Appendix ‘Nutrient Removal and Biomass Production in an Outdoor Pilot-Scale Phototrophic Biofilm Reactor for Effluent Polishing’

N.C.Boeleea,b,c, M. Janssena,b, H.Temminka,c, R. Shresthaa, C.J.N.Buismana,c, R.H.Wijffelsb

aWetsus- centre of excellence for sustainable water technology, P.O. Box 1113, 8900 CC Leeuwarden, The Netherlands

bBioprocess Engineering, AlgaePARC, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands

cSub-department of Environmental technology, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands

Corresponding author: N.C. Boelee

Telephone: +31 (0)58 2843000

Fax: +31 (0)58 2843001

E-mail address:

Penetration of NO3-, PO43- and HCO3-

The algal growth on NO3-, PO43- and CO2 can be described by a stoichiometrical reaction equation. With the measured elemental composition of the biomass this equation is as follows:

From this equation also the yield of the different components can be calculated. The biomass content and the yields are shown inTable 1.

The penetration depths of NO3-, PO43- and HCO3- are calculated according to the following formula as described for instance in [1]:

[m] / 1

with Lp,i the penetration depth of nutrient i (m), Di the diffusion coefficient of nutrient i (m2/s), Ci l/b the concentration of nutrient i at the liquid-biofilm interface (g/m3), μmax the maximum specific growth rate (s-1), Yi the yield of biomass on nutrient i (g biomass/g nutrient i) and Cx the algae concentration (g/m3)

Table 1shows the parameters that were used for the calculation. For the concentrations at the biofilm surface it was assumed no mass transfer limitation occurred at the liquid-biofilm interface.

Penetration of light

The following formula was used to calculate the light intensity at depth z inside the biofilm:

[μmol/m2/s] / 2

with PFDin the photon flux density of the incoming light (μmol/m2/s), En,PAR,λ the normalized spectral distribution of the PAR photons (400-700 nm, nm-1), aλ the specific absorption coefficient (m2/g), Cx the algae concentration (g/m3), z the biofilm depth (m) d a light-path enhancement factor[1] (-), and Δλ the wavelength interval (nm)

Table 1 Parameters for calculating the penetration depth of NO3-, PO43- and HCO3-in the biofilm and parameters for calculating the light intensity at the penetration depths

Parameter / Value / Reference
Δλ / 1 / Chosen
µmax (s-1) / 1.2·10-5 / Average for Phormidium from[2-4]
aλ1 / for Chlorella sorokiniana
Biomass content / C1H1.61O0.49N0.16P0.012S0.0055 / The measured average
CHCO3 l/b (g C/m3) / 52.1 / Calculated from the measured average total inorganic carbon during the day of 53.8 mg/L at the average pH of 8.7
CNO3 l/b (g N/m3) / 4.1 / The measured average
CPO4 l/b (g P/m3) / 0.85 / The measured average
Cx (g/m3) / 9.1·104 / The measured average
d / 2
DHCO3-(m2/s) / 9.38∙10-10 / Average from [5,6]
DPO4 3-(m2/s) / 4.16∙10-10 / Average from [7,8]
DNO3-(m2/s) / 1.29∙10-9 / Average from [6,7,9]
En,PAR,λ (nm-1) / Sunlight spectrum / [10]
YN (g biomass/g N) / 16.5 / Calculated
YP (g biomass/g P) / 99.3 / Calculated
YC (g biomass/g P) / 3.1 / Calculated
z / 50 steps / Calculated

1 Data shown in Figure 1

Table 1 shows the parameters that were used for this calculation. The aλ used for phototrophs adapted to high light conditions (top layer of the biofilm) was the aλ measured for Chlorella sorokinianashown in Figure 1(for details on the cultivation see [11]and for details of the measurement protocol see [12]).

Figure 1 The specific absorption coefficient (aλ) for Chlorella sorokiniana

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[1] Since light will not travel perpendicular to the biofilm surface a light path enhancement factor was included. This factor was chosen to be 2 simulating the situation in which the light field is isotropic in the forward direction. Back scattering of light was neglected.