Anaerobic Process for Treating Sewage

The Anaerobic process for treating sewage is considered to be an economical and eco-friendly process.

The process involves the digestion of organic material in the sewage in the absence of air and produces biogas.

Sewage treatment through anaerobic processes works effectively in removing biodegradable organic compounds and has the advantage of reducing the amount of sludge being produced.

The biogas produced during the process also acts as a source of energy, making the overall process energy efficient.

Microbiology of the Anaerobic Process for Treating Sewage

The process of degradation occurs in 4 stages:

• Hydrolysis: Complex undissolved material broken into less complex compounds through enzymes secreted by acidogenic bacteria. The products of this process are used as substrates for the bacteria.
• Acidogenesis: Products formed during the hydrolysis step get diffused into bacterial cells of fermentative bacteria where dissolved compounds in the sewage get converted into simple material producing fatty acids, alcohols, lactic acids, and new cell material.
• Acetogenesis: Acetogenic bacteria act on products from the acidogenesis stage and convert them into acetate, carbon dioxide, hydrogen, and new cell material.
• Methanogenesis: The final stage of anaerobic degradation of the organic matter occurs in this stage, where methane gets produced from acetic acid.

A few conditions to be met for anaerobic reactor systems are as follows :

• Sufficient contact time between the microbes in the sewage (biomass) and the wastewater.
• The biomass needs to be adapted and acclimatized well to be able to handle the specific characteristics of the wastewater.
• The high retention rate of the viable biomass in the reactor is able to increase the loading of the system.

High-rate anaerobic secondary treatment of wastewater was designed to handle high-strength industrial wastewater characterized by very high COD. Municipal sewage treatment in most parts of the world deals with concentrations of sewage below 1000 mg/l.

In the initial developmental stages of biological wastewater treatment through anaerobic processes, there were limitations, such as uncontrolled greenhouse gas emissions, that occurred due to financial constraints.

With multiple there were multiple issues associated with the anaerobic process for sewage treatment, it has a big potential to solve major wastewater-related problems in developing countries.

The main advantages and constraints of the anaerobic process of treating sewage are as follows:

• At least 90% cost saving in operational costs due to lesser energy requirements.
• 40-60% cost saving in investment costs due to the lesser requirement of treatment units.
• Methane produced can be used as a source of energy.
• Can handle high hydraulic loads and organic loads
• Excess sludge production is low, but sludge can be easily stabilized and dewatered for efficient disposal.

Constraints:

• Collected methane produced is often not recovered
• Gases like H2S produced might escape causing odour problems.
• The produced methane gets dissolved in the effluent, and measures are not taken to prevent the CH4 from escaping into the atmosphere.