The present situation and development direction of sewage treatment are analyzed

0. Introduction

With the continuous improvement of social and economic level, people's requirements for the quality of water resources are also constantly improving. For the quality of water resources, people have begun to realize the serious harm caused by water pollution to the environment and economic development. Therefore, sewage treatment has become one of the indispensable links in urban construction.

The treatment of urban sewage is not only an indispensable link in the process of urban development planning and construction, but also has a great impact on social and economic life. At present, many domestic enterprises invest less money in sewage treatment, and the technology is not perfect, which leads to the serious situation of frequent water pollution events in some areas. In addition, some local governments lack effective and reasonable management measures and scientific and reasonable systems to regulate the urban environment and treat the amount of waste water. Meanwhile, many water bodies are damaged, resulting in ecological crisis.

1. The harm of sewage

The harm caused by sewage is obvious, and the construction of sewage treatment plants in cities will also cause great harm to the environment. Its specific performance in the following three aspects:

1.1 Due to the existence of a large number of suspended matter and organic pollutants in the water layer, the water quality deteriorates.

1.2 Water pollution seriously affects people's domestic water use, production and biological development

Water pollution seriously affects people's domestic water consumption, production and biological development, so it is necessary to make full preparations before sewage discharge to avoid unnecessary losses caused by various reasons and waste of water resources [1]. At the same time, it is also necessary to take into account some factors that may cause damage to the environment: for example, human activities or industrial wastewater discharged into the ground, these are problems that cannot be ignored and need to be effectively controlled and treated accordingly. As urban sewage discharge has certain rules, the impact of different stages must be taken into account in sewage treatment [2].

2. Necessity of sewage treatment

The concept of sewage treatment refers to the separation, purification and reuse of pollutants in urban domestic sewage, so as to make them useful information and realize resource recycling [3]. In China's urban sewage treatment, the main treatment is industrial wastewater and waste gas produced in the production process. Industrial wastewater mainly comes from a large amount of ferrochrome slag and domestic waste discharged from iron and steel smelters. In addition, a large number of pollutants containing heavy metal ions such as lead, cadmium (arsenic) compounds discharged from the production process will also cause serious harm to the environment, so it is very necessary and effective to treat sewage [4].

3. China's current water treatment industry chain

Water treatment industry chain refers to the separation, purification and application of pollutants in sewage through the development and utilization of polluted water bodies for the purpose of sewage treatment, forming a series of new products and putting into production [5].

At present, there are two main models in our country: one is government-led [6]. In this case, the government departments are only responsible for formulating corresponding policies to guide the local environmental planning and construction work; The second is the enterprise model dominated by development investment which the market operates spontaneously. At present, China is mainly composed of enterprise self-produced sewage, self-purification sewage and related ancillary facilities. Due to the lack of unified planning and management, as well as the lack of complete systematic design and other reasons, a lot of resources are wasted. On the other hand, it has also led to the emergence of many problems, which have a negative impact on People's Daily life, and bring pollution and destruction to the environment. Sewage treatment is a complex system project, involving a wide range and comprehensive. Therefore, it is necessary for the government and enterprises to cooperate to complete the project [7].

4. Test items and definition of their concepts

The detection items in this experiment are TP, TN, COD, SS, and NH3-N.

TP: refers to the sum of all kinds of phosphorus in sewage, the greater the TP value, the higher the degree of pollution.

TN refers to the sum of all kinds of phosphorus in sewage, and the greater the TN value, the higher the degree of pollution.

NH3-N refers to the content of ammonia nitrogen in water, and the greater the value of NH3-N, the higher the degree of pollution.

CODcr refers to chemical oxygen demand, which is a chemical method to measure the amount of reducing substances in a water sample that need to be oxidized.

BOD5 refers to the 5-day biological oxygen demand, which means that in a certain period of time, microorganisms decompose some oxidized substances in a certain volume of water, and the greater the value of BOD, the higher the degree of pollution.

SS suspended matter refers to a solid substance suspended in water, and the greater the NH3-N value, the higher the degree of pollution.

5. Experimental instruments, instruments, implementation standards and principles

5.1 Experimental technology and implementation standards

This experiment adopts A20+MBR wastewater treatment process, implements G18918-2002 Grade A standard, the average daily treatment capacity is 35,000 cubic meters, the average comprehensive treatment capacity is 35,500 cubic meters, and the designed treatment capacity is 40,000 tons per day.

5.2 Equipment configuration of MBR process sewage treatment device

1. 1 set of grid pool (spacing 2mm), 1 set of aerated sand settling pool, membrane bioreactor: transparent plexiglass material, thickness 12mm.

2, vertical flow initial sedimentation tank 1 set: transparent plexiglass material, thickness 8mm, volume 25L.

3, UV sterilization device 2 sets: UV lamp 2 sets, plexiglass column 2 sets, shading aluminum platinum paper 2 sets.

4, the original water tank, the middle water tank (30L) and the clean water tank are each 1: white PP board, thickness 12mm, the bottom plate is installed with a vent valve, easy to drain the water.

5, mixing motor 1 set (power 20W, speed 110rpm), 304 stainless steel mixing paddle 1 set.

6, anti-corrosion lifting magnetic pump 3 sets, flow: 15 ~ 18(L/min), head: 2.6 ~ 3.3(m) power 25W.

7, 1 aeration pump, (power 220V, power 60W, maximum gas: 9L/min), including 1 set of aeration pipeline.

8, flat film component 1 set (PVDF flat film, area: 0.1m2/ piece, a total of 10 pieces).

9, water diaphragm pump 1, water flow meter 1, (range 3-30L/H).

10, mixed liquid reflux device: reflux pump 1 set, reflux pipeline 1 set.

11, flow measurement and regulation: rotor flow meter, liquid flow 3 (range 3-30L/H), gas flow 1 (range 100~1000L/h).

12, power control system: double-sided matte spray plastic electric control box 1, leakage protector, voltmeter, button switch with lock, line tube, etc.

13, supporting UPVC connection pipes and valves.

14, stainless steel frame test bench.

5.3 Equipment configuration of A2O process sewage treatment device

1, mixing motor 1: power 35W, speed 100rpm; Stainless steel mixing paddle 1.

2, lift pump 1: flow 1.5T/h, lift 2.8m, power 30W.

3, secondary sedimentation tank: transparent plexiglass material, wall thickness of 6mm, effective volume of 25L.

4, hypoxia pool: transparent plexiglass material, wall thickness of 6mm, effective volume of 20L.

5, anaerobic pool: transparent plexiglass material, wall thickness 6mm, effective volume 15L.

6, aerobic pool: transparent plexiglass material, thickness 12mm, effective volume 45L.

7. 2 sets of mixing device: adjustable speed.

8, the original water tank and the clean water tank each 1: white PP board, thickness 12mm, the original water tank volume 100L, the clean water tank volume 50L, the tank bottom plate is installed with a vent valve, easy to drain the water.

9, return pump 2 sets: flow digital display and stepless speed regulation, with timing quantitative transmission and suction function (prevent dripping), the maximum flow can reach 32L/h and 14L/h.

10, 1 air pump: power 95W, exhaust 95L/min, pressure > 0.035Mpa; 2 aeration systems.

11, flow measurement and regulation: rotor flow meter, liquid flow 1: range 2-20L/H; Gas flow 1: range 0.1-1m3/h.

12, 304 stainless steel table.

13, power control system: double-sided matte spray plastic electric control box 1, leakage protector, voltmeter, self-locking button switch with light, line slot, etc.

14, transparent silicone pipe, valve, elbow.

15, stainless steel frame test bench.

Operating conditions: normal temperature and pressure operation, power supply voltage 220V.

5.4 Experimental Principles

5.4.1 Experimental principle of MBR wastewater treatment process

MBR is a new wastewater treatment process with high efficiency and high function. It uses a membrane separation tool to screen the sludge from the first reaction tank with organic matter, eliminating the need for a secondary sedimentation tank [8]. As a result, the activated sludge concentration is greatly increased, HRT and SRT can be controlled separately, and hard-to degrade materials are frequently used and degraded in the machine. Compared with traditional methods, this MBR method combining membrane with biochemical reaction is effective [9].

mbr process Description:

Raw water → Grid → regulating tank → lifting pump → Bioreactor → circulating pump → membrane assembly → Disinfection device → reclaimed water storage tank → reclaimed water system [10]

The function of the regulating tank is mainly to collect the generated sewage, balance the overall water quality, and adjust the pH in the overall water quality, so as to ensure that the experiment can be carried out smoothly.

The role of the anaerobic tank is mainly to gradually disintegrate large molecular organic matter into small molecules, so that it is easier to handle later, and can also remove local phosphorus.

The main function of the anoxic tank is to remove a series of ammonia containing sewage such as ammonia nitrogen.

Aerobic tank: The degraded organic matter is further degraded into carbon dioxide and water by the aerobic microorganisms in the tank under the condition of aeration and oxygenation, thoroughly decomposing the organic matter, and at the same time, the phosphorous releasing microorganisms absorb phosphorus in excess to remove phosphorus.

MBR membrane pool refers to the step of membrane separation by using the characteristics of the membrane after the sewage has been treated in the normal steps, and the water quality can be further improved.

The function of the clear pool is either to reuse the water or to discharge it directly.

5.4.1 Experimental principle of A2O wastewater treatment process

A2O sewage treatment means that the sewage first enters the anaerobic tank stage, after a certain period of decomposition, flows into the anoxic tank, and the denitrifying bacteria in the anoxic tank can further purify the water quality, and then flows into the aerobic tank stage. At this time, the water can re-enter the anoxic stage through the self-circulation system, or enter the sedimentation tank after decomposition, and directly discharge the water [11].