**1. Introduction**

Anthropogenic eutrophication is caused by the release of nutritive salts, such as phosphates and nitrates from effluents after sewage treatment of domestic and industrial wastewater. The impact of these effluents on the water environment is likely to escalate, especially in closed waters such as ponds, lakes, and dams. In the conventional activated sludge method (ca. 50%) or advanced treatment method (ca. 75%), the nutrient contained in the effluent is not completely removed because only heterotrophic microorganisms, i.e., ecological decomposers, are employed [1].

Excessive influx of nutrient salts into the closed water causes intense growth of blue-green algae (cyanobacteria), and their remains cause organic pollution as

**Figure 1.** *Influences of blue-green algae on anthropogenically eutrophied water.*

excess organic matters [2] (**Figure 1**). When the decomposition of excess organic matter changes from aerobic to anaerobic, anaerobic substances such as hydrogen sulfide and methane are generated, and elution of heavy metal ions occurs. In Japan, it is known that the main species of blue-green algae is *Microcystis aeruginosa* [3, 4]. During daytime, dissolved carbon dioxide (CO2) is taken by the active photosynthesis of phytoplankton. When a lot of blue-green algae occur, bicarbonate ion (HCO3 <sup>−</sup>) and carbonate ion (CO3 <sup>2</sup><sup>−</sup>) take precedence in the afternoon on a clear day. Then, the pH of the surface water rises to around pH 10. Such water environment is more severe for other algae that rely on dissolved CO2 than algae that consume HCO3 <sup>−</sup>. In other words, in both light and carbon environments, blue-green algae are less likely to be limited by environmental changes as a result of growth.

*M. aeruginosa* that makes the water blooms has a kind of floating bag called gas vesicle inside the cell. *M. aeruginosa* floats on the water surface with the gas vesicles and looks like a green powder called "Aoko" [3]. The inside of the gas vesicles contains a gas with a composition similar to air [5]. The gas vesicle does not always expand, and it collapses when the osmotic pressure in the cell is high. When photosynthesis is actively conducted, there are many low-molecular-weight compounds that are the initial products, and the osmotic pressure in the cell is increased. However, when the initial products are consumed at night or in deep layer for polymer synthesis such as cell structures and stored products, permeation occurs. When the osmotic pressure in the cells decreases, the gas vesicles expand again and increase their buoyancy. Thus, the cells rise to the water surface with light. By the growth cycle, the number of the *M. aeruginosa* cells is increased (**Figure 2**).

When intensely grown, the blue-green algae of *M. aeruginosa* produce cyanotoxins known as microcystins [6]. There are about 50 derivatives of microcystins, which have hepatotoxicity to mammalians. In particular, microcystin-LR is the most toxic substance in microcystins (LD50 in mice and rats of 36–122 μg/kg) [7]. The toxic effects of potential human carcinogen microcystin-LR are also investigated [8]. In Japan, the water supply law was defined in 1957, and the concentration of

**23**

**Figure 2.**

*Circadian rhythm of blue-green algae.*

*Water Chemical Remediation for Simultaneous Removal of Phosphate Ion and Blue-Green Algae…*

microcystin-LR in raw water and purified drinking water has been determined. Although microcystin-LR has been detected in raw water, it has not been detected in drinking water. This indicates that microcystin-LR has been removed or degraded in the water purification system [9–11]. In fact, in Japanese water purification system, there is no report of health hazard of microcystins caused by drinking water, although problems such as offensive odor of drinking water occasionally occur [12]. The mechanism of anthropogenic eutrophication in closed water body is illustrated in **Figure 3**. By continuous influx of nutrient salts from anthropogenic source to closed water body, its water quality is gradually eutrophied [1]. In the steps from oligotrophic to eutrophic, the aquatic ecosystem continues to increase biomass such as algae, hydrophytes, and fishes. However, in the final step of hypertrophic, its productive ecosystem is rapidly declining, and blue-green algae become dominant species in the water environment. During daytime, the photosynthetic activity by blue-green algae is greatly enhanced, the pH of surface water is increased, and the concentration of dissolved oxygen becomes supersaturated [13]. And since sunlight is absorbed by the thick layer of the water bloom on the surface water, it becomes difficult for the sunlight to reach the water, making it difficult to grow aquatic plants. Similarly, the growth of fish also becomes a difficult situation due to the production

*DOI: http://dx.doi.org/10.5772/intechopen.88490*

*Water Chemical Remediation for Simultaneous Removal of Phosphate Ion and Blue-Green Algae… DOI: http://dx.doi.org/10.5772/intechopen.88490*

**Figure 2.** *Circadian rhythm of blue-green algae.*

microcystin-LR in raw water and purified drinking water has been determined. Although microcystin-LR has been detected in raw water, it has not been detected in drinking water. This indicates that microcystin-LR has been removed or degraded in the water purification system [9–11]. In fact, in Japanese water purification system, there is no report of health hazard of microcystins caused by drinking water, although problems such as offensive odor of drinking water occasionally occur [12].

The mechanism of anthropogenic eutrophication in closed water body is illustrated in **Figure 3**. By continuous influx of nutrient salts from anthropogenic source to closed water body, its water quality is gradually eutrophied [1]. In the steps from oligotrophic to eutrophic, the aquatic ecosystem continues to increase biomass such as algae, hydrophytes, and fishes. However, in the final step of hypertrophic, its productive ecosystem is rapidly declining, and blue-green algae become dominant species in the water environment. During daytime, the photosynthetic activity by blue-green algae is greatly enhanced, the pH of surface water is increased, and the concentration of dissolved oxygen becomes supersaturated [13]. And since sunlight is absorbed by the thick layer of the water bloom on the surface water, it becomes difficult for the sunlight to reach the water, making it difficult to grow aquatic plants. Similarly, the growth of fish also becomes a difficult situation due to the production

*Water Chemistry*

excess organic matters [2] (**Figure 1**). When the decomposition of excess organic matter changes from aerobic to anaerobic, anaerobic substances such as hydrogen sulfide and methane are generated, and elution of heavy metal ions occurs. In Japan, it is known that the main species of blue-green algae is *Microcystis aeruginosa* [3, 4]. During daytime, dissolved carbon dioxide (CO2) is taken by the active photosynthesis of phytoplankton. When a lot of blue-green algae occur, bicarbonate ion

Then, the pH of the surface water rises to around pH 10. Such water environment is more severe for other algae that rely on dissolved CO2 than algae that consume

less likely to be limited by environmental changes as a result of growth.

<sup>−</sup>. In other words, in both light and carbon environments, blue-green algae are

*M. aeruginosa* that makes the water blooms has a kind of floating bag called gas vesicle inside the cell. *M. aeruginosa* floats on the water surface with the gas vesicles and looks like a green powder called "Aoko" [3]. The inside of the gas vesicles contains a gas with a composition similar to air [5]. The gas vesicle does not always expand, and it collapses when the osmotic pressure in the cell is high. When photosynthesis is actively conducted, there are many low-molecular-weight compounds that are the initial products, and the osmotic pressure in the cell is increased. However, when the initial products are consumed at night or in deep layer for polymer synthesis such as cell structures and stored products, permeation occurs. When the osmotic pressure in the cells decreases, the gas vesicles expand again and increase their buoyancy. Thus, the cells rise to the water surface with light. By the growth cycle, the number of the *M. aeruginosa* cells is increased (**Figure 2**).

When intensely grown, the blue-green algae of *M. aeruginosa* produce cyanotoxins known as microcystins [6]. There are about 50 derivatives of microcystins, which have hepatotoxicity to mammalians. In particular, microcystin-LR is the most toxic substance in microcystins (LD50 in mice and rats of 36–122 μg/kg) [7]. The toxic effects of potential human carcinogen microcystin-LR are also investigated [8]. In Japan, the water supply law was defined in 1957, and the concentration of

<sup>2</sup><sup>−</sup>) take precedence in the afternoon on a clear day.

**22**

(HCO3

**Figure 1.**

HCO3

<sup>−</sup>) and carbonate ion (CO3

*Influences of blue-green algae on anthropogenically eutrophied water.*

**Figure 3.** *Mechanism of anthropogenic eutrophication in closed water body.*

of microcystins by blue-green algae and the reduced substances generated by the anaerobic decomposition of organic matters [14–16]. Especially in the case of small fishes, excessive consumption of oxygen by nighttime algae causes a deficiency of dissolved oxygen, which makes survival more difficult compared to large fishes.

As mentioned above, it can be seen that the progress of eutrophication in closed waters has a serious impact on the aquatic ecosystem. Various environmental remediation technologies have been developed to improve the situation of such water environment. Among them, one of the surest methods is one of the physical remediation methods. However, this method has problems such as being limited to the place where heavy equipment can be introduced for dredging and high cost of dredging. Therefore, studies on bioremediation that can be performed more easily are actively conducted [17]. As for bioremediation, soil or grand water quality improvement using plants (phytoremediation) or microorganisms (bioaugmentation or biostimulation) has been developed. In particular, the bioaugmentation for sea pollution such as crude oil spill is well-known. But also in water environment, active studies have been made on water quality improvement using plants or algae as a sustainable and environmental friendly method.

Employing plants, the hydroponic phytoremediation using floating raft for water quality improvement has been studied for wastewater treatment [18]. This remediation method has also been developed into an "aquaponics" that applies nutrients contained in aquaculture wastewater to hydroponic cultivation of the plants such as agricultural products [19]. Employing algae, the so-called phycoremediation has also been studied for the improvement of water quality in the eutrophic water body [17, 20]. Algae are highly adaptive and can grow autotrophically, heterotrophically, or mixotrophically in any environment. In the ecosystem, algae as the autotrophic organism belong to the producer; therefore, they intake mineralized substances. The feature can be applied to cost-effective nutrient removal processes [21] and also be applied to a synergistic approach for simultaneous bioremediation and biomass generation [22]. The biomass produced by the algae is energy-rich

**25**

**Figure 4.**

*Principle of our water chemical remediation method.*

*Water Chemical Remediation for Simultaneous Removal of Phosphate Ion and Blue-Green Algae…*

which can be further processed to make biofuel, biodiesel, and other bio-hydrocarbons. Further, the algae biomass can also be used to obtain a product called as a bio-based product such as bioplastic, fertilizer, animal food, and many more [23]. The phycoremediation employing cyanobacteria calls microalgal remediation or cyanoremediation [24]. The *M. aeruginosa* cells form colonies and have the outer layer of which is surrounded by a gelatinous sheath with a well-defined boundary. The gelatinous sheath adsorbs nutrients [3]. The adsorptive property of the gelatinous sheath has another property as the remediation tools, i.e., it can remove pollutants such as heavy metal ions, nutrients salts, and other chemical and organic contaminants from the water environment and CO2 from air. In detail, the gelatinous sheath of *M. aeruginosa* is thought to play a role such as maintenance of colony formation, adsorption and concentration of ions, protection against predation, protection against bacterial attack, and relationship with sink-float. The sheath materials were mainly composed of 35.4–47.0% of polysaccharides with uronic acids and 18.2–24.5% of protein [25]. In particular, *M. aeruginosa* is intensively an intake phosphate ion as limiting factor of the water environment and produces polyphosphates and stores them in the cell [3]. Such property of *M. aeruginosa* is also suitable as one of the remediation tools. Chemical remediation which uses chemicals has been studied especially for soil and grand water. For water quality improvement in the aquatic environment, heavy metal ions, organic contaminants, and radionuclides have been removed by polymeric membranes, microporous solids, and hybrid chemoenzymatic materials [26]. For phosphate removal, calcium compounds such as calcium hydroxide (lime), calcium carbonate, and calcium silicate have been used [27–29]. However, these calcium compounds have low solubility to fresh water; therefore, these compounds are not suitable for effective removal of phosphate ion which dissolved in fresh water. On the other hand, the chemical remediation for blue-green algae has been performed using algaecides (permanganate, aluminum chloride, sodium chloride, acid-soluble cuprous chloride, etc.) [30]. However, the use of the algaecides is concerned about the influences on the aquatic ecosystem. To recover the

*DOI: http://dx.doi.org/10.5772/intechopen.88490*

#### *Water Chemical Remediation for Simultaneous Removal of Phosphate Ion and Blue-Green Algae… DOI: http://dx.doi.org/10.5772/intechopen.88490*

which can be further processed to make biofuel, biodiesel, and other bio-hydrocarbons. Further, the algae biomass can also be used to obtain a product called as a bio-based product such as bioplastic, fertilizer, animal food, and many more [23].

The phycoremediation employing cyanobacteria calls microalgal remediation or cyanoremediation [24]. The *M. aeruginosa* cells form colonies and have the outer layer of which is surrounded by a gelatinous sheath with a well-defined boundary. The gelatinous sheath adsorbs nutrients [3]. The adsorptive property of the gelatinous sheath has another property as the remediation tools, i.e., it can remove pollutants such as heavy metal ions, nutrients salts, and other chemical and organic contaminants from the water environment and CO2 from air. In detail, the gelatinous sheath of *M. aeruginosa* is thought to play a role such as maintenance of colony formation, adsorption and concentration of ions, protection against predation, protection against bacterial attack, and relationship with sink-float. The sheath materials were mainly composed of 35.4–47.0% of polysaccharides with uronic acids and 18.2–24.5% of protein [25]. In particular, *M. aeruginosa* is intensively an intake phosphate ion as limiting factor of the water environment and produces polyphosphates and stores them in the cell [3]. Such property of *M. aeruginosa* is also suitable as one of the remediation tools.

Chemical remediation which uses chemicals has been studied especially for soil and grand water. For water quality improvement in the aquatic environment, heavy metal ions, organic contaminants, and radionuclides have been removed by polymeric membranes, microporous solids, and hybrid chemoenzymatic materials [26]. For phosphate removal, calcium compounds such as calcium hydroxide (lime), calcium carbonate, and calcium silicate have been used [27–29]. However, these calcium compounds have low solubility to fresh water; therefore, these compounds are not suitable for effective removal of phosphate ion which dissolved in fresh water. On the other hand, the chemical remediation for blue-green algae has been performed using algaecides (permanganate, aluminum chloride, sodium chloride, acid-soluble cuprous chloride, etc.) [30]. However, the use of the algaecides is concerned about the influences on the aquatic ecosystem. To recover the

**Figure 4.** *Principle of our water chemical remediation method.*

*Water Chemistry*

**Figure 3.**

of microcystins by blue-green algae and the reduced substances generated by the anaerobic decomposition of organic matters [14–16]. Especially in the case of small fishes, excessive consumption of oxygen by nighttime algae causes a deficiency of dissolved oxygen, which makes survival more difficult compared to large fishes.

waters has a serious impact on the aquatic ecosystem. Various environmental remediation technologies have been developed to improve the situation of such water environment. Among them, one of the surest methods is one of the physical remediation methods. However, this method has problems such as being limited to the place where heavy equipment can be introduced for dredging and high cost of dredging. Therefore, studies on bioremediation that can be performed more easily are actively conducted [17]. As for bioremediation, soil or grand water quality improvement using plants (phytoremediation) or microorganisms (bioaugmentation or biostimulation) has been developed. In particular, the bioaugmentation for sea pollution such as crude oil spill is well-known. But also in water environment, active studies have been made on water quality improvement using plants or algae

Employing plants, the hydroponic phytoremediation using floating raft for water quality improvement has been studied for wastewater treatment [18]. This remediation method has also been developed into an "aquaponics" that applies nutrients contained in aquaculture wastewater to hydroponic cultivation of the plants such as agricultural products [19]. Employing algae, the so-called phycoremediation has also been studied for the improvement of water quality in the eutrophic water body [17, 20]. Algae are highly adaptive and can grow autotrophically, heterotrophically, or mixotrophically in any environment. In the ecosystem, algae as the autotrophic organism belong to the producer; therefore, they intake mineralized substances. The feature can be applied to cost-effective nutrient removal processes [21] and also be applied to a synergistic approach for simultaneous bioremediation and biomass generation [22]. The biomass produced by the algae is energy-rich

as a sustainable and environmental friendly method.

*Mechanism of anthropogenic eutrophication in closed water body.*

As mentioned above, it can be seen that the progress of eutrophication in closed

**24**

blue-green algae, iron salt, aluminum salt, permanganate potassium composite, or calcium phosphate precipitation was employed as a coagulation reagent [31–34]. In the calcium phosphate precipitation method, phosphate ion was intensively precipitated with calcium ion by addition of sodium hydroxide [34]. Blue-green algae are coagulated by calcium phosphate precipitation due to that the algae cell surface is negatively charged [35, 36]. The coagulate substance is suitable for algae biomass production due to contain calcium phosphate precipitation as nutrient salt.

As described above, most of chemical remediation methods have problems as the environmentally friendly method. In the present study, we propose a water chemical remediation (WCR) system for simultaneous removal of phosphate ion and blue-green algae from the surface water of the anthropogenically eutrophied pond [37]. The system employs calcium chloride dihydrate for both precipitation with phosphate ion and coagulation with blue-green algae (**Figure 4**). The calcium chloride dihydrate has no ecotoxicity, low toxicity reagent (LD50 2045 mg/kg, rat male/oral), and widely used as food additive and snow-melting agent in Japan. Further, calcium chloride has high water solubility (74.5 g/100 mL at 20°C); the feature is able to reduce the amount of the reagent. For the study, we had been investigating the water quality of the anthropogenically eutrophied pond from 2006 to 2009 [38]. The results are also shown in the present study.
