Enrichment of anammox bacteria from activated sludge using anaerobic digester effluent

The use of anaerobic ammonium oxidation processes is becoming increasingly widespread. The Partial Nitritation-Anammox process, the most known of the anaerobic ammonium oxidation processes, is the most innovative and sustainable method of nitrogen removal, due to the relatively low carbon and oxygen requirements compared with conventional biological nitrogen removal. In this study, AOB and Anammox which are the key bacteria of Partial-Nitritation and Anammox processes were enriched from conventional municipal sludge taken from aeration tank and sludge recycle line. Domestic waste water sludge digestion effluent was used at each stage of the Partial Nitration process. The enrichment of Anammox bacteria was carried out using synthetic wastewater and sludge digestion effluent in two different reactors, and the effects of real wastewater and synthetic wastewater on enrichment were examined. The Partial Nitritation, Anammox enrichment study fed with natural wastewater and Anammox enrichment study fed with synthetic wastewater studies, which were performend in 3 different continuously stirred tank reactor, operated for 161 days, 87 days and 55 days, respectively. The Partial Nitritation reactor was operated in three different ways; phase I: stimulation of the growth of AOB (Enrichment), phase II: maintaning AOB stability and Stage III: Providing a suitable feed for Anammox stoichiometry. The combination of pH, SA, SNA, DO, temperature, and SRT parameters was used as a control strategy to enrich the AOB and to keep the activity stable. In order to determine the feasibility of the work to full-scale installations, the pH value gradually increased from 7.8 to 7; the temperature was lowered from 35 °C to 22 °C and suitable wastewater stoichiometry (NO2--Nproduced: NH4+-Nremoval ratio 1.26 ± 0.1:1) was provided to Anammox without pH and temperature control. AOB enrichment was completed on day 55, NOB activity ceased completely from day 90 to end of study. Between days 90 and 161, the wastewater from this reactor was fed to the Anammox reactor, with an ammonium removal rate of 55.7±1.8% and an AOB activity of 99.6±0.08%. In the Anammox enrichment study carried out in 2 different reactors, the first effects of Anammox began to appear on the 40th day of the R2 reactor fed with Partial Nitritation effluent, while nitrification effects continued in the R3 reactor fed with synthetic wastewater. The concentration of DO decreased and the pH tended to increase in the R2 reactor with production of nitrogen gas from the 40th day. The stoichiometric ratios of NO2--Nremoval: NH4+-Nremoval and NO3--Nproduced:NH4+-Nremoval changed to 1.29±0.08:1 and 0.4±0.3:1, respectively. The NO3--N concentrations produced by the wastewater feed in the reactor, which has been operating for a further 47 days, have begun to decrease and nitrogen removal rate was increased from 10,7 mg N/L/d (40th day) to 136,2 mg N/L/d (87th day) and nitrogen removal efficiency was calculated as 82.2±14% between days 40 and 87. Despite being operated on co-reactors and conditions, the increase of DO in the R3 reactor fed with synthetic wastewater was more frequent and the pH tended to decrease. The stoichiometric ratios of NO2--Nremoval:NH4+-Nremoval and NO3--Nproduced:NH4+-Nremoval in the R3 reactor were respectively 0.99±0.34 and 1.18±0.79, which were far from the Anammox stoichiometry