CN105271599B - A kind of processing method of azotate pollution raw water - Google Patents

Abstract

The invention belongs to the field of environmental protection and water treatment, and provides a treatment method for nitrate-contaminated raw water. By allowing formate to participate in the regeneration of anion exchange resin, in the ion exchange link, the nitrate-contaminated raw water is converted into formate-containing ion exchange The water is effluent, and the formate is removed by aerobic digestion or denitrification. The present invention reduces the difficulty of treatment and recycling of high-nitrate and high-salt resin regeneration wastewater under the condition of moderately increasing the treatment cost of ion exchange effluent, and is very suitable for large-scale treatment of nitrate-contaminated groundwater and nitrate pollution control of circulating aquaculture systems .

Description

A kind of treatment method of nitrate polluted raw water

technical field

The invention belongs to the field of environmental protection and water treatment and provides a treatment method for nitrate polluted raw water.

Background technique

The inefficient use of N fertilizer in agricultural production and the improper treatment and disposal of urban wastewater and solid waste lead to a large amount of N entering the environment, and finally exists in the soil and various surface and low water bodies in the form of nitrate. Among them, the impact of large-scale and intensive facility agriculture, animal husbandry, fishery production and urban landfills on the accumulation of nitrate in the soil and water environment is particularly obvious.

Nitrate is a form of N available to plants, however, soil nitrate is easy to move downward with soil water, especially in semi-humid and semi-arid areas, a considerable part of soil nitrate is not in the root zone of plants , and eventually enter the groundwater body with the movement of soil water. Therefore, the nitrate pollution of groundwater in many northern regions of my country is serious.

Nitrate enters the human body through diet, which can change the microenvironment of the intestinal system, which is not conducive to the activities of beneficial functional flora; it may also be converted into nitrite and combined with hemoglobin, making it lose its ability to transport oxygen; or combined with organic amines , generating carcinogens.

Nitrate pollution of water body is also not conducive to the healthy growth of aquatic products, livestock and poultry breeding animals. The accumulation of high concentration of nitrate in the water not only directly affects the fishery production, but also leads to the eutrophication of the water and causes the outbreak of blue-green algae. Taking intensive fishery production as an example, due to the extensive use of bait and feed, the nitrate concentration in the aquaculture water body rises rapidly, which accelerates the degradation of water quality, reduces the efficiency of aquaculture, frequent water changes increase the cost of aquaculture, and direct discharge without treatment will endanger the environment. This adverse effect is particularly significant in northern regions where water resources are scarce.

In summary, the nitrate pollution of natural and artificial water bodies has had adverse effects on people's production and life. Whether it is nitrate excess in underground drinking water sources or nitrate pollution in surface water (such as aquaculture water), it is necessary to take appropriate measures to remove nitrate to eliminate its adverse effects.

The removal methods of nitrate in water mainly include physical chemical method, chemical method and biochemical method. Physical and chemical methods mainly include distillation, electrodialysis, reverse osmosis, ion exchange, etc. Among them, the first three are not selective, and other elements beneficial to the human body in the water are also removed while removing nitrate; the ion exchange method is fast and easy to automatically control, but produces high-nitrate and high-salt wastewater. In fact, all physical and chemical methods only transfer and enrich nitrate, and the resulting nitrate wastewater needs to be properly treated before it can enter the environment. However, in water-scarce areas with less surface runoff, the regenerated brine cannot be easily discharged after denitrification, because the discharged brine is not easy to be carried away by surface runoff, but most of it eventually enters the ground, thereby promoting the salinization of soil and groundwater. Therefore, in water-scarce areas, the denitrification and regeneration of brine by ion exchange resin can be recycled to minimize its adverse impact on the environment.

The chemical reduction denitrification method can use active metals such as aluminum and iron as reducing agents, and can also use hydrogen, formic acid, etc. as reducing agents to reduce nitrates under the action of catalysts. In addition, photochemical and electrochemical catalytic methods can also be used to remove nitrate in water. However, all these chemical methods are easy to form nitrite or ammonium by-products, and the practical application is also limited by many factors.

Biological denitrification is a process in which denitrifying bacteria reduce nitrate to nitrogen, including autotrophic and heterotrophic denitrification. Among them, autotrophic denitrification uses inorganic substances such as hydrogen and elemental sulfur as electron donors, and the denitrification rate is slow, but the effluent quality is better. However, hydrogen has low solubility and is explosive, and it is difficult to apply hydrogen autotrophic denitrification on a large scale; sulfur autotrophic denitrification will produce sulfate and acidity, so it is only suitable for treating raw water where the nitrate is not seriously exceeded and the sulfate concentration is not high. Heterotrophic denitrification uses organic carbon sources as electron donors, and the denitrification rate is relatively fast. However, the addition of carbon sources requires high control. Excessive additions will remain and increase the difficulty of subsequent treatment. Insufficient additions will easily lead to the accumulation of nitrite in the effluent.

The respective advantages of ion exchange method and chemical method or biochemical method can be combined to transfer and enrich raw water nitrate by ion exchange method, and then chemical and biochemical methods can be used to completely remove high-concentration nitrate in ion exchange resin regeneration wastewater. However, biochemical or chemical denitrification of high-nitrate and high-salt ion-exchange wastewater is difficult. Therefore, when choosing the ion exchange method to remove nitrate in water, it is necessary to comprehensively consider the practical problems in the ion exchange and regeneration links. In the case that the quality of the ion exchanged water is not greatly affected, it is possible to consider changing the ion exchange mode, including changing the regeneration agent, etc., to improve the composition of the resin regeneration water, reduce the difficulty of biochemical or chemical denitrification, and promote the recycling of the resin regeneration water.

Contents of the invention

The purpose of the invention is to provide a treatment method for nitrate polluted raw water.

To achieve the above object, the technical solution adopted in the present invention is:

A method for treating nitrate-contaminated raw water. By allowing formate to participate in the regeneration of anion exchange resins, in the ion exchange link, the nitrate-contaminated raw water is converted into formate-containing ion-exchanged effluent, and the formate is removed biochemically.

The above-mentioned ion-exchanged effluent containing formate is removed by aerobic digestion; or, the ion-exchanged effluent is mixed with nitrate-contaminated raw water so that the molar ratio of nitrate and formate in the mixed water is 2:7-8, and then Denitrification simultaneously removes formate and nitrate.

Wherein, the formate participates in the regeneration of the anion exchange resin, and the molar concentration ratio of the formate to the total anions in the regenerated brine exceeds 50%.

The molar ratio of formate and chloride ions in the resin regeneration brine is controlled to be >4:1, so that the ion-exchanged water can be recycled for aquaculture after undergoing formate removal treatment.

The molar ratio of formate and chloride ions in the resin regeneration brine is controlled to be >1:1, so that the ion-exchanged water can be used for drinking purposes after undergoing formate removal treatment.

The device for treating nitrate-contaminated raw water includes raw water tank, ion exchange resin column, formate biochemical treatment reactor, post-treatment tank, resin regeneration inlet tank, resin regeneration first stage outlet tank, calcium sulfate sedimentation tank, resin regeneration first stage Two-stage outlet tank, resin cleaning inlet tank and resin cleaning outlet tank.

The advantages that the present invention has are:

1. The present invention converts the removal of raw water nitrate into the removal of formate by means of ion exchange. Compared with the biochemical removal of raw water nitrate, the difficulty of biochemical removal of formate and the COD load are significantly reduced.

2. The treatment method of the present invention is based on formate-based high-nitrate and high-salt resin regeneration wastewater, which is very easy to regulate and control its pH in a large range, and is suitable for biochemical and chemical treatment to realize recycling.

3. The treatment method of the present invention is to remove the formate by microbial aerobic or denitrification, and the ion exchanged water does not increase the salinity but increases the bicarbonate alkalinity, which is not only suitable for large-scale control of groundwater nitrate pollution, but also suitable for The circulating aquaculture system reduces the difficulty of pH control of the aquaculture water and improves the recycling rate of water.

Description of drawings

Fig. 1 is the device of the treatment method of the nitrate polluted raw water used in the embodiment of the present invention.

Among them, 1. Raw water tank, 2. Ion exchange resin column, 3. Formate biochemical treatment reactor, 4. Post-treatment tank, 5. Resin regeneration inlet tank, 6. Resin regeneration first stage outlet tank, 7. Sulfuric acid Calcium sedimentation tank, 8. Resin regeneration second stage outlet tank, 9. Resin cleaning inlet tank, 10 Resin cleaning outlet tank.

detailed description

Example 1

As shown in Figure 1, the water outlet of raw water pool 1, the water inlet of water outlet pool 6 in the first stage of resin regeneration, the water inlet of water outlet pool 8 in the second stage of resin regeneration, and the water inlet of resin cleaning water outlet pool 10 respectively pass through pipelines with valves and One end of the ion exchange resin column 2 is connected in parallel; the water inlet of the formate biochemical treatment reactor 3, the water outlet of the resin regeneration water inlet tank 5, and the resin cleaning water inlet tank 9 water outlet respectively pass through the pipeline with a valve and the ion exchange resin column The other end of 2 is connected in parallel.

Ion-exchange resin treatment of nitrogen-containing water: ion-exchange column 2 is 100 cm high, filled with regenerated 717-type anion-exchange resin. The raw water is simulated aquaculture wastewater with a pH value of 7.4, a nitrate concentration of 6mmol/L, a sulfate concentration of 2mmol/L, a chloride ion concentration of 6mmol/L, and a bicarbonate concentration of 2mmol/L. Open the valves of the water outlet of the raw water tank 1 and the water inlet of the formate biochemical treatment reactor 3, and treat the raw water at a flow rate of 13.5BV/h under the condition of 20-24°C. After running for 6 hours, when the nitrate concentration in the effluent exceeds 2mmol/L, close the above two valves and enter the resin regeneration stage.

Ion exchange resin regeneration and cleaning: The resin regeneration solution contains 0.07N sodium chloride and 0.7N sodium formate. First, open the water inlet and outlet valves of the resin regeneration inlet pool 5 and the resin regeneration first-stage outlet pool 6, and perform the first-stage resin regeneration at a flow rate of 4.0BV/h. After 1 hour, when the concentration of sulfate in the regeneration wastewater is less than 80mmol/L, close the water inlet valve of the outlet pool 6 in the first stage of resin regeneration, and open the water inlet valve of the outlet pool 8 in the second stage of resin regeneration, at a flow rate of 4.0BV/h Proceed to the second stage of resin regeneration. After 2.5 hours, the nitrate concentration of the regeneration wastewater was 18.5mmol/L, and the water inlet and outlet valves of the resin regeneration inlet pool 5 and the resin regeneration second stage outlet pool 8 were closed. Open the water inlet and outlet valves of the resin cleaning water inlet pool 9 and the resin cleaning water outlet pool 10, and clean the resin for 1 hour with the raw water treated with the ion exchange resin at a flow rate of 5.5BV/h, then close the resin cleaning water inlet pool 9 and the resin cleaning outlet The water inlet and outlet valves of the pool 10 complete the regeneration and cleaning of the ion exchange resin.

Collection of resin regeneration waste water: The regeneration waste water collected in the outlet pool 6 of the first stage of resin regeneration enters the calcium sulfate precipitation tank 7, and excessive calcium formate is added to produce calcium sulfate precipitation, so that the residual concentration of sulfate is reduced to below 60mmol/L, and then the sulfuric acid The supernatant of the calcium precipitation tank 7 flows into the second-stage outlet tank 8 of resin regeneration, and after a certain amount is collected, it is prepared for biochemical or chemical denitrification.

Aerobic biochemical treatment of formate-containing ion-exchanged effluent: Formate biochemical treatment reactor 3 consists of an activated carbon filter with a length of 40mL and an inner diameter of 5cm (effective volume: 350mL) and a 10L aerobic aeration tank. Before officially treating the ion exchange effluent, the activated carbon filter uses the activated sludge of the urban sewage treatment plant as the bacterial source and 6mmol/L sodium formate as the carbon source. water and aeration for 1 minute, each water intake is 200mL), for the enrichment culture of formate aerobic oxidizing bacteria, each cycle is 2 days, after 8 days, the formic acid treatment load reaches more than 80mgCOD/L/h, Start the aerobic filtration removal for ion exchange effluent. The formal treatment is as follows: 7L of ion-exchange effluent was collected in the aerobic aeration tank, in which the formate concentration was 9.4mmol/L, and the water was fed and aerated for 1 minute at intervals of 6 minutes, each time 200mL of water was fed, and after 48 hours of operation The concentration of formate is <0.2mmol/L; the effluent after aerobic treatment with formate enters the post-treatment tank 4 for clarification and is used for aquaculture purposes.

Example 2

The structure of the ion exchange resin column and the collection of resin regeneration wastewater are the same as in Example 1.

Ion exchange resin treatment of raw water: the raw water is simulated drinking water with excessive nitrate, pH value is 7.3, nitrate concentration is 3.0mmol/L, sulfate concentration is 1.0mmol/L, chloride ion concentration is 1.0mmol/L, bicarbonate Concentration 1mmol/L. Open the valve connecting the water outlet of raw water tank 1 and the water inlet of formic acid biochemical treatment reactor 3, and treat the raw water at a flow rate of 13.5BV/h under the condition of 20-24°C. Run to 10 hours, the nitrate concentration in the effluent exceeds 0.7mmol/L, close the above two valves, and enter the resin regeneration stage.

Ion exchange resin regeneration and cleaning: The resin regeneration solution contains 0.18N sodium chloride and 0.7N sodium formate. First, open the water inlet and outlet valves of the resin regeneration inlet pool 5 and the resin regeneration first-stage outlet pool 6, and perform the first-stage resin regeneration at a flow rate of 4.0BV/h. After 1 hour, when the concentration of sulfate in the regeneration wastewater is less than 80mmol/L, close the water inlet valve of the outlet pool 6 in the first stage of resin regeneration, and open the water inlet valve of the outlet pool 8 in the second stage of resin regeneration, at a flow rate of 4.0BV/h Proceed to the second stage of resin regeneration. After 2.5 hours, the nitrate concentration of the regeneration wastewater was 15.2mmol/L, and the water inlet and outlet valves of the resin regeneration inlet pool 5 and the resin regeneration second stage outlet pool 8 were closed. Open the water inlet and outlet valves of the resin cleaning water inlet pool 9 and the resin cleaning water outlet pool 10, and clean the resin for 1 hour with the raw water treated with the ion exchange resin at a flow rate of 5.5BV/h, then close the resin cleaning water inlet pool 9 and the resin cleaning outlet The water inlet and outlet valves of the pool 10 complete the regeneration and cleaning of the ion exchange resin.

Denitrification and biochemical treatment of ion-exchanged effluent: Formate biochemical treatment reactor 3 is composed of an activated carbon filter (effective volume 700 mL) with a length of 80 mL and an inner diameter of 5 cm. Before formally treating the ion exchange effluent, the activated carbon filter uses the activated sludge of the urban sewage treatment plant as the bacterial source, 4.0mmol/L sodium formate as the carbon source, and 1.0mmol/L sodium nitrate as the electron acceptor, and the water cut-off time is 40 minutes, 10 days of denitrifying bacteria enrichment culture, when the formic acid load to be treated reaches 70mgCOD/L/h or more, it will be used for the synchronous removal of formate and nitrate after mixing the ion exchange effluent and the raw water with nitrate exceeding the standard . The formal treatment is as follows: Refer to the average concentration of formate in the ion-exchange effluent (2.7mmol/L), the ion-exchange effluent is mixed with the raw water with nitrate exceeding the standard at a ratio of 6:1, and then enters the formate biochemical treatment reactor 3, and the water is stopped. The time is 30 minutes, the concentration of nitrate and nitrite in the effluent is lower than 0.05mmol/L, and the concentration of formate is lower than 0.1mmol/L; the effluent of denitrification treatment enters the post-treatment tank 4, sand filter, activated carbon filter and After ozone disinfection, it is used for drinking water purposes.

Claims (4)

1. A kind of 1. processing method of azotate pollution raw water, it is characterised in that：By allowing formate to participate in anion exchange resin Regeneration, in ion exchange link, change azotate pollution raw water is the ion exchange water outlet containing formates, and biochemical removal is therein Formates；

   Ion exchange water outlet containing formates removes wherein formates by aerobic sigestion；Or ion exchange water outlet and nitre Hydrochlorate polluted raw mixes, and it is 2 to make the mol ratio of nitrate anion and formate in mixing water：7-8, then denitrification synchronization remove first Hydrochlorate and nitrate.
2. 2. the processing method of the azotate pollution raw water as described in claim 1, it is characterised in that：

   Formate participates in anion exchange resin regeneration link, and the molar concentration rate for regenerating formate and total anion in salt solution surpasses Cross 50%.
3. 3. the processing method of the azotate pollution raw water as described in claim 1 or 2, it is characterised in that：

   Control the mol ratio of formate and chlorion in resin regeneration brine>4:1, so as to which ion exchange water outlet receives formates Except being circularly used for aquaculture after processing.
4. 4. the processing method of the azotate pollution raw water as described in claim 1 or 2, it is characterised in that：

   Control the mol ratio of formate and chlorion in resin regeneration brine>1:1, so as to which ion exchange water outlet receives formates Except after processing can be used for drink.