Wastewater Filters and Filtration Services by ProAct
Industrial wastewater may be from manufacture, plating, tank cleaning, mining, or any other industrial process. For some wastewater, filtration alone may be sufficient for meeting discharge requirements. Often, a wastewater filter is a step in a treatment system that may include many other components. Filtration may be used at several steps in a treatment train, as other processes create solids that the filters then remove.
Filtration captures particles of various sizes, such as clays, sands, colloids, microorganisms and organic particulates. Contaminants that are attached to particulate matter via sorption may also be removed. Filtration, alone or with other processes, can reduce total suspended solids (TSS), dissolved solids (turbidity), biological oxygen demand (BOD), chemical oxygen demand (COD), and metals.
Filtration is the primary technology for reducing TSS. These particulates are not heavy enough to settle out of the water. Various filter types are used to capture these particulates, depending on their size, composition, and concentration. Several different types of filters may be arranged in series to reduce TSS to acceptable levels.
COD is how much oxygen in water can be consumed by chemical reactions, such as oxidation of inorganic chemicals. BOD is how much dissolved oxygen is needed by organisms in the water to break down organic material. Both indicate organic matter in the water. Filtration reduces BOD and COD by removing organic particles. Sometimes, additional treatment may be needed to meet BOD and COD discharge requirements.
Heavy metals in the particulate form can be removed by filtration. Divalent iron and magnesium are often found in anaerobic groundwater. When exposed to air, these soluble ions oxidize and react with hydroxides to form insoluble particles that can be removed by filtration. Oxidation can be enhanced by pH adjustment.
Types of Wastewater Filters We Use
ProAct uses many different types of wastewater filters to treat industrial wastewater. These include bag and cartridge filters, sand filters, multi-media filters, and membrane filters. Carbon vessels and media vessels, which work primarily through adsorption, do also filter out some particulates.
Bag Wastewater Filters
A bag filter uses fabric elements (“socks” or “bags”) to capture solids and let the water flow through. Bag filter socks come with different size openings, measured in microns (µm). The filter catches solids that are smaller than the openings and lets water and anything smaller to pass through. Specialized bags with various characteristics are available for targeted contaminants.
Over time, the sock eventually clogs with solids, reducing the entire system’s flow rate. When this happens, the bag filter sock needs to be changed. It is removed and the bag with the captured solids is safely disposed of.
Typically, multiple bag filter housings are used in parallel flow. These may be assembled “in-line,” or in a canister. Cartridge filters are similar to bag filters, but the filter element is a cartridge packed with filter media.
Sand Wastewater Filters
Sand filters can handle more solids and higher flow rates than bag filters. Sand filters are used mainly to remove solids from a wastewater stream that has high levels (between 250 mg/L – 10,000 mg/L) of suspended solids and sediments. Sand filters strain solids from the water treatment stream. Water is pumped into the top of a sand filter vessel. As the solids-laden water trickles through the sand, most solids of 50 µm or larger 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.
Sand filters may include two to five pods (vessels). More pods mean a higher flow rate. Depending on the specific job, water leaving the sand filter may be discharged or may be further treated.
Over time, the sand starts to clog or become less effective at removing solids. When this happens, the filter needs servicing (backwashing or media replacement). Backwashing flushes solids from the sand bed. The backwash is captured for treatment or safe disposal. When the media is removed, the captured solids are removed with it, and can be safely disposed.
A multi-media filter is similar to a sand filter but may sometimes be more efficient. A multi-media filter has one or two media layers above the gravel bed. The media are ordered in decreasing porosity. Larger, lighter media stays on top and the denser, smaller media stays on the bottom. The largest particles are removed near the top of the media bed, and as particles get smaller, they are captured deeper and deeper in the media. Multi-media filters trap more particles than sand filters before needing backwashing.
Membrane Wastewater Filters
A membrane filter is a thin layer of semi-permeable material that only lets pass materials up to a certain size, or of a specific shape or character. Contaminated water is forced through a membrane, which separates the water into retentate and the permeate. The retentate, with concentrated contaminants, is disposed of safely. The treated water permeate continues through the system.
Different types of membranes are used for different contaminants. RO membranes have the smallest pores. RO depends on ionic diffusion to reverse the solution’s osmotic process to drive water away from dissolved molecules. RO can effectively remove radium, natural organic substances, pesticides, and pathogens. RO is the type of membrane filtration most commonly used by ProAct.
Filtration alone may not be sufficient to meet discharge limitations. In such cases, flocculation by adding polymers may be used. Filtration is ineffective at treating some contaminants, such as oil and grease and pesticides. ProAct frequently uses wastewater filtration in concert with other treatment technologies. A filtration system may be preceded by an upstream oil/water separator, for example. A filtration system effluent might undergo additional treatment, such as adsorption by carbon or media vessels.
ProAct Services has the solution to help you meet your discharge limits. Our experienced engineers can design a system for your flow rates and wastewater volume. Contact a ProAct Services Water Treatment Specialist for more information and to discuss your project!