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The use of aquatic plants for wastewater treatment

The use of aquatic plants for wastewater treatment

By Cristian Frers

Constructed wetlands or wetlands have advantages over alternative treatment systems, because they require little or no energy to operate. They also provide a habitat for wildlife.

Introduction


The importance of wetlands has varied over time. Wetlands are transitional zones between the terrestrial and aquatic environment and serve as a dynamic link between the two. The water that moves up and down the humidity gradient assimilates a variety of chemical and physical constituents in solution, either as detritus or sediments, these in turn are transformed and transported to the surroundings of the landscape.

Wetlands provide effective nutrient sinks and buffer sites for organic and inorganic pollutants. This ability is the mechanism behind constructed wetlands, also called wetlands, to simulate a natural wetland for the purpose of treating wastewater from companies and municipalities.

The biotechnological solution consists of the installation of artificial wetlands that act as natural filters. Located between the plant and the aquatic resources (rivers, lakes, lagoons), these systems, in addition to not needing maintenance or consuming electricity, cost less than a quarter of a traditional treatment system. The wetlands are built using different species of plants that are abundant in the area: cattails, water cabbage, camalotes or reeds.

Artificial wetland of sewage and industrial waste


1 - The sewage waste flows into the wetland, which is a cave full of sand that works as an insulator so that odors do not come to the surface.
2 - The wetland filter consists of a large plantation, in this case of reeds with their roots in the sand, which feed on the water.
3 - The nutrients in the water are absorbed by the reeds, which trap them in their tissues and use them for their growth.
4 - The nutrients absorbed are eliminated with the change of stem of the reed. Those remains form an insulating layer.
5 - The water, already free of nutrients, flows from the wetland into the lagoon.
6 - The size of the wetland: The necessary surface is calculated based on the number of inhabitants of the city that produces the waste, according to the following relationship: 1 person = around 5 m2.

Aquatic plants in wastewater treatment

Aquatic plant systems are in shallow tanks such as floating or submerged aquatic plants. The most fully studied systems are those that use duckweed. These systems include two types based on dominant plant types. The first type uses floating plants and is distinguished by the ability of these plants to derive carbon dioxide and oxygen needs from the atmosphere directly. Plants receive their mineral nutrients from water.

The second type of system consists of submerged plants, it is distinguished by the ability of these plants to absorb oxygen, carbon dioxide, and minerals from the water column. Submerged plants are easily inhibited by high turbidity in water because their photosynthetic parts are under water.

Background

This is María Alejandra Maine who was part of a UNL team to investigate effluent treatment at the Bahco company. On the premises of the plant in Santo Tomé - Province of Santa Fe - Argentina, a wetland was built to carry out the final polishing of industrial and sewage liquids.

The idea of ​​building an open-air wetland with plants to absorb and purify liquid waste arose in 2001 when Bahco Argentina decided to improve its environmental management strategy. To reduce the impact generated by the manufacturing processes, the company decided to add a final polishing stage to its effluent treatment system.

Artificial wetlands


An artificial wetland is a shallow wastewater treatment system (pond or channel), no more than 0.60 meters, built by man, in which aquatic plants have been planted, and relied on natural processes to treat wastewater . Constructed wetlands or wetlands have advantages over alternative treatment systems, because they require little or no energy to operate. Constructed wetlands or wetlands provide habitat for wildlife, and are aesthetically pleasing to the eye.

Advantages:

1) Plants can be used as low-cost extraction pumps to purify polluted water.

2) Some degradative processes occur faster with plants than with microorganisms.

3) It is an appropriate method to decontaminate large surfaces or to complete the decontamination of restricted areas in long periods.

Limitations:

1) The process is limited to the depth of penetration of the roots or shallow water.

2) Processing times can be long.

3) The bioavailability of compounds or metals is a limiting factor in uptake.

Plants can incorporate pollutants through different processes that are represented in the following illustration and explained in the table that follows:


Types of phytoremediation, where the area of ​​the plant where the process occurs is indicated.

Functions of constructed wetlands

Human activities have given and continue to give rise to various types of wetlands of interest to some plant species.

Physical removal processes:

Constructed wetlands are capable of providing high physical efficiency in removing pollutants associated with particulate matter.

-Biological removal processes :

Biological removal is perhaps the most important pathway for pollutant removal in constructed wetlands. Widely recognized for the removal of pollutants in these wetlands is the uptake of the plant. Pollutants that are also forms of essential plant nutrients, such as nitrate, ammonium, and phosphate, are easily taken up by plants from these wetlands.

-Chemical removal processes:

The most important chemical process in soil removal from constructed wetlands is absorption, which results in the short-term retention or long-term immobilization of various classes of pollutants.

* Cristian Frers He is a Senior Technician in Environmental Management and an Environmental Consultant.


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