectively protect EPA from oxidation stress and stimulate proactive accumulation. EPA derived from TFW-fed N. oceanica exhibited promising in vitro antihyperlipidaemia efficacy in constructed hyperlipopyte HepG-2 cells. Further, the molecular docking indicated that the hypolipidemic activity partly contributed to that EPA inhibited PPARα signaling to trigger fatty acids β-oxidation and cholesterol transport suppression. The outcomes present a viable route that utilization of microalgae for TFW eutrophication mitigation and EPA valorization to advance carbon neutrality and resource recycling.

Efficient Low-Temperature Nutrient Removal from Agricultural Digestate Using Microalgae

Humanity is facing an energy crisis triggered by the depletion of fossil fuels, rapid industrialization, and the growthof the global population. These trendsput an emphasis on searching for alternative energy sources. Additionally, the rising concentration of carbon dioxide in the atmosphere is driving climate change, which poses serious threats. In this scenario, microalgae emerge as a promising solution for both sustainable energy production and CO2 sequestration. Digestate, a nutrient-rich by-product of anaerobic digestion, is considered a cost-effective nutrient source for microalgae cultivation. Utilizing digestate not only enhances the sustainability and economic feasibility of microalgal biofuels but also offers a method for wastewater treatment. Nevertheless, the application of digestate is limited by its high optical density and substantialamount of total solids.In this study, several pretreatment methods were tested to increase the feasibility of digestate application for microalgae cultivation. Our findings show that various centrifugation methods and vacuum filtration decrease the content of total solids but are not effective in reducing optical density. Although the use of microalgae in treating various wastewaters has shown promising outcomes, the effectiveness of nutrient removal at low temperatures remainslargely unexplored.To fill this gap, green microalga Chlorella sorokiniana was cultivated in pretreated diluted liquid digestate in dynamic springtime weather conditions in a covered open race-way pond integrated into a biogas plant.During the cultivation, high solar irradiance and low temperatures were recorded resulting in suboptimal conditions for C. sorokinianagrowth. Although low productivity of C. sorokiniana was detected, the nutrient removal efficiency was high. C. sorokiniana could efficiently remove 83% of nitrogen and 85% of phosphorus showing very promising results of the use of microalgae for wastewater treatment in high latitude regions.