Diyala Agricultural Sciences Journal Vol (14) No 1, 2022:40-46 

Prabhasha Jayasundara 

ISSN: 2073-9524 

eISSN: 2310-8746 

 

40 
 

Wastewater Treatment by Azolla: A review 

Prabhasha Jayasundara  

Department of Chemical and Process Engineering, Faculty of Engineering, University of Peradeniya, Sri Lanka 

Corresponding author: prabhashajayasundara@gmail.com

Article history:  
Received: 6 January 2022  

Accepted: 27 February 2022 

Published: 30 June 2022 

Abstract 

Water is vital for humans and other living things, but water pollution has become a 

significant issue today. Various anthropogenic agricultural, industrial, and home activities 

produce multiple organic and inorganic substances dissolved or suspended in water. The 

goal of wastewater treatment is thus twofold: to reduce water pollution while also 

maintaining the water supply to demand. It is based on the three 3 Rs: reduce, reuse, and 

recycle. However, many of the methods used are ineffective or expensive. As a result, 

water purification is a matter of great interest. Eco-friendly approaches are essential 

among the new technologies and techniques tested in wastewater treatment. Aquatic 

macrophytes treat water by accumulating harmful metals and nutrients. Like water filters, 

a variety of aquatic floats can be suggested. Azolla is one among them, and it has been 

used for decades. Researchers have discovered that Azolla can reduce Chemical Oxygen 

Demand (COD), Biochemical Oxygen Demand (BOD), nitrogen, phosphorus, and heavy 

metal concentrations in wastewater; therefore, it can be utilized for wastewater treatment. 

Azolla also produces a lot of biomasses in wastewater. The use of Azolla in reducing 

eutrophication in lakes and streams and other benefits is discussed in this study. 

According to the literature, Azolla has a high growth rate, with a doubling date of 2-4 

days. Azolla's cell wall is composed of pectin, which has a high affinity for the adsorption 

of organic substances. Azolla serves as a "biofilter" during wastewater treatment in this 

way. 

 

Keywords: Azolla, 

Wastewater Nitrate and 
Phosphate, Treatment, 

Heavy metals  
 

https://dx.doi.org/10.52951/dasj.22140105 

This article is open-access under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).

Introduction 

Environmental pollution has been discussed 

since the industrial revolution, and today, it is 

an essential topic all over the world in economy 

and politics. The pollutants in the form of 

organics from herbicides, insecticides, and 

inorganics like trace elements, heavy metals, 

and metalloids are being discharged into 

different compartments of the earth- soil, water, 

and air (Soman and Arora, 2018). Water 

pollution can be divided into groundwater and 

surface water pollution. Surface water pollution 

happens for many reasons; releasing organic 

and inorganic nutrients to the water discharging 

untreated sewage, heavy metals, and chemicals 

to water bodies. While water is a limited 

resource, the quality and quantity decrease day 

by day. Unless environmentally and 

economically sustainable management 

technologies are developed, the accumulation of 

these wastes may cause disposal and 

contamination difficulties. As a result, the 

development of cost-effective wastewater 

treatment methods should be studied (Amuda 

and Ibrahim, 2006).    

Some plants can absorb and accumulate 

high concentrations of nutrients and heavy 

metals; this process is known as 

phytoremediation, and this process can be used 

in wastewater treatment. So many researchers 

have found that aquatic macrophytes have a 

high potential to absorb nutrients and heavy 

metals in water, with high biomass yield. 

Researchers have found that among the fern 

used in constructed wetlands, such as duckweed 

cattails, Azolla is more efficient than others. For 

decades, the symbiotic relationship has been 

used as green manure in rice fields because of 

its habitat and nitrogen-fixing capabilities. 

Because of its ability to extract phosphorous 

mailto:prabhashajayasundara@gmail.com
http://creativecommons.org/licenses/by/4.0/
https://orcid.org/0000-0002-1516-8151


Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

41 
 

and nitrogen from the water medium, there is 

growing interest in employing the fern for 

additional applications, such as a decontaminant 

plant in low-cost wastewater treatment systems 

(Forni et al., 2001). 

The findings of A.A.Deshmukh et al. 

demonstrated that the treatment of sewage 

Azolla does not require the installation of a 

complicated unit or any elaborate mechanism. 

As a result, it is effective and should be used, 

particularly in developing nations. Because the 

treated water compares favorably to untreated 

water, it can be discharged into the environment 

without causing harm to the environment or 

human health. As a result, a low-cost, 

environmentally friendly, and effective 

treatment method has been developed. Azolla is 

a beneficial plant for controlling the number of 

nutrients in sewage and for helping to tackle the 

problem of overcrowding. Eutrophication and 

phytoremediation are environmentally friendly 

sewage treatment methods that are particularly 

effective when combined with other treatment 

methods  (Deshmukh et al., 2013). 

 

Figure 1:Azolla (Sood et al., 2012)  

Azolla can be used as a biofertilizer in rice 

agriculture, as green manure, in saline soil 

reclamation, as a component of space cuisine, 

mosquito repellant, weed control, and biogas 

production. The current review focuses on 

Azolla's phytoremediation potential in various 

wastewaters and biomass output. This review 

aims to analyze the phytoremediation potential 

of Azolla and to analyze the growth kinetics of 

Azolla for different kinds of wastewater. 

 

Characteristics and Uses of Azolla 

The genus Azolla was established by 

Lamarck in 1783. Azolla is derived from two 

Greek words, "azo," which means to dry, and 

"alloy," which means to kill. It has several 

advantages, the most important being the ability 

to grow in the least time, due to which it is 

referred to as a "super-plant" (Soman and Arora, 

2018). Azolla is a small floating plant species. It 

is a genus name belonging to the family 

Azollacea. Azolla has different species such as 

A.pinnata, A.caroliniana, A.filiculoides, 

A.microphylla, and A.imbricata. It is 

widespread in aquatic bodies. Their leaves are 

water repellent and like small-scale roots 

hanging in the water. Azolla form symbiosis 

with Cyanobacteria, Namely Anabaena azollae. 

These bacteria can fix nitrogen. Therefore, the 

plant can quickly get nutrients. They have a 

higher growth rate. Phosphorous is one of the 

limiting minerals. Phosphorous abundance 

sometimes leads to Azolla blooms. Symbiotic 

bacteria transfer from one generation to the 

next. 

The nitrogen sequestering potential of the 

organism makes it play a significant role in 

agriculture by increased rice productivity due to 

Its application as a dual crop, and a biofertilizer 

and biomass can be used as a bio-fertilizer or as 

a feed supplement for aquatic and terrestrial 

animals due to its protein; crude fiber and 

mineral content; Moreover, the growth of 

Azolla in natural water bodies forms a mat 

which can help reduce the evaporation of water 

from them thereby making water available year-

round (Soman and Arora, 2018). 

According to the results of previous 

continuous assays, using Azolla, an aquatic fern 

with a high growth rate and productivity, to 

improve treated urban wastewater quality 

appears to be very promising, primarily because 

of its phosphorus removal efficiencies (40-65 

%) and heavy metal biosorption using living 

Azolla (phytoremediation) or dried biomass as a 

bioadsorvent material are both relatively new 

technologies for metal removal (Costa et al., 

2010). 



Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

42 
 

Research has been investigated Azolla can 

be used as a space diet and Space agriculture 

based on the menu with Azolla. According to 

the International Rice Research Institute reports, 

"The use of Azolla in controlling water 

pollution" is a major research priority. 

Phytoremediation Ability of Azolla 

Chemical oxygen demand (COD) 

The COD value represents the extent of 

pollution of a water body; the more the COD, 

the more the pollution is. However, its value 

numerically depends on the number of 

compounds that can be oxidized present in the 

water sample only. Different physical, chemical, 

and biological methods in conventional 

wastewater treatment reduce COD load. 

Wastewater supplies macronutrients such as 

carbon, nitrogen, phosphorus, and 

micronutrients such as sodium, chlorine, and 

iron. When an aquatic plant is used for water 

treatment, it absorbs that nutrient and grows up. 

Azolla biomass has been used to reduce COD in 

wastewater by various researchers (Golzary et 

al., 2018; Amuda and Ibrahim, 2006; Soman 

and Arora, 2018). Table 1 shows their results. 

The petroleum wastewater mainly consists of 

organic compounds, and hence with time, the 

COD removal percentage increases as the 

biomass of Azolla increases. 

Azolla is also efficient in the removal of 

nitrogen and phosphorous. Hence, the 

wastewater mixed with cow dung increased the 

nitrogen and phosphorus content of the sample 

and decreased the percentage COD removal rate 

than unmixed sewage water, for COD takes 

only an amount of organic substance into the 

calculation. A part of Azolla removes 

phosphorus and nitrogen, and thereby the 

percentage of COD removal rate decreases. 

After secondary treatment, the system's 

physiochemical parameters like temperature and 

pH have also changed, affecting the percentage 

COD removal rate. 

 

Growth kinetics  

The laboratory studies showed that Azolla 

could double its biomass in 3.5 days and grow 

in a nitrogen-free solution since it does not need 

a nitrogen nutrient medium for its biomass 

growing (Golzary et al., 2018). Because of this 

fast-growing kinetics and the floating nature of 

Azolla help in its easy harvest for disposal or 

recovery of heavy metals from biomass. 

At a particular experimental condition, 

Figure 2 shows the influence of temperature on 

the Azolla growth rate. Azolla growth was 

reported to be better at room temperature. The 

temperature influence on Azolla growth rate 

was studied at temperatures ranging from 10 to 

50 C°. The optimal temperature for the Azolla 

growth rate was 30 C°. As can be seen, Azolla 

growth was reduced at temperatures above and 

below 30 C° (Zazouli et al., 2014). 

 

Figure 2: Effect of temperature on Azolla growth (initial 

biomass = 0.9 g) 

Phytoremediation of heavy metals 

Naghipour et al. (2018) have studied the 

phytoremediation of heavy metals (Ni, Cd, Pb) 

by Azolla. They have followed the following 

method. "The Azolla was taken from a lake near 

Rasht city and rinsed in tap water before being 

weighed (0.2, 0.4, and 0.8g) and maintained in a 

100 mL disposable container for 15 days in the 

presence of 5, 10, and 25 mg L
-1

 of Lead, 

Nickel, and Cadmium ions." The samples were 

kept in polyethylene containers to determine the 

metal concentration using "ICP-

OES."(Naghipour et al., 2018). 

The maximum efficiencies they have found are 

listed in table 2.

  



Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

43 
 

Table 1: Literature on COD removal percentages by Azolla 

Type of wastewater 
COD/ 
mg L

-1
 

Number 

of days 

COD 

removal 

percentage 

Reference 

 

Petroleum refinery 

wastewater 

4326 0 

 

(Golzary et al., 2018) 

3042 7 29.68 

1324 14 69.39 

135 21 96.88 

51 28 98.82 

sewage water 

199 0 

 

  

128 15 35.68 

(Amuda and Ibrahim, 

2006) 

54 30 72.86   

Sewage water+ cow dung  

117 0 

 

  

71 15 39.31   

48 30 58.97   

Secondary treated sewage 

water 

676 0 
87.42 

 (Soman and Arora 2018) 

85 NA   

 

Table 2: Literature on heavy metal removal efficiency by Azolla 

Heavy 

Metal 

Biomass of Azolla/g Initial concentration/ 

mgL
-1

 

contact 

days 

Removal 

efficiency % 

Cd 0.8 5 15 92.84 

Pb 0.8 10 15 97.12 

Ni 0.8 25 15 76.82 

 

But there is a problem with discharging dead 

Azolla after treatments as heavy metal should 

not be released directly to the environment.  

Pandey has studied the efficiency of Azolla 

caroliniana for phytoremediation of fly ash 

(FA) pond because of its higher 

bioconcentration factor. The metal 

concentrations ranged from 175 to 538 and 86 

to 753 mg kg
-1

 in roots and fronds. 

Bioconcentration factor (BCF) values of all 

metals in root and frond ranged from 1.7 to18.6 

and 1.8 to 11.0, respectively, which were 

greater than one and indicated the metal 

accumulation potential of Azolla caroliniana. 

Translocation factor (TF) ranged from 0.37 to 

1.4 for various heavy metals (Pandey, 2012), 

and figure 3 shows heavy metals concentration 

in roots, fronds, and FA effluents. 

 

Figure 3: Heavy metals concentration in roots, fronds, 

and FA effluents (Pandey, 2012) 

Nitrogen and phosphorous  

The eutrophication of lakes and streams has 

been increased by nutrients, particularly 

nitrogen and phosphorus, released through 

wastewater treatment facilities. In eutrophic 

water, the growth of aquatic weeds and algae 

typically renders the water non-potable or unfit 

for recreational use. Overproduction of algae is 

frequently linked to oxygen deficiency and taste 

and odor issues in water. Because preventing 



Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

44 
 

further eutrophication is costly, current 

pollution control research eliminates fertilizing 

ingredients from effluents before they enter 

natural rivers (Kitoh et al., 1993). 

Nitrogen and Phosphorous are the primary 

nutrients in wastewater and cause 

eutrophication. Azolla can absorb and 

accumulate nitrogen and phosphorous from 

wastewater. (Forni et al., 2001; Amuda and 

Ibrahim, 2006; Golzary et al., 2018; Soman and 

Arora, 2018) have studied the characteristics of 

Azolla. Figure 4 shows the different forms of 

nitrogen in wastewater that Azolla can remove. 

 

 

Figure 4: Different types of nitrogen in wastewater

Researchers have concluded the following 

essential points regarding Azolla. Azolla algae 

can remove nutrients (phosphorus and nitrogen) 

from aqueous solutions; therefore, it can be used 

for the advanced treatment of wastewater to 

improve the quality of effluent. However, it is 

unsuitable for nitrogen removal at low nitrogen 

content wastewaters. (Golzary et al., 2018). The 

ability of Azolla to carry out sewage 

bioremediation was analyzed. The study has 

shown promising results in removing total 

organic carbon, phosphorous, and nitrogen and 

efficiently removing ammonia (Soman and 

Arora, 2018). Azolla's performance after two 

weeks, particularly in the summer, revealed 

stress conditions caused primarily by high 

temperatures. As a result, it is advised that the 

fern be used to remove nitrogenous substances 

from aquaculture effluent for a short period in 

the spring and summer (Forni et al., 2001). 

The naturally growing aquatic fern Azolla 

algae are an excellent approach for wastewater 

treatment in the experimental tests. Its primary 

function is to reduce metabolic and chemical 

oxygen demand. This method can also reduce 

other nitrogen, phosphate, and potassium 

variables. Azolla alga may store contaminants 

in its tissues by consuming water for 

development. (Amuda and Ibrahim, 2006). 

Muvea et al. (2019) have tabled the nitrogen 

and phosphorus fixing abilities of Azolla, as 

shown in Table 3. 

Table 4. Nutrients removal efficiency by the 

Azolla (Muvea et al., 2019) 

Nutrient Removal efficiency (%) 

Nitrite 63.16 

Nitrate 89.89 

Ammonia 16.29 

Total phosphorous 46.45 

Soluble reactive 

Phosphorous 
69.66 

Total nitrogen 25.57 

Average 68.67 

 

Benefits and Applications 

 

Figure 5 represents the benefits and different 

applications of Azolla: 

Nitrate-Nitrogen 

NO3
-
 

Nitrite-Nitrogen 

NO2
-
 

Ammonia-Nitrogen 

NH3-N 

Organic-Nitrogen 

 

TKN (Total Kjeldahl 

Nitrogen) 

Total Nitrogen 



Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

45 
 

  
    Experiments have demonstrated that Azolla 

can help plants overcome nutritional limitations 

by improving nutrient absorption. Azolla 

provides different benefits to plants and the 

environment depending on the plant species and 

growing practices and conditions, such as 

increased yields and crop quality, reduced 

disease occurrence, improved flowering and 

fruiting, increased plant establishment, and 

survival at seedling or transplanting, and so on. 

Produce plants that are more vigorous and 

healthier. Drought tolerance is improved, 

reducing watering (Raja et al., 2012). Improve 

soil salinity tolerance and contribute to soil 

quality and nutrient cycling through optimizing 

fertilizer use, particularly nitrogen (Raja et al., 

2012).

 

Figure 5: Benefits and application of Azolla 

Conclusion 

Due to their cheap construction, operation, 

and maintenance costs compared to existing 

conventional systems, water treatment systems 

with aquatic plants are an efficient and cost-

effective choice for wastewater treatment, 

eliminating microorganisms and physical-

chemical pollutants. Removing suspended 

particles and organic matter in macrophyte-

dominated systems is attributed to 

sedimentation, absorption, and removal 

mechanisms. Experimental results show that 

Azolla can be used differently for wastewater 

treatment, such as nutrient remover and heavy 

metal absorber. But most researchers haven't 

been forced into real situations and have studied 

only laboratory scale. Some practical problems 

will occur in real cases because Azolla may not 

grow well in deep tanks, such as treatment tanks 

used in wastewater treatment. Azolla needs a 

large surface area for its growth; Providing a 

large surface area may not be a practical 

situation in wastewater treatment. As a result, 

more research is needed to improve Azolla's 

efficiency and gain a more profound knowledge 

of this symbiosis. 

  

 

Conflict of interest 

The author declares that the publishing of this 

article does not include any conflicts of interest. 

Furthermore, the author has strictly adhered to 

ethical problems such as plagiarism, informed 

consent, misconduct, data fabrication and 

falsification, multiple publishing and 

submission, and redundancy. 

Acknowledgment 

This paper was written as a part of the CP308 

course of the undergraduate program, 

department of chemical and process 

engineering, university of Peradeniya; hence 

special thanks go to the department. 

References 

Costa, M. L., Santos, M. C. R., and Carrapiço, 

F. (2010). Potential uses of Azolla 

filiculoides’ biomass grown in natural 

ecosystems and urban wastewater. 

In Proceedings of the 14th RAMIRAN 

International Conference.‏ 

Deshmukh, A. A., Bandela, N. N., Chavan, J. 

R., and Nalawade, P. M. (2013). Studies on 

potential use of water hyacinth, Pistia and 

Azolla for municipal waste water 

treatment. Environment, 3(11), 226-228.‏ 

Benefits 

Fast Growing rate 

Easy to harvest 

Accumulate heavy metals 

Fix nitrogen and phosphorus  

Application 

Animal feed 

Medicine 

Green manure 

Biogas production  



Diyala Agricultural Sciences Journal Vol (14) No 1, 2022: 40-46 

46 
 

Forni, C., Chen, J., Tancioni, L., and Caiola, M. 

G. (2001). Evaluation of the fern Azolla 

for growth, nitrogen and phosphorus 

removal from wastewater. Water 

research, 35(6), 1592-1598.‏ 

Golzary, A., Tavakoli, O., Rezaei, Y., and 

Karbassi, A. (2018). Wastewater treatment 

by Azolla filiculoides: A study on color, 

odor, COD, nitrate, and phosphate 

removal. Pollution, 4(1), 69-76.‏ 

Kitoh, S., Shiomi, N., and Uheda, E. (1993). 

The growth and nitrogen fixation of Azolla 

filiculoides Lam. in polluted 

water. Aquatic botany, 46(2), 129-139.‏  

Muvea, F. M., Ogendi, G. M., and Omondi, S. 

O. (2019). Nutrient removal efficiency by 

floating macrophytes; Lemna minor and 

Azolla pinnata in a constructed 

wetland. Global Journal of Environmental 

Science and Management, 5(4), 415-430.‏  

Naghipour, D., Ashrafi, S. D., Gholamzadeh, 

M., Taghavi, K., and Naimi-Joubani, M. 

(2018). Phytoremediation of heavy metals 

(Ni, Cd, Pb) by Azolla filiculoides from 

aqueous solution: a dataset. Data in 

brief, 21, 1409-1414. ‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏‏ ‏‏‏‏‏‏ 

https://doi.org/10.1016/j.dib.2018.10.111 

Pandey, V. C. (2012). Phytoremediation of 

heavy metals from fly ash pond by Azolla 

caroliniana. Ecotoxicology and       ‏ ‏ ‏ ‏

Environmental Safety, 82, 8-12.‏‏ ‏ ‏ ‏ ‏  
https://doi.org/10.1016/j.ecoenv.2012.05.002 

Amuda, O. S., and Ibrahim, A. O. (2006). 

Industrial wastewater treatment using 

natural material as adsorbent. African 

journal of Biotechnology, 5(16).‏ 

Raja, W., Rathaur, P., John, S. A., and Ramteke, 

P. W. (2012). Azolla: An aquatic 

pteridophyte with great potential. Int. J. 

Res. Biol. Sci, 2(2), 68-72.‏ 

Soman, D., Anitha, V., and Arora, A. (2018). 

Bioremediation of municipal sewage water 

with Azolla microphylla. International 

Journal of Advanced Research, 6(5), 101-

 ‏.108

Sood, A., Uniyal, P. L., Prasanna, R., and 

Ahluwalia, A. S. (2012). Phytoremediation 

potential of aquatic macrophyte, 

Azolla. Ambio, 41(2), 122-137.‏ 

Zazouli, M. A., Mahdavi, Y., Bazrafshan, E., 

and Balarak, D. (2014). Phytodegradation 

potential of bisphenolA from aqueous 

solution by Azolla Filiculoides. Journal of 

Environmental Health Science and 

Engineering, 12(1), 1-5.‏ 

 

https://doi.org/10.1016/j.dib.2018.10.111
https://doi.org/10.1016/j.dib.2018.10.111