Integrated treatment process for electric ferry wastewater

     The knowledge of belt filter press talk about the integrated treatment process of electric aeration wastewater;
With the advancement of science and technology and the rapid development of environmental protection technology, many new technologies have begun to be applied to the environmental protection industry. Among them, the technology with iron/carbon internal electrolysis reactor as the core is more and more widely used in environmental protection projects. This integrated treatment technology has a wide range of application prospects in electroplating wastewater treatment projects with its unique advantages.

　　1. Process mechanism of integrated technology to treat mixed electroplating wastewater
Pretreatment measures such as CN-breaking and redox Cr6+ to Cr3+ are necessary in the traditional electroplating wastewater treatment process. Due to its large investment, high degree of technical parameter control, and complex operation, it has certain limitations in engineering design and application .
In contrast, the main technology process avoids the classification and collection of sewage, pretreatment and other preliminary processes. The waste water can be directly mixed and enters an independent adjustment tank to adjust the water volume and quality, and then is upgraded to cast iron/coke electrolysis by hydraulic power. The reactor enters the next step after reacting under certain conditions. Since this type of technology does not require classified pretreatment of sewage, it is directly mixed and treated, so it is also called “integrated treatment technology”. Its typical reaction mechanism can be expressed as follows:
　　 anode cast iron:
　　Fe-2e→Fe2+ E0(Fe2+/Fe)=-0.44V (1)
　　Cu2++Fe→Fe2++Cu (2)
　　 cathode coke:
　　2H++2e→2[H]→H2↑ E0(H+/H2)=0.00V (3)
　　O2+2H2O+4e→2OH- E0(O2/OH-)=0.41V (4)
　　O2+4H++4e→2H2O E0(O2/H2O)=1.22V (5)
　　 The continuously generated Fe2+ will generate Fe3+ with good flocculation under the action of strong oxidant Cr6+, and at the same time transform Cr6+ into Cr3+, the reaction is:
　　6Fe2++Cr2O2-7+14H+→2Cr3++6Fe3++7H2O (6)
　　At the same time, if the sewage still contains cyanide, it can happen:
　　CN-＋O2→CNO-〔→…→N2〕 (7)
　　Through the above series of countless internal electrolysis reactions, the heavy pollutants in the sewage have been converted, and then further removed in the subsequent treatment unit.
　　 2. Process flow and main facility description
The mixed wastewater flows to the regulating tank through the collection pipeline in the plant area, and is lifted by the corrosion-resistant first-stage sewage pump to the cast iron/coke reactor. With the aid of air, the heavy metal ions and CN- in the water undergo numerous internal electrolysis on the surface of the cast iron/coke. The reaction, through a series of (1)-(7) reactions to achieve the purpose of conversion. After the effluent is added to the automatic control system to adjust the pH, the effluent flows to the inclined tube sedimentation tank for mud-water separation, and the clean water can be discharged or reused after being sand filtered.
　　The sludge discharged from the inclined pipe sedimentation tank is concentrated in the thickening tank and then dehydrated by the filter press. The dry mud cake contains a large amount of heavy metals, which is a hazardous waste, and is recycled by a special organization.

　　2.2.1 Mixed conditioning tank
　　 is used to adjust irregular drainage and balance water quantity and quality. Set the hydraulic retention time to 8 h, and the liquid level controller controls the operation of the lift pump.
　　2.2.2 Dissolving gas tank
　　 to ensure the full mixing of water and gas, so that the oxygen molecules contained in the sewage can form an internal electrolysis environment on the surface of the coke. The hydraulic retention time of the dissolved gas tank is set at 3 to 5 min.
　　 2.2.3 Cast iron/coke reactor
The cast iron/coke reactor is the core component of the process. The heavy metals contained in the sewage and the dissolved oxygen molecules undergo numerous micro-electrolysis reactions on its surface [see above (1)-(7) reaction mechanism], and good reaction conditions can be guaranteed High-hazard pollutants such as heavy metals and cyanide in the sewage are converted into low-hazard substances, which are then removed in the subsequent ion solidification process. The hydraulic residence time of the cast iron/coke reactor is 45 min, and the contact reaction time is 25-30 min.
　　2.2.4 Degassing tank
　　Remove a large number of tiny air bubbles in the sewage, avoiding being brought into the reaction tank and being wrapped by the dosing agent to form flocs, which will make the flocs light and float. The hydraulic retention time is 15 min, and mechanical stirring is set to speed up degassing.
　　2.2.5 Reaction cell
　　 is divided into a two-stage reaction. In the first stage, the pH value is adjusted by adding sodium hydroxide solution through the automatic control system of the pH meter, and the heavy metals are solidified, and the PAM flocculant is added in the latter stage to accelerate the precipitation of the flocs. The two-stage reaction time is 15 min.
　　 In addition, compared to other processes, the Fe3+ produced by the cast iron/coke reactor itself has a good flocculation effect. When the pH is controlled at 7-10, the produced flocs are large and stable and easy to precipitate.
　　2.2.6 Inclined tube sedimentation tank
　　 is used to separate the muddy water in the effluent from the reaction tank. The surface load is 1.0 m3/(m2.h).
　　2.2.7 Sand filter
The effluent of the sedimentation tank generally contains tiny suspended substances. These heavy metal substances forced to solidify by mechanical action may re-dissolve and cause the heavy metal substances in the effluent to exceed the standard. A sand filter can effectively remove the tiny suspended substances. Remove. The design flow rate of the sand filter should not exceed 1.0 m/h.
　　2.2.8 Clean water reuse pool
　　 Temporarily store clean water and provide backwash water or reuse water for the sand filter.
　　3. Results and experience
　　3.1. Factors affecting water quality
　　 3.1.1 The impact of cast iron/coke reactor on the system
　　The cast iron/coke reactor is the key treatment facility of this technology, and the design of its main parameters directly determines the quality of the system’s effluent effect. In the case of certain water quality, the mass ratio of cast iron to coke, installation method, coke particle size and contact reaction time are key design parameters.

Under the condition of inlet water pH value of 1～3, the used cast iron: coke mass ratio is about 1～1.5:1, layered installation, the cast iron particle size is small (ф=5～15 mm), the coke is thin and thin When the contact time of the entire reactor is 20-30 min, and the air volume provided is 0.1-0.13 m3/min, water sample analysis shows that under these conditions, the high-risk substances Cr6+ and CN- contained in the sewage can be Good conversion into low-risk, easy-to-remove Cr3+ and CNO- etc.
　　 3.1.2 The influence of air in water
　　The effluent in the integrated treatment tank contains a large amount of air, which must be removed as much as possible before dosing. Since the degassing problem was not fully considered at the beginning of the project design, the sludge floating phenomenon often occurred in the inclined tube sedimentation tank. The reason is that the air contained in the water has been added alkali and PAM wrapped in flocculation before it is completely removed. In the body, the density of the sludge becomes smaller and floats. Setting a larger surface area in the degassing tank and increasing agitation are conducive to rapid degassing.
　　 3.1.3 The influence of pH
　　 Heavy metal precipitation requires high pH, ​​so an automatic pH controller is used to add NaOH.
　　 3.1.4 Influence of sand filter flow rate
The 　　 sand filter mainly removes the tiny suspended solids that may be contained in the effluent, and avoids the re-dissolution of solidified heavy metals into the clean water. The excessively high filtration rate is not conducive to filtering the tiny suspended solids.
　　 3.2. Project investment and operating costs
　　The sewage treatment process with internal electrolysis technology as the main body has matured in both ethics and engineering application. Especially the integrated treatment process with such technology as the core is applied to electroplating wastewater treatment projects and has advantages that traditional processes cannot match. The integrated technology to treat electroplating wastewater does not need to lay multiple pipelines, avoiding the complicated pipelines, multiple equipment, large dosages, and high control requirements caused by classified collection for pretreatment. Therefore, project investment costs and operating costs are saved. low.

3.3. The impact of reactor replacement packing on the system
The cast iron in the reactor is always in a state of consumption. When its content drops to a certain level, the treatment effect of the reactor becomes poor, and even the effluent cannot meet the standard. At this time, the cast iron needs to be replenished in time, which may affect the continuous operation of the system. Therefore, this situation must be considered when designing the reactor structure, which can be done by setting up multiple independent parallel processing units, or when the factory is shut down for maintenance.

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