Synthetic Dyes, Phycoremediation and Agricultural Bioremediation

When it comes to waste management one of the hardest wastes to handle and eco-friendly manage are dyes and textile effluents.

As humanity, we utilize dyes in several applications in various industries. Dyes are extremely difficult to remove from wastewater or any other environment they contaminate due to their aromatic structure. The industries which adopt the usage of dyes are textile, rubber, plastic and cosmetics. Especially with the increase in cosmetics and textile production and consumption, dyes are part of a crucial waste management problem now.

Dyes which are synthetically made are the ones which cause serious environmental pollution. According to the article by Abate Ayele published in 19 May 2021, annually one million tones of dyes are produced on earth. This synthetic dyes are released into environment through industries such as pharmaceuticals, textile and chemical industries.

 The largest consumer of dyes can be indicated as textile industry among others. This great consumption of synthetics dyes in textile has variety of advantages from longevity of lifetime of clothes to having antibacterial clothing and firmness against fire when they are compared to natural dyes. However, the environmental aspect associated with waste management has become harder to manage as the anthropogenic needs have become extreme.

The high concentration of synthetic dyes in wastewater effluents affect marine environment in variety of ways, firstly, dyes block the sunlight and decrease the sunlight which is needed for the oxygenation of water body for plants and animals results in negative impact on aquatic biodiversity and photosynthesis. When they find a medium to interact with the other substances they can also form harmful byproducts. Industrial effluents containing dyes highly affect the growth of microorganism and progression of photosynthetic activities of underwater flora by diminishing the light penetration in water bodies- which results in reduced dissolved oxygen in water by forming a layer on the water surface. This type of effluents cause chemical oxygen demand (COD) and biological oxygen demand increase which a symptom of high-level of pollution in aquatic environments. In addition to these if dye contaminated water used for irrigation, it might enter our food chain and may result in bioaccumulation and development of toxicity, mutagenicity and carcinogenicity in living systems.

How do they end up in wastewater discharges? During dying process, almost 15% of the dyes are discharged into wastewater which leads to potential pollution occurrences in the environment. This discharge cannot be 100% reduced since efficient of the dye fixation process varies between 60%-90%. There are a lot of procedures to eliminate and remove dyes from wastewater treatment system and through those procedures removing dyes from discharge water is expected. These operational systems can be named as flocculation and coagulation, electrochemical treatment, adsorption and so on. Although these methods have been existing for some time, they have their own disadvantages such as being expensive, requiring later treatment for removing organic metabolites and less efficiency in decolorization effect.

Due to limiting and disadvantageous sides of these treatments, bioremediation concept is introduced into waste management. In bioremediation microbes such as fungi, algae, yeast and plants are utilized in order to facilitate the degradation of harmful substances or transform them into a less toxic version of what they have been before.

 Phycoremediation is one of these innovative technologies which creates a suitable environment for both removing the synthetic dye and conserving the environment using algae.

 It is highly eco-friendly due to the existence of algae and it is on the cheap side with widely available resources and its quick operative features.

Figure 1: Hazardous effects of synthetic dyes on environment (Abate Ayele, 2021)

Phycoremediation as a technique embraces the usage of macroalgae, microalgae and cyanobacteria for the biotransformation or removing of contaminants, synthetic dyes, heavy metals and xenobiotics.

Since this technique is a bio-remediation technology, different microorganisms have their different routes or pathways to degrade and biotransform the different wastes, in above case its different synthetic dyes. The pathways are also changing as the dye structure changes. This microbial removal usually occurs through adsorption or degradation which are also named as biosorption and biodegradation.

Biosorption: removes dye molecules by transferring them from liquid phase to solid phase.

Biodegradation: breaks down the bonds which constitute chemical structure of dyes.

The most studied algae are efficient to degrade dyes are found out as blue-green algae and green algae. Algae biomass also has the highest efficiency when it comes to absorbing pollutants in the wastewater because of its high binding ability and wide surface area.

Algae is able to conduct this removal process due to their cell wall containing variety of functional groups such as amino, carboxyl, hydroxyl and phosphate groups. While utilizing algae for the removal, operational conditions required to remove dyes such as solution pH in contact time and initial dye concentration should be taken into consideration. When algal capacity performances in evaluating, these factors are taken into account to understand dye abatement functionality of the whole system.

In addition to these microbial procedure, there are also agricultural based bioremediation techniques.

For the color removal in dye contaminated water, agricultural residues are utilized as low-cost sorbents such as Corn-cob shreds and wood-chips. There are other usages of some locally available low-cost materials as bio-sorbents such as apple residue pomace after the apple juice process is completed. Wheat straw also used for the removal of color as well. To test their efficiency, different types of dyes were mixed and put into various concentration groups. When their efficiency were evaluated apple pomace was found better for color removal with 81% and increased to 91% when dry apple pomace was used.

Since wheat has a complex lignin –containing structure it has less sorption power compared to apple pomace and its lignin ratio.

To conclude, it can be said that every innovative or/and low-cost environmental technology has its downfalls, however, in any circumstances they have the potential to be the most promising technology of future, perhaps one day, a common way to manage our dangerous wastes out there. With the technological improvement and our coping mechanism to use or re-use/cycle a material or an organism to manage another accelerates efficiently, waste management will only become better.