BIOTIM^® anaerobic wastewater ­treatment

Waterleau acquired the company BIOTIM in 2004 and so Waterleau became one of the world's top-3 players in the field of anaerobic wastewater treatment.

In recent years, anaerobic wastewater treatment has become a technology of growing importance, especially for highly polluted wastewater. Two major advantages of anaerobic wastewater treatment explain its progress at the expense of the classic aerobic activated sludge treatment:

sludge growth is significantly less compared with the aerobic treatment 
considerable energy saving : no costly aeration and production of energy-rich biogas.

Depending on the system scale the biogas (> 100 Nm^³/hr) may be recovered to produce heat or electricity.

Other advantages 

lower nutrient requirements
lower plan area requirements because of higher volumetric loading rates
lower capital investment and overall operation costs.

However, due to ever more stringent requirements for removal efficiencies of COD, BOD and nutrients, an aerobic post treatment is often required (see also LUCAS® anaerobic-aerobic).

Or alternatively, advanced membrane technologies such as ultrafiltration/microfiltration followed by reverse osmosis ensures emission standards are met.

How it works

Anaerobic treatment is based on microbiological processes, namely methane fermentation, which occurs in an anaerobic environment. Numerous species of bacteria have to cooperate in order to convert the organic pollution in the water to a mixture of methane (CH₄) and carbon dioxide (CO₂), called biogas. The bacteria are generally present as sludge flocs or bacterial clusters (aggregates).

This process has been traditionally more complex and consequently harder to control than the aerobic biological process used in the classic activated sludge wastewater treatment. Better understanding of the microbiology of anaerobic processes has resulted in the successful develop­ment of new, improved and practical systems.

 Schematic representation of the methane fermentation pathway

1. Hydrolysis & acidogenesis

Complex particulate and solubilized polymeric substrates (e.g. polysaccharides and proteins) are hydrolysed to simpler soluble mole­cules (amino acids and sugars). These products are then further catabolized by fermentative micro-organisms, to produce mainly volatile fatty acids (VFA), aldehydes, alcohols, carbon dioxide and hydrogen. 

2. Acetogenesis

The majority of the fermentation products, except H₂, CO₂, formate and acetate, is further degraded by the ­acetogens to yield acetate and H₂ and additional CO₂. The acetogens grow in close association with the ­methanogenic bacteria.

3. Methanogenesis

The final step in the anaerobic digestion is carried out by the methanogenic bacteria and is the formation of methane­ gas from acetate and from hydrogen and carbon dioxide.

 
The main parameters determining the efficiency of the anaerobic activated sludge process are:

Temperature

BOD/COD ratio
Sludge retention time
Suspended solids concentration 
pH

VFA/COD ratio

Partial effluent recycle
Nutrients 
Toxic compounds

Anaerobic reactor types

The appropriate choice of anaerobic reactor type depends on the composition of the effluent. Successful anaerobic wastewater treatment is only possible if the characteristics and specific problems for each individual wastewater are known in advance.

The immense diversity in industrial wastewater creates the need to have several different treatment techniques, each of them offering the best solution for a particular type of wastewater. Waterleau offers a complete range (four types) of design concepts that can be applied for anaerobic wastewater treatment.

They are commonly classified as:

1. Anaerobic Contact (AC) Reactor.

2. Upflow Anaerobic Sludge Blanket (UASB) Reactor

3. Anaerobic Filter (AF)

4. Hybrid Type of Reactors (UAC + UACF)

5. Continuous Stirred Tank Reactor (CSTR)