Biological treatment process

The biological method of wastewater treatment is based on the ability of micro-organisms to break down sinking, colloidal and dissolved organic matter. Continuous aeration maintains a uniform microbial growth, distribution and activity. Groups of micro-organisms working in coordination break down organic pollutants into suspensions and colloids, which are then oxidised to minerals, carbon dioxide (CO₂) and water (H₂O).

Biochemical reaction:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

This process is similar to the natural self-cleaning mechanisms of water bodies, where organic pollutants are broken down by micro-organisms and oxidised. If sufficient oxygen is present in the effluent, the pollutants are broken down to their final oxidation products, a process known as biochemical oxidation under aerobic conditions.

The oxygen required for the oxidation of pollutants can be supplied from ambient air, either naturally or artificially. The oxidation process takes place in two steps:

Primary phase: oxidation of organic substances containing carbon. In addition to bacteria, enzymes are also involved in this process.

Secondary phase: nitrogen compounds are oxidised to nitrite and nitrate.

Description of the aerobic process

The optimum number of BioCleaner units and the most appropriate consortium of micro-organisms are selected based on the flow and process parameters to ensure the best cleaning results. The BioCleaner is immersed in an existing activated sludge reactor or other tank and started.

To improve the efficiency of the BioCleaner OS micro-organisms and the activity of the anaerobic bacteria, 5-10% of the effluent flow is returned to the start of the main treatment plant.

Nitrogen removal: nitrification and denitrification

The anaerobic stage of biological treatment is designed to remove nitrogen and phosphorus. Nitrogen is removed by two main processes: nitrification and denitrification.

Nitrification: In this step, the ammonium (NH₃) in the wastewater is oxidised to nitrite (NO₂⁻ ) and subsequently to nitrate (NO₃⁻ ). The process is carried out by two groups of bacteria:

Ammonium-oxidizing bacteria (AOB): NH₃ → NO₂⁻

Nitrite-oxidizing bacteria (NOB): NO₂ ⁻→ NO₃⁻

Denitrification: in an anaerobic reaction, denitrifying bacteria convert nitrate (NO₃⁻ ) into molecular nitrogen (N₂), which evaporates into the atmosphere. As there is no free oxygen in anaerobic environments, the bacteria use nitrate as an alternative source of oxygen.

Chemical reaction:
4NO₃⁻ + 5CH₂O + 4H ⁺→ 2N₂ + 5CO₂ + 7H₂O
(CH₂O is a general description of organic matter)

Description of the anaerobic process

Nitrogen removal takes place in the bottom layer of the tank, where an anaerobic medium favourable to denitrification is formed.

In an anaerobic environment, some micro-organisms are able to convert some of the phosphorus compounds into soluble polyphosphates by breaking down readily biodegradable organic matter. These polyphosphates are then used as an energy source in the aeration compartment, thus favouring the growth of phosphorus-accumulating organisms.

Phosphorus removal under anaerobic conditions

Some of the micro-organisms are killed and the phosphorus they absorb is deposited at the bottom of the tank, forming a biolayer.

Phthalates can be degraded under both anaerobic and aerobic conditions, and Chem5's microbial concorsium enhances these reactions by increasing microbial activity.

1. Anaerobic degradation of phthalates

In the absence of oxygen, anaerobic micro-organisms act on the carbon base of phthalates.
The microbial reflux of Biocleaner OS helps to recycle the partially degraded compounds, enhancing their effect on anaerobic bacteria.
Phthalate esters are first hydrolysed by decomposing them into phthalate acid and alcohols, which are further degraded into simpler organic acids, methane (CH₄) and carbon dioxide (CO₂).

2. Aerobic degradation of phthalates

After anaerobic digestion, the remaining carbon molecules can be further oxidised by aerobic microorganisms.
In the presence of oxygen, aerobic bacteria finally break down the intermediate compounds into water (H₂O) and carbon dioxide (CO₂), completing the biodegradation process.

Phthalate degradation steps:

1. Initial hydrolysis:
Phthalates, as esters, have ester bonds (-COO-). Micro-organisms (bacteria and fungi) produce enzymes (esterases) that hydrolyse (break) these bonds. The first step is to convert phthalates (e.g. DEHP) into monoesters (e.g. MEHP - mono-2-ethylhexyl phthalate) and alcohol molecules.

2. Further hydrolysis:
The monoesters (e.g. MEHP) are again hydrolysed to phthalic acid and other alcohol products. Phthalic acid is more soluble in water and therefore easier to further degrade.

3. Degradation of the aromatic ring:
Specialised bacteria can act on phthalic acid by first adding hydroxyl groups (hydroxylation). This is followed by the cleavage of the ring by enzymes such as dioxygenases to form a stable benzene ring.

4. Complete mineralisation:
After the aromatic ring has been cleaved, the products (e.g. small organic acids) enter central metabolic pathways (e.g. the TCA cycle - Krebs cycle). Finally, the final breakdown products are CO₂ and H₂O.

Degradation of phthalates during biological treatment

The Chem5 microbial concorsium increases microbial density and improves oxygen transfer, accelerating the degradation of phthalates and other complex organic molecules.

Odours are caused by the decomposition of organic matter in anaerobic environments, which produces hydrogen sulphide (H₂S), ammonia (NH₃) and other volatile compounds.

BioCleaner OS ensures a balanced action of aerobic and anaerobic processes, resulting in faster degradation of organic compounds and lower concentrations of odours.

Odour removal

By maintaining the anaerobic-aerobic degradation cycle, Chem5 ensures more efficient degradation of pollutants and reduces the amount of toxic by-products and intermediate, odorous compounds.

In conventional treatment systems, activated sludge accumulates as a result of an excess of undecomposed organic matter.

The anaerobic process produces organic acids, methane and CO₂, allowing part of the sludge to be converted into gas, while the aerobic process completes the digestion cycle.

Sludge volume reduction

BioCleaner OS promotes the self-digestion of biomass, reducing the volume of excess sludge and making the system more efficient and cost-effective.

Improved wastewater treatment process

More efficient decomposition of organic pollutants results in higher treated water parameters and less secondary pollution.

Optimised nitrification and denitrification processes improve nitrogen removal, reducing the risk of eutrophication.

Phosphorus removal becomes more efficient thanks to micro-organisms capable of accumulating and precipitating it.

The end result is a higher quality of treated wastewater that meets stringent environmental requirements