INTRODUCTION

Investigation of the impact of wood ashes

on nitrifying granule formation Jamile Wagner*, Bastien Schoonbroodt, Christophe Meunier**

CEBEDEAU - Research and Expertise Center for Water, Allée de la Découverte, 11 (B53),

Quartier Polytech 1, 4000 Liège, Belgium

*jwagner@cebedeau.be

**cmeunier@cebedeau.be

Cultivation of nitrifying granules is not as easy and fast as

heterotrophic or hybrid granules, due to the slow growth rate and the

high sensitivity of nitrifying bacteria (Chen et al., 2015).

Addition of carriers option to stimulate nitrifying granulation.

Example: granular activated carbon (GAC) core for microbial

growth and granule formation (Li et al., 2013).

The use of GAC can significantly increase the operational costs

demand for alternative and cost-effective products.

METHODS RESULTS AND DISCUSSION

CONCLUSIONS

• Nitrifying granular sludge successfully cultivated in both reactors.

• The use of ashes as a carrier did not accelerate the granulation process but the granules

formed in R2 displayed better settleability and higher relative abundance of nitrifying

bacteria.

• Possibility to treat ammonium-rich wastewaters the stability of the reactors will be

evaluated and N load will be further increased up to 1g N/L.

inspiring change

Acknowledgement: This work was co-financed by the Marie Curie Actions under the grant BEWARE EU-FP7. We would like to thank the lab technicians at Cebedeau for their technical support. We are also grateful to Olivier Henriet for his

help with the microbial composition analyses.

References:

Chen, F.Y., Liu, Y.Q., Tay, J.H. (2015) Rapid formation of nitrifying granules treating high-strength ammonium wastewater in a sequencing batch reactor. Appl Microbiol Biotechnol, 99: 4445-4452.

Li, A.J., Li, X.Y., Yu, H.Q. (2013) Aerobic sludge granulation facilitated by activated carbon for partial nitrification treatment of ammonia-rich wastewater. Chemical Engineering Journal, 218: 253-259.

Winkler, M.K.H., Bassin, J.P., Kleerebezem, R., Sorokin, D.Y., van Loosdrecht, M.C.M. (2012) Unravelling the reasons for disproportion in the ratio of AOB and NOB in aerobic granular sludge. Appl Microbiol Biotechnol, 94: 1657-1666.

RESULTS AND DISCUSSION

The sludge exhibited a very good settleability, especially in R2. SVI30 decreased from 99

mL gTSS-1 (inoculum) to 38 mL gTSS

-1 in R1 and to 15 mL gTSS-1 in R2 (Fig. 3b).

An increase in the SVI30/SVI10 ratio (Fig. 3c) indicates granule formation. This ratio

reached 1 after 64 d of operation in R1, while in R2, 99 d were required to achieve the

same ratio. The presence of the ashes did not have an impact in speeding up the

granulation process.

The solids composition in R2 is much more complex than in R1 combination of sludge

and wood ashes in R2. The ashes provided the core for granule formation and growth

(Fig.4b).

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Figure 3. (a) TSS in the reactor, (b) SVI30, and (c) SVI30/SVI10 ratio during the operation time of R1, no

ashes (∆), and R2, with ashes (●).

Figure 5. Influent NH4+-N concentration (●), effluent NH4

+-N concentration (x), and NH4+-N efficiency

removal (∆) during the operation time of R1, no ashes (a), and R2, with ashes (b).

Figure 1 – Reactors for granule

cultivation.

Two reactors (Fig. 1) were operated in sequencing batch

mode (Fig.2) for nitrifying granular sludge cultivation in

absence (R1) or presence (R2) of wood ashes.

Inoculum: activated sludge from a municipal wastewater

treatment plant operated for full biological nitrogen

removal.

Stepwise increase of NH4+-N in the influent.

120

210

25 5

Cycle phases (in min)

Feeding

Aeration

Settling

Discharge

6 h cycle

Figure 2 – Sequencing batch mode configuration.

Figure 6. Relative abundance of nitrifying bacteria in

the inoculum and in both reactors after 100 days of

operation revealed by high-throughput sequencing

analyses.

The granules were highly enriched

with ammonium-oxidizing bacteria

(AOB) and nitrite-oxidizing bacteria

(NOB).

The relative abundance of nitrifying

bacteria in the inoculum was 1.2% of

total bacteria. After 100 days of

operation, the relative abundance

increased to 18.4% in R1 and 22.8%

in R2 (Fig. 6).

Nitrobacter was the dominant NOB in

both reactors.

NH4+-N was mainly converted to nitrate and no nitrite accumulation was observed in the

reactors (data not shown) no free ammonia (FA) or free nitrous acid (FNA) inhibition.

These ratios were much higher than the theoretical ratio of 0.5 for conventional activated

sludge. The disproportion of the amount of AOB and NOB in granular sludge was also

observed by Winkler et al. (2012).

NOB/AOB ratio:

R1 = 2.7

R2 = 1.3

Characteristics of the granular sludge:

Ammonium removal:

Microbial composition:

Figure 4. Nitrifying granular sludge developed in R1, no ashes (a), and R2, with ashes (b).

R1 was more sensitive to the

increase of the nitrogen load than R2

Objective: evaluate the impact of the use of wood ashes as biomass carriers on nitrifying granule formation and

substrate removal efficiency. Microbial population shifts during the formation of granules were also investigated.

Ashes

High mineral content, alkalinitypotential, low cost, and good adsorbent

properties

Carriers for microbial attachment initiation step for granule formation

Ashes Initial cell

attachment

Biofilm

growthGranules

formation

Amount of ashes in the

influent determined

considering the inhibitory

thresholds of heavy

metals concentrations

for nitrifying organisms

possibility of sludge

valorization.