BNR Processes
Due to environmental concerns caused by excessive nutrient discharges, regulatory agencies are implementings
tringent limitations on both point source and non-point source nutrient discharges.
Upgrades to some wastewater treatment facilities to incorporate biological nutrient removal (BNR)
processes are required to achieve the necessary nutrient load reductions.
In addition to controlling eutrophication in receiving water bodies and environmental benefits,
BNR facilities have demonstrated economic and operational benefits. Their utilization is potentially
more economic than conventional activated sludge treatment or physical/chemical processes.
Incorporation of an un-aerated zone ahead of the aerobic zone in BNR processes, results in a substantial
reduction of aeration energy costs. Also, the aeration energy needs are reduced because most
of the substrate removal and some stabilization of organics occur in the un-aerated zone.
Enhanced biological phosphorus removal (EBPR) provides an economic benefit through
the reduction or elimination of chemical addition for phosphorus removal.
The BNR processes are also known to produce less waste activated sludge due to lower sludge yield.
An additional benefit of BNR processes is that the de-nitrification process recovers approximately
one-half of the alkalinity consumed during autotrophic nitrification.
It has been shown that anaerobic and/or anoxic zones placed ahead of aerobic zones in BNR processes act as biological
selectors that discourage the growth of filamentous organisms, generally improve sludge settling properties and enhance process stability.