Comparison of first-order kinetic models for sewage treatment in horizontal subsurface-flow constructed wetlands

Wastewater treatment in tropical, vertical up-flow constructed wetlands with selected macrophytes species: A preliminary analysis

The aim of this study was to investigate the growth characteristics of different local macrophyte species (n = 7) capable of growing in untreated coffee wastewater, select the dominant species for use in mesocosms, to study the efficacy of three major species in three replications (3 x 3) in improving the physicochemical characteristics of coffee wet mill wastewater, and to assess the contribution of macrophyte biomass to nutrient sequestration in the constructed wetlands. The current study showed that Polygonumhydropiperoides(PH), Chrysopogonzizanioides (CZ), and Cyperusexaltatus(CE) can sustain water logging and partially saturated conditions. The conducted wetland experiments pointed out the feasibility of VUFCW technology in ameliorating the impurities in wet coffee processing mills wastewater. Each of the three plant species has a peculiar ability to trap potential impurities. Cyperusexaltatus, for instance, is significantly efficient (α < 0.05) in reducing turbidity, minimizing PO4 3- and NO3 -, and sequestrating it in the biomass as compared with the other two macrophytes. Polygonumhydropiperoides is good at improving DO; and Chrysopogonzizanioides is good at pH, EC, and TDS reduction. Therefore, the most effective constructed wetland can be designed by combining the three macrophytes vitalizing the ultimate potential of each of them in the system. However further studies and extended data collections are needed to ensure the enhanced quality of wastewater through the plant based treatment methods.

Impact of water depth and flow velocity on organic matter removal and nitrogen cycling in floating constructed wetlands

The configuration of water depth (WD) and flow velocity (FV) in floating constructed wetlands (FCWs) reflects the complex interactions between hydraulic conditions and wastewater treatment performance. Properly configuring hydraulic conditions can optimize performance. This study explored the removal and degradation of organic matter and nitrogen (N) in FCWs with three different WDs (50 cm (SD), 70 cm (MD), and 95 cm (DD)) under four FV conditions (0, 0.3, 1.0, and 1.5 m/d). It also analyzed the regulatory effects of hydraulic conditions on microbial community structure to provide new insights for configuring hydraulic conditions in FCWs. The results indicate that variations in WD and FV do not significantly affect COD removal (p > 0.05), with removal efficiency (RE) consistently reaching 90 % across all conditions. However, hydraulic conditions do influence the degradation rate (k) of COD, with increased FV enhancing the k in MD and DD. In contrast, WD significantly impacts the removal of NH4+-N (p < 0.05), with RE in SD exceeding 80 % across all four FVs. The primary reason is that increased WD reduced the abundance of nitrifying bacteria (Nitrosomonas and Nitrospira) and functional genes (hao and pmoABC-amoABC). Meanwhile, increased WD and FV significantly enriched the denitrifying bacteria genera (such as Massilia, Bacillus, Ensifer, and Rhodobacter) and certain functional genes (nap and nir), favoring the denitrification process and enhancing the dissimilatory nitrate reduction to ammonium (DNRA) process. Furthermore, microbial community diversity, richness, and the number of operational taxonomic units (OTUs) were highest in SD, but decreased with increased WD. This is mainly related to changes in oxygen (O2) transmission and nutrient concentration. These findings help us understand the mechanisms by which hydraulic regulation affects the removal of organic matter and N in FCWs. They also propose potential solutions from a hydraulics perspective to enhance N removal.

Exploring the Removal of Organic Matter in Constructed Wetlands Using First Order Kinetic Models

Mathematical models have become an excellent tool to evaluate the characteristics and performance of Constructed Wetlands (CWs). They help to characterize the dynamics of pollutant removal in these systems. The aim of this research was to evaluate the kinetics of organic matter removal in CWs using two models: (i) the conventional first order model and (ii) the sigmoidal or k-n model. For this purpose, data from 41 CWs where domestic sewage is treated were used. The cluster analysis was performed to identify similar groups of CWs based on the estimation of model coefficients. According to the results obtained, the model that provides a better fit for the removal of organic matter in CWs is the sigmoidal-type. However, its “n” coefficient, which would represent an increase in resistance to degradation, remains a not totally explained variable. The sigmoidal or k-n model is promising, presenting good adjustment indices.