Nitrate and nitrite inhibition of methanogenesis during denitrification in granular biofilms and digested domestic sludges

Abstract

Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO(3) (-)) and nitrite (NO(2) (-)) to methanogenesis. The methanogenic toxicity of the NO (x) (-) compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and hydrogen, was studied. The inhibition was the severest when the NO (x) (-) compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis was evident at the lowest concentrations of added NO(2) (-) tested (7.6-10.2 mg NO(2) (-)-N l(-1)) or 8.3-121 mg NO(3) (-)-N l(-1) of added NO(3) (-), depending on substrate and inoculum source. The inhibition imparted by NO(3) (-) was not due directly to NO(3) (-) itself, but instead due to reduced intermediates (e.g., NO(2) (-)) formed during the denitrification process. The toxicity of NO (x) (-) was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NO (x) (-) concentrations; whereas the recovery was only partial at high added NO (x) (-) concentrations. The recovery is attributed to the metabolism of the NO (x) (-) compounds. The assay substrate had a large impact on the rate of NO(2) (-) metabolism. Hydrogen reduced NO(2) (-) slowly such that NO(2) (-) accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was inversely proportional to the amount of NO (x) (-) compounds added indicating that they were the preferred electron acceptors compared to methanogenesis.

Bakteri Denitrifikasi Inaktif Sebagai Suplemen Untuk Mengurangi Gas Metana dari Cairan Rumen Sapi

“…Kemudian denitrifikasi mengalihkan akseptor elektron dari metanogenesis ke dalam proses denitrifikasi [27]. Produksi akhir metana berbanding terbalik dengan jumlah senyawasenyawa NO x -awal, sehingga mengindikasikan bahwa mereka merupakan akseptor elektron yang lebih disukai daripada metanogenesis [28]. Hasil penelitian ini membuktikan bahwa penggunaan bakteri denitrifikasi inaktif dapat menekan produksi metana lebih baik daripada bakteri denitrifikasi aktif, sehingga dapat dijadikan inokulum dalam pakan ternak.…”

Enhancing algal biomass and biofuels recovery from open culture systems

“…Other factors can also significantly inhibit AD, including ammonium toxicity, sodium toxicity, and nitrite toxicity, etc. (Banihani et al, 2009; Model based process control of algae production has been considered by some researchers and engineers (Baquerisse et al, 1999;Béchet et al, 2013;Goldman et al, 1974). But only a handful of models on biomass production in open algae cultivation system are currently available, especially considering the activity of heterotrophic bacteria (Buhr & Miller, 1983;Fallowfield & Garrett, 1985;Jupsin et al, 2003;Mesplé et al, 1996).…”

“…It is known that NO2 -is a preferred electron acceptor (Banihani et al, 2009). Table 5.7 shows the COD requirements for nitrite reduction and growth of denitrifiers.…”

“…The other drawback of carrying pre-treatment liquor into the digester is that nitrite present in the pretreatment liquor has potential toxicity to methanogenesis (Banihani et al, 2009;.…”

“…Based on the study of Banihani et al (2009), methanogenesis was inhibited completely in the present of NO2 -(8-153 mg N L -1 ) ; but it started once the NO2 -was denitrified.…”