Introduction

Most wastewater treatment systems have at least two primary and secondary treatment procedures and some extra preparatory approaches. Tertiary wastewater management methods are the third degree of treatment that is more sophisticated and severe. 

Primary and secondary treatment usually only cleans wastewater to the point that it can be safely discharged into the environment. On the other hand, Tertiary treatment can purify water to the point that it can be reused in water-intensive activities or even used as drinking water.

The final phase of the multi-stage wastewater management process is tertiary water treatment. Inorganic chemicals, bacteria, parasites, and viruses are all removed during the third stage of therapy. The treated water is safe to reuse, recycle, or discharge into the environment after these dangerous chemicals have been removed.

In most cases, tertiary wastewater management methods include the final filtration of the treated wastewater. It may be necessary to use alum to eliminate phosphate contaminants from water when necessary. Alum also causes any particulates that were not eliminated by primary and secondary wastewater management methods to clump together, allowing filters to extract them.

Types of Tertiary Methods

Advanced Oxidation Methods

Introduction

Advanced oxidation processes (AOPs), which are defined as oxidation processes including the formation of hydroxyl radicals (OH) in sufficient quantities to impact water purification, were initially proposed for potable water treatment in the 1980s. The AOP concept was further expanded to include oxidative reactions using sulfate radicals (SO4). AOPs are used to destroy organic or inorganic impurities in water and wastewater, unlike typical oxidants like chlorine and ozone, which have a dual duty of decontamination and disinfection.

AOP can be used in conjunction with ozone (O3), catalysts, or ultraviolet (UV) irradiation to provide strong wastewater treatment. AOPs are well-known for bridging the gap between traditional physicochemical and biological processes and their treatability.

Types of AOP Process

For tertiary methods of wastewater management, several AOPs such as photocatalysis, Fenton-like processes, and ozonation are being applied. 

• Photocatalysis: Photochemical AOPs are extensively employed in wastewater treatment as an effective barrier to the oxidation of organic contaminants. The elimination of a larger variety of chemicals is confirmed by the combined impact of UV irradiation and hydrogen peroxide (H2O2) reaction.
• Fenton-like Process – Iron is the most often utilized metal among those that can activate H2O2 and create hydroxyl radicals in water. H2O2 interacts with Fe2+ to produce highly reactive species in the Fenton reaction. Although alternative molecules, such as ferryl ions, have been hypothesized, the reactive species generated are typically identified as hydroxyl radicals.
• Ozonation: Ozone (O3) is a powerful oxidant with a 2.07 V oxidation potential than SCE. Direct O3 oxidation, on the other hand, is a selective reaction in which O3 preferentially interacts with the ionized and dissociated forms of organic molecules rather than the neutral form.

Pros and Cons of the AOP Process

Pros:

• Retention periods are shorter than with other treatment methods.
• The system’s required flow rate does not necessitate a large amount of land.
• AOP can transform organic molecules in water into stable inorganic chemicals.
• Interacts directly with contaminants, converting them to harmless substances.

Cons: 

• Capital and operating/maintenance expenditures are both somewhat expensive.
• Chemicals that are complex and suited to certain pollutants.
• Leftover peroxide likely has to be removed.

Application in Industrial Treatment 

Advanced Oxidation Processes (AOPs) promise to remove non-biodegradable contaminants from municipal and industrial wastewater since they are based on radical reactions that are highly rapid, non-selective, and may totally oxidize compounds.

AOPs can be employed in wastewater treatment for a variety of reasons: 

• The general decline in organic content (COD)
• Particular pollutant removal
• Treatment of sludge
• Enhancing resistive organics’ bioavailability
• Reduction of colour and odour. 

Electron Beam Method

When wastewater is treated using an electron beam, it is frequently purified of numerous impurities. Pollutants decompose as a result of their interactions with highly reactive species generated by water radiolysis, causing it (hydrated electron, OH free radical, and H atom).

Other processes may accompany such reactions, and the synergistic impact of coupled techniques such as electron beam treatment with ozonation, electron beam and adsorption, and others increases the effect of electron beam treatment of wastewater purification.

Purification of industrial wastewater with low impurity levels, such as polluted groundwater, cleaning water, and so on, is only achievable with an electron beam, but it necessitates a large number of irradiation doses.

Purification using electron beam alone for industrial wastewater with high contaminant levels, such as dyeing wastewater, leachate, and so on, takes a large number of doses and is much beyond economics.

Electron beam treatment in combination with traditional purification procedures such as coagulation, biological treatment, and other ways effectively reduces non-biodegradable pollutants in wastewater and expands the electron beam’s application area.

Ultrasound/ Cavitation process

Cavitation causes various intriguing physical-chemical reactions that can be used to identify and oxidize pollutants in water. Pressure pulses inside a liquid create tiny bubbles that operate as miniature reactors, attaining severe P-T values in a short amount of time and creating oxidant radicals highly like OH. Advanced Oxidation Processes have a chemical behavior similar to this (AOPs).

Ultrasonic equipment (horns and baths) is probably the most effective approach to research cavitation effectively. The majority of commercial equipment is designed to function in a lab setting. The pressure pulse’s properties, such as amplitude and frequency, are simple to manipulate and duplicate. 

Furthermore, observations and measurements are straightforward because the entire process takes place inside a static liquid with no change in environmental conditions. Because of these benefits, ultrasonic cavitation has been the primary focus of research for most cavitation organizations.

Plasma Technology

The treated water is subsequently passed through a plasma volume with a large specific plasma-water interaction surface area. The formation of numerous OH-radicals on the interface is aided by increasing the contact surface area, contributing to the efficient oxidation of dissolved contaminants.

The plasma technique for wastewater treatment makes use of non-thermal plasma. To create an ambient-temperature plasma field within a reactor, the system includes electrode stacks that generate unique sorts of electric discharges.

For water treatment purposes, many reactor topologies with various types of plasmas have been investigated. A simple gas-phase discharge in contact with liquid water is typically considered to be a superior option to attempting to break the discharge via water with submerged electrodes.

Comparison of Tertiary Methods

Depending on the wastewater state, several tertiary methods of wastewater management can be applied (pH, clarity, etc.) Electron Beam, ozone, and ultraviolet (UV) radiation are the most frequent among them. There are benefits and drawbacks to each. 

• Ultraviolet light disinfection does not leave any residues or substances in the water, but the effluent must be pure for it to be successful.
• The use of an electron beam to treat wastewater was shown to be highly successful in lowering pathogens and organic load.
• Cavitation uses severe pressures and temperatures generated by cavitation collapses to dissolve tiny organic molecules that would be difficult to disintegrate using traditional biological processes and disintegration of bigger particles to increase the specific surface area.
• The use of plasma technology in conjunction with the treatment of catalysts is a viable strategy. Ultraviolet light and the Fenton reaction in combination with plasma are likewise being explored and employed more and more.

There are still certain obstacles to overcome, such as partial mineralization of impurities, chemical waste, the formation of secondary pollution, excessive energy consumption and expense, and so on, all of which must be factored into the Tertiary method of wastewater Management application and devices.

Application of Tertiary Methods

In a typical wastewater management system, tertiary treatment is the third and final stage. Once the effluent has been treated in the primary and secondary stages, it is ready to enter the tertiary stage by removing suspended particulates, balancing the pH, and lowering the biochemical oxygen demand (BOD).

The final stage of the multi-stage wastewater treatment process is tertiary water treatment. Inorganic chemicals, disease-causing bacteria, viruses, and pathogens are all killed during this tertiary method of wastewater management. The treated water is safe to reuse, recycle, or discharge into the environment after these dangerous chemicals have been removed.

The purpose of tertiary treatment is to guarantee that the treated water is physiologically accepted by all other freshwater creatures, such as weeds and algae, before it is returned to the environment. 

This section of the treatment includes physical water treatment, lagoons, and excessive nutrient removal methods. Before moving on to the final phases, be sure the effluent quality of the released water has improved.