JPH0141118B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention rationally treats phosphorus-containing organic wastewater, such as human waste, sewage, wastewater, etc., using a new and simple process, and always obtains stable and high-quality highly treated water. It provides a process system. [Prior Art] Taking human waste as an example of organic sewage containing phosphorus, the most typical process at present is undiluted biological nitrogen → coagulation sedimentation → activated carbon adsorption. However, this process has the drawback of generating a large amount of coagulated and settled sludge that is difficult to dewater. On the other hand, very recently, undiluted biological denitrification → UF
A process of membrane separation → activated carbon adsorption → phosphorus removal using a zirconium-based adsorbent was proposed. However, while this process does not require a coagulation-sedimentation step, it does require a phosphorus adsorption step, which involves complicated steps (PH adjustment, re-neutralization of treated water, adsorbent regeneration, and crystallization operations). It has the disadvantage of The reason why such a phosphorus adsorption process is required is
Because the UF membrane does not have the ability to separate inorganic ions, 100% of the PO ₄ ^3- ions pass through the UF membrane, so we had no choice but to adopt such a troublesome process. . Furthermore, even with this process, it was impossible to omit the activated carbon adsorption step in order to obtain treated water with low COD. [Problems to be Solved by the Invention] The present invention aims to fundamentally solve the problems of the conventional process described above. Specifically, it is possible to omit the coagulation-sedimentation step and still achieve a sufficient phosphorus removal rate. to obtain. It becomes unnecessary to provide a phosphorus adsorption step after the UF membrane separation step. Further simplify the process configuration. Eliminates the need for activated carbon adsorption process. This is the problem to be solved. [Means for solving the problem] Organic sludge, a magnesium compound, and a polymer flocculant are added to organic wastewater containing phosphorus, followed by solid-liquid separation, and the separated liquid is subjected to biological nitrification and denitrification treatment. Furthermore, the activated sludge slurry flowing out from the process is treated by solid-liquid separation using an RO membrane with a NaCl removal rate of 80% or less. The present invention will be explained in more detail below with reference to the drawings. FIG. 1 is a flow sheet of one embodiment of the invention. When surplus activated sludge 3 and Mg(OH) ₂ or MgO4 discharged from biological nitrification and denitrification treatment process 2 (hereinafter referred to as biological treatment process) are added to human waste 1 and stirred, NH ₄ contained in human waste 1 is removed. ⁺ ,
PO ₄ ^3- ions and Mg ²⁺ ions undergo a rapid chemical reaction (precipitate formation reaction) to form fine granular precipitates of NH ₄ MgPO ₄ , and approximately 90% of the PO ₄ ^3- ions in human waste are removed. Next, a polymer flocculant (suitably a cationic polymer) 5 is added to form a large-sized floc, followed by solid-liquid separation using a screen 6 (preferably an inclined wedge wire screen or a drum screen). NH ₄ MgPO ₄ separated by screen 6
The contained organic sludge 7 is dehydrated by, for example, a screw press dehydrator 8, and becomes a dehydrated cake 9 having a water content of about 60%. On the other hand, the screen separated liquid 10 and dehydrated separated water 11 from which phosphorus and SS have been removed flow into the biological treatment step 2 without adding dilution water, and BOD and nitrogen are removed biologically. At this time, a small amount of phosphoric acid remaining in the screen separation liquid is also BOD: P≒
It is removed by being incorporated into activated sludge at a ratio of 100:1. Activated sludge MLSS concentration in biological treatment process 2 is 15000
~20000mg/set. Conventionally, when human waste was aerated without being diluted, it suffered from severe foaming, but in the present invention, the foaming substances are
Since SS and colloids are coagulated and removed, severe foaming does not occur, and antifoaming machines and antifoaming agents are not required. Therefore, the activated sludge slurry 15 flowing out from the biological treatment process 2 is directly filtered through a so-called loose RO membrane with a low NaCl removal rate (RO membrane with a NaCl removal rate of 80% or less).
membrane) flows into separation step 12, SS, soluble COD,
Chromaticity, phosphorus, viruses, etc. are highly captured and separated by the loose RO membrane, resulting in a colorless and transparent membrane permeate liquid 13 and a high SS membrane separation slurry 14. The conventional process of biological treatment → UF membrane separation → has major problems in that PO ₄ ^3- is not captured at all by the UF membrane, and the removal rate of COD and chromaticity is inferior to the coagulation-sedimentation method. However, in the present invention, most of the phosphorus in human waste is removed in the first stage of the biological treatment process, the remaining phosphorus is further removed in the biological treatment process, and a loose RO membrane is used for the polishing removal of phosphorus. This process configuration eliminates the need for the phosphorus adsorption step (which follows the UF membrane separation step and activated carbon) in the conventional process. Moreover, loose RO membranes can pass inorganic ions with small charge numbers such as Na ⁺ and Cl ^- , but unlike UF membranes, they almost completely capture polymeric substances such as COD components and chromaticity components. This eliminates the need for the activated carbon adsorption step that follows the UF membrane separation step in conventional processes. Therefore, the loose RO membrane separation slurry 14 is recycled to the biological treatment process, and the surplus activated sludge slurry 3 is added to and mixed with the human waste 1 as described above, and is effectively used to improve the pretreatment effect of the human waste. . The output of the process of the present invention is membrane permeated water 13
and dehydrated cake 9, and membrane permeated water 13
contains almost no phosphorus or chromaticity. Therefore,
The dehydrated cake 9 inevitably contains a high concentration of chromatic components similar to phosphorus and humic acid, and can be used as an organic fertilizer that is highly effective as a fertilizer and soil conditioner. This is an effect that cannot be expected with the conventional UF membrane separation method. In addition, in the present invention, the following energy-saving effects appear. In other words, a loose RO membrane does not allow 100% of NaCl to pass through, but captures some NaCl. Since this captured NaCl is recycled to the biological treatment step 2, the concentration of salts mainly consisting of NaCl in the biological treatment step increases. As a result, the diameter of the aeration air bubbles supplied to the biological treatment process becomes fine, the oxygen absorption efficiency improves, and the amount of aeration air supplied can be reduced. (It is known that the bubble diameter becomes finer as the salt concentration is higher.) [Example] A demonstration test of the present invention was carried out on a scale of human waste treatment of 1 m ³ /day using the processing flow shown in Figure 1. I did this. For the biological nitrification and denitrification treatment process, a nitrifying solution circulation type (no dilution) was adopted, and the MLSS was 15,000 mg/day, and the human waste was retained for several days and 9 days. First, the total amount of excess activated sludge slurry (SS20000mg/) and Mg(OH) ₂ 1000mg/
After stirring for 5 minutes, 400 to 500 mg of a cationic polymer flocculant was added and stirring for 2 minutes to form a flocculated floc. Next, solid-liquid separation was performed using a 60° inclined wedge wire screen with an opening of 1 mm, resulting in NH ₄ MgPO ₄
Contains thickened sludge (solids concentration 4%) and screen separated water (SS500-600mg/, soluble PO ₄ 70-120
mg/) was obtained. The screen thickened sludge was dehydrated using a screw press dehydrator (without steam heating) to obtain a dehydrated cake with a low moisture content of 58%. Next, the mixed liquid of the wedge wire screen separated liquid and the screw press dehydrator separated water was subjected to biological nitrification nitrogen treatment without dilution (methanol was added to the second denitrification tank), and the MLSS activity of 15000mg/ Sludge slurry is made by N company Tubular type loose
Direct membrane separation was performed using an RO membrane (NaCl rejection rate 40%, tube diameter 15 mm). The water that permeated through the membrane was clear and colorless, and had the quality shown in Table 1. The flow rate of the liquid inside the loose RO membrane tube module was set at 3 to 3.5 m/s, and the membrane was cleaned using a combination of mechanical cleaning with a sponge ball and chemical cleaning with NaOCl, and a stable flux was maintained for a long period of time. We were able to. The activated sludge slurry separated by the loose RO membrane is recycled to the first denitrification tank, and the equivalent amount of surplus activated sludge (6.0Kgd.s/day) is mixed with human waste.
It was supplied to the Mg(OH) ₂ addition tank described above.

【table】

[Table] [Effects of the invention] The present invention can reduce PO ₄ in organic wastewater containing phosphorus.
As a result of introducing a new method in which SS is first removed using a unique method and then further processed through a process of biological nitrification and denitrification → loose RO membrane separation, the following important effects appear. There is no need to provide an activated carbon adsorption step and a phosphoric acid adsorption step subsequent to the membrane separation step, which greatly simplifies the process and facilitates maintenance. Naturally, construction costs will also be reduced. As a result of the increase in salt concentration in the biological treatment process, the oxygen absorption efficiency in aeration improves, resulting in an energy saving effect. The phosphorus concentration in the dehydrated cake increases compared to conventional processes, increasing its value as a fertilizer. In the RO membrane separation process, SS, which causes blockage of the module, is highly removed in the coagulation separation process before the biological treatment process, so there is no worry about blockage of the RO membrane module, making it trouble-free.

[Brief explanation of drawings]

FIG. 1 shows a flow sheet of one embodiment of the present invention. 1... Human waste, 2... Biological nitrification and denitrification treatment process, 3... Excess activated sludge, 4... Magnesium compound (Mg(OH) ₂ or MgO), 5... Polymer flocculant, 6... Screen, 7... Screen separated organic sludge, 8... Screw press dehydrator, 9
...Dehydrated cake, 10...Screen separation liquid, 1
1... Dehydrated separated water, 12... Loose RO membrane separation step, 13... Membrane liquid permeation, 14... Membrane separation slurry, 15... Activated sludge slurry.

Claims (1)

[Claims] 1 Organic sludge, a magnesium compound, and a polymer flocculant are added to organic sewage containing phosphorus, followed by solid-liquid separation, and the separated liquid is subjected to biological nitrification and denitrification treatment, and activated sludge flows out from the process. So-called loose RO with a NaCl removal rate of 80% or less for slurry
A method for treating organic wastewater containing phosphorus, characterized by solid-liquid separation using a membrane.