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.

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE\'s effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

This study explores the novel use of mixed cultures of microalgae-Spirulina platensis, Micractinium, and Chlorella-for nutrient removal from dairy wastewater (DW). Microalgae were isolated from a local wastewater treatment plant and cultivated under various light conditions. The results showed significant biomass production, with mixed cultures achieving the highest biomass (2.51 g/L), followed by Spirulina (1.98 g/L) and Chlorella (1.92 g/L). Supplementing DW (75%) with BG medium (25%) significantly enhanced biomass and pH levels, improving pathogenic bacteria removal. Spirulina and mixed cultures exhibited high nitrogen removal efficiencies of 92.56% and 93.34%, respectively, while Chlorella achieved 86.85% nitrogen and 83.45% phosphorus removal. Although growth rates were lower under phosphorus-limited conditions, the microalgae adapted well to real DW, which is essential for effective algal harvesting. Phosphorus removal efficiencies ranged from 69.56% to 86.67%, with mixed cultures achieving the highest removal. Microbial and coliform removal efficiencies reached 97.81%, with elevated pH levels contributing to significant reductions in fecal E. coli and coliform levels. These findings suggest that integrating microalgae cultivation into DW treatment systems can significantly enhance nutrient and pathogen removal, providing a sustainable solution for wastewater management.

The dairy industry is becoming one of the biggest sectors within the global food industry, and these industries use almost 34% of the water. The amount of water used is governed by the production process and the technologies employed in the plants. Consequently, the dairy industries generate almost 0.2-10 L of wastewater per liter of processed milk, which must be treated before being discharged into water bodies. The cultivation of microalgae in a mixotrophic regime using dairy wastewater enhances biomass growth, productivity, and the accumulation of value-added product. The generated biomass can be converted into biofuels, thus limiting the dependence on petroleum-based crude oil. To fulfill the algal biorefinery model, it is important to utilize every waste stream in a cascade loop. Additionally, the harvested water generated from algal biomass production can be recycled for further microalgal growth. Economic and sustainable wastewater management, along with proper reclamation of nutrients from dairy wastewater, is a promising approach to mitigate the problem of water scarcity. A bibliometric study revealing limited work on dairy wastewater treatment using microalgae for biofuel production. And, limited work is reported on the pretreatment of dairy wastewater via physicochemical methods before microalgal-based treatment. There are still significant gaps remains in large-scale cultivation processes. It is also crucial to discover robust strains that are highly compatible with the specific concentration of contaminants, as this will lead to increased yields and productivity for the targeted bio-product. Finally, research on reutilization of culture media in photobioreactor is necessary to augument the productivity of the entire process. Therefore, the incorporation of the microalgal biorefinery with the wastewater treatment concept has great potential for promoting ecological sustainability.

Mixotrophic microalgal solutions are efficient nutrient recovery methods, with potential to prolong the cultivation seasons in temperate climates. To improve operation sustainability, the study used landfill leachate for nitrogen source and whey permeate for phosphorus and organic carbon. A non-axenic polyculture, dominated by green algae, was cultivated in mixotrophic mode on glucose or whey permeate compared to a photoautotrophic control in outdoor pilot-scaled raceway ponds during Nordic spring and autumn. The whey permeate treatment had the highest algal growth rate and productivity (0.48 d-1, 183.8 mg L-1 d-1), nutrient removal (total nitrogen: 21.71 mg L-1 d-1, total phosphorus: 3.05 mg L-1 d-1) and recovery rate (carbon: 85.19 mg L-1 d-1, nitrogen: 17.01 mg L-1 d-1, phosphorus: 2.58 mg L-1 d-1). When grown in whey permeate, algal cultures demonstrated consistent productivity and biochemical composition in high (spring) and low light conditions (autumn), suggesting the feasibility of year-round production in Nordic conditions.

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.

This paper presents a study on reducing sewage sludge by an oxic-settling-anaerobic (OSA) pilot plant compared to the conventional activated sludge (CAS) process in view of resource recovery and moving towards plant carbon neutrality. The OSA plant was supplied with real wastewater and the anaerobic reactor was operated under two hydraulic retention times (HRT) (4 and 6 h). Greenhouse gas (GHG) emissions were monitored for the first time to determine the OSA process\'s production mechanism. The results highlighted that under the lowest HRT (4 h), the removal efficiencies of COD and PO4-P, increased from 75 to 89% and from 39 to 50% for CAS and OSA configurations, respectively. The observed yield coefficient was reduced from 0.58 gTSS gCOD-1 (CAS period) to 0.31 gTSS gCOD-1 (OSA period). A remarkable deterioration of nitrification efficiency under OSA configuration was obtained from 79% (CAS) to 27% (OSA with HRT of 6 h). The huge deterioration of nitrification significantly affected the GHG emissions, with the N2O-N fraction increasing from 1% (CAS) to 1.55% (OSA 4 h HRT) and 3.54% (OSA 6 h HRT) of the overall effluent nitrogen, thus suggesting a relevant environmental implication due to the high global warming potential (GWP) of N2O.

Replete with ammonia nitrogen and organic pollutants, landfill leachate typically undergoes treatment employing expensive and carbon-intensive integrated techniques. We propose a novel microalgae technology for efficient, low-carbon simultaneous treatment of carbon, nitrogen, and phosphorus in landfill leachate (LL). The microbial composition comprises a mixed microalgae culture with Chlorella accounting for 82.58%. After seven days, the process with an N/P ratio of approximately 14:1 removed 98.81% of NH4+-N, 88.62 % of TN, and 99.55% of TP. Notably, the concentrations of NH4+-N and TP met the discharge standards, while the removal rate of NH4+-N was nearly three times higher than previously reported in relevant studies. The microalgae achieved a removal efficiency of 64.27% for Total Organic Carbon (TOC) and 99.26% for Inorganic Carbon (IC) under mixotrophic cultivation, yielding a biomass of 1.18 g/L. The treatment process employed in this study results in a carbon emissions equivalent of -8.25 kgCO2/kgNremoved, representing a reduction of 33.56 kgCO2 compared to the 2AO + MBR process. In addition, shake flask experiments were conducted to evaluate the biodegradability of leachate after microalgae treatment. After microalgae treatment, the TOCB (Biodegradable Total Organic Carbon)/TOC ratio decreased from 56.54% to 27.71%, with no significant improvement in biodegradability. It establishes a fundamental foundation for further applied research in microalgae treatment of leachate.

In recirculating aquaculture systems (RAS), waste management of nutrient-rich byproducts accounts for 30-50% of the whole production costs. Integrating microalgae into RAS offers complementary solutions for transforming waste streams into valuable co-products. This review aims to provide an overview of recent advances in microalgae application to enhance RAS performance and derive value from all waste streams by using RAS effluents as microalgal nutrient sources. Aquaculture solid waste can be converted by hydrothermal liquefaction (HTL), then the resultant aqueous phase of HTL can be used for microalgae cultivation. In addition, microalgae generate the required oxygen while sequestering carbon dioxide. The review suggests a novel integrated system focusing on oxygenation and carbon dioxide capture along with recent technological developments concerning efficient microalgae cultivation and nutrient recovery techniques. In such system, microalgae-based biorefineries provide environmentally-conscious and economically-viable pathways for enhanced RAS performance and conversion of effluents into high-value products.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.