Elutriated acid fermentation of municipal primary sludge

The performance of a novel fermentation process, adopting a sludge blanket type configuration, for higher hydrolysis/acidogenesis of the municipal primary sludge was investigated under batch and semi-continuous conditions with varying pH and temperature. This acid elutriation slurry reactor provided higher system performance with a short HRT (5 d) and higher acidogenic effluent quality under pH 9 and thermophilic (55 °C) conditions. The hydrolysis of the sludge was revealed to be significantly dependent on seasonal effects for sludge characteristics but with little impact on acidogenesis. Based on the rainy season at the optimal conditions, VFA production and recovery fraction (VFACOD/COD) were 0.18 g VFACOD/g VSSCOD and 63%. As byproducts, nitrogen and phosphorus release were measured at 0.006 g N/g VSSCOD and 0.003 g P/g VSSCOD, respectively. For the mass balance in a full-scale plant (Q=158,880 m3/d) based on the rainy season, the VFA and non-VFA (as COD) production were 3110 kg VFACOD/d and 1800 kg COD/d, resulting in an increase of organics of 31 mg COD/L and 20 mg VFACOD/L and nutrients of 0.7 mg N/L and 0.3 mg P/L in the influent sewage. The economical benefit from this process application was estimated to be about $67 per 1000 m3 of sewage except for energy requirements and also, better benefits can be expected during the dry season. Moreover, the results revealed that the process has various additional advantages such as pathogen-free stabilized solids production, excellent solids control and economical benefits.