A Universal Method for Flocculating Harmful Algal Blooms in Marine and Fresh Waters Using Modified Sand

A universal environmental friendly method was developed to turn sand into effective flocculants for mitigating harmful algal blooms (HABs) in marine and freshwater systems. The isoelectric point of sand was largely increased from pH 4.5 to 10.5 after been modified by <i>Moringa oleifera</i> coagulant (MO) abstracted form MO seeds. However, when sand was modified by MO alone, maximum removal efficiencies of 80% and 20% for <i>Amphidinium carterae</i> (A.C.) and <i>Chlorella</i> sp. (C.S.) in seawater and 60% for <i>Microcystis aeruginosa</i> (M.A.) in fresh water were achieved in 30 min. The limited removal improvement was due to the form of only small flocs (20–100 μm) by surface charge modification only. Large flocs (270–800 μm) and high removal rate of 96% A.C. and C.S. cells in seawater and 90% of M.A. cells in fresh water were achieved within 30 min when the small MO-algae-sand flocs were linked and bridged by chitosan. High HAB removal rate is achievable when the sand is modified by the bicomponent mechanism of surface charge and netting-bridging modification using biodegradable modifiers such as MO and chitosan. The optimized dosage of modified sand depends on the property of algal cells and water conditions

Influence of pH on Initial Concentration Effect of Arsenate Adsorption on TiO₂ Surfaces: Thermodynamic, DFT, and EXAFS Interpretations

Under the same thermodynamic condition where the total mass of arsenate was fixed, when the initial arsenate was added to TiO2 suspension by multiple batches, adsorption isotherms declined as the multi-batch increased, which was termed initial concentration (C0) effect. The extent of C0 effect decreased gradually as pH decreased from 7.0 to 5.5. Extended X-ray absorption fine structure analysis of 1-batch and 3-batch isotherm samples showed that the relative proportion of bidentate binuclear (BB) and monodentate mononuclear (MM) complex was rarely affected by pH change from 5.5 to 7.0, indicating that the dependence of C0 effect on pH was not due to inner-sphere chemiadsorption. The influence of pH on adsorption was simulated by density functional theory through changing the number of H+ in model clusters. Calculation of adsorption energy showed that BB surface complex was the most thermodynamically favorable mode (−244.5 kJ mol−1) at low pH, but MM surface complex was the most thermodynamically favorable mode (−135.6 to 27.5 kJ mol−1) at intermediate and high pH, which indicated the influence of surface functional groups (−H2O and −OH) on adsorption reaction pathways. As pH decreased, C0 effect weakened gradually because outer-sphere H-bond adsorption became thermodynamically favorable (−203.1 kJ/mol). The dependence of C0 effect on pH showed that traditional equilibrium adsorption constants could not accurately describe the real adsorption equilibrium at solid−liquid interface, because real equilibrium adsorption state is generally a mixture of various outer-sphere and inner-sphere metastable-equilibrium states

Coordination Structure of Adsorbed Zn(II) at Water−TiO₂ Interfaces

The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water−TiO2 interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average ∼4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn−O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments

Two operations to process a new edge linking a new node to an existing node.

<p>(a) A new node attaches to an existing node with degree two, it joins the same community as the existing node; (b) Another new node attaches to the previous new node with degree one, it splits as a new community.</p

The evolution of temporal modularity over time by <i>OLEM</i> and <i>OLTM</i>.

<p>The evolution of temporal modularity over time by <i>OLEM</i> and <i>OLTM</i>.</p

NMI Benchmark by three community detection algorithms comparing with Yang's labeled community structure.

<p>NMI Benchmark by three community detection algorithms comparing with Yang's labeled community structure.</p

DataSheet_1_Characteristics of Dissolved Organic Matter in a Semi-closed Bay in Summer: Insights from Stable Isotope and Optical Analyses.docx

Dissolved organic matter (DOM) serves as the most active and sensitive organic component in the bay, and its biogeochemical characteristics and reactivity are affected by the properties of terrestrial and marine substances significantly. In this study, in order to study the distribution and characteristics of DOM in a semi-closed bay, 34 water samples from 19 stations were collected from Zhanjiang Bay and analyzed for δ13C of dissolved inorganic carbon (DIC) and fluorescent components of DOM. The results showed that there were many sources of organic matter in the bay, including soil input, algae input, and sewage input. Influenced by freshwater input, DOM in the bay decreased from the upper bay to the outer bay. The organic matter in the bay displayed two characteristics, where the northern bay is composed of terrigenous organic matter mainly with high humus, while the southern bay is more inclined to marine sources with a high biological index (BIX) and low humification index (HIX). The correlation between organic matter with different characteristics and environmental parameters such as salinity, pH, and chlorophyll a was analyzed. The discrepancy may be caused by the weak turbulent mixing in the semi-closed bay.</p

Modularity by three community detection algorithms.

<p>Modularity by three community detection algorithms.</p

Modularity by three community detection algorithms.

<p>Modularity by three community detection algorithms.</p

Two situations of a new edge linking two existing nodes.

<p>(a) Nodes belong to a same community; (b) Nodes belong to different communities.</p