Various strategies are needed to remove different types of contamination from wastewater. One such strategy is brine treatment, which aims to eliminate dissolved salt ions from the waste stream. While there are similarities to desalination processes used for seawater or brackish water, industrial brine treatment may have a distinct mixture of dissolved ions, such as hardness ions or other metals. As a result, specific processes and equipment are necessary for effective treatment.
Brine treatment systems are usually optimized to either decrease the volume of the final discharge for more cost-effective disposal (since disposal costs often depend on volume) or maximize the retrieval of fresh water or salts. These systems may also be optimized to minimize electricity consumption, chemical usage, or physical space.
Brine treatment is often encountered in the treatment of various wastewater types, such as cooling tower blowdown, produced water from steam assisted gravity drainage (SAGD), produced water from natural gas extraction (such as coal seam gas), frac flowback water, acid mine or acid rock drainage, reverse osmosis reject, chlor-alkali wastewater, pulp and paper mill effluent, and waste streams from food and beverage processing.
When treating brine, there are several technologies that can be used. These include membrane filtration processes like reverse osmosis, ion exchange processes like electrodialysis or weak acid cation exchange, and evaporation processes such as brine concentrators and crystallizers with mechanical vapour recompression and steam. However, reverse osmosis may not be an effective option for brine treatment. This is because it can be prone to fouling from hardness salts or organic contaminants, and the reverse osmosis membranes can be damaged by hydrocarbons. Among these technologies, evaporation processes are the most commonly used for brine treatment. They allow for the highest level of concentration, reaching levels as high as solid salt.
The highest purity effluent, even distillate-quality, is produced by evaporation processes. These processes are also more tolerant of organics, hydrocarbons, or hardness salts. However, there is a high energy consumption and corrosion may be an issue due to the concentrated salt water prime mover. Therefore, evaporation systems usually use titanium or duplex stainless steel materials. In 2012, Saltworks Technologies, a Canadian firm, introduced a brine treatment process that uses humidification-dehumidification instead of steam and includes non-metallic wetted parts that are corrosion-free.
The subject of brine management encompasses various aspects such as brine treatment within the larger framework of government policies and regulations, corporate sustainability, environmental impact, recycling, handling and transport, containment, centralized versus on-site treatment, avoidance and reduction strategies, technologies, and economics. Brine management shares similarities with leachate management and other waste management practices. To remove solids from brine, sedimentation techniques can be used, resulting in the retrieval of solids in the form of slurry or sludge.
Very fine solids and solids with densities close to the density of water present unique challenges, requiring filtration or ultrafiltration. Flocculation, accomplished with alum salts or polyelectrolytes, may also be utilized. For the removal of oils and grease, an API oil-water separator is often employed in various industries. Skimming devices are a cost-effective and reliable method for recovering oils, grease, and other hydrocarbons from water, sometimes achieving the desired purity level.
Skimming is a cost-efficient method for removing most of the oil before using membrane filters and chemical processes. It helps prevent premature blinding of filters and reduces chemical costs. To handle higher viscosity hydrocarbons, skimmers need heaters powerful enough to keep grease fluid for discharge. If floating grease solidifies, a spray bar, aerator or mechanical apparatus can aid in its removal. However, hydraulic oils and most degraded oils have a soluble or emulsified component that requires further treatment. Using surfactants or solvents to dissolve or emulsify oil usually exacerbates the problem, resulting in more difficult-to-treat wastewater. Industries like oil refineries, petrochemical plants, chemical plants, and natural gas processing plants often release wastewaters containing significant amounts of oil and suspended solids.
Industries in need of separating oil and suspended solids from their wastewater effluents use an API oil-water separator, named after the American Petroleum Institute’s (API) standards. The API separator serves as a gravity separation device and incorporates Stokes Law to determine the rise velocity of oil droplets based on their size and density.
The design is based on the specific gravity difference between the oil and the wastewater, as this difference is smaller than the specific gravity difference between the suspended solids and water. The separator settles the suspended solids as a sediment layer at the bottom, while the oil rises to the top. The cleansed wastewater is located between the oil layer and the solids. Normally, the oil layer is skimmed off and processed or disposed of, while the sediment layer at the bottom is removed using a chain and flight scraper or similar device, along with a sludge pump.
The water layer undergoes additional treatment which typically involves an Electroflotation module to remove any remaining oil and then a biological treatment unit to eliminate undesirable dissolved chemical compounds. A typical option for this process is a parallel plate separator, which is similar to API separators but with tilted parallel plate assemblies, also known as parallel packs. These parallel plates increase the surface area for suspended oil droplets to merge into larger globules.
Such separators still rely on the specific gravity between the suspended oil and water. However, the parallel plates improve the effectiveness of oil-water separation. In turn, a parallel plate separator requires less space compared to a conventional API separator for achieving the same level of separation. Biodegradable organic material, derived from plants or animals, can typically be treated using extended conventional sewage treatment processes like activated sludge or trickling filter. Nonetheless, problems may arise if the wastewater is excessively diluted with washing water or highly concentrated, such as undiluted blood or milk. The presence of cleaning agents, disinfectants, pesticides, or antibiotics can negatively impact treatment processes. The activated sludge process is a biochemical method for treating sewage and industrial wastewater that utilizes air (or oxygen) and microorganisms to biologically oxidize organic pollutants. As a result, a waste sludge (or floc) is produced containing the oxidized material.
In general, an activated sludge process includes: * An aeration tank where air (or oxygen) is injected and thoroughly mixed into the wastewater. * A settling tank (usually referred to as a “clarifier” or “settler”) to allow the waste sludge to settle. Part of the waste sludge is recycled to the aeration tank and the remaining waste sludge is removed for further treatment and ultimate disposal. Trickling filter process Main article: Trickling filter Image 1: A schematic cross-section of the contact face of the bed media in a trickling filter
A trickling filter system is usually composed of a bed of rocks, gravel, slag, peat moss, or plastic media. This bed allows wastewater to flow downwards and come into contact with a layer of microbial slime that covers the media. The presence of aerobic conditions is achieved either through forced air that passes through the bed or through natural air convection. The system works by adsorbing organic compounds from the wastewater through the microbial slime layer and allowing air to diffuse into the slime layer for the biochemical oxidation of the organic compounds.
The end products include carbon dioxide gas, water, and other oxidation byproducts. As the slime layer thickens, it hinders air penetration, resulting in the formation of an inner anaerobic layer. The essential components of a complete trickling filter system are: a bed of filter medium where microbial slime is promoted and developed, an enclosure or container to house the filter medium bed, a system to distribute wastewater flow over the filter medium, and a system for removing and disposing of sludge from the treated effluent.
Trickling filters are one of the oldest and most well-known treatment technologies for sewage or other wastewater. They can also be referred to as trickle filters, trickling biofilters, biofilters, biological filters, or biological trickling filters. Treating synthetic organic materials such as solvents, paints, pharmaceuticals, pesticides, and coking products can be quite challenging. The treatment methods for these materials are often tailored to their specific characteristics.
Methods for wastewater treatment include a variety of options such as Advanced Oxidation Processing, distillation, adsorption, vitrification, incineration, chemical immobilisation, or landfill disposal. Some materials like detergents may undergo biological degradation, allowing for a modified form of treatment. Acids and alkalis can be neutralised under controlled conditions. The neutralisation process often results in a precipitate that needs to be treated as solid waste, which could also be toxic. In certain situations, gasses may be released and require treatment for the gas stream.
Following neutralisation, additional forms of treatment are often necessary. If waste streams contain a high level of hardness ions, such as those from de-ionisation processes, the hardness ions can be easily expelled and form a buildup of precipitated calcium and magnesium salts. This precipitation process can lead to significant pipe blockages and severe pipe furring. In fact, there was an incident in the 1970s where a 1-metre diameter industrial marine discharge pipe, which served a major chemicals complex, became blocked due to the accumulation of such salts. To address this issue, de-ionisation waste waters can be concentrated and disposed of in landfills or careful pH management can be employed when releasing the wastewater.
The treatment of toxic materials, such as organic materials, metals (including zinc, silver, cadmium, thallium, etc.), acids, alkalis, and non-metallic elements (such as arsenic or selenium), is typically challenging for biological processes unless highly diluted. Changing the pH or using other chemicals can often cause precipitation of metals. However, some metals are resistant to treatment and may need to be concentrated and then disposed of in landfills or recycled. Dissolved organics in wastewater can be incinerated through an Advanced Oxidation Process.
