JPH0317559B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is an energy saving method that efficiently uses biological and physicochemical means to remove nitrogen from ammonia-containing wastewater such as human waste water, livestock wastewater, and landfill leachate wastewater. This article relates to a method of removing [Conventional technology and its problems] After nitrifying and denitrifying human waste water using activated sludge, a UF membrane (ultrafiltration membrane) is used instead of a settling tank.
The concentrated and separated activated sludge is returned to the activated sludge treatment tank (denitrification tank), and the permeated water is treated with activated carbon and further subjected to phosphoric acid adsorption treatment. The water is then discharged as treated water. That is, raw water is supplied to the first reaction tank (first denitrification tank) together with the thickened sludge to perform denitrification treatment, then introduced into the aeration tank to perform nitrification treatment, and this treated liquid is transferred to the second reaction tank (first denitrification tank). The liquid in the ultrafiltration tank is circulated through the ultrafiltration machine and separated into concentrated activated sludge and permeated liquid, and a part of the concentrated activated sludge is is returned to the denitrification tank as described above, and the remainder is circulated to the ultrafiltration tank. As mentioned above, the permeate is treated with activated carbon and then discharged as treated water (Mitsui Engineering & Shipbuilding Engineering Co., Ltd.; Asmex, undiluted human waste). By using a UF membrane instead of a settling tank, this technology can stably perform solid-liquid separation even with highly concentrated activated sludge.
Since COD _Mo can also be separated, the coagulation treatment for removing COD _Mo can be omitted, and since SS is completely separated by the UF membrane, there is no need for sand filter equipment, which is commonly used in night soil wastewater treatment. There is an advantage to having one. However, when separating and concentrating activated sludge and soluble polymer substances using a UF membrane, the UF
In order to prevent increases in permeation resistance and membrane contamination due to concentration gradients within the membrane, and to ensure a predetermined amount of permeated water, an extremely large amount of activated sludge mixture is circulated at high pressure, and a large amount of electrical energy is consumed in this circulation. and accounts for a large proportion of wastewater treatment costs. On the other hand, in the biological treatment process (denitrification process and aeration (nitrification) process),
To denitrify NO _X using BOD in wastewater,
A large amount of nitrification liquid is circulated to the denitrification tank in the previous stage.
This circulation consumes a considerable amount of energy. [Problems to be Solved by the Invention] The present invention solves the problems in the prior art described above and provides an energy-saving method for treating ammonia-containing wastewater. [Means for Solving the Problems] The present invention provides a method for removing ammonia from ammonia-containing wastewater containing chloride ions substantially without dilution using biological means and physicochemical means. The activated sludge mixture from the denitrification process into which wastewater and nitrifying solution flow is transferred to the nitrification process via a membrane separation device to nitrify ammonia, and then flowed down to the denitrification process for denitrification and the membrane separation process. A method for treating ammonia-containing wastewater, characterized by electrolytically treating ammonia remaining in the permeated water of the device using chlorine ions present in the permeated water, wherein the treated liquid in the denitrification tank is passed through a membrane separation device. The above-mentioned problems were solved by introducing the concentrated liquid into a nitrification tank (aeration tank) and by attaching an electrolytic treatment device for permeated water. The present invention uses a reverse circulation path (denitrification tank → nitrification tank) with a membrane separation device in between. ) → first reaction tank (denitrification tank), membrane separation: ultrafiltration tank → ultrafiltration machine → ultrafiltration tank] to reduce power costs and equipment required for circulation. Furthermore, in the present invention, Cl ^- contained in wastewater is electrolyzed and gasified, and remains in the membrane-permeated water.
Electrolytic treatment is combined to treat _NH3 , but the _NH3 -N concentration in permeated water can be significantly reduced by circulating nitrification and denitrification in the biological treatment process. Even if Cl - such as Cl ^- is not supplied, the wastewater originally contains Cl ^-
Only biological treatment can decompose residual ammonia. An embodiment of the present invention will be described with reference to FIG. The wastewater 1 flows into the denitrification tank 2 under anaerobic conditions and is stirred together with the nitrification liquid that overflows from the nitrification tank 3. _NO It is denitrified using a reducing agent such as _N2 gas. Denitrification tank 2
The mixed liquid is circulated to the nitrification tank 3 via the membrane separator 6, and the ammonia in the liquid is nitrified and becomes _NOx , which overflows over the partition wall 4 into the denitrification tank 2. A part of the circulating fluid 5 is permeated from the membrane separator 6,
The MLSS of the circulating fluid is correspondingly concentrated. Since the amount of permeated water is small compared to the amount of circulation, the increase in MLSS concentration is small. The permeated water 7 is led to an electrolytic treatment step 8, and the water in the liquid is
_NH3 in permeate water by _Cl2 generated from ^Cl- ,
COD components and chromaticity components are oxidized and decomposed. The amount of Cl ₂ for decomposing NH ₃ only needs to be about 10 times that of NH ₃ -N. COD components that could not be decomposed by electrolytic treatment are
Although not shown, it can be removed by activated carbon treatment. Since the electrolytically treated water 10 of the present invention contains _Cl2 , if the concentration is sufficient, the treated water
_Cl2 sterilization equipment can be omitted. On the other hand, if the residual Cl ₂ concentration is too high and there is a problem in discharging the treated water 10, an activated carbon treatment step may be arranged and part or all of the electrolyzed water 10 may be passed through the activated carbon. If the ratio of BOD/NH ₃ -N in the wastewater is less than about 3.0, the BOD in the wastewater alone will be insufficient to denitrify the NO ₃ flowing in from the nitrification tank 3, so methanol 9 etc. It is necessary to install reducing agent injection equipment in the denitrification tank to replenish the shortage. When the surplus sludge 11 produced by biological treatment is extracted from the nitrification tank 3, _NOx is contained in the sludge, so that putrefaction in the sludge treatment step 12 can be prevented. Sludge can be dehydrated using only polymers, but if an inorganic flocculant such as ferric chloride is used, polymeric COD components will be flocculated in addition to the sludge and removed along with the dehydrated sludge, making it an effective material in the biological treatment process.
The concentrated concentration of COD can be reduced, and the COD load on the membrane can be reduced. In the present invention, as shown in FIG. 2, an ejector 15 can also be provided at the outlet of the circulating fluid 5 discharged from the membrane separator 6 to supply oxygen. However, when processing NH ₃ under high load, the oxygen supplied by the ejector 15 alone is insufficient, so it is necessary to separately provide aeration equipment such as a blower 18. If wastewater contains phosphorus and it is necessary to remove it, at least one of the following means may be added to the present invention. A method of adding an inorganic flocculant to wastewater before biological treatment to insolubilize phosphorus and separate solid-liquid. A method of adding an inorganic flocculant to the biological treatment process to make it insolubilized and then pulling it out along with excess sludge. A means of coagulating solid-liquid separation or adsorption of phosphorus in the liquid after it passes through the membrane. [Example] Using the biological treatment tank (made of transparent acrylic: 20) shown in Figure 1, which is not equipped with a UF membrane separation device, filtered human waste, pig wastewater, and landfill leachate sewage were continuously treated at a water temperature of 25°C. In addition to nitrification and denitrification treatment,
The activated sludge mixture in the denitrification tank was separated batchwise using a flat-membrane UF membrane (molecular weight cutoff 15,000) test device, the concentrated liquid was injected into the nitrification tank, and the permeated water was sent to an electrolytic treatment device. The electrolytic treatment apparatus used was one in which one tank filled with activated carbon was treated with a direct current using a platinum plate as an anode and a stainless steel plate as a cathode. The treatment conditions for human waste, pig farm wastewater, and landfill leachate sewage are shown in Table 1, and the treatment results are shown in Tables 2, 3, and 4, respectively. Although not shown, electrolytic treatment of permeated water of circulating fluid obtained using a MF (microfilter 0.1μ) membrane was performed under the same conditions as shown in Table 1.
Although the NH ₃ removal rate was almost the same as when using the UF membrane, the COD of the electrolytically treated water increased significantly. This means that the COD of permeated water is MF compared to UF membrane.
This is because the membrane was 3 to 4 times more expensive.

[Table] Added.

【table】

【table】

〔effect〕

Since the conventional dual circulation systems for membrane treatment and biological treatment have been combined into one, it is possible to reduce power for circulation, operating costs due to the reduction in equipment, and construction costs. Furthermore, by providing an ejector at the circulating water outlet, oxygen can also be supplied. The conventional second reaction tank (second denitrification tank) could be replaced with a compact electrolytic treatment device. Since the MLSS concentration of the biological treatment process mixture and the mixture supplied to the membrane are almost the same, the MLSS load on the membrane can be reduced compared to conventional methods. SS is completely removed by the UF membrane, so
Problems with electrolytic treatment caused by SS are resolved. The NH ₃ in the wastewater is diluted with the effluent from the nitrification tank, and the NH ₃ ^−N concentration in the permeate water is significantly reduced ^.
However, electrolytic treatment of permeated water can be performed. By electrolytic treatment, COD components and chromaticity components as well as NH ₃ can be treated at the same time, and the Cl ₂ produced sterilizes the treated water.

[Brief explanation of the drawing]

FIG. 1 is a schematic flow diagram for explaining the method of the present invention, and FIG. 2 is a diagram for explaining an ejector provided at the outlet of the circulating liquid from the membrane separation device 6. 1...Raw water, 2...Denitrification tank, 3...Nitrification tank, 4
... Partition wall, 6 ... Membrane separation device, 8 ... Electrolytic treatment step, 9 ... Reducing agent, 10 ... Treated water, 12 ... Sludge treatment step, 14 ... Dehydration liquid, 15 ... Ejector, 18 ... ...Blower.

Claims (1)

[Scope of Claims] 1. A method for removing ammonia in ammonia-containing wastewater containing chloride ions substantially without dilution using biological means and physicochemical means, wherein said wastewater and nitrification solution are The activated sludge mixture in the denitrification process is transferred to the nitrification process via a membrane separation device to nitrify ammonia, and then flowed down to the denitrification process to be denitrified and remain in the permeated water of the membrane separation device. A method for treating ammonia-containing wastewater, comprising electrolytically treating ammonia using chlorine ions present in the permeated water. 2. The method for treating ammonia-containing wastewater according to claim 1, wherein oxygen is supplied to the nitrification process by passing the liquid transferred from the membrane separator to the nitrification process through an ejector.