Navid Moheimani

Nitrogen (N) availability is a key factor for sustainable production in rice-crayfish co-culture system (RC), and the appropriate N rate should be determined in RC by considering grain yield, N uptake, grain quality as well as soil fertility under different N rate. Between 2020 and 2022, different N levels (0, 60, 120, 180 and 240 kg N ha− 1) were tested to explore the optimal amount of fertilizer application in RC. Soil NO3−-N, NH4+- N and inorganic N (Nmin) increased as N rate increased at the tillering stage (TS) and full heading stage (HS) of rice, and soil urease and catalase activity in N treatments increased significantly. The cumulated dry matters and plant N of N treatments were also increased by 4%~69% and 23%~164% (TS), 16%~69% and 30%~98% (HS), and 12%~49% and 26%~70% (mature stage), respectively. N increased rice yield by 8.47%~43.22%, the yield stability of N120 was highest, and the total benefit reached its peak under N120 and N180. The optimal N rate was 136 ~ 143 kg N·ha− 1, achieving maximum yield (7,861 kg·ha− 1) and maximum income (16,433 Yuan ha− 1). N addition increased brown rice rate and milled rice rate by 4.95%~13.14% and 0.31%~10.87%, and reduced chalky rice rate by 19.57%~45.82%. After N fertilization, microbial biomass carbon, microbial biomass N and microbial biomass phosphorus were increased. AOA, AOB, nirS, nirK, nosZ, and narG of 0–20 cm soil were also increased. N fertilizer rates of RC systems should be 136 ~ 143 kg N ha− 1 to achieve a high grain yield with high soil microbial diversity and suitable water quality for crayfish. N addition had similar water quality than the control after 7 days of base fertilization but had higher soil N for rice that N addition is beneficial for both crayfish feeding and rice production.

Magnetic flocculation using magnetite nanoparticles (MNPs) has emerged as a promising technique for microalgae harvesting and dewatering, offering advantages over conventional methods. This study evaluated the key factors influencing the efficacy of magnetic harvesting of Chlorella sp. using commercial MNPs in two comparisons with pH-adjustment-sonication-extraction and pH-adjustment-sonication recovery methods for testing the recyclability of MNPs. Results showed that magnetic harvesting efficiencies exceeding 99 % were achieved within the pH range of 7–9 when MNPs were applied at concentrations between 5 and 10 g/L. From pH 7–9, there was no statistically significant variability in performance. In contrast, MNP concentration had a more pronounced effect: less than 50 % harvesting efficiencywas observed at 0.1–0.3 g/L, whereas increasing the concentration to 0.5–1 g/L resulted in 70–90 % efficiency. To enable MNP recycling, pH adjustment—with and without ultrasonication—and solvent extraction were tested and compared. The pH-only method enabled up to two reuse cycles with less than a 20 % reduction in efficiency, whereas the combined method extended reuse to three cycles but involved higher chemical usage and a greater risk of cell damage. These findings suggest that the pH-only detachment approach can be a more cost-effective and sustainable method for achieving efficient (>99 %) harvesting of Chlorella sp., particularly at neutral to alkaline pH levels. Additionally, this approach enables the repurposing of spent MNPs in applications such as soil and environmental remediation, offering potential to add value to waste materials and contribute to a more sustainable future.
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•Magnetite nanoparticles simultaneously harvest and dewater Chlorella. sp. effectively.•High harvesting and dewatering performance maintained across the pH 7–9.•The effect of MNPs concentration on biocompatibility and harvesting efficiency was synergistically observed.•Three MNPs reuse and recycling were demonstrated.

Optimizing photobioreactor (PBR) design is essential for improving the productivity and energy efficiency of microalgal cultivation systems. This study employed Computational Fluid Dynamics (CFD) simulations to assess the hydrodynamic performance of an inclined flat plate PBR for Arthrospira platensis cultivation. The CFD model, validated against experimental data (maximum discrepancy: 8.4 %, R2 = 0.81), reliably predicted biomass productivity and internal flow dynamics. Five sparger configurations and four aeration rates were investigated for their effects on radial velocity, turbulence kinetic energy (TKE), and dead zone formation.

The results highlighted the hydrodynamic advantages of the rear-most sparger position (R). At 0.21 vvm (volume of air per volume of culture per minute), position R achieved a radial velocity of 0.125 m·s−1, a TKE of 4.32 × 10−3 m2·s−2, and a dead zone fraction of 18.23 %, closely matching the middle sparger position at 0.23 vvm. Notably, 0.23 vvm represented the highest tolerable aeration rate experimentally, as exceeding this threshold induced shear-related mechanical stress, negatively impacting microalgal cell integrity and reducing productivity. Thus, sparger position R provided equivalent mixing at reduced aeration, lowering energy demand and operational stress.

The inclined geometry enhanced flow uniformity and turbulence, particularly with rearward sparger placement. Integrating dead zone analysis with velocity and TKE metrics, this study offers a validated framework for optimizing sparger design in inclined flat plate PBRs. These findings have significant implications for improving energy efficiency and scalability in laboratory and industrial scale microalgal cultivation systems.

The microalgae Botryococcus braunii holds significant promise for biofuel generation. This study delves into an innovative B. braunii biofilm cultivation approach to trim energy consumption as well as harvesting costs. The investigation encompassed two distinct processes, i.e., algae turf scrubber (ATS) biofilm and open raceway pond (ORP) systems. The simulation of integrated cultivation, harvesting, and lipid extraction processes was conducted using SuperPro Designer. Furthermore, capital and operational expenses were calculated to be further discussed in terms of techno-economics and profitability. The ATS biofilm reached a notably high biomass productivity of 38 g m− 2 d− 1 when compared to the ORP system (7.5 g m− 2 d− 1). Likewise, the ATS biofilm cultivation demonstrated lesser water consumption by up to 6-fold and facilitated a remarkable 77.3% reduction in total OPEX. Besides, the microalgae cultivation plant using the ATS biofilm system with a lifetime of 12 years leads to an IRR of up to 26.43% with a DPBP of 5.9 y if the biofuel product is sold at 3.7 USD L− 1. Given this potential, biofuel production from B. braunii in the ATS biofilm system can be an attractive option in terms of process reliance and feasibility for future large- and commercial-scale microalgae industries.

Machine learning has opened the door for the automated sorting (classification) of images, holograms and acoustic backscatters of individual plankton, invertebrates, fish and marine mammals. However, this field is complicated by decades of paradoxically promising reports of classifier performance that do not correlate with real-world uptake of this technology in aquatic sciences. Simple metrics of classifier performance are essential for optimizing, evaluating and comparing machine learning classifiers, but a wide variety of metrics and calculation variants have been proposed. Several characteristics of species count data influence metric behavior: severe imbalance and variance, zero-inflation, high class numbers and contamination with non-target classes. This study explores the hidden complexity of classifier performance metrics for species count data using synthetic datasets and simulated classifier outputs. It demonstrates how these data characteristics can severely distort metric values, with seven of eight variants of the most common metric, Accuracy, returning near-perfect scores (up to 98%) even when no instances are correctly classified. Clear recommendations are made for classifier evaluation pitfalls and metric variants to avoid, ultimately finding one variant of the F1-Score (mF1) to be the most suitable single metric, with several important calculation caveats specific to species count data. Due to ambiguous terminology and inconsistent definitions, it is often impossible to identify which variant of a performance metric has been applied in classifier studies. It is vital that authors are intentional and transparent about their metric use to support the vast potential for machine learning to revolutionize the research and monitoring of aquatic environments.

Alexandrium spp. blooms produce a range of toxins, including spirolides, goniodomins, and paralytic shellfish toxins (PSTs). Of these, PSTs are the most impactful due to their high affinity for voltage-gated sodium ion channels in nerve cell membranes. This interaction can cause neurological effects such as paralysis and, in severe cases, may lead to death. Given the implications of Alexandrium blooms on public health, all mitigation, prevention, and treatment strategies aim to reduce their socioeconomic impacts. However, monitoring harmful algal blooms remains difficult due to confounding influences such as pollution, climate change, and the inherent variability of environmental conditions. These factors can complicate early detection and management efforts, especially as the intensity and frequency of blooms continue to rise, further exacerbating their socioeconomic consequences. This review offers insights into several management approaches to prevent and control Alexandrium blooms, focusing on modified nano-clays as a promising emergency mitigation measure for low-density toxic algal blooms, especially in areas predominantly used for recreational fishing. However, it is recommended that treatment be coupled with monitoring to alleviate reliance on treatment alone.

Key Contribution
Prevention and control strategies for Alexandrium blooms should consider the specific use of the affected waterway, the carbon footprint associated with modified clay production, and the broader ecological and environmental impacts of clay application. These factors are essential when evaluating the overall efficiency and sustainability of clay-based treatment methods.

Alexandrium spp. blooms and paralytic shellfish poisoning pose serious economic threats to coastal communities and aquaculture. This study evaluated the removal efficiency of two Alexandrium minutum strains using natural kaolinite clay (KNAC) and kaolinite with polyaluminum chloride (KPAC) at three concentrations (0.1, 0.25, and 0.3 g L−1), two pH levels (7 and 8), and two cell densities (1.0 and 2.0 × 107 cells L−1) in seawater. PAC significantly enhanced removal, achieving up to 100% efficiency within two hours. Zeta potential analysis showed that PAC imparted positive surface charges to the clay, promoting electrostatic interactions with negatively charged algal cells and enhancing flocculation through Van der Waals attractions. In addition, the study conducted a cost estimate analysis and found that treating one hectare at 0.1 g L−1 would cost approximately USD 31.75. The low KPAC application rate also suggests minimal environmental impact on benthic habitats.

Arthrospira platensis has been a dietary staple for decades. While raceway ponds are commonly used for mass cultivation, closed photobioreactors (PBRs) offer higher productivity and reduced contamination risks. Mixing rate is a critical factor influencing microalgal growth and productivity. This study examines the impact of air injection flow rates (0.17–0.27 vvm), corresponding to superficial gas velocities of 0.00315–0.0050 m·s−1, on the growth, productivity, and effective quantum yield (f'q/f'm) of A. platensis in a 140 L self-cooling flat plate PBR with an infrared-reflective thin-film coating that enables passive temperature control and reduces energy demand for cooling.

The optimal gas velocity of 0.00389 m·s−1 yielded an average productivity of 0.126 g·L−1·d−1. Beyond this velocity, at 0.00426 m·s−1, there was neither significant increase in productivity, nor a notable decrease in f'q/f'm. However, at higher gas velocities of 0.00463 m·s−1 and 0.0050 m·s−1, f'q/f'm decreased significantly, by up to 48.6 %, indicating adverse effects on the microalgal cells. Lower velocities (<0.00389 m·s−1) did not affect f'q/f'm but resulted in inadequate mixing, reducing biomass productivity by 16.4 % and 23.8 % for 0.00352 and 0.00315 m·s−1.

A validated growth model accurately predicted A. platensis growth (R2 = 94.5 % for biomass, 81.2 % for temperature). Moreover, Experimental data from Perth, Australia, during spring and winter aligned closely with model predictions. This integration of experimental data and predictive modelling highlights the importance of precise mixing rate optimization in maximizing microalgal productivity and demonstrates the reliability of such models for advancing large-scale algal cultivation.
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Microalgae could serve as an improved source of bioavailable heme b for the treatment of chronic anemia in humans and animals and/or be used as an additive for plant-based protein products to provide a ‘meaty’ taste. Unfortunately, ‘standard’ spectrophotometric assays developed for heme b -rich samples, particularly meat and blood samples, are not viable for microalgae due to lower heme b levels and spectral interference from pigments such as chlorophyll. Removing interferents in heme b extracts from photosynthetic organisms is time-consuming and risks loss of product. Analysis of 6 different microalgal strains using a spectrophotometer and literature best-practice HPLC method revealed that HPLC was consistently more sensitive and had a 1000-fold lower LoD compared to the spectrophotometric method (0.1 pmol cf 230 pmol). The HPLC method also offered the advantage of not having to remove pigment interferences in the extraction phase. The instrumental method comparison highlighted the inefficiencies in the traditional sequential acetone extraction process, prompting trials of several alternate extraction protocols. It was found that a single-step acidic N,N -dimethylformamide (DMF: HCl, 98:2 v/v) extraction improved heme b yield by ~ 50%, reduced extraction time and solvent use by ~ 90%, and extracted heme b remained stable for two weeks at -25 °C, enabling batch analysis. Coupling this extraction procedure with HPLC analysis provides a robust analytical tool for advancing the evaluation of microalgae-derived heme b in medicinal and functional food settings.

Membrane filtration has emerged as a viable technique for microalgal dewatering. However, fouling constraints limit their large-scale implementation. In this research, the fouling patterns during ultrafiltration of Chlorella sp. and Dunaliella salina were investigated using both dead-end and crossflow filtration modules. Chlorella sp. filtration in the dead-end module revealed an initial flux of 72.02 L.m−2.h−1 in the first cycle, which rapidly decreased to 19.18 L.m−2.h−1 within 30 min. In the second and third cycles, the initial flux exhibited decreases of 23 % and 50 %, respectively. Chlorella sp. demonstrated lower fouling than D. salina in a dead-end. However, in the crossflow module, D. salina maintained a consistently higher flux compared to Chlorella sp. Across both configurations, Chlorella sp. caused greater irreversible fouling (22 % in dead-end, 13 % in crossflow) than D. salina (8 % and 7 %, respectively), likely due to higher organic molecule production by Chlorella sp. SEM micrographs revealed a gradual cake layer buildup on membrane surfaces despite backwashing, and FTIR spectroscopy confirmed the presence of microalgal functional groups post-backwash, highlighting cake resistance as the dominant fouling mechanism. Flux significantly improved as the transmembrane pressure (TMP) increased, while flocculation with 100 mg.L−1 FeCl3 yielded the best results. Although a higher pH slightly improved the initial flux, the overall effect of pH was minimal. These findings highlight that ultrafiltration harvesting of microalgae could be greatly improved through transmembrane pressure (TMP) optimization and flocculation as effective strategies for enhancing filtration efficiency.