Design of arsenic-containing wastewater treatment process
Metallurgical, mining, chemical, dye and leather industries in the production process will produce a large number of arsenic containing wastewater, if not properly treated, will cause serious pollution to soil, water, affect the growth of crops, threaten the health of humans and animals. Gb5749-2006 and GB8978-1996 stipulate that the mass concentration of arsenic in drinking water and discharge wastewater cannot exceed 0.01×10-6 and 0.5×10-6kg/m3, respectively.
At present, the main methods for removing arsenic from water include sulfide precipitation, calcium and iron salt combined removal, adsorption removal, ion exchange, microfiltration and arsenic removal agent removal. However, the arsenic in solid wastes produced by sulfide precipitation and calcium-iron salt combined removal of arsenic is easy to be removed, resulting in secondary pollution. This paper mainly introduces a project example of treating arsenic-containing wastewater with high efficiency arsenic removal filter.
1. Design basis
(1) As content in influent water: 3~4mg/L, TDS: 4000~6000mg/L.
(2) Discharge standard of As content in effluent: ≤0.4mg/L; Treatment water: 20m3/h.
2. Process plan description
The process flow is shown in Figure 1.
2.1 Integrated Comprehensive Pool
The integrated comprehensive tank consists of three parts: regulating tank, settling tank and outlet tank. The raw water first enters the regulating tank for homogenization, and then is pumped under pressure into the sand filter by the pump. The backwashing effluent from the sand filter and activated carbon filter enters the sedimentation tank, where the suspended matter settles naturally, and the effluent from the sedimentation tank enters the regulating tank again. The effluent from the activated carbon filter enters the outlet pool, where the water sample is taken for effluent monitoring. If it is qualified, it will enter the pipe network again. If it is not qualified, it will enter the high-efficiency arsenic removal filter again.
2.2 Sand filter filter
Sand filter filter with different particle size filter material, from top to bottom, from small to large in order. When the water flows through the filter layer from the top, some of the solid suspended substances in the water enter the tiny holes formed by the upper filter material, which are intercepted by the surface layer of the filter material by adsorption and mechanical retention. At the same time, these suspended substances are overlapped and bridged, just as a film is formed on the surface of the filter layer to continue to filter the suspended substances in the water, which is the so-called membrane filtration of the surface layer of the filter material. This filtration effect is not only on the surface of the filter layer, but also when the water enters the middle filter layer, which is different from the surface layer of filtration, called osmosis filtration. In addition, because the filter material is closely arranged with each other, when the suspended particles in the water flow through the curved pores in the filter material layer, there are more opportunities and time to collide and contact with the surface of the filter material, so the suspended substances in the water adhere to each other on the surface of the filter material and the flocculation, resulting in the contact coagulation filtration process. Sand filter filtration has the advantages of mature technology, stable operation and small investment scale. The sand filter needs to be backwashed, and the backwashed water enters the sedimentation tank in the integrated tank.
2.3 High efficiency arsenic removal filter
The high efficiency arsenic removal filter is equipped with a new type of special high efficiency arsenic removal nanomaterial. When the water flows through the filter layer from above, the arsenic in the water is adsorbed by the filter material. The advantage of this filter material is that the adsorption capacity is large, only 1-2 times a year regeneration repair, each regeneration water is about 10t, due to the limited space on the site, it is not recommended to design deep treatment of recycled water, the wastewater generated by regeneration should be directly recycled by the waste liquid treatment company.
2.4 Activated Carbon filtration
Activated carbon filter is a more commonly used water treatment equipment, filled with activated carbon, as a pre-treatment of water treatment desalination system, can adsorb the residual chlorine that can not be removed in the pre-filtration, can effectively ensure the service life of the post-stage equipment, improve the quality of effluent water, prevent pollution, especially to prevent the free residual oxygen poisoning pollution of the post-stage reverse osmosis membrane; At the same time, it also adsorbs polluting substances such as small molecule organic matter that leaks from the previous stage, and has a more obvious adsorption removal effect on odors, colloids, pigments, and heavy metal ions in water.
3. Description of system composition
3.1 Integrated Comprehensive Pool
(1) Quantity: 1 set.
(2) Material: carbon steel (glass fiber reinforced plastic anti-corrosion).
(3) Specification: 50m3.
(4) Regulating pool lift pump: Q=30m3/h, H=30m, the number is 2 sets (1 used and 1 standby).
(5) Sedimentation tank self-priming sludge pump: Q=8m3/h, H=10m, the number of 2 sets (1 standby 1).
(6) Backwash pump: specification: Q=25m3/h, H=12m, the number is 2 sets (1 used 1 standby).
(7) Return pump: Q=30m3/h, H=30m, the number is 2 sets (1 used 1 standby).
3.2 Sand filter filter
3.2.1 Ontology Design
(1) Quantity: 1 set.
(2) Material: carbon steel (glass fiber reinforced plastic anti-corrosion).
(3) Specification: ￠1800mm, straight side height 1800mm.
(4) Packing: The pebble with a particle size of ￠4 ~ ￠32mm is used as the support layer, and the quartz sand with a particle size of ￠0.8 ~ ￠4mm is used as the filter material.
(5) Accessories: pressure gauge, pipeline, valve, etc.
3.2.2 System technology and backwashing device
During operation, the output of a single device is 30m3/h and the flow rate is 12m/h. When the inlet and outlet pressure difference reaches a certain value or the outlet turbidity increases, the system carries out backwashing, and the backwashing time is about 15min. When backwashing, turn on the backwashing pump, backwashing is assisted by compressed air, backwashing water strength is 10L/(m2·s), compressed air strength is 10L/(m2·s), backwashing time is 15min, divided into 3 stages, air washing, air washing, water washing, each time is 5min.
3.3 High efficiency arsenic removal filter
3.3.1 Ontology design
(1) Quantity: 2 sets.
(2) Material: carbon steel (glass fiber reinforced plastic anti-corrosion).
(3) Specification: ￠1800mm, straight side height 2400mm.
(4) Packing: the use of high efficiency arsenic removal filter material.
(5) Accessories: pressure gauge, pipeline, valve, etc.
(6) Supporting equipment: a set of repair and regeneration dosing device.
3.3.2 System process and backwashing device
Two filters are connected in series. During operation, the output of a single device is 30m3/h, and the flow rate is 12m/h. When the adsorption is saturated, regeneration repair is required.
3.4 Active carbon filter body design
Quantity: 1 set. Material: Carbon steel (FRP anti-corrosion). Specification: ￠1800mm, straight side height 1800mm. Packing: The pebble with a particle size of ￠4 ~ ￠32mm is used as the support layer, the quartz sand with a particle size of ￠1 ~ ￠4mm and 10 ~ 40 mesh activated carbon are used as the filter material. The accessories are pressure gauge, temperature meter, pipe, valve, etc. Among them, when the system process and backwashing device are running, the output of a single device is 30m3/h, and the operating flow rate is 12m/h. When the inlet and outlet pressure difference reaches a certain value or the outlet turbidity increases, the system carries out backwashing, and the backwashing time is about 15min.
3.5 Online monitoring instrument
In order to monitor the normal operation of the system and assist the system to realize automatic operation under certain conditions, the corresponding control points in the system are designed with relevant on-site online detection and control instruments. In order to make all the testing data can be through a programmable logic controller (ProgrammableLogicController, PLC) concentration processing, the field monitoring instrument part 4 ~ 20 ma output standard signal.
Monitoring instrument:
(1) One liquid level meter (installed in the regulating tank);
(2) Electromagnetic flowmeter (installed in the water inlet pipe)1;
(3) 1 pH online monitor (installed in the adsorption reaction tank).
3.6 Electrical control system
The system automatic control adopts PLC program controller to realize automatic and manual operation control mode. The standard signal collected by the on-site online detection instrument is processed centrally, and the control signal and alarm signal are output. When the system water supply is insufficient and the film inlet pressure exceeds the standard, the system can automatically alarm. The cost estimates are shown in Table 1.
4. Conclusion
Arsenic containing wastewater is a kind of industrial wastewater which is difficult to treat. The treatment of arsenic-containing wastewater by physical adsorption combined with high efficiency arsenic removal nanomaterials has good treatment effect and is not easy to come out. While ensuring the treatment effect, the energy consumption and operation cost are low, and the operation management is simple and reliable, which can provide reference for the design of arsenic-containing wastewater treatment.
