Wastewater treatment refers to the physical, chemical, and biological processes used to remove pollutants from wastewater before discharging.

The primary materials requiring treatment in domestic wastewater are organic matter, nitrogen and phosphorus. Treatment processes can take many forms depending on community needs and resources. Treatment of wastewater treatment  usually consists of pretreatment, followed by primary and secondary treatment, and additional advanced processes if resources are being recovered.

Pretreatment can consist of removal of bulky matter with screens or grinders, removal of grit and other solids to improve downline processes and protect pipelines and equipment, and if required, removal of fat, oil and grease. Primary treatment is usually accomplished with sedimentation and clarification equipment to separate settleable and floating matter from the water using physical and chemical methods. Primary treatment reduces the total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD).

Secondary treatment uses biological processes to further reduce solids in the effluent. Bacteria feed on organic matter; the excess sludge is removed to be made into biosolids and the water goes through secondary clarification, followed by disinfection. Advanced treatment includes processes to dewater the sludge and reduce pathogens, and treat the water to meet regulatory limits before reuse or discharge.

Wastewater Technologies

• Clarification/Filtration
• Physical/Chemical Treatment
• Advanced Oxidation (WAO)
• Wet Air Oxidation (WAO)
• Heavy metals removal
• Oil/water separation

Wastewater Treatment Processes

I-Aerobic biological treatment:

Aerobic treatment of wastewater is a biological process that uses oxygen to break down organic contaminants and other pollutants like nitrogen and phosphorous. Oxygen is continuously mixed into the wastewater or sewage by a mechanical aeration device, such as an air blower or compressor. Aerobic microorganisms then feed on the wastewater’s organic matter, converting it into carbon dioxide and biomass which can be removed.

There are several different technologies for the aerobic treatment of wastewater and sewage. These include:    

Conventional activated sludge:

organic matter is broken down by aerobic microorganisms in an aeration tank. This forms biological flocs (sludge) which are then separated from the treated water in a sedimentation tank.

Moving bed biofilm reactor (MBBR):

 biofilm grows on plastic carriers suspended and circulated in an aeration tank. These are kept in the tank by retention sieves.

Membrane bioreactor (MBR):

advanced technology combining the activated sludge process with membrane filtration

Integrated Fixed Film Activated Sludge (IFAS)

 Integrated fixed film activated sludge (IFAS) is an innovative wastewater treatment technology that offers several advantages over conventional activated sludge technologies. IFAS involves adding an attached growth media to an activated sludge tank to facilitate biomass growth and strengthen the treatment process.

IFAS VS. CONVENTIONAL ACTIVATED SLUDGE 

IFAS and conventional activated sludge systems are similar, but some major differences include the combination of aerobic, anaerobic and anoxic zones and the increased sludge retention time in IFAS.

Because fixed film wastewater treatment systems typically require less volume than conventional activated sludge systems, they tend to involve less capital cost. New IFAS systems typically cost less than new conventional activated sludge systems, and adding IFAS technology to existing activated sludge systems can avoid the costs of expanding the system’s capacity.

DIFFERENCES BETWEEN IFAS AND MBBR

MBBR stands for moving bed biofilm reactor, a wastewater treatment technique that is similar to IFAS. MBBR involves the use of a reaction tank that contains a plastic carrier combined in water or a mixture of water and sludge. The main difference between MBBR and IFAS is that the activated sludge from sludge recirculation is also used in IFAS. This means carrier-fixed biofilms and activated sludge are both used in one reaction tank.

Sequencing batch reactor (SBR)

A sequencing batch reactor (SBR) is a treatment process that consists of a sequence of steps that are carried out in the same containment structure, usually a tank reactor. They are also referred to as “fill-and-draw” systems. Although SBR systems exist that do not use aeration (anaerobic SBRs), a typical SBR system is designed to include aeration in the treatment step. A typical sequence for a SBR system is: (1) FILL, when the tank is filled with fresh wastewater, (2) REACT, when aeration and mixing are used to promote microbial removal of waste constituents, (3) SETTLE, when aeration and mixing devices are turned off to allow settling of suspended solids, and (4) DRAW, when clear effluent is drawn from the top of the reactor.

Waste solids can be removed from the reactor after the DRAW stage from the bottom of the tank, or during the REACT stage while the wastewater is completely mixed. The SBR treatment process requires a liquid waste input, so it is more suitable for flush systems than for scrape or pit-storage systems

II-Anaerobic biological treatment:

Anaerobic water treatment is a biological process that breaks down organic contaminants found in wastewater using microorganisms in the absence of oxygen. The anaerobic wastewater treatment process consists of two stages:

1. Acidification stage: In this initial stage, the anaerobes break down complex organic compounds into acid or short-chain volatile acids.
2. Methane production phase: This second stage consists of two steps:

– Acetogenesis :The anaerobes synthesize the acids to form acetate, carbon dioxide and hydrogen gas.

– Methanogenesis: The anaerobes will act upon the newly created molecules to form carbon dioxide and gas. The byproducts can be used for fuel if needed, while the wastewater is routed for further treatment or discharge.

The anaerobic treatment systems can be designed and configured as single-or-multi-stage units, depending on the application and requirements of the facility.

Basically, an anaerobic treatment cycle involves wastewater entering a bioreactor receptacle containing a thick semi-solid substance called sludge, full of anaerobic bacteria and other microorganisms which break down the organic contaminants present in the wastewater.

• Upflow Anaerobic Sludge Blanket Reactor (UASB)
• High rate anaerobic reactor

Anaerobic membrane bioreactor