Domestic sewage treatment in full-scale UASBB plant at Mangueira, Recife, Pernambuco L. Florencio, M. Takayuki Kato and J. Cardoso de Morais Universidade Federal de Pernambuco (UFPE), Centro de Tecnologia e Geociências, Departamento de Engenharia Civil, Grupo de Saneamento Ambiental, Avenida Acadêmico Hélio Ramso s/n, Cidade Universitária, 50.740-530 Recife PE Brazil. Fax: (+55 81) 271-8719/8205. E-mail: flor@npd.ufpe.br; kato@npd.ufpe.br Abstract The anaerobic technology application for domestic sewage treatment in Pernambuco State (Brazil) is relatively recent. Some UASB reactors of less than 250 m 3 were built in the Recife Metropolitan Region (RMR) in the 1990s. Mangueira (18,000 inhabitants) was the first neighborhood where the municipality built a plant with a bigger UASB reactor of 810 m3. It was intended to evaluate the performance and verify if such technology would be feasible. The objective would be the possible application of UASB reactors to the RMR, according to the new sewage master-plan under elaboration that would benefit about 3 million inhabitants. The monitoring of the Mangueira UASB reactor over 30 months showed that satisfactory results were obtained. Three distinct operational phases occurred, in which efficiency varied from 60% up to 90% based on COD removal. The results were very dependent on the operation and maintenance, either in the plant or in the sewage collection. Significant amount of inert solids was measured inside the reactor. Despite the operational problems, the UASB was shown to be very robust and stable. Under high fluctuation of influent concentrations (150–750 mg COD/L) during the period, resulting in applied organic loading rate of 0.5 to 2.5 kg COD/m 3 .d, the average values of COD removal efficiency did not change significantly. An active biomass with specific methanogenic activity varying from 0.18 to 0.25 g COD/g VSS.d was measured at the end of the period. Keywords Anaerobic technology; domestic sewage; full-scale UASB reactor; long term operation; performance Introduction The anaerobic technology application for domestic sewage treatment in Pernambuco State (Brazil) is relatively recent. After some initial difficulties at institutional level in accepting the advantages and recognizing the adequacy for local conditions, some full-scale UASB reactors were built in the Recife Metropolitan Region (3 million inhabitants) in the 1990s. Most of them were of small size, up to 250 m 3 and serving 5,000 inhabitants of isolated housing projects (Florencio and Kato, 1998). Mangueira (18,000 inhabitants) was the first neighborhood where the municipality built a plant with a bigger UASB reactor of 810 m 3 . It was intended to evaluate the performance and verify if such technology would be technically and economically feasible. The objec- tive at long term would be the possible use of UASB reactors to upgrade the 3 existing sewage plants, as well to the new plants according to the new sewage master-plan under elaboration (PCI, 2000). The plant in Mangueira neighborhood at Recife was built in 1997 by URB (Recife Municipal Urbanization Company). Since the start-up in July, the operation has been under the responsibility of COMPESA (Pernambuco water and sewage company). The treatment plant was designed to receive an average flowrate of 31 L/s with maximum of 51 L/s at peak hours. Due to partial implantation of the sewerage system in Mangueira, the current flowrate corresponds to the contribution of about 13,000 inhabitants (72%) (Morais et al., 1999). At that time, the decision to build an 810 m 3 reactor was a local, pioneering challenge for Water Science and Technology Vol 44 No 4 pp 71–77 © IWA Publishing 2001 71 Downloaded from http://iwaponline.com/wst/article-pdf/44/4/71/430121/71.pdf by guest on 20 April 2021