Salinity-Aided Selection of Progressive Onset Denitrifiers as a Means of Providing Nitrite for Anammox

Abstract

Anaerobic ammonium oxidation (anammox) combined with partial-denitrification (NO → NO) is an innovative process for the simultaneous removal of ammonia and nitrate from wastewaters. An efficient method for the selection of partial denitrifying community, which relies on increasing influent salinity, is described. Using this method, a denitratating community was enriched, which showed a nitrite accumulation efficiency higher than 75% as well as a high nitrate conversion efficiency. Community analysis using 16S rDNA indicated that Halomonas became the dominant genus as salinity increased. Metagenomic analysis revealed that there was not a significant difference in reads mapping to downstream denitrification genes in a comparison of samples from cultures with 5% salinity to those without salinity. The majority of the reads mapping to the genes encoding dissimilatory nitrate and nitrite reductases nar and nirS came from Halomonas under high salinity conditions. Two metagenome-assembled genomes taxonomically assigned to Halomonas were obtained, one of which accounted for ∼35% of the reads under high salinity conditions. Both genomes harbored the genes for the complete denitrification pathway. These results indicate progressive onset denitrifiers, a phenotype where nitrite reduction only occurs after nitrate exhaustion, could be successfully enriched with increasing salinity. Progressive onset denitrifiers may be more widespread in natural and artificial habitats than anticipated and are shown here to be valuable for nitrogen mitigating processes.

Salinity effects on biological treatments

“…A direct impact of the presence of high salt concentrations is the increase of osmotic pressure, causing water leakage out from bacteria. In this sense, microorganisms have developed two strategies in order to maintain an osmotic balance with their external environment (Figure 3.3) (Li et al, 2018): (1) pumping inorganic ions (generally K + ) into the cell by mechanisms such as contractile vacuoles; and (2) accumulating compatible solutes from their environment or synthesizing such compatible solutes as sugars, amino acids, glycine betaine, trehalose and ectoine (Trüper & Galinski, 1990) which help to stabilize the cell membrane and cell ultrastructure (Ontiveros-Valencia et al, 2014).…”

“…In any case, both strategies have allowed the anaerobic process to be successfully applied for treating high salinity industrial effluents (15-71 g NaCl/L), such as seafood-processing effluents or tannery soak liquor, obtaining high efficiencies of organic matter removal (70-90%) (Guerrero et al, 1997;Mosquera-Corral et al, 2001;Picos-Benítez et al, 2019). In order to alleviate the toxic effect of Na + , some authors also proposed the addition of potassium ions (Li et al, 2018) or exogenous compatible solutes such as glycine betaine (Zhang et al, 2016) since they can be used by anaerobic microorganisms to maintain the osmotic balance with their external environment. These strategies could shorten the acclimation periods but their application at full scale would be limited by the operating costs involved.…”

Treatment and Valorisation of Saline Wastewater: Principles and Practice

“…A direct impact of the presence of high salt concentrations is the increase of osmotic pressure, causing water leakage out from bacteria. In this sense, microorganisms have developed two strategies in order to maintain an osmotic balance with their external environment (Figure 3.3) (Li et al, 2018): (1) pumping inorganic ions (generally K + ) into the cell by mechanisms such as contractile vacuoles; and (2) accumulating compatible solutes from their environment or synthesizing such compatible solutes as sugars, amino acids, glycine betaine, trehalose and ectoine (Trüper & Galinski, 1990) which help to stabilize the cell membrane and cell ultrastructure (Ontiveros-Valencia et al, 2014).…”

“…Moreover, under saline conditions, bacteria can increase their production of extracellular polymeric substances (EPS) (Li et al, 2018). EPS contribute to enhancing the aggregation of the biomass but also to counteracting the osmotic pressure (Steele et al, 2014).…”

Dominance ofCandidatus saccharibacteriain SBRs achieving partial denitrification: effects of sludge acclimating methods on microbial communities and nitrite accumulation

“…Chen et al 13 stated that salinity decreased the nitrogen removal efficiency of activated sludge and increased the extracellular polymeric substance (EPS) content. Li et al 14 described an efficient method that increased the inuent salinity for enriching the community of partial denitriers. The nitrite accumulation efficiency was higher than 75%, the nitrate conversion efficiency was high, and Halomonas was the dominant genus.…”