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

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

Modularity by three community detection algorithms.

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

The percentage of different operations of <i>OLTM</i> over time.

<p>The height of each color segment represents the percentage of an operation at a certain progress. “Op” is the abbreviation for “Operation” of <i>OLTM</i> at each step.</p

Number of communities by three community detection algorithms and Yang's labeled community structure.

<p>Number of communities by three community detection algorithms and Yang's labeled community structure.</p

The statistics of modularity on 10 reordered data sets as well as modularity on original data set by our algorithm.

<p>The statistics of modularity on 10 reordered data sets as well as modularity on original data set by our algorithm.</p

Modularity by three community detection algorithms.

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

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