Anaerobic Digestion of Screened Swine Waste Liquids in Suspended Particle-Attached Growth Reactors

Abstract

ABSTRACT Astudy was conducted to determine performance characteristics of anaerobic suspended particle-attached growth (SPAG) reactors treating liquid swine waste. This innovative reactor technology combines characteristics of attached-growth and conventional completely-mixed reactors by fixing active bacterial mass on light weight, highly porous support particles which are suspended in the reactor liquor by fluid mixing. Two reactor temperatures were used, mesophilic (35 C) and thermophilic (55 C), with two replicates at each temperature. Hydraulic retention time (HRT) varied from 10 to 2 days for the mesophilic reactors, and 5 to 1 days for the thermophilic reactors, with volatile solids (VS) loading rates ranging between 0.98 to 11.34 g/L-day, based on an empty-tank volume. The SPAG reactors performed well at all HRT's examined, with some signs of stress occurring at the shortest HRT's for both mesophilic and thermophilic reactors (2 and 1 day, respectively). Volumetric methane productivities ranged from 0.42 to 2.43 L/L-day, and VS reduction ranged from 36.0 to 66.9%. As expected, the thermophilic reactors consistently out-performed the mesophilic reactors at equal VS loading rates. Analysis of the bacteria support particles at the end of the study indicate bacterial concentrations between 14 and 27 g/L particle can be obtained using anaerobic SPAG reactor technology. Of the two support materials examined, a reticulated nylon cuboid appeared to be capable of retaining higher concentrations of bacterial mass than a polyurethane foam, but both material performed adequately.