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This study demonstrated that partial nitritation using nitrifying activated sludge entrapped in a polyethylene glycol (PEG) gel carrier, as a pretreatment to anammox process, could be successfully applied to digester liquor of biogas plant at a nitrogen loading rate of 3.0 kg-N/m(3)/d. The nitritation process produced an effluent with a NO(2)-N/NH(4)-N ratio between 1.0 and 1.4, which was found to be suitable for the subsequent anammox process. A high SS concentration (2000-3000 mg/l) in the digester liquor did not affect partial nitritation treatment performances. Effluent from this partial nitritation reactor was successfully treated in the anammox reactor using anammox sludge entrapped in the PEG gel carrier with T-N removal rates of greater than 4.0 kg-N/m(3)/d. Influent BOD and SS contents did not inhibit anammox activity of the anammox gel carrier. The combination of partial nitritation and anammox reactors using PEG entrapped nitrifying and anammox bacteria was shown to be effective for the removal of high concentration ammonium in the digester liquor of a biogas plant.

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.

Recently, a new segment of the nitrogen cycle, anaerobic ammonium oxidation (anammox), was discoverd. This reaction consists of the oxidation of ammonium to nitrogen gas using nitrite as electron acceptor under anaerobic conditions. This autotrophic process produces very little sludge and does not need supplementation of extra carbon sources, thus it reduces much treatment cost compared to the traditional method. For application of the anammox process to ammonium removal, only partial nitritation (PN) is required instead of complete nitrification. In order to make the stoichiometry in accordance with anammox reaction, it is desirable for PN of about 60% of the ammonium to nitrite. According to the merits mentioned above, the anammox process shows potential for nitrogen removal of wastewater. PN-anammox is a completely autotrophic system and is better suited for the treatment of high concentrations of ammonium in wastewaters. However, application of this process to the treatment of digester liquor of livestock manure has not been widely reported. Thus, PN-anammox process was applied to the treatment of digester liquor of livestock manure in this study.

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.

In this study, combination of a partial nitritation reactor, using immobilized polyethylene glycol (PEG) gel carriers, and a continuous stirred granular anammox reactor was investigated for nitrogen removal from livestock manure digester liquor. Successful nitrite accumulation in the partial nitritation reactor was observed as the nitrite production rate reached 2.1 kg-N/m(3)/day under aerobic nitrogen loading rate of 3.8 kg-N/m(3)/day. Simultaneously, relatively high free ammonia concentrations (average 50 mg-NH(3)/l) depressed the activity of nitrite oxidizing bacteria with nitrate concentration never exceeding 3% of TN concentration in the effluent of the partial nitritation reactor (maximum 35.2 mg/l). High nitrogen removal rates were achieved in the granular anammox reactor with the highest removal rate being 3.12 kg-N/m(3)/day under anaerobic nitrogen loading rate of 4.1 kg-N/m(3)/day. Recalcitrant organic compounds in the digester liquor did not impair anammox reaction and the SS accumulation in the granular anammox reactor was minimal. The results of this study demonstrated that partial nitritation-anammox combination has the potential to successfully remove nitrogen from livestock manure digester liquor.

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.