JPS61234990A - Process for setting quantity of air to be fed to aeration tank - Google Patents

Abstract

PURPOSE:To stabilize purifying function of activated sludge and to enable production of treated water having good quality by setting the quantity of air to be fed to an aeration tank basing on an oxygen feeding coefft. corresponding to the water temp. in an aeration tank which is stabilized following to oxygen respiration activity which is changed depending on temp., etc. CONSTITUTION:If purification function of activated sludge is stabilized using oxygen feeding coefft. L which expresses conveniently the proportion of the quantity of oxygen in the air fed by a blower to the necessary quantity of oxygen consumed continuously per 1m<3> aeration tank, the value of the coefft. L changes meteorologically and biologically along 8 character shaped locus for through one year for all kinds of substrate with respect to the relation between the water temp. in the aeration tank to the coefft. L. The quantity of the air to be fed is set utilizing this fact, and the value of L is operated by an operator after sensing daily mean water temp., air temp., electroconductivity, and aeration time with sensors. The air quantity is decided so as to match the operated value to the values of the graph for daily water temp. of the aeration tank, coefft. L, and annual time series graph.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application This invention relates to a method for setting the amount of air supplied to an aeration tank in an activated sludge method.

(b) Conventional technology The amount of air supplied to the aeration tank is set by blowing the amount of air based on the conventional design value into the aeration tank as stipulated by various management guidelines.

O,zwq/L or more ~2. This was done empirically by manually restricting the flow rate valve so that it was within the range of o rag/L. In addition, even if a single or multiple Do meters are installed in the aeration tank with the main purpose of saving energy, the output signal from the DO meter should be used as the main output so that the DO concentration in the aeration tank is kept at an arbitrary constant concentration as low as possible. The amount of air in the aeration tank was adjusted and set by controlling the air flow rate valve opening and rotation speed. For this reason, seasonal changes in water temperature, respiratory activity of activated sludge, and
Multivariate control that takes into account changes in multiple factors such as actual aeration time per day has not yet been performed.

(/1 Problem to be solved by the invention The amount of air supplied from the puller to the aeration tank is calculated and set based on design standards and structural standards based on various laws and regulations.
If the design air volume is continuously supplied to the aeration tank that maintains the LSS volume, even if it is normal in the summer due to the physicochemical effects of water temperature and air temperature, it will gradually become excessive in the winter. Become. Therefore, it has become impossible to release excess air or adjust the throttle of the flow valve, making it necessary to control the number of blowers and the operating rate in large-scale facilities. Furthermore, during the transition period that brings about rapid temperature changes from spring to summer and from autumn to winter, a common phenomenon unique to the biological world is that the activated sludge treatment phase becomes unstable, resulting in the so-called summer preparation and winter preparation phenomena. It was necessary to clarify the set amount of air to stabilize the purification function during the transition period. In addition, with regard to the relationship between the amount of air required for the aeration tank and the temperature determined by natural weather conditions, we attempted to quantify the set air amount, and using the relationship between the overall oxygen transfer capacity coefficient and temperature, we calculated the amount of air for the aeration tank. It was difficult to perform highly reliable and stable activated sludge treatment even when increasing and decreasing settings were performed. In addition, there is a term for the amount of BOD removed in the formula, and it takes a long time to measure it, so in addition to empirical judgment and measuring the dissolved oxygen concentration in the aeration tank, it is necessary to make practical decisions for each wastewater substrate. There were few ways to set the atmosphere.

2) Measures to solve the problem Under Japan's geographical conditions, reverse electricity in the air temperature and aeration tank water temperature is observed twice a year (from April to May and from October to November). Although it has been scientifically proven, the oxygen supply characteristics in the aeration tank based on this phenomenon are expressed in the following equation in a simple way and as effective characteristic values for water quality management. The oxygen supply coefficient (L
) was devised.

However, -=Oxygen supply coefficient (f)=Amount of oxygen in 1rPl of air corrected for temperature (01
m3fA5Cs - Saturated dissolved oxygen concentration (f/d) corrected for chlorine ions by an electrical conductivity meter CL = Dissolved oxygen concentration in the aeration tank measured by a dissolved oxygen meter (η Top = Content ratio of MLVSS in the MLSS mixture The reciprocal of here is the absolute amount of oxygen contained in the air supplied from the blower, relative to the amount of oxygen continuously consumed per hour in the aeration tank. In other words, the saturation rate varies depending on the substrate decomposition rate supplied to activated sludge, the oil concentration in the substrate, the efficiency of the aeration equipment, the water temperature, the air temperature, and the electrical conductivity of each wastewater. It is a characteristic value that comprehensively reflects the influence of the amount of dissolved oxygen, etc. Therefore, in the process of managing a certain amount of activated sludge,
Even if a facility with an average amount of substrate flowing into the aeration tank is supplied with aeration equipment and air volume under certain conditions, it will inevitably be affected by the air temperature and wastewater temperature under natural weather conditions. In order to stabilize the sludge purification function and obtain good treated water, the amount of air must be adjusted based on the oxygen supply coefficient corresponding to the aeration tank water temperature so that it follows and stabilizes the oxygen respiration activity due to temperature dependence as shown in Figure 1. This is possible by setting.

According to the present invention, the y-axis and the y-axis are provided so as to be centered on the average value of the aeration tank water temperature and the average value of the oxygen supply coefficient.
It has been confirmed that when the annual average daily, monthly, and seasonal average oxygen supply coefficients are plotted against water temperature, the time series always follows an 80-character trajectory, and the 80-character pattern is based on the wastewater substrate and treatment. Hung heater analysis has revealed that it is expressed in a facility-specific manner.

Applying the above principles, the amount of air supplied to the aeration tank can be set using the daily average water temperature meter, Do meter, thermometer, and electrical conductivity to correct the saturated dissolved oxygen concentration. Based on the input from the water meter for measuring the aeration time and the aeration time, the calculation device calculates the oxygen supply coefficient, sets the standard figure-of-eight pattern, and compares and converts the aeration time with the comparison calculation device. Based on the output, the daily supply air amount is set so that the aeration tank water temperature and oxygen supply coefficient trajectory on the graph progresses. In addition, the automatic operation moves the trajectory for 30 days every month in equal parts using a time series function, and calculates the number of blowers, blower operation rate, and blower rotation speed based on the determined air amount. This is done by obtaining a final output signal that looks like this.

(e) Effect: Oxygen supply coefficient under Japan's geographical conditions However, an average oxygen supply coefficient ■ exists during the period when air temperature and water temperature are reversed.
Each type of sewage, sewage, and industrial wastewater has its own unique value. For example, the average oxygen supply coefficient for the design air volume is 60 to 1200 for urban sewage, and 20 for septic tanks.
~60, and some industrial wastewater can reach 10-350. Incidentally, no matter what kind of substrate is used, the oxygen supply coefficient in the aeration tank (which maintains and manages a certain amount of activated sludge in the activated sludge process) increases during the summer period from July to August. It reaches its highest peak in 2018, and bottoms out in the low turn period from 2018 to February. The table below shows an example of industrial wastewater.
As shown in 1.

Table 1: Changes in the oxygen supply coefficient As shown above, the oxygen supply coefficient is a result of the direct effect of temperature on activated sludge growth, resulting in a relative fluctuation rate of oxygen respiration activity from approximately 50% in winter to approximately 160% in summer. It changes a lot. Therefore, the design air volume based on various design standards is 15
If we calculate the set amount of air to be supplied into the aeration tank by converting it to 0%, it will be reduced to about 50% in winter and 100% in spring and autumn. In the spring from May to July, which corresponds to the summer preparation period for activated sludge, an average increase of 20% is set compared to the autumn preparation period, which moves from August to October. For the period corresponding to the preparation period, it is sufficient to set an average increase of 20% compared to the spring preparation period from February to April.

(f) Effects of the invention In recent years, due to the improvement of aeration pipes and the current demands for energy conservation, the set amount of air supplied to the aeration tank in the activated sludge treatment process has been changed to the necessary and minimum set amount of air, rather than an excessive amount. The concept of technology has been changed to establish the sludge method, and the present invention reflects changes in not only the DO meter installed in the aeration tank but also multiple factors, and the activated sludge treatment water Functional stability can be achieved as a main effect. In other words, in an aeration tank where the amount of activated sludge held in the aeration tank is normally operated and managed, if the fluctuation rate of the daily inflow BOD load is within the average range of about 20%, the Do meter should be operated by the main human operator. Compared to the air amount setting method, this method can obtain more stable treated water. In addition, although hydraulic power plants generally use a deheater, if there is a large change in the amount of air supplied to the aeration tank, the set air amount displayed on the blower control panel can be improved by manual operation. After that, it will automatically operate. In this way, setting the amount of air supplied to the aeration tank by this method can be used as an effective means of quantifying when the technical judgment of increasing or decreasing the amount of air has conventionally been made by a professional engineer. In this method, a calculation device is built in, and the set air amount calculated from the oxygen supply coefficient based on the actual conditions of the aeration tank is displayed on the blower control panel, and the current location on the 80-character trajectory is displayed. Therefore, the air supply operation from the blower can be automated without requiring a professional engineer. In addition, the power cost saved by the amount of air supplied on the figure-eight trajectory is about 35%.

[Brief explanation of the drawing]

In the figure, the X-axis represents the water temperature in the aeration tank, and the Y-axis represents the oxygen supply coefficient (T).The number above the 80th character with each year's average value as the origin is the monthly average oxygen supply coefficient that exists on the time series pattern. (
L). Further, the arrow indicates the direction of the trajectory in which the oxygen supply coefficient (L) changes every day.

Claims (1)

[Claims] In contrast to the required oxygen amount Rr (O_2・g/m^3・hour) per 1m^3 of the aeration tank that is continuously consumed in the aeration tank, the amount of oxygen in the air per hour blown from the blower is If the activated sludge purification function is stabilized by applying the oxygen supply coefficient (L), which simply expresses how many times the contained oxygen amount Qc (O_2・g/h) is supplied, in what kind of substrate can the activated sludge purification function be stabilized? The relationship between the water temperature in the aeration tank and (L) is based on the fact that, meteorologically and biologically, (L) circulates through a figure-eight trajectory during one year, as shown in Figure 1. After setting the air supply amount and detecting the daily average water temperature, air temperature, electrical conductivity, and aeration time using a sensor, a calculation device calculates the oxygen supply coefficient (
L) is calculated, and the air supply amount is determined each day to match this to the aeration tank water temperature, oxygen supply coefficient (L), and annual time series graph on the graph, and the number of blowers and blowers are determined based on the determined air amount. A method for setting the amount of air supplied daily into an aeration tank, characterized by obtaining an output signal that corresponds to the operating rate and the number of rotations of the blower.