JPH0487694A - Waste water treating device - Google Patents

Abstract

PURPOSE:To remove the sludge stuck to the surfaces of ultrafilter membranes by the flow in a pressurized aeration tank by immersing these membranes into the aeration tank, permeating purified water through the inside of the membranes by the pressure in the pressurized aeration tank and draining this water as treated water. CONSTITUTION:The circulating flow in the aeration tank 5 is risen in an inside cylinder 8 by withdrawing the liquid mixture on the outer side of the inside cylinder by a circulating pump 10 and ejecting the same from a nozzle 7 of a diffuser in the bottom of the aeration tank, by which the flow falling on the outside of the inside cylinder is occurred. The pressurized air from a compressor 6 is mixed with the circulating water and the air is sheared at the time of ejecting the water from the nozzle 7, by which fine bubbles are generated and the water is aerated. The circulating pump 10 withdraws the liquid from the pressurized aeration tank 5 and maintains this water under the same pressure and, therefore, there is no need for such a pressurizing pump which is heretofore used for ultrafiltration. The pump of the pressure as low as to correspond to the pressure drop of the nozzle and piping is thus usable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wastewater treatment device using an ultrafiltration membrane for purifying organic wastewater by an activated sludge method.

[Conventional technology]

Conventionally, a method shown in FIG. 3 has been known as a method for treating wastewater by combining an ultrafiltration membrane and biological treatment. Biological treatment uses a normal aeration tank 31, pressurizes the sludge mixture drawn from the aeration tank 31 with a pressurizing pump 32, sends it to an ultrafiltration device i33, separates it into sludge and treated water with a membrane, and separates it. The dirt and concentrated liquid after IIl is returned to the aeration tank 3], but it is discharged as surplus.

[nH that the invention attempts to solve]

However, in this known method, as the treatment progresses, sludge and colloidal substances adhere to the membrane surface and the amount of permeation of the treated water decreases. The membrane surface had to be cleaned.

An object of the present invention is to combine a pressurized aeration tank and an ultrafiltration membrane to provide wastewater treatment that is compact, efficient, and does not require a membrane cleaning device.

[ff! Means to solve the problem]

The present invention was made in order to achieve the above object, and an ultrafiltration membrane is immersed in a pressurized aeration tank, and purified water is permeated through the membrane by the pressure in the pressurized aeration tank and is discharged as treated water. The gist of the system is that it self-cleans by peeling off sludge and colloidal substances adhering to the surface of the shield due to the flow in the aeration tank.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The wastewater treatment apparatus of the present invention will be explained below based on the illustrated embodiments.

In FIG. 1, sewage, gray water, and other organic wastewater l is pretreated in a pretreatment tank 2 by removing dust or sand using a screen 3, and then sent to a pressurized aeration tank 5 by a raw water pump 4. Ru. The pressurized aeration tank 5 is provided with a diffuser nozzle 7 at the bottom, an inner cylinder 8 inside, and an air discharge valve 9 at the top. An ultrafiltration membrane 11 is provided at a position in the tank where the flow is large, such as inside the inner chamber 8, and the membrane-permeated water is discharged to the outside of the thread through a water pipe 12. The ultrafiltration membrane to be used is not particularly limited, but in consideration of the amount of permeated water and the installation space, a method in which a hollow fiber membrane is flowed is most suitable.

The circulating flow in the aeration tank is controlled by the circulation pump 10. J
By drawing out the mixed liquid outside of the aeration tank 8 and spouting it from the nozzle 7 of the diffuser at the bottom of the aeration tank, a welt rises inside the inner cylinder and descends outside the inner cylinder. At this time, pressurized air is mixed with the circulating water from the compressor 6, and the air is sheared when it is ejected from the nozzle 7, thereby generating fine bubbles and performing aeration. Circulation Pump] 0 draws water from the pressurized aeration tank to maintain the same pressure, so there is no need for a pressurizing pump like the one used for conventional ultrafiltration, and a low-pressure pump that is sufficient to compensate for the pressure loss in the nozzle and piping is used. be able to. Further, since the appropriate pressure range of the pressurized aeration tank 5 is 2 to 4 kg/cd, the compressor 6 is used at a pressure of about 3 to 5 kg/aIi, which is the pressure loss of the nozzle piping added thereto.

FIG. 2 shows another embodiment of the present invention, in which an aeration device is provided over the entire bottom of the pressurized aeration tank 5, and the entire surface is aerated to flow the ultrafiltration [111]. Compared to Figure 1, the flow velocity inside the tank is much smaller. Conventional equipment such as air diffusers, air diffuser pipes, and disc phasers can be used as is for the air diffuser W21, but in the case of pressurized aeration, it is unique in that it holds particularly high-concentration sludge. , it is necessary to use a method that is as unlikely to cause clogging as possible.

Next, the operation of the present invention will be explained.

When converting a sludge mixture into solid-liquid using an ultrafiltration membrane, if the sludge concentration is 2% or less, the solid-liquid separation speed and treated water quality will hardly change. The higher the sludge concentration, the higher the load on the incoming raw water and the faster it can be processed, so if the operation is continued without sludge extraction, activated sludge with a high concentration of 1% or more can be obtained. In the conventional activated sludge method, solid-liquid separation is performed by gravity sedimentation, so from the viewpoint of solid-liquid separation, the standard activated sludge method has a concentration of 0.2% or less, and even modified methods such as long-term aeration can achieve 0.2% or less.
．． The limit is 5 to 0.7%, but if solid-liquid separation is performed using ultrafiltration, it is possible to hold more than twice as much sludge as conventional methods, making it possible to more than double the inflow load per unit volume. .

On the other hand, the higher the sludge concentration, the more oxygen is required, so a B1 gas device with high oxygen dissolution efficiency and large oxygen supply capacity per unit volume is required. Conventional normal pressure lI
When introducing an aeration tank and ultrafiltration, operation is performed at an :If3 concentration of about 0.8 to 1% due to the capacity of the aeration system, whereas a pressurized air tank operates at a #I element concentration of about 0.8 to 1%. Due to its high dissolution efficiency, it is possible to operate at a sludge concentration of 1 to 2%.

The reason why the #l elementary dissolution efficiency becomes high in the pressurized aeration tank is as follows. The rate at which the m element contained in the air diffused into the water dissolves into the water is determined by the performance of the aeration device and the saturated dissolved m element t. When the same aeration device is used, the higher the saturated dissolved oxygen concentration, the higher the oxygen dissolution efficiency. In order to increase the saturated M element concentration, there are two methods: increasing the oxygen concentration in the diffused air and placing it under pressurized conditions, but the pressurized aeration tank of the present invention uses a conventional aeration device. Even if the air in the atmosphere is diffused, the saturated oxygen concentration increases, so the rate of oxygen dissolution is fast, and the oxygen dissolution efficiency improves in proportion to the pressure of the aeration tank.

As mentioned above, a system that combines a pressurized aeration tank and ultrafiltration can efficiently aerate while retaining high-concentration sludge, so the BOD volumetric load can be reduced from 0.3 to 0.3 for the semi-activated sludge method. 25yi= for 0.8μ1rrj days
However, if it is sewage or gray water, it can be treated in as little as two hours.

The biologically treated water permeates from the outside to the inside of the ultrafiltration membrane of the pressurized aeration tank, is collected, and is discharged outside the tank as treated water. In solid-liquid separation using such a membrane, sludge and colloidal substances gradually accumulate on the membrane surface. The membrane surface was cleaned by injecting cleaning and chemical solutions into the membrane. However, in the present invention, the membrane is placed in a pressurized 111 gas tank and
Since sludge, etc. adhering to the membrane surface is removed by the flow of the air tank, no special membrane cleaning equipment is required. However, if the cleaning effect is insufficient with the flow in the normal processing state, by increasing the amount of water circulated by the circulation pump 10 in Fig. 2, and by increasing the amount of air supplied from the compressor 6 in Fig. 2,
The self-cleaning effect can be enhanced.

[Effects of the present invention]

According to the invention, pressurization q! An ultrafiltration membrane is immersed in the aeration tank, and purified water is permeated through the membrane by the pressure in the pressurized aeration tank, and is discharged as treated water. 81% to remove and prevent adhesion
The tank is compact, no membrane cleaning equipment is required, and good water quality can be stably obtained in a short treatment time.

[Brief explanation of the drawing]

The drawings show embodiments of the wastewater treatment apparatus of the present invention, and FIG. 1 is an explanatory diagram of the first embodiment, FIG. 2 is an explanatory diagram of the second embodiment, and FIG.
The figure is between explanations of known examples. 1 is raw water, 2 is a pre-treatment tank, 3 is a screen, 4 is a raw water pump, 5 is a pressurized aeration tank, 6 is a compressor, 7 is a nozzle, 8 is an inner cylinder, 9 is an air discharge valve, 10 is a circulation pump, ] 1 is an ultrafiltration membrane, 12 is a drain pipe, 21 is an aeration device, 31 is an aeration tank, 32 is a pressure pump, 33 is an ultrafiltration device, 34 is a washing water tank, and 35 is an excess sludge pipe.

Claims (1)

[Claims] (1) A wastewater treatment equipment that biologically treats organic wastewater using activated sludge is composed of a pressurized aeration tank that performs aeration under pressurized conditions and an ultrafiltration membrane installed in the aeration tank. Wastewater treatment is characterized by solid-liquid separation by permeating treated water through a membrane using pressure.