Occurrence of nitrification inhibition in Swedish municipal wastewaters

The occurrence of substances inhibiting nitrification in Swedish municipal wastewaters was investigated using three methods: a screening method based on activated sludge and two pure culture methods based on Nitrosomonas and Nitrobacter. Influent samples from 109 wastewater treatment plants collecte d every day during one specific week were investigated. The three test meth ods were also compared. The results of the screening method showed that abo ut 60% of the plants received wastewater containing inhibitory substances, although only 4% had considerable inhibition (>20%). With the two pure cult ure methods, inhibition was found at about 45% of the plants investigated, with considerable inhibition found at 13% and 20% of the plants with the Ni trosomonas and the Nitrobacter methods, respectively. The limit of detectio n was determined to be 5% inhibition for the screening method, 11% inhibiti on for the Nitrosomonas method and 13% inhibition for the Nitrobacter metho d. The pure culture methods found more samples strongly inhibitory or stimu lating than the screening method. The highest correlation between the inhib ition results from the three methods was found between the screening method and the Nitrosomonas method. It was also shown for sludge from several act ivated sludge treatment plants, that they were adapted to the toxic compoun ds present in the influent. At high inhibition this acclimatisation was les s pronounced. No correlation was found for any of the methods between the i nhibition and parameters such as the size of the plant, the geographic loca tion, the content of ammonia, COD or conductivity in the influent, the pres ence of leachate or the percentage of industrial wastewater in the influent , or types of industries in the catchment area. However, the constantly hig hest inhibition was found at a plant with a large number of different indus tries connected. Any clear pattern for the variation of inhibition during t he week was not found. (C) 2000 Elsevier Science Ltd. All rights reserved.