Production and release of 2-MIB in Pseudanabaena: Effects of growth phases on cell characteristics and 2-MIB yield.

2-methylisoborneol (2-MIB), a secondary metabolite produced by cyanobacteria, often causes a musty odour in water, threatening the safety of drinking water supplies. This study investigated the effects of the growth phases on the production of 2-MIB by Pseudanabaena. The effects of cell characteristics on the production and release of 2-MIB were also explored. The total 2-MIB concentration increased during the exponential phase and decreased during the declining phase, which was consistent with the changes in cell density. However, the total 2-MIB yield (1.12-1.27 fg cell-1) of Pseudanabaena did not significantly differ throughout the growth cycle (p > 0.05). Meanwhile, the extracellular 2-MIB yield increased significantly from 0.31 fg cell-1 in the exponential phase to 0.76 fg cell-1 in the declining phase (p < 0.05), and the corresponding proportion of extracellular 2-MIB improved from 25.13% to 59.16% (p < 0.05). The surge in extracellular 2-MIB during the declining phase could be attributed to the breaking of the Pseudanabaena filament, as indicated by the decrease in Dmean during cell ageing. The findings of this study contribute to a more inclusive comprehension and management of musty odour issues resulting from cyanobacteria in the water supply.

Influence of algal organic matter in the in-situ flotation removal of Microcystis using positively charged bubbles.

Positively charged bubbles efficiently capture and remove negatively charged algal cells without relying on coagulation-flocculation. However, the efficiency is notably influenced by the presence of algal organic matter (AOM). This study investigated the impact of AOM composition on flotation performance by analyzing AOM from various growth phases of Microcystis flos-aquae. The results indicated that low-concentration AOM (<5 mg C L-1), particularly the high molecular weight (>30 kDa) fractions containing high percentages of protein during the exponential growth phase, significantly improved the flotation efficiency by >18%. A high-speed camera system illustrates the pivotal role of low-concentration protein-containing AOM in forming network structures that enhance cell capture. These protein-driven network structures, which enhance the flotation efficiency, provide valuable insights into the development of effective in-situ algal bloom prevention techniques.

Carbon-negative and high-rate nutrient recovery from municipal wastewater using mixotrophic Scenedesmus acuminatus.

The efficiency of mixotrophic microalgae in enhancing the recovery of waste nutrients has been well established; however, the recovery rate is crucial in meeting the needs of field applications. This study evaluated the impact of media characteristics on nutrient recovery under mixotrophic conditions. The mixotrophic N recovery rate with S. acuminatus in modified BG-11 reached 2.59 mg L-1h-1. A mixotrophic growth optimization strategy was applied to achieve a high-rate nutrient recovery from municipal wastewater treatment plant effluents. The contribution of waste chemical oxygen demand (COD) to nutrient recovery was assessed using secondary effluent (SE) under heterotrophy. The results highlighted a significant increase in total nitrogen (TN) and total phosphorus (TP) recovery rates when glucose was supplied, indicating the additional carbon requirements for efficient nutrient recovery. The TN and TP recovery rates under mixotrophic conditions with the addition of trace metals and high cell density were enhanced by 91.94% and 92.53%, respectively, resulting in recovery rates of 3.43 mg L-1h-1 and 0.30 mg L-1h-1. The same conditions were used for nutrient recovery from primary effluent (PE), and the results were more satisfactory as the TN and TP recovery rates reached 4.79 and 0.55 mg L-1h-1, respectively. Additionally, the study estimated the carbon footprints (C-footprints) and areal footprints of mixotrophy-based nitrogen recovery. The findings revealed carbon footprints and areal footprints of -15.93 ± 4.57 tCO2e t-1 N recovery and 0.53 ± 0.19 m3 m-2d-1 wastewater, respectively. This high-rate nutrient recovery, achieved under a carbon-negative (C-negative) budget through mixotrophy, presents a novel strategy for efficiently recovering resources from municipal wastewater, thus facilitating resource recycling and ensuring environmental sustainability.

The development of commitment: Attention for intention.

Adhering to a partially defined plan requires an intentional commitment that curbs distracting desires conflicting with the planned course of action, enabling humans to act coherently over time. Two studies (N = 50, 27 girls, ages 5-6, Han Chinese, in Hangzhou, China, 2022.02-2022.03) explored the development of commitment to partial plans in a sequential decision-making task and the underlying cognitive capacity focusing on its correlation to attentional control. Results suggest that only 6-year-olds committed to partial plans (d = .51), and children's commitment ratio was positively correlated with the use of proactive control (r = .40). These findings indicate that intentional commitment does not develop simultaneously with intention understanding, but rather matures gradually with the development of attentional control.

Intention beyond desire: Spontaneous intentional commitment regulates conflicting desires.

The human mind is a mosaic composed of multiple selves with conflicting desires. How can coherent actions emerge from such conflicts? Classical desire theory argues that rational action depends on maximizing the expected utilities evaluated by all desires. In contrast, intention theory suggests that humans regulate conflicting desires with an intentional commitment that constrains action planning towards a fixed goal. Here, we designed a series of 2D navigation games in which participants were instructed to navigate to two equally desirable destinations. We focused on the critical moments in navigation to test whether humans spontaneously commit to an intention and take actions that would be qualitatively different from those of a purely desire-driven agent. Across four experiments, we found three distinctive signatures of intentional commitment that only exist in human actions: "goal perseverance" as the persistent pursuit of an original intention despite unexpected drift making the intention suboptimal; "self-binding" as the proactive binding of oneself to a committed future by avoiding a path that could lead to many futures; and "temporal leap" as the commitment to a distant future even before reaching the proximal one. These results suggest that humans spontaneously form an intention with a committed plan to quarantine conflicting desires from actions, supporting intention as a distinctive mental state beyond desire. Additionally, our findings shed light on the possible functions of intention, such as reducing computational load and making one's actions more predictable in the eyes of a third-party observer.

Enhanced Microcystis Aeruginosa removal and novel flocculation mechanisms using a novel continuous co-coagulation flotation (CCF).

Co-coagulation flotation (CCF) is a novel flotation technology that renders more efficient algal removal compared to traditional mechanical coagulation flotation (MCF) due to a short residence time (< 30 s) and fast rising behavior of algal flocs (> 250 m·h-1). This study compared the algal removal performance using continuous CCF and MCF using water samples taken from Lake Dianchi with severe Microcystis aeruginosa blooms. Removal efficiency, dosage of coagulant/flocculant, rising velocity and structural characteristics of the resulting flocs in the two processes were systematically compared. The results show that CCF could save >50 % polyaluminum chloride (PAC) and polyacrylamide (PAM) compared with MCF when the removal efficiency was both over 95 %. The average rising velocity of flocs in CCF could reach 254.3 m·h-1, much higher than that in MCF (154.5 m·h-1). In the respective optimal coagulation conditions, the flocs formed in CCF (G = 164.8 s-1) were larger (1843 ± 128 µm) and more spherical with a higher fractal dimension (Df = 1.85 ± 0.01) than those generated in MCF (G = 34.1 s-1). The Stokes's Law was found to correctly predict the rising velocity of spherical flocs with large fractal dimensions (Df > 1.7). In contrast, the Haarhoff and Edzwald's extended equation was more suitable for calculating the rising velocity of irregular flocs with small fractal dimension. This study provides new insights into the mechanisms of the enhanced algal removal by CCF and lays foundation for developing cost-efficient algal mitigation processes.

Harvesting of Microcystis flos-aquae using dissolved air flotation: The inhibitory effect of carboxyl groups in uronic acid-containing carbohydrates.

Harvesting algal biomass reduces nutrient loading in eutrophicated lakes and the protein-rich microalgal biomass could be recycled as feedstocks of feed and fertilizer. Due to the complexity of algogenic organic matter (AOM), the key components and functional groups in AOM that inhibit coagulation-based microalgal harvesting have not been disclosed thus far. This study quantitatively analysed the responsive compositions and functional groups of AOM involved in the dissolved air flotation (DAF) harvesting of M. flos-aquae with 1 × 109 cell L-1 density at coagulation pH 6.2. The results showed that harvesting efficiency dropped drastically from 95.5 ± 0.7% to 43 ± 0.7% in the presence of AOM (26.77 mg L-1) at the coagulant dosage of 0.75 mg L-1 and further deteriorated with increasing AOM concentration. Carbohydrates contributed 81% of the total composition of substances involved in the DAF, while the contribution of protein and humic-like substances were only 18% and 1%, respectively. Stoichiometric analysis of functional groups in carbohydrates, proteins, and humic-like substances using model components revealed that carboxyl groups in uronic acid-containing carbohydrates accounted for 76% of the total reduction in carboxyl groups, which was much higher than that in proteins (23%) and humic-like substances (1%), indicating that carboxyl groups in uronic acids containing carbohydrates were the major inhibitors. A conceptual model of charge competition was proposed to explain the inhibition mechanism of carboxyl functional groups in uronic acid-containing carbohydrates on microalgal DAF. Strategies such as preventing carboxyl deprotonation by pH reduction and employment of sweeping/bridging polymeric coagulants/flocculants were proposed for the to reduce the inhibitory effect of carboxyl functional groups.

Study on the cell-collector-bubble interfacial interactions during microalgae harvesting using foam flotation.

Foam flotation is an economical and efficient technology for microalgae harvesting. However, the mechanism of cell-collector-bubble interfacial interactions remains to be elucidated. There are two distinct hypotheses regarding the mechanism of microalgae foam flotation. In this study, the cationic surfactant N-cetyl-N-N-N-trimethylammonium bromide (CTAB), which acts as a partition between Chlorella sorokiniana cells and bubbles, is quantified and the zeta potential response of cells and bubbles after adsorption of CTAB is calculated to reveal the interfacial mechanism of the cells-collector-bubble interfacial interactions. The results indicated that more than 90% of CTAB was preferentially adsorbed on the bubbles, which reversed the surface charge of bubbles from negative (-20 mV) to positive (6.1 mV). However, only 0%-3% CTAB was observed on the microalgae cells, suggesting its limited influence on the negatively charged microalgae cells (from -22.3 to -18.6 mV). During microalgae foam flotation, the nonpolar tails of CTAB were first inserted into the bubble through hydrophobic interactions, leaving the positively charged polar heads outside; further, the CTAB-covered positively charged bubbles captured the negatively charged cells by electrostatic attraction. A feasible mechanism was proposed to understand the interfacial interaction of the microalgae cell-CTAB-bubble. By understanding the mechanism of foam flotation, efficient and cost-effective collectors and devices for microalgae harvesting using foam flotation can be developed.

Effect of shear rate on floc characteristics and concentration factors for the harvesting of Chlorella vulgaris using coagulation-flocculation-sedimentation.

Coagulation-based separation has been increasingly applied to microalgal harvesting because of its competitive cost and high scalability. The characteristics of flocs formed during coagulation/flocculation are critical for efficient harvesting. However, few studies have been devoted to systematically investigating the structural characteristics of microalgal flocs and their influences on subsequent settling performance. In this paper, the dynamic mean size and fractal dimension, strength, regrowth and settling performance of Al3+ coagulated Chlorella vulgaris flocs were characterized at various flocculation shear rates. The influence of shear rate on floc characteristics was revealed. An appropriate shear rate (9 s-1) produced more desirable microalgal flocs (in terms of size and compactness), with better settling performance and a higher concentration factor, than higher or lower shear rates, favoring their separation and subsequent harvesting. At this condition, the concentration factor reached 13.50, which was a 177.21% improvement over the 4.87 reached at a low shear rate.

Miscanthus accessions distinctively accumulate cadmium for largely enhanced biomass enzymatic saccharification by increasing hemicellulose and pectin and reducing cellulose CrI and DP.

In this study, total eight distinct Miscanthus accessions were collected from the cadmium (Cd)-supplied soil pots, and mild alkali pretreatments (0.5%, 1% NaOH) were then performed to enhance biomass enzymatic saccharification. Due to large Cd accumulation, all Miscanthus accessions showed significantly reduced cellulose levels and features (CrI, DP) with much increased hemicellulose and pectin contents in the mature stems. Under mild alkali pretreatments, all Miscanthus samples exhibited largely increased hexoses yields released from enzymatic hydrolysis, and one desirable accession had an almost complete biomass saccharification with the hexoses yield at 100% (% cellulose). Notably, the biomass residues remained from enzymatic hydrolysis upon 1% NaOH pretreatment could absorb 73-96% Cd (% of total), suggesting an applicable approach for Cd phyto-remediation. Hence, a hypothetic model was proposed to elucidate that the enhanced biomass saccharification should be mainly due to much reduced cellulose CrI and DP in the Cd-accumulated Miscanthus accessions.