New biological processes for treating textile wastewater

The textile industry generates vast amounts of wastewater rich in pollutants, including dyes, chemicals, and organic compounds, which are often challenging to treat. Biological processes offer an eco-friendly, cost-effective alternative for breaking down organic pollutants, including certain dyes and chemicals.

By leveraging naturally occurring microorganisms, biological treatment can effectively degrade many of these organic substances. However, for a truly comprehensive approach, and to meet increasingly stringent discharge requirements while addressing the rising concentration of contaminants in wastewater, biological methods are often paired with other filtration techniques, which serve as effective pre- and post-treatment steps.

This combination allows biological processes to target organic pollutants while filtration captures persistent contaminants, resulting in a cleaner, more sustainable solution that meets the textile industry’s environmental standards.

SOLUTIONS

Key biological processes for treating textile wastewater

Several biological processes are available for treating textile wastewater, each with unique advantages based on the type of contaminants and the level of treatment required.

1. Activated sludge process

The activated sludge process is one of the most widely used biological treatment methods. It involves introducing microorganisms into the wastewater, which break down organic matter and pollutants, including dyes and chemicals. The process is typically carried out in aerated tanks where bacteria thrive and metabolize contaminants.

• Applications: this process is effective in removing organic pollutants, dye compounds, and chemical oxygen demand (COD) from textile wastewater.
• Best practices: maintaining proper aeration and a balanced microbial population are key to ensuring the efficiency of the activated sludge process. Regular monitoring of oxygen levels and sludge concentration is essential.

2. Anaerobic digestion

Anaerobic digestion is a biological process that works without oxygen, using microbial activity to degrade organic pollutants in wastewater. This method is particularly effective for textile wastewater that contains very high COD levels. One of the major advantages of anaerobic digestion is that it produces biogas, which can be used as an energy source.

• Applications: suitable for high-strength wastewater with high organic loads, including textile industry effluents with dyes and chemicals.
• Best practices: ensuring the proper temperature and pH levels is critical for optimizing microbial activity. A balanced organic load should also be maintained to maximize biogas production.

3. Tertiary treatments

In textile wastewater treatment, tertiary treatment is crucial for enhancing color removal, especially after biological treatment. The biological stage (such as activated sludge or MBBR) can degrade organic pollutants but often leaves residual dyes, recalcitrant colorants, and oils & fats.

The most effective tertiary treatment options for color removal include:

• Coagulation-Flocculation: chemical coagulants (alum, FeCl₃, Polyaluminum Chloride – PAC) help in aggregating dye molecules for sedimentation, while organic polymers can improve dye removal efficiency.
• Dissolved Air Flotation (DAF): an effective treatment method for the removal of oils and fats from textile wastewater. The process utilizes microbubbles of air to float suspended solids, oils, and grease to the surface, where they can be removed by a skimming mechanism.
• Ion Exchange by Resins: anion exchange resins can remove certain dye types, especially acidic and reactive dyes.
• Activated Carbon Adsorption: powdered activated carbon (PAC) or granular activated carbon (GAC) can effectively adsorb residual dyes. This method works well as a post-treatment step after oxidation.
• Membrane Filtration: these methods physically remove dyes and other residual pollutants. These are nanofiltration (NF), which removes color and dissolved salts, and reverse osmosis (RO), which provides nearly complete dye removal but generates reject water that requires further disposal.

SOLUTIONS

New technologies in biological textile wastewater treatment

The development of new biological technologies has further improved the efficiency of treating textile wastewater. These advancements focus on enhancing microbial activity and increasing the overall treatment effectiveness for more -friendly solutions.

1. Moving Bed Biofilm Reactor (MBBR) in biological treatment of textile wastewater

MBBR is an advanced biological treatment method widely used for treating textile wastewater, which is often rich in organic pollutants, dyes, surfactants, and toxic compounds. This process uses suspended plastic media to support biofilm growth, enhancing the biological degradation of contaminants.

MBBR is a suitable solution when space for construction is limited, as it allows a significant reduction in the required volume.

2. Membrane bioreactors (MBRs)

Membrane bioreactors combine biological treatment with membrane filtration, providing a high level of solids removal, as well as the elimination of all bacteria present in wastewater and a significant reduction of colloids and viruses. The membrane acts as a physical barrier, preventing solid particles from passing through while microorganisms break down the pollutants.

Membrane bioreactors are suitable for high-load textile wastewater treatment and water reuse applications, where they offer efficient contaminant removal. As best practice, maintaining membrane integrity and preventing clogging are crucial for ensuring the longevity of the system, making regular cleaning and maintenance essential.

3 BEST PRACTICES FOR OPTIMIZING BIOLOGICAL WASTEWATER TREATMENT
For successful biological wastewater treatment, it is important to follow best practices that ensure the efficiency of microbial processes and the overall performance of the system.
✓ Regular monitoring: continuously monitor key parameters such as oxygen levels, temperature, pH, and microbial health to detect any issues early and ensure optimal treatment.
✓ Balanced nutrient supply: provide the right nutrients to support microbial activity. A lack of essential nutrients can limit the performance of the biological system.
✓ System maintenance: regular cleaning and maintenance of biological systems, including aeration tanks, filters, and biofilm carriers, will help prevent fouling and ensure consistent operation.

CONCLUSIONS

The future of biological processes for wastewater treatment

Biological processes provide a highly effective and environmentally friendly solution for the treatment of textile wastewater. To date, biological processes are the most:

• highly performing in terms of COD, BOD, TSS, and turbidity reduction
• eco-sustainable, as they do not require the dosing of chemical reagents and do not produce toxic sludge
• cost-effective, with the lowest operating costs in terms of energy and maintenance.

However, given the increasingly restrictive discharge regulations and the trend in the textile industry to reduce water consumption – resulting in a higher concentration of contaminants in wastewater – the integration of additional technologies is necessary to further refine the treatment process.