Hospital Wastewater Treatment System

Hospital sewage treatment mainly includes three parts: sewage pretreatment, physical and chemical or biochemical treatment and disinfection. In order to prevent the secondary pollution of pathogenic microorganisms, the sludge and waste gas generated in the sewage treatment process should also be treated.

1 Pretreatment

The main purpose of pretreatment of hospital sewage is to remove solid dirt in sewage, adjust water quality and water volume and reasonably absorb feces, which is conducive to subsequent treatment.

1.1 Septic tank

The septic tanks used for hospital sewage treatment mainly include ordinary septic tanks and biogas purification tanks.

The principle of ordinary septic tanks and biogas purification tanks is to trap organic solid pollutants by sedimentation, and then degrade organic matter by the action of anaerobic microorganisms. The treatment efficiency of biogas purification tank is better than that of ordinary septic tank.

The calculated volume of the sedimentation and decayed part of the septic tank should be based on the residence time of sewage in the septic tank should not be less than 36h. For sewage treatment systems without sludge disposal, the septic tank volume should also include the volume of sludge storage.

1.2 Pre-sterilization tank

The purpose of pre-disinfection is to reduce the content of pathogenic microorganisms in sewage to reduce the chance of operators being infected by pathogenic microorganisms.

1. The excreta of patients in infectious disease hospitals are pre-sterilized and discharged into the septic tank.

2. The infectious disease hospital sewage must be pre-disinfected before entering the sewage treatment system. The contact time of the pre-disinfection tank should not be less than 0.5 hours. Commonly used disinfectants include sodium hypochlorite, peroxyacetic acid and chlorine dioxide. Lime can also be used for fecal disinfection.

3. For ordinary general hospitals, pre-disinfection tanks are not required.

4. For biochemical treatment, if chlorine is used for pre-sterilization, dechlorination is required, or ozone is used for pre-sterilization.

1.3 Grille

It is advisable to set up a grille in front of the sewage treatment system or the pump. The grille well and the regulating tank can be constructed in a joint way.

1. The grille of infectious disease hospitals should use automatic mechanical grilles; in ordinary hospitals, automatic mechanical grilles should be used (small-scale manual grilles can be used according to the actual situation).

2. The grille well should be closed, and a ventilation hood should be set up to collect exhaust gas for centralized treatment;

3. The grid slag and sludge produced by sewage treatment are sterilized together and transported to incineration. Disinfection can be done by pasteurization or lime addition.

1.4 Regulation pool

1. The hospital sewage treatment should be equipped with regulating pool. During continuous operation, its effective volume is calculated as 30-40% of the daily water treatment. During intermittent operation, its effective volume is calculated according to the process operating cycle.

2. The regulating pool should be divided into two groups, each group is calculated according to 50% of the water.

3. The regulating tank should adopt a closed structure with an air vent, and the anti-sedimentation measures should adopt the underwater stirring method.

4. The sludge produced by the regulating tank is regularly cleaned and treated together with the sludge produced by sewage treatment.

2 Primary treatment to enhance treatment effect

Strengthening the primary treatment effect should be achieved through two ways: transforming the existing primary treatment process to strengthen the removal effect and adopting primary enhancement treatment technology.

2.1 First-level strengthening treatment

The first-level enhanced treatment of hospital sewage generally adopts processes such as coagulation and sedimentation, filtration, and air floatation. The filtering solid-liquid separation method requires backflushing, the operation and management is relatively complicated, and the gas release in the air floatation process is easy to cause secondary pollution. Therefore, coagulation and sedimentation processes are generally used in hospital sewage.

Intensified treatment of hospital sewage should adopt coagulation and sedimentation process. The coagulation and sedimentation tank should be divided into two groups, and each group is calculated according to 50% of the water.

1. When the sewage treatment capacity is less than 20m3 / h, the sedimentation tank should be equipmentized, and the integrated equipment of steel structure or other structural forms can be used. The pool shape should be vertical flow or inclined plate sedimentation tank. When the sewage treatment capacity is greater than 20 m3 / h, the sedimentation tank should be a reinforced concrete structure, and the pool shape should be vertical or horizontal flow sedimentation tank.

2. When the sedimentation tank body adopts steel structure, effective and effective anti-corrosion measures must be taken.

3. When the inclined plate sedimentation tank is used, the inclined plate washing facility must be installed. For other types of sedimentation tanks, measures shall be taken to facilitate cleaning and maintenance.

2.2 Reinforce the treatment effect of the existing primary treatment process

Reform should be based on the actual situation, make full use of the existing treatment facilities, the existing hospitals used more septic tanks, contact tanks in the structure or operation mode of transformation, if necessary, add some facilities.

When there is a reconstruction site, the adjustment tank can be used as a sedimentation tank, and an adjustment tank is added beside the septic tank.

When the space is insufficient, a coagulation sedimentation tank can be added on the ground.

3 Biological treatment

Biological treatment of hospital sewage is on the one hand to reduce the concentration of pollutants in the water and reach the discharge standard; on the other hand, it can guarantee the disinfection effect. The biological treatment process mainly includes activated sludge method, biological contact oxidation method, membrane bioreactor, aerated biological filter and simple biochemical treatment.

3.1 Activated sludge method

Activated sludge method is a biological treatment process of wastewater that degrades organic pollutants, ammonia nitrogen and other pollutants in sewage under aerobic conditions.

1. Process characteristics

The advantage of activated sludge process is that it has strong adaptability to different types of sewage and the construction cost is low.

The disadvantage of the activated sludge process is poor running stability, prone to sludge expansion and sludge loss, and the separation effect is not ideal.

2. Design parameters
The design of aeration tank and secondary settling tank shall comply with relevant regulations;

Aeration tank sludge load is based on effluent organic matter and ammonia nitrogen requirements, and should meet nitrification requirements when needed.

parameterReference range
HRT (h)4 ~ 12
Gas-water ratio6 ~ 10
MLSS (g / L)/td>2 ~ 4
Sludge load (kg-BOD5 / (kg-VSS d))0.1 ~ 0.4
Mud age (d)5 ~ 20

Main process parameters of activated sludge process aeration tank

3. Scope of application
The traditional activated sludge method is suitable for hospital sewage treatment projects with a large water volume of more than 800 beds. For hospitals with less than 800 beds and a small amount of water, the deformation process of the activated sludge method, the sequential batch activated sludge method (SBR), is often used.
SBR process is a variant of activated sludge process. SBR operates in cycles, and each cycle includes five processes: water intake, reaction (aeration), precipitation, discharge, and standby. SBR’s single cycle inflow, reaction, precipitation, discharge and standby can be controlled. Each process is associated with specific reaction conditions (mixing / resting, aerobic / anaerobic), which promote selective changes in the physical and chemical properties of sewage.
SBR process has the advantages of simple process, convenient management, low capital investment, low operating cost and good processing effect.

3.2 Biological contact oxidation process

Biological contact oxidation process uses fixed biological filler as the carrier of microorganisms. The carrier with microorganisms is submerged in water. The aeration system supplies oxygen to microorganisms in the reactor. Because the microorganisms of the biological contact oxidation method are fixedly grown on the biological filler, the shortcomings of the suspended activated sludge are easily lost, and a high biomass can be maintained in the reactor.
1. Process characteristics
(1) The biological contact oxidation method has strong tolerance to impact load and water quality changes, and is stable in operation.
(2) The biological contact oxidation method has a high volume load, a small footprint, and a low construction cost.
(3) The biological contact oxidation method has low sludge output, no sludge return, and simple operation and management.
(4) Biological contact oxidation method sometimes peels off some finely divided biofilms, and the poor sedimentation performance causes the suspended solids concentration in the effluent to be slightly higher, generally reaching about 30mg / L.
2. Design parameters
(1) The filler of biological contact oxidation tank should be a combination of light weight, high strength, anti-corrosion, easy to hang film, large specific surface area and high porosity.
(2) The biological contact oxidation method has been used in practice for a long time. For the relevant process parameters, please refer to the relevant design manual.

parameterReference range
HRT (h)0.5~1.5
Gas-water ratio10~15
Sludge load (kg-BOD5 / (kg-VSS d))2~5

Main process parameters of biological contact oxidation

3. Scope of application
Biological contact oxidation method is suitable for the sewage treatment project of small and medium-sized hospitals with 500 beds or less. Especially suitable for small area, small amount of water, large fluctuations in water quality and low pollutant concentration, difficult to cultivate activated sludge, etc., easy management.

3.3 Membrane-bioreactor

Membrane BioReactor (MBR) is a new wastewater treatment process that combines membrane separation technology with bioreactor. According to the installation position of the membrane separation module, it can be divided into two categories: split MBR and integrated MBR.
1. Process characteristics
MBR process replaces the secondary sedimentation tank in the traditional activated sludge process with a membrane module, which can carry out efficient solid-liquid separation, overcome the insufficiency of the effluent water quality in the traditional process is not stable, and the sludge is easy to expand.
(1) Strong impact load resistance, high quality and stable effluent water quality, can completely remove SS, and has a good retention effect on bacteria and viruses.
(2) Complete separation of the hydraulic residence time (HRT) and sludge age (SRT) of the reactor, making the operation control more flexible and stable; the concentration of microorganisms in the bioreactor is high, which can be as high as 10g / L or more, and the volume load of the treatment device High and small footprint, reducing the volume required for nitrification.
(3) It is conducive to the interception and growth of microorganisms that grow slowly, and the system nitrification efficiency is improved. It can extend the hydraulic retention time of some refractory organics in the system, which is conducive to the improvement of the degradation efficiency of refractory organics.
(4) The output of MBR residual sludge is low, and even no residual sludge is discharged, which reduces the cost of sludge treatment.

parameterReference range
HRT (h)3~5
Gas-water ratio20~30
MLSS (g / L)/td>6~10
Sludge load (kg-BOD5 / (kg-VSS d))0.1~0.2
Membrane flux (L / (m2h))10~20

Main process parameters of integrated MBR

 3. Scope of application
This process is suitable for small-scale hospital sewage treatment projects of less than 300 beds, especially suitable for small site area, high water quality requirements and ultraviolet disinfection.

3.4 Biological aerated filter

Aerated biological filter (BAF) is a kind of biofilm treatment process. A new type of coarse and porous granular filter material has a large specific surface area, a biofilm is grown on the surface of the filter material, and aeration is provided at the bottom of the tank. When the sewage flows into the filter bed, the pollutants are filtered and adsorbed first, and then the filter material surface Oxidative decomposition of microorganisms. At present, BAF has gradually developed from a single process to a series of comprehensive processes, which have the functions of removing suspended solids, COD, BOD, nitrification and nitrogen removal.

1. Process characteristics
(1) The effluent quality is good. BAF can remove suspended solids, COD, bacteria and most of ammonia nitrogen in sewage, and the effluent SS is less than 10mg / L.
(2) Microorganisms grow on the surface of rough and porous filter material, which is not easy to be lost. It has certain adaptability to toxic and harmful substances, high operational reliability, and strong resistance to impact load. No sludge swelling problem.
(3) The BAF volume load is higher than the conventional treatment process, and the secondary sedimentation tank and sludge return pump room can be omitted, and the area is usually 1/3 to 1/5 of the conventional process.
(12) Backwashing is required. The backflushing water volume is large and the operation mode is complicated, but it is easy to realize automatic control.

parameterReference range
Diameter of filter material (mm)3 ~ 6
Biological filter bed height (m)3 ~ 4
Hydraulic load (m3 / (m2 · h))2 ~ 3
Gas-water ratio4 ~ 6
Volumetric load (kgBOD5 / (m3 · d))1 ~ 2
Flushing water flow rate (m / h)30 ~ 50
Flushing gas speed (m / h)40 ~ 70
Rinse cycle (h)24
Flushing time (min)15 ~ 30

The main technological parameters of BAF

3. Scope of application
This process is suitable for small-scale hospital sewage treatment projects of less than 300 beds, especially suitable for small area and high water quality requirements.

3.5 Simple biochemical treatment process

1. Process characteristics:
Biogas purification tanks use the principle of anaerobic digestion to degrade solid organic matter. The treatment efficiency of the biogas purification tank is better than that of the decay tank and biogas tank, the cost is low, the power consumption is low, and the management is simple.
2. Applicable conditions
For small general hospitals in economically underdeveloped areas, when conditions are not available, simple biochemical treatment can be used as a transitional treatment measure, and then gradually achieve secondary treatment or primary treatment to enhance the treatment effect.

Comprehensive comparison of different biological treatment processes

Process typeadvantageDisadvantagesScope of applicationProcess type
Activated sludge methodStrong adaptability to different types of sewage.Poor running stability, prone to sludge expansion and sludge loss, the separation effect is not idealSewage treatment projects in hospitals with a large amount of water above 800 beds; SBR method for hospitals under 800Lower
Biological contact oxidation processHigh impact load resistance, stable operation; high volume load, small footprint; low sludge output; no sludge return, simple operation and management.Partial shedding of biofilm caused a slightly higher concentration of suspended solids in the effluent.Sewage treatment project for small and medium-sized hospitals under 500 beds. It is suitable for small space, small water volume, large fluctuations in water quality and difficult to cultivate microorganisms.medium
Membrane-bioreactorStrong impact load resistance, high quality and stable effluent quality, effective removal of SS and pathogens; small footprint; low or no residual sludge production.The gas-to-water ratio is high, the membrane needs to be backwashed, and the energy consumption and operating costs are high.Small-scale hospital sewage treatment project under 300 beds; small hospital area and high water quality requirements.high
Biological aerated filterThe effluent quality is good; the operation reliability is high and the impact load resistance is strong; there is no problem of sludge expansion; the volume load is high and the secondary sedimentation tank and sludge return are omitted, and the area is small.Backwashing is required, and the operation mode is more complicated; the amount of backwashing water is larger.Small-scale hospital sewage treatment project of less than 300 beds.Higher
Simple biochemical treatment processLow cost, low power consumption and simple management.The effluent COD, BOD and other physical and chemical indicators cannot be guaranteed.As a transitional measure for hospital sewage treatment in remote mountainous areas and economically underdeveloped areas, gradually implement secondary treatment or primary treatment that strengthens treatment effects.low

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