284812 Improved Volatile Solids Reduction in Aerobic Digesters by Application of Sludge Ozonation Using the Lyso™ Process

Thursday, November 1, 2012: 9:50 AM
403 (Convention Center )
Richard Novak1, Malcolm Fabiyi1, Alessio Colleti2, Fabrizio Mariani3 and Emilio D'Amato4, (1)Praxair, Inc., Burr Ridge, IL, (2)Rivoira, S.p.A., (3)Acqualatina, S.p.A., (4)DICEA - Universita di Firenze

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


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.


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).


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.


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.


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.


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.      Kobayashi et al (2001). Stuidy on Sludge reduction and other Factors by Use of an Ozonation Process in Activated Sludge Treatment. Proc. 15th Ozone World Congress, London 2001. IOA 321.

6.      Sakai, et al. (1997). An Activated Sludge Process without Excess Sludge Production. Wat Sci Tech. 36 (11) 163 – 170

7.      Sievers et al. (2004). Sludge Treatment by Ozonation – Evaluation of Full Scale Results. Water Science & Tech. 49 (4) 247 – 253

8.      Vergine, P., Menin, G., Canziani, R., Ficara, E., Fabiyi, M., Novak, R., Sandon., A., Bianchi, A., Bergna, G. Partial Ozonation of Activated Sludge to Reduce Excess Sludge Production: Evaluation of Effects on Biomass Activity in a Full Scale Demonstration Test. IWA Conference, Moncton, Canada. 2007

9.      Yasui et al. (1996). A Full Scale Operation of a Novel Activated Sludge Process Without Excess Sludge Production. Wat. Sci. tech. 34 (3-4) 395 – 404


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.



Ozone consumption kgs O3/TSS Eliminated

Yasui et al. (1996)


Sakai et al. (1997)


Kobayashi et al (2001)


Sievers et al (2004)



0.01 - 0.03

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.


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