Strategies to Reduce Emissions of Microconstituents. Emissions from Wastewater Treatment

Transcription

1 (Un)successful Strategies to Reduce Emissions of Microconstituents Hugh Monteith ScorePP Workshop Quebec City, October 4 and 5, 2009 Emissions from Wastewater Treatment Effluent (most often considered as the source of contamination?) Biosolids (now a hot topic) Air Emissions (likely not much of an issue for microconstituents) 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 1

2 What Controls Microconstituent Fate? Sorption to solids (biomass, activated carbon, other sorbents) Ends up in residual solids Stripping or volatilization Ends up in air emissions Biodegradation Likely the best option to minimize environmental effects Thus we want to optimize biodegradation Photolysis no a major mechanism yet * What Can be Done to Limit Emissions? Improve treatment methods Impose effluent and biosolids quality limits Restrict inputs (industrial source control) Municipal effort E.g. metals (Hg, Cd,, Ag), FOG, ph, etc. Restrict inputs (product re-formulation or outright bans) Federal action E.g. phosphates, PCBs, PBDEs (47 and 99) 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 2

3 Optimization of Biodegradation The rate of biodegradation is dependent on: The molecular properties (structure) of the compound The temperature of the reaction tank The concentration of microorganisms that can degrade the compounds The time available for the organisms to work We can exert some control over these! Why SRT as a Control Action? SRT Increases the biomass concentration May allow tolerant, adapted organisms to develop, grow and utilize microconstituents Clara, M., Kreuzinger,, N., Strenn,, B., Gans,, O., Kroiss,, H. (2005). The Solids Retention Time a Suitable Design Parameter to Evaluate the Capacity of Wastewater Treatment Plants to Remove Micropollutants. Water Res., 39,, , Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 3

4 Effect of SRT on Removal of Nonylphenol Effluent NP Concentration (μg/l) Temp. range o C From Melcer et al., 2007 Effect of SRT on Removal of E2 From Gaulke, , Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 4

5 SRT Control as a Successful Strategy In aerobic treatment NP(EO) n is stepwise reduced to NP(EO) n-1 by elimination of glyoxalate After aerobic biological treatment, AP(EO) 1 and AP(EO) 2 are predominant AP(EC) 1 and AP(EC) 2 also observed Preliminary modeling by stepwise reduction of EO chain length has been completed, matching observed trends Base Case: 5d SRT, 20 o C 5 d SRT, 20 C Concentration, mg/l HRT, hr NP16EO NP12EO NP8EO NP4EO NP2EO NP1EO NP2EC NP1EC NPE16 degrades quickly NPEC1 and NPE1 are principal metabolites, and form rapidly 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 5

6 Winter: 5d SRT, 8 o C 5d SRT, 8C Concentration. mg/l HRT, hr NP16EO NP12EO NP8EO NP4EO NP2EO NP1EO NP2EC NP1EC NPE16 degrades much more slowly NPEC1 and NPE1 are principal metabolites, but appear later Winter: 12d SRT, 8 o C 12 d SRT, 8 C Concentration (mg/l) HRT (hr) NP16EO NP12EO NP8EO NP4EO NP2EO NP1EO NP2EC NP1EC NPE16 degrades relatively quickly, even at low temperature NP1EC and NPE1 are principal metabolites, formed quickly 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 6

7 Conclusion Compounds that are readily biodegradable in aerobic treatment can be managed using SRT control When Does Biodegradation Not Work so Well? Some compounds appear to be virtually non-degradable (e.g., musk fragrances, carbamazepine, PBDEs) Some compounds are not completely biodegraded (mineralized), but undergo a biotransformation Some metabolites become more hydrophobic (e.g NP(EO) n to NP) and accumulate in solids Some metabolites can be more toxic than the parent (e.g. triclosan to Me-triclosan) 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 7

8 When does SRT Control not Work so Well? When compounds are recalcitrant (non- biodegradable) When compounds are highly hydrophobic Two modeling examples indicate the problems with these types of compounds Synthetic Musk Fragrances Hydrophobic (log Kow > 5) Recalcitrant HHCB (Galaxolide) and AHTN (Tonalide) 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 8

9 Effect of Increased MLVSS on Fate of Synthetic Musk Fragrances % 100 % to Air Emissions % to Sludge % Biodegraded % to Effluent ,000 4,000 6,000 8,000 10,000 Activated Sludge MLSS Concentration, mg/l Effect of Increased MLVSS on Fate of Synthetic Musk Fragrances An increase in SRT (higher MLVSS) results in lower concentrations in effluent (good) Higher concentrations in residual solids (not so good, especially if land applied) Effect on increased biodegradation or biotransformation is minimal 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 9

10 Brominated Flame Retardants (PBDEs) Class of flame retardants used in textiles, computer cases, etc. Structure is similar to PCBs Persistent and bioaccumulative High level of bromination makes them difficult to biodegrade in wastewater treatment Biodegradation of PBDEs in WW Unlikely Mass balance data from Rayne and Ikonomou (2005) Aerated section of BNR process Both biodegradation and stripping Sum of PBDEs in = 1,773 g/d; ; out = 1,795 g/d Anaerobic section of BNR process Sum of PBDEs in = 393 g/d; ; out = 507 g/d Anaerobic fermenter for primary sludge Sum of PBDEs in = 2.0 g/d; ; out = 1.9 g/d 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 10

11 Effect of Increased MLVSS on Fate of hexa-bde99 % % to Air Emissions % to Sludge % Biodegraded % to Effluent ,000 4,000 6,000 8,000 10,000 Activated Sludge MLSS Concentration, mg/l Effect of Increased MLVSS on Fate of PBDEs An increase in SRT (higher MLVSS) results in lower concentrations in effluent (good) Higher concentrations in residual solids (not so good, especially if land applied) Effect on increased biodegradation or biotransformation is minimal 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 11

12 If Not Biodegradation, What? Adoption of new treatment technologies Source control Product re-formulation or outright bans Possible Reasons for Optimism Help from Photolysis? UV light disinfection may cause PBDE re- arrangement and photo-debromination and (Rayne and Ikonomou,, 2005) (not completely understood) Stabilization ponds reduce concentrations of some recalcitrant compounds (e.g., carbamazepine) (POSEIDON, Lishman et al., 2008) (Long retention time help as well) May be even better in advance oxidation processes (e.g. UV/peroxide) 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 12

13 Summary (1) A goal to minimize microconstituent emissions must include all phases (water, solids, air) Improving biodegradation within WWT is usually the best hope for minimizing emissions Longer SRT works when compounds are readily biodegradable Longer SRT causes hydrophobic non- degradable compounds to load onto solids Summary (2) Some existing technologies (e.g. stabilization ponds) may allow photolysis to degrade biologically recalcitrant compounds Advanced oxidation involving UV light, and other processes (O 3, RO) can also work As a last resort, government intervention (bylaws, effluent and biosolids concentration limits, use restrictions, bans) may be required to reduce environmental emissions 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 13

14 Thank-You! Any Questions? 10, Tuesday 06OCT2009, H Monteith, Hydromantis Inc. 14