Innovative strategies for the reduction of sludge production in activated sludge 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 wastewater treatment 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 water treatment 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 Total suspended solids (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