Aims:  Characterization of the ammonia‐oxidizing archaea (AOA) community in activated sludge from a nitrogen removal bioreactor and wastewater treatment plants (WWTPs). Methods and Results:  Three primer sets specific for ammonia mono‐oxygenase α‐subunit (amoA) were used to construct clone libraries for activated sludge sample from a nitrogen removal bioreactor. One primer set resulted in strong nonspecific PCR products. The other two clone libraries retrieved both shared and unique AOA amoA sequences. One primer set was chosen to study the AOA communities of activated sludge samples from Shatin and Stanley WWTPs. In total, 18 AOA amoA sequences were recovered and compared to the previous reported sequences. A phylogenetic analysis indicated that sequences found in this study fell into three clusters. Conclusions:  Different primers resulted in varied AOA communities from the same sample. The AOA found from Hong Kong WWTPs were closely similar to those from sediment and soil, but distinct from those from activated sludge in other places. A comparison of clone libraries between Shatin WWTP and bioreactor indicated the AOA community significantly shifted only after 30‐day enrichment. Significance and Impact of the Study:  This study confirmed the occurrence of AOA in a laboratory scale nitrogen removal bioreactor and Hong Kong WWTPs treating saline or freshwater wastewater. AOA communities found in this study were significantly different from those found in other places. To retrieve diverse AOA communities from environmental samples, a combination of different primers for the amoA gene is needed.

The concentrations and removal of Cryptosporidium, Giardia, and microbial indicators, including somatic coliphages and fecal coliforms were investigated through the wastewater treatment processes at three municipal wastewater treatment plants in Beijing, China. The experimental results showed that the concentrations of Cryptosporidium in untreated wastewater, primary treatment effluent, secondary treatment effluent, tertiary treatment effluent were 33-600, 67-333, 0-9 and 0-0.4 oocysts L(-1), and that of Giardia were 130-3,600, 533-2,033, 0-32 and 0-2.1 cysts L(-1), respectively. The reduction ratios of Cryptosporidium and Giardia by the primary treatment process were 0.12 log and 0.18 log, respectively. Oxidation ditch process had higher reduction efficiency to Cryptosporidium and Giardia than anaerobic-anoxic-oxic process and conventional activated sludge process, probably because of longer retention time and higher sludge concentration. Membrane ultrafiltration had a notably better efficiency to reduce microorganisms, especially Cryptosporidium and Giardia, than conventional flocculation sedimentation and sand filtration process, as the tertiary treatment. Comparing with total coliforms, fecal coliforms and heterotrophic bacteria, concentration of somatic coliphages was correlated better with that of Cryptosporidium and Giardia in untreated wastewater and secondary treatment effluent.