Requirements for Efficient Nitrification / Denitrification 

Two principle factors influence the efficiency of the nitrification  / denitrification processes: the biological community and the water physico-chemistry.  Nitrification requires specific conditions, and treatment must follow an ordered procedure.  Reduction of carbonaceous BOD  (cBOD) is a preliminary requirement for nitrification; cBOD can inhibit nitrification.  Best results are achieved when the cBOD is < 30 mg/L.  The sooner that the cBOD is removed, in the treatment process, the sooner nitrification can begin.  This is critical in systems with limited hydraulic retention time and in cold weather, when microbial activity is slower.

Biological Community 

Two bacterial strains are involved in nitrification; Nitrosomonas converts ammonia into nitrite, and Nitrobacter converts nitrite into nitrate.  Nitrifying bacteria are very sensitive to environmental conditions; this is particularly true of Nitrobacter.  Many factors can inhibit these bacteria including excessive soluble organics and even light.   A balanced population of heterotrophic bacteria is essential to control levels of soluble organic pollutants and for denitrification.  Lack of any member, of the essential communities will stop or reduce the efficiency of the processes.   

Nitrifiers occur in the surface layers of the soil as well as in surface waters.  Freezing eliminates runoff of nitrifiers entering combined sewers.  Similarly, sealed or just sanitary sewers or septic systems do not contain nitrifiers.   They do not come from digestive tracts. 

Simply adding bacteria to a wastewater plant does not guarantee that they will achieve the targeted task.   It is essential to provide the cultures with the conditions required for their growth.

Water Physical-Chemistry  

The first step to achieve efficient nitrification is to establish the conditions required for this process.  Ammonia and nitrite are only sources of nitrogen for nitrifying bacteria. Other nutrients including carbon, phosphorus and trace elements are also essential.  

Carbon must be inorganic and is measured as carbonate alkalinity, the alkalinity due to carbonate and bicarbonate.  Nitrifiers prefer stable they are slow to return to active growth.   

Sodium bicarbonate  (baking soda) is commonly used to increase the alkalinity.  The alkalinity should always be at least eight times the level of ammonia.   Water with more than 100 mg CaCO3/L is normally adequate for low levels of ammonia.  Lack of carbonate alkalinity will stop nitrification.

The alkalinity provides pH buffering.  The optimal pH for nitrification is near 8.0.   Values outside of 6.0  - 8.5 can be expected to reduce nitrification efficiency.  Nitrosomonas produces acid during its growth; the pH must be monitored and adjusted

Nitrifying bacteria absolutely require adequate oxygen.  At least 3 ppm of oxygen should be maintained.  The optimal temperature for nitrification is about 30°C; the rate can be expected to be cut in half for every decrease of 10°C.  Thus a WWTP or biofilter working at 30°C (86°F) may remove the same amount of ammonia as one twice as large but operating at 20°C  (68°F).

Denitrification largely occurs in anoxic conditions, which can even occur within bacterial floc even in environments with measurable oxygen.   Denitrification increases the pH and regenerates alkalinity.   The denitrifiying bacteria require an electron donor.   Products used for this purpose vary from starches to methanol amongst others.   

Nitrification in wastewater

The first step to achieve efficient nitrification is to establish the conditions required for this process.   Bacta-Pur® XLG provides the optimal community of beneficial microbes, which eliminate cBOD  (and chemicals that can inhibit nitrifiers).    Bacta-Pur® XLG provides the conditions to permit nitrification and will also remove ammonia by assimilation.   The sooner, in the treatment, that required conditions for nitrification are obtained, means more time, within the treatment system is available for nitrification.  The process of reducing cBOD can even begin upstream, before the WWTP, with the use of the BACTIVATOR® LS models.  This maximizes the time within the WWTP for nitrification. 

Bacta-Pur® N3000 assures the presence of a balanced community of nitrifying / denitrifying strains. All packaged products must be dormant to have shelf life.  Bacta-Pur® N3000 has a 5-year shelf life from bottling.   Dormant cultures, particularly nitrifiers, can be very slow to activate; the BACTIVATOR® LSN models overcome and simplify the activation process.   The BACTIVATOR® LSN models continuously  (24/7) add active nitrifiers to wastewater system.  The product use rates of the BACTIVATOR®s are adjustable for changing conditions:  

• Commercial models — 1.0 to 1.5 L / day,
• Industrial models — 10 to 40 L Bacta-Pur® N3000/ day, 10 to 50 L Bacta-Pur® XLG/ day 

(Treatment of batches can be accomplished with manual preactivation, instructions available.)

Dose rates for nitrification*

FLOWING SYSTEMS: Dose rates are calculated, in one of two ways, by daily flow or system volume:

• Ppm based on flow — this method is used if flow is greater than 10% of hydraulic retention time (HRT)  (< 10 days HRT); Bacta-Pur® is continuously added, with a BACTIVATOR®, based on the flow.
• Ppm based on volume — this method is used if flow is less than 10% of HRT (≥ 10 days HRT).  If this method is used the dose rate (ppm) is either applied once per week, in a batch, or if a BACTIVATOR® is used, the weekly dose is divided by seven, and this amount is preactivated and automatically applied daily by the BACTIVATOR®.

BATCH TREATMENT:  Batches are treated weekly based on their volume.  Daily additions can be made with a BACTIVATOR®.

Temperature effects — Eliminating ammonia from municipal and/or industrial sources is more complicated than from natural sources or from aquacultural production.  Temperature is a master factor affecting activity of cold-blooded organisms.  Activity rates, within the viable range, double with every increase of 10°C and are reduced by 50% for every decrease of 10°C.  This applies to the bacteria in a wastewater treatment plant and similarly to fish in a pond.  Thus cold water will reduce both bacterial activity and ammonia production in a fishpond.  This reduction of ammonia production, however, does not apply to most wastewater treatment systems. Cold weather does not reduce ammonia entering the treatment plant; concentrations may actually increase, if people spend more time indoors.  The problem is also exacerbated by freezing of surface layers of the soil and lack of runoff. 

More cells are required to get a job done at colder temperatures than at warmer ones.  This can be accomplished in two ways:  

• Either with a biofilter sized for winter conditions or
• With a higher dose rate of nitrifiers 

Optimal dose rates — three parameters are most important:

• Temperature
• Time available to accomplish the targeted task (HRT) and
• Ammonia concentration 

There are three steps to calculate the dose rate:

1.  Determine the temperature specific dose rate  (TSDR).

2.  Multiply the TSDR by the Concentration Factor. 

*Every wastewater treatment facility or biodegradation product is unique, with its own set of physical, chemical and biological realities.  The dose rates suggested here should be considered a starting point; they can be adjusted as the treatment progresses.  Generally speaking larger doses give faster results.  It is better to start with higher doses. 

Bacta-Pur®, BACTIVATOR®Ⓓ & ECOPROBIOTICS® are trademarks of Aquaresearch Canada Ltd used under license.

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