METHODS
Anaerobic baffled reactor (ABR)
Four anaerobic baffled reactors (ABR) were constructed from thin sheet plastic (Fig. 1). The only difference among the four reactors was the number
of chambers (two, three, four and five). The total volume of the reactors was 15 1. The baffles were angled at 40 ° to the horizontal to reduce entrance velocities and direct incoming material to the center of the chamber. Two small, plastic-tube (20 cm dia)settlers were used at the discharge end of the ABRs. All the reactors were operated at 35°C (by keeping them in a temperature-controlled room) and at a hydraulic retention time (HRT) of 14 days. Biogas production was measured with wet tip gas meters.
Swine waste
A single batch of swine manure was collected from a concrete feeding floor, thoroughly mixed, and frozen until used. Characteristics of the waste are given in Table 1.
Reactor start-up and loading
All ABRs were started with inoculum obtained from
an operating pilot-scale swine manure digeste r . The total and volatile solids of the inoculum were 8966 and 4341 mg/1, respectively. Initial loading was 1 g VS/l/day and gradually increased to 4 g VS/1/day over a period of 57 days. After 220 days, the loading
was increased gradually to 8 g VS/1/day. The reactors were operated for 28 days at this high loading rate. All reactors were loaded 6 days per week.