JPS5950400B2 - How to treat human waste liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for highly treating the desorbed liquid produced by anaerobic digestion of human waste.

The concentration of raw human waste decreases due to the contamination of human waste collected from simple flush toilets and septic tank sludge, and the BOD/N ratio of the human waste desorbed liquid obtained by anaerobic digestion of this human waste has become extremely small.

Such wastewater is subjected to aerobic biological treatment, especially nitrification and denitrification treatment, and the hydrogen donor B contained in this wastewater is
Since the amount of OD is less than the amount required to biologically denitrify the entire amount of NOx-N, a large amount of NOx-N will remain.

When the pH of the treated water drops to below 5 due to the remaining NO and H, a large amount of colloids will be generated in the solution, increasing SS, COD, BOD, etc. in the treated water, deteriorating the water quality and reducing the transparency. is also decreasing.

That is, in wastewater with a small BOD/N ratio such as human waste desorbed liquid, the smaller this ratio is, the more insufficient the N removal by the denitrification reaction becomes, and a decrease in pH in the nitrification reaction process is unavoidable.

For example, the biological denitrification reaction of N03-N is expressed as 2NOi + 5H2 → N2 + 4H20+ 20H-, and since the equivalent amount of oxygen (BOD) to the hydrogen donor (N2) is 16 g, denitrifying 1 g of NO3-N The required OD is approximately 2.9g.

Therefore, in wastewater with a BOD/N ratio of 1.0 or less, most of the NOx-N remains without being denitrified.

In conventional advanced treatment methods for desorbed liquid, nitrification and denitrification are performed as secondary treatment, followed by coagulation and precipitation treatment.
In order to prevent the pH from dropping in the nitrification tank, an alkaline agent is injected into the nitrification tank.

However, according to this treatment method, pH adjustment is required in both the secondary treatment step and the coagulation treatment step, and furthermore, the treatment effect of the coagulation-sedimentation treatment is not sufficient.

The present invention aims to provide an advanced treatment method including nitrification and denitrification treatment of human waste desorbed liquid, which is more effective in removing BOD, COD, SS, chromaticity, etc. than conventional methods.

Next, an embodiment of the present invention will be described with reference to the drawings.

In the flow sheet shown in the figure, the desorbed liquid produced by anaerobic digestion of human waste in the usual manner passes through a denitrification tank 1 and a nitrification tank 2 in sequence, flows into the first settling tank 3, and is nitrified. A considerable portion of the liquid leaving the tank 2 is returned to the denitrification tank 1 as circulating liquid, and the sludge separated in the first settling tank is returned as return sludge.

Further, dilution water is introduced into the nitrification tank 2 as needed.

The ratio of flow rates of each part is as shown in the figure.

The treatment (secondary treatment) performed in this process is the same as in the conventional nitrification and denitrification treatment, and is clear to those skilled in the art, so detailed explanation will be omitted here.

In any case, if the BOD/N ratio of the desorbed liquid is small,
The pH of the nitrification tank is low at 5.0 to 3.5, and the pH of the first settling tank 3
The secondary treated water taken out has a high content of colloids.

The secondary treated water taken out from the first settling tank 3 is sent to the next flocculation tank 4, where a flocculant is added.

As the flocculant, in addition to inorganic flocculants such as aluminum salts and iron salts, known flocculants such as organic polymer flocculants are used alone or in the form of a mixture in any combination.

Since the colloidal particles in the secondary treatment water are suspended by being reliably negatively charged due to the low pH, they can be coagulated very efficiently by adding the above-mentioned flocculant.

At this time, phosphorus also aggregates. Therefore, if the liquid taken out from the coagulation tank 4 is transferred to the second settling tank 5 and left to stand still, the coagulated flocs will quickly settle and treated water with good quality can be obtained.

The treated water is pH-adjusted as necessary and then discharged.

In addition to precipitation, other solid-liquid separation means such as filtration and centrifugation can also be used as means for separating and removing solids from the liquid taken out from the flocculation tank.

Furthermore, if solid matter is removed in advance using a centrifugal filtration concentrator or the like before the secondary treated water is introduced into the flocculation tank 4, it is possible to reduce the amount of flocculant added.

Next, we will show actual and experimental results using the desorbed liquid from the U human waste treatment plant.

The experiment was conducted according to the flow sheet shown in the drawing. In the present invention, the pH of the nitrification tank was not adjusted, but the pH of the flocculation tank was adjusted to 6. In the conventional example, the pH of the nitrification tank was adjusted to 7, and the pH of the flocculation tank was adjusted to 6. did.

In addition, in the coagulation tank, sulfuric acid band was used as A 1203 and 20
0 mg/l was added, and the water quality of the first sedimentation tank supernatant liquid and the second sedimentation tank supernatant liquid was analyzed.

The results are shown in Table 1 below. As is clear from this, in this invention, although the quality of the secondary treated water is poor (particularly SS and COD), the quality of the coagulated water is actually improved (particularly chromaticity).

The mechanism of why this happens is not clearly elucidated, but it is thought that it is because colloids produced at low pH in the nitrification tank incorporate chromaticity components into them.

Further, according to the method of the present invention, pH adjustment may be performed only once, and the amount of alkaline agent consumed may be small.

An experiment was conducted on different treated water to confirm the effect of adding the flocculant in the flocculating tank 4.

In this experiment, 500 ml of secondary treated water taken out from the first settling tank 3 was placed in a beaker, and 50 mg of sulfate band/
1 (A1203 equivalent) and further added caustic soda as a pH adjuster to adjust the pH to 6.0.
After stirring at pm for 15 minutes, the mixture was allowed to stand for 30 minutes to obtain a supernatant.

Further, the same operation was repeated by changing the amount of sulfuric acid band added.

The properties of the supernatant obtained are shown in Table 1 in comparison with those obtained without the addition of sulfuric acid.

As is clear from the above results, as the amount of sulfate added increases, the quality of the treated water significantly improves, and it can be seen that phosphorus is almost completely removed at about 200 mg/l.

When the pH of the nitrification tank was continuously adjusted to 7, the quality of the final treated water was worse than the above.

As described above, according to the present invention, colloids are flocculated by adding a flocculant to the secondary treatment liquid in which the desorbed liquid is subjected to secondary treatment to bring the pH to below 5 without adjusting the pH in the nitrification tank. A flocculation process is performed.

This not only eliminates the need for a pH adjustment device in the nitrification tank, but also provides good quality treated water.

[Brief explanation of drawings]

The figure is a flow sheet showing an example of the steps of the method of this invention. 1... Denitrification tank, 2... Nitrification tank, 3... First settling tank, 4... Coagulation tank, 5... Second settling tank.

Claims (1)

[Claims] 1. A secondary treatment process having at least a nitrification tank for performing aerobic biological treatment on the desorbed liquid produced by anaerobic digestion of human waste, and secondary treatment water obtained in this secondary treatment process. The method includes a step of adding a flocculant to perform a flocculation treatment, and a step of removing the flocculates generated in this flocculation step, and without adding an alkali agent in the nitrification step, the pH is lower than 5 due to the generated nitrous acid and nitric acid. 1. A method for treating human urine desorbed liquid, the method comprising: producing a colloid.