ABSTRACT:
Thermal sludge conditioning liquor was successfully treated by a pilot‐scale upflow anaerobic hybrid system with an effective volume of 10.4 m3. The reactor was similar to the HYAN reactor in Lakeview but without a recirculation system. A gas‐solid separator was installed above a filter packed with polypropylene pall rings. The organic loading rate was increased stepwise to 30 kg chemical oxygen demand (COD)/m3· d. The hydraulic retention time was only 6 hours at the target loading rate.
More than 70% of soluble COD in the influent was removed, even at an organic loading as high as 30 kg COD/m3· d. Soluble 5‐day biochemical oxygen demand (BOD5) removal efficiency at the loading rate exceeded 95%. Volatile fatty acids concentration in the effluent was consistently less than 60 mg/L after the day when stable treatment had been obtained. The methane production fluctuated between 0.3 and 0.4 L/g COD removed. Solids production including effluent suspended solids (SS) was between 0.16 and 0.24 kg SS/kg COD removed.
The inside of the reactor consisted of two zones, a sludge blanket zone with less than 1% solids concentration and a sludge bed zone with 47% solids concentration. Although the reactor was seeded with an anaerobically digested sludge, granular sludge was produced in the reactor. The ratio of granules to the solids remaining in the reactor increased to approximately 70% at the end of the experiments. Most of the granules had diameters of less than 1 mm and their settling velocity was 0.6 cm/s or more. The granules were composed of bacteria likeMethanothrixaccording to SEM observations. The methane production rate was between 0.8 and 1.1 kg methane as COD/kg SS · d in an acetate solution.
According to substrates distribution in the reactor and tracer tests, the bed zone in the reactor worked similarly to a continuously stirred tank reactor (CSTR). Evaluation of soluble COD removal rates in the reactor indicated that the rate could be simulated by a Monod type reaction.