Analysis and application of residential sewage treatment technology?

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An ecological environment of fresh air, shady trees, tranquility and comfort has become the development concept of modern residential communities. However, as the pace of urbanization accelerates, the most direct manifestation is that water consumption is increasing, urban pollution is becoming more and more serious, and water resources are becoming increasingly tense. How to solve the contradiction between urban construction and water resource shortage? Sewage treatment and reuse is the most direct and important method to reuse urban water resources. By treating domestic sewage and reusing it, it can not only green and beautify the community environment, but also reduce the waste of water resources, achieving the purpose of protecting the environment and reducing pollution.

1. Characteristics of sewage in residential areas

1. Main sources of sewage

Sewage in residential areas is mainly domestic sewage, including toilet sewage, kitchen sewage and washing Sewage, etc.

2. The main components of sewage

Domestic sewage contains a large amount of organic matter such as fiber, grease, starch and protein, as well as inorganic matter such as vegetable scraps, sediment and domestic impurities. Contains pathogenic bacteria, viruses and parasite eggs. The concentration of pollutants in domestic sewage is generally low, BOD5/CODcr is usually around 0.5, and it has good biodegradability.

3. Characteristics of sewage production

Since the composition of residential areas is relatively simple, most of them are office workers and students, and a few are idle people, the water consumption time is very concentrated, mainly concentrated in the three areas. Water consumption varies greatly between meals and before going to bed, which also causes large changes in sewage volume.

2. Treatment process for community sewage reuse

Because the sewage in residential communities has good biodegradability, biochemical treatment methods can be used. After the effluent water quality reaches the standard, it can be used for greening and landscape water. , watering roads, washing cars, etc.

1. Sewage treatment process

Septic tank → primary treatment (primary sedimentation tank) → biochemical secondary treatment → advanced treatment (coagulation and filtration) → disinfection → reuse.

Since the volume of sewage treatment water in the community is small, and the property management personnel are not necessarily professional, it is necessary to adopt a method that requires less investment, saves land, is simple to operate, has reliable technology, and is unmanned based on the characteristics of the sewage in the community. Managed processing technology. During process design, a treatment process that generates less sludge should be used as much as possible to prevent pollution of the community environment due to insufficient sludge treatment.

2. Processes suitable for community sewage treatment

(1) Sequential batch intermittent activated sludge method (SBR method) or CASS method

The SBR method is Abbreviation for sequential batch intermittent activated sludge process. It has the characteristics of small floor space, low investment, high degree of automation, less sludge and easy sedimentation, phosphorus and nitrogen removal, etc. It is better than other aerobic treatment methods. The process consists of reactors operating intermittently in a certain time sequence.

The CASS reaction tank is a new process developed on the basis of the SBR process. That is, a biological selector is added to the water inlet end of the SBR tank to achieve continuous water inflow (continuous water inflow during the sedimentation period and drainage period). ), intermittent drainage. It has the characteristics of small size, low cost, high degree of automation, high treatment efficiency, phosphorus and denitrification, etc. It is an ideal process for residential sewage treatment. The reuse process is: sewage→grill→regulating pool→lift pump→SBR or CASS→filtration→disinfection→water reuse.

(2) Biological contact oxidation method

Biological contact oxidation method is a sewage biological treatment technology between activated sludge method and biofilm method, which has the advantages of both. , is one of the earliest technologies adopted for domestic sewage treatment in residential areas. It has the characteristics of small footprint, strong impact load resistance, many biological species, less sludge and easy sedimentation, no sludge backflow, phosphorus and nitrogen removal, etc. The process is: fill the biological reaction tank with fillers, and the oxygenated sewage submerges all the fillers and flows through the fillers at a certain flow rate. The filler is covered with biofilm, and the sewage is in extensive contact with the biofilm. Under the action of the metabolism of microorganisms on the biofilm, organic pollutants in the sewage are removed and the sewage is purified.

The reuse process is: sewage → grille → regulating tank → lifting pump → contact oxidation tank → sedimentation tank → filtration → disinfection → effluent reuse.

(3) Two-stage activated sludge method (AB method)

Two-stage activated sludge method, referred to as AB method. It has the characteristics of strong impact load resistance, stable treatment effect, low operating cost, phosphorus and nitrogen removal, etc. The process is: there is no primary sedimentation tank, high load in section A, low load in section B, and the sludge in sections A and B is returned respectively, making full use of the metabolism of microorganisms in the sludge to remove organic pollutants in the sewage.

The reuse process is: sewage → grille → top air conditioning tank → section A aeration tank → section A sedimentation tank → section B aeration tank → section B sedimentation tank → filtration → disinfection → Discharge water for reuse.

(4) A/O process

A/O process is anoxic-aerobic sewage treatment process. It has the characteristics of strong adaptability, resistance to impact load, high volume load, low sludge volume, and good denitrification effect. It is especially suitable for small and medium-sized sewage treatment stations. This process is: first introduce the sewage into the anoxic tank, and the denitrifying bacteria in the return sludge use the organic matter in the original sewage as a carbon source to reduce a large amount of nitrate nitrogen in the return mixed liquid into nitrogen, thereby achieving the purpose of denitrification. ; The sewage then enters the aerobic tank, where most organic matter is digested and degraded. A secondary sedimentation tank is set up after the aerobic tank, and part of the settled sludge flows back to the anoxic tank to provide sufficient microorganisms, and at the same time, the mixed liquid in the aerobic tank is returned to the anoxic tank to ensure that there is enough nitrate in the anoxic tank. The reuse process is: sewage → primary sedimentation tank → anoxic tank → aerobic tank → secondary sedimentation tank → filtration → disinfection → effluent reuse.

(5) Anaerobic biological filter

Anaerobic biological filter is an anaerobic biofilm treatment device with filler inside as a microbial carrier. It has the characteristics of no energy consumption, low cost, simple management, no noise, no odor, fast film hanging, less residual sludge, good effluent quality, and stable operation effect. This process is: anaerobic microorganisms grow on the surface of the carrier. When the sewage rises from bottom to pass through the fixed bed composed of the carrier, under the action of the anaerobic microorganisms, the organic matter in the sewage is anaerobically decomposed and biogas is produced. The essence of this process is similar to the A/O method, but the facultative anaerobic biological filter strengthens the anaerobic section. The reuse process is: sewage → sedimentation tank → anaerobic digester → anaerobic biological filter → air extraction pipe → oxidation ditch → air inlet and outlet well → filtration → disinfection → effluent reuse.

3. Sewage reuse technology

(1) Membrane technology

Domestic sewage in the residential area is discharged through secondary treatment and reverse osmosis (RO) and other membrane technologies After advanced treatment, the effluent can be used as industrial water or domestic water. Membrane technology mainly refers to membrane separation technologies such as nanofiltration, ultrafiltration, osmosis and reverse osmosis. Membrane technology has high investment costs and troublesome operation and management, and is rarely used in domestic advanced sewage treatment.

(2) Membrane bioreactor (MBR)

Membrane bioreactor (MBR) treatment technology is a high-efficiency sewage treatment technology that combines membrane separation technology and traditional sludge method Processing technology. Due to the filtration effect of the membrane, organisms are completely trapped in the bioreactor, achieving complete separation of hydraulic retention time and sludge age, maintaining a high MLSS in the bioreactor, strong nitrification capacity, and high pollutant removal rate . As a new type of sewage treatment and reuse technology, MBR has good application prospects in the reuse of residential sewage. However, the cost of the membrane itself is high, the operating system is complex and the operating cost is high. Used sparingly.

(3) Multi-media filter

Multi-media filter (filter bed) is a media filter that uses two or more media as the filter layer, also known as mechanical filter . Commonly used filter materials include quartz sand, anthracite, activated carbon, magnetite, garnet, porous ceramics, plastic balls, etc. It is used to remove suspended or colloidal impurities in sewage and absorb oil stains. It can especially effectively remove tiny particles and bacteria that cannot be removed by sedimentation technology, so that the quality of the effluent meets the requirements for reuse. It is a commonly used treatment method for advanced sewage treatment.

3. Project examples

Take the residential area where the author lives as an example.

This community is a newly built high-end residential community with complete living facilities and 24-hour hot water. The residential population is about 1,200 people and the per capita water consumption standard is 300L/d.

1. Maximum design sewage volume

1200×300/100×0.80=288m3/d (12m3/h).

2. Design sewage water quality

(1) pH=7.5;

(2) COD=360mg/L;

( 3) BOD5=200mg/L;

(4)SS=180mg/L;

(5)N-NH4=25mg/L.

3. Designed effluent water quality

The treated effluent water quality meets the standard requirements of "Urban Wastewater Reuse Landscape Environment Water Quality" (GB/T18921-2002), that is: pH=6.0- 9.0, COD≤50mg/L, BOD5≤6mg/L, SS≤10mg/L, N-NH4≤5mg/L, total residual chlorine≥0.2mg/L (terminal), LAS≤1.0mg/L, fecal coliform Group ≤3/L.

4. Adopt treatment technology

This community uses underground sewage treatment integrated equipment with a processing capacity of 15m3/h. It is used for greening or landscape on the ground. The A/O method is used as the secondary treatment, and the multi-media filter is used as the third level treatment. It is reused after disinfection with hypochlorous acid and is used for community landscape water and greening and beautification water. The generated The odor is deodorized through the soil and surrounding flowers and plants to assist in deodorization. The entire set of equipment adopts a fully automatic control and alarm system, and is unattended. The equipment only needs to be maintained and maintained regularly, making operation and maintenance relatively simple.

IV. Benefit Analysis

The total investment of the project is 450,000 yuan, and the operating cost is 0.50 yuan, which is lower than the sewage charge standard. Taking COD as an example, the design COD of sewage is 360mg/L, and the remaining 50mg/L in the recycled water after treatment is 310mg/L. Calculated based on the sewage treatment capacity of 288m3/d, the maximum daily reduction of 0.09kgCOD can be achieved in a community. COD emissions can be reduced by 32.85kg per year.

Construct a community sewage treatment and reuse station, and reuse the effluent for planting aquatic plants in artificial wetlands, breeding fish and ducks in landscape ponds, spraying lawns, watering trees, etc., which not only achieves sewage treatment and reuse to save water resources The effect is to reduce the urban sewage treatment load and improve the living environment of the community, which has considerable environmental benefits. Treating sewage and reusing it is the best way to save water and control pollution, and it is imperative.

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