Abstract
The quality of micropolluted water is unstable and its substrate concentration fluctuates greatly. The goal is to predict the concentration effect on the treatment of nitrogen in a river with an actual low C/N ratio for the proposed full-scale Xiaoyi River estuary wetland, so that the wetland project can operate stably and perform the water purification function effectively in the long term. Two pilot-scale multistage constructed wetland–pond (MCWP) systems (S1 and S2, respectively) based on actual engineering with the same “front ecological oxidation ponds, two-stage horizontal subsurface flow constructed wetlands and surface flow constructed wetlands (SFCWs) as the core and postsubmerged plant ponds” as the planned process were constructed to investigate the effect of different influent permanganate indexes (CODMn) and total nitrogen (TN) contents on nitrogen removal from micropolluted river water with a fixed C/N ratio from summer to winter in the field. The results indicate that the TN removal rate in the S1 and S2 systems was significant (19.56% and 34.84%, respectively). During the process of treating this micropolluted water with a fixed C/N ratio, the influent of S2 with a higher CODMn concentration was conducive to the removal of TN. The TN removal rate in S2 was significantly affected by the daily highest temperature. There was significant nitrogen removal efficiency in the SFCWs. The C/N ratio was a major determinant influencing the nitrogen removal rate in the SFCWs. The organic matter release phenomenon in SFCWs with high-density planting played an essential role in alleviating the lack of carbon sources in the influent. This research strongly supports the rule that there is seasonal nitrogen removal in the MCWPs under different influent substrate concentrations, which is of guiding significance for practical engineering.
Highlights
With an increasing number of human activities, aquatic environments around the world, such as groundwater, rivers, lakes, and other surface water, have been polluted to varying degrees [1]
Mn (Table 2), we found that horizontal subsurface flow constructed wetland (HSCW) had a better organic matter removal the two multistage constructed wetland–pond (MCWP) on CODMn (Table 2), we found that HSCWs had a better organic matter effect than other units during operation, indicating that the majority of C of removal effect thantreatment other treatment units during operation, indicating that the majority sources were consumed by heterotrophic microorganisms in the aerobic area of
The results suggest that the performance of total nitrogen (TN) from the surface flow constructed wetlands (SFCWs) of S1 and S2 is better during the early and later stages removal performance of TN from the SFCW of S1 and S2 is better during the early and of operation, which is likely relevant to the release of organic matter from plant tissue later stages of operation, which is likely relevant to the release of organic matter from to promote the denitrification of microorganisms
Summary
With an increasing number of human activities, aquatic environments around the world, such as groundwater, rivers, lakes, and other surface water, have been polluted to varying degrees [1]. Sustainability 2021, 13, 12456 farming practices, nitrogen-containing pollutants that cannot be effectively controlled during industrial and agricultural production will enter nearby surface water bodies along with sewage or rainwater. Micropolluted water generally has the characteristics of a relatively low chemical oxygen demand (COD) (
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