Continuous sand filter


Trap organics,suspended solid,colloidal solid,microorganisms in water.
Remove nitrogen and phosphorus .


Working Principle
Continuous sand filter is widely used in many fields,especially for drinking water,industrial process water,sewage and industrial waste water purification. It is a kind of continuous filter,combined flocculent,settling,filtering together.For tertiary filtration of reclaimed water, the gravity sand filter offers advanced treatment:efficiently remove suspended and colloidal solid, oil,iron and manganese oxide,and kill the bacterial,algae,virus in water.

Route of water: Raw water enter into inlet pipe(1)feed into sand filter,(2)and water distributor,(3) into sand bed(4), Raw water will be purified when passing through the sand bed.The filtrate flow out from(5).

Route of Sand: when the water flow upward,sand bed move downward continuously.The dirty sand was drawn from the bottom of sand bed,and begin to wash the dirty sand,return the clean sand back to the top of sand bed(7)

Route of Air: Circulation of sand is based on “gas principle”,compressed air will push the mixture of sand and water into the center pipe(8),and move upward.Suspended solid and sand separated by strong friction.Reject water pour out (9).Sand falling down in sand washer,amount of sand in air lifting pipe is decided by the amount of compressed air.

Sand Washer: The washer(10)with its well-designed hydraulic features is positioned around the airlift pipeline.The sand particles fall through the washer,where they are finally washed by a small amount of clean filtrate,flowing through the washer counter currently.The filtrate flow is generated by a difference in discharge level between the  filtrate(11) and the wash water(9)

Continuous sand filter 1



Continuous sand filter 2

Control Manners
Automatic control manner: include electric control and Air control.
Electrical control cabinet:start up, operation,alarm and other functions.During normal operation, the electrical control cabinet make it continuous flushing; when running abnormal, the warning signal will be transmitted to the control box, then the program will be issued a directive to stop filtering.
Air control cabinet: control the compressed air passing through the solenoid valve and feed into the air flow meter. The pressure switch is set to detect the inlet pressure of the solenoid valve, so that when the compressed air pressure is lower than the set value, the pressure switch and the alarm starts, while stopping the supply of compressed air. Further, when the pressure control valve or solenoid valve fails, it will alarm and stop the supply of compressed air.


High Efficiency: Work online 24 hours,no need stop to backwash
Low operating cost:No need the high flow and high lift backwash pump,and it can be programmed to control intermittent wash sand control mode, greatly reducing operating costs.
Low maintenance cost: without any moving parts, low failure rate during operation and low maintenance costs.
Low one-time investment: no coagulation tank, clarify pool and other facilities, filters, high utilization
Lower requirements on inlet water quality: long-time bear SS: 50mg / L. Can withstand short-time SS:100mg / L.
Low Head Loss: Due to the single-stage filter,we clean the sand timely, head loss will be reduced to 0.5m
Efficient Filtration, Stable outlet water quality: Due to the timely clean filter can ensure stable and efficient filtration, no water quality cyclical fluctuations.
Easy for expansion: Unit operating mode can be adjusted according to changes in water quality and quantity of filters, easy to renovate and expansion of existing facilities.

Continuous sand filter 3

Applied to the town water supply, water plants, municipal wastewater treatment, industrial wastewater treatment, recycling cooling water treatment, process water treatment, seawater purification, algae-laden water filtration.

Continuous sand filter 4

Continuous sand filter 5


Manner of feeding compressed air

Continuous sand filter 6

External Circulation :Air compressor push the sand-water mixture into sand washer by compressed air through
an external tube Internal Circulation: compressed air flow from the bottom of the device,push sand-water mixture
into the sand washer,which locates in the central.


Surface load in the unit time per filter surface impurities trapped, units:mgSS / m2h.
Recommended active sand filter surface load values are as follows:
Continuous sand filter can withstand a higher load than the value of the surface in a short time.
Filtering area can be determined by the largest surface area of the filter load and raw water quality and quantity.
For security, the actual selection should be slightly larger than the calculated value of the filter area.


Work flow rate can be calculated by the raw water flow and filters the wash service area. Note that when the flow rate rises to a certain level, the biological flocculation experience disintegration or dissolution of the filter or filters will produce flow phenomenon. In the modeling work should ensure that the filter flow rates below this level.


Temperature factors should also be considered, in the low-temperature region,the sand depth is generally  greater than 2 meters.


Under normal operating conditions, the activity of continuous sand filter can ensures the following effects:

SS<5mg/l(dose flocculant)
<10mg/l(without flocculant)
Algae removal rate close to 100%


 Model  Filtration area m2  Height of sand bed (m)
 HSLQ-03T  0.3  1  1.5  –  –
 HSLQ-07T  0.7  1  1.5  2  –
 HSLQ-15T  1.5  1  1.5  2  –
 HSLQ-20T  1.5  1  1.5  2  –
 HSLQ-30T  3.0  1  1.5  2  –
 HSLQ-45T  4.5  –  1.5  2  –
 HSLQ-50T  5.0  –  1.5  2  2.5
 HSLQ-70T  7.0  –  1.5  2  2.5
 HSLQ-50T  5.0  –  1.5  2  2.5
 HSLQ-60T  6.0  –  1.5  2  2.5
 HSLQ-70T  7.0  –  1.5  2  2.5


How to choose the suitable model
1.Choose the height of sand bed by inlet and outlet water quality.
2.B type is concrete structures, T type is movable active sand filters; material can be SS304, SS316L,FRP,
high chrome alloy steel, carbon steel (corrosion-resistant) or other specified materials.
Stripping mode: you can select internal circulation or external circulation.

SS:≦5mg/l(dose flocculant)
SS:≦10mg/l(without flocculant)
Total phosphorus removal:70~95%(dose flocculant)
Total phosphorus removal:5~20%(without flocculant)
Ammonia removal:10~20%


Complete Technology
1.Conventional treatment process
Process Description
Add flocculant before continuous sand filters, it is mixed by pipeline mixer with raw water. Water flow into the continuous sand filter, due to the cohesion effect,tiny suspended particles and colloidal particles become larger particles, For particle size> 20um, generally dosing PAC.

Continuous sand filter 7


2.Biochemical treatment process
Process Description
Add carbon source before continuous sand filter, and culture microorganisms (denitrifying bacteria) in the active sand system, in order to achieve denitrification. If there are two filters in series, the first unit do nitrification, the second unit do denitrification,it’s better to remove the nitrogen in water.

Continuous sand filter 8

3.Denitrification treatment process

Continuous sand filter 9

Process Description
Pretreated water pass through the anoxic tank, previously part of the original nitrate ions in the water is reduced to nitrogen, play a role in pre denitrification. Then pass through the aeration tank, and make organic matter degradation by oxygenate water.It can be trapped after two sedimentation tank flows from the aeration tank sludge, eventually enter into active sand denitrification filters, as well as adding methanol nitrate to nitrogen gas, the whole process is finished.






Installation Chart

Continuous sand filter 10


Continuous sand filter 11

1.The installation ground should be level hard concrete
2.Equipment foot fixed by anchor bolt
3.Connect inlet pipe,filtrate outlet,drain outlet,air pipe.
Pay attention: Make sure the position of raw water inlet must be higher than water level, in avoid of “Syphonage”.


Cautions for installation
1.When carrying the filter, you should consider their weight and size, combined with on-site construction conditions, decided the transportation equipment. During installation, you must inspect rigging, rope sling length should be consistent,in order to prevent uneven force, tank deformation or damage.
2. During installation, should protect the control box, sensor and transmission parts, and shall not prevent the destruction of quartz sand directly into the filter, the filter should be artificial sand paved bottom, inside again to filter water to a certain height, then pour the remaining quartz sand into the filter.


Cautions for operation
a.Height of sand bed: Pour the sand down from the vessel wall, don’t pass through the sand washing device in the middle.The distance between the lowest point of washing chamber and sand bed level should be 600-650mm. The diameter of sand should not bigger than 5mm.
b.Inlet & Outlet pipeline:Check the status of valve,Ensure that the front and rear lifting pump valves, inlet and outlet valve are all open; to ensure the smooth flow of the overflow pipe.
c.Ensure the valves in air pipe are all opened, stripping meter close to the smallest scale, to prevent damaging the glass rotor by sudden air supply. the valve of sand washer pipeline, adjust the level to the middle, make sure the water level is below the weir level 10-30mmm.
e.Control the flow rate of filtration and cleaning of gas, water, mixing sand and quartz sand settling velocity by adjusting the degree of opening of the inlet valve and the air valve.


1.If the downtime is less than 3 days,don’t drain away the residual water
2.If the downtime is during 3-15 days,drain away the residual water on the day of closing filter,in avoid of sea sand hardening,algae growing
3.If the downtime is more than 15 days,drain away the residual water,and inject the clean water from the top of filter to wash the sand inside the tank.Don’t stop until you get the clean water from the bottom of tank.