JPS5919590A - Disposal of sulfurous acid-contg. waste water - Google Patents

Abstract

PURPOSE:To efficiently perform the removal of inhibitors and the adjustment of a pH, by introducing sulfurous acid-contg. waste water into a fermentation tank, and controlling a pH by the separate direct injection of slaked lime into the fermentation tank to perform methane fermentation. CONSTITUTION:Sulfurous acid-contg. waste water, e.g. pulp mill waste liquor, is introduced through a conditioner tank 11 and a line 13 into a fermentation tank 15. On the other hand, slaked lime is directly injected through a line 16 into the fermentation tank 15 to adjust a pH in the fermentation tank 15. The liquid waste after being biologically treated in the fermentation tank 15 is withdrawn through a line 17, further treated in a precipitation tank 19 and then drained as treated water. Methane-contg. digestion gas is introduced through a line 21 into a gas holder 23. A part of said gas may be used for agitation and as carrier gas for H2S by desulfurizing it in a scrubber 25 and then blowing it into the deep part of a draft tube 14.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating sulfite-containing wastewater, and particularly to a method for treating pulp wastewater by methane fermentation.

Treatment of sulfite-containing wastewater is one of the most difficult.

Pulp waste liquor contains a large amount of sulfite and also has high COD and BODJ. Methane fermentation is useful for treating such concentrated wastewater, but as with other biological treatment methods, microbial activity is inhibited by the sulfur dioxide in the wastewater, and There were problems such as sulfurous acid being reduced in the tank and generating hydrogen sulfide.

In addition, ・Terup YFJ liquid contains a large amount of sulfites and has a low pH.
Since the wastewater has an H(p) of 42 to 3), it is necessary to adjust the pH when treating it by methane fermentation.

Conventionally, the pH was adjusted by moving the 1C pH adjustment tank in the front stage of the fermenter, and the raw water that had been plEI adjusted was injected into the fermenter. Therefore, in the conventional method, when the pH of the fermenter drops to, for example, about 6, it is not possible to inject only alkali into the fermenter without introducing raw water and adding an organic load, and it is not possible to immediately respond to p)I adjustment. I was lacking in sex.

In methane fermentation, the balance between the decomposition of the substrate by the M bacteria into organic acids and the decomposition of this organic acid into gas by the methane bacteria is disrupted, and when the pH drops to, for example, about 6 due to the accumulation of organic acids. It is necessary to restore this balance as soon as possible.

Furthermore, according to the conventional method, p Fl
Adjusted raw water for injection (for example, p11 value is about 4) will cause V! It should be diluted by the fermentation liquid in the tank at the same time as it flows into the tank, but considering that the fermenter itself has a buffering capacity against 911, it is also possible that the conventional method would have added more alkali than necessary. It will be done.

The present invention was made with the aim of eliminating the drawbacks of the conventional methods as described above, and it is necessary to remove inhibitory substances and adjust the pH level when treating wastewater containing sulfites such as pulp wastewater.
The purpose of the present invention is to provide a processing method that can efficiently perform the adjustment.

That is, the method for treating sulfite-containing wastewater of the present invention is characterized in that when the sulfite-containing wastewater is introduced into a fermentation tank and treated by a methane fermentation method, slaked lime is directly injected into the fermentation tank to control the pH.

FIG. 1 is a flow diagram for explaining the present invention, in which sulfite-containing wastewater such as pulp waste liquid is led from line 13 to fermenter 15° through adjustment 4v11, and is biologically treated in 411. Later, it was discharged from 2-in-17,
After further treatment in the sedimentation tank 19, the treated water is discharged. Digestion gas containing methane is led from line 21 to gas holder 23. Further, a part of this gas may be desulfurized by the sucrano-26 and then blown into the deep part of the draft tube 14 to be used for stirring and as H, S carrier gas.

A feature of the process of the present invention is that slaked lime, ie, Ca(on), is directly introduced into this fermenter 15. Slaked lime may be in either solid or liquid form, but it is preferable to introduce it in the form of a solution or slurry. In the present invention, "directly" means that the wastewater is not mixed with the wastewater in advance and is introduced into the wastewater.
It is meant to be introduced into the fermenter 15 separately from the waste water (regardless of whether the same two-in, specifically piped line is used). According to the present invention, by directly injecting slaked lime into the fermenter tank 5 from the liner 6, the pH inside the fermenter can be efficiently adjusted. As already explained, the fermentation solution itself has buffering capacity, so the pI
Even if pulp waste liquid with a low i flows in, the pH can be prevented from decreasing to some extent. Then, to make up for the insufficient amount, all you have to do is measure and manage the pH of the fermenter and inject slaked lime, so you can add only the minimum amount of slaked lime, eliminate waste, and maintain optimal conditions for methane fermentation. can do. In addition, even when the pax between organic acid production and gas production is disrupted due to shock four-daying, etc., organic acids accumulate and the pH decreases, the organic matter load remains unchanged (in the case of pulp waste liquid, it is particularly concentrated). )
, it is possible to stop or freely control the inflow of organic matter, and on the other hand, it is possible to independently adjust the pH in the fermenter, allowing for rapid recovery of sludge and early recovery of pax in methane fermentation. Can be done.

Furthermore, the sulfites Sarak contained in Nokulp waste liquid are sulfates, and the hydrogen sulfide produced is a substance that inhibits methane fermentation, but by injecting slaked lime, these can be neutralized and the following can be done: Reactions such as the following can occur to cause precipitation.

Ca(OH), →-804"--' Ca804↓+2
0H-Ca (0I()1 + Son'-→ Ca8
04↓+20H-Ca(OH)1+H,S-'p
Ca8↓ + 2TI! 0(Ca(OR), dec acid
- Neutralization) In this way, by adding slaked lime, p)I[[[at the same time 1S
By removing fl harmful substances as soluble salts, it becomes possible to stabilize the sludge and improve the load.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing an embodiment of the processing method of the present invention.

Claims (1)

[Claims] 1. When introducing sulfite-containing wastewater into a fermentation tank and treating it using the methane fermentation method, slaked lime is directly injected into the fermentation tank.
I (a method for treating nitrous acid-containing polishing water, characterized by carrying out control).