The printing and dyeing industry is the major discharger of industrial wastewater. According to incomplete statistics, China discharges 3 or 4 million tons of printing and dyeing wastewater each day. Printing and dyeing wastewater is the industrial wastewater difficult to treat because of its large amount, high level of inorganic pollutants, deep colour, high alkalescence and diversity. In recent years, chemical fabric has been developed, imitated silk has emerged and finishing technology has progressed. Therefore, dyeing wastewater has been added with a large amount of organics difficult to degradate biochemically i.e. PVA, alkali decomposers(mainly phthalates) of artificial silk and new types of auxiliaries. The level of COD rises from hundreds mg/L to 2000 or 3000 mg/L and the remove rate of traditional biological treatment system drops from 70% to 50% or even lower. The traditional treatment techniques are facing a fierce challenge. Chemical precipitation and air flotation can only remove about 30% of COD in this type of dyeing wastewater. Development of an economic and effective treatment technology is becoming a concerned subject of today’s environmental protection industry.

People always notice the black colour of the dyeing wastewater and imagine a lot. In fact, dyeing wastewater is not dirty. Its special colour always triggers bad impression.

First of all, let’s take a look at the raw materials of some main pigments for dyeing clothes.In terms of categories of coating technologies, colouring could be divided into pigment and dope. Pigment should be grinded before colouring because of particles in it in order to strengthen its adhesion, to which Nano technology provides an extended solution. When the length unit is 10-9m, the particle state is opaque, but is transparent only when the unit is the threshold of 70nm.This type of pigment could be furthuer divided into inorganic and organic pigments. Inorganic pigment is always cheap,fadeless but not colourful.But organic pigment is mainly compounded artificially and colourful. Before being used,the organic pigment should be tested whether it reacts with host materials for membrane because it is a chemical product compunded artificially. And the ultraviolet resistance level of the organic pigment should be tested,because it is clearly classified into different ranks. Some are faded easily. Some can be compared favourably with inorganic pigment,but are expensive.Under this condition, people improve its ultraviolet resistance by inventing auxiliaries and UV resistant agents. But what exists in the wastewater we treat is dye,which can be classified into organic dye and inorganic dye. Under the categories, dye can be classified into direct dye and acid dye according to different features.According to usage, pigment and dye can both be classified into oil and aqueous types. Printing and dyeing industry mainly uses aqueous organic dye. But with the introduction of Nano technology, aqueous inorganic dye will be the future.Knowing the related information of printing and dyeing industry will be helpful for us to effectively remove colour in the dyeing wastewater.

The main tool for removing dye from wastewater is flocculant, which includes inorganic and organic macromolecular flocculants. Inorganic flocculant’s unit price is low, but that of organic macromolecular flocculant is high. Inorganic flocculant’s dosage is high, but that of organic macromolecular flocculant is low and produces better removal effects.In spot investigation of dyeing wastewater discharged by Tae Chang Enterprise Co.,Ltd, we found inorganic flocculants and encountered its disadvantages of high dosage.Its dosage is 2500ppm. But in our rebuilding project, we used several types of efficient organic flocculants in comprehensive decolouring of dyeing wastewater. This part of work is vital to the later treatment. Small dosage of flocculants and circulation method reduce the costs of treatment and the amount of sludge.

After the wastewater’s dye has been quickly removed by preliminary flocculants, the wastewater needs to be treated comprehensively with biological and other methods and qualifies for the standard of reused water, which is better than qualified water.

The biological treatment we are talking about is Biological Oxidation, which is different from operation of active sludge because of its little amount of sludge. The method, which includes our inventive patent, doesn’t need return sludge pump and automatic residual sludge deportation. Also, it can improve the rate of oxigen utilization by 3 times with a gadget extracting 20.9% oxigen in air.It is very energy-saving with just 30% of the former treatment method, and makes profits for enterprises in another way by reducing dyeing wastewater’s running costs and expenses.

The solution has two other important technical features i.e. the aerator has twice efficiency or more and scrolling biological filling technology. The good combination of these technologies will bring the biological treatment system with efficient biological degradation and high running stability, but does not need special management. The factory won’t be impacted by a short-time power cut because of its low running costs.

Various technolgies are integratively adopted in the final phase of dyeing wastewater treatment.In this phase, filtration of pressure-intensified shell activated carbon and repeated utilization of oxidated regeneration are designed in an artificial sight of rokeries, falls and brooks. The treatment of this phase adopts the principle of biological filtration pool, i.e. natural aerobic biological membrane. In the effluent pool, the plants further purify the water and produce nutrient foods. If you dislike products of ecological circulation, you can feed livestocks with them because they are good feeds. It brings multiple effects at the same time.