Methods and systems are provided for drying wet biosolids to produce a class A biosolids. Generally described, the method of treating biosolids includes drying a wet biosolids in an indirect dryer to produce a partially dried biosolids and drying the partially dried biosolids in a direct dryer in series with and downstream of the indirect dryer to produce a class A biosolids. The indirect dryer and direct dryer may be operated at an average temperature of greater than about 100° C. and may have a total combined residence time of less than about 60 minutes. Also provided are systems for drying wet biosolids including an indirect biosolids dryer and a direct biosolids dryer in series. The methods and systems are particularly effective at reducing the moisture content of the biosolids from greater than 85% to less than 10% by weight.
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