JPH0389993A - Method for controlling concentration of phosphorus in waste water - Google Patents

Abstract

PURPOSE:To control the concn. of phosphorus in treated water constant by calculating the estimated quantity value of the phosphorus removing quantity of this water treatment process on the basis of the change of the detected phosphorus concentration value of treated water and controlling the addition amount of a flocculant so as to eliminate the fluctuation of phosphorus removing quantity. CONSTITUTION:A flocculant injection point 2 is provided to an aeration tank 1 and a detection point 4 and a treated water outflow port 5 are provided to a final sedimentation tank and phosphorus in the water to be inspected collected at the detection point 4 is monitored by a colorimetric phosphorus detector 6 and a concn. signal is inputted to a program type operational controller 7. The program type operational controller 7 sends a pump control signal to a flocculant injection pump 8 so as to inject an estimated amount of a flocculant and a controlled amount of the flocculant is sent to the flocculant injection point 2 from a flocculant storage tank 9 by the flocculant injection pump 8. Even when there are the difference in biological dephosphorizing capacity and the difference in natural environment, a proper amount of the flocculant can be always supplied and, therefore, phosphorus in waste water can be effectively removed by the min. injection of the flocculant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a treatment method for water treatment, particularly wastewater treatment, in which phosphorus is removed from treated water using a chemical coagulant, or a biological water treatment method;
This invention relates to a method of efficiently removing phosphorus from wastewater by adding a flocculant to remove phosphorus from treated water in the so-called activated sludge method and its various modifications using an appropriate amount of flocculant depending on the phosphorus concentration of the treated water. .

[Conventional technology]

Conventionally, the so-called anaerobic/aerobic activated sludge method, which utilizes biological dephosphorization, has been used to treat phosphorus in wastewater from domestic and industrial sources. Because sufficient dephosphorization function may not be obtained due to changes in the concentration of B○D (biological oxygen demand) in Various modified methods of the activated sludge method for removing phosphorus, such as the flocculant-added circulating nitrification-denitrification method and the flocculant-added activated sludge method, have also been carried out.

[Problem to be solved by the invention]

The above-mentioned activated sludge method combined with the addition of a flocculant has the disadvantage that the amount of sludge generated increases, so biological dephosphorization is suitable for sewage treatment plants. It is believed that there are. However, in biological dephosphorization methods, when the BOD concentration required by living organisms decreases, the dephosphorization function decreases and phosphorus removal becomes unstable.

Therefore, research has been conducted on a method that combines this biological dephosphorization method with the dephosphorization effect of a flocculant, but it is extremely difficult to determine how much flocculant to add to the treated water, which has an unstable phosphorus content. That was the point.

To solve this problem, either predict the degree of removal by biological dephosphorization and add an appropriate amount of flocculant, or analyze the treatment results of the treated water and use this value to determine the appropriate amount of flocculant. One method is to determine the amount of addition, but the former method is impossible at present because the mechanism of biological dephosphorization has not been fully elucidated, and the latter method:
It takes about 1 hour to analyze the water treatment results, and it takes a considerable amount of time to obtain the results of adjusting the flocculant addition. could not be added. In addition, when adding a flocculant to a process using activated sludge, it was thought that the phosphorus removal effect of the added flocculant would take place after the concentration of flocculant in the activated sludge increased. If you try to suppress this by changing the amount of coagulant injected in response to time fluctuations, you will have to increase or decrease a huge amount of coagulant.
It was considered impractical.

In a water treatment method by adding a flocculant, the present invention predicts the excess or deficiency of the amount of phosphorus removed in the entire process from the phosphorus concentration of the treated water by selecting an appropriate injection position, and then selects the appropriate amount. The object of the present invention is to provide a method for controlling the phosphorus concentration of treated water to a constant level by adding a flocculant to compensate for excess or deficiency in the amount of phosphorus removed in the process.

[Means to solve the problem]

The present invention removes soluble phosphorus from wastewater by chemical coagulation,
Or, in a water treatment process that uses a combination of biological action and chemical flocculation, the amount of flocculant to be added is determined based on the change in the phosphorus concentration value of the treated water detected by a phosphorus detector. This is a method for appropriately controlling the phosphorus concentration of wastewater by calculating the predicted value of excess or deficiency in the amount of phosphorus removed, and controlling the amount of coagulant added so as to eliminate excess or deficiency in the amount of phosphorus removed.

Although the wastewater of the present invention is mainly used for domestic wastewater containing a large amount of soluble phosphorus, it can also be used for other wastewater such as industrial wastewater.

The method of the present invention is used in a wastewater treatment process that uses chemical flocculation of wastewater or a combination of biological and chemical flocculation. In particular, even better effects can be obtained if applied to a wastewater treatment process that uses both biological action and chemical flocculation action.

The method of the present invention uses a phosphorus detector such as a colorimetric method, an ion electrode method, or a plasma emission spectrometry detector, particularly a colorimetric detector, to treat water in the final stage of a wastewater treatment system. , the phosphorus concentration (PO) at the beginning of the control cycle is measured, and the phosphorus concentration (P
l) and the rate of change in phosphorus concentration over a certain period of time (d) d
= (P + Po) / b is calculated, and based on this rate of change, the predicted value of phosphorus concentration (P
c) as a function of the rate of change d and the predicted time C Pc = f (d, c)
Calculated by When the function f(d, c) is the simplest, Pc=P, +d−c.

Next, the difference (e) between the calculated value (Pc) obtained as above and the target value (S) of the phosphorus concentration to be controlled, e=P
Calculate c-3 and calculate the appropriate amount of phosphorus flocculant, e.g. aluminum sulfate (i) by increasing or decreasing i=g(e) inject.

This phosphorus concentration detection, calculation, and increase/decrease in the amount of coagulant to be injected can all be performed by automatic control.

In addition, when adding a flocculant to a process using activated sludge, the injection position of the flocculant should be placed within the flow path from the final stage of activated sludge treatment to the final solid-liquid separation device, and the added flocculant By setting the position so that it can receive sufficient stirring and mixing, the phosphorus concentration in the treated water can be controlled according to changes in the injected flocculant concentration, regardless of changes in the flocculant concentration in the activated sludge. Control techniques can be applied.

By using the method of the present invention described above, it is possible to inject an amount of flocculant that immediately responds to changes in the phosphorus concentration of incoming wastewater, and even when using both biological and chemical effects, The amount of coagulant to be injected can also be controlled depending on the level of the dephosphorization function of the organism.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

〔Example〕

The aeration tank (1) with a capacity of 200 mm has a flocculant (aluminum sulfate) injection point (2), and the final settling tank (3) has a detection point (
In a wastewater treatment system equipped with 4) and a treated water outlet (5), a colorimetric phosphorus detector (6) monitors the phosphorus in the water sampled from the detection point (=7), and the concentration signal is recorded. A programmable arithmetic controller (manufactured by Yokoguri Denki ■, SCMS type) (7) is used to control the coagulant injection pump (8).
) to the flocculant injection pump (8).
In a wastewater treatment system (shown in Figure 1) that pumps a controlled amount of flocculant from the flocculant storage tank (9) of the same pump to the flocculant injection point (2), the inflow water is pumped at a rate of 480 m/d.
For each period from the beginning of June to the end of October, I, I [, I
II (A-1, A-2, B-1, B2 and C), the influent water (INF) and the treated water after treatment (EF
F) Soluble phosphorus (PD), total nitrogen (T-N), biological oxygen demand (BOD), and the injection rate of the flocculant (aluminum sulfate) used in the treatment were measured (see Table 1). .

This is illustrated in Figure 2 with respect to the phosphorus concentrations of inflow water and treated water.

Table [Effects of the Invention] The present invention can always supply an appropriate amount of flocculant even if there are differences in the dephosphorization ability of living organisms or other differences in the natural environment, so it is effective with the minimum injection of flocculant. This method makes it possible to remove phosphorus from wastewater. Therefore, this invention is extremely useful for reducing the amount of phosphorus loaded into closed water bodies due to wastewater.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the wastewater treatment system of the present invention, and FIG. 2 is a drawing showing the phosphorus concentrations of inflow water and treated water in an example. In the figure, 1 is an aeration tank, 2 is a flocculant injection point, 3 is a final settling tank, 4 is a detection point, 5 is a wastewater treatment outlet, 6 is a phosphorus detector, and 7
8 shows a flocculant injection amount control device, 8 a flocculant injection pump, and 9 a flocculant storage tank. 0

Claims (1)

[Claims] 1. In a water treatment process in which soluble phosphorus in wastewater is removed by chemical flocculation or a combination of biological and chemical flocculation, the amount of flocculant to be added is measured using a phosphorus detector. Calculate the predicted excess or deficiency of the amount of phosphorus removed in this water treatment process based on the change in the phosphorus concentration value of the treated water detected by
A method for controlling the concentration of phosphorus in wastewater, characterized by controlling the amount of phosphorus removed to eliminate excess or deficiency. 2. When applying the phosphorus concentration control method to a process that uses the activated sludge method or its various modified methods in combination with a flocculant, the injection position of the flocculant should be changed from the final stage of activated sludge treatment to the final solid liquid. 2. The method for controlling phosphorus concentration in wastewater according to claim 1, wherein the location is within the flow path leading to the separator and where the added flocculant can receive sufficient stirring and mixing.