Land Disposal of Centrate from Biosolids Production

Arid land and riparian plants were irrigated with a liquid wastewater stream (centrate) from biosolids production at a municipal sewage treatment facility. Centrate containing approximately 1000 mg/l ammonia nitrogen was diluted with Tucson city tap water to provide treatments of 2.5, 5, 10, 25, 50, and 100% centrate, along with a dilution water control. Plants grown in 19-l containers in a greenhouse were irrigated daily with 6.7 l of solution over a 7-week period. All species exhibited a fertilizing effect at concentrations up to 5 and 10% centrate, equivalent to approximately 50 and 100 mg/l NH₃–N, but then inhibitory above 100 mg/l. No plants survived on the 50 or 100% treatments. If centrate were to be diverted from the wastewater facility to be disposed of on the land, it was estimated that the total nitrogen content of the biosolids produced by the plant would be reduced by 11%. This reduction would have only a small impact on the value of the biosolids for soil amendment applications.