Performance of a pilot demonstration-scale hybrid constructed wetland system for on-site treatment of polluted urban river water in Northwestern China

Immobile Iron-Rich Particles Promote Arsenic Retention and Regulate Arsenic Biotransformation in Treatment Wetlands

Remediation of arsenic (As)-contaminated wastewater by treatment wetlands (TWs) remains a technological challenge due to the low As adsorption capacity of wetland substrates and the release of adsorbed As to pore water. This study investigated the feasibility of using immobile iron-rich particles (IIRP) to promote As retention and to regulate As biotransformation in TWs. Iron-rich particles prepared were immobilized in the interspace of a gravel substrate. TWs with IIRP amendment (IIRP-TWs) achieved a stable As removal efficiency of 63 ± 4% over 300 days, while no As removal or release was observed in TWs without IIRP after 180 days of continuous operation. IIRP amendment provided additional adsorption sites and increased the stability of adsorbed As due to the strong binding affinity between As and Fe oxides. Microbially mediated As(III) oxidation was intensified by iron-rich particles in the anaerobic bottom layer of IIRP-TWs. Myxococcus and Fimbriimonadaceae were identified as As(III) oxidizers. Further, metagenomic binning suggested that these two bacterial taxa may have the capability for anaerobic As(III) oxidation. Overall, this study demonstrated that abiotic and biotic effects of IIRP contribute to As retention in TWs and provided insights into the role of IIRP for the remediation of As contamination.

Alterations in microbial community during the remediation of a black-odorous stream by acclimated composite microorganisms

Microbial application is an efficient, economical, and ecofriendly method for remediating black-odorous rivers. In this study, the field treatment effect and microbial community changes were monitored during remediation by the acclimated complex microorganisms of a typical black-odorous stream. After the treatment, the total phosphorus and ammonia contents decreased by 74.0% and 76.3% and the concentrations of dissolved oxygen increased from 1.65 to 4.90 mg/L, indicating the effectiveness of the acclimated composite microorganisms. The proportion of Bacteroidetes decreased significantly by 48.1% and that of Firmicutes increased by 2.23% on average, and the microbial diversity index first increased and then tended to be uniform. Redundancy analysis demonstrated that the pH, dissolved oxygen, and oxidation-reduction potential together determined the composition of the microbial communities (p < 0.05). These findings showed that the acclimated composite microorganisms can effectively remediate the black odor.

Effect of the Matrix Dam in the Paddy Field Drainage Ditch on Water Purification Based on the Physical Model Test

(1) Setting a matrix dam in the paddy field drainage ditch has been recognized as an effective method to lower the velocity of water discharged from a paddy field in the drainage ditch, which can improve the purification efficiency of the drainage ditch for nitrogen and phosphorus pollutants, but the specific placement and thickness of the matrix dam have not been supported due to the insufficient research results. (2) Three thicknesses of the matrix dam were set in three locations of the physical model of the drainage ditch. By measuring the flow rate and water level in different sections, the optimal layout location and thickness of the matrix dam were determined. (3) When the matrix dam was located in section 1-1, the flow rate from sections A-A to C1-C1 was reduced by 0.159 m/s; when the matrix dam was located in section 2-2, the flow rate was reduced by 0.331 m/s; when the matrix dam was located in section 3-3, the flow rate was reduced by 0.360 m/s. (4) We concluded that the optimal design position of the matrix dam was section 3-3, 9.2 m from the entrance of the water flume, and the optimal design thickness was 0.3 m.

Spatial performance assessment of reed bed filtration in a constructed wetland

Constructed wetlands (CW) are implemented to improve water quality through filtration by plants (macrophytes), which sequester nutrients and contaminants. Macrophyte beds in CWs reduce the speed of water flow, aiming to improve the water quality by sedimentation and filtration with increasing distance from the inflow. Few studies have assessed spatial distribution and accumulation concentrations of nutrients and contaminants in CW macrophytes as a performance indicator for wetland functionality and management. Macrophytes and water were analysed for nutrient and contaminant accumulation in-situ at a stormwater-fed CW and water remediation site in South Australia. During the austral summer, macrophytes were sampled at 36 sites and water at 46 sites selected by a systematic GIS produced grid covering the entire wetland, which determined distance from the inflow for each site. A total of 144 Schoenoplectus validus (stems and roots) macrophyte samples (i.e. carbon-C, nitrogen-N, Trace elements) and 183 water samples (i.e. total suspended solids-TSS, total nitrogen-TN, total carbon-TC, nitrate-NO₃^-/ nitrite-NO₂^- and ammonia-NH₄⁺) were analysed. Concentrations of water chemistry parameters that significantly increased with distance away from inflow included; TC (P = 0.0008), TN (P = 0.0001), and NH₄⁺ (P = 0.0001), while there was significant decrease in TSS (P = 0.0001). The macrophyte S. validus significantly decreased in height (P = 0.0001) and biomass (P = 0.03) with distance from the inflow. Spatial mapping of nutrients and contaminants with distance from inflow identified increasing TC and C characteristics from inflow to outflow and identified where TSS were removed from the water column. Through this spatial assessment approach of the Oaklands CW, management has identified problem areas with flow regimes that require further investigation to enhance macrophyte water filtration performance which can be used in CWs elsewhere in the world.

Waste Brick as Constructed Wetland Fillers to Treat the Tail Water of Sewage Treatment Plant

Adopting the concept of "using waste to treat waste", the waste bricks will be used for constructed wetland filling. Integrated vertical-flow constructed wetland (IVCW) studied on the purification effect in influent water under three hydraulic loads (0.15, 0.25, 0.35 m/day). The results show that the waste bricks can be used as the carrier for the growth of the system biofilm, and have positive effects on the removal of pollutants in the influent water. Under three different hydraulic load conditions, the vertical flow of CWs can significantly reduce the load of water intake. In the low hydraulic load condition of 0.15 m/day, the average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total nitrogen (TN), and total phosphorus (TP) can reach 66.52%, 72.10%, 56.53% and 91.55% in this system, respectively. The influent pool on removal efficiency of pollutants was obviously higher than that of the upper pool, especially in the inlet surface 0-30 cm ranges. This research has achieved the effect of using "waste" to treat wastewater, which has strong practical significance and popularization value.

Nitrifying activity and ammonia-oxidizing microorganisms in a constructed wetland treating polluted surface water

Ammonia oxidation, performed by both ammonia oxidizing bacteria (AOB) and archaea (AOA), is an important step for nitrogen removal in constructed wetlands (CWs). However, little is known about the distribution of these ammonia oxidizing organisms in CWs and the associated wetland environmental variables. Their relative importance to nitrification in CWs remains still controversial. The present study investigated the seasonal dynamics of AOA and AOB communities in a free water surface flow CW (FWSF-CW) used to ameliorate the quality of polluted river water. Strong seasonality effects on potential nitrification rate (PNR) and the abundance, richness, diversity and structure of AOA and AOB communities were observed in the river water treatment FWSF-CW. PNR was positively correlated to AOB abundance. AOB (6.76×10⁵-6.01×10⁷ bacterial amoA gene copies per gram dry sediment/soil) tended to be much more abundant than AOA (from below quantitative PCR detection limit to 9.62×10⁶ archaeal amoA gene copies per gram dry sediment/soil). Both AOA and AOB abundance were regulated by the levels of nitrogen, phosphorus and organic carbon. Different wetland environmental variables determined the diversity and structure of AOA and AOB communities. Wetland AOA communities were mainly composed of unknown species and Nitrosopumilus-like organisms, while AOB communities were mainly represented by both Nitrosospira and Nitrosomonas.

Sequential Sedimentation-Biofiltration System for the purification of a small urban river (the Sokolowka, Lodz) supplied by stormwater

The study analyses the efficiency of a Sequentional Sedimentation-Biofiltration System (SSBS) built on the Sokolowka river in Lodz (Poland). It was constructed to purify a small urban river whose hydrological regime is dominated by stormwater and meltwater. The SSBS was constructed on a limited area as multi-zone constructed wetlands. The SSBS consists of three zones: sedimentation zone with structures added to improve sedimentation, a geochemical barrier made of limestone deposit and biofiltration zone. The purification processes of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TP) and other nutrients: phosphates (PO₄^3-), ammonium (NH₄⁺) and nitrates (NO₃^-) of the SSBS were analyzed. Chloride (Cl^-) reduction was investigated. Monitoring conducted in the first two hydrological years after construction indicated that the SSBS removed 61.4% of TSS, 37.3% of TP, 30.4% of PO₄^3-, 46.1% of TN, 2.8% of NH4+, 44.8% of NO₃^- and 64.0% of Cl^-. The sedimentation zone played a key role in removing TSS and nutrients. The geochemical barrier and biofiltration zone each significantly improved overall efficiency by 4-10% for TSS, PO₄^3-, TN, NO₃^- and Cl^-. Although the system reduced the concentration of chloride, further studies are needed to determine the circulation of Cl^- in constructed wetlands (CWs), and to assess its impact on purification processes.