Anammox biomass has a relatively long duplication time and low yield. This is an advantage because the production of surplus sludge is reduced; however it also implies that the process must be operated in reactors with very good sludge retention. Some of the systems used to improve biomass retention are based on biofilm reactors; therefore, the objective of this work was to study the ability of the Anammox biomass to form biofilms under different conditions of shear stress and under the presence of salts.
Results and discussion
In order to monitor the growth of the biofilm along time, a Mechatronic Surface Sensor (MSS) was utilized (Pereira et al., 2006). To study the biofilm formation in the flow cell, an external Sequencing Batch Reactor (SBR) of 1 L of working volume was used. The reaction medium was pumped from the bottom of the reactor to the bottom of the flow cell and, then, it was recirculated to the reactor. The SBR was operated in cycles of 6 hours distributed in four periods: mixed fill (300 min), mix (30 min), settle (15 min) and draw (15 min). Temperature was controlled at 30 ºC and pH at 7-8. Complete mixture was achieved by means of a mechanical stirrer at 70 rpm. The reactor was inoculated with enriched Anammox biomass and fed with a synthetic medium at a nitrogen loading rate of 0.06 g N/L·d (Dapena-Mora et al., 2004). A series of experiments were performed in order to research the influence of the flow rate and the salinity of the medium (Table 1).
Table 1. Experimental strategy.