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Abstract: An actual engineering design for treating high-temperature printing and dyeing wastewater using a combined process of \"microwave-free-ultraviolet photocatalytic oxidation + adsorption catalytic oxidation\" is presented, providing experience for the treatment of similar types of printing and dyeing wastewater. Keywords: free-ultraviolet； Photocatalytic oxidation ； High-temperature printing and dyeing wastewater 1. Introduction Among industrial wastewater in China, printing and dyeing wastewater accounts for a significant proportion; according to incomplete statistics, the daily discharge volume of such wastewater in China ranges from 3 million to 4 million cubic meters. It is one of the most difficult industrial wastewater types to treat due to its high organic content, high color intensity, high alkalinity, significant variations in water quality, and large volume of waste water. Recently, in China, physicochemical and biochemical treatment processes are commonly used for the treatment of textile printing and dyeing wastewater. The quality of the treated water generally meets the first-class standards set out in GB4287—1992, the Standards for Discharge of Pollutants from Textile Dyeing and Finishing Industries, but it is often difficult to reach these first-class discharge standards. Most domestic enterprises focus on the centralized treatment of mixed wastewater, while comprehensive treatment aimed at recovering useful pollutants for resource utilization is relatively rare. This not only increases the volume of wastewater that needs to be treated and raises the associated costs, but it also makes treatment more difficult; as a result, it is often impossible to ensure effective treatment of the wastewater so that it meets regulatory standards. Therefore, it is urgent to research and develop new technologies. To this end, based on laboratory pilot tests, this experiment employs a new type of high-efficiency physical-chemical combination technology and equipment to carry out advanced treatment of high-temperature printing and dyeing wastewater, followed by reuse experiments. 2. Project Overview 2.1 Design Background The Shanghai Hubang Dyeing and Printing Factory is located in the Pudong Free Trade Zone of Shanghai, and it is primarily engaged in dyeing and printing fabrics made from various materials. The dyes used in production are mostly reactive dyes. Its original wastewater treatment facility was built in the 1990s; it was primarily used to treat wastewater from dyeing and printing processes as well as some domestic sewage. It employed a single aerobic treatment process and consisted of a pH adjustment tank, aeration tank, sedimentation tank, sludge tank, sludge drying system, pump room, and laboratory. With the continuous rise in water supply fees and sewage disposal charges, the company has placed increasing emphasis on clean production, and the reuse of printing and dyeing wastewater has also begun to receive attention. Therefore, a set of recycling equipment was designed for one of its production lines. 2.2 Description of wastewater treatment process: The printing and dyeing wastewater generated by this company is characterized by high temperature, high color intensity, and high COD levels. Based on the experience accumulated over many years in treating wastewater from the textile and printing and dyeing industry, traditional treatment methods for such wastewater involve anaerobic followed by aerobic processing. High-temperature dyeing wastewater has a high temperature, preventing bacteria from surviving; as a result, biochemical methods cannot be used, and only physicochemical methods can be employed for treatment. Activated carbon adsorption treatment is costly and difficult to regenerate ； Membrane separation technology requires a high initial investment, presents significant technical challenges, makes it difficult to clean the membrane systems, and demands a large amount of water for backwashing. Simple materialization methods are difficult to meet the requirements of advanced wastewater treatment processes. Due to the high requirements for the quality of recycled water, it is generally difficult for a single treatment process to bring wastewater up to the standards required for use in dyeing and printing. Therefore, building on previous technologies for the photocatalytic decolorization and recycling of dyeing and printing wastewater, a new process called \"microwave, extreme ultraviolet photocatalytic oxidation + adsorption-catalytic oxidation\" has been developed. This process consists of three main components: sand filtration, extreme ultraviolet photocatalytic oxidation, and microwave plasma-enhanced activated carbon adsorption-catalytic oxidation. Sand filtration is used primarily to remove suspended solids, while the combination of extreme ultraviolet photocatalytic oxidation and activated carbon adsorption-catalytic oxidation ensures thorough treatment of the wastewater so that it meets strict requirements for recycling. The wastewater from printing and dyeing processes is passed through a sand filter to remove most of the suspended solids, ensuring that the turbidity and suspended solid levels meet the requirements for reuse. After operating for a certain period of time, the sand filter needs to be backwashed and regenerated. The effluent from the sand filter enters the photocatalytic oxidation system, which utilizes the \"polarization-free ultraviolet photocatalytic oxidation\" technology. During operation, the water output from the sand filter is fed into a microwave-induced polarozone catalytic oxidation reactor, where the strong oxidant O3 is pumped in using a jet pump. Under microwave stimulation, UV light is generated; air, under the intense catalytic action of this UV light, produces ozone. This, together with the oxidant, leads to intense chemical oxidation reactions that cause long-chain macromolecules or hard-to-degrade pollutants containing benzene rings or azo groups to break apart and undergo ring-opening, resulting in their partial or complete decomposition. The chromophoric groups in dye molecules are destroyed, thereby causing the dyes to lose their color. The photocatalytic oxidation reactor can ensure that the colority of wastewater meets the requirements for reuse, while also removing a certain amount of COD. Whether an oxidant is added to the photocatalytic oxidation reactor and how intense the unpolarized ultraviolet light source should be depend on the quality of the wastewater. The water resulting from photocatalytic oxidation is fed into the adsorption-catalytic oxidation system, where activated carbon absorbs organic substances and a small amount of suspended solids. Subsequently, catalytic oxidation is used to remove excess oxidants from the water, while also regenerating the activated carbon to maintain its activity. The wastewater, after passing through the activated carbon adsorption and catalytic oxidation system, is reused in the enterprise for processes such as circulating water use and washing dyed fabrics. The effluent is automatically adjusted using an online pH controller to maintain a neutral water quality. 2.3 Design water quality: The designed wastewater volume is 240 m3/day, with most of it being high-concentration dyeing wastewater. Dyeing wastewater is primarily composed of wastewater containing dyes, surfactants, and additives resulting from the dyeing of various types of raw fabrics; bleaching and dyeing wastewater contains small amounts of dyes and sizing agents. The organic components in this wastewater are mainly based on aromatic and heterocyclic compounds, and they contain chromophoric groups as well as polar groups. 2.4 Main design parameters: Number of reservoirs: 1, underground concrete structure; Process dimensions: 4×4×2.0 m, effective volume of the reservoir: 32 m3. There are 2 lift pumps, model WQ8—6—0.4, with a flow rate of 10 m3/h and a power consumption of 2.4 kW. Sand filter: 1 unit, above-ground steel structure; process dimensions: 2000mm×1500mm, H=2500mm. Backwash pump: 1 unit, model G—3.7—65, N=3.7kw. Continuous ultraviolet photocatalytic oxidation reactor: 1 unit, above-ground steel structure; process dimensions: 3000mm×4000mm, H=2500mm. Jet pumps: 2 units, model G—2.2—50, Q=10m3/h, N=2.2kw. It is equipped with 6 adjustable UV lamps and one ozone dosing system. Adsorption catalytic oxidation reactor: 1 unit, above-ground steel structure. Process dimensions: 3000mm×4000mm, H=2500mm. 2.5 Process characteristics: 1. Electrodeless ultraviolet photocatalytic oxidation reactor – This reactor is developed on the basis of the existing patented technologies and processes for the photochemical decolorization of printing and dyeing wastewater; it incorporates the latest research findings and makes use of advanced artificial intelligence for system control. It offers excellent results for the advanced treatment of such wastewater, representing an evolution of traditional photocatalytic technologies. (2) The light source system utilizes a new electrodeless ultraviolet lighting system, which offers advantages such as energy savings, safety, and ease of operation and replacement compared to traditional light source systems. (3) This system features rapid response, low space requirement for equipment, easy operation, stable and reliable performance, as well as the ability to remove chroma and CODcr. 2. Adsorption catalytic oxidation reactor: (1) Activated carbon is used for rapid decolorization to adsorb residual organic substances, ensuring the quality of the effluent. (2) The adsorption catalytic oxidation reactor uses catalytic oxidation to oxidize the organic substances adsorbed on activated carbon, thereby enhancing the adsorption process of the activated carbon; at the same time, microwave plasma regenerates the activated carbon to maintain its optimal activity. (3) The activation method for activated carbon in the adsorption catalytic oxidation reactor is faster than traditional methods, and the equipment is easy to operate. 2.6 Test Method: High-temperature printing and dyeing wastewater was pumped into the unpolarized ultraviolet photocatalytic oxidation reactor; ozone at different concentrations was added simultaneously. The unpolarized ultraviolet light source was activated using microwaves to initiate the reaction. The effects of using oxidants at various concentrations in combination with ultraviolet light on the removal of COD and color intensity from high-temperature printing and dyeing wastewater were compared, in order to determine the optimal amount of oxidant to be used. Examine the effect of UV intensity on the treatment effect. Compare the treatment effects of UV alone, oxidant alone, and UV/oxidant. Determine the optimal reaction parameters for the reaction. 2.7 Water quality analysis methods: The methods for monitoring water samples are in accordance with **standard operating procedures. 3. Results and discussion of photooxidation: 3.1 Effect of oxidants on the treatment of high-temperature printing and dyeing wastewater; 3.1.1 Determination of the optimal flow rate of oxidants. High-temperature printing and dyeing wastewater is pumped into the electrodeless ultraviolet photocatalytic oxidation reactor, while O3 flow rate is adjusted as well. Microwaves are used to activate the ultraviolet lamps for degradation purposes. After 260 minutes of treatment using \"microwave-electrodeless ultraviolet photocatalytic oxidation + activated carbon adsorption catalytic oxidation\", samples are taken for analysis. 3.1.2 Comparison of COD removal efficiency by O3 at different flow rates The effect of UV/O3 combined treatment on the removal of COD from high-temperature printing and dyeing wastewater was examined under conditions of maximum UV intensity. The COD removal rate increased as the amount of O3 added increased; the best COD removal efficiency was achieved when the ozone flow rate was >14 m3/h. The UV/O3 combination resulted in a stable COD removal rate of over 90%. The first step in the photolysis of ozone in water is the formation of H2O2. Under ultraviolet light, H2O2 undergoes a series of reactions: O3 + νγ → O2 + O•; O• + H2O + νγ → 2•OH; O3 + H2O → H2O2 + O2; H2O2 + νγ → 2•OH. The formation of •OH free radicals **increases the oxidizing capacity of ozone, thereby reducing the COD value of wastewater. 3.2 Effect of UV intensity on degradation efficiency: The reactor was filled with printing and dyeing wastewater, and the microwave-free polarized UV photocatalytic oxidation reactor was operated intermittently. With different numbers of groups of non-polar ultraviolet lamps (1–6) and an O3 flow rate of 14 m3/h, the COD removal rate can reach 90% after the synergistic degradation of printing and dyeing wastewater using UV/O3. An increase in UV intensity enhances the efficiency of COD removal. This is because, under the catalysis of ultraviolet light, O3 undergoes the following reactions: O3 + νγ → O2 + O•; O• + H2O + νγ → 2•OH; O3 + H2O → H2O2 + O2; H2O2 + νγ → 2•OH. As UV intensity increases, more photons are available, which facilitates more effective initiation of free-radical chain reactions and increases the production of highly oxidizing atomic oxygen (•OH), thereby accelerating the rate of COD removal. 3.3 Comparison of the degradation effects of UV, O3, and UV/O3 on printing and dyeing wastewater 3.3.1 Removal of COD Under conditions of a water inflow rate of 10 m3/h and an O3 flow rate of 14 m3/h, printing and dyeing wastewater was filled into the reactor; all 6 sets of polar-free ultraviolet lamps were turned on, and the photo-oxidation reactor operated intermittently. Based on the removal efficiency of UV/O3, O3, and O3 in oxidizing the COD of printing and dyeing wastewater, the order of their effectiveness in removing COD from high-temperature printing and dyeing wastewater is: UV/O3 > O3 > UV. After 160 minutes of exposure to UV radiation, the COD removal rate in printing and dyeing wastewater is only about 5%. The reason for this is that ultraviolet light with wavelengths of 200–250 nm provides an energy of 478.2–597.7 kJ/mol, which is sufficient to break the single bonds in most organic compounds; as a result, some of the readily degradable organic substances are removed, leading to a decrease in the COD concentration of the wastewater. However, the main component of the dyeing and printing wastewater used in this experiment is reactive dyes, which contain a large number of double bonds or conjugated double bonds and require higher dissociation energy; UV light is ineffective against such substances. When O3 is used to oxidize printing and dyeing wastewater, the removal rate of COD remains essentially constant over time, staying at around 80%, which indicates that the O3 reaction is rapid and thorough. After 160 minutes of UV/O3 oxidation of printing and dyeing wastewater, the COD removal rate was approximately 90%. The efficiency of UV/O3 in removing COD from such wastewater is significantly higher than the simple sum of the effects of O3 and UV used alone, indicating a synergistic effect between UV and O3. 3.3.2 Removal of chroma UV/O3 and O3 possess strong decolorizing capabilities for printing and dyeing wastewater, achieving complete decolorization after 160 minutes of reaction. Generally, the functional groups responsible for coloration are certain conjugated unsaturated groups. O3 and ·OH are highly effective at destroying these conjugated unsaturated groups, converting them into groups with saturated structures, thereby eliminating the color of water. 4. Results and Discussion on Adsorption Catalysis The printing and dyeing wastewater treated in the unpolarized ultraviolet photocatalytic oxidation reactor was pumped into an activated carbon tank using a lift pump; the COD and residual ozone levels in the water exiting the activated carbon tank were measured, with the results shown in Tables 5-6. As shown in Table 5-6, after adsorption by activated carbon, the COD removal rate of the wastewater can reach over 30%, while the removal rate of residual ozone exceeds 99%. 5. Engineering commissioning and operation results: The printing and dyeing wastewater from this company is first subjected to physicochemical pretreatment, after which it is pumped into a polar-free UV catalytic oxidation reactor for treatment, and then further treated in an adsorption-catalytic oxidation reactor. After being calibrated, this device monitored the water quality of both the inlet and outlet waters of the system for 8 consecutive months. After the high-temperature dyeing wastewater was treated, the **Key Laboratory of Pollution Control and Resource Recycling** at Tongji University analyzed parameters such as COD in the inlet and outlet waters. The test results showed that the COD level in the inlet water ranged from 80 to 600 mg/L, while the COD level in the outlet water was below 50 mg/L; thus, the overall COD removal rate of the system was over 90%. The pH is near neutral. The colority of the influent is high, but the colority of the effluent after treatment is always less than 20 times that of the influent. No ozone content was detected; the above data indicate that the requirements for recycled water are met. 6. Reuse test analysis: There are two ways to use reclaimed water in the production process: one is to utilize it in certain steps of the dyeing and printing process, such as boiling and washing processes ； Another approach is to use it directly for dyeing certain varieties. Among them, the dyeing effect imposes stricter requirements on recycled water than simple reuse. In the experiment, we mainly tested and compared the differences between recycled water and fresh water. Test the effect of using recycled water on the dyeing effect, and examine and compare the quality of fabrics dyed with recycled water. 6.1 Comparison of water quality between tap water and recycled water 6.2 Comparison of dyeing effects (1) Shilin dye: Tap water-treated sample: Recycled water-treated sample: (2) Reactive Z Navy Blue: Tap water-treated sample: Recycled water-treated sample: (3) Reactive Z Army Green: Tap water-treated sample: Recycled water-treated sample: (4) Reactive Blue: Tap water-treated sample: Recycled water-treated sample: (5) Shilin Blue: Tap water-treated sample: Recycled water-treated sample: (Figures omitted) By comparing the sample images and undergoing factory acceptance, recycled water can be used in the dyeing and rinsing processes for actual fabric samples. 7. Economic and environmental analysis: (1) The water consumption per dyeing machine for washing fabric is 7.5 tons per hour, at a cost of 1.5 yuan per ton. With an average operating time of 24 hours per day, the daily cost per dyeing machine is: 1.50 × 7.5 × 24 = 270 yuan per day ； (2) If the future costs associated with wastewater disposal are taken into account (approximately 2 yuan per ton), the daily cost of wastewater disposal for each dyeing machine would be: 2.00 × 7.5 × 24 = 360 yuan per day. (3) Considering the cost of utilizing the thermal energy contained in the wastewater, the company assumes that each ton of steam can be used to heat 12 tons of water by 60°C; given that the price of steam is 129 yuan per ton, the value of the thermal energy in each ton of wastewater is 10.75 yuan per ton. The value of the lost thermal energy is therefore: 10.75 × 10 × 24 = 2536 yuan per day ； (4) Each horizontal washer saves 3376 yuan per day in costs by using recycled water, which is the sum of (1) + (2) + (3). 8. Market prospects: At present, there are approximately 100,000 flat washers or overflow dyeing machines across the country. Many manufacturers seek equipment for the decolorization and reuse of high-temperature printing and dyeing wastewater. Assuming a 10% market share, 10,000 sets of such equipment are needed nationwide. With a unit price of around 1 million yuan per set, the additional output value would amount to 10 billion yuan. Reusing water after decolorization saves 60% in water consumption; washing with hot water after dyeing reduces the need for reheating, thereby lowering energy use (calculated based on raising the average annual water temperature from 15°C to 60°C). There is no need for additional costs related to wastewater treatment or discharge fees, and savings of around 60 yuan per ton of fabric can be expected. Based on our country’s annual production of 100 million tons of textiles, this can result in cost savings of around 6 billion yuan per year. Based on the calculation that 1 ton of wastewater can contaminate 20 tons of water, an output of 1,500 tons of wastewater per day (the amount generated by a continuous printing and dyeing production line) results in a reduction of 30,000 tons of water contamination per day after treatment. References: Stover. Water Crisis – Seeking Solutions to Freshwater Pollution. Beijing: Lixue Publishing House, 2000, p. 47. Yang Kewan. Chemicals for Pollution Control. Wuhan: Wuhan Publishing House, 1998, pp. 96–97. Li Jiazhen. Treatment of Wastewater from Dye and Dyeing Industries. Beijing: Chemical Industry Press, 1997, p. 75. Li Yaozhong, Jiang Liwen, et al. Study on the Photocatalytic Degradation of the Azo Dye 4BS. Environmental Engineering, 2001, 19(1): 59–61. Last edited by hesonchang214 on 2009-2-18 07:54