The China Coal Tuoke Coal Chemical Water Treatment Project has passed the zero-discharge certification

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The zero-discharge certification for the coal chemical water treatment project of China Coal Tuoke was obtained. Author/Source: Date: 2016-04-12 Clicks: 30 Recently, the research project on the development and application of a coal chemical wastewater treatment and zero-discharge system for Tuoke Fertilizer Co., Ltd. under China Coal Group’s Ordos Energy and Chemicals Company, successfully passed the expert evaluation organized by the China Coal Industry Association. This project enables the recycling of 4.702 million tons of wastewater each year, with a wastewater reuse rate of 98%. At a cost of 10 yuan per ton of water, it is possible to save around 5 million yuan annually through wastewater recycling. Case Analysis of Zero Discharge of Coal Chemical Wastewater from China National Coal Group Tuke 1 Introduction The EBA process is a combined treatment technology developed by Harbin Institute of Technology for treating high-concentration phenol-ammonia wastewater generated by Lurgi furnaces, BGL furnaces, and low-temperature cracking furnaces. Although high-concentration phenol-ammonia wastewater is treated through phenol-ammonia recovery processes, the composition of the wastewater entering the biochemical treatment system remains complex and toxic; the concentration of phenolic compounds can reach 200–1000 mg/L, while the concentration of ammonia nitrogen can reach 100–300 mg/L. The EBA process utilizes technologies such as improving the biodegradability of wastewater, reducing its toxicity, and enhancing the activity of sludge, to ensure that the treated wastewater with high concentrations of phenols and ammonia meets the standards for reuse. It provides a solid foundation for the safe, stable, energy-efficient, and continuous operation of coal chemical wastewater treatment processes over extended periods of time. 2. Technical Introduction: The EBA process offers advantages such as a high organic load, strong flexibility, short hydraulic retention time, small land area required, low capital investment, as well as low energy consumption and operating costs. This biological combination technology includes a series of biochemical treatment processes based on EC external circulation anaerobic process, BE biological enhanced process, and multi-stage A/O denitrification process; subsequent advanced treatment is carried out using high-density sedimentation technology, advanced oxidation technology, and BAF (biological aerated filter) technology. In the pretreatment stage, nitrogen air flotation oil removal technology (**patented technology**) is employed. This technique prevents the increase in wastewater coloration and foam formation that result from air pre-oxidation, as well as the problem of the difficulty in biologically degrading the quinone compounds that are produced during pre-oxidation, thereby creating favorable conditions for subsequent biological treatment. The EC external circulation anaerobic technology (**patented technology**) enables the anaerobic co-metabolic process; it improves the quality of wastewater containing high concentrations of phenols and ammonia, simultaneously facilitating the carboxylation and benzoylation of certain organic compounds. This prevents the conversion of polyphenols into quinone substances, thereby reducing the difficulties associated with subsequent aerobic biological treatment and easing the operational burden. BE biological concentration technology (**patented technology**) effectively reduces the toxicity of phenolic substances under conditions of low dissolved oxygen by controlling specific hydraulic parameters, high levels of biological additives, high sludge concentrations, and long sludge retention times. It enables a process that combines organic matter removal with short-term nitrification, denitrification, and nitrogen removal. The reflux ratio in the multi-stage A/O denitrification process can be adjusted as needed. To address the issue of an insufficient C:N ratio of residual organic matter and ammonia nitrogen in the water produced by BE biological concentration treatment, enhanced nitration and denitrification processes for ammonia nitrogen are employed. The alternating anoxic and aerobic operating conditions of the multi-stage A/O denitrification process enable the modification of the properties of refractory pollutants, thereby facilitating the degradation of residual organic pollutants in the wastewater. High-density precipitation technology primarily utilizes the physicochemical adsorption properties of activated diatomite to further adsorb and remove the refractory COD present in the effluent from multi-stage A/O processes; at the same time, it causes the activated diatomite along with suspended solids in the wastewater to precipitate as well. Some of the active diatomaceous earth present in the settled sludge is returned together in flocs to the beginning of the adsorption section to continue the reaction, while some of it is discharged to the sludge dewatering unit along with the settled sludge. Advanced oxidation technologies employ heterogeneous ozone oxidation; this technique is an advanced oxidation process aimed at generating highly reactive free radicals such as ·OH radicals. It operates according to the reaction mechanism of hydroxyl radicals, and thus offers broader application prospects and a wider range of uses. The BAF technology uses hydrophilic filter media and possesses functions of adsorption, filtration, and biodegradation to further treat residual organic matter and ammonia nitrogen in wastewater. In 3 typical cases, the wastewater treatment project of China Coal Ordos Energy Chemical Co., Ltd. is designed to treat wastewater from BGL gasifiers. The characteristics of this wastewater include: ① It contains a large amount of surfactants, which result in significant foaming during aerobic aeration ； ②The oil substances in wastewater are in an emulsive state, and processes such as oil separation and pressurized air flotation yield poor removal effects ； ③The main pollutants in wastewater include monophenols, polyphenols, ammonia nitrogen, organic nitrogen, fatty acids, as well as smaller amounts of recalcitrant organic substances such as aromatic hydrocarbons, naphthalene, anthracene, thiophene, and pyridine. The biodegradability of this wastewater is poor (B/C less than 0.3) ； ④The main pollution parameters in the wastewater are: COD=3500–4000 mg/L, BOD=900–1120 mg/L, total phenols=600–800 mg/L, ammonia nitrogen=250–350 mg/L, and the wastewater flow rate=350 m3/h. The wastewater treatment project for China Coal Ordos Energy Chemical Co., Ltd. began construction in May 2012. In January 2014, a technical team from Harbin Institute of Technology supervised the commissioning of this wastewater treatment plant. Currently, the inlet water load has reached the designed capacity. After 15 months of stable operation, 100% of the effluent from the biological treatment system is reused in the original water supply system. 600–720 tons of high-concentration water enter the evaporation system each day, resulting in 12–20 tons of salt. The wastewater treatment facility of China Coal Ordos Energy Chemical Co., Ltd. achieves true zero discharge. 3.1 Process Introduction The treatment process for high-concentration phenol-amine wastewater at China Coal Ordos Energy Chemical Co., Ltd. is shown in Figure 1. http://s13.sinaimg.cn/mw690/001wbQd9zy6SsKQ4n0wdc&690 High-concentration phenol-ammonia wastewater and domestic wastewater from the factory are sent to respective treatment tanks for phenol-ammonia wastewater and domestic wastewater, where their quality and volume are adjusted. The pretreated domestic wastewater and phenol-amine wastewater are mixed in an anaerobic water distribution well before being fed into the EC external circulation anaerobic tower. This process reduces the toxicity of the phenol-amine wastewater, improves its biodegradability, and simultaneously lowers the concentrations of COD and total phenols. Before entering the BE biological concentration system, the effluent from the EC external circulation anaerobic tower passes through an anaerobic circulation tank for the circulation of anaerobic sludge; the settled sludge is then discharged to the anaerobic water storage tank and fed back into the EC external circulation anaerobic tower via an anaerobic lift pump. The BE biological concentration system features a corridor design, whereby the phenol-ammonia wastewater first passes through an annular outer corridor before entering a baffle-type inner corridor. The multi-stage A/O system is integrated with a secondary sedimentation tank; the A/O system features a baffled channel design, with a sedimentation tank installed at the end. Aeration devices are evenly installed at the bottom of the channels in the multi-stage A/O system; their operation is controlled via valves. By adjusting the relative volume ratio between tank A and tank O, it is possible to achieve optimal removal of organic matter and nitrogen removal. To enhance the effectiveness of ozone advanced oxidation, suspended solids are removed in a high-density sedimentation tank before the effluent from the secondary sedimentation tank enters the ozone contact oxidation tank, thereby improving the efficiency of ozone oxidation. The water treated by ozone oxidation requires a 30-minute buffering period to allow any unreacted ozone in the water to be released, after which it enters a BAF filter to further remove organic matter and ammonia nitrogen. http://s16.sinaimg.cn/mw690/001wbQd9zy6SsKVSirJ1f&690 Figure 2: Panoramic view of the high-concentration phenol-ammonia wastewater treatment plant operated by China Coal Ordos Energy & Chemical Co., Ltd. http://s15.sinaimg.cn/mw690/001wbQd9zy6SsKUBIrcde&690 Figure 3: Changes in color intensity of the wastewater after treatment through various processes. http://s11.sinaimg.cn/mw690/001wbQd9zy6SsKWIyme6a&690 Figure 4: Crystallization site for concentrated brine. http://s6.sinaimg.cn/mw690/001wbQd9zy6SsKXGoole5&690 Figure 5: Operational parameters related to the crystallized salts from concentrated brine. This wastewater treatment plant is primarily used for removing COD, ammonia nitrogen, and phenol. After 15 months of stable operation (from December 2013 to March 2015), the removal rates for COD, ammonia nitrogen, volatile phenol, and total phenol reached 98%, 99%, 100%, and 98%, respectively. The quality of the treated wastewater meets the requirements specified in the standard HG/T3923-2007, titled \"Quality Standards for Reused Water in Circulating Cooling Systems\", which is part of the Chemical Industry Standards of the People’s Republic of China. The specific water quality control indicators are as follows: http://s15.sinaimg.cn/mw690/001wbQd9zy6SsL3tnWede&690 http://s5.sinaimg.cn/mw690/001wbQd9zy6SsL3GueU14&690 Figure 6: Online monitoring values of COD in the clarifier tank http://s1.sinaimg.cn/mw690/001wbQd9zy6SsL4EmY000&690 Figure 7: Online monitoring values of ammonia nitrogen in the clarifier tank 4. Conclusion The EBA process developed by Professor Han Hongjun’s team from Harbin Institute of Technology has been successfully applied in the “zero discharge” wastewater treatment project at China Coal Ordos Energy Chemical Co., Ltd. This technology features a small footprint, low investment costs, low operating expenses, high quality of treated water, simple operation, and stable performance. Since January 2014, the zero-waste discharge project at China Coal Ordos Energy Chemical Co., Ltd. has been in operation for 17 months; the plant has no discharge outlets, and all wastewater is treated and reused within the original water system for unified distribution. The total investment for the EBA process is 0.8 million yuan per m3/day (1000 m3/h = 190 million yuan). The operating costs calculated by enterprises are currently between 2.85 and 3.15 yuan per m3. Compared with conventional processes such as physical-chemical strong oxidation plus biological treatment, this process reduces investment costs by 40–60% and operating costs by 50–80%, achieving true zero discharge of wastewater.