Effects of the seed sludge on the performance of UASB reactors for treatment of toxic wastewater.

A comparative study of different sludges (anaerobic sewage sludge and anaerobic sewage sludge cultivated for 30 days) as the seed of UASB reactors for treatment of synthetic resin production wastewater was carried out on a laboratory scale. Significant differences in reactor performance were observed. With anaerobic sewage sludge seed, the reactor obtained a 71% COD removal efficiency and produced 2.94 dm3 biogas per dm3 wastewater under an organic loading rate of 4.5 kg COD m-3 day-1. The sludge in the reactor was diffuse and possessed poor settling ability, which led to effluent SS as high as 1200 mg dm-3. However, with anaerobic sewage sludge cultivated with synthetic substrate for 30 days as a seed, the same reactor gave 78% COD removal efficiency and produced 3.5 dm-3 biogas per dm3 wastewater at the same loading rate. Moreover, the sludge in the reactor was completely granulated and possessed good settling ability, which resulted in effluent SS as low as 200 mg dm-3. The granular sludge produced less biomass per gram COD removed than the diffused sludge. Anaerobic sewage sludge cultivated for a short time could form the nuclei of granules for the reactor, allowing granulation to proceed smoothly. Therefore, sludge nuclei are a prerequisite of sludge granulation in UASB reactors for treatment of toxic wastewater.