Anaerobic treatment

ANAEROBIC TREATMENT:

Microorganisms transform organic materials into bio gas in the absence of oxygen during anaerobic treatment. It’s a low-energy treatment method for high-strength industrial wastewater that’s heated and contains a lot of biodegradable organic matter (measured as BOD, COD, and/or TSS). Before discharging to a municipal wastewater treatment facility or polishing in an aerobic process, an anaerobic system can be employed for pretreatment.

Microorganisms break down wastewater or other materials without the use of dissolved oxygen in anaerobic treatment. Anaerobic bacteria, on the other hand, can and will use oxygen from the oxides put into the system or from organic material in the effluent. Many industrial systems, including food production and municipal sewage treatment facilities, utilise anaerobic systems.

For well over a century, anaerobic methods have been utilised to treat concentrated industrial wastewaters. These techniques turn organic resources into methane, a fuel that can result in a net energy gain from the process. Treatment of dilute industrial wastewaters is now possible thanks to recent advancements in treatment technology and knowledge of process microorganisms. Austro’ experts have handled the advantages of anaerobic treatment over aerobic treatment, as well as contemporary microbiology and modern techniques.

When it comes to treating dilute wastewater, bio film techniques appear to be more stable than dispersed growth procedures. The reasons behind this aren’t totally clear, and they’re most likely several. The involvement of diatomic hydrogen (H2) in the regulation of process dynamics is one factor that makes bio film processes more favorable.

Method and Installation Description

When dealing with more concentrated effluent, anaerobic treatments are typically used. The anaerobic sludge contains a variety of microorganisms that collaborate to convert organic matter to biogas through hydrolysis and acidification. Biogas is typically composed of 70% methane (CH4) and 30% carbon dioxide (CO2), with minor amounts of other gases (e.g. H2 and H2S). Methane can be used as a source of energy. Anaerobic reactors can be used in a number of different ways. A contact reactor and an up flow reactor are depicted in the diagram.

The contact reactor is comparable with a conventional active sludge system, but under anaerobic conditions. The sludge is mixed with wastewater in the reactor and is then separated in the sedimentation tank and returned to the reactor.

In the anaerobic upflow reactor, the influent is introduced at the bottom of the vertical reactor. The sludge in the reactor is primarily grain shaped and forms a blanket in the reactor, with the most compact sludge grains at the bottom and the lighter grains and heavier sludge floccules above it. Very light sludge floccules will be released by the upward flow, but can potentially be collected in a sedimentation tank. The biogas is collected and disposed of at the top of the reactor, separately from the partly purified water and the sludge.

In addition to the contact reactor and the upflow reactor, other types are also available:

Conventional digester

This type is generally used for RWZI sludge and liquid organic waste fermentation. In order to obtain the longest feasible retention time, the system has very low loads and a huge volume. The anaerobic sludge is not recirculated in this sort of reactor.

Packed anaerobic filter (sludge on carrier)

This reactor is filled with carrier material and is normally used as an upflow reactor.

UASB (upflow anaerobic sludge blanket) or EGSB (expanded granular sludge bed)

Both systems are variations of the upflow reactor. The main difference between the two is the increased recirculation of the EGSB reactor. Together with the prominent sludge grain, this enables higher loads in the EGSB (15-30 kg COD/m³/day).

Anaerobic membrane reactor

This type of application uses membranes for sludge-water separation. To date, little use has been made of this system.

An extra purification phase will often be implemented after anaerobic purification, e.g. for the removal of residual fractions of COD and nutrients N and P. This often involves the use of an aerobic post-purification treatment.

APPLICATIONS :

• Pretreatment, pretreatment prior to aerobic treatment, and pretreatment of segregated waste streams are all excellent candidates for anaerobic treatment. An anaerobic system can be employed as the only biological component of a treatment system for wastewater discharged to a POTW if used for standalone pretreatment.
• An anaerobic system can be very effective and cost-effective for eliminating high quantities of BOD and COD prior to final treatment by an aerobic process when used before aerobic treatment.
• Many industrial facilities have waste streams that make up a small percentage of overall flow yet account for the majority of pollution load. Prior to merging with the overall flow, these high-BOD waste streams can be separated and treated in an anaerobic process. In a number of industrial establishments, ETS anaerobic systems are particularly effective in wastewater treatment.

ADVANTAGES OF ANAEROBIC TREATMENT SYSTEMS :

• Incomplete break-down of organic compounds: Need for post-purification via, for example, aerobic purification;
• No thorough nutrient removal: Again, later aerobic purification with nutrient removal is often needed;
• Most efficient purification in the mesophilic range, i.e. between 30-37°C, whereby the influent must be heated in most cases;
• Less robust system with regards to toxicity and inhibition;
• Risk of odor problems.