Processing industries face a significant challenge when it comes to industrial wastewater. Due to the difficulties or high cost of industrial wastewater treatment, many processing projects have been canceled. Many countries have implemented large-scale environmental initiatives, which has resulted in strict environmental regulations regarding industrial wastewater discharge.
Although operators might have installed industrial wastewater treatment plants to comply with local regulations, these systems required expensive upgrades to meet the newer and more stringent regulations. Many could not reach these tight limits even after extensive modifications.
Inorganic and organic matter in industrial wastewater are often found in different concentrations. Many substances are toxic, mutagenic and carcinogenic. The wastewater contains many substances that are not easily biodegradable.
Primary treatment is the process of removing solids, particles, and oils from the industrial wastewater stream. Therefore, primary treatment often includes basic physical methods as well as solid/oil separators like primary clarifiers, oil separators, and screens.
Secondary treatment is where residual organic compounds and suspended particles are broken down. Secondary treatment involves the biological (bacterial) destruction of contaminants and pollutants. Secondary treatment is best done with activated sludge. It's simple, economical, and highly effective.
Combinations of aerobic and anaerobic treatment have been effective in removing many pollutants, including soluble biodegradable organic pollutants. Industrial wastewater treatment is increasingly using membrane-based technologies.
Due to stricter wastewater treatment limits, chemical oxidation techniques for wastewater treatment are on the rise. Modern industrial wastewater units have used both classical and advanced chemical treatment. Tertiary treatment typically includes polishing, final filter steps and finishing stages.
This article focuses on industrial wastewater treatment technologies. These include physicochemical and biological processes and advanced oxidation processes.
Removal of Oil
There are several conventional methods to treat oily wastewater. These include gravity separation and skimming and dissolved air flotation. For industrial wastewater, it is possible to remove oil free of the water by using gravity separation and skimming.
The API separator, and other variations of it, are widely accepted as a low-cost, effective primary treatment option. The API oil-water separator separates oil and suspended solids from water. However, an API separator or another basic oil-water separator is not effective at removing small oil droplets and emulsions. Sedimentation in a primary clarifier can effectively remove oil that sticks to solid particles.
DAF is one of most efficient methods to treat small oil droplets or emulsions. DAF uses air to improve the separation and buoyancy of small oil droplets. DAF removes emulsified oil by using thermal energy, chemicals or both. DAF units often use chemicals to encourage coagulation and increase flock sizes to facilitate separation.
Chemical pretreatment is used to stabilize emulsified oil in industrial waste water. Then, gravity separation is performed. To reduce viscosity, increase density differences, and weaken interfacial film stability of the oil phase, wastewater is frequently heated. The acidification process is followed by the addition of cationic polmer/alum to neutralize any oil droplets' negative charge.
Finally, the pH is raised to the alkaline zone to incite flock formation of the organic salt. After the oil drops are removed from the flock, it is separated by sludge thickening followed by sludge dewatering.
Coagulation and Flocculation
Many industrial wastewater treatment units incorporate sedimentation into their processes. The process of sedimentation (also known as clarification) is when the velocity of wastewater drops below its suspension velocity and suspended particles are forced out by gravity. Sludge is used to remove settled solids, while scum is used to remove floating solids.
The sedimentation tank is filled with industrial wastewater. Retention time, temperature, tank details, and other factors affect the efficiency or performance of the process. However, without coagulation/flocculation, sedimentation can remove only coarse suspended matter that will settle rapidly out of the wastewater without the addition of chemicals.
This type of sedimentation is usually performed in a reservoir, sedimentation, or clarification tank at beginning of treatment. Coagulation/flocculation is based on the addition of chemical products that accelerate the sedimentation (coagulants) in the clarification tanks. Inorganic or organic compounds, such as aluminum sulphate or aluminum hydroxide chloride, are used as coagulants. This coagulant is used to remove nearly 90 percent of industrial wastewater suspended solids at this stage of the treatment process.
Biotreatment of Wastewater for Treatment Plants
The main focus of biological processes is organic impurities. For the treatment of industrial wastewater, microbial-based technologies were developed over the past century. These technologies have enabled the successful destruction of waste components that are easily biodegradable under aerobic conditions.
Aerobic degrading in the presence oxygen can be an inexpensive, simple and eco-friendly way to reduce wastes. The factors that affect the optimal degradation of the substrate are temperature, humidity, pH, nutrients, and the aeration rate. Temperature and aeration are the two most important parameters that determine the degradation rates of the microorganism.
Any viable microbial process can remove soluble organic sources of biochemical oxygen requirement (BOD). Because aerobic microbial processes are faster than anaerobic, they are often the main means of reducing BOD in wastewater. Aerobic reactors are small and easily accessible to the atmosphere. This makes them the most cost-effective way to reduce BOD.
The main disadvantage of aerobic bioprocesses to treat wastewater is the high amount of sludge that they produce. The aerobic bioreactor can accumulate a lot of biomass because the biomass yield (mass per unit of biodegradable material) for aerobic microorganisms tends to be higher than that for anaerobic ones. Reactor effluent may contain residual BOD, which should be reduced and disposed of as solid waste.
The aerobic degradation process can involve many mechanisms, including the attack of xenobiotics with organic acids, the production noxious compounds like hydrogen sulphide and the production chelating agents. These agents are capable of increasing the solubility and availability of insoluble xenobiotics to microorganisms for mechanical degradation.
Industrial wastewater can have a toxic effect upon microorganisms in activated sludge systems. These contaminants and compounds cannot be used by microorganisms as their sole source of carbon and can vary in their toxicity. These components can be a major factor in the degrading process, as they can inhibit the growth of microorganisms and cause system failure.
Modifying or optimizing the cell and substrate contact times is key to the success of biotreatment technology for industrial wastewater. This will allow biodegradation to proceed quickly and reduce the potential toxicity of the wastewater to bacteria.
For industrial wastewater treatment, activated sludge has been extensively used. The new membrane bioreactors (MBR), which have been inoculated using activated sludge, have proven to be effective at treating high-strength organic waste. The two-phase partitioning reactor is also effective in treating toxic substrates.
Anaerobic reactors are different from aerobic reactors in that the former must be closed to prevent oxygen from entering the system. This is to ensure anaerobic metabolism does not interfere. An anaerobic reaction vessel should have a suitable vent or collection system for the removal of gases, mainly methane (mainly carbon dioxide) during anaerobiosis.
There are many advantages to anaerobic microbial process:
Operable at toxic and influent levels higher than the BOD
There is no cost to deliver oxygen to the reactor
Methane (biogas), is a useful byproduct.
Sludge produced at a lower rate
Anaerobic processes are more expensive than aerobic processes due to the fact that they require more capital and operating costs. Anaerobic bioprocesses to treat hazardous wastewater streams are usually limited to low flow rates streams. Additional provisions should be made.
Anaerobic digestion is a complex series of interdependent and sequential biological reactions. The products of one microorganism serve as the substrates of the next. This results in the transformation of organic matter into methane and carbon dioxide.
Anaerobic digestion takes place in four phases: hydrolysis/liquefaction, acidogenesis, acetogenesis and methanogenesis. The various biological conversions should be sufficiently coupled to ensure that the digestion process is balanced and does not accumulate any intermediates. For industrial wastewater treatment, anaerobic reactors like the up-flow anaerobic batch reactor (ASBR), and anaerobic sequencing bulk reactor (UASB), have been used.
Advanced Oxidation for Wastewater Treatment in Processing Plants
Oxidation is, by definition, the process where electrons are transferred between substances. This leads to a potential expressed as volts, which is known as normalized hydrogen electrode. This is how you can determine the oxidation potentials for different compounds. Chemical oxidation is a solution that conforms to treated wastewater legislation. It is often used in conjunction with secondary treatment to destroy non-biodegradable substances. The chemical oxygen demand (COD) is a reference parameter for chemical oxidation. These processes can usually be used to treat wastewater with low COD content. Higher COD would require expensive reactants. There are two types of chemical oxidation processes:
Chemical treatment in the classic way
Advanced oxidation (AOPs).
AOPs refer to wastewater treatment processes at near ambient temperatures and pressures that produce highly reactive radicals, especially hydroxyl radicals, in sufficient quantities for wastewater purification. These treatments are promising for remediating contaminated ground, surface, and wastewater containing non-biodegradable organic pollutant pollutants. Hydroxyl radicals, which are extremely reactive species, attack almost all organic molecules.
There are technical and economic limitations to AOPs' use. There are limitations to their application to whole-site wastewater flow and in permanent operation. AOPs are required for large critical treatment units to handle peak COD and meet strict treatment limits. They are often used following biotreatment. These units are very effective at converting recalcitrant compounds to intermediates that can be biologically oxidized via recirculation to their inlet or, even better - completely mineralizing them when they’re applied to the outlet of a biologic treatment facility as a final polishing stage.
If you’re looking for a wastewater treatment option that uses top-of-the-line technology, get in touch with In-Pipe today.
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