Method to identify potential phosphorus rate-limiting conditions in post-denitrification biofilm reactors within systems designed for simultaneous low-level effluent nitrogen and phosphorus concentrations.
Water-quality standards requiring simultaneous low level effluent N and P concentrations are increasingly common in Europe and the United States of America. Moving bed biofilm reactors (MBBRs) and biologically active filters (BAFs) have been used as post-denitrification biofilm reactors in processes designed and operated for this purpose (Boltz et al., 2010a). There is a paucity of information describing systematic design and operational protocols that will minimize the potential for phosphorus rate-limited conditions as well as a lack of information describing the interaction between these post-denitrification biofilm reactors and unit processes that substantially alter phosphorus speciation (e.g., chemically enhanced clarification). In this paper, a simple mathematical model for estimating the threshold below which P becomes rate-limiting, and the model is presented and evaluated by comparing its predictions with operational data from post-denitrification MBBRs and BAFs. Ortho-phosphorus (PO(4)-P), which is the dissolved reactive component of total phosphorus, was a primary indicator of P rate-limiting conditions in the evaluated post-denitrification biofilm reactors. The threshold below which PO(4)-P becomes the rate-limiting substrate is defined: S(PO4-P):S(NOx-N) = 0.0086 g P/g N and S(PO4-P):S(M) = 0.0013 g P/g COD. Additional analyses indicate J(NOx-N)(avg) =0.48 g/m2/d when S(PO4-P):S(NOx-N) > 0.0086, and J(NOx-N)(avg) = 0.06 g/m2/d when S(PO4-P):S(NOx-N) < 0.0086. Effluent nitrate-nitrogen plus nitrite-nitrogen concentration (S(NOx-N)) from the evaluated post-denitrification biofilm reactors began to rapidly increase when S(PO4-P):S(NOx-N) was 0.01, approximately (consistent with the rate-limitation threshold of S(PO4-P):S(NOx-N) < 0.0086 predicted by the mathematical model described in this paper). Depending on the processes used at a given WWTP, optimizing chemically enhanced clarification to increase the amount of PO(4)-P that remains in the clarifiers effluent stream, dosing phosphoric acid in the MBBR or BAF influent stream, and/or optimizing secondary process EBPR may overcome phosphorus rate-limitations in the biofilm-based post-denitrification process.
CH2M HILL, Inc., 4350 W. Cypress Street, Tampa, FL 33607, USA. jboltz@ch2m.com
Joshua P
JP
Boltz
Eberhard
E
Morgenroth
Glen T
GT
Daigger
Christine
C
deBarbadillo
Sudhir
S
Murthy
Kim H
KH
Sørensen
Beverly
B
Stinson
D018441:Biofilms; D019149:Bioreactors; D058440:Denitrification; D008962:Models, Theoretical; D009584:Nitrogen; D010710:Phosphates; D010758:Phosphorus; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods*
D010710:Phosphates; D010758:Phosphorus; D009584:Nitrogen