In the 80s, when the demand of people was “Eat well, dress warmly”. today’s trend has moved to “Eat well, dress well” leading to the textile industry playing a vital role in investment and development. For that reason, Vietnam’s textile and garment industry has become one of the spearhead industries in exporting goods to many different markets around the world, contributing to boosting the country’s economy. To create high-quality products for export, the production process will go through many stages such as bleaching, dyeing, printing, etc., creating a large amount of wastewater, which has a great impact on the environment. So what are the characteristics of textile wastewater? And how to treat wastewater to ensure the correct process and be environmentally friendly?
1. Characteristics of textile wastewater
Textile wastewater is diverse and complex because it contains many typical chemicals such as dyes, yeast starch, electrolytes, etc. Therefore, the main characteristics of wastewater are revealed as follows:
The pH level ranges from 9 to 12: This indicates that the textile wastewater is alkaline because most of the steps use bleach and detergents. In addition, pH has fluctuations because they depend on each fabric and play a significant role in the dissolution of dyes in the dyeing process of the factory, affecting aquatic organisms and corroding equipment.
High suspended matter concentrations range from 830 to 1580 mg/L, due to insoluble substances from the fabric and chemicals precipitated by pH. In addition, textile wastewater has a vicious phenomenon because it contains a large number of suspended solids, causing water quality and aquatic resources. Thereby, it will produce H2SO4, NaOCl, NaCl, heavy metals, etc, greatly affecting the decomposition of microorganisms to purify water. Moreover, it forms metal ions that are difficult to decompose, causing serious harm to the ecosystem.
BOD ranges from 500 to 1010 mg/L because wastewater contains oxidized organic substances. Through many different stages, cotton will be partially removed, to the sizing and size reduction stage, the fabric will be treated with starch and enzymes. This process leads to high BOD in the wastewater.
COD ranges from 1600 to 3200 mg/L: This represents highly chemically contaminated dyeing wastewater, due to the use of many oxidizing compounds in different steps of production.
Because of the high fluctuation of BOD and COD, the wastewater containing starch discharged from the sizing process reduces the dissolved oxygen concentration in the water affecting the respiration of aquatic plants and animals as well as generating CH4, CO2, NH4, H2S. Therefore, it causes a stench, impacting human health, and water pollution sources.
Color pollution is a characteristic of textile dyeing wastewater, due to the dependence on the degree of color binding between dye and textile fibers. Heavy toxins such as heavy metal sulfites, organic halide compounds (AOX) can accumulate in the organism with increasing concentrations along the food chain in the aquatic ecosystem; causing several chronic diseases in humans and animals.
2. Textile wastewater treatment method
Currently, there are three methods for treating textile wastewater: biological, physicochemical, and biological methods. However, the effective way of textile wastewater is biological measures.
Wastewater is led through anaerobic tanks to remove organic matter. This process can be combined into four simultaneous stages: Hydrolysis, Acidification, Aceticization, Methanolization to convert complex substances into simple and soluble substances, helping the anaerobic decomposition of acetic acid, H2, CO2 rapidly forms methane, CO2, and new biomass.
CHC + anaerobic microorganisms CH4 + H2S + CO2 …+ new biomass
Simultaneously, the reduction of N and P is also taking place.
Therefore, Biofix 114 microorganisms need to be added to the anaerobic system to promote organic decomposition in wastewater.
Decomposition of pollutants by microorganisms in an anoxic (low oxygen) environment and where nitrification takes place in a facultative environment. In order to increase the efficiency of the operation, in the tank, there is a stirrer installed, with a slow speed to create the right conditions for microorganisms to work.
NH3 → NO3 → NO2 → NO → N2O → N2 (gas)
After restarting the system, it is necessary to add the microorganism Biofix Ammonia to promote nitrogen treatment in the anoxic tank.
This is the process of oxidizing organic compounds under the action of aerobic microorganisms in the Aerotank tank. In this process, aerobic microorganisms use organic matter as a source of nutrients to grow biomass and break it down into inorganic substances.
CHC + aerobic microorganisms O2 and CO2 + H2O + new biomass
Wastewater after the biological treatment process is led through the settling tank to settle the generated biological sediment. Part of the used sludge will be led through the sludge tank and the rest will be recirculated into the aerobic biological tank to ensure the density of microorganisms in the tank.