Method for evaluating total phosphorus in effluent of biological tank

Abstract

The invention relates to a biological tank effluent total phosphorus evaluation method which comprises the following steps: collecting an inflow water sample of a biological tank, water samples in different stages in the biological tank and an effluent water sample of the biological tank, and pretreating the water samples in different stages in the biological tank to obtain a sludge sample; respectively acquiring total phosphorus data in an inlet water sample and an outlet water sample and microflora composition data in the sludge sample in each stage; processing and analyzing the microflora composition data to obtain data of three bacteria in the sludge sample; establishing an evaluation system among the three types of bacteria, the total phosphorus content of the inlet water and the total phosphorus content of the outlet water according to the data of the three types of bacteria, the total phosphorus content of the inlet water and the total phosphorus content of the outlet water; acquiring data of three bacterial genus in a sludge sample corresponding to a to-be-evaluated effluent water sample and data of total phosphorus in inflow water, and evaluating the total phosphorus of the effluent water sample by using the evaluation system. The evaluation method can quickly evaluate the phosphorus removal effect of the biological tank and the total phosphorus in the effluent.

Description

Technical Field

[0001] The present application relates to sewage treatment technology, and in particular to a method for evaluating total phosphorus in effluent from a biological pond. Background Art

[0002] Phosphorus is the main element that causes eutrophication of water bodies. When the phosphorus content exceeds 0.02 mg / L, eutrophication will occur, changing the physical and chemical properties of water bodies, leading to deterioration of water quality, causing the death of aquatic organisms and increasing the cost of water purification. In recent years, total phosphorus has gradually replaced ammonia nitrogen as one of the main pollution indicators affecting surface water quality. In order to solve the increasingly acute problems of water environment pollution and eutrophication of water bodies, many countries and regions in the world have formulated strict phosphorus emission standards. The maximum allowable emission concentration of total phosphorus (in terms of P) stipulated in the Class A emission standard of my country's "Pollutant Emission Standards for Urban Wastewater Treatment Plants" (GB18918-2002) is 0.5 mg / L, and some regions implement stricter local standards.

[0003] Wastewater treatment plants mainly use a combination of biological and chemical phosphorus removal to remove phosphorus. In order to ensure that the effluent quality meets the standards, phosphorus removal agents are often added in excess, becoming one of the main sources of carbon emissions in the sewage treatment process. At present, the dosage of some water plants is determined by irregular small-scale tests, and is adjusted by feedback based on the total phosphorus content of the effluent from the water plant. The operation is cumbersome and has poor timeliness. Therefore, there is an urgent need for a method that can quickly assess the total phosphorus in the effluent. Summary of the invention

[0004] In order to overcome the above-mentioned defects, the present application provides a method for evaluating the total phosphorus in the effluent of a biological pond, which can quickly evaluate the phosphorus removal effect of the biological pond and the total phosphorus in the effluent, and can provide a reference basis for the dosage of the phosphorus removal agent.

[0005] The technical solution adopted by this application to solve its technical problems is:

[0006] A method for evaluating total phosphorus in biological pond effluent comprises the following steps:

[0007] Water sampling: Collect inlet water samples of the biological pool, water samples at different stages in the biological pool, and effluent samples of the biological pool, and pre-treat the water samples at different stages in the biological pool to obtain sludge samples;

[0008] Water sample analysis: Obtain the total phosphorus data in the influent water sample and the effluent water sample respectively as the influent total phosphorus and effluent total phosphorus, and test the microbial community composition data in the sludge samples at each stage;

[0009] Data processing: The data of microbial community composition are processed and analyzed to obtain data of three bacterial genera in the sludge sample, including phosphate-accumulating bacteria, glycogen-accumulating bacteria, and denitrifying phosphate-accumulating bacteria;

[0010] Establish an evaluation system: Based on the data of three bacterial genera, influent total phosphorus and effluent total phosphorus, establish an evaluation system between three bacterial genera, influent total phosphorus content and effluent total phosphorus content;

[0011] Evaluation of effluent total phosphorus: Obtain data on three bacterial genera in the sludge sample corresponding to the effluent sample to be evaluated and the total phosphorus data of the influent, and use the evaluation system to evaluate the total phosphorus of the effluent sample.

[0012] Optionally, the water samples at different stages in the biological pond include water samples in an anaerobic pond, an anoxic pond and an aerobic pond in the biological pond.

[0013] Optionally, the pretreatment process includes: filtering water samples at different stages of the biological pool using a 0.22 μm polyethersulfone filter membrane to obtain sludge samples.

[0014] Optionally, the sludge sample is subjected to 16S sequencing to obtain microbial community composition data, and the total phosphorus data of the inlet water sample and the outlet water sample are determined according to the national standard method GB11893-89.

[0015] Optionally, the polyphosphate-accumulating bacteria genus includes Accumulibacter and Tetrasphaera; the polysaccharide-accumulating bacteria genus includes Competibacter, Contendobacter and Defluviicoccus; the denitrifying polyphosphate-accumulating bacteria genus includes Dechloromonas, Thauera, Pseudomonas, Paracoccus, Acinetobacter, Bacillus, Arthrobacter, Enterobacter and Pseudoxanthomonas.

[0016] Optionally, obtaining the data on the composition of the microbial community in the sludge sample specifically includes: calculating the total amount of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the sludge samples of each stage of the biological pool, calculating the mean of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the entire biological pool based on the total amount, and calculating the proportional relationship between the mean values ​​of the three genera.

[0017] Optionally, the evaluation system includes:

[0018] The calculation formula for the total phosphorus removal rate of effluent is as follows:

[0019] R=∑4α·β

[0020] Where, R—total phosphorus removal rate;

[0021] α—coefficients corresponding to different bacterial genera;

[0022] β—the proportion of different bacterial genera in the three bacterial genera;

[0023] The calculation formula of total phosphorus in effluent is as follows:

[0024] P1=P2×(1-R)

[0025] Where, P1 is the total phosphorus in the effluent of the biological pool;

[0026] P2—Total phosphorus in influent.

[0027] The beneficial effects of this application are:

[0028] (1) In this application, the evaluation system, the total phosphorus in the influent water sample and the data of three bacterial genera in the sludge sample can be used to quickly evaluate the total phosphorus data in the effluent water sample of the biological pool, and the amount of phosphorus removal agent added can be determined based on the total phosphorus in the effluent water sample, thereby avoiding excessive addition of phosphorus removal agent, thereby reducing carbon emissions in the sewage treatment process.

[0029] (2) This application is based on the number of microbial species in the activated sludge system. In the same process of the same sewage treatment plant, the community structure is relatively stable. The data of a single microbial colony measurement has a long validity period, and can quickly evaluate the phosphorus removal effect of the biological pool and the total phosphorus in the effluent. It can cope with the situation where the online water quality detection equipment of the sewage treatment plant is missing or the equipment fails suddenly, and provide a reference for the dosage of the phosphorus removal agent, which helps to more accurately control the dosage, save drug consumption, and is conducive to the low-carbon operation of the water plant. This evaluation method is simple, efficient and highly operational. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] A method for evaluating total phosphorus in biological pond effluent comprises the following steps:

[0032] Water sampling: Collect inlet water samples of the biological pool, water samples at different stages in the biological pool, and effluent samples of the biological pool, and pre-treat the water samples at different stages in the biological pool to obtain sludge samples;

[0033] Water sample analysis: Obtain the total phosphorus data in the influent water sample and the effluent water sample respectively as the influent total phosphorus and effluent total phosphorus, and test the microbial community composition data in the sludge samples at each stage;

[0034] Data processing: The data of microbial community composition are processed and analyzed to obtain data of three bacterial genera in the sludge sample, including phosphate-accumulating bacteria, glycogen-accumulating bacteria, and denitrifying phosphate-accumulating bacteria;

[0035] Establish an evaluation system: Based on the data of three bacterial genera, influent total phosphorus and effluent total phosphorus, establish an evaluation system between three bacterial genera, influent total phosphorus content and effluent total phosphorus content;

[0036] Evaluation of total phosphorus in effluent: Obtain the data of three bacterial genera in the sludge sample corresponding to the effluent sample to be evaluated and the data of total phosphorus in the influent, and use the evaluation system to evaluate the total phosphorus in the effluent sample. Obtaining the data of three bacterial genera in the sludge sample corresponding to the effluent sample to be evaluated and the data of total phosphorus in the influent specifically means: using the influent sample corresponding to the effluent sample to be evaluated and the water samples at different stages in the biological pool, pre-treating the water samples at different stages in the biological pool to obtain the sludge sample, and determining the total phosphorus in the influent sample and the data of three bacterial genera in the sludge sample. Finally, bring the data of total phosphorus and three bacterial genera in the influent into the evaluation system to estimate the data of total phosphorus in the effluent sample.

[0037] In this application, the evaluation system, the total phosphorus in the influent water sample and the data of three bacterial genera in the sludge sample can be used to quickly evaluate the total phosphorus data in the effluent water sample of the biological pool, and the amount of phosphorus removal agent added can be determined based on the total phosphorus in the effluent water sample, so that excessive addition of phosphorus removal agent will not be caused, thereby reducing carbon emissions in the sewage treatment process. This application is based on the number of microbial genera in the activated sludge system. In the same process of the same sewage treatment plant, its community structure is relatively stable, and the data of a single microbial colony measurement has a long time validity. It can quickly evaluate the phosphorus removal effect of the biological pool and the total phosphorus in the effluent, and can cope with the situation where the sewage treatment plant has no online water quality detection equipment or equipment emergencies, and provide a reference for the dosage of phosphorus removal agent, which helps to more accurately control the dosage, save drug consumption, and is conducive to the low-carbon operation of the water plant. This evaluation method is simple, efficient and highly operational.

[0038] The water samples at different stages in the biological pool include the water samples in the anaerobic pool, the anoxic pool and the aerobic pool in the biological pool. The sampling points are determined according to the distribution of the anaerobic pool, the anoxic pool and the aerobic pool in the biological pool.

[0039] The pretreatment process includes: filtering water samples at different stages of the biological pool using a 0.22 μm polyethersulfone filter membrane to obtain sludge samples, separating the water samples into sludge samples and clean water using a polyethersulfone (PES) filter membrane, and analyzing the composition of the microbial community using the sludge samples.

[0040] The sludge sample was subjected to 16S sequencing to obtain the microbial community composition data, and the total phosphorus data of the inlet and outlet water samples were determined according to the national standard method GB11893-89.

[0041] The genus of polyphosphate-accumulating bacteria includes Accumulibacter and Tetrasphaera; the genus of polysaccharide-accumulating bacteria includes Competibacter, Contendobacter and Defluviicoccus; the genus of denitrifying polyphosphate-accumulating bacteria includes Dechloromonas, Thauera, Pseudomonas, Paracoccus, Acinetobacter, Bacillus, Arthrobacter, Enterobacter and Pseudoxanthomonas.

[0042] Obtaining the data on the composition of the microbial community in the sludge samples specifically includes: calculating the total amount of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the sludge samples of each stage of the biological pool, calculating the mean of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the entire biological pool based on the total amount, and calculating the proportional relationship between the mean values ​​of the three genera.

[0043] The evaluation system includes:

[0044] The calculation formula for the total phosphorus removal rate of effluent is as follows:

[0045] R=∑4α·β

[0046] Where, R—total phosphorus removal rate;

[0047] α—coefficients corresponding to different bacterial genera;

[0048] β—the proportion of different bacterial genera in the three bacterial genera;

[0049] The calculation formula of total phosphorus in effluent is as follows:

[0050] P1=P2×(1-R)

[0051] Where, P1 is the total phosphorus in the effluent of the biological pool;

[0052] P2—Total phosphorus in influent.

[0053] In this evaluation method, a calculation formula for the total phosphorus removal rate of the effluent is obtained, and the α value in the formula is derived. When it is necessary to evaluate the total phosphorus in the effluent of the biological pond in a certain period of time, the data of the influent total phosphorus P2 and the three bacterial genera, namely the β value, are obtained. The known α value is used, and the β value is substituted into the calculation formula for the total phosphorus removal rate of the effluent to calculate the total phosphorus removal rate R value. Then the R value and P2 are substituted into the calculation formula for the effluent total phosphorus to calculate the effluent total phosphorus P1.

[0054] Example: Taking the biological pool of a sewage treatment plant in the Yangtze River Delta region as the evaluation object, the technical solution of the present application is further explained;

[0055] 1. The establishment of the evaluation system for total phosphorus in biological pool effluent includes the following steps:

[0056] Step 1: Water sampling: Three groups of samples were collected from the sewage treatment plant, namely: samples from the first phase process in April, samples from the second phase process in April, and samples from the second phase process in July. Each group of samples included influent water samples, water samples at different stages in the biological pool, and effluent water samples. Water samples at different stages in the biological pool included water samples from the anaerobic pool, anoxic pool, and aerobic pool.

[0057] Step 2: Sludge samples: The water samples at different stages in the biological pool in the three groups of samples were filtered using a 0.22 μm polyethersulfone (PES) filter membrane to obtain sludge samples;

[0058] Step 3: Determination of total phosphorus: Determine the influent total phosphorus P2 and effluent total phosphorus P1 in the three groups of samples according to the national standard GB11893-89, and use the influent total phosphorus P2 and effluent total phosphorus P1 to calculate the total phosphorus removal rate. The total phosphorus removal rate is (P2-P1) / P2. The results are shown in Table 1.

[0059] Step 4: Microbial data: Obtain data of three bacterial genera in the sludge sample, including polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria. See below for details:

[0060] (1) Taking July of the second phase process as an example, the data analysis process of the three bacterial genera, that is, the process of obtaining the β value, takes the average value of the microbial data of all the pools in the biochemical reaction stage: the second phase process includes pre-anoxic, anaerobic I, anoxic I, aerobic I, anoxic II, and aerobic II. The water samples of these six pools are tested for microbial data and the average value is taken. Specifically, taking polyphosphate bacteria as an example, polyphosphate bacteria include Accumulibacter (A bacteria) and Tetrasphaera (T bacteria). Accumulibacter in the six pools has a β value of 0. The relative abundances of libacter were 0.095%, 0.092%, 0.108%, 0.059%, 0.123%, 0.072%, and the average relative abundance of A bacteria was 0.091%; the relative abundances of Tetrasphaera were 0.000%, 0.120%, 0.143%, 0.110%, 0.095%, 0.179%, and the average relative abundance of T bacteria was 0.108%; the average relative abundance of total polyphosphate bacteria was 0.199%;

[0061] The same method was used to obtain the average relative abundance of glycogen-accumulating bacteria and denitrifying phosphate-accumulating bacteria: 0.549% and 0.894%, respectively. The percentage of phosphate-accumulating bacteria in the three bacteria was (0.091% + 0.108%) / (0.199% + 0.549% + 0.894%) = 6% + 7% = 13%. Similarly, glycogen-accumulating bacteria accounted for 33%, and denitrifying phosphate-accumulating bacteria accounted for 54%, that is, the ratio of the three bacteria was 13:33:54, the β value of phosphate-accumulating bacteria was 0.13, the β value of glycogen-accumulating bacteria was 0.33, and the β value of denitrifying phosphate-accumulating bacteria was 0.54;

[0062] (2) The data of three bacterial genera in water samples of Phase I process in April and Phase II process in April were obtained using the same method.

[0063] In this embodiment, water samples were collected and analyzed at different times of different processes in the sewage treatment plant. The specific results are shown in Table 1;

[0064] Table 1 Analysis of water sample data in sewage treatment plant example

[0065]

[0066]

[0067] Step 5: Evaluation system: Establish an evaluation system between the data of the three bacterial genera in the biological pool, the total phosphorus in the inlet water and the total phosphorus in the outlet water, that is, the calculation formula for the removal rate of the total phosphorus in the outlet water:

[0068] R=Σ4α·β

[0069] In the formula, R—total phosphorus removal rate;

[0070] α—coefficients corresponding to different bacterial genera;

[0071] β—the proportion of different bacterial genera in the three bacterial genera;

[0072] The known β and R values ​​in Table 1 are used to fit the α value, and the rule of: polyphosphate bacteria coefficient * 2 + polysaccharide bacteria coefficient + denitrifying polyphosphate bacteria coefficient = 1 is followed; finally, the coefficient α values ​​of the three bacterial genera in the sewage treatment plant are obtained, as shown in Table 2;

[0073] Table 2 Coefficient α values ​​of three bacterial genera in sewage treatment plants

[0074] Phosphate Accumulating Bacteria Glycogen-accumulating bacteria Denitrifying phosphate-accumulating bacteria Alpha value 0.282 0.266 0.17

[0075] 2. Use the evaluation system to evaluate the total phosphorus in the biological pool effluent, including the following steps:

[0076] Step 1: Sampling of water samples to be evaluated: The samples of the first phase of the sewage treatment plant in July were collected, including the influent water sample and water samples at different stages in the biological pool. The water samples at different stages in the biological pool include water samples from the anaerobic pool, anoxic pool, and aerobic pool; the purpose is to evaluate the total phosphorus in the effluent of the biological pool based on the above samples;

[0077] Step 2: Sludge sample: The water samples at different stages in the biological pool in the sample are filtered using a 0.22 μm polyethersulfone (PES) filter membrane to obtain a sludge sample;

[0078] Step 3: Determination of total phosphorus in influent: The total phosphorus P2 in the influent water sample was determined according to the national standard method GB11893-89; the P2 result was 5.18 mg / L;

[0079] Step 4: Microbial data: Obtain data of three bacterial genera in the sludge sample, including polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria, as detailed below:

[0080] (1) This sample was collected in July of the first phase of the process. The data analysis process of the three genera, that is, the process of obtaining the β value, is as follows: take the average value of the microbial data of all pools in the biochemical reaction stage: the first phase of the process includes anaerobic pools, anoxic pools, and aerobic pools. Take water samples from the three pools to test the microbial data and take the average value. Specifically, take polyphosphate bacteria as an example. Polyphosphate bacteria include Accumulibacter (A bacteria) and Tetrasphaera (T bacteria). The relative abundance of Accumulibacter in the three pools is 0.082%, 0.077%, and 0.110%, respectively, and the average relative abundance of A bacteria is 0.090%; the relative abundance of Tetrasphaera is 0.138%, 0.108%, and 0.223%, respectively, and the average relative abundance of T bacteria is 0.156%; the average relative abundance of total polyphosphate bacteria is 0.246%, that is, the sum of the average abundance of A bacteria and the average abundance of T bacteria;

[0081] (2) The same method was used to obtain the average relative abundances of glycogen-accumulating bacteria and denitrifying phosphate-accumulating bacteria: 1.101% and 0.719%, respectively. The percentage of phosphate-accumulating bacteria in the three bacteria was (0.090% + 0.156%) / (0.246% + 1.101% + 0.719%) = 12%. Similarly, glycogen-accumulating bacteria accounted for 53%, and denitrifying phosphate-accumulating bacteria accounted for 35%, that is, the ratio of the three bacteria was 12:53:35, the β value of phosphate-accumulating bacteria was 0.12, the β value of glycogen-accumulating bacteria was 0.53, and the β value of denitrifying phosphate-accumulating bacteria was 0.35;

[0082] Step 5: Total phosphorus removal rate: Calculate using the calculation formula for total phosphorus removal rate of effluent, where the α value is known and the β value has been measured. The specific calculation process is as follows:

[0083] R=Σ4α·β

[0084] =4×(0.282×0.12+0.266×0.53+0.17×0.35)

[0085] =93.78%

[0086] Step 6: Total phosphorus in the biological pool effluent; use the effluent total phosphorus calculation formula to evaluate the total phosphorus P1 in the biological pool effluent. The specific calculation process is as follows:

[0087] P1=P2×(1-R)

[0088] =5.14×(1-0.9378)

[0089] =0.32mg / L

[0090] Step 7: Verification: The corresponding biological pool effluent samples were collected and the total phosphorus was determined. The total phosphorus in the biological pool effluent was 0.34 mg / L, which is very close to the predicted value of 0.32 mg / L. This evaluation method is feasible.

[0091] The specific test results of the water samples to be evaluated are shown in Table 3.

[0092] Table 3 Water sample data to be evaluated in sewage treatment plants

[0093]

[0094] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these modifications and improvements are all within the scope of protection of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for evaluating total phosphorus in biological pond effluent, characterized in that: The following steps are involved: Water sampling: Collect inlet water samples of the biological pool, water samples at different stages in the biological pool, and effluent samples of the biological pool, and pre-treat the water samples at different stages in the biological pool to obtain sludge samples; Water sample analysis: Obtain the total phosphorus data in the influent water sample and the effluent water sample respectively as the influent total phosphorus and effluent total phosphorus, and test the microbial community composition data in the sludge samples at each stage; Data processing: The data of microbial community composition are processed and analyzed to obtain data of three bacterial genera in the sludge sample, including phosphate-accumulating bacteria, glycogen-accumulating bacteria, and denitrifying phosphate-accumulating bacteria; Establish an evaluation system: Based on the data of three bacterial genera, influent total phosphorus and effluent total phosphorus, establish an evaluation system between three bacterial genera, influent total phosphorus content and effluent total phosphorus content; Evaluation of effluent total phosphorus: Obtain data on three bacterial genera in the sludge sample corresponding to the effluent sample to be evaluated and the total phosphorus data of the influent, and use the evaluation system to evaluate the total phosphorus of the effluent sample.

2. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: The water samples at different stages in the biological pool include the water samples in the anaerobic pool, the anoxic pool and the aerobic pool in the biological pool.

3. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: The pretreatment process includes: using a 0.22 μm polyethersulfone filter membrane to filter water samples at different stages of the biological pool to obtain sludge samples.

4. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: The sludge sample was subjected to 16S sequencing to obtain the microbial community composition data, and the total phosphorus data of the influent water sample and the effluent water sample were determined according to the national standard method GB11893-89.

5. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: The genus of polyphosphate-accumulating bacteria includes Accumulibacter and Tetrasphaera; the genus of polysaccharide-accumulating bacteria includes Competibacter, Contendobacter and Defluviicoccus; the genus of denitrifying polyphosphate-accumulating bacteria includes Dechloromonas, Thauera, Pseudomonas, Paracoccus, Acinetobacter, Bacillus, Arthrobacter, Enterobacter and Pseudoxanthomonas.

6. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: Obtaining the data on the composition of the microbial community in the sludge samples specifically includes: calculating the total amount of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the sludge samples of each stage of the biological pool, calculating the mean of polyphosphate-accumulating bacteria, polysaccharide-accumulating bacteria, and denitrifying polyphosphate-accumulating bacteria in the entire biological pool based on the total amount, and calculating the proportional relationship between the mean values ​​of the three genera.

7. The method for evaluating total phosphorus in biological pond effluent according to claim 1, characterized in that: The evaluation system includes: The calculation formula for the total phosphorus removal rate of effluent is as follows: R＝∑4α·β Where, R—total phosphorus removal rate; α—coefficients corresponding to different bacterial genera; β—the proportion of different bacterial genera in the three bacterial genera; The calculation formula of total phosphorus in effluent is as follows: P1=P2×(1-R) Where, P1 is the total phosphorus in the effluent of the biological pool; P2—Total phosphorus in influent.

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