At present there are over 30 full-scale BNR WWTPs using BIOGRADEX
technology with flows from under 500 m3/d up to 35,000 m3/d in service.
Feasibility designs for 300,000 m3/d applications indicate BIOGRADEX
technology to be very cost effective at this size as well. Designs completed
for plants of 50,000 - 60,000 m3/d flow per train indicate this technology will
also be effective for very large BNR WWTPs.
The most sophisticated leading-edge suspended growth activated sludge
BNR Processes used with BIOGRADEX technology can also benefit from
substantially reduced land requirements, and lower construction and
operating cost with this new technology.
For conventional BNR WWTPs, denitrification typically occurs also in the
secondary clarifiers settled sludge. Water in the sludge is also normally
Nitrogen Saturated. This situation produces micro nitrogen bubbles that are
released and trapped in the settled sludge floc structure. As more nitrogen is
produced, more and more micro bubbles are enmeshed and that causes the
sludge to be bulky, stop settling / thickening and produce scum on clarifiers.
In contrast for BIOGRADEX technology WWTPs, MLSS degassing reduces
100 % saturation of dissolved nitrogen conditions down to the range of
50-75% saturation as the MLSS enters secondary clarification. The sludge
can then operate in stable, nitrogen non-saturated conditions, is not bulky and
can continue to settle and thicken in the clarifiers even during continuing
denitrification conditions. Nitrogen released during denitrification is thus
dissolved in water rather than otherwise becoming micro nitrogen bubbles
enmeshed in sludge floc which contributes to high SVI conditions. The
resulting thick, low SVI settled sludge even with high levels of filamentous
organisms in the MLSS, can then be recycled to Biotreatment Cells with low
RAS flow and high % solids concentration. Very high RAS concentrations
then allow ground-breaking high MLSS concentrations to be achieved which
proportionally reduces the size of the WWTP Biotreatment tanks.
The BIOGRADEX technology MLSS vacuum degassing process also breaks
up the activated sludge floc as dissolved gas micro bubbles are removed. The
floc is then reformed by BIOGRADEX technology to produce floc that
settles better than before degassing. The degassed sludge in the clarifier does
not become bulky after settling. Also the resulting elimination of scum on
secondary clarifiers helps prevent nocardia infestation which is one of the
major operating risks for BNR type WWTPs.
Treatment process and operation enhancements by BIOGRADEX technology
vacuum degassing of mixed liquor has been proven to achieve full-scale,
ground-breaking WWTP enhancements that are unparalleled for BNR
activated sludge wastewater treatment technology. A new BNR treatment
benchmark has now been established by BIOGRADEX technology for cost
effective, compact wastewater Biological Nutrient Removal, as well as a new
standard of WWTP operational efficiencies, stability and flexibility.