AMMONIA VOLATILISATION IN WSP: A CASCADE OF MISINTERPRETATIONS?

Transcription

1 AMMONIA VOLATILISATION IN WSP: A CASCADE OF MISINTERPRETATIONS? Miller Alonso Camargo-Valero Universidad Nacional de Colombia University of Leeds Duncan Mara University of Leeds

2 Outline Feasible mechanisms for nitrogen removal in WSP Ammonia volatilisation in alkaline waters Pano and Middlebrooks model Ammonia volatilisation in WSP Ammonia removal in WSP

3 Feasible mechanisms for nitrogen transformation and removal in WSP Ammonia volatilisation Biological ammonium uptake Sedimentation of dead biomass and accumulation on sludge layer after partial hydrolysis Conventional nitrification-denitrification Nitrification and simultaneous biological uptake Denitrification by nitrifiers Nitrification denitrification supported by methanotrophs Anaerobic ammonia oxidation

4 Ammonia volatilisation in alkaline waters Ammonia ammonium equilibrium reaction NH 3 + H 2 O NH 4+ + OH - Ammonia dissociation ionization equilibrium constant (Kb) Kb as a function of water temperature Percentage of free ammonia in an aqueous solution

5 Ammonia volatilisation in alkaline waters Krefx et al. (1958) published a short note on the possibility of removing ammonia from sewage effluents by raising the ph. They were working on sewage works effluent and found that ammonium disappeared from solutions of the order of 20 to 50 mg N/l within hours when these solutions were buffered to a ph of over 8.4; whilst at ph values of 4.5 to 6.5, there was no appreciable disappearance after a week. Kreft G., Van Eck H., Stander G. J. (1958) A short note on the possibility of removing ammonia from sewage effluents by raising the ph. Water and Waste Treatment Journal, 7, 53.

6 Ammonia volatilisation in alkaline waters Stratton s experimental set up (Stratton, 1968) Stratton F. E. (1968). Ammonia nitrogen losses from streams. Journal of the Sanitary Engineering Division ASCE, December, SA6,

7 Ammonia volatilisation in alkaline waters Stratton s laboratory results

8 Ammonia volatilisation in alkaline waters Initial assumptions for Stratton s model C Co t

9 Ammonia volatilisation in alkaline waters Stratton s model for removal rate coefficients Predicted k values are not mass transfer coefficients

10 Ammonia volatilisation in alkaline waters INFLUENT NH 3 EFFLUENT NH 3 Free NH 4 + Org -N soluble & suspended Org -N algae & bacteria Org -N settled Org-N in sediments

11 Ammonia volatilisation in alkaline waters Stratton s field work (Stratton, 1969) Outdoor experiments with synthetic pond water. Ex-pond ammonia volatilisation rates conducted under summer conditions (ph > 9.0; T > 23ºC). Locations: Site 1 Elfin Forest Lake (Escondido, CA) Site 2 Pond receiving WWTP effluent (Santee, CA) Stratton F. E. (1969). Nitrogen losses from alkaline water impoundments. Journal of the Sanitary Engineering Division ASCE, April, SA2,

12 Ammonia volatilisation in alkaline waters Stratton s field results The measured ex-pond rates of ammonia losses were considerably below the predicted volatilisation rates from experiments with synthetic lake water (between 14% and 23% of the predicted value). It was estimated that ammonia volatilisation would contribute to remove only 5.8 percent of the total daily influent ammonia entering site 1 (Elfin Forest Lake, Escondido, CA).

13 Ammonia volatilisation in alkaline waters Stratton s work (1968, 1969) gave a clear panorama about the possibility of removing ammonia from alkaline waters. Therefore, ammonia volatilisation could be considered the main mechanism for ammonium removal when waters are buffered to ph values higher than 8.5, but and most importantly, very low ammonia volatilisation rates should be expected in alkaline waters with high algal activity such as in-pond WSP waters.

14 Pano and Middlebrooks model* Initial considerations Completely mixed flow regime Continuous flow and steady state conditions First-order kinetics for ammonia removal Low biological activity due to low temperatures Ammonia mass transfer coefficients as reported by Stratton (1968) *Pano A. and Middlebrooks E. J. (1982). Ammonia nitrogen removal in facultative wastewater stabilization ponds. Journal of Water Pollution Control Federation, 54(4),

15 Pano and Middlebrooks model Initial equation for ammonium removal via ammonia volatilisation General expression for ammonium removal including other feasible removal mechanisms Model for a non-conservative pollutant in a completely mixed reactor

16 Pano and Middlebrooks model T 20ºC 21 T 25ºC Ce Ci = 1 + A Q 1 ( ) exp[ 1.540( ph 6.6) ]

17 Ammonia removal in WSP Tracer experiments with 15 N-stable isotopes in maturation ponds in the UK

18 Ammonia removal in WSP Tracer experiments in maturation ponds: summer conditions

19 Ammonia removal in WSP Tracer experiments in maturation ponds: summer conditions Accumulative 15 N mass balance Recovery, % M1 effluent Suspended organic N 48.9 Soluble organic N 4.9 Ammonium N 8.8 Oxidised nitrogen N 0.2 Accumulation Water column 24.8 Sludge layer 7.4 Volatilisation 0.0 Total recovery after 3 θ 100

20 Ammonia removal in WSP Tracer experiments in maturation ponds: winter conditions

21 Ammonia removal in WSP Tracer experiments in maturation ponds: winter conditions Accumulative 15 N mass balance Recovery, % M1 effluent Suspended organic N 2.0 Soluble organic N 0.8 Ammonium N 55.7 Oxidised nitrogen N 3.0 Accumulation Water column 4.0 Sludge layer 24.5 Volatilisation 0.0 Total recovery after 3 θ 90

22 Ammonia removal in WSP Pano and Middlebrooks model for ammonia removal in maturation ponds in the UK

23 Ammonia removal in WSP Pano and Middlebrooks model for ammonia removal in WSP Bastos R.K.X., Rios E.N., Dornelas F.L., Assunçäo F.A.L., Nascimento L.E. (2007). Ammonia and phosphorus removal in polishing ponds: a case study in Southeast Brazil. Water Science and Technology, 55(11), Silva S. A., de Oliveira R., Soares J., Mara, D. D. (1995). Nitrogen removal in pond systems with different configurations and geometries. Water Science and Technology, 31(12), Soares J., Silva S. A., de Oliveira R., Araújo A. L. C., Mara D. D., Pearson, H. W. (1996). Ammonia removal in a pilot-scale waste stabilization pond complex in Northeast Brazil. Water Science and Technology, 33 (7),

24 Conclusions In agreement with the hypothesis formulated by Pearson et al. (1988), as an increasing pond water temperature increases phytoplanktonic activity and consequently, inpond algal biomass would take up and remove ammonium at a faster rate than expected via ammonia stripping. Pano and Middlebrooks model and its variations fairly predict ammonia removal in WSP but does not confirm ammonia volatilisation as the main mechanism for permanent nitrogen removal. The increment of ph in WSP is a consequence of algal activity and it makes a small contribution to ammonia volatilisation as ammonia concentration drops due to algal uptake.

25 AMMONIA VOLATILISATION IN WSP: A CASCADE OF MISINTERPRETATIONS? Miller M.A.Camargo-Valero@leeds.ac.uk Duncan D.D.Mara@leeds.ac.uk Institute of Pathogen Control Engineering School of Civil Engineering University of Leeds Leeds, UK. LS2 9JT