Method for judging construction rationality of village and town sewage treatment station and matched pipe network

Abstract

The invention belongs to the field of municipal and environmental engineering, and relates to a method for judging construction rationality of rural sewage treatment stations and matched pipe networks. The invention provides two references for judging whether the rural sewage treatment station and the matched pipe network are put into operation to improve the surface water quality or not: one is that the evaluation section water quality under the influence of tail water discharge after the operation is better than the river assessment standard formulated by the local government; and secondly, the evaluation section water quality under the influence of tail water discharge after commissioning should be superior to the condition of sewage scattered discharge before commissioning, and a calculation method is specifically provided. According to the method provided by the invention, the possibility that the pollutants in the rural domestic sewage enter the surface water is simply measured and calculated, and whether the water quality of the surface water can be effectively improved by sewage treatment facilities and matched pipe networks built in rural areas or not can be conveniently judged.

Description

Technical Field

[0001] The invention belongs to the field of municipal engineering and environmental engineering, and particularly relates to a method for judging the rationality of construction of a village sewage treatment station and a supporting pipe network. Background Art

[0002] Municipal infrastructure such as sewage treatment plants / stations and supporting pipe networks collect and centrally treat domestic sewage, reduce the discharge of pollutants into surface water, and improve the quality of surface water. At present, the construction of municipal infrastructure in rural areas of my country is insufficient. In order to improve the rural living environment and surface water environment, the construction of municipal infrastructure such as sewage treatment plants and supporting pipe networks with smaller treatment scales is the key work in the field of rural revitalization and ecological environmental protection at present and in the future. Rural settlements are small in size and scattered in residence. The small-scale sewage treatment plants and scattered supporting pipe network systems implemented have high construction and operation and maintenance costs, and the tailwater discharge standards are low.

[0003] In addition to the scattered domestic sewage that directly enters the river in rural areas, the sewage that indirectly enters the river through ditches, farmland, forest land, etc. has a certain reduction in pollutant concentration due to interception and natural degradation. Moreover, the scattered sewage that enters the river directly or indirectly is relatively scattered and random in time and space. The construction of sewage treatment station network will transform the original scattered sewage into tail water that is still high in pollutant concentration after centralized treatment and is stably discharged into the river surface water. This transformation can theoretically reduce the total amount of pollutants entering the surface water, but it may increase the pollution load impact of the tail water discharge river section, which will not only fail to improve the surface water quality, but even pose a risk of water quality deterioration. However, before the construction of sewage treatment station network in rural areas, there is a lack of evaluation methods to evaluate whether the implementation of these municipal infrastructure can improve the surface water quality. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for determining the rationality of the construction of rural sewage treatment stations and supporting pipeline networks, which can quickly determine whether the newly built sewage treatment facilities and supporting pipeline networks in villages and towns with relatively dispersed populations can improve the surface water quality.

[0005] The technical purpose of the present invention is achieved through the following technical scheme: a method for judging the rationality of the construction of village and town sewage treatment stations and supporting pipe networks, characterized in that it includes:

[0006] S1 Determine the river water quality assessment section downstream of the proposed sewage treatment station network serving the rural area;

[0007] S2 There are two criteria for judging whether the operation of rural sewage treatment stations and supporting pipe networks can improve the surface water quality: first, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the assessment standard of the river formulated by the local government; second, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the condition of sewage discharge before operation. When the above two conditions are met, it is judged to be reasonable. When any one of the conditions is not met, it is judged to be unreasonable, that is:

[0008]

[0009] In the formula, It is the concentration of pollutants of type i in the evaluation section at the jth period under the influence of tailwater discharge after the sewage treatment station network is put into operation, in mg / L; i represents the pollutants mentioned in the local standards for water pollutant discharge of rural domestic sewage treatment facilities, including chemical dissolved oxygen, ammonia nitrogen, total nitrogen, total phosphorus, suspended solids, etc.; j represents the specific period, with four hours as one period; The limit value of the i-type pollutant in the river assessment standard (such as Class II, Class III, Class IV, etc. surface water grades) formulated by the local government, in mg / L; is the concentration of pollutant i at the evaluation section in the jth period under the influence of domestic sewage discharge before the sewage treatment station network is put into operation, in mg / L;

[0010] in, It can be obtained by consulting the information; and Further estimation is needed.

[0011] Preferably, the fecal sewage in rural domestic sewage that enters the surface water through scattered discharge is defined as "black water", and cooking, laundry and bathing are defined as "grey water". The water quality of the surface water in the water quality assessment section under the influence of scattered sewage discharge before the sewage treatment station network is put into operation is estimated. The calculation formula is as follows:

[0012]

[0013] In the formula, is the concentration of pollutant i in the upstream water of the rural river in the jth period, in mg / L; is the total amount of upstream water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 ;

[0014] in, and It can be obtained by consulting historical data, with winter data as the standard; and Further estimation is needed.

[0015] Preferably, the scattered ash water in rural areas mainly enters the river surface water through two paths: direct discharge and ditch discharge. For some farmers who are far away from the river and lack ditch connection, their scattered ash water can be considered unable to enter the river. The calculation formula is:

[0016]

[0017] In the formula, and are the total amount of gray water entering the river through direct discharge during period j, in m 3 ; and The calculation formula is:

[0018]

[0019] In the formula, e 直 V is the total number of people with direct greywater discharge in the area, in units; 排污定额 The amount of grey water used by rural residents in their normal 24-hour life, in L, is generally 120-180 L, and can be selected based on the specific rural economic development level, water use habits, etc.; h j is the proportion of greywater discharge in the jth period of a day. Greywater discharge generally occurs at two peaks: 06:30-10:30 in the morning and 17:30-21:30 in the evening. j Take 40%;

[0020]

[0021] In the formula, and are the total amount of grey water discharged into the river through the concrete / mortar-laid stone channel and earth channel during period j, in m 3 ;e 砼渠 and e 土渠 are the total number of people discharged into the river through concrete / mortar-laid stone channels and earth channels in the region, in units of individuals; ρ is the retention coefficient, which indicates the proportion of gray water that passes through the earth channel and enters the surface water after being lost due to infiltration, evaporation, etc., and can be selected according to the length, slope, and vegetation coverage of the earth channel;

[0022] Calculate according to the following formula:

[0023]

[0024] In the formula, and are the concentrations of pollutants i when they enter the river channel directly, through concrete / mortar-laid stone channels, and earth channels, respectively. It can be obtained by consulting the specifications; when the gray water flows through the ditch and is discharged into the surface water, some pollutants will be intercepted by the ditch. and The calculation formula is:

[0025]

[0026] In the formula, γ 砼 and γ 土 are the proportions of i pollutants that can enter the surface water of the river under the influence of concrete / mortar-laid stone canals and earth canals. The interception efficiency of pollutants is affected by factors such as ditch material, vegetation coverage, and hydraulic retention time. The maximum interception efficiency of the ditch for pollutants is 50%-60%. Therefore, γ 砼 and γ 土 Depending on the ditch conditions, the value ranges from 50% to 100%.

[0027] Preferably, rural black water mainly enters river surface water through two paths: direct discharge and septic tank leakage. The calculation formula is:

[0028]

[0029] In the formula, and are the total amount of black water entering the river through direct discharge and septic tank leakage during period j, in m 3 ;in, and The calculation formula is:

[0030]

[0031] In the formula, V is the total number of people discharged directly into black water in the area, in units; 排泄定额 The black water volume of rural residents in 24 hours, in L, usually 2L; is the proportion of black water discharge in the jth period of a day. Black water discharge is generally concentrated in breakfast (06:30-10:30), which is the period that needs special attention. Take 30%;

[0032]

[0033] Where K is the leakage coefficient, in m / d, which is selected according to the soil conditions between the septic tank and the river channel, and can be between 0.005 and 1.0; Δh is the height difference between the septic tank liquid level and the winter base flow water level of the river, in m; A is the cross-sectional area of ​​the septic tank where leakage occurs, in m 2 ; When the outer wall is made of soil, A can be the cross-sectional area of ​​the outer wall of the septic tank facing the river; when the outer wall is made of stone, brick or concrete, A can be the crack area of ​​the outer wall of the septic tank facing the river; L is the distance between the septic tank and the river; t j 4 hours, which is consistent with the above-mentioned sewage discharge calculation period;

[0034] The calculation formula is:

[0035]

[0036] In the formula, is the concentration of pollutant i in feces of rural residents (adults), in mg / L; is the concentration of pollutants that can enter the river through leakage from the septic tank, in mg / L, and the calculation formula is:

[0037]

[0038] In the formula, is the concentration of pollutant i in the septic tank, in mg / L; α is the interception coefficient of soil for pollutant i; and α can be obtained by consulting relevant literature.

[0039] Preferably, after the sewage treatment station network is put into operation, tail water is an important source of pollution for river surface water, and also contains some domestic sewage that has not been collected and treated centrally; therefore, the water quality status of the surface water in the water quality assessment section under the influence of tail water discharge is calculated as follows:

[0040]

[0041] In the formula, is the concentration of pollutant i in tail water discharged during period j, in mg / L; is the total amount of tailwater in period j, in m 3 ; It is the sum of i types of pollutants discharged into river surface water by domestic sewage that has not been collected and treated centrally during period j, in mg; is the total amount of domestic sewage discharged into river surface water that is not centrally collected and treated during period j, in m 3 ;

[0042] in, and Can be selected according to the design standards of sewage treatment plants; resemblance, There are significant seasonal changes: low temperatures will reduce the activity of microorganisms in sewage treatment facilities, making the discharge standards for agricultural sewage treatment tail water In winter there are higher limits; and The above changes in winter will lead to The increase in tailwater makes the evaluation section under the influence of tailwater in the most unfavorable situation. Therefore, the evaluation of whether the operation of sewage treatment station network can improve the surface water quality should select the evaluation section in winter as the evaluation object.

[0043] Compared with the existing method, the present invention has the following beneficial effects:

[0044] 1. The present invention realizes a simple calculation of the possibility of pollutants in rural domestic sewage entering surface water.

[0045] 2. The present invention can more conveniently determine whether the sewage treatment facilities and supporting pipe networks built in rural areas can effectively improve the surface water quality. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with specific implementation modes.

[0047] This embodiment provides a method for determining the rationality of construction of a rural sewage treatment station and a supporting pipe network, including:

[0048] S1: This invention determines the rationality of the construction of rural sewage treatment stations and supporting pipe networks from the perspective of improving surface water quality. First, the river water quality evaluation section needs to be clarified. The water quality evaluation section should be located downstream of the rural area served by the proposed sewage treatment station network to ensure that the scattered sewage in the service area and the tail water after construction can be fully controlled and not affected by other external water.

[0049] S2: There are two criteria for judging whether the operation of rural sewage treatment stations and supporting pipe networks can improve the surface water quality: first, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the assessment standard of the river formulated by the local government; second, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the condition of sewage discharge before operation, that is:

[0050]

[0051] In the formula, It is the concentration of pollutants of type i in the evaluation section at the jth period under the influence of tailwater discharge after the sewage treatment station network is put into operation, in mg / L; i represents the pollutants mentioned in the local standards for water pollutant discharge of rural domestic sewage treatment facilities, including chemical dissolved oxygen, ammonia nitrogen, total nitrogen, total phosphorus, suspended solids, etc.; j represents the specific period, with four hours as one period; The limit value of the i-type pollutant in the river assessment standard (such as Class II, Class III, Class IV, etc. surface water grades) formulated by the local government, in mg / L; It is the concentration of pollutant i in the evaluation section in the jth period under the influence of domestic sewage discharge before the sewage treatment station network is put into operation, in mg / L.

[0052] in, It can be obtained by consulting relevant documents and materials; and Further estimation is needed.

[0053] S3: Rural domestic sewage that enters surface water through bulk discharge is mainly divided into "black water" (fecal sewage) and "grey water" (cooking, laundry and bathing sewage). The water quality of the surface water in the water quality assessment section under the influence of bulk discharge of sewage before the sewage treatment station network is put into operation is estimated. The calculation formula is as follows:

[0054]

[0055] In the formula, is the concentration of pollutant i in the upstream water of the rural river in the jth period, in mg / L; is the total amount of upstream water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 .

[0056] in, and It can be obtained by consulting historical data, with winter data as the standard. In addition to being affected by rainfall-runoff effects, and There is little variation between times of day, but there is significant seasonal variation: as rainfall decreases in winter, the amount of water and pollutants entering the river decreases, so and In winter, it is the lowest in the whole year and is relatively stable. and It reflects the surface water environmental capacity. In rural areas where pollutant concentrations are low and water volume changes dramatically, The impact on environmental capacity is more significant, therefore, the water environment capacity is minimal in winter.

[0057] and Further estimation is needed.

[0058] S4: Rural ash water mainly enters river surface water through direct discharge and ditch. For some farmers who are far away from the river and lack ditch connection, their ash water can be considered unable to enter the river. The calculation formula is:

[0059]

[0060] In the formula, and are the total amount of gray water entering the river through direct discharge during period j, in m 3 ; and The calculation formula is:

[0061]

[0062] In the formula, e 直 V is the total number of people with direct greywater discharge in the area, in units; 排污定额 The normal amount of domestic sewage (grey water) produced by rural residents (adults) in 24 hours, in L, is obtained according to relevant standards and is generally 120-180 L. It can be selected based on the specific rural economic development level, water use habits, etc.; h j is the proportion of greywater discharge in the jth period of a day. Greywater discharge is generally concentrated in the morning (06:30-10:30) and evening (17:30-21:30), which are the periods that need special attention. j 40% is acceptable.

[0063]

[0064] In the formula, and are the total amount of grey water discharged into the river through the concrete / mortar-laid stone channel and earth channel during period j, in m 3 ;e 砼渠 and e 土渠are the total number of people discharged into the river through concrete / mortar-laid stone channels and earth channels in the region, in units of individuals; ρ is the retention coefficient, which indicates the proportion of gray water that passes through the earth channel and enters the surface water after being lost due to infiltration, evaporation, etc., and can be selected according to the length of the earth channel, slope, and vegetation coverage; h j Same as above.

[0065] S5: The calculation formula is:

[0066]

[0067] In the formula, and are the concentrations of pollutants i when they enter the river channel directly, through concrete / mortar-laid stone channels, and earth channels, respectively. This can be obtained by consulting relevant specifications and literature; when gray water flows through ditches and is discharged into surface water, some pollutants will be intercepted by the ditches. and The calculation formula is:

[0068]

[0069]

[0070] In the formula, γ 砼 and γ 土 are the proportions of i pollutants that can enter the surface water of the river under the influence of concrete / mortar-laid stone canals and earth canals. The interception efficiency of pollutants is affected by factors such as ditch material, vegetation coverage, and hydraulic retention time. Relevant literature shows that the maximum interception efficiency of ditches for pollutants is 50%-60%. Therefore, γ 砼 and γ 土 According to the ditch conditions, the value is between 50%-100%.

[0071] S6: Rural black water discharge mainly enters river surface water through two paths: direct discharge and septic tank leakage. For some farmers far away from the river (septic tank is more than 15 meters away from the river), their black water discharge can be considered unable to enter the river. The calculation formula is:

[0072]

[0073] In the formula, and are the total amount of black water entering the river through direct discharge and septic tank leakage during period j, in m 3 ; and The calculation formula is:

[0074]

[0075] In the formula, V is the total number of people discharged directly into black water in the area, in units; 排泄定额 It is the amount of feces (black water) of rural residents (adults) in 24 hours, in L, obtained according to relevant standards, generally 2L; is the proportion of black water discharge in the jth period of a day. Black water discharge is generally concentrated in breakfast (06:30-10:30), which is the period that needs special attention. 30% is also available.

[0076]

[0077] Where K is the leakage coefficient, in m / d, which is selected according to the soil conditions between the septic tank and the river channel, and can be between 0.005 and 1.0; Δh is the height difference between the septic tank liquid level and the winter base flow water level of the river, in m; A is the cross-sectional area of ​​the septic tank where leakage occurs, in m 2 When the outer wall is made of soil, A can be the cross-sectional area of ​​the outer wall of the septic tank facing the river; when the outer wall is made of stone, brick or concrete, A can be the crack area of ​​the outer wall of the septic tank facing the river. L is the distance between the septic tank and the river. j It is 4 hours, which is consistent with the above-mentioned sewage discharge calculation period.

[0078] S7: The calculation formula is:

[0079]

[0080] In the formula, is the concentration of pollutant i in feces of rural residents (adults), in mg / L, which can be obtained by consulting relevant literature; is the concentration of pollutants that can enter the river through leakage from the septic tank, in mg / L, and the calculation formula is:

[0081]

[0082] In the formula, is the concentration of pollutant i in the septic tank, in mg / L; α is the interception coefficient of soil for pollutant i. and α can be obtained by referring to relevant literature.

[0083] S8: After the sewage treatment station network is put into operation, tailwater is an important source of pollution for river surface water, and also contains some domestic sewage that has not been collected and treated centrally. Therefore, the water quality status of the surface water in the water quality assessment section under the influence of tailwater discharge is calculated as follows:

[0084]

[0085] In the formula, is the concentration of pollutant i in tail water discharged during period j, in mg / L; is the total amount of tailwater in period j, in m 3 ; It is the sum of i types of pollutants discharged into river surface water by domestic sewage that has not been collected and treated centrally during period j, in mg; is the total amount of domestic sewage discharged into river surface water that is not centrally collected and treated during period j, in m 3 .

[0086] in, and It can be selected according to the design standards of sewage treatment plants. resemblance, There are significant seasonal changes: low temperatures will reduce the activity of microorganisms in sewage treatment facilities, making the discharge standards for agricultural sewage treatment tail water There are higher limits in winter. and The above changes in winter will lead to The increase in tailwater makes the evaluation section under the influence of tailwater in the most unfavorable situation. Therefore, the evaluation of whether the operation of sewage treatment station network can improve the surface water quality should select the evaluation section in winter as the evaluation object.

[0087] and It can be obtained through the calculation formulas in S3 to S7.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for determining the rationality of construction of village and town sewage treatment stations and supporting pipe networks, characterized in that: include: S1 Determine the river water quality assessment section downstream of the proposed sewage treatment station network serving the rural area; S2 There are two criteria for judging whether the operation of rural sewage treatment stations and supporting pipe networks can improve the surface water quality: first, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the assessment standard of the river formulated by the local government; second, the water quality of the evaluation section under the influence of tail water discharge after operation should be better than the condition of sewage discharge before operation. When the above two conditions are met, it is judged to be reasonable. When any one of the conditions is not met, it is judged to be unreasonable, that is: In the formula, It is the concentration of pollutants of type i in the evaluation section at the jth period under the influence of tailwater discharge after the sewage treatment station network is put into operation, in mg / L; i represents the pollutants mentioned in the local standards for water pollutant discharge of rural domestic sewage treatment facilities, including chemical dissolved oxygen, ammonia nitrogen, total nitrogen, total phosphorus, suspended solids, etc.; j represents the specific period, with four hours as one period; The limit value of the i-type pollutant in the river assessment standard (such as Class II, Class III, Class IV, etc. surface water grades) formulated by the local government, in mg / L; It is the concentration of pollutant i in the evaluation section in the jth period under the influence of domestic sewage discharge before the sewage treatment station network is put into operation, in mg / L.

2. A method for determining the rationality of construction of village and town sewage treatment stations and supporting pipe networks according to claim 1, characterized in that: The fecal sewage in rural domestic sewage that enters the surface water through scattered discharge is defined as "black water", and cooking, laundry and bathing are defined as "grey water". The water quality of the surface water in the water quality assessment section under the influence of scattered sewage discharge before the sewage treatment station network is put into operation is estimated. The calculation formula is as follows: In the formula, is the concentration of pollutant i in the upstream water of the rural river in the jth period, in mg / L; is the total amount of upstream water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 ; is the sum of i pollutants in the gray water entering the river surface water during the jth period, in mg; z represents various sources; is the total amount of gray water entering the river surface water in the jth period, in m 3 ; in, It can be obtained by consulting historical data, with winter data as the standard; and Further estimation is needed.

3. A method for determining the rationality of construction of village and town sewage treatment stations and supporting pipe networks according to claim 1, characterized in that: Rural ash water discharge mainly enters river surface water through direct discharge and ditch. For some farmers who are far away from the river and lack ditch connection, their ash water discharge can be considered unable to enter the river. The calculation formula is: In the formula, and are the total amount of gray water entering the river through direct discharge during period j, in m 3 ; and The calculation formula is: In the formula, e 直 V is the total number of people with direct greywater discharge in the area, in units; 排污定额 The amount of grey water used by rural residents in their normal 24-hour life, in L, is generally 120-180 L, and can be selected based on the specific rural economic development level, water use habits, etc.; h j is the proportion of greywater discharge in the jth period of a day. Greywater discharge generally occurs at two peaks: 06:30-10:30 in the morning and 17:30-21:30 in the evening. j Take 40%; In the formula, and are the total amount of grey water discharged into the river through the concrete / mortar-laid stone channel and earth channel during period j, in m 3 ; e 砼渠 and e 土渠 are the total number of people discharged into the river through concrete / mortar-laid stone channels and earth channels in the region, in units of individuals; ρ is the retention coefficient, which indicates the proportion of gray water that passes through the earth channel and enters the surface water after being lost due to infiltration, evaporation, etc., and can be selected according to the length, slope, and vegetation coverage of the earth channel; Calculate according to the following formula: In the formula, and are the concentrations of pollutants i when they enter the river channel directly, through concrete / mortar-laid stone channels, and earth channels, respectively. It can be obtained by consulting the specifications; when the gray water flows through the ditch and is discharged into the surface water, some pollutants will be intercepted by the ditch. and The calculation formula is: In the formula, γ 砼 and γ 土 are the proportions of i pollutants that can enter the surface water of the river under the influence of concrete / mortar-laid stone canals and earth canals. The interception efficiency of pollutants is affected by factors such as ditch material, vegetation coverage, and hydraulic retention time. The maximum interception efficiency of the ditch for pollutants is 50%-60%. Therefore, γ 砼 and γ 土 Depending on the ditch conditions, the value ranges from 50% to 100%.

4. A method for determining the rationality of construction of village and town sewage treatment stations and supporting pipe networks according to claim 1, characterized in that: Rural black water discharge mainly enters river surface water through two pathways: direct discharge and septic tank leakage. The calculation formula is: In the formula, and are the total amount of black water entering the river through direct discharge and septic tank leakage during period j, in m 3 ;in, and The calculation formula is: In the formula, V is the total number of people discharged directly into black water in the area, in units; 排泄定额 The black water volume of rural residents in 24 hours, in L, usually 2L; is the proportion of black water discharge in the jth period of a day. Black water discharge is generally concentrated in breakfast (06:30-10:30), which is the period that needs special attention. Take 30%; Where K is the leakage coefficient, in m / d, which is selected according to the soil conditions between the septic tank and the river channel, and can be between 0.005 and 1.0; Δh is the height difference between the septic tank liquid level and the winter base flow water level of the river, in m; A is the cross-sectional area of ​​the septic tank where leakage occurs, in m 2 ; When the outer wall is made of soil, A is the cross-sectional area of ​​the outer wall of the septic tank facing the river; when the outer wall is made of stone, brick or concrete, A is the crack area of ​​the outer wall of the septic tank facing the river; L is the distance between the septic tank and the river; t j 4 hours, which is consistent with the above-mentioned sewage discharge calculation period; The calculation formula is: In the formula, is the concentration of pollutant i in feces of rural residents (adults), in mg / L; is the concentration of pollutants that can enter the river through leakage from the septic tank, in mg / L, and the calculation formula is: In the formula, is the concentration of pollutant i in the septic tank, in mg / L; α is the interception coefficient of soil for pollutant i; and α can be obtained by consulting relevant literature.

5. A method for determining the rationality of construction of village and town sewage treatment stations and supporting pipe networks according to claim 1, characterized in that: After the sewage treatment station network is put into operation, tailwater is an important source of pollution for river surface water, and also contains some domestic sewage that has not been collected and treated centrally; therefore, the water quality status of the surface water in the water quality assessment section under the influence of tailwater discharge is calculated as follows: In the formula, is the concentration of pollutant i in tail water discharged during period j, in mg / L; is the total amount of tailwater in period j, in m 3 ; It is the sum of i types of pollutants discharged into river surface water by domestic sewage that has not been centrally collected and treated during period j, in mg; is the total amount of domestic sewage discharged into river surface water that is not collected and treated centrally during period j, in m 3 ; in, and Can be selected according to the design standards of sewage treatment plants; resemblance, There are significant seasonal changes: low temperatures will reduce the activity of microorganisms in sewage treatment facilities, making the C i水 尾 In winter there are higher limits; and The above changes in winter will lead to The increase in tailwater makes the evaluation section under the influence of tailwater in the most unfavorable situation. Therefore, the evaluation of whether the operation of sewage treatment station network can improve the surface water quality should select the evaluation section in winter as the evaluation object.

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