Industrial Wastewater Treatment
Introduction
Industrial wastewater is a byproduct of a certain plant or factory’s production process.
Industrial wastewater has many risk characteristics that are far more diverse than those of domestic wastewater, and in some cases defined as hazardous substances. Different risk characteristics apply to hazardous substances. Those risk characteristics are described in “the orange book” and are divided into nine main categories with some sub-categories.
Industrial wastewater is sometimes categorized as organic or inorganic wastewater according to its content.
Organic wastewater is defined by a high content of organic matter, pH levels around neutral, FOG, TOC, N, P. In many cases the wastewater is composted or anaerobically treated.
Some organic wastewater comes from a mineral source such as garage oil separators, chip processing emulsions, etc. Organic wastewater of a mineral source (oil and distillates) is treated by phase separation and treatment of each fraction separately.
Inorganic wastewater is usually derived from industrial leachate, acids, bases, etc., and is defined by high concentrations of salts, heavy metals, extreme pH levels (either very acidic or very basic). Treatment of inorganic wastewater is done using physicochemical methods that include neutralization, sedimentation, evaporation, membrane separation, etc.
Industrial Wastewater Treatment Technologies
Centrifugal Separation
This is usually one of the first steps of the treatment. Centrifugal separation can be done using a three-phase centrifuge, where one centrifuge separates the material into three phases (solid, liquid, oil) or using a decanter separator that first separates the solids, and then separates the oil from the water. The system works using the materials’ different densities.
DAF- Dissolved Air Flotation System
This is a useful system that is commonly used in the food industry for TSS separation, oils and grease. The system inserts coagulants and flocculants into the liquid, which results in the creation of flocs (aggregates) of the material, which allows easier separation of solids and liquids. The separation is done by air flow through the liquid. The air makes the solids float, and they are separated using a skimmer.
Physicochemical Treatment
This is an inclusive name for separation treatments using chemicals. Some of these treatments include neutralization of acids and bases, sedimentation of heavy metals, chemical oxidation, etc. Physicochemical treatments are very common in the wastewater treatment industry because they allow a reliable, relatively low-priced separation of various pollutants.
AOP- Advanced Oxidation Processes
The difference between Advanced Oxidation Processes and regular oxidation is that regular oxidation is done using OH radicals, which are strong, unselective oxidants that are suitable for the chemical breakdown of a large number of organic molecules, including non-biodegradable molecules. The radicals are made in room temperature and atmospheric pressure conditions. Technologies in the field include high pH ozonation, hydrogen peroxide with UV light or ozone, sonication, the Fenton method, and various combinations of those.
These methods are very effective for the chemical breakdown of organic materials as solvents and non-biodegradable organic materials. Nevertheless, these methods are effective for relatively low concentrations because the operation, establishment and maintenance costs are quite high. The Sutok Company is a representative of some world class companies in the field. For more information, please Contact Us.
Biological Aerobic Treatment
At low to medium organic load rates, aerobic biological reactors are used. In these reactors, air is inserted (forced) into the reactor, and serves as available oxygen for bacterial breakdown. Aerobic reactors are very effective and the breakdown rate in them is much larger than in anaerobic reactors. The main breakdown products are carbon dioxide (CO2) and water.
Let it be noted that the main disadvantage of treatment using biological processes is the high sensitivity to environmental conditions- pH, temperature, salinity, toxicity, heavy metals, etc.
Biological Anaerobic Treatment
Biological reactors in anaerobic conditions are suitable for wastewater from organic sources only. These reactors have several advantages:
Low generation rate of excess sludge, low nutrient requirements, produces methane as a final product that can be converted into energy, and the process itself does not require energy. Usually when the organic load rates are high, a biological anaerobic reactor is used at first, rather than an aerobic one.
A noticeable disadvantage of the anaerobic treatment is the slow breakdown rate and the production of sulfides. Factors that affect the process- temperature, pH levels, ammonia concentrations, sulfides, etc.
Thermal Treatment
The three most common thermal methods are incineration, distillation and evaporation. During the combustion of organic materials in the appropriate incinerators, the caloric value and heat that are produced are used for various processes such as creating steam or heating furnaces. In the distillation method, the liquids are separated based on different boiling points.
In some cases, distillation is done in a vacuum in order to avoid treatment at high temperatures that could possibly create an explosive environment that includes temperatures above the flash point and autoignition temperature, or cause harm to the distillate molecules. Evaporation is a simple technology where the wastewater is heated and its volume is reduced by evaporation of the most volatile compound. Wastewater evaporation can be done either by using an evaporator or by using evaporation ponds such as those in the Ramat Hovav site, where the wastewater is evaporated using existing environmental conditions and no energy input. The evaporation method is especially common in Israel, because of the high standards regarding salt content in treated wastewater, which is used for the irrigation of crops.
Adsorption by Polymers and Activated Carbon
Another method used for the separation of pollutants and material residues from water is adsorption. This method is mostly used today in water treatment as a last “polishing” treatment. There is a vast array of adsorption materials and types of activated carbon with various functional groups that are more effective for specific materials. Some factors that affect this method are pH levels, temperature, and the porosity of the adsorbing material. However, this method isn’t suitable for high concentrations of pollutants, because of the high cost of the adsorbing material regeneration.
Membrane Separation
Membrane separation processes have become widely used in the past few years in the field of wastewater treatment. A good example of this is the MBR biological reactor, which performs the final membrane separation of biomass. Membranes have many applications and advantages, and yet the technology is hard to apply, especially in industrial wastewater, because of the vast daily variation in wastewater types. Membranes are very sensitive to fouling. Fouling can be caused by different materials, including oils that accumulate on the membrane or biofouling caused by microorganisms that create a biofilm on the membrane and prevent the flow through the pores.
In many cases, wastewater separation is ideal, and the wastewater fits the criteria for organic and inorganic wastewater optimally. In other cases, there may be (intentional or unintentional) mixing of wastewater types, and organic wastewater is “contaminated” by heavy metals or salts, or alternatively, acids are contaminated by oil. These incidents may happen due to the nature of the process, lack of separation at the source, lack of awareness, etc. Formation of organic wastewater that contains salts or heavy metals makes it very difficult to effectively operate and properly treat the wastewater. For example, while treating wastewater for compost or biological treatment, toxins such as heavy metals or halogens will affect the treatment’s kinetics. Correct environmental consulting may help you choose the right technology for you.
In some cases, wanting to dilute the inorganic materials or lower transportation costs may in fact cause the price to go up. Therefore the processes of separation at the source and waste classification are of great importance, as well as finding the right technological solutions for each specific plant. In the environmental consulting process, it is important to have expertise in the field of wastewater and a deep understanding of the technology, regulations and the market, both in Israel and around the globe.