The two sludge tanks at Carey’s Gully store sewage sludge pumped from the Moa Point wastewater treatment plant located about 10 kilometers away. Due to the age of the sludge, considerable quantities of corrosive hydrogen sulphide gas are released within the tanks. H2S concentrations over 50 ppm have been recorded, and resulted in severe corrosion to the concrete walls and concrete roof of these two tanks.
Air given off from the biosolids treatment plant at Watercare’s Mangere wastewater treatment plant contains ammonia and odours. This air had to be captured and ducted away for treatment in soil bed filters. However firstly the ammonia had to be removed as it would have had an adverse effect on the soil bed filter biology.