Phosphorus Removal In Constructed Wetlands Research Articles

Synergistic simultaneous nitrification-endogenous denitrification and EBPR for advanced nitrogen and phosphorus removal in constructed wetlands

• Achieving EBPR with high phosphorus removal performance in CWs. • SNED was dominant nitrogen removal pathway in EBPR-CW without specific control. • Coordination of nitrifiers, APAOs, DPAOs and DGAOs facilitated N and P removal. • Average removal efficiency of PO 4 3 - -P and TN were 92.68% and 96.21%, respectively. This study assessed the feasibility of achieving phosphorus removal through enhanced biological phosphorus removal (EBPR) in an intermittent aeration constructed wetland (CW). The results showed that within just 3 weeks, a polyphosphate-accumulating organisms (PAOs)-enriched biofilm was successfully established in the CW by integrating a pre-anaerobic stage, intermittent aeration and periodic PO 4 3- -P release strategies. This strategy enabled a high PO 4 3- -P removal efficiency of 92.68% using normal gravel as a substrate. Moreover, simultaneous nitrification-endogenous denitrification (SNED) was found to be the main nitrogen removal pathway in the EBPR-CW without specific control. SNED significantly reduces the demand for oxygen and organic carbon compared with classical nitrification-denitrification, and allowed the system to reach 96.21% total nitrogen (TN) removal even under carbon limiting conditions. With control experiment, EBPR combined with SNED in CWs improved the phosphorus and nitrogen removal by about 73% and 48%, respectively, compared with normal nitrification-denitrification and media storage-based nitrogen and phosphorus removal processes. Based on stoichiometric analysis, 71.25% of PO 4 3- -P was removed by aerobic PAOs (APAOs), with 27.50% removed by DPAO Ni (denitrifying PAOs using nitrite as electron acceptor) and 1.25% removed by DPAO Na (denitrifying PAOs using nitrate as electron acceptor). DGAOs were the main organisms providing nitrite to DPAOs. Overall, our results demonstrate a novel approach to combine SNED with EBPR for advanced nitrogen and phosphorus removal in CWs.

Review: recent developments of substrates for nitrogen and phosphorus removal in CWs treating municipal wastewater.

Substrates are the main factor influencing the performance of constructed wetlands (CWs), and especially play an important role in enhancing the removal of nitrogen and phosphorus from CWs. In the recent 10years, based on the investigation of emerged substrates used in CWs, this paper summarizes the removal efficiency and mechanism of nitrogen and phosphorus by a single substrate in detail. The simultaneous removal efficiency of nitrogen and phosphorus by different combined substrates is emphatically analyzed. Among them, the reuse of industrial and agricultural wastes as water treatment substrates is recommended due to the efficient pollutant removal efficiency and the principle of waste minimization, also more studies on the environmental impact and risk assessment of the application, and the subsequent disposal of saturated substrates are needed. This work serves as a basis for future screening and development of substrates utilized in CWs, which is helpful to enhance the synchronous removal of nitrogen and phosphorus, as well as improve the sustainability of substrates and CWs. Moreover, further studies on the interaction between different types of substrates in the wetland system are desperately needed.

Long-term effects of silver nanoparticles on performance of phosphorus removal in a laboratory-scale vertical flow constructed wetland

Silver nanoparticles (AgNPs) have been widely used in many fields, which raised concerns about potential threats to biological sewage treatment systems. In this study, the phosphorus removal performance, enzymatic activity and microbial population dynamics in constructed wetlands (CWs) were evaluated under a long-term exposure to AgNPs (0, 50, and 200 μg/L) for 450 days. Results have shown that AgNPs inhibited the phosphorus removal efficiency in a short-term exposure, whereas caused no obviously negative effects from a long-term perspective. Moreover, in the coexisting CW system of AgNPs and phosphorus, competition exhibited in the initial exposure phase, however, cooperation between them was observed in later phase. Enzymatic activity of acid-phosphatase at the moderate temperature (10–20°C) was visibly higher than that at the high temperature (20–30°C) and CWs with AgNPs addition had no appreciable differences compared with the control. High-throughput sequencing results indicated that the microbial richness, diversity and composition of CWs were distinctly affected with the extension of exposure time at different AgNPs levels. However, the phosphorus removal performance of CWs did not decline with the decrease of polyphosphate accumulating organisms (PAOs), which also confirmed that adsorption precipitation was the main way of phosphorus removal in CWs. The study suggested that AgNPs and phosphorus could be removed synergistically in the coexistence system. This work has some reference for evaluating the influences of AgNPs on the phosphorus removal and the interrelation between them in CWs.

Phosphorus removal from lagoon-pretreated swine wastewater by pilot-scale surface flow constructed wetlands planted with Myriophyllum aquaticum

Although constructed wetlands (CWs) are used as one relatively low-cost technology for livestock wastewater treatment, the improvement of phosphorus removal in CWs is urgently needed. In this study, a three-stage pilot-scale CW system consisting of three surface flow CWs (SFCWs; CW1, CW2, and CW3) in series from inlet to outlet was constructed to treat swine wastewater (SW) from a lagoon. The CWs were planted with Myriophyllum aquaticum. Considering different inlet loading rates, three strengths of swine wastewater (low: 33% SW, medium: 66% SW, and high: 100% SW) were fed to the CW system to determine total phosphorus (TP) removal efficiency and clarify the important role of plant harvest. Results from the period 2014–2016 indicate that the three-stage CW system had mean TP cumulative removal efficiencies and removal rates of 78.2–89.8% and 0.412–0.779gm−2d−1 respectively, under different inlet loading rates. The TP removal efficiency and removal rate constant had temporal variations, which depended on temperature condition and the annual growth pattern of M. aquaticum. The harvested phosphorus mass was 15.1–40.9gm−2yr−1 in the CWs except for CW1 with high strength SW, and contributed 22.5–59.6% of TP mass removal rate by the SFCWs. The TP removal was mainly by adsorption and precipitation in the substrate in CW1 but by uptake and multiple harvests of M. aquaticum in CW2 and CW3. The results suggest the three-stage CW system planted with M. aquaticum is suited for removing high TP concentrations from swine wastewater with a high removal efficiency. However, TP removal in high strength SW amounted to 70.1±23.3%, and the outflow concentration of 17.0±14.9mgL−1 was still high. Optimal loading rates for high strength SW still need to be investigated for the CW system presented here.

Study of oyster shell as a potential substrate for constructed wetlands

We tested the suitability of oyster shell (OS) as a substrate for phosphorus removal in constructed wetlands (CWs) treating swine wastewater. OS is proven to have a significant phosphorus adsorption capacity; significant phosphorus removal was achieved in vertical subsurface flow constructed wetlands (VSSFs) that were filled with OS and used to treat swine wastewater. In the VSSF system, OS adsorption and precipitation played the greatest role in phosphorus removal, and the phosphorus distribution in the substrate layers was attributed to the vertical flow state of wastewater in the system. Ca–P was the predominant form of phosphorus in the system. Overall, the study results showed that OS could be used for phosphorus removal in CWs. OS also allowed for reuse of a waste substance, making the overall system more environmentally friendly.

Study of oyster shell as a potential substrate for constructed wetlands

We tested the suitability of oyster shell (OS) as a substrate for phosphorus removal in constructed wetlands (CWs) treating swine wastewater. OS is proven to have a significant phosphorus adsorption capacity; significant phosphorus removal was achieved in vertical subsurface flow constructed wetlands (VSSFs) that were filled with OS and used to treat swine wastewater. In the VSSF system, OS adsorption and precipitation played the greatest role in phosphorus removal, and the phosphorus distribution in the substrate layers was attributed to the vertical flow state of wastewater in the system. Ca-P was the predominant form of phosphorus in the system. Overall, the study results showed that OS could be used for phosphorus removal in CWs. OS also allowed for reuse of a waste substance, making the overall system more environmentally friendly.