ProAct has a variety of sand filters for water treatment to remove suspended solids and reduce turbidity. Whether suspended solids are the primary concern at a site, or if water needs to have solids removed to facilitate further treatment, sand filters are a reliable technology. ProAct uses sand filter water treatment at construction sites, remediation sites, and in other applications.
Sand filter technology is simple – ProAct’s pressurized sand filters strain solids from the water treatment stream. Water is pumped into the top of a sand filter vessel, where a plate or other device disperses the water evenly across the media bed. This dispersion helps ensure the water does not “channel” through the sand.
As the solids-laden water trickles through the sand, larger particulates in the water are caught in the pores between the sand. Some tiny particulates are adsorbed onto the surface of the sand. Filtered water, free of these particulates, continues through the sand. Lateral screens with a slot width <0.012 in. ensure the water is collected uniformly across the bottom of the filter. This also helps prevent channeling. The treated water exits at the bottom of the filter vessel.
Usually, a sand filter for water treating is a set of two to six stainless steel or carbon steel “pods” connected in parallel flow. A typical pod is 32 in. to 54 in., but ProAct can also use larger vessels – up to 10 ft. in diameter – as sand filter pods, to allow higher flow rates. Since the hydraulic loading is typically 5 gpm/ft2, it follows that the larger the pods, the higher the flow rate.
Removal efficiency depends on many factors, including the sand bed depth. The deeper the sand in the filter, the higher the removal efficiency. Sometimes ProAct uses the larger vessels to increase removal efficiency.
The pods are filled with sand layered over gravel. ProAct usually gets good results using sand that is 0.45 – 0.55 mm, with a uniformity of 1.4 – 1.7. Gravel that is 1/8 in. – 1/4 in. is used to cover the screens at the bottom of the pod that collect the treated water.
Sand filters can remove 30 – 50 micron suspended solids to less than 5 ppm. In many industrial water treatment systems, ProAct installs bag filters after a sand filter to remove fine solids that the sand filters cannot capture. Sometimes, treatment before the sand filter is needed.
The maximum allowed influent turbidity for a sand filter is 200 ntu. With high influent turbidity, chemical flocculation and sedimentation pretreatment are needed. When this process is used, ProAct technicians continually monitor influent quality to be sure it is free of excess polymer, which could clog the filter.
As sand filters for water treatment are used, the pores eventually fill with solids, and the sand media bed needs to be cleaned to keep the filter from becoming clogged. This cleaning process, called “backwashing” is also simple – water is run backwards, from the bottom to the top of the sand bed. The backwash water, with solids that have been flushed out of the sand, exits the top of the filter vessel and is captured for treatment or disposal. In a typical sand filter with one or more connected pods, the backwash water is water that has been treated by the other vessels in the assembly. Each pod in the filter is backwashed individually.
Many of ProAct’s sand filters are equipped with an automated backwash controller. The controller can be set to start the backwash process at regular time intervals, determined by ProAct’s experienced technicians. The controller can also be triggered to start a backwash by the pressure difference between the water entering the filter and the water leaving the filter. As particulates collect in the sand bed, the pressure difference increases, so a high pressure difference signals that the media bed is getting loaded with solids.
Sand filters can be used on any site with enough space for the equipment needed to place them, so long as provisions can be made for backwash water disposal. Typically-sized sand filters are mounted on skids and can be moved with a fork lift or attached to a flat-bed trailer. Larger vessels used as sand filters may require a crane to place them on solid level ground. While automated sand filters often need a site with accessible electricity, ProAct has some units fitted with a solar collector, for use on remote sites.
ProAct has a sand filter for your application and site. ProAct technicians are experienced in maximizing the effectiveness of its sand filters, to ensure efficient operation. Call a ProAct specialist today to discuss how best to meet your water treatment needs.
Contact a ProAct Water Treatment Specialist to discuss your project needs and obtain a proposal.