Sodium inhibition and sulphate reduction in the anaerobic treatment of mussel processing wastewaters

An anaerobic filter treating high saline wastewaters from a sea food processing industry was subjected to sodium and sulphate shocks. Sodium concentrations ranging from 5 to 12 g dm −3 had no significant influence on the methane production rate, with maximum value of 15 kg COD   CH   4m −3 day −1 . The sulphate‐reducing capacity of the filter was estimated at 2.2 kg SO 4 2‐ m −3 day −1 . When using propionic or acetic acid as substrates, the sulphate‐reducing activities were 0.021 and 0.006 g SO 4 2‐ g −1 VSS day −1 respectively. Determination of the methanogenic activity of the sludges indicated that sodium concentrations of 14 g dm −3 caused a 50% inhibition of the methanogenic activity from the anaerobic filter. However, when using the anaerobic filter effluent as the assay medium, the sodium concentration giving the same percent inhibition was 17.7 g dm −3 , indicating a beneficial effect probably due to the antagonism caused by the presence of other sea salts. The sludge showed a higher tolerance to sodium toxicity than that reported in previous literature, which can be explained as a consequence of sludge adaptation.