Use of two stage biological aerobic systems for winery effluents: assessment of two processes during the peak pollution period in the Bordeaux area
Application du traitement biologique aérobie double étage aux effluents vinicoles : évaluation de deux procédés lors des vendanges en Bordelais
Résumé
In this paper, two aerobic first stage treatment processes are investigated. The first one is a high rate activated sludge, while the other is a recent process in which yeasts are predominant in biomass. The secondary treatment stage is a conventional low rate activated sludge. One key point in the operating of these processes is the biomass control in the first stage, in terms of quality (action on pH) and quantity (sludge concentration). Two plants, representative of each process and located in the Bordeaux area, were monitored in depth during two vintage periods. These plants are treating the wastewater of two wineries with a capacity of 140 000 hl and 60 000 hl respectively. The study was mainly focused on the behaviour of the processes during the 5 to 6 weeks after the beginning of vintage season, a critical period when no buffer storage of effluent is provided in the winery. Measurements were performed during all the period of increasing organic loading, and permitted to set up a detailed analysis of the process efficiency (variations in the removal rate at the different treatment phases ; recording of the pH, aeration rate, sludge concentration ; microscopic observation of the biomass, ...). The « high rate + conventional activated sludge » process had a total hydraulic residence time in the range of 10 to 15 days. It was able to reach a 97-98% COD removal rate during the peak organic loading period, with 80 to 90% attributed to the first step alone, in which the sludge concentration was kept within the range of 7 to 10 g/l. In order to comply with the discharge standards, the high rate activated sludge required careful operation and an appropriate strategy to prepare the tank before the beginning of vintage season. Sludge production during the peak period was in the range 0,32 - 0,43 kg SS/kg CODremoved. The « yeast + activated sludge » process is very compact, and showed a good ability to start quickly at the beginning of the season, owing to the rapid yeast growth. The first step was able to remove 75 to 85% of COD in one tank where loading rates were up to 10 kg COD/m3.d. The total COD removal reached 98%. This process, involving yeast centrifugal separation after the first stage, is rather complex. In spite of the automation, it needs a careful operation during vintage period to be reliable. The energetic cost is above those observed in the other aerobic processes, principally because of the high yeast oxygen requirements.
Deux procédés biologiques double étage ont été évalués et sont comparés. L'un est constitué d'un premier étage avec des boues activées à forte charge volumique, l'autre utilise une biomasse à dominante levures comme première étape. Le second étage de traitement est constitué dans les deux cas par une boue activée faible charge. Deux installations représentatives de chacun de ces procédés et implantées dans le Bordelais ont fait l'objet de suivis approfondis durant deux cycles de vinification. Elles traitent respectivement les effluents d'une cave de 140 000 hl et de 60 000 hl. L'étude a porté principalement sur le comportement des systèmes d'épuration lors des 5 à 6 premières semaines suivant le début des vendanges, période la plus critique lorsqu'un établissement doit traiter ses rejets sans stockage. Ces deux procédés fonctionnant avec un volume tampon très réduit conduisent à des rendements élevés. Ils demandent cependant une exploitation attentive en période de pointe pour garantir les niveaux de rejet requis.