With the rapid development of social economy and continuous improvement of industrialization and urbanization, water pollution problem becomes more and more serious so water environment pollution and water quality eutrophication become prominent. In order to meet the new requirements of water environment protection project, key projects of urban sewage plant’s pollutants discharge standard （GB18918-2002） use A standard of the 1st class as required by the nation. Currently, the regular deep treatment technique process includes the following plans:

Coagulation,sedimentation, filtration treatment and disinfection

micro flocculation reaction+filtration+disinfection (or pipe blending+filtration+disinfection)

Film treatment which means micro flocculation +reverse osmosis double membrane processing+disinfection

micro flocculation reaction+disk micro filter processing+disinfection

The above four plans can meet the requirements for deep treatment. The 1st and 2nd plans will produce good quality water with stable operation. However, the two plans cover a large area with high investment and 1st class water pumps are needed so the operation cost is high and management is complicated. The 3rd plan will produce good quality water with small area but much investment and operation cost especially when the membrane is replaced. The 4th plan is a new process used in deep treatment abroad in recent years. This process saves investment with no need to improve sewage, low operation cost, small space, easy management and is adaptive to deep treatment and upgrading and rebuilding plan for urban municipal sewage. It filters sewage finely and removes suspended solids like SS, CODcr, BOD5 and total phosphorous. The outlet water can reach A level of 1st class discharge standard. It is widely recognized as good outlet water quality, stable effect, low operation cost and easy management after real operation.

Wide application areas

Upgrading and reconstructing of the current sewage treatment factory: Emission standard is raised from 1st class B level to 1st class A level.

Recycle water from industrial production: recycling cooling water in steel plant and power plant.

Recycling of urban non-drinking water

Water for paper-making and printing and dyeing industry

Water treatment in aquaculture, etc.

Working principle of equipment

Disk filter is made up of central drum, turnplate, reverse flushing system and matched electric system, etc. Turnplate is fixed around the central drum and has the connection hole with central drum. Raw water(sewage) flows into the drum at the opening in one end of central drum and enters all turnplates through connection holes. Both sides of turnplate are installed with filter cloth woven by stainless steel wire or polyester filament and the minimum diameter of filtration hole is 10μm. Clean water then outflows after raw water is filtered by filter cloth and is discharged from water filtration outlet. With the process of filtration, impurities in the inner side of filter cloth increase and the filtration pressure gap increases. Then the clean water which flows from the filter disk decreases gradually. When impurities accumulated to a certain level, the liquid level in the central drum reaches the set value inside the filter disk and reverse flushing starts to wash away the impurities stored inside the filter cloth. Reverse flushing water pump extracts the clean water through filter cloth and spray the water to the outer side of filter disk while the impurities in the inner side of filter cloth are washed away and sewage falls into liquid collection box and is discharged out of the system. When the turnplate rotates during reverse flushing, reverse washing water is sprayed to different angles of filter cloth. Reverse washing will not stop until the turnplate rotates for one round and filter cloth is all washed. After this step, the system enters static filtration process and then enters reverse washing process again.

Rotary disk filter uses imported and efficient filter cloth as filtration medium. Filter cloth is woven by metal wire of special lines of longitude and latitude and features high precision, high throughput, strength and strong ability to gather slag, etc. Maximum filtration precision can reach 10um with maximum throughput volume per unit area of 76L/s•m2 (@300mmHydrostatic head). It can bear reverse flushing water pressure of 7.5bar, which can enhance the reverse flushing effect efficiently.

Raw water enters center drum through center water inlet pipe and then enters the filter disk fixed around the drum through the holes at the center drum. The two sides of filter disk is installed with filter cloth woven by stainless steel wire or polyester filament. Raw water becomes clean water and flows out of filter disk after filtration by cloth and discharges from effluent weir. With the process of filtration, impurities in the inner side of filter cloth increase and the clean water which flows from the filter disk decreases gradually. Water level in the disk increases. When the liquid level reaches the set value inside the filter disk, the drum starts to rotate and when the high-pressure water provided by reverse flushing device washes the filter disk surface, impurities will fall into the sewage collection trough fixed in the filter and then enter dredge pipe for discharge. With the progress of washing, water level inside the disk reduces continuously. When it reaches at the set liquid level, reverse flushing will stop automatically and drum will stop rotating. The system then reenters static filtration process.

Reverse-flushing stage will not influence operation of equipment. Filter will operate by continuous water inflow, step-by-step reverse flushing and continuous water outflow.

Figure 1 : Structure and operation principle of filter disk

Components of equipment

The whole set disk filter system includes raw water collection device, central water inflow and distribution equipment, filter disk, drive device, reverse-flushing device (including reverse-flushing pump and spray system), sludge discharge system, liquid level tank and matched liquid level instrument and controlling system.

Raw water collection device

It is equipped with a “to-be-filtered” device which collects flocculation pool water. The material is 304 stainless steel and it is connected to center water distribution drum.

Central water inflow and distribution equipment

It is equipped with a central inflow pipe, water drum, gearing, drive chain, rolling bearing and sealing element and other accessories. The upper end of central water distribution drum is equipped with a collection sewage tank. All main parts are made of 304 stainless steel.

Filter cloth and filter disk

Each filter disk is made up of 14 independent fan shards and is installed around the center drum. Both sides of fan shard are installed with filter cloth woven by stainless steel wire or polyester filament. Special assembled structure of fan frame enables each fan shade to be moved up easily for replacement instead of using any special tools. The connection part between filter cloth and fan frame is impermeable to guarantee good filtration result.

Reverse flushing system

Reverse flushing system uses high pressure pump to flush the filter cloth from outside to inside so that the impurities stored inside the filter cloth can be removed. In order to ensure good cleaning effect, we use umbrella-shape high-speed injection system with resistance to high pressure.

Reverse flushing system can be manually operated and its reverse-flushing times and period can be adjusted and controlled automatically by liquid level. It will not influence the filtration procedures in normal cleaning process.

Reverse-flushing system consists of reverse-flushing device, security filter, sewage collection trough, sludge discharge pipe and reverse-flushing pump.

Drive device

Drive device includes motor, gear case, drive gear and drive chains. Gear case is high torque oblique gear type with service factor of no less than 1.5 and drive motor power of 380V/50HZ/3 phase, protection grade of IP65 and operation noise of less than 75dB.

Matched instrument

Each disk filter is equipped with a set of liquid level detector for detecting water level and automate controlling of operation of reverse flushing system.

Automate controlling system

Automate controlling system can be manually or automatically switched or have far-distance monitoring function. It can also control pump by feedback control through liquid level detector.

Fixed supports and parts

All fixed supports and parts are made of 304 stainless steel.

Equipment property

Advantages of equipment

The design is solid and compact with long service life. It is normally made of 304 stainless steel or 316L stainless steel.

It covers small space (is beneficial to upgrading project). The space is 75% smaller compared to that of sand filter.

It has simple design with low head loss which greatly reduces energy consumption.

It features easy operation and maintenance and is operated automatically with no need for special personnel to look after it.

Early-stage investment and operation cost are much lower than those of other techniques.

Outlet water quality is stable.

Surface dimensions of equipment