CN1239413C

CN1239413C - Method for treatment of waste water containing ammonia using caustic soda as alkali source

Info

Publication number: CN1239413C
Application number: CNB021163944A
Authority: CN
Inventors: 李德勇; 李德新
Original assignee: Anyang Iron and Steel Co Ltd
Current assignee: Anyang Iron and Steel Co Ltd
Priority date: 2002-04-01
Filing date: 2002-04-01
Publication date: 2006-02-01
Anticipated expiration: 2022-04-01
Also published as: CN1448346A

Abstract

The present invention relates to a method for treating waste water containing ammonia by using caustic soda as alkali sources, which belongs to the technology for treating industrial waste water. The present invention is the improvement of a traditional AO method (oxygen deficiency /oxygen sufficiency) for treating waste water containing ammonia, which provides a new carbon source and an alkali source for treating waste water containing ammonia. The method comprises the step of replacing Na2CO3 with a relatively cheap alkali source of NaOH, and uses the nature that a water solution of the NaOH is easy to carry out reaction with CO2 in air to generate NaHCO3 and Na2CO3 to achieve the purpose of obtaining inorganic carbon salts. The present invention reduces the cost for treating waste water, decreases dust pollution and saves investment and power consumption.

Description

Method for treating ammonia-containing wastewater by using sodium hydroxide as alkali source

Technical Field

The invention relates to a wastewater treatment technology, in particular to the type and requirement of alkali added for treating ammonia nitrogen in wastewater, and belongs to an industrial wastewater treatment technology.

Background

At present, the more perfect and reasonable method for treating ammonia nitrogen in wastewater in China is an AO (anaerobic-anoxic/aerobic) process. The process is as follows: the method comprises the following steps of mixing ammonia nitrogen-containing wastewater with return water from a secondary sedimentation tank, then feeding the mixed wastewater into an anoxic tank, controlling the pH value to be 7-8, and converting nitrate nitrogen in the return water into nitrogen to escape. The effluent of the anoxic tank enters an aerobic tank and is fully mixed and contacted with activated sludge from a sedimentation tank through aeration, pollutants in the wastewater are adsorbed and degraded under the action of microorganisms and oxygen, and because nitrosobacteria and nitrobacter which decompose ammonia nitrogen belong to autotrophic bacteria, an inorganic nitrogen source is required to be used as nutrition for synthesizing life substances, and the total reaction equation of oxidation and self synthesis is as follows:

therefore, Na is respectively added at the water inlet of the aerobic tank, the return sludge inlet and the outlet 1/3 of the aerobic tank₂CO₃The solution meets the requirement, the effluent alkalinity is kept to be more than 150mg/L, the effluent of the aerobic tank is precipitated by a sedimentation tank, activated sludge flows back into the aerobic tank, most of the effluent enters the anoxic tank as the return water, and the rest of the effluent enters a post-treatment process and is discharged after being treated. As can be known from the oxidation of nitrifying bacteria and the self-synthesis total reaction equation, 1.7 g of inorganic carbon needs to be consumed for treating 1 g of ammonia nitrogen, namely 15 g of Na is consumed₂CO₃Therefore, the process has high treatment cost, and 3-4 kg of Na is consumed for treating 1 ton of wastewater containing ammonia nitrogen at about 200mg/L₂CO₃Due to each ton of Na₂CO₃The market price of the process is 2000 yuan, which is equivalent to about 7 yuan of the alkali adding cost for treating 1 ton of wastewater with the concentration, and the process is seriously highThe treatment cost is high, and the popularization in China is restricted. In addition, adding the same Na₂CO₃Corresponding devices for dissolving, hoisting and the like are required to be added, and a specially-assigned person is equipped for operation, so that the labor cost is increased, and the dust pollution is increased in the process of pouring the solid alkali.

Disclosure of Invention

The invention aims to provide a method for treating ammonia-containing wastewater by using sodium hydroxide as an alkali source, which is an improvement of the conventional method for treating ammonia-containing wastewater by an AO (anaerobic-anoxic/aerobic) method, and provides a new carbon source and an alkali source for treating ammonia-containing wastewater, namely, a relatively cheap alkali source NaOH is used for replacing Na₂CO₃The NaOH aqueous solution is easy to react with CO in the air under the condition of continuous aeration₂Reaction to produce Na₂CO₃Thereby achieving the purpose of obtaining the inorganic carbon salt. The reaction equation is as follows:

(this process is essential)

And simultaneously, the effluent alkalinity of the aerobic tank is further reduced, so that the alkali consumption is reduced, and the aim of further reducing the cost is fulfilled.

The purpose of the invention is realized as follows:

the ammonia-containing wastewater with the ammonia nitrogen concentration less than or equal to 300mg/l (or with the ammonia nitrogen concentration less than or equal to 300mg/l after dilution) is firstly mixed with the return water from the secondary sedimentation tank and then enters an anoxic tank, the PH value is controlled to be 7-8, and nitrate nitrogen in the return water is converted into nitrogen to escape. The effluent of the anoxic tank enters an aerobic tank. And respectively adding 3-5 wt% of NaOH dilute solution at a return sludge inlet and a wastewater inlet of the aerobic tank, wherein the total amount of the NaOH dilute solution is added by adding 5.5-6 g of 100% NaOH per gram of ammonia nitrogen in the ammonia-containing wastewater. The alkali adding amount of the two alkali adding points is distributed according to the ratio of 1: 1-3, namely the alkali adding amount atthe inlet of the returned sludge of the aerobic tankThe total alkali addition amount of the aerobic tank is 25-50%, and the alkali addition amount of the wastewater inlet of the aerobic tank is 50-75% of the total alkali addition amount of the aerobic tank. Under the condition that the aerobic pool is continuously aerated with air, the added sodium hydroxide reacts with carbon dioxide in the air to generate NaHCO₃And a small amount of Na₂CO₃Activated sludge from the sedimentation tank is fully mixed and contacted with the wastewater through aeration, and microorganisms (mainly nitrite bacteria and nitrate bacteria) in the sludge adsorb ammonia nitrogen in the wastewater and convert the ammonia nitrogen into NO under the action of oxygen by utilizing a carbon source captured by NaOH₃-. The effluent alkalinity of the aerobic tank is CaCO₃Meter) is controlled to be 80-160 mg/l, and the pH value of the effluent of the aerobic tank is 6-7 at the moment. If the alkalinity of the effluent of the aerobic tank is too large (more than 160mg/l), although the conversion of ammonia nitrogen into nitrate and the conversion of NaOH into NaHCO are facilitated₃、Na₂CO₃But can cause waste of alkali; the alkalinity of the effluent of the aerobic tank is too small (less than 80mg/l), which reduces the PH value in the aerobic tank, thereby inhibiting CO₂Absorption and ammonia nitrogen conversion. In order to promote the absorption of CO by NaOH₂Conversion to NaHCO₃And Na₂CO₃The process is carried out to fully meet the requirement of microorganisms on inorganic carbon, and 30 to 50 percent of the total amount of NaOH required by the aerobic pool can be continuously added in any water storage pool in front of the anoxic pool in advance, and the water is continuously aerated with the CO-rich water₂The pH value of the anoxic tank is less than 8.5, because the excessive pH value inhibits the denitrification process in the anoxic tank. Therefore, under the condition that the alkali added in the aerobic tank can meet the system requirement, the adding amount of the alkali before the anoxic tank is reduced as much as possible.

After the effluent of the aerobic tank is precipitated by the sedimentation tank, the activated sludge flows back into the aerobic tank, most of the effluent enters the anoxic tank as the backflow water, and the rest of the effluent enters the post-treatment process and is discharged after being treated.

For ammonia-containing wastewater with ammonia nitrogen concentration of more than 300mg/l (such as a coking plant), ammonia distillation treatment is carried out before biochemical treatment of the wastewater, and NaOH is added to decompose fixed ammonium salt in the wastewater, so that excessive NaOH can be added into an ammonia distillation tower, inorganic carbon in a large amount of carbonate contained in the wastewater can be converted into Na by NaOH₂CO₃Is retained in the wastewater without being converted into CO₂The ammonia is escaped and dissipated in the air, and the ammonia distillation efficiency of the ammonia distillation tower is improved, but the excessive degree of adding alkali into the ammonia distillation tower is preferably that the pH value in the anoxic pond is not more than 8.5. If the inorganic carbon fixed in the process can not meet the requirements of the microorganisms in the aerobic tank, namely the alkalinity of the effluent of the aerobic tank is lower than 80mg/l, and the pH value can not reach 6-7, NaOH is still added into the reflux sludge inlet and the wastewater inlet of the aerobic tank according to the proportion of 1: 1-3, and CO in the air is captured₂To supplement the deficiency of inorganic carbon and meet the alkalinity of the effluent of the aerobic pond system (by CaCO)₃In terms of) 80-160 mg/l, and the pH value is 6-7. The effluent of the aerobic tank meets the requirements.

It is to be noted that NaOH added in the aerobic tank is converted into NaHCO₃And a small amount of Na₂CO₃A process is required whereby sufficient time is allowed for sufficient conversion of NaOH to NaHCO₃(Na₂CO₃) But not to be lost with water, that is, the position for adding the alkali is far away from the effluent of the aerobic tankAnd removing an alkali adding point closest to a water outlet of the aerobic tank, changing the original three-point alkali adding into two-point alkali adding, reserving two alkali adding points of a return sludge inlet of the aerobic tank and a waste water inlet of the aerobic tank, and adding the total amount according to the addition of 5.5-6 g of NaOH into ammonia nitrogen per gram of ammonia nitrogen entering the system. The alkali adding amount of the two alkali adding points is distributed according to the ratio of 1: 1-3.

In addition, the alkalinity of the effluent of the aerobic tank is too high, which easily causes alkali waste, and experiments prove that the alkalinity of the effluent of the aerobic tank (as CaCO)₃Meter) is controlled to be slightly larger than 80mg/L to meet the requirement of microorganisms, and the pH value of effluent of the aerobic tank is 6-7 at the moment. Therefore, the alkali adding amount needs to be adjusted by taking the alkalinity of the effluent as a main index so as to further reduce the alkali consumption in the wastewater treatment process.

The invention uses cheap NaOH concentrated solution to replace expensive solid Na₂CO₃As an alkali source, solid Na is added into the continuously added alkali source₂CO₃The prepared dilute solution is changed into a dilute NaOH solution with the addition concentration (weight percentage) of3-5 percent and is utilized inContinuously aerating air in the aerobic tank to provide oxygen and simultaneously providing CO₂Reacting NaOH with CO₂Chemical reaction occurs to produce NaHCO₃And a small amount of Na₂CO₃Thereby obtaining the inorganic carbon necessary for the life activities of the nitrifying bacteria and reducing the treatment cost of the ammonia-containing wastewater. The invention also reduces the effluent alkalinity of the aerobic tank to reduce the waste of alkali and achieve the purpose of reducing the cost. Experiments prove that NaOH is used for replacing Na₂CO₃The alkaline source added into the aerobic tank has no adverse effect on the life activities of bacteria in the aerobic tank and the treatment effect of wastewater, and the excessive alkalinity of the effluent of the aerobic tank only causes the waste of alkali.

Compared with the alkali adding technology of the prior ammonia-containing wastewater treatment process AO method (namely anoxic/aerobic), the invention has the following advantages under the same treatment effect:

1. greatly reduces the treatment cost of the wastewater, and reduces the alkali addition cost of each ton of wastewater from about 7 yuan to about 2 yuan.

2. Saving investment and power consumption, and reducing solid Na₂CO₃The dissolving tank and the transportation and hoisting equipment.

3. The labor cost is saved, and the post does not need to be configured with a specially-assigned person for operation.

4. And dust pollution is reduced.

5. Avoid the solid Na₂CO₃Insoluble impurities contained in the waste water block an alkali pool and a pipeline, so that the pipeline replacement and the heavy pool cleaning work are reduced.

Drawings

FIG. 1 is a flow chart of the ammonia-containing wastewater treatment process of the invention.

In the figure: 1-high tank, 2-pump, 3-ammonia still, 4-pump, 5-wastewater adjusting tank, 6-pump, 7-flotation oil removing tank, 8-water distribution well, 9-pump, 10-anoxic tank, 11-aerobic tank, 12-sedimentation tank, 13-water distribution well, 14-sludge well, 15-pump, 16-dilute alkali tank, 17-pump, 18-post treatment process.

Detailed Description

Example 1

The present invention will be further described with reference to FIG. 1 (excluding the portion indicated by the dashed line) and examples.

The flow rate is 36m³About one hour of ammonia-containing wastewater (containing 120mg/l of ammonia nitrogen, less than 2000mg/l of COD value and 7-8 of PH value) is distributed between the water distribution well 8 and 150m from the water distribution well 13³About/h of reflux water mixtureThen, the mixed wastewater (pH 7) is fed into an anoxic tank 10 by a pump 9. NO contained in the return water₃Is converted here to N₂Then the wastewater flows into the aerobic tank 11 automatically. Here, the wastewater is thoroughly mixed with the return sludge from the sedimentation tank 12 under vigorous agitation by continuously introduced compressed air. The concentrated NaOH solution with concentration (weight percentage) of about 40% enters a dilute alkali tank 16, is diluted into the dilute NaOH solution with concentration (weight percentage) of about 4% by 9 times of clean water under the stirring of compressed air, and is continuously pumped by a pump 17 at a speed of about 0.7m³The total flow of the flow/h is controlled by a valve to be added into the aerobic tank 11 at two positions of a sludge return inlet and a waste water inlet of the aerobic tank respectively according to the proportion of 1: 2. Effluent of the aerobic tank (alkalinity is 80-160 mg/l, pH value is 6-7) automatically flows into a sedimentation tank 12, sludge is settled, sludge at the bottom automatically flows into a sludge well 14, then the sludge is sent back to the aerobic tank 11 by a pump 15 to be used as return sludge, clear liquid at the upper part automatically flows into a water distribution well 13, most of the clear liquid is used as return water to enter a water distribution well 8, and the rest of the clear liquid enters a post-treatment process 18 and is discharged as discharged water after treatment.

Example 2

The present invention is described in detail with reference to the accompanying FIG. 1 (the portion within the dotted line) and the following examples:

passing the concentrated NaOH solution with concentration (weight percentage) of about 40% through the high-position tank 1 at a speed of 0.45m³Flow rate/h and flow rate of 32m³The ammonia-containing wastewater (containing 3000-3300 mg/l ammonia nitrogen and having a pH value of 9) of the coking plant is sent into an ammonia still 3 by a pump 2. Introducing steam from the bottom of the tower to evaporate most of ammonia in the ammonia water from the top of the tower, and discharging water from the bottom of the tower (the flow rate is 36 m)³About 120mg/l of ammonia-containing nitrogen, about 4200mg/l of COD value and 10-11 of PH value) by a pump 4 to a wastewater adjusting tank 5 of a wastewater treatment device. The wastewater is sent to a flotation oil removal tank 7 by a pump 6 to remove light oil, and then automatically flows to a water distribution well 8 with the diameter of 40m³About/h of clean water and 150m from water distribution wells 13³The reflux water is mixed for about/h, and then the mixed wastewater (the PH value is 7.5-8.5) is sent into an anoxic pond 10 by a pump 9. NO contained in the return water₃Is converted here to N₂Then the wastewater flows into the aerobic tank 11 automatically. Here, the wastewater is thoroughly mixed with the return sludge from the sedimentation tank 12 under vigorous agitation by continuously introduced compressed air. The concentrated NaOH solution with concentration (weight percentage) of about 40% enters a dilute alkali tank 16, is diluted into dilute NaOH solution with concentration (weight percentage) of about 4% by clean water under the stirring of compressed air, and is continuously pumped by a pump 17 at a speed of about 0.4m³The total flow of the flow/h is respectively added into the aerobic tank at the sludge return inlet and the waste water inlet of the aerobic tank according to the proportion of 1: 2. Effluent of the aerobic tank (alkalinity is 80-160 mg/l, pH value is 6-7) automatically flows into a sedimentation tank 12, sludge is settled, sludge at the bottom automatically flows into a sludge well 14, then the sludge is sent back to the aerobic tank 11 by a pump 15 to be used as return sludge, clear liquid at the upper part automatically flows into a water distribution well 13, most of the clear liquid is used as return water to enter a water distribution well 8, and the rest of the clear liquid enters a post-treatment process 18 and is discharged as discharged water after being treated.

Claims

1. A method for treating ammonia-containing wastewater by taking sodium hydroxide as an alkali source is characterized by comprising the following steps:

(1) firstly mixing ammonia-containing wastewater with the concentration of less than or equal to 300mg/l with return water from a sedimentation tank, then feeding the mixture into an anoxic tank, controlling the pH value to be 7-8, and feeding effluent from the anoxic tank into an aerobic tank; respectively adding 3-5 wt% of NaOH dilute solution into a return sludge inlet and a wastewater inlet of an aerobic tank, wherein the total amount of the added NaOH dilute solution is that 100% NaOH with the amount of ammonia nitrogen contained in the ammonia-containing wastewater being 5.5-6 g per gram of ammonia nitrogen is added, the alkali adding amount of the two alkali adding points is distributed according to the ratio of 1: 1-3, namely the alkali adding amount at the return sludge inlet of the aerobic tank accounts for 25-50% of the total alkali adding amount of the aerobic tankThe alkali adding amount at the wastewater inlet of the aerobic tank accounts for 50-75% of the total alkali adding amount of the aerobic tank; the effluent alkalinity of the aerobic tank is CaCO₃Controlling the pH value of the effluent of the aerobic tank to be 80-160 mg/l, and controlling the pH value of the effluent of the aerobic tank to be 6-7; after the effluent of the aerobic tank is precipitated by a sedimentation tank, the activated sludge flows back into the aerobic tank, most of the effluent enters an anoxic tank as reflux water, and the rest of the effluent enters a post-treatment process and is discharged after being treated;

(2) ammonia distillation treatment is carried out on ammonia-containing wastewater with the concentration of more than 300mg/l before the ammonia-containing wastewater is treated in the steps, namely the wastewater passes through an ammonia distillation tower before entering an anoxic pond, and excessive NaOH is added into the ammonia distillation tower, so that inorganic carbon in a large amount of carbonate contained in the ammonia-containing wastewater can be converted into Na by the NaOH₂CO₃Is retainedin the wastewater without being converted into CO₂The ammonia is escaped and lost in the air, but the excess degree of the ammonia evaporation and the alkali addition is to ensure that the pH value in the anoxic pond is not more than 8.5; if the inorganic carbon fixed in the process can not meet the requirement of the microorganisms in the aerobic tank, namely the alkalinity of the effluent of the aerobic tank is CaCO₃The pH value of the effluent of the aerobic tank is not 6-7; respectively adding 3-5 wt% of NaOH dilute solution into a return sludge inlet and a wastewater inlet of the aerobic tank, wherein the alkali adding amount of the two alkali adding points is distributed according to the ratio of 1: 1-3, namely the alkali adding amount at the return sludge inlet of the aerobic tank accounts for 25-50% of the total alkali adding amount of the aerobic tank, and the alkali adding amount at the wastewater inlet of the aerobic tank accounts for 50-75% of the total alkali adding amount of the aerobic tank; the total addition amount of NaOH is based on the alkalinity of the effluent of the aerobic tank and CaCO₃The pH value is controlled to be 80-160 mg/l and 6-7.

2. The method of claim 1, wherein NaOH is added to the aerobic tank to react with CO₂The reaction takes place to form NaHCO₃And a small amount of Na₂CO₃。

3. The method of claim 1, wherein the added NaOH reacts with carbon dioxide in the air to form NaHCO under the condition that the aerobic pool is continuously aerated with the air₃And a small amount of Na₂CO₃To obtain inorganic carbon; or continuously adding 30-50% of NaOH required by the aerobic pool in any water storage pool in front of the anoxic pool in advance, and continuously adding CO-rich water₂The PH of the anoxictank should be less than 8.5.