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A swim-bed reactor using the biofringe acryl-fiber biomass carrier was used for partial nitritation treatment for anaerobic digestion liquor of swine wastewater. The sludge in the reactor demonstrated excellent settling properties, and the sludge volumetric index (SVI) was always about 50 ml g(-1). The mixed liquor suspended solids (MLSS) concentration was maintained above 10,000 mg l(-1) with a maximum of 16,800 mg l(-1). Satisfactory and stable partial nitritation was obtained at a nitrogen loading rate (NLR) of 1.9 kg-N m(-3) d(-1) without any operational control. Only a little nitrate was produced almost during the whole operational period and the nitrite to total oxidized nitrogen ratio (NO(2)-N/(NO(2)-N+NO(3)-N)) was always above 95%. In addition, the influence of temperature on partial nitritation efficiencies was also investigated and non-controlled efficiencies were maintained stably between 15 degrees C and 30 degrees C at an NLR of 1.9 kg-N m(-3) d(-1), but suddenly deteriorated when the temperature fell below 15 degrees C. Nitrite oxidizing bacteria were inhibited by free ammonia and free nitric acid, which prevented the conversion of nitrite to nitrate and the inhibition due to free nitric acid weaken with a decrease in temperature. It was apparent that these phenomena were crucial to the control of partial nitritation treatment.

Underground brine waste containing high concentrations of ammonium and with a salinity of 3% is usually generated during the production of methane gas and iodine in the gas field of Chiba Prefecture, Japan. In this study, one swim-bed reactor, packed with a novel acrylic fiber biomass carrier (Biofringe), was applied to the partial nitritation treatment of this kind of underground brine waste. A stable nitrite production rate of 1.6 kg NO(2)-N m(-3) d(-1) was obtained under a nitrogen loading rate of 3.0 kg-N m(-3) d(-1), at a pH of 7.5 and a temperature of 25 degrees C. Nitrate production was negligible and the effluent NO(2)-N/NO(x)-N ratio was above 98% due to the successful inhibition of nitrite-oxidizing bacterial activity. Free ammonia was considered to be the main factor for inhibiting the activity of nitrite-oxidizing bacteria. A microbial community shift was demonstrated by 16S rRNA analysis, and it was shown that the ammonium-oxidizing bacteria became the predominant species after successful nitrite accumulation was observed.

Effect of high salt concentration on the anammox treatment was investigated to establish an acclimation strategy under high salt concentration conditions. An anammox fixed-bed reactor with non-woven biomass carrier was used and the salt concentration was gradually increased from 2.5 g L− 1 to 33 g L− 1. The anammox reactor demonstrated stable nitrogen removal rate (NRR) of 1.7 kg-N m− 3 d− 1 for 65 days under a salt concentration of 30 g L− 1. However, the NRR sharply declined at a salt concentration of greater than 30 g L− 1. The bacterial community was examined by 16S rRNA gene analysis and DGGE after the acclimation of the anammox sludge to high salt conditions. Although the salt concentration was almost sea level, the freshwater anammox bacteria, KU2, were detected. In addition, the unidentified bacteria which perhaps belong to candidate division OP10 and Lysobacter sp. were found to coexist with anammox bacteria at a salt concentration of 30 g L− 1.