What are the different types of secondary treatment processes used in wastewater treatment plants?

The second step of wastewater treatment is known as secondary treatment. Oil, colloidal particles and grease, are eliminated during basic treatment. To eliminate the organic stuff present, biological treatment is applied to the wastewater during secondary treatment. This treatment is carried out by local and marine bacteria and protozoa that consume biodegradable soluble contaminants including sugar, detergent, fat, and food waste. These processes are temperature-sensitive, and biological reactions advance more quickly as the temperature rises.

Secondary wastewatertreatment consists of two different treatment processes:

1. Aerobic Treatment: This biological method of wastewater treatment uses oxygen to break down organic matter and eliminate other pollutants like nitrogen and phosphorus.

Technologies for aerobic therapy include:

Sequential Batch Reactor/Activated Sludge Process (ASP)/ Extended Aeration System (EAS) (SBR)

Biofilm Reactor with Moving Bed (MBBR)

Membrane Bioreactor (MBR)

2. Anaerobic Treatment: Secondly, anaerobic therapy Wastewater or other materials are broken down by microorganisms during anaerobic treatment without the help of dissolved oxygen. However, both the organic matter in the effluent and the oxygen contained in the system's provided oxides may and will be used by anaerobic bacteria.

Activated-Sludge-Process/ Extended Aeration process:

Organisational structure and extended Aeration process's mixing regime are comparable to those of the fully mixed process. Prolonged aeration, low organic loading, high MLSS concentration, and low F/M are all used in the process. High elimination effectiveness for BOD.

The rising oxygen demand has an effect on the system's total operating expenses. However, the procedure is made simpler by eliminating the first settling and separate sludge digestion. However, the removal of initial settling and separate sludge digestion simplifies the process.

Sequential-Batch-Reactor (SBR)

For treatment of sewage, sequential batch reactor uses an active sludge system. In a single batch reactor, aeration, equalisation, and clarification may all be accomplished. For big industrial effluents, the SBR system is effective.

The SBR does away with the requirement for an additional clarifier. Since the process is PLC-based, SBR has required more maintenance while in operation, but it also exhibits better efficiency and requires less space for the ETP. Settlement and secondary treatment are combined in SBR. With a combination of wastewater and activated sludge, oxygen is bubbled in order to remove the organic matter (BOD and COD). The water can then be dumped onto surface waters after this treatment.

Moving Bed Biofilm Reactor (MBBR)

An aeration tank, similar to an activated sludge tank, and unique plastic carriers give a moving bed biofilm reactor (MBBR) a greater surface area where a biofilm may form.

Membrane Bioreactor (MBR)

The processes of activated sludge and ultrafiltration are combined in the Membrane Bioreactor (MBR). Surface water can be used to reclaim high-quality MBR wastewater. It is adaptable to existing installations

Upflow Anaerobic Sludge Blanket (UASB)

The leftover substrate then passes through the "sludge blanket," a layer of less dense biomass. The sludge is combined and cycled by a sludge recirculation cum disposal pump. A methane-producing digester known as the UASB reactor employs an anaerobic process to create a layer of granular sludge, which is then broken down by anaerobic microorganisms.

UASB assists in reducing greater organic loads so that the remaining loads may be treated aerobically in the event of higher organic loads.

The substrate typically goes through an enlarged sludge bed with a high concentration of biomass initially during the treatment of the UASB reactor.

Anoxic Tank

The presence of anoxic conditions is necessary for denitrification to take place. Although dissolved molecular oxygen is scarce in anoxic circumstances, it is possible for oxygen to be chemically bonded, as is the case with nitrate. The dissimilation process needs both an electron acceptor and an electron donor in order to convert the nitrate molecule into chemically bound oxygen. A carbon source loses (donates) electrons and is oxidised to carbon dioxide, whereas nitrate obtains (accepts) electrons and is reduced to nitrogen gas.

Simply put, anoxic circumstances make sure that nitrate, rather than oxygen, will act as a "electron acceptor" in the dissimilation process. In the pre-anoxic basin, influent wastewater is combined with return sludge from the clarifier and mixed liquor that is high in nitrate and pumped from the effluent end of the aeration tanks.

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