The overall planning of wastewater treatment in the smelting plant area has been carried out, and water treatment projects such as rainwater and sewage diversion, sewage cleaning diversion and cascade utilization, and upgrading and upgrading of external drainage of sewage treatment stations have been implemented successively, realizing the emission reduction of external drainage and total pollutants.
Wastewater treatment and recycling before renovation
The wastewater from non-ferrous smelters is mainly rainwater, production wastewater and domestic wastewater. Different types of wastewater are mixed and sent to the sewage treatment station for disposal. The wastewater has a large amount of water, is acidic and contains heavy metal ions.
The wastewater in the smelting plant area is mixed and sent to the sewage treatment station for treatment. The external drainage indicators meet the GB25467-2010 “Copper, Nickel and Cobalt Industrial Pollutant Discharge Standards”, but there is still a certain gap between the basic requirements for wastewater reuse.
1.2 Wastewater reuse
In 2014, the average water consumption of Daye Nonferrous Metals Smelter is 18.3kt/d, of which 15.0kt/d is used for new water and 7.2kt/d is discharged. The unit consumption of new water per ton of copper is about 18.16t. Wastewater recycling facilities are built in some areas of the plant, and the water recycling (reuse) volume is about 3300t/d.
In order to respond to the national policy of energy conservation and emission reduction and meet the increasingly strict environmental protection policies, it is necessary to carry out the overall transformation of the wastewater treatment facilities in the plant area, improve the recycling rate of wastewater, and reduce the amount of wastewater discharge and pollutant discharge.
2.1 Rain and sewage diversion
Daye Nonferrous Metals Smelter covers an area of about 9.0×105m2, the average annual rainfall is 1330mm, the annual rainfall days are 130-150d, and the rainfall is abundant. According to the layout of the plant, a flood intercepting ditch is set up on the boundary of the plant to prevent clean rainwater from outside the plant from entering the plant and being polluted. Rainwater collection tanks in the east and west areas and a rainwater transfer lifting system are added to the plant to collect and dispose of rainwater by category.
The clean rainwater from the flood intercepting ditch outside the plant is directly discharged to the outside, and the initial rainwater collection tank is set up in the east area of the plant to collect the initial rainwater within 30 minutes of the rainfall in the east area. The initial rainwater collection tank and the later rainwater collection tank are set up. The initial rainwater is collected by the rainwater pipe network to the initial rainwater collection tank and then transported to the sewage treatment station through the rainwater pipeline for disposal. The later clean rainwater enters the later rainwater collection tank for clarification and reuse. See Figure 1 for the rainwater treatment process in the plant.
2.2 Cleanup and diversion
By comprehensively sorting out the water system in the plant area, according to different water quality, the classification and collection of heavy wastewater and non-heavy wastewater are implemented. Wastewater discharge, and formulate corresponding management systems to strengthen control. See Figure 2 for the waste water cleaning and diversion in the factory area and the three-stage discharge outlet.
1) The main waste water outlet and the waste water treatment station outlet set up in the whole plant for external environment drainage are the first-class outlet.
2) The sewage acid treatment station, electrolysis area and material preparation area respectively collect heavy-related wastewater and set up 3 heavy-related wastewater discharge outlets, which are secondary discharge outlets and are jointly supervised by functional departments and workshops. The heavy-duty wastewater in the acid production area is collected and pumped to the sewage acid treatment station for disposal and then discharged. The heavy-duty wastewater such as dust reduction and washing in the material preparation area is collected in the sedimentation tank of the car washing platform of the mining truck. After precipitation, the supernatant is recycled and the remaining water is discharged. , the heavy-duty wastewater in the electrolysis area is collected to the initial rainwater collection tank in the west area and then discharged. The three heavy-duty waste water outlets are all transported to the sewage treatment station by pipelines, and then reused or discharged outside the standard after advanced treatment.
3) The plant area does not involve heavy industrial wastewater, clean water or rainwater. The outlet is a three-level outlet, which is supervised by the relevant workshop. The waste water that does not involve heavy waste is also collected and transported by pipeline to the slag slow cooling area for use.
2.3 Cascade utilization
According to the principle of cascade utilization, process wastewater, cooling water, and steam condensate water do not enter the heavy-duty wastewater system, and the non-heavy wastewater is used for cascade utilization.
1) The drainage volume of the circulating water system in the acid production area and the power generation area is 400t/d, the water hardness is less than or equal to 600mg/L, and the total salt mass concentration is less than or equal to 1.2g/L, which can be directly reused in the slag slow cooling area for use in Cooling of slag bales.
2) Collect process discharge water from each production area, establish clear water pools, and reuse them for locations with lower water quality requirements. Such as flushing water, pharmaceutical preparation water produced by the process, etc.
3) Collect high-quality equipment condensate water and steam condensate water for equipment cooling or circulating water supplementary water.
2.4 New domestic water treatment system
The domestic wastewater includes the water from the bathhouse, the canteen and the toilet flushing water for the workers in the factory area. It is characterized by relatively stable water quality indicators, good biodegradability, and belongs to low-concentration organic wastewater. A new 550m3/d domestic water treatment system will be built to dispose of domestic wastewater, and the aerated biological filter process will be used for treatment. The treated wastewater is used as make-up water for converter circulating water.
2.5 Upgrading and renovation of external drainage
In 2013, the sewage treatment station began to use the biological preparation method to treat the wastewater in the factory area. The technology is relatively mature and reliable, and a variety of heavy metals can be removed simultaneously. Ultrafiltration is a membrane separation technology that uses hollow fiber filtration method and pressure as the driving force, and cooperates with pretreatment to remove impurities in water. It has the characteristics of high filtration accuracy, strong pollution resistance, easy cleaning, and small footprint of equipment and facilities.
On the basis of the original equipment and facilities of the sewage treatment station, a tertiary biological agent dosing point and an ultrafiltration device are added to realize the standard discharge of external drainage.
1) Add a tertiary biological agent dosing point to carry out advanced treatment of heavy metals such as arsenic, copper and cadmium in the smelting external drainage.
2) Establish a 4500m3/d ultrafiltration system, and use ultrafiltration membranes to intercept impurities such as suspended solids (SS) in water.
3) Add 150m3/h wastewater reuse facilities.
The process flow of the sewage treatment station after the renovation is shown in Figure 3.
Main structures and equipment configuration
The main structures and equipment configuration of Daye Nonferrous Metals Smelter’s rain and sewage diversion system, circulating water reuse system, heavy-duty wastewater collection system, domestic water treatment system, and sewage treatment station are shown in Table 2.
4.1 Water saving and emission reduction effect
See Table 3 for the increased water recycling points after the renovation.
After the renovation, the newly added waste water recycling volume of the whole plant is 6250t/d, the new water consumption is reduced by 6.0kt/d, the unit consumption of new water per ton of copper is reduced from 18.16t to 13.6t, and the external drainage volume is reduced from 7.2kt/d to 3.0kt/d. d.
4.2 External drainage index
After the renovation, the sewage treatment station operates stably, and indicators such as heavy metals and suspended solids (SS) in the external drainage continue to reach the first-class A standard in GB18918-2002 “Pollutant Discharge Standards for Urban Sewage Treatment Plants”. The specific indicators are shown in Table 4.
4.3 Economic benefits
Compared with before the renovation, the cost of wastewater treatment has increased from 5,500 yuan/d to 9,500 yuan/d, the cost of new water consumption has been reduced by about 9,000 yuan/d, and the actual cost has been reduced by about 5,000 yuan/d, achieving certain economic benefits. benefit.
In view of the problems of large volume and complex composition of non-ferrous smelting wastewater, through the implementation of rain and sewage diversion, cleaning and diversion, and cascade utilization, and the upgrading of sewage treatment stations, the reduction of external drainage and total pollutants has been better achieved. It has achieved great economic and environmental benefits, and at the same time laid the foundation for the “zero discharge” of wastewater in the later stage.