ZSL Medium-Speed Filter|Multi-Media Filter|Oily Wastewater Filtration

Working Principle Raw water comes in through the top distribution system and flows down through the anthracite, quartz sand, and gravel layers. The anthracite catches the bigger particles and some of the oil, the quartz sand traps fine suspended solids and whatever oil is left, and the gravel layer supports the media and collects the water. Clean water drains out from the bottom. After the filter runs for a while, the bed picks up more and more contaminants and the head loss starts to climb. Once it reaches the set point or the cycle time is up, backwashing kicks in. Backwash water flows up through the media, washing the trapped solids and oil out of the tank, and then filtration picks back up. You can run the backwash with water alone or with a combined air-water method. With oily wastewater, emulsified oil and suspended solids get adsorbed and trapped by the media first. Larger oil droplets and flocs stick to the media surface, then get captured further down by the quartz sand layer. After backwashing, the media is back to full filtration capacity. The unit runs at medium speed, moves a lot of water, puts out a steady effluent, and takes up little space. It works well for circulating water side-stream filtration and oily wastewater treatment in metallurgy, chemical, and light industries. Application Fields 1.Steel and metallurgy: turbid circulating water systems for rolling, continuous casting, and blast furnaces, removing mill scale, suspended solids, and oil. 2.Machinery manufacturing: filtration of oily wastewater from machining and cleaning processes, recovering oil and cutting down contaminants. 3.Chemical and petrochemical: filtration of process cooling water, reactor cooling water, and oily process wastewater. 4. Power and energy: side-stream filtration of circulating cooling water in thermal power plants, condenser cooling water cleanup, and makeup water pretreatment. FAQ Q1: How is backwashing triggered on the ZSL medium-speed filter? A: There are usually two ways. One is on a timer — once the set run cycle is up, it backwashes automatically. The other is by pressure differential — as the media picks up more contaminants, head loss rises, and once the pressure drop between inlet and outlet hits the set point, backwashing kicks in. In practice, you can combine both, so the media doesn't get too clogged before it's washed, and it doesn't wash so often that it wastes water. Q2: Why should floating oil be removed before oily wastewater filtration? A: Floating oil is different from emulsified oil. It comes in larger droplets, spreads across the media surface easily, and gums up the media. If too much floating oil gets in, the bed cakes up fast and backwashing can't clean it out. That's why oily wastewater usually goes through an oil separator, skimmer, or cyclone de-oiler first to take out the floating oil, then into the filter for the emulsified and dispersed oil. That way the media lasts longer and the system runs more steadily. Q3: What's the difference between the ZSL medium-speed filter and a gravity valveless filter? A: A gravity valveless filter runs on water level difference and uses the siphon principle to backwash automatically — no electrical controls, no valves, and it suits surface water purification where turbidity isn't too high. The ZSL medium-speed filter is a pressure-type unit, fed by a pump, running at higher pressure, and it's built for circulating water side-stream filtration and oily wastewater treatment. They fit different jobs — one leans toward water supply purification, the other toward industrial circulating water and oily wastewater.