Rural decentralized sewage treatment facilities

Rural decentralized sewage treatment facilities

National universal equipment, a popular equipment in the sewage treatment industry.

The integrated equipment adopts new processes, technologies, and materials, and is a new type of heavyweight equipment.

It has been well applied in domestic wastewater, medical wastewater, washing wastewater, slaughter wastewater, spraying wastewater, and similar industrial wastewater.

The structure of the contact oxidation tank consists of an aeration system, packing material, and tank body. The aeration system provides oxygen to microorganisms attached to the packing material, allowing them to fully contact the sewage and decompose organic matter. It can be divided into diversion type and direct type. The diversion type aeration device is located on one side of the tank, and the packing is installed on the other side. It relies on the lifting effect of a pump or air to circulate the water flow in the packing layer and supply oxygen to the biofilm on the packing; The direct method involves blowing air directly at the bottom of the oxidation tank packing for aeration.
The treatment process of contact oxidation tank generally includes two methods: one-stage method (primary biological contact oxidation) and two-stage method (secondary biological contact oxidation).

One stage method: The raw water first passes through the regulating tank, then enters the biological contact oxidation tank, and then flows into the secondary sedimentation tank for sludge water separation.
Two stage method: The purpose of using the two-stage method is to increase the biological oxidation time, improve the efficiency of biochemical treatment, and better adapt to changes in raw water quality, so as to stabilize the treated water quality. After being regulated by the regulating tank, the raw water enters the biological contact oxidation tank and then flows into the intermediate sedimentation tank for mud water separation. The upper layer water continues to enter the second contact oxidation tank and finally flows into the secondary sedimentation tank for mud water separation again. The effluent is discharged, and the sludge in the sedimentation tank is regularly discharged.

With the change of practice, these two processes can also change accordingly: for example, dividing the contact oxidation tank into grids, not setting up an intermediate sedimentation tank, and operating according to the push flow pattern. The one-stage method has a simple and easy process, convenient operation, and lower investment, but its ability to degrade BOD is not as good as the two-stage method. The two-stage process has a good processing effect and can shorten the total time required for biological oxidation, but it increases the processing equipment and maintenance management work, and the investment is also higher than the one-stage process. Generally speaking, when the organic load is low and the hydraulic load is high, it is better to use a one-stage method. When the organic load is high, it is more appropriate to use two-stage method or push flow method. The experiment shows that in the two-stage method, the volume ratio of the contact oxidation tank to the second contact oxidation tank should be 7:3. In the push flow process, it can be divided into grids according to the conditions of BOD changes (* grid maximum, gradually decreasing thereafter); It can also be divided into grids according to hydraulic load (each grid is of equal size).

The source of ammonia nitrogen wastewater
The pathways through which nitrogen-containing substances enter the water environment mainly include two aspects: natural processes and human activities. The natural sources and processes of nitrogen-containing substances entering the water environment mainly include precipitation, dust deposition, non urban runoff, and biological nitrogen fixation. Human activities are also an important source of nitrogen in water environments, mainly including untreated or treated urban domestic and industrial wastewater, various leaching fluids, and surface runoff. Artificially synthesized chemical fertilizers are the main source of nitrogen nutrients in water bodies. The vast majority of nitrogen compounds that have not been utilized by crops are carried into groundwater and surface water by agricultural drainage and surface runoff. With the development of industries such as petroleum, chemical, food, and pharmaceuticals, as well as the continuous improvement of people's living standards, the content of ammonia nitrogen in urban domestic sewage and leachate from garbage has sharply increased. In recent years, with the development of the economy, the arbitrary discharge of more and more nitrogen-containing pollutants has caused great harm to the environment. Nitrogen exists in various forms in wastewater, including organic nitrogen, ammonia nitrogen (NH4+- N), nitrate nitrogen (NO3-- N), and nitrite nitrogen (NO2-- N), with ammonia nitrogen being one of the most predominant forms. Ammonia nitrogen in wastewater refers to nitrogen that exists in the form of free ammonia and ionized ammonium, mainly from the decomposition of nitrogen-containing organic compounds in domestic wastewater, industrial wastewater such as coking and synthetic ammonia, and agricultural drainage. There are many sources of ammonia nitrogen pollution, with large emissions and varying concentrations of emissions.

Rural decentralized sewage treatment facilities

contact oxidation tank
The structure includes the tank body, filling material, water distribution device, and aeration device. The working principle is to set up fillers in the aeration tank and use them as carriers for the biofilm. The wastewater to be treated flows through the packing material at a certain flow rate after oxygenation, and comes into contact with the biofilm. The biofilm and suspended activated sludge work together to purify the wastewater.
Contact oxidation method is a new wastewater biochemical treatment method that combines the characteristics of activated sludge method and biofilm method. The main equipment for this method is a biological contact oxidation filter. In an airtight aeration tank, there are fillers such as coke, gravel, and plastic honeycomb. The fillers are submerged in water and are aerated and oxygenated at the bottom of the fillers using a blower. This method is called blower aeration; Air can carry the wastewater to be treated from bottom to top, freely passing through the filter material to reach the ground. After the air escapes, the wastewater returns to the bottom of the pool from top to bottom in the filter material compartment. Activated sludge adheres to the surface of the packing material and does not flow with water. Due to the strong agitation of the rising airflow, the biofilm is constantly renewed, thereby improving the purification effect.

Reaction mechanism: Fill materials are set up in the tank, and aeration is carried out at the bottom of the tank to oxygenate the sewage and keep the sewage in a flowing state to ensure sufficient contact between the sewage and the filling materials in the sewage, avoiding the defect of uneven contact between sewage and filling materials in the biological contact oxidation tank. In this method, the oxygen demand of microorganisms is supplied by air blowing aeration. After the biofilm grows to a certain thickness, the microorganisms on the packing wall will undergo anaerobic metabolism due to hypoxia. The gas produced and the scouring effect formed by aeration will cause the biofilm to fall off and promote the growth of new biofilm. At this time, the fallen biofilm will flow out of the pool with the effluent.
Principle: Install packing material in the aeration tank as a carrier for the biofilm. Biofilms are composed of bacteria, fungi, and protozoa. These microorganisms rely on the organic matter adsorbed and precipitated on the membrane as nutrients, synthesizing some of the organic matter into cellular substances, which become active substances in cells; The other part is decomposed into metabolites, and the energy released during decomposition metabolism is used for microbial growth.

The concept of hydrolysis (acidification)
Hydrolysis in chemistry refers to a general term for a type of reaction between a compound and water. For example, the reaction of ester substances hydrolyzing to produce alcohols and organic acids. In wastewater biological treatment, hydrolysis refers to the biochemical reaction that occurs outside the cell before organic matter (matrix) enters the cell. The typical feature of this stage is that the site of biological reactions occurs outside the cell, and microorganisms complete the biocatalytic oxidation reaction by releasing extracellular free enzymes or fixed enzymes attached to the outer wall of the cell (mainly including the breaking of chains and water solubility of large molecular substances). Research has shown that many substances in nature, such as proteins, sugars, fats, etc., can be hydrolyzed smoothly under aerobic, anaerobic, or anaerobic conditions.
Acidification is a typical fermentation process. The basic characteristic of this stage is that the metabolic products of microorganisms are mainly various organic acids (such as acetic acid, propionic acid, citric acid, etc.). Hydrolysis bacteria are actually a type of fermentation bacteria with hydrolysis ability. Hydrolysis is an energy consuming process, and the purpose of fermentation bacteria investing energy in hydrolysis is to obtain a water-soluble substrate that can be fermented, and to obtain energy through intracellular biochemical reactions, while eliminating metabolites (mainly various organic acids under anaerobic conditions). In practical engineering, it is hoped that the acid production process can be controlled within the minimum range. Because acidification causes a significant decrease in pH, it is not conducive to hydrolysis.

The difference between hydrolysis (acidification) and anaerobic digestion
In principle, hydrolysis (acidification) is a two-stage anaerobic digestion process, but the goals pursued by hydrolysis (acidification) technology and anaerobic digestion are different, so they are completely different treatment methods. The main purpose of hydrolysis (acidification) system is to convert insoluble organic matter in raw water into dissolved organic matter, especially in industrial wastewater treatment. The main purpose is to convert difficult to biodegrade substances into easily biodegradable substances, improve the biodegradability of wastewater, and facilitate subsequent aerobic biological treatment. Considering the energy consumption issue of subsequent aerobic treatment, hydrolysis (acidification) is mainly used for the pretreatment of low concentration and difficult to degrade wastewater.

In a mixed anaerobic digestion system, hydrolysis acidification is organically integrated with the entire digestion process, sharing a reactor. The purpose of hydrolysis and acidification is to provide a substrate for the methanogenesis stage in the mixed anaerobic digestion process. The acid producing stage (acid producing phase) in two-phase anaerobic digestion separates the acid producing and methane producing stages in mixed anaerobic digestion to form their own environments. At the same time, the form of the acid produced also has requirements (mainly acetic acid). In addition, when wastewater contains high concentrations of nitrate, nitrite, sulfuric acid, and sulfite, these substances and their transformation products are not only toxic to methane seedlings, but also affect the quality of biogas and are removed in the acid producing phase.

Acidification:
(1) Improve the biodegradability of wastewater: it can convert large organic molecules into small molecules.
(2) Removing COD from wastewater: Since it is a heterotrophic microbial bacterium, it must extract nutrients from the environment, so some organic matter must be degraded and synthesized into its own cells.
Problems with hydrolysis acidification method
(1) The development and application time of hydrolysis acidification method is relatively short. Due to the lack of reference materials for hydrolysis acidification method design, there are many errors in engineering design, which makes it difficult to fully utilize the process effect of hydrolysis acidification method and affects the promotion of the process.
(2) The hydrolysis acidification method is different from traditional anaerobic processes, and its water distribution, sludge discharge, and other issues need to be considered. It cannot be simply applied and needs to be constructed reasonably according to the process requirements during construction.

(3) The hydrolysis acidification method is the first two stages of anaerobic degradation, which requires reasonable design and operation debugging, otherwise it is easy to enter the methane production stage and difficult to achieve the hydrolysis acidification function.
(4) The hydrolysis acidification method has been used for wastewater treatment in various industries, and there are specific process design parameters in various engineering applications. Currently, there is a lack of unified and reasonable design standards.

Hydrolytic acidification is mainly used in wastewater treatment processes with high organic matter concentration and high SS, and is a relatively important process. Several typical high concentration organic wastewater, such as coking wastewater, pharmaceutical wastewater, textile wastewater, printing and dyeing wastewater, beer wastewater, petroleum wastewater, chemical wastewater, etc. In this type of organic wastewater, there are often high concentrations of biologically recalcitrant substances, even biotoxicants, with a wide variety of types. Wastewater with high SS concentration includes papermaking wastewater, printing and dyeing wastewater, pig farm wastewater, fecal wastewater, fertilizer plant wastewater, pharmaceutical plant wastewater, food plant wastewater, etc.

Biological fluidized bed
Biological fluidized bed technology is a technology that uses gas or liquid to fluidized solid particulate filter materials with attached microorganisms, purifying wastewater. The biological fluidized bed method fully utilizes the characteristics of different stages of microbial life activities, and divides the treatment stage into three stages based on the growth characteristics of microorganisms: fixed bed stage, fluidized bed stage, and liquid transport stage. The main advantages of a biological fluidized bed are:
1. High volumetric load and strong impact resistance. Due to the use of small-sized solid particles as the carrier in a fluidized bed, the unit volume surface area of the biological fluidized bed is much larger than that of other biofilm methods, and its resistance ability is higher than other biological treatment methods.
2. Good purification effect. Due to the intense movement of the carrier particles, the interface is constantly updated, which not only facilitates the adsorption and degradation of pollutants by microorganisms, but also accelerates the biochemical reaction rate, thereby improving the purification effect.
3. Microorganisms have strong activity. Due to the continuous collision and friction between biological particles, the thickness of the biofilm is thin and uniform. For similar types of wastewater, under the same treatment conditions, biofilm not only has a fast reaction rate but also a very fast respiration rate, so the activity of microorganisms is strong.

The application advantages of biofilm in sewage treatment
1. Adaptability to the quality and quantity of incoming and outgoing water.
2. The biofilm method is easy to manage and has low shipping costs.
3. Biological methods have high requirements for environmental temperature. If the temperature is too high or too low, it can affect the vitality of membrane operation and lead to membrane damage.
4. The specific surface area of this carrier has a significant impact on the effectiveness of biofilm treatment.
5. It can overcome the disadvantage of filamentous expansion of sludge in activated sludge process and significantly reduce the amount of remaining sludge.
6. Biofilm method is a consumable, and the membrane needs to be regularly updated to avoid damage and blockage of the filter material, which can reduce the quality of the effluent.

The treatment process of hydrolysis acidification tank: Anaerobic biological treatment of wastewater refers to the process of decomposing various complex organic compounds in wastewater into substances such as methane and carbon dioxide through the action of anaerobic microorganisms under the condition of no oxygen molecules.

Anaerobic biochemical treatment process: The anaerobic degradation of polymer organic matter can be divided into four stages: hydrolysis stage, acidification (also known as fermentation) stage, acetic acid production stage, and methane production stage.
Hydrolysis stage: Hydrolysis can be defined as the process of converting complex insoluble polymers into simple soluble monomers or dimers.
Acidification (also known as fermentation) stage: Acidification can be defined as the biodegradation process of organic compounds that act as both electron acceptors and electron donors. During this process, dissolved organic compounds are converted into end products mainly composed of volatile fatty acids. Therefore, this process is also known as acidification.

Acetic acid production stage: Under the action of hydrogen producing acetic acid producing bacteria, the products of the previous stage are further converted into acetic acid, hydrogen gas, carbonic acid, and new cellular substances.
Methane production stage: During this stage, acetic acid, hydrogen, carbonic acid, formic acid, and methanol are converted into methane, carbon dioxide, and new cellular substances.
In general, the hydrolysis stage is a necessary process for the degradation of large organic molecules. In order for large organic molecules to be utilized by microorganisms, they must first be hydrolyzed into small organic molecules before entering bacterial cells for further degradation. The acidification stage is an accelerated process of organic matter degradation, as it further converts hydrolyzed small molecule organic matter into simple compounds and secretes them outside the cell. This is also why hydrolysis acidification is often used as a pretreatment unit in actual industrial wastewater treatment projects.
The biological contact oxidation method is a comprehensive sewage treatment process that combines an submerged aerated biofilter with an aeration tank. Its advantages are strong shock resistance and high volumetric load. The oxygen supply of the biological contact oxidation method is very sufficient, which accelerates the membrane renewal speed, improves the activity of the biofilm, enhances its impact resistance, reduces pollution, and lowers mechanical wear. However, the filter material of the biological contact oxidation method needs to be regularly managed to avoid blockage.