Method for calculating oxygen demand of sequencing batch sewage treatment process

Abstract

The invention discloses a sequencing batch sewage treatment process oxygen demand calculation method, and belongs to the technical field of sewage treatment. The method comprises the following steps: step 1, determining the lowest water level Hmin, the highest water level Hmax, the influent BOD concentration So, the effluent BOD concentration Se, the influent Kjeldahl nitrogen concentration Nk, the effluent Kjeldahl nitrogen concentration Nke, the influent total nitrogen concentration Nt, the effluent total nitrogen concentration Nte, the influent nitrate nitrogen concentration No, the effluent nitrate nitrogen concentration Noe, the influent suspended matter concentration SS0 and the effluent suspended matter concentration SSe; 2, calculating an initial BOD concentration Sstart, an initial Kjeldahl nitrogen concentration Nk, start, an initial total nitrogen concentration Nt, start, an initial nitrate nitrogen concentration No, start and an initial suspended matter concentration SSstart; 3, the sludge discharge amount delta Xv is calculated; step 4, calculating equivalent flow Qe; and 5, calculating the oxygen demand O2 of the sewage. According to the method, the oxygen demand of the sequencing batch SBR reactor can be calculated, the corresponding air supply amount is calculated according to different designed aeration time, and the accuracy of air supply amount design is improved.

Description

Technical Field

[0001] The invention relates to a method for calculating oxygen demand in a sequencing batch sewage treatment process, and belongs to the technical field of sewage treatment. Background Art

[0002] Sewage treatment plants are large energy consumers and carbon emitters. The research and development of carbon reduction and carbon replacement technologies for sewage treatment plants is of great significance to my country's realization of dual carbon goals. The aeration system accounts for 50% of the energy consumption of the entire sewage treatment plant and is the main energy consumption unit. At the same time, aeration is also crucial for the degradation of pollutants. Insufficient aeration will cause the effluent of the sewage treatment plant to fail to meet the standards. Due to the contradiction between energy consumption and standard emissions, optimizing the aeration system is the top priority for the efficient operation of sewage treatment plants.

[0003] The sequencing batch reactor (SBR) is a wastewater treatment process with water inlet, aeration reaction, sedimentation, and decanting as the basic cycle. It does not require the establishment of an additional secondary sedimentation tank, saving construction land. Since it works intermittently, the water inlet flow of the sequencing batch reactor is not continuous, and the design of various parameters should be different from that of the continuous flow reactor.

[0004] However, in the current technical regulations, especially the calculation of aeration volume, SBR is not distinguished from continuous flow reactors. For example, in the "Technical Specifications for Sequencing Batch Activated Sludge Wastewater Treatment Engineering" (HJ 577-2010) issued by the Ministry of Ecology and Environment, the calculation of aeration volume is based on the designed continuous flow rate of sewage, which is obviously inconsistent with the actual operation of the sequencing batch reactor and will cause large deviations. The total amount of pollutants treated in each treatment cycle of the sequencing batch reactor (SBR) is similar, and the different designed aeration times obviously correspond to different air supply volumes, but this is not considered in the existing technology.

[0005] Based on the above background, this patent proposes a method for calculating oxygen demand in a sequencing batch wastewater treatment process. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for calculating oxygen demand in a sequencing batch sewage treatment process.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for calculating oxygen demand in a sequencing batch sewage treatment process, characterized in that it comprises the following steps:

[0009] Step 1: Determine the minimum water level H of the SBR reactor min , maximum water level H max , Influent BOD concentration S o , effluent BOD concentration S e , Influent Kjeldahl nitrogen concentration N k, Outlet Kjeldahl nitrogen concentration N ke , total nitrogen concentration in influent N t , effluent total nitrogen concentration N te , Influent nitrate nitrogen concentration N o , effluent nitrate nitrogen concentration N oe , inlet suspended solids concentration SS0 and outlet suspended solids concentration SS e ;

[0010] Step 2: Calculate the initial BOD concentration S of the sewage in the SBR reactor start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start , initial nitrate nitrogen concentration N o,start and initial suspended solids concentration SS start ;

[0011] Step 3: Calculate the amount of sludge discharged ΔX v ;

[0012] Step 4: Calculate the equivalent flow rate Q e ;

[0013] Step 5: Calculate the oxygen demand O2 of sewage.

[0014] The initial BOD concentration S in step 2 start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start , initial nitrate nitrogen concentration N o,start and initial suspended solids concentration SS start Calculate according to the following formula:

[0015]

[0016]

[0017] The amount of sludge discharged in step 3 ΔX v Calculate according to the following formula:

[0018] ΔX v =YV(S start -S e )-K d VX v T+fV(SS start -SS e ),

[0019] Where: Y is the sludge yield coefficient, V is the effective volume of the SBR reactor, K d is the attenuation coefficient, X vis the average mass concentration of volatile suspended solids in the mixed liquor of the reaction tank, f is the sludge conversion rate of suspended solids in the influent, and T is the designed single-cycle aeration time.

[0020] The equivalent flow rate Q in step 4 e Calculate according to the following formula:

[0021] Q e =V / T,

[0022] Where: V is the effective volume of the SBR reactor.

[0023] The oxygen demand O2 of the sewage in step 5 is calculated according to the following formula:

[0024] O2=0.001aQ e (S start -S e )-cΔX v +b[0.001Q e (N k,start -N ke )-0.12ΔX v ]-0.62b[0.001Q e (N t,start -N ke -N oe )-0.12ΔX v ],

[0025] In the formula: a is the oxygen equivalent of carbon, b is the amount of oxygen required to oxidize each kilogram of ammonia nitrogen, and c is the oxygen equivalent of bacterial cells.

[0026] The invention also includes a method for calculating the air supply amount of the aeration equipment, wherein the method for calculating the air supply amount of the aeration equipment comprises the following steps:

[0027] Step A: Calculate the oxygen demand of sewage under standard conditions O s :

[0028] O s =K O O2,

[0029]

[0030] Where: K o is the oxygen demand correction factor, C s is the saturated dissolved oxygen concentration in clean water under standard conditions, α is the ratio of the total oxygen transfer coefficient in the mixed solution to the total oxygen transfer coefficient in clean water, β is the ratio of the saturated dissolved oxygen value in the mixed solution to the saturated dissolved oxygen value in clean water, C sw is the actual saturated dissolved oxygen concentration of clean water, C O is the residual dissolved oxygen in the mixed solution, T is the design water temperature;

[0031] Step B: When using aeration, the oxygen demand of sewage under standard conditions O can be calculated according to the following formula: s , converted to the gas supply volume G under standard conditions s :

[0032]

[0033] Where: E A is the oxygen utilization rate of the aeration equipment.

[0034] E in step B A The value is 25%.

[0035] The beneficial effects of the present invention are that the oxygen demand of the SBR reactor can be calculated more accurately, and the corresponding air supply can be calculated according to different designed aeration times, thereby improving the accuracy of the air supply design, so as to match the aeration equipment with correct parameters and optimize the sewage treatment process. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0037] The method for calculating oxygen demand in a sequencing batch sewage treatment process of the present invention is characterized by comprising the following steps:

[0038] Step 1: Determine the minimum water level H of the SBR reactor min , maximum water level H max , Influent BOD concentration S o , effluent BOD concentration S e , Influent Kjeldahl nitrogen concentration N k , Outlet Kjeldahl nitrogen concentration N ke , total nitrogen concentration in influent N t , effluent total nitrogen concentration N te , Influent nitrate nitrogen concentration N o , effluent nitrate nitrogen concentration N oe , inlet suspended solids concentration SS0 and outlet suspended solids concentration SS e ;.

[0039] In the Technical Specifications for Sequential Batch Activated Sludge Wastewater Treatment Engineering (HJ 577-2010), the oxygen demand of sewage O2 is calculated according to the following formula:

[0040] O2=0.001aQ(S o -S e )-cΔX v +b[0.001Q(N k -N ke )-0.12ΔX v]-0.62b[0.001Q(N t -N ke -N oe )-0.12ΔX v ]

[0041] Where: Q is the sewage design flow rate (m 3 / d), S o is the influent BOD concentration (mg / L), S e is the effluent BOD concentration (mg / L), ΔX v is the amount of sludge discharged (kg / d), N k is the influent Kjeldahl nitrogen concentration (mg / L), N ke is the effluent Kjeldahl nitrogen concentration (mg / L), N t is the total nitrogen concentration in the influent (mg / L), N oe is the effluent nitrate nitrogen concentration (mg / L), a is the oxygen equivalent of carbon, b is the amount of oxygen required to oxidize each kilogram of ammonia nitrogen, and c is the oxygen equivalent of bacterial cells.

[0042] Therefore, the present invention needs to first determine the influent BOD concentration S of the SBR reactor in step 1. o , effluent BOD concentration S e , Influent Kjeldahl nitrogen concentration N k , Outlet Kjeldahl nitrogen concentration N ke , total nitrogen concentration in influent N t , effluent nitrate nitrogen concentration N oe and other parameters, and determine the daily sludge discharge ΔX of the SBR reactor v .

[0043] Step 2: Calculate the initial BOD concentration S of the sewage in the SBR reactor start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start , initial nitrate nitrogen concentration N o,start and initial suspended solids concentration SS start .

[0044] The initial BOD concentration S in step 2 start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start and initial nitrate nitrogen concentration N o,start Calculate according to the following formula:

[0045]

[0046] Since some of the treated sewage from the previous batch remains in the SBR reactor, the initial concentration of the SBR reactor is not the inlet concentration, but the concentration of the sewage after mixing inside it. Therefore, once all the parameters in step 1 are determined by the designer, S can be calculated according to step 2. start 、N k,start 、N t,start 、N o,start and SS start The value of .

[0047] Step 3: Calculate the amount of sludge discharged ΔX v .

[0048] The amount of sludge discharged in step 3 ΔX v Calculate according to the following formula:

[0049] ΔX v =YV(S start -S e )-K d VX v T+fV(SS start -SS e ),

[0050] Where: Y is the sludge yield coefficient, V is the effective volume of the SBR reactor, K d is the attenuation coefficient, X v is the average mass concentration of volatile suspended solids (MLVSS) in the reaction tank mixed liquor, f is the sludge conversion rate of suspended solids in the influent (MLSS / SS), and T is the designed single-cycle aeration time.

[0051] In the Technical Specification for Sequential Batch Activated Sludge Wastewater Treatment Engineering (HJ 577-2010), the sludge discharge volume ΔX v The calculation is based on the sewage design flow rate Q, which obviously does not conform to the characteristics of the SBR process. In SBR, water will no longer enter after reaching the highest water level in the reactor, which is very different from continuous flow. Directly applying the calculation method of the sludge discharge volume of continuous flow will result in a very large error. Therefore, the present invention considers the total sludge discharge volume required to meet the sewage treatment standards after the SBR reactor is filled with sewage. In the sludge discharge volume ΔX of the present invention, v In the calculation formula, the sewage design flow rate Q is replaced by the effective volume V of the SBR reactor, and it is assumed that organic matter, SS, etc. are completely converted into sludge in each sewage treatment cycle. This calculation formula can describe the sludge discharge in one cycle of the SBR reactor.

[0052] Step 4: Calculate the equivalent flow rate Q e .

[0053] The equivalent flow rate Q in step 4 eCalculate according to the following formula:

[0054] Q e =V / T,

[0055] Where: V is the effective volume of the SBR reactor.

[0056] Equivalent flow Q e is defined as the volume of wastewater treated per batch divided by the aeration time for that batch of wastewater.

[0057] Step 5: Calculate the oxygen demand O2 of sewage.

[0058] The oxygen demand O2 of the sewage in step 5 is calculated according to the following formula:

[0059] O2=0.001aQ e (S strt -S e )-cΔX v +b[0.001Q e (N k,start -N ke )-0.12ΔX v ]-0.62b[0.001Q e (N t,start -N ke -N oe )-0.12ΔX v ],

[0060] In the formula: a is the oxygen equivalent of carbon, b is the amount of oxygen required to oxidize each kilogram of ammonia nitrogen, and c is the oxygen equivalent of bacterial cells.

[0061] In the "Technical Specification for Sequencing Batch Activated Sludge Wastewater Treatment Engineering" (HJ 577-2010), the sewage oxygen demand O2 is calculated according to the sewage design flow rate Q, which obviously does not conform to the characteristics of the SBR process. In the SBR reactor, water will no longer enter after the water volume reaches the highest water level of the reactor, which is very different from the continuous flow. Directly applying the sewage oxygen demand calculation method of the continuous flow will result in a very large error. Here, consider the total sewage oxygen demand required to meet the sewage treatment standards after the SBR reactor is filled with sewage. The present invention replaces the sewage design flow rate Q in the sewage oxygen demand O2 calculation formula in the technical specification with the equivalent flow rate Q of the SBR reactor. e , replace the required pollutant influent concentration with the initial BOD concentration S calculated in step 2 start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start and initial nitrate nitrogen concentration N o,start .

[0062] The invention also includes a method for calculating the air supply amount of the aeration equipment, wherein the method for calculating the air supply amount of the aeration equipment comprises the following steps:

[0063] Step A: Calculate the oxygen demand of sewage under standard conditions O s :

[0064] O s =K O O2,

[0065]

[0066] Where: K o is the oxygen demand correction factor, C s is the saturated dissolved oxygen concentration in clean water under standard conditions, α is the ratio of the total oxygen transfer coefficient in the mixed solution to the total oxygen transfer coefficient in clean water, β is the ratio of the saturated dissolved oxygen value in the mixed solution to the saturated dissolved oxygen value in clean water, C sw is the actual saturated dissolved oxygen concentration of clean water, C O is the residual dissolved oxygen in the mixed solution, T is the design water temperature;

[0067] Step B: When using aeration, the oxygen demand of sewage under standard conditions O can be calculated according to the following formula: s , converted to the gas supply volume G under standard conditions s :

[0068]

[0069] Where: E A is the oxygen utilization rate of the aeration equipment.

[0070] According to the above method, the gas supply volume G of the SBR reactor can be accurately calculated. s , in order to configure appropriate aeration equipment.

[0071] E in step B A The value is 25%. A Generally, it is taken between 20% and 25%, and here we take the higher value of 25%.

[0072] Example:

[0073] The target sewage treatment plant adopts the CASS process in the SBR process, with a total of four parallel reaction tanks. The dissolved oxygen in all aerobic tanks is lower than 0.5mg / L for a long time, which is far lower than the 2mg / L required by the design standard. This causes the sewage treatment time of the plant to be too long and causes energy waste. The air supply of its aeration equipment is designed according to the standard formula, and the air supply of each reaction tank is 35m 3 / min.

[0074] The gas supply volume G is calculated according to the method of the present invention. s .

[0075] Step 1: The lowest water level H of the SBR reactor in the plant min and the highest water level H max According to the preliminary design, the water quality of the plant is: S0 = 150mg / L, S e =10mg / L, N k =30mg / L, N ke =5mg / L, N t =40mg / L, N te =15mg / L, N o =10mg / L, N oe =10mg / L, SS0=200mg / L, SS e =10mg / L.

[0076] Step 2: Calculate the initial BOD concentration S of the sewage in the SBR reactor start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start and initial nitrate nitrogen concentration N o,start . According to the calculation formula of the present invention, we can get

[0077] S start =49.57mg / L

[0078] N k,start =12.07mg / L

[0079] N t,start =22.07mg / L

[0080] N o,start =10.00mg / L

[0081] SS start =63.70mg / L

[0082] Step 3: Calculate the amount of sludge discharged ΔX v . According to the calculation formula of the present invention, ΔX is obtained. v =YV(S start -S e )-K d VX v T+fV(SS start -SS e ),

[0083] =113.72kg / d

[0084] The effective volume of the plant is V = 3300m 3 , according to the standard value, Y = 0.6, K d=0.06, f=0.6, designed sludge concentration is 4300mg / L, assuming that the single-cycle aeration time T=2h is designed for each sewage treatment cycle.

[0085] Step 4: Calculate the equivalent flow rate Q e .

[0086]

[0087] Step 5: Calculate the oxygen demand O2 of sewage.

[0088] Substitute the above calculation results into the public calculation:

[0089] O2=0.001αQ e (S start -S e )-cΔX v +b[0.001Q e (N k,start -N ke )-0.12ΔX v ]-0.62b[0.001Q e (N t,start -N ke -N oe )-0.12ΔX v ]

[0090] The α=1.47,b=4.57,c=1.42 in the formula are all the recommended values ​​in the technical specifications. The oxygen demand of the sewage in this plant is O2=2604.47kg / d.

[0091] The invention also includes a method for calculating the air supply amount of the aeration equipment, wherein the method for calculating the air supply amount of the aeration equipment comprises the following steps:

[0092] Step A: Calculate the oxygen demand of sewage under standard conditions O s :

[0093]

[0094] Take α=0.825, β=0.935, C s =C sw =9.17, C O =2, T = 25, then K o =1.50;

[0095] The oxygen demand of sewage under standard conditions can be calculated s =K O ·O2=3906.71kg / d.

[0096] Step B: When using aeration, the oxygen demand of sewage under standard conditions O can be calculated according to the following formula: s, converted to the gas supply volume G under standard conditions s :

[0097] In addition, E A The oxygen utilization rate of the aeration equipment is generally 20% to 25%, and here we take the higher value of 25%;

[0098]

[0099] It can be seen that the actual aeration volume (35m 3 / min) is lower than the theoretical aeration rate of 38.8 (m 3 / min). Once the aeration disc ages or the influent concentration fluctuates, the designed aeration time will not be able to meet the effluent requirements. The only option is to extend the aeration time, which makes the sewage treatment plant inflexible and wastes energy. In fact, the aeration efficiency of the plant is lower than 15%, and the ammonia nitrogen in the influent is often higher than 40mg / L. Therefore, the original designed air supply does not have enough safety redundancy, resulting in the sewage treatment plant's operating dissolved oxygen being lower than 0.5mg / L for a long time, and the aeration time being higher than 2h for a long time.

[0100] Comparative Example:

[0101] If the target sewage treatment plant in the above embodiment is designed according to the Technical Specification for Sequential Batch Activated Sludge Wastewater Treatment Engineering (HJ 577-2010), the design flow rate Q of the plant is 20000m 3 / d, the total effective volume of the four-stage reaction pool is 13200m 3 . Substitute into the formula:

[0102] O2=0.001αQ(S o -S e )-cΔX v +b[0.001Q(N k -N ke )-0.12ΔX v ]-0.62b[0.001Q(N t -N ke -N oe )-0.12ΔX v ]

[0103] ΔX v =YQ(S0-S e )-K d VX v +fQ(SS0-SS e ),

[0104] =554.40kg / d

[0105] The solution is:

[0106] O2=4081.5kg / d

[0107] The oxygen demand of sewage under standard conditions is:

[0108] O s =K O O2 = 6122.3 kg / d,

[0109] Similarly, the oxygen utilization rate of the aeration equipment E A Take 25% of the high value:

[0110]

[0111] Therefore, the total designed aeration volume of the four-stage reaction pool of the plant should be 60.7m 3 / min, the average aeration volume distributed to each reaction pool is 15.2m 3 / min, the current aeration volume has a larger safety margin than this value (the actual aeration volume of each reaction tank is 35m 3 / min).

[0112] Therefore, by comparison, it can be seen that the sewage oxygen demand G under standard conditions calculated according to the design specifications is s (15.2m 3 / min), which is significantly smaller than the oxygen demand of sewage under standard conditions calculated according to the present invention. s (38.8m 3 / min). Moreover, this deviation increases with the decrease of the single-cycle aeration time T designed for each sewage treatment cycle. For example, if the designed single-cycle aeration time T is only one hour, the sewage design aeration volume Gs=80.3m under the standard state obtained by the present invention is 3 / min, while the sewage design aeration volume Gs under standard conditions obtained according to the design specifications is still 15.2m 3 / min.

Claims

1. A method for calculating oxygen demand in a sequencing batch sewage treatment process, characterized in that: The following steps are involved: Step 1: Determine the minimum water level H of the SBR reactor min , maximum water level H max , Influent BOD concentration S o , effluent BOD concentration S e , Influent Kjeldahl nitrogen concentration N k , Outlet Kjeldahl nitrogen concentration N ke , total nitrogen concentration in influent N t , effluent total nitrogen concentration N te , Influent nitrate nitrogen concentration N o and effluent nitrate nitrogen concentration N oe , inlet suspended solids concentration SS0 and outlet suspended solids concentration SS e ; Step 2: Calculate the initial BOD concentration S of the sewage in the SBR reactor start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start , initial nitrate nitrogen concentration N o,start and initial suspended solids concentration SS start ; Step 3: Calculate the amount of sludge discharged ΔX v ; Step 4: Calculate the equivalent flow rate Q e ; Step 5: Calculate the oxygen demand O2 of sewage.

2. The method for calculating oxygen demand for a sequencing batch sewage treatment process according to claim 1, characterized in that: The initial BOD concentration S in step 2 start , initial Kjeldahl nitrogen concentration N k,start , initial total nitrogen concentration N t,start , initial nitrate nitrogen concentration N o,start and initial suspended solids concentration SS start Calculate according to the following formula:

3. The method for calculating oxygen demand for a sequencing batch wastewater treatment process according to claim 1, wherein: The amount of sludge discharged in step 3 ΔX v Calculate according to the following formula: ΔX v =YV(S start -S e )-K d VX v T+fV(SS start -SS e ), Where: Y is the sludge yield coefficient, V is the effective volume of the SBR reactor, K d is the attenuation coefficient, X v is the average mass concentration of volatile suspended solids in the mixed liquor of the reaction tank, f is the sludge conversion rate of suspended solids in the influent, and T is the designed single-cycle aeration time.

4. The method for calculating oxygen demand for a sequencing batch sewage treatment process according to claim 1, wherein: The equivalent flow rate Q in step 4 e Calculate according to the following formula: Q e =V / T, Where: V is the effective volume of the SBR reactor, and T is the designed single-cycle aeration time.

5. The method for calculating oxygen demand for a sequencing batch wastewater treatment process according to claim 1, wherein: The oxygen demand O2 of the sewage in step 5 is calculated according to the following formula: O2=0.001aQ e (S start -S e )-cΔX v +b[0.001Q e (N k,start -N ke ) -0.12ΔX v ]-0.62b[0.001Q e (N t,start -N ke -N oe ) -0.12ΔX v ], In the formula: a is the oxygen equivalent of carbon, b is the amount of oxygen required to oxidize each kilogram of ammonia nitrogen, and c is the oxygen equivalent of bacterial cells.

6. The method for calculating oxygen demand for a sequencing batch wastewater treatment process according to claim 1, wherein: The invention also includes a method for calculating the air supply amount of the aeration equipment, wherein the method for calculating the air supply amount of the aeration equipment comprises the following steps: Step A: Calculate the oxygen demand of sewage under standard conditions O s : THE s =K O ·O2, Where: K o is the oxygen demand correction factor, C s is the saturated dissolved oxygen concentration in clean water under standard conditions, α is the ratio of the total oxygen transfer coefficient in the mixed solution to the total oxygen transfer coefficient in clean water, β is the ratio of the saturated dissolved oxygen value in the mixed solution to the saturated dissolved oxygen value in clean water, C sw is the actual saturated dissolved oxygen concentration of clean water, C O is the residual dissolved oxygen in the mixed solution, T is the design water temperature; Step B: When using aeration, the oxygen demand of sewage under standard conditions O can be calculated according to the following formula: s , converted to the gas supply volume G under standard conditions s : Where: E A is the oxygen utilization rate of the aeration equipment.

7. The method for calculating oxygen demand for a sequencing batch wastewater treatment process according to claim 6, wherein: E in step B A The value is 25%.

Images