(640e) Improved Volatile Solids Reduction in Aerobic Digesters by Application of Sludge Ozonation Using the Lyso™ Process

Improved
Volatile Solids Reduction in Aerobic Digesters by Application of Sludge
Ozonation using the Lyso? Process

^aMalcolm
Fabiyi, ^bAlessio Colleti, ^cFabrizio Mariani, ^dEmilio
D'Amato, ^aRichard Novak

^aPraxair, Inc.7000 High Grove
Boulevard, Burr Ridge, IL

^bRivoira, S.p.A. Via Tiburtina,
271, Rome, Italy

^cAqualatina, S.p. A, Sabaudia,
Italy

^dDICEA ? Universita di Firenze

Introduction

Sludge ozonation
is an effective means for achieving sludge reduction in wastewater treatment
facilities (Vergine et al, 2007). Sabaudia WWTP is a municipal plant in Italy.
The plant treats up to 30,000 Person Equivalents (PE) of wastewater in two
parallel trains. One train treats a third of the flow (10,000 PE) while the
other handles two thirds (20,000 PE) of the influent capacity. Sludge stabilization
at the facility is handled in an aerobic digester. Digester volumes are 900 m³.
About 100 m³/day of WAS is fed to the system, with TSS of
approximately 7000 mg/l. The plant has a 155 kW compressor that services the
aeration requirements of the combined secondary activated sludge and aerobic
digester systems. Airflow to the digester is controlled to maintain DO of 1
ppm. Aeration is provided using a Fine Bubble Diffuser system.

 Objectives

Sludge digestion
is a critical unit operation for achieving stabilization of sludge. The
traditional digestion process relies on natural hydrolytic processes to facilitate
the degradation of the WAS fraction of the excess solids by breaking down the
bacterial cell wall to facilitate the release of intracellular organic
compounds. VSS reduction in the digesters was minimal. To enhance VSS
reduction, a sludge ozonation process using Praxair's Lyso?
process was adopted. At Sabaudia, the VSS actually increased in the digester
during some operational periods (Figure 1). Sludge ozonation is an effective
means of lysing cells to facilitate the rupture of the bacterial cell. This
paper will present data from the Pilot and Full Scale implementations of sludge
ozonation at Sabaudia WWTP. The paper will also discuss the effectiveness of
sludge ozonation for enhancing VSS destruction in digesters and elaborate on the
mechanisms that enable the very low level of ozone required for achieving VSS
destruction using the Lyso? sludge ozonation
process (Figure 2).

Status

Pilot testing
was undertaken from February to August 2010, and the viability of ozone for
sludge reduction was demonstrated.  The Lyso?
sludge digestion treatment process enabled 64%-85% solids destruction in the
digester using ozone dosage levels of 0.5 to 0.67 kg/hr (D'Amato et al, 2011). 
The pilot testing has now been completed and Sabaudia WWTP has implemented a
full scale system that has been installed and commissioned at the facility.

Methodology

Sludge drawn
from the aerobic digester on the 20,000 PE line is circulated through a Lyso?
sludge ozonation system comprising a pump and a plug flow reactor for contacting
ozone with the sludge. Ozone was supplied using a Wedeco ozone generator.
Oxygen supply was from a liquid oxygen source provided by Rivoira S.p.A. The
Lyso?
pump can handle up to 70 m³/hr of flow. Applied ozone dosages ranged
from 0.06 to 0.67 kg/hr. The ozone is aspirated into the contactor using a
venturi.

Results

The Lyso?
process provided significant reduction in VSS. The specific ozone utilization
values obtained during the tests were about 0.01-0.03 kg O₃/kg SS removed.
This specific ozone consumption value is about an order of magnitude lower than
alternative sludge ozonation concepts (Figure 3). The Lyso?
process uses a novel plug flow reactor approach for sludge ozonation (Fabiyi et
al, 2007a, Fabiyi et al, 2007b) that minimizes excessive ozone consumption by
enhancing the selectivity of ozone for cell lysis rather than random COD
oxidation. About 64-85% reduction in sludge was achieved (see Figure 4, also
D'Amato, 2011) with an estimated cost savings of ?63,000/year. Significant
enhancements to sludge settling and dewatering characteristics was also
observed, in line with previous observations (Vergine et al, 2007).  By
providing as much as 85% sludge reduction within less than 10 days of HRT in
the digester, sludge ozonation offers the possibility for enabling the
construction of smaller digesters.

References

1.     
D'Amato,
E., Sirini, P., Gori, R., Lubello, C., Chiavola, A., Mariani, F., Cima, E.,
& Liberati, L. Application of Ozone in the Digestion Tank of a Full Scale
WWTP for Sludge Minimization. IWA Specialist Group on Sludge Management:
Newsletter January 2011

2.     
D'Amato,
E., Sirini, P., Gori, R., Lubello, C., Chiavola, A., Mariani, F., Cima, E.,
& Liberati, L. l'ozonolisi per la riduzione della produzione dei fanghi.
esperienza presso l'impianto di depurazione di sabaudia. Perugia 2010

3.     
Fabiyi,
M., & Novak, R. System and Method For Eliminating Sludge Ozonation. US
Patent 7309432 B1. 2007a

4.     
Fabiyi,
M., Novak, R., Ried, A., Wieland, A., Capra, R., and Sandon, A. Sludge
Reduction Using Ozone Induced Lysis. Aug. 2007b World Congress, IOA-UV, Los
Angeles, CA

5.     
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et al (2001). Stuidy on Sludge reduction and other Factors by Use of an
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6.     
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8.     
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P., Menin, G., Canziani, R., Ficara, E., Fabiyi, M., Novak, R., Sandon., A.,
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Figure 1: Data
taken in March ? May 2010 in non ozonated digester shows no VSS destruction in
digester during this period. Source: D'Amato et al, 2010

Figure 2: Lyso?
Sludge ozonation skid showing the plug flow contactor.

Figure 3: Comparative table of specific ozone
consumption and the corresponding sludge reduction (Adapted from Fabiyi et al,
2007)

Figure 4:
Cumulative sludge production in last three years. Reproduced from D'Amato et
al, 2011.