Innovative technologies for biological nitrogen removal; ANAMMOX and SHARON processes

Bu çalışmada ANAMMOX ve SHARON reaktörlerinde azot giderim performansı incelenmiştir. Her iki sistemin performansları farklı amonyak yükleri ve farklı hidrolik bekletme süresi gibi dinamik koşullar altında incelenmiştir. SHARON reaktörünün başlangıç periyodunu oluşturan süreçte nitrifikasyon bakterilerinin kültür zenginleştirme çalışmalarında en yüksek spesifik amonyum oksidasyon hızı 0.1 mg NH4+-N/mg UAKM.saat olarak elde edilmiştir. Kemostat reaktörde çamur yaşı 1.15 gün ve reaktör sıcaklığı 35±2oC olarak gerçekleştirilen işletme koşullarında kısmi nitrifikasyona ulaşılmış ve işletme boyunca ortalama %90 amonyum azotu giderim verimi ile 2.8 mg NH4+-N/mg UAKM.saat spesifik amonyum oksidasyon hızı elde edilmiştir. Sistem metanol ilavesi ile döngüsel anoksik-aerobik fazlarla çamur yaşı 1.5 gün olan işletme koşullarında çalıştırıldığında oluşan nitritin ortalama %25’i denitrifiye edilebilmiştir. ANAMMOX reaktörü ise tam karışımlı sürekli akımlı bir reaktörde sistemden biyokütle atılmaksızın işletilmiş ve işletme boyunca sisteme verilen amonyum azotunun %90’nın ve nitrit azotunun %99’unun giderildiği görülmüştür. Çalışmada ayrıca ANAMMOX prosesini gerçekleştiren mikroorganizma topluluğunun FISH analizi ile karakterizasyonu yapılmıştır. Prosesi oluşturan biyokütle topluluğunun Planktomisit türünde ANAMMOX bakterilerinin Dokhaven-2 alt türünden oluştuğu görülmüştür. Deneysel bulgular yüksek amonyum içeren atıksuların arıtımında ANAMMOX ve SHARON proseslerinin yüksek verimlerle ve düşük çamur üretimiyle alternatif teknolojiler olarak kullanılabileceğini göstermektedir. Anahtar Kelimeler: Anaerobik amonyum oksidasyonu(ANAMMOX), kısmi nitrifikasyon-denitrifikasyon (SHARON), floresan yerinde hibritleşme (FISH), kemostat.It is widely acknowledged that nitrogen in wastewater has become one of the major pollutants to the water resources. Nitrate, nitrite and ammonium are important pollutants in municipal and industrial wastewaters. Conventional methods for the biological removal of these compounds involve two discrete steps namely nitrification and denitrification. Firstly, nitrification is an energy demanding process for aeration and due to low growth rate of nitrifiers, large nitrification volumes are required. Secondly, denitrification requires organic carbon as electron donor. If the carbon content in the wastewater is not sufficient, an extra carbon source has to be supplied which causes an increase of overall treatment costs. Stringent standards on disposal of treatment sludges require aerobic or anaerobic biological sludge treatment. The effluents from anaerobic sludge digesters contain high ammonium and low organic matter and they have relatively low flow rates. In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the inlet nitrogen load is recycled with the return liquors from sludge dewatering. Separate treatment of this digester supernatant would significantly reduce the nitrogen load of the main stream and improve nitrogen elimination. Chemical elimination of ammonium with magnesium ?ammonium ?phosphate (MAP) precipitation or with air stripping is feasible but it seems to be more expensive than classical biological processes. Anaerobic ammonium oxidation process (Anammox) is a new low-cost alternative to conventional denitrification systems especially for sludge digestion effluents. Anaerobic ammonium oxidation is the oxidation of ammonium to dinitrogen gas with nitrite as the electron acceptor. The process is mediated by autotrophic bacteria that use CO2 as the only carbon source. Another promising process is SHARON process that is suitable for the treatment of high strength wastewaters (high in ammonia, low in organic matter concentration). The SHARON process makes use of the growth rates of ammonia and nitrite oxidizers at sufficiently high temperatures (more than 26±C). It works at a hydraulic retention time higher than the growth rate of nitrite oxidizers but lower than ammonia oxidizers (about 1 day). This process has no sludge retention thus nitrite oxidizers are not able to remain in the reactor and they are washed out. Process is operated alternating oxic and anoxic conditions with instantaneous methanol addition. If the Anammox process is combined with a preceding nitrification step, only part of the ammonium needs to be nitrified to nitrite while the Anammox process combines the remaining ammonium with the nitrite to yield dinitrogen gas and a small amount of nitrate. Consequently, complete nitrogen removal would be achieved without addition of methanol. Partial nitrification will reduce oxygen demand in the nitrification reactor and leads to a second reduction in costs. The biomass yield of the Anammox process is very low; consequently little sludge is produced. The low sludge production is the third factor that contributes to the substantially lower operation costs compared to conventional biological nitrogen removal systems. In this study, results obtained from Anammox and SHARON reactors are presented comparatively. An enriched culture of Anammox reactor was run for 262 days where high ammonium removal efficiency was observed. Reactor was fed with increasing nitrogen loads without biomass wastage. 90% of ammonia and 99% of nitrite were converted into dinitrogen gas. Due to complete biomass retention and increased nitrogen loadings, ammonia and nitrite conversion rates were increased. Molecular examination of Anammox culture with FISH analysis showed that culture was dominated by Dokhaven-2 subclass. Ammonium oxidizers were formerly enriched in fill and draw reactors for SHARON reactor with increasing ammonium loadings. Once reliable ammonium oxidation was obtained, the culture was transferred into a chemostat and fed with higher ammonia loads. Reactor was operated with a hydraulic retention time of 0.98-1.15 days and temperature was kept about 35±2oC which is suitable for selective enrichment of ammonia oxidizers. The observed high specific ammonia oxidation rate and formation of nitrite indicated that highly active ammonia oxidizing culture was enriched. The SHARON process was established with alternating oxic and anoxic conditions with subsequent addition of methanol. In SHARON reactor only 25% of nitrite was denitrified principally due to insufficient methanol addition. Keywords: ANAMMOX, SHARON, ammonium oxidation, denitrification, Fluorescent in situ hybridization (FISH)