Coliform and helminth eggs removal in a combined UASB reactor – baffled pond system in Brazil: performance evaluation and mathematical modelling M. von Sperling, C.A.L. Chernicharo, A.M.E. Soares and A.M. Zerbini Department of Sanitary and Environmental Engineering, Federal University of Minas Gerais, Av. Contorno 842 – 7 o andar; 300110-060 – Belo Horizonte – Brazil ( E-mail: marcos@desa.ufmg.br) Abstract The paper presents the monitoring results of a pilot UASB reactor followed by a baffled polishing pond treating domestic sewage in Brazil. Longitudinal profiles of E. coli and helminth eggs along the baffled pond have been undertaken. The experimental results have been compared with von Sperling’s model for coliform removal and Ayres’ model for helminth eggs removal, and the fitting was considered satisfactory in both cases. The distribution of the helminth species along the system is also presented. Keywords Coliforms; domestic sewage; helminth eggs; polishing ponds; UASB reactors Introduction This paper aims at evaluating the fate of Escherichia coli and helminth eggs in a combined UASB reactor – baffled pond. The system is comprised of large pilot-scale units, treating actual domestic sewage from the city of Itabira, Brazil. The UASB reactor (9 m 3 ) is a partitioned reactor, representing a novel configuration, constituted of three digestion com- partments, three gas separation devices and a single settler compartment for solids separa- tion. The working principle of the reactor, with the three digestion compartments operating in parallel, aims to provide a more stable hydraulic regime inside the reactor, as described in Chernicharo and Cardoso (1998). The polishing pond (32 m 3 ) is included with the main objective of removing pathogens, acting in a similar way as maturation ponds. In order to enhance pathogen removal, the pond was designed with 4 internal baffles, which produce a large L/B (length/breadth) ratio of 12.5. The UASB reactor operated with a low HDT (hydraulic detention time), with an average value of 5.5 h, whereas the pond had an average HDT of 6.3 d. In spite of its substantial importance for warm-climate countries, there are very few data in the literature representing in detail the combined system of UASB reactors and polishing ponds. The present paper investigates the fate of E. coli and helminth eggs in the UASB reactor and inside the pond, through a series of sampling points comprising a longitudinal profile along the system. The paper presents values of the coliform first-order removal coefficient K b , according to the hydraulic regimen of CSTR, plug flow and dispersed flow. The K b value obtained for dispersed flow is compared with the one obtained according with the methodology proposed by von Sperling (1999). The internal behaviour of the pond is modelled, and the estimated data are compared with the observed data on E. coli inside the pond. Helminth eggs removal in the pond are also modelled using the Ayres et al. (1992) equation and the internal pond behaviour is evaluated. The helminth eggs are also investigated in terms of the prevalence and fate of the nematode species along the system, giving an indication of the relative degree of easiness or difficulty in their removal. Water Science and Technology Vol 45 No 10 pp 237–242 © IWA Publishing 2002 237 Downloaded from https://iwaponline.com/wst/article-pdf/45/10/237/424861/237.pdf by guest on 04 November 2018