A novel prototype instrument was developed to measure biomass catalase activity of suspended cultures. The technology was applied to develop a batch method of measuring activity in other media (e.g. soils) and a method of measuring hydrogen peroxide concentration. The biomass catalase activity of different microbial populations was measured successfully semi-continuously on-line (activated sludge, nitrifying culture) and off-line (soils). Garden soil, soil undergoing bioremediation and a characterised soil demonstrated catalase activities between 78 and 696 catalase units g-1 dry weight of soil. Catalase activity was linearly correlated with different weights of each soil and was an indicator of bioremediation efficiency. Nitrifying cultures (enrichment nitrifying culture and pure cultures of Nitrosomonas) were shown to have a specific activity between 79,012 and 265,965 catalase units g-1 MLVSS. Nitrification ability of the cultures was inhibited by ATU and 3,5-DCP while catalase activity remained stable for more than one hour following inhibitor addition in continuous studies. Activated sludges taken from Cynon Sewage Treatment Works then maintained in the laboratory were shown to have a specific activity between 8,392 and 107,136 catalase units g-1 MLVSS. Using a 100 litre activated sludge plant operating at varying OLR (between 0.5 and 2.0 kg COD m-3 reactor day-1 , corresponding to changes in F/M of between 0.12 and 0.65 kg COD/kg MLVSS day-1) in 8 experiments lasting up to 15 days, an increase in organic loading rate was reflected by an increase in catalase activity and increased utilisation of dissolved oxygen. Starvation caused by a decrease in OLR also increased catalase activity by up to seven times within 36 hours. The catalase activity monitor provides additional knowledge of the effects of environmental changes on biological processes occurring within a wastewater treatment plant that may not be reflected by current standard methods alone.
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