Anaerobic treatment of wastewater

If oxygen does not reach the wastewater, aerobic bacteria lose their activity and growth and anaerobic bacteria start their activity. Anaerobic wastewater treatment is a set of biological processes that are used to treat industrial and sanitary wastewater without the presence of oxygen. Sanat Water Research Company, a consultant, designer and implementer of all types of wastewater treatment systems, will continue to examine all types of anaerobic wastewater treatment processes and will fully describe the various stages of these processes. In addition, the advantages of using these methods in wastewater treatment will be stated.

?What is anaerobic treatment of wastewater

Anaerobic wastewater treatment or anaerobic digestion of sludge is one of the common methods of removing organic solids in industrial and sanitary wastewater, which is based on the activity of anaerobic microorganisms. These microorganisms need very little oxygen, which they obtain from the decomposition of organic and inorganic materials in wastewater. The result of the activity of anaerobic microorganisms is the decomposition of unstable organic substances and their conversion into stable mineral salts and gases such as hydrogen sulfur, methane gas, carbon dioxide and nitrogen gas. In a way, it can be said that in anaerobic wastewater treatment, organic solids are the source of food for microorganisms. In this way, organic materials including proteins, carbohydrates and fats are converted into fatty acids, amino acids and sugars after being hydrolyzed

Basics of anaerobic wastewater treatment process

The activity of anaerobic microorganisms includes three stages

 Turning solids into liquids

 Digestion of dissolved solids

Gas production

In the case of proper management, the produced gas contains 55-75% methane, 25-45% carbon dioxide and small amounts of other gases such as sulfur, hydrogen, nitrogen and hydrogen

Factors affecting the process of anaerobic wastewater treatment

Various factors can affect the treatment process in anaerobic wastewater reactors. Therefore, it is necessary to regularly measure and control these factors in the process of anaerobic digestion of wastewater. Among these factors, the following can be mentioned:

• Required temperature

Temperature changes affect the activity of microorganisms.

• Anaerobic conditions
• Food minerals

including nitrogen, phosphorus and other nutrients

• PH of wastewater

The acceptable pH of wastewater is between 6.5 and 8.5

• Absence of toxic substances

The presence of inhibiting and toxic substances such as sulfides prevents proper purification.

The factors that cause the loss of balance in the performance of the anaerobic wastewater treatment system on a temporary basis are:

• Sudden change in temperature
• Sudden change in sewage quality
• Sudden change in the load of incoming organic matter
• The presence of toxic substances
• Extreme pH changes
• Slow growth of microorganisms during the operation of the treatment plant

Steps of the anaerobic wastewater treatment process

As mentioned, the activity of anaerobic microorganisms includes the conversion of suspended organic matter into new cells, energy for vital processes and some gaseous products such as methane and carbon dioxide. In general, the process of anaerobic wastewater treatment is divided into the following three important stages:

1. Hydrolysis

In the first stage of purification, which is the hydrolysis stage, complex organic materials are broken down and converted into soluble organic materials. It is at this stage that the suspended matter of the sewage also turns into a solution. The hydrolysis stage, which is the most important stage of anaerobic treatment, takes 5 to 15 days and will generally continue very slowly.

2. Acidification and acetate production

With the appearance of volatile fatty acids, the pH of the environment has definitely decreased and the time to perform the second stage of anaerobic treatment is related to the quality. If there are simple sugars in the wastewater, this step will be done quickly, and if the content of protein and organic substances is complex, the second purification step will be performed, and if the content of protein and organic substances is complex, the second step of anaerobic purification will need time.

3. Methane biogas productionThe third stage of anaerobic treatment is the stage of methane production, and in this stage, COD producing materials are converted into methane. At this stage, the operator must constantly monitor the pH, temperature, toxic substances in the system and nutrients. In most anaerobic reactors, this step lasts about 5 hours.

Types of anaerobic process in wastewater treatment

Considering the many benefits of anaerobic processes in the treatment of industrial and sanitary wastewater, various methods have been introduced based on the anaerobic digestion of wastewater, which are used according to the quantitative and qualitative characteristics of wastewater and the conditions of the treatment plant. Anaerobic wastewater treatment reactors are classified into the following groups based on the biomass retention mechanism:

• Suspended growth reactors
• Fixed film reactors
• Hybrid reactors

The most common types of anaerobic wastewater treatment systems are briefly described below

Anaerobic purification by UASB method

reactor increases adhesion and settling power. The layer of accumulated masses of microorganisms in this reactor is known as sludge blanket.

 The advantages of using this reactor are:

• Appropriate efficiency in the treatment of wastewater with high organic pollution load
• Low sludge production
• Reducing the use of treatment plant land
• The possibility of collecting methane gas by gas separators and the possibility of obtaining energy from it
• The process of this method requires very little energy.

The disadvantages of this type of system are:

• The need to keep the temperature between 30 and 38 degrees Celsius to prevent the reduction of efficiency
• High sensitivity to PH changes
• Difficult control of the gas separator system in operation

• Long time to set up the process to create a sludge bed

ABR anaerobic reactor

Anaerobic baffled reactors (ABR) are a special type of anaerobic wastewater treatment method in which the wastewater entering the reactor moves up or down from multiple chambers. This reactor separates the two phases of acidification and methane production. The design of the baffles in this reactor is done in such a way that the wastewater flow passes through the sludge bed. In this reactor, it is suggested to use packing media in the upper part of each chamber of series reactors to store as many biological solids as possible. This wastewater treatment method is used in urban wastewater treatment plants with small capacity and pre-treatment of industrial and large units and has high efficiency for industrial wastewater.

Anaerobic treatment by UAFB method

UAFB wastewater treatment is also referred to as anaerobic treatment reactor with attached growth. In this reactor, wastewater moves in a column towards the top of the tank in tubular modules and corrugated plastics. The biological bed in UAFB anaerobic reactors is often made of plastic, and because of less sludge production and 80% efficiency for BOD and COD targets, they are often used as pre-treatment of industrial wastewater. One of the most important advantages of using this method of anaerobic wastewater treatment is its high resistance against hydraulic and organic shocks.

Anaerobic floating bed filter reactor (AFBR)

This reactor is a type of fixed film reactors in which the media is fine grains such as sand or granular activated carbon. This reactor is used in the treatment of industrial wastewater with high COD and has a volumetric loading capacity of nearly 100 (kg.COD)/(m^3.day). Due to the high usage of activated carbon in this method, this reactor will not be economical

Advantages of using anaerobic method in wastewater treatment

• A very large amount of wastewater can be stabilized

  • Less sludge production than other treatment methods
  • No need for mechanical sewage aeration equipment
  • Production of biogas and consumption of produced methane as fuel
  • Low energy consumption
  • Low need for minerals
  • High resistance against organic and hydraulic shock loads

Design and construction of anaerobic reactors for wastewater treatment

With more than 20 years of successful experience in industrial and sanitary wastewater treatment, PASENCO is a consultant, designer and implementer of all types of wastewater treatment systems. The chosen strategy for wastewater treatment may be different for each production unit. This is determined by the water industry research company in such a way that the employer’s needs and environmental standards are fully covered. To get more information and free expert advice, you can communicate with our experts through the communication methods mentioned on this page.