Effects of partially saturated conditions on the metabolically active microbiome and on nitrogen removal in vertical subsurface flow constructed wetlands

Abstract

Nitrogen dynamics and its association to metabolically active microbial populations were assessed in two vertical subsurface vertical flow (VF) wetlands treating urban wastewater. These VF wetlands were operated in parallel with unsaturated (UVF) and partially saturated (SVF) configurations. The SVF wetland exhibited almost 2-fold higher total nitrogen removal rate (5 g TN m d) in relation to the UVF wetland (3 g TN m d), as well as a low NO-N accumulation (1 mg L vs. 26 mg L in SVF and UVF wetland effluents, respectively). After 6 months of operation, ammonia oxidizing prokaryotes (AOP) and nitrite oxidizing bacteria (NOB) displayed an important role in both wetlands. Oxygen availability and ammonia limiting conditions promoted shifts on the metabolically active nitrifying community within 'nitrification aggregates' of wetland biofilms. Ammonia oxidizing archaea (AOA) and Nitrospira spp. overcame ammonia oxidizing bacteria (AOB) in the oxic layers of both wetlands. Microbial quantitative and diversity assessments revealed a positive correlation between Nitrobacter and AOA, whereas Nitrospira resulted negatively correlated with Nitrobacter and AOB populations. The denitrifying gene expression was enhanced mainly in the bottom layer of the SVF wetland, in concomitance with the depletion of NO-N from wastewater. Functional gene expression of nitrifying and denitrifying populations combined with the active microbiome diversity brought new insights on the microbial nitrogen-cycling occurring within VF wetland biofilms under different operational conditions.

Addition of Corn Cob in the Free Drainage Zone of Partially Saturated Vertical Wetlands Planted with I. sibirica for Total Nitrogen Removal—A Pilot-Scale Study

“…Consequently, BOD 5 removals were very high, without statistical difference between the PS VF wetlands (p > 0.05), with 91.9% and 92.2% for SI and SII, respectively. Such efficiencies are similar to those reported by [30] (higher than 90%) in a comparative study of PS VF wetlands with four different heights (5,30,45 and 60 cm) of the SZ fed with digested wastewater (resulting in a low BOD 5 /TN) and four corresponding different heights of FDZ (75, 50, 35 and 20 cm), without the addition of a SCS and using oyster shell as filter medium. However, in that study, the BOD 5 concentration in the influent was much higher (230.59 ± 92.57) mg/L than the value in this research, so future research could be conducted to assess the behavior of our systems with higher concentration of BOD 5 .…”

“…Such efficiencies were much higher than the average 62% obtained by [26] in similar PS VF wetlands with the corncob in the SZ; and also higher than the 67% obtained by [22] in a PS VF wetlands with a saturation height of 35 cm planted with Phragmites australis and treating urban wastewater without the addition of an external source of carbon. In addition, [5] reported a lower TSS efficiency (74.3%) in comparison to that obtained in this study, in a pilot-scale PS VF wetland with a similar height of the SZ (35 cm) and without the addition of a solid carbon source. These findings demonstrate that the aerobic conditions in the FDZ diminished the release of suspended solids from the corncob, preventing an increase in the concentrations of TSS in the effluents.…”

“…Nitrification-denitrification is considered as the most effective pathways to remove total nitrogen (TN) from wastewater with different wastewater treatment technologies such as treatment wetlands (TWs) [3]. Nitrification is a two-step process by which autotrophic ammonia-oxidizing bacteria (AOB) and archaea (AOA) oxidize NH 4 + to NO 2 − through the ammonia monooxygenase (AMO) enzyme [4], followed by nitrite-oxidizing bacteria (NOB) that oxidize NO 2 − to NO 3 − via the nitrite oxidoreductase (NXR) enzyme [5], under aerobic conditions [6,7]. Although, recently it was discovered that some bacteria, members of the genus Nitrospira, are capable to perform a complete nitrification; this kind of bacteria are currently called COMAMMOX (complete ammonia oxidizer) [8,9].…”

Removal of High-Strength Ammonia Nitrogen in Biofilters: Nitrifying Bacterial Community Compositions and Their Effects on Nitrogen Transformation

“…Nitrobacter was the dominant NOB in the system because the low NO 2 − -N concentration at the inflow provided a selective advantage for Nitrobacter. This finding, which was similar to that reported in previous studies [6,37], revealed that Nitrobacter was the dominant NOB in activated sludge treated with high-N wastewater. Furthermore, in this CFM-DAS system from April to September, AOA and AOB were more sensitive to temperature than NOB.…”

Reverse transcriptase enzyme and priming strategy affect quantification and diversity of environmental transcripts

“…In environmental microbiology it is an invaluable approach to further link microbial activity, via gene expression, to microbial and ecosystem processes, compared to DNA approaches alone (Smith and Osborn, ; Saleh‐Lakha et al ., ; Gadkar and Filion, ). As a result the approach has been used to quantify transcripts to distinguish different pathways of the nitrogen cycle in sediments (Smith et al ., ; Santoro et al ., ; Zheng et al ., ; Damashek et al ., ; Duff et al ., ; Santos et al ., ; Zhang et al ., ), soil (Leininger et al ., ; Graham et al ., ; Wang et al ., ; Li et al ., ; Pierre et al ., ), water column (Santoro et al ., ; Kapoor et al ., ; Tolar et al ., ; Posman et al ., ; Feng et al ., ; Gonçalves et al ., ; Liu et al ., ; Christiansen et al ., ) and other microbial processes including water treatment (Botes et al ., ; Gadkar and Filion, ; Wang et al ., ; Pelissari et al ., , ) and bioremediation (Yergeau et al ., ; Marzorati et al ., 2010; Gadkar and Filion, ). In addition to this, cDNA from mRNA or rRNA can undergo PCR for amplicon sequencing to reveal actively transcribing organisms within the environment (Duff et al ., ; Zhang et al ., ; Cholet et al ., ).…”