JPS62125900A - Method for cleaning up of sludge deposited in culture farm for fish and shellfishes - Google Patents

Abstract

PURPOSE:To make the cost of a sludge treatment lower than for the conventional method by adopting biochemical oxidation and biochemical denitrification methods, eliminating the need for land treatment of sludge and sand and utilizing activated sludge as auxiliary feed. CONSTITUTION:(1) The sludge 1 of a culture farm is pumped up into a tank 3 and is settled so that the sludge is separated to sand and sludge sewer. (2) The separated sand is cleaned with the supernatant from the following stage (5) in a tank 5 and is then returned to the culture farm. (3) The above-mentioned sludge sewer and the waste water of cleaning the above-mentioned sand are supplied to a denitrification tank 9 and are subjected to biochemical denitrification while part of the waste sludge water of the following stage (4) and part of the activated sludge of the following stage (5) are circulated to the tank 9 and are stirred. (4) The sludge sewer of the tank 9 is supplied to an aeration tank 10 and is subjected to the biochemical oxidation to form the waste sludge water. (5) The waste sludge water of the tank 10 is supplied to a settling tank 13 to settle the activated sludge. Part of the supernatant is supplied to the tank 5 and the balance is returned to the culture farm. Part of the activated sludge is supplied to the tank 9 and the remainder is returned to the culture farm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for purifying sludge deposited on the bottom of water in a fish and shellfish breeding farm.

[Prior art]

In general, fish and shellfish breeding is carried out in waters with relatively low ocean currents, such as bays and inland seas, or in semi-enclosed or closed waters such as ponds.

As a result, the excrement and carcasses of fish and shellfish, as well as excess feed, settle on the bottom of the water body, forming so-called sludge, which leads to abnormal growth of plankton and further causes problems such as the occurrence of red algae and blue-green algae. are doing.

For this reason, dissolved oxygen, which is essential for fish [IIn], has decreased, and in severe cases, dissolved oxygen has fallen below 2 mg/e, which is said to be the critical value for the survival of fish and shellfish.

In addition, harmful ammonia is generated from the sludge, and E. coli bacteria grows which is harmful and reduces freshness.
This is becoming a worrying problem from the perspective of fish and shellfish aquaculture.

By the way, as methods for purifying such sludge, the (al dredging method) and the method of blowing an oxygen source such as air into the sludge are known.

However, the method of (Al) has the following drawbacks, and until now only a few examples have been implemented, and most of the methods remain as plans.

b) Large-scale dredging equipment is required.

The problem is how to dispose of the large amount of dredged sludge.

C. Even if dredged sludge is disposed of in a landfill, large-scale sewage purification equipment is required to prevent secondary pollution.

Second, most of the solid content in dredged sludge is sand, and it is difficult to turn this sand into a resource.

Furthermore, the method (b) is still being considered at the research stage and has the following drawbacks.

B. Injecting an oxygen source close to the ocean floor may actually spread the sludge layer, worsening the habitat for fish and shellfish.

B. Since the oxygen source is blown directly into the sludge layer, the efficiency of oxygen transfer (dissolution into water) is low.

Ha, harmful ammonia and E. coli cannot be removed.

[Purpose of the invention]

The present invention aims to eliminate the drawbacks of the above-mentioned conventional methods.

[Structure of the invention]

The method for purifying sludge deposited at a fish and shellfish farm according to the present invention, which achieves the above object, is characterized by comprising the following steps.

(1) Pump up the sludge deposited on a fish and shellfish farm, allow the sludge to settle, and separate it into sand and sludge wastewater.

(2) The separated sand is washed with the supernatant liquid from step (5) below and then returned to the # breeding farm.

(3) The sludge wastewater and the sand washing wastewater are supplied to the denitrification tank, and a part of the sludge wastewater formed in the aeration tank in the following step (4) and a part of the sludge wastewater formed in the following step (5) are separated by sedimentation water. A part of the activated sludge is circulated to the denitrification tank, and nitrate or nitrite nitrogen based on the recycled sludge wastewater is biochemically denitrified under anaerobic conditions while being pumped and stirred. Decomposes and removes some organic matter.

(4) The sludge wastewater treated in the denitrification tank is supplied to the aeration tank, and air is blown into it to biochemically oxidize and decompose organic matter in the sludge wastewater under aerobic conditions, and ammonia nitrogen is removed. is oxidized to nitric acid or nitrite to form sludge wastewater.

(5) Supplying the sludge wastewater treated in the aeration tank to the settling tank, allowing the activated sludge to settle, supplying a portion of the supernatant liquid to the sand washing tank, and returning the remainder to the aquaculture farm; A portion of the activated sludge is supplied to the denitrification tank and the remainder is returned to the farm.

Embodiments of the present invention will be explained below with reference to the drawings.

First, in the present invention, sludge 1 deposited on the bottom of a fish and shellfish culture hot water area is pumped up through pipe a.

Pumping is performed by, for example, a raw sludge pump 2, and the pumped sludge is transported to a dedicated purge ship or land facility.

The sludge may be pumped up by either a hatch type or a continuous type, including all operations of the present invention described below.

The pumped up sludge is supplied to a sand separator 3, where the sand constituting the sludge settles and is separated into sand 4 and sludge water 7.

As the sand separator 3, for example, a liquid cyclone is used, and the separated sand 4 is sent to a sand purification tank 5, and a supernatant is sent to this sand purification M5 from a sedimentation tank 13, which will be described later, via a pipe and i. A liquid 14 is supplied to wash the sand 4.

The washed sand 6 is returned to the aquaculture hot water area 22 via a pipe.

The sludge wastewater 7 separated by the sand separator 3 is sent to a denitrification tank 9 via a pipe C, and the cleaning waste water 8 from the sand clarification tank 5 is supplied to a denitrification tank N9 via a pipe d.

On the other hand, a part of the activated sludge 16 formed in the aeration tank 10, which will be described later, and settled and concentrated in the settling tank 13, which will be described later, is also supplied to the denitrification tank 9 by the activated sludge pump 12 via pipes e and f. A portion of the sludge waste water 11 formed in the aeration tank 10 is also supplied to the denitrification tank 9 via the pipe g.

The denitrification tank 9 is preferably of a sealed type in order to maintain an anaerobic state, and the sludge forming the sludge sewage 7 is stirred gently enough to keep it in a free state, for example, mechanically stirred by a stirrer 15.

In addition, sludge drainage 11 is circulated and supplied from the aeration tank 10.
Although the amount varies depending on the composition of the sludge 1, it is usually 4 to 6 times the amount of the sludge wastewater 7.

The reaction in this denitrification tank 9 is expressed by the following equation (1), and the sludge wastewater 11 is circulated and supplied from the aeration tank 10, which will be described later.
Nitrate or nitrite nitrogen is denitrified by nitrifying bacteria to form and release nitrogen gas.

In this case, the organic matter in the sludge is used as a hydrogen donor, so that some of the organic matter is decomposed and removed.

The pH during denitrification is usually 7.5 to 8.5, but
Since hydroxide ions are generated as shown in equation (1), there is no need to particularly adjust the pH.

Note that the cellular material formed by the above formula (1) is bacterial cell sludge itself.

The sludge wastewater 7'' from which some organic matter has been decomposed and removed in the denitrification tank 9 is then sent to the aeration tank 10.

Air is supplied to the aeration tank 10 by a blower 17,
Air is dispersed and dissolved into the sludge wastewater 7' through the aeration device 18.

The reaction in the aeration tank 10 is the biochemical oxidation of organic matter and nitrogen compounds (organic and inorganic! oxidative decomposition of organic matter by biochemical oxidizing bacteria;
and nitrification (nitrification) of ammonia due to nitrification.

As is clear from the above equation (3), hydrogen ions are generated as a result of the reaction, so alkali is added from the alkali tank 19 to the aeration tank 10 in order to adjust the pt+ of the reaction system.

The preferred pH for nitrification (nitrification) is usually 6.8 to 7.3. The amount of alkali required for pH adjustment is also related to the alkalinity of seawater and varies somewhat depending on the season.

Note that the cellular material produced by the above formulas (2) to (4) is bacterial sludge itself, that is, activated sludge.

Sludge wastewater 11 after being biochemically oxidized in the aeration tank 10
is supplied to a settling tank 13, where activated sludge 16 is settled and supernatant liquid 14 is separated by overflow.

As mentioned above, the supernatant liquid 14 is piped by the pump 21,
A part of the water is sent to the sand septic tank 5 via i, and the remainder is returned to the aquaculture hot water area 22 via pipe j.

This supernatant liquid 14 is beneficial for growth as water rich in dissolved oxygen.

In addition, the activated sludge 16 taken out from the bottom of the settling tank 13
A part of the activated sludge is sent to the denitrification tank 9 via the pipes e and f by the activated sludge pump R2 as described above, and the remaining activated sludge is returned to the aquaculture water area 22 via the pipes e and k.

Since this activated sludge contains a large amount of protein, it is useful as supplementary feed for breeding farms.

Furthermore, activated sludge generally consists of an aggregate of various microorganisms such as bacteria and protozoa, forming a so-called pyramid-shaped food chain system, and harmful bacteria such as E. coli are preyed on by the protozoa.

Therefore, the supernatant liquid 14 and activated lη mud 16 returned to the aquaculture hot water area 22 do not require any particular sterilization treatment.

〔Effect of the invention〕

As described above, according to the present invention, the following effects can be achieved.

(1) Since the sludge is pumped up and treated, for example, by a dedicated purge ship or land facility, there is no problem of the sludge spreading into the treated water area.

(2) Since the sludge wastewater is subjected to biochemical oxidation, the organic matter and nitrogen-containing compounds that are the main cause of oxygen deficiency (/8 oxygen deficiency) in the sludge water area are removed without producing harmful substances by the action of microorganisms. , can be effectively oxidized and decomposed and removed.

(3) Furthermore, since a biochemical denitrification method is used in combination, nitrogen-containing compounds can be decomposed into harmless nitrogen gas.

(4) The microorganisms involved in the reaction may be naturally occurring, and therefore can be easily cultured by conventional methods, and since they proliferate using sludge as a substrate, there is no need for replenishment.

(5) Harmful bacteria such as E. coli are also captured and removed by protozoa coexisting in the activated sludge in the aeration tank.

(6) Activated sludge produced as a result of the reaction is returned to the farm, so there is no need to dispose of it on land.

In addition, activated sludge is rich in protein content and can be used (resourced) as supplementary feed for aquaculture.

(7) The large amount of sand contained in the sludge is returned to the water area of the farm after washing, so there is no need to dispose of the sand on land.

(8) By adopting the above-mentioned biochemical oxidation and denitrification methods, eliminating the need for terrestrial disposal of sludge and sand, and using activated sludge as supplementary feed, sludge treatment costs are significantly reduced compared to conventional methods. can do.

Examples of the present invention will be described below.

〔Example〕

According to the method of the present invention described above, sludge deposits in an oyster farm were purified.

The composition of the sludge subjected to the test was 27.0% by weight of sand, 380mg of organic matter/12mg/j of R1 total nitrogen! (inner ammonia nitrogen 5 mg/f), BOD (biochemical oxygen demand) was 270 mg/β.

The sludge wastewater, in which the sand had been precipitated and separated, was stored in a wastewater tank and supplied to the treatment system using a pump for continuous treatment.

The separated sand was washed with initially treated water, and the washing wastewater was put into a wastewater tank where it was combined with sludge wastewater.

The treatment system includes a 51-volume denitrification tank, a 51-volume aeration tank, and 1 and 3.
5 I! It consists of a volume sedimentation tank (the above volumes are all effective volumes), the temperature is 15.1±1℃, and the amount of sludge sewage supplied is 0.
．． 83#/hour, aeration tank has BOD sludge load 0.4Kg/
Kg/day, ventilation speed 0.1m/r+?・The pH was adjusted to 7±0.2 by adding aqueous caustic soda solution, the denitrification tank had a sludge wastewater circulation ratio 4 times, and the nitrogen volume load was 0.03Kg/m
・The operating conditions were set as day.

The above operating conditions are within the general conditions in activated sludge treatment, nitrification and denitrification of industrial wastewater.

The BOD of treated water (supernatant water flowing out of the settling tank) during continuous operation is 25 to 35 mg/(1 (removal rate 85 to 90%)
), total nitrogen 3-4 mg/j! (removal rate 65-75%).

Additionally, activated sludge equivalent to approximately 90 mg/j2 (based on the amount of inflowing sludge sewage) was generated.

In addition, prior to the steady operation test, activated sludge from which industrial wastewater with an inorganic salt concentration of 20,000 to 30,000 mg/E was being treated was introduced as seed sludge, and sludge sewage was poured out to allow bacteria to acclimatize according to the usual method. went.

[Brief explanation of drawings]

The figure is a process diagram showing the steps of the present invention. 171. Sludge, 3-sand separation tank, 5-sand cleaning tank, 9.-
・Denitrification tank, 10-Aeration tank, 13-Settling tank.

Claims (1)

[Claims] A method for purifying sludge deposited on a fish and shellfish farm, characterized by comprising the following steps: (1) Pump up the sludge deposited on the fish and shellfish farm, and let the sludge settle to form sand and sludge wastewater. Separate into two parts. (2) The separated sand is washed with the supernatant liquid from step (5) below and then returned to the farm. (3) The sludge wastewater and the sand washing wastewater are supplied to the denitrification tank, and a part of the sludge wastewater formed in the aeration tank in the following step (4) and separated in the settling tank in the following step (5) are A part of the activated sludge is circulated to the denitrification tank, and while stirring, biochemically denitrifies the nitric acid or nitrite nitrogen based on the recycled sludge wastewater under anaerobic conditions, and removes the organic matter in the sludge wastewater. Part of it is disassembled and removed. (4) The sludge wastewater treated in the denitrification tank is supplied to the aeration tank, and air is blown into it to biochemically oxidize and decompose organic matter in the sludge wastewater under aerobic conditions, and ammonia nitrogen is removed. is oxidized to nitric acid or nitrite to form sludge wastewater. (5) Supplying the sludge wastewater treated in the aeration tank to the settling tank, allowing the activated sludge to settle, supplying a portion of the supernatant liquid to the sand washing tank, and returning the remainder to the aquaculture farm; A portion of the activated sludge is supplied to the denitrification tank and the remainder is returned to the farm.