Innovative strategies for the reduction of sludge production in plant: BIOLYSIS® O and BIOLYSIS® E

Stdphane Del6ris1, A. Larose1, V. Geaugey2 and Thierry Lebrun1 1: ONDEO-Degr6mont research center, 87 chemin de Ronde 78290 Croissy-sur-Seine, France Tel: 33 (0)1 46 25 38 24 - Fax : 33 (0)1 39 76 35 41 e-mail :stephane.deleris@ondeo-deg remont.com 2: CIRSEE Suez-Environnment, 38 rue du president Wilson , 78230 LE PECO,

Abstract: Management of the excess sludge production resulting from biological is one of the most important economic and environmental issues for the next decade. New stringent regulations regarding sludge treatment and disposal imposed in several countries as well as social and environmental concerns, have resulted in an increasing interest in processes allowing the reduction of excess sludge production. Following a 5 years research program, Ondeo-Degr&mont has developed two processes, Biolysis® O and Biolysis® E, designed to reduce sludge production during biological wastewater treatment. Experiment performed with Biolysis® technologies confirmed that high (up to 80%) reduction of excess sludge production can be reached while good treatment performances are maintened, in agreement with regulation standards. Economical data demonstrate the competitiveness of Biolysis® processes. Such processes appear to be a valuable alternative to solve the problem of sludge treatment, to protect operators from the evolution of legislation of sludge treatment and from risks inherent to final sludge disposal. Key words: enzymatic, ozone, wastewater treatment, reduction of sludge production

Introduction Management of the excess sludge production resulting from biological wastewater treatment are from the most important economic and environmental issues for the next decade. Due to the intensification of wastewater treatment, a large increase in sludge production from biological processes must be anticipated. Moreover, sludge agricultural valorisation and landfilling, which are the main solutions adopted for final sludge disposal, are debated and sludge incineration cannot be a systematic solution. Also, new stringent regulations regarding sludge treatment and disposal imposed in several countries as well as social and environmental concerns, have resulted in an increasing interest in emergent processes aiming at the minimization of excess sludge production. Such processes consist in new integrated strategies for sludge management based on the reduction of the biomass growth rate and on the intensification of sludge mineralization, by applying a thermal or chemical stress, for instance, to the sludge directly in the main-stream process instead of working on the sludge already extracted. Following a 5 years on-going research program, Ondeo-Degremont has developed a new set of processes designed to reduce the amount of sludge generated during biological wastewater treatment : Biolysis® O and Biolysis® E. This innovative strategy is based on the association of a conventional activated sludge process and either an ozonation treatment or a thermophilic and enzymatic treatment. The results presented in this paper relate to two industrial scale experiment aiming at assessing the impact of the implementation of Biolysis® O and Biolysis® E on the performance of an activated sludge process. This paper highlights results concerning reduction of excess sludge production and provides a comprehensive and accurate set of results dealing with the influence of Biolysis® processes on the remaining sludge and effluent characteristics. An economical evaluation of the Biolysis® technologies is also provided.

Fundamental aspects of excess sludge reduction Results of batch experiments (Deleris et al., 2000) demonstrated that ozone is able to affect, i.e. to solubilize or mineralize, most of the organic material contained in an activated sludge. Moreover, an increase in biodegradability of the solubilized matter was also reported. As a matter of fact, applying ozone on sludge results in a significant increase of the bio-availability of the slowly

55 biodegradable or even inert organic material accumulated in the sludge. In the case of thermophilic and enzymatic treatments, Sakai et al. (2000) have demonstrated that application of such treatment allows to solubilize the organic content of excess sludge generated in an activated sludge process. Moreover, Chudoba et al., (1992); Canales (1991) and Rocher et al. (1999) have reported that the application of a stress on the micro-organisms contained in activated sludge can cause a high increase in substrate consumption for maintenance purposes instead of growth, resulting in a significant decrease of the net biomass production yield.. Both solubilization effects and increase in maintenance energy requirement (c.f. Figure 1) result in an increase in the mineralization of organic matter in the biological treatment and can explain why Biolysis® processes have an impact on the excess sludge production.

wastewater Conventional biological treatment biological treatment combined with Biolysis® O

Bio|ysis® Increased

8 mineralization Soluble co2 CM matter r Growth y K of biomass > / Particulate inert > (solids) particulate matter V ▼ Biolysis® r Conventional system Reduced sludge sludge production production

Figure 1 : effects of Biolysis® processes on a conventional activated sludge system

Industrial scale experiments of Biolysis® technologies

Background of Biolysis® processes In Biolysis® processes, a significant reduction of excess sludge production is obtained (up to 80%) through the use of ozonation or specific enzymatic activity to stress and solubilize the sludge. In both cases the complementary treatment is directly applied on the MLSS taken from the biological reactor before returning the treated mixed liquor to the aerated tank as depicted in Figure 2.

56 |— BIOLYSIS

pre-treatment Secondary settler

\ctivated sludge Treated water

Sludge treatment

Wastewater

Figure 2 : Simplified set-up of the Biolysis® O process Industrial scale experiments were conducted with both Biolysis® processes in order to evaluate the technology and the effect of these excess sludge reduction processes on the wastewater treatment performance and the remaining sludge quality. Biolysis® E experiments were conducted at Verberie’s WWTP (3000 p.e., France) whereas Biolysis® O trials were done at Aydoilles (1000 p.e., France). Both WWTP are low loaded activated sludge systems and the sludge residence time (SRT) was set to approximately 20 days, so that nitrification was performed.

Biolysis® E industrial scale experiments (WWTP of Verberie, France) In the Biolysis E (15 to 30 kg SS/m3). Conditions maintained in the thermophilic reactor (50 to 60 °C and aeration) allows the growth of specific bacteria (Bacillus stearothermophilus), which have the capability to release the enzymes responsible for the break down and the solubilization of the sludge. The treated and degraded sludge is then returned to the biological system. This technology was originally developed by the Japanese company Shinko Pantec, which claimed that over to 80 % sludge reduction is possible for some completely biological sludge. Ondeo Degremont is now licensed for this technology. The demonstration plant at Verberie (France, 3000 p.e.) has been now running for 1 year and. Figure 3 presents the results obtained after 300 days of experimentation, confirming that high levels of sludge reduction are reachable. Depending on the quantity of the sludge sent daily to the thermophilic reactor, sludge reductions ranging from 30 and 80 % have been observed. For the whole period about 25 tons of dry sludge were eliminated (60% of the normal excess sludge production at Verberie without Biolysis E). Considering 25 % of dry solid content after dewatering, that means that a production of more than 100 tons of sludge has been avoided.

57 50000 8 45000 o Reference sludge production 3 40000 Without Biolysis E) "~~~~ O Global sludge reduction 35000 over the global period 0) 30000 60 % (25 tons eliminated) 05 "O 3 25000 CO 20000 Biolysis E 15000 start up I 10000 E 80 % sludge reduction period O

days

Figure 3: Effect of Biolysis® E process on sludge production (experiments of Verberie)

The experiments performed at Verberie allowed us to evaluate the influence of the Biolysis® E process on the performances of the line. The effluent characteristics are presented in Table 1.

Table 1 : effect of Biolysis® E on effluent characteristics

Parameters measured in the Reference results Results with effluent without Biolysis® E Biolysis® E (g SS/ m3) 5 10

Total COD (g COD/ m3) 30 43

Soluble COD (g COD/ m3) 25 30

Total suspended solids (g SS/ m3) 5 10

NH4+ (g N-NHV m3) 1 0.3

N03‘ (g N-NOs/m3) 6 6

PO,3" (g P-POVm3) 4 4.8 *: Results obtained during a period with a sludge reduction ratio of 60 %

Small increases of the effluent SS and COD concentrations are observed. Nevertheless these concentrations remain under regulation standards. Nitrogen treatment (nitrification and denitrification) remains constant when Biolysis E is implemented. Concerning phosphorus treatment, it was observed that Biolysis® E induces an increase in the P content of the sludge due to a precipitation phenomenon. Indeed, as depicted in Figure 4, the P content of the sludge move from 1.8 % to 3 % of TSS after Biolysis® E start up. Identification of the precipitation mechanism is still under investigation, but the amplification and the control of this phenomenon could be a possible way of removing phosphorus specifically.

58 • 3 h- • # « E • • • • * Q> 2.5 • |1 2 l> 8 g 1.5 i g 5 X Start-up of II 1 W m Biolysis E 0.5

0 50 100 150 200 250 300 Days Figure 4: Effect of Biolysis® E on phosphorus content of the activated sludge

Biolysis® O industrial scale experiments (WWTP of Aydoilles, France) In the Biolysis® O process ozone is directly applied on the MLSS taken from the biological reactor before returning the ozonated liquor to the aerated tank. High ozone transfer rate is obtained using a mechanical mixing device, which insures high level of reaction between MLSS and ozone. With the aim of demonstrating the Biolysis® O technology a prototype plant was run for more than one year on an 1000 p.e. existing activated sludge plant located at Aydoilles, France. As shown in Figure 5, during the experimental period, the global sludge reduction efficiency was 60 %. Nevertheless higher reduction efficiency (up to 80 %) can be reached depending on the ozone dosage applied.

16000 i Reference sludge 14000 production ,'

12000 BIOLYSIS® O 10000 start-up

=> O) 80 % sludge reduction

4000 -

2000 -

Time (days)

Figure 5 : Effect of Biolysis® O process on sludge production (experiments of Aydoilles)

59 The influence of the application of the Biolysis® O process on the treatment performance and on sludge characteristics are presented in Table 2.

Table 2 : Effect of Biolysis® O on sludge production and effluent quality

Reference results Results with Biolysis® Parameters without Biolysis® O O 8.8 Sludge production (Kg SS/ p.el yr) 22 (60 % reduction) Decantability (SVI ml/g) >200 <80 COD removal efficiency (%) 90 85* SS removal efficiency (%) 95 95 N-NH4 removal efficiency (%) 96 98 P-P04 (g P-P04/m3) 4 7.2 *: obtained during tough winter conditions

A slight decrease in the COD removal efficiency was observed whereas SS and ammonia removal efficiencies were maintained and even improved (see Table 1). Regarding phosphorous treatment, the behaviour with Biolysis® O process is not similar to the one observed for Biolysis® E. Indeed, the phosphorus content of the sludge is not changed and the fraction of P eliminated with the sludge in a conventional activated sludge system is solubilised. This explain the increase of 3.2 g P-POV m3 observed in the effluent when Biolysis® O is operated. When enhanced phosphorus elimination is required, tertiary treatment will be necessary. A significant improvement in sludge settling and dewatering characteristics were also observed. Evolution of sludge settling characteristics is well depicted in Figure 6. Sludge volume index is approximately divided by 3 after the start-up of the Biolysis® O process and remains stable under 80 ml/g, which ensures very good settling characteristics.

250 Biolysis® O g Start-up E 200 -D V a -o _c 150 D 0) E CP 3 □ -go 100 > 0) • illFi o> "O 50 _3 cn

to o to Ot N> 03 -i l\3 N3 00 N> 03 o * N> 03 03 O 03 -si Oi o C_ Z CD 6 to E $ Tl c 2^ O CD to CD F to to to to 3 c — 3 O 3 O" *< *< 3 Figure 6 : evolution of sludge settling characteristics (SVI) after star- up of Biolysis® O

60 It was already reported by Van Leeuwen (1988) that application of ozone on sludge can solve the bulking problems resulting from the growth of filamentous bacteria. A similar effect is obtained with Biolysis® O. The improvement of sludge settling characteristics is likely to be related to the eradication of filamentous bacteria subsequent to ozonation treatment.

Economical Analysis of the Biolysis® technologies Analysis of the impact of Biolysis® on a 100 000 p.e. activated sludge plant on operating and investments cost was performed (operation cost i.e. OPEX and capital cost i.e. CAPEX). Results are presented in Table 3. Operating costs include not only energy and reagents related to the operation of Biolysis® process but also the cost due to the increase in oxygen demand in the activated sludge system resulting from the sludge solubilization. CAPEX costs are calculated on the basis of a 15 years depreciation period. Table 3 : costs analysis of Biolysis® technologies

Costs expressed in Euros per ton of TSS not produced

CAPEX OPEX Total

Biolysis® O 140 260 400

Biolysis® E 170 160 330

For both processes, total cost remains under 400 euros per ton of TSS not produced. This cost is competitive with a classical route for sludge disposal including for example dewatering, thermal drying and agricultural valorization.

Conclusions Experiment performed with Biolysis® technologies confirmed that high (up to 80%) reduction of excess sludge production can be reached with good treatment performances and with effluent quality in agreement with regulation standards. Economical data demonstrate the competitiveness of Biolysis® processes. Such process appears to be a valuable alternative to solve the problem of sludge treatment, to protect operators from the evolution of legislation of sludge treatment and from risks inherent to final sludge disposal.

References Canales J. (1991). Croissance cryptique en bioreacteur a membrane : application au traitement d'eaux residuaires urbaines. Doctoral thesis INSA Toulouse, n°155. Chudoba, P., Morel, A. , Capdeville, B. (1992) : The case of both energetic uncoupling and metabolic selection of micro-organism in the OSA activated sludge. Env. Tech., 13, pp. 761-770. Deleris, S., Paul, E., Audio, J.M., Roustan, M., Debellefontaine, H. (2000): Effect of ozonation on activated sludge solubilization and mineralization. Ozone Sci. & Eng., 22 (5), pp. 473-487. Rocher, M., Goma, G., Pilas Begue, A., Louvel, L., Rolls, J.L. (1999) Towards a reduction in excess sludge production in activated sludge processes : biomass physiochemical treatment and biodegradation. Appl Microbiol Biotechnol, 51, pp. 883-890.. Sakai Y., Aoyagi T., Shiota N., Akashi A. and Hasegawa S. (2000) Complete decomposition of biological sludge by thermophilic bacteria. Wat. Sci. Tech., 42(9), 81-88 Van Leeuwen, H. (1988) : Domestic and industrial wastewater treatment with ozonated activated sludge. Ozone Sci. & eng., 10 (5), pp. 291-307.

61 62 Sludge characterization