Influence of organic shock loads in an ASBBR treating synthetic wastewater with different concentration levels Mariana Bueno Moreira a , Suzana Maria Ratusznei a , Jose ´ Alberto Domingues Rodrigues a, * , Marcelo Zaiat b , Euge ˆnio Foresti b a Escola de Engenharia Maua ´ , Instituto Maua ´ de Tecnologia (IMT), Prac ¸a Maua ´ 1, CEP 09.580-900, Sa ˜o Caetano do Sul, SP, Brazil b Departamento de Hidra ´ ulica e Saneamento, Escola de Engenharia de Sa ˜o Carlos, Universidade de Sa ˜o Paulo (USP), Av. Trabalhador Sa ˜o-Carlense 400, CEP 13.566-590, Sa ˜o Carlos, SP, Brazil Received 16 November 2005; received in revised form 9 July 2006; accepted 5 May 2007 Available online 31 July 2007 Abstract Safe application of the anaerobic sequencing biofilm batch reactor (ASBBR) still depends on deeper insight into its behavior when faced with common operational problems in wastewater treatments such as tolerance to abrupt variations in influent concentration, so called shock loads. To this end the current work shows the effect of organic shock loads on the performance of an ASBBR, with a useful volume of 5 L, containing 0.5-cm polyurethane cubes and operating at 30 °C with mechanical stirring of 500 rpm. In the assays 2 L of two types of synthetic wastewater were treated in 8-h cycles. Synthetic wastewater I was based on sucrose–amide–cellulose with concentration of 500 mg COD/L and synthetic wastewater II was based on volatile acids with concentration ranging from 500 to 2000 mg COD/L. Organic shock loads of 2–4 times the operation concentration were applied during one and two cycles. System efficiency was monitored before and after application of the perturbation. When operating with concentrations from 500 to 1000 mg COD/L and shock loads of 2–4 times the influent concentration during one or two cycles the system was able to regain stability after one cycle and the values of organic matter, total and intermediate volatile acids, bicarbonate alkalinity and pH were similar to those prior to the pertur- bations. At a concentration of 2000 mg COD/L the reactor appeared to be robust, regaining removal efficiencies similar to those prior to perturbation at shock loads twice the operation concentration lasting one cycle and stability was recovered after two cycles. However, for shock loads twice the operation concentration during two cycles and shock loads four times the operation concentration during one or two cycles filtered sample removal efficiency decreased to levels different from those prior to perturbation, on an average of 90–80%, approximately, yet the system managed to attain stability within two cycles after shock application. Therefore, this investigation envi- sions the potential of full scale application of this type of bioreactor which showed robustness to organic shock loads, despite discon- tinuous operation and the short times available for treating total wastewater volume. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Shock load; ASBBR; Synthetic wastewater; Organic load 1. Introduction Wastewater characteristics usually fluctuate during operation, both qualitatively and quantitatively, i.e., in composition, flow rate and concentration, which may cause process destabilization, making operation of an anaerobic reactor vulnerable to feed and environmental perturba- tions. This is especially important in reactors operating with high organic load, where a perturbation may cause total failure of the system. It is important to determine when a process becomes overloaded and how this process behaves under this condition, i.e., when and how a pertur- bation may affect efficiency. Moreover, it is convenient to identify how the system can regain stable condition, before the negative effects become irreversible, since extended 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.05.068 * Corresponding author. E-mail address: rodrigues@maua.br (J.A.D. Rodrigues). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 3256–3266