Wat. Res. VoL 21, No. 7, pp. 789-799, 1987 0043-1354/87 $3.00+0.00 Printed in Great Britain. All rights reserved Copyright © 1987 Pergamon Journals Ltd CULTIVATION OF ANAEROBIC GRANULAR SLUDGE IN UASB REACTORS WITH AEROBIC ACTIVATED SLUDGE AS SEED WEIMIN Wu, l* JIcuI Hu, 1 XIASHENGGU, 1 YIZHANG ZHAO, 2 HUI ZHANG 2 and GUOGUAN Gu 3 IDepartment of Environmental Engineering, Tsinghua University, Beijing, 2Chengdu Biogas Research Institute of Agriculture Ministry of China, Chengdu, Sichuan and 3Changzhou Environmental Pollution Monitoring Centre, Changzhou, Jiangsu, Peoples Republic of China (Received February 1986) Abstraet--Methanogenic bacteria of 108g SS-~ in the activated sludges from an aeration tank treating sewage and from a secondary sedimentation tank of an activated sludge plant treating textile dyeing wastewater were enumerated by the Most Probable Number (MPN) technique. By using the two activated sludges as the seed material, anaerobic granular sludges were obtained at 35°C in two Iab-UASB reactors having volumes of 29 and 481. and treating a glucose molasses solution of 1000-3500 mg COD 1 -~ and citrate wastewater of 20,000-36,000 nag COD 1- ~respectively. The characteristics of granulation using the activated sludge as the seed were similar to those using digested sewage sludge as the seed. It is shown that activated sludge is readily available seed material for an anaerobic reactor. The growth of methanogenic bacteria in the activated sludge can be attributed to the existence of some anaerobic nuclei in the activated sludge flocs. The factors for the cultivation of granular sludge by using the activated sludge are also discussed. Key words--upflow anaerobic sludge blanket (UASB), anaerobic, digestion, activated sludge, meth- anogenic bacteria, wastewater, granulation INTRODUCTION The upflow anaerobic sludge blanket (UASB) reactor is a demonstrated high efficiency, energy-saving an- aerobic biological process which has been applied to the treatment of various organic wastewaters with different COD concentrations under a wide range of temperature conditions (Lettinga et al., 1980, 1983, 1984, 1985; Wang et al., 1985). The operation sta- bility and satisfactory performance of the UASB reactor is, to a great extent, dependent on the kind of sludge cultivated in it. A good sludge should have good settleability and high methanogenic activity, and should be in granular form. The start-up of the UASB reactor has been emphasized and investigated widely. The first problem encountered in the start-up is to choose seed material. Several seed materials including granular sludge, digested sewage sludge, cow manure and sewer slurry have been used. Per- haps the best seed material is the granular sludge from another UASB reactor treating similar waste- water. In this way, satisfactory results can be achieved within a short start-up period (Lettinga et aL, 1985; Pette and Versprille, 1981). However, at present it is difficult and often impossible to obtain enough granular sludge to start-up a large-scale UASB reactor in many countries, and other seed materials usually have to be chosen. In general, a *To whom correspondence should be addressed. digested sewage sludge is considered to be available seed material because it has relatively high meth- anogenic activity together with a complicated micro- organism ecosystem that is suitable for the treatment of many kinds of wastewater. By using the digested sludge as the seed, granular sludge can be obtained under mesophilic temperature conditions when many organic wastewater such as sugar-beet, potato pro- cessing, methanol, distillery, brewery, citrate and pulping wastewater are treated (Lettinga et al., 1980, 1984, 1985; Habets and Knelissen, 1985; Vuorianta et al., 1985; Hu et al., 1985). Nevertheless, there is still the problem of not enough digested sludge to start-up a full-scale UASB reactor. In addition to the digested sludge, cow manure has been used as the seed of the UASB reactor under thermophilic temperature con- ditions (Wiegant et al., 1985). Although it is indeed an alternative to the digested sludge, it is also difficult to obtain a sufficient amount in some places. In China, sewer slurry has been used as the seed, but this also has such problems as too little availability, high content of sand and soil, and low methanogenic activity (Lui et al., 1985). Recently we have found that activated sludge, for several reasons, is a good alternative to the digested sewage sludge. First, a considerable amount of meth- anogenic bacteria is found in the activated sludge. Second, it is easy to obtain large amount of the sludge from activated sludge plants. Finally, the activated sludge usually contains little sand and soil and is 789