Performance evaluation of wastewater treatment using horizontal subsurface flow constructed wetlands optimized by micro-aeration and substrate selection

Mechanism of Iris sibirica and aeration combination on promoting the water purification performance of constructed wetland under low temperature

Temperature is an important factor affecting the water purification performance of constructed wetland (CW). In the previous study, the combined measures of Iris sibirica and aeration at the bottom of the first quarter filtration chamber could improve the pollutant removal capacity of CW at low temperature. However, the mechanism between the combined measures of Iris sibirica and aeration on enhancing the performance of domestic sewage treatment is unclear. Our study aims to provide scientific validation for the combined measure through monitoring the concentrations of dissolved oxygen (DO), chemical oxygen demand (CODCr), ammonia nitrogen (NH4+-N), and total nitrogen (TN) along the water flow pathway of the CW and measuring the superoxide dismutase (SOD) activities of the plants and the abundance of nitrogen cycle-related microbial functional genes in the substrates of CW to explore the mechanism of combined measures promoting the removal efficiency of the CW under low-temperature stress. Results showed that aerating at the bottom of the first quarter filtration chamber increased DO concentration in the front part of the CW, which benefited the aerobic removal of pollutants and the activities of microorganisms, and the removal CODCr and NH4+-N occurred mainly in the front part of the CW. SOD activities showed that I. sibirica had better resistance to low temperature than Canna indica did. The combined measures of I. sibirica and aeration activated the activities of microorganisms, increased the abundance of the denitrification process genes along the water flow pathway and formed a clear nitrification-denitrification zone in the CW, thus promoted the nitrogen removal efficiency at low temperature. Therefore, this study confirmed the feasibility of the combined measures from a mechanistic perspective.

The Interaction Effects of Aeration and Plant on the Purification Performance of Horizontal Subsurface Flow Constructed Wetland

Aeration and plants exhibit influence on the water purification performance in constructed wetlands (CWs). However, the interaction between aeration and plants on enhancing performance of domestic sewage treatment is unclear. Our study aims to optimize the combination of aeration position and plant species, promoting the extensive and effective application of CWs. Herein, six horizontal subsurface flow (HSSF) CWs small scale plots were established and divided into two groups according to the plant (i.e., Canna indica and Iris sibirica). To adjust the distribution of dissolved oxygen (DO) in CWs, each group had three plots of HSSF CWs. One plot was aerated at the bottom of the first quarter of the filtration chamber, one plot was aerated at the bottom of the inflow chamber, and the remaining plot was not aerated as a control. Results showed that aeration at the bottom of the first quarter filtration chamber could contribute to the highest removal efficiency of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and total nitrogen (TN). The COD, NH4+-N, and TN removal percentages decreased with the drop in temperature. However, the plot aerated at the bottom of the first quarter filtration chamber with I. sibirica exhibited the best average CODCr, NH4+-N and TN removal percentages in both the warm season (83.6%, 82.7% and 76.8%) and the cool season (66.3%, 44.1% and 43.8%). Therefore, this study indicated that the combination of aerating at the bottom of the first quarter filtration chamber and planting with I. sibirica in the HSSF CWs would be a promising way forward for wastewater treatment, especially in low temperature seasons.

Boosting pharmaceutical removal through aeration in constructed wetlands

This work evaluated the removal efficiency of 13 wastewater-borne pharmaceuticals in a pilot constructed wetland (CW) operated under different aeration strategies (no aeration, intermittent and continuous). Aeration improved the removal of conventional wastewater parameters and the targeted micropollutants, compared to the non-aerated treatment. Reduction of chemical oxygen demand (COD) and total nitrogen (TN) was slightly higher applying intermittent aeration than applying continuous aeration, the opposite was observed for the investigated pharmaceuticals. Seven targeted compounds were found in influent wastewater, and five of them (acetaminophen, diclofenac, ketoprofen, bezafibrate and gemfibrozil) were efficiently removed (> 83%) in the aerated systems. The overall risk of the investigated samples against aquatic ecosystems was moderate, decreasing in the order influent > no aeration > intermittent aeration > continuous aeration, based on the hazard quotient approach. Lorazepam, diclofenac and ketoprofen were the pharmaceuticals that could contribute the most to this potential environmental impact of the CW effluents after discharge. To the authors' knowledge this is the first sound study on the removal and fate of ketoprofen, bezafibrate, and lorazepam in aerated CWs, and provides additional evidence on the removal and fate of acetaminophen, diclofenac, gemfibrozil, and carbamazepine in this type of bioremediation systems at pilot plant scale.

Preparation of ceramsite from municipal sludge and its application in water treatment: A review

Municipal sludge is a solid waste material, and resource utilization is the optimal way to dispose of this material. The amount of municipal sludge produced in China is large, and it can be used in the preparation of ceramsite. The content of Al₂O₃ in drinking water treatment sludge is significantly higher than that in wastewater treatment sludge, while the content of K₂O, Na₂O and MgO in the two kinds of sludge is similar. When sludge is used to prepare ceramsite, the amount of sludge in most raw materials for ceramsite is less than 50%. The bulk density of the prepared sludge ceramsite is less than 1000 kg m^-3, and the highest water absorption rate is close to 40%. The leaching content of heavy metals in municipal sludge-based ceramsite is within the standard health safety limit, and heavy metals are better stabilized. The fitting effect of the pseudo-second-order kinetic equation of the dynamic adsorption of sludge ceramsite is obviously better than that of the pseudo-first-order kinetic equation. Sludge ceramsite used in bio-filter media and constructed wetland (CW) substrates is good able to purify wastewater. In the future, the preparation method of municipal sludge ceramsite and purification research of CW substrates based on sludge ceramsite need to be further improved.

Nutrient Removal Process and Cathodic Microbial Community Composition in Integrated Vertical-Flow Constructed Wetland - Microbial Fuel Cells Filled With Different Substrates

An integrated vertical-flow constructed wetland-microbial fuel cell system (CW-MFC), consisting of an up-flow chamber and a down-flow chamber, was constructed to treat synthetic sewage wastewater. The performance of CW-MFCs filled with different substrates [i.e., ceramsite (CM-A), quartz (CM-B), and zeolite (CM-C) granules] under various hydraulic retention times (HRTs, 7.6, 4.0, and 2.8 d) was evaluated. Efficient and stable nitrogen (N) and phosphorus (P) removals were observed in CM-A under different HRTs, while the voltage outputs of the CW-MFCs was greatly reduced as the HRTs decreased. With an HRT of 2.8 d, the ammonium (NH4 +-N) and orthophosphate (PO4 3--P) removal efficiencies in CM-A were as high as 93.8 and 99.6%, respectively. Bacterial community analysis indicates that the N removal in the cathode area of CM-A could potentially benefit from the appearance of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and relatively high abundance of denitrifiers involved in simultaneous nitrification and denitrification (e.g., Hydrogenophaga, Zoogloea, and Dechloromonas) and denitrifying sulfide removal (e.g., Thauera). Additionally, the difference in N removal efficiency among the CW-MFCs could be partly explained by higher iron (Fe) content in milled ceramsite granules and higher abundance of denitrifiers with nitrate reduction and ferrous ions oxidation capabilities in CM-A compared with that in CM-B and CM-C. Efficient PO4 3--P removal in CM-A was mainly ascribed to substrate adsorption and denitrifying phosphorus (P) removal. Concerning the substantial purification performance in CM-A, ceramsite granules could be used to improve the nutrient removal efficiency in integrated vertical-flow CW-MFC.

Operational Performances and Enzymatic Activities for Eutrophic Water Treatment by Vertical-Flow and Horizontal-Flow Constructed Wetlands

In this study, pilot-scale vertical-flow constructed wetland (VFCW) and horizontal-flow constructed wetland (HFCW) were constructed to treat eutrophic water, and dissolved oxygen (DO) distributions, decontamination performances and key enzymes activities were compared under different influent loads. The influent load increase caused reductions of DO levels and removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), NH4+−N and organic nitrogen, but it had no remarkable effect on the removal of NO3−−N and total phosphorus (TP). The interior DO concentrations of VFCW were higher than those of HFCW, indicating a vertical hydraulic flow pattern was more conducive to atmospheric reoxygenation. The VFCW and HFCW ecosystems possessed comparable removal capacities for TN, NO3−−N and TP. VFCW had a remarkable superiority for COD and organic nitrogen degradation, but its effluent NH4+−N concentration was higher, indicating the NH4+−N produced from organic nitrogen degradation was not effectively further removed in the VFCW system. The activities of protease, urease and phosphatase declined with the increasing depth of substrate layers, and they were positively correlated with DO concentrations. The enzymatic activities of VFCW were significantly higher than that of HFCW in the upper layers. Taken together, VFCW and HFCW presented a certain difference in operational properties due to the different hydraulic flow patterns.

Effect of packing substrates on the purification of municipal wastewater treatment plant effluent

The effluents of municipal wastewater treatment plant (WWTP) contain excessive nitrogen and phosphorus compared with the concentration in rivers or lakes. To reduce the pollutant load placed on aqueous environments, constructed wetland (CW) technology has been widely applied to advanced wastewater treatment. Packing substrates in CW could remove various pollutants. Steel slag, yellow earth, kaolin, volcanic rock, anthracite, and ceramsite could effectively remove phosphorus (P); volcanic rock, ceramsite, zeolite, yellow earth, manganese sand, and activated carbon have an affinity for ammonia nitrogen (NH₄⁺-N). After 24 h reactions with the WWTP standard 1B synthetic wastewater, four packing substrates, i.e., volcanic rock and anthracite (1:1), volcanic rock and yellow earth (2:1), zeolite and yellow earth (2:1), and manganese sand and activated carbon (1:3), could remove over 56% and 30% of NH₄⁺-N and phosphorus respectively. In addition, anthracite and volcanic rock (1:3), anthracite and activated carbon (1:40), anthracite and manganese sand (1:5), and anthracite and zeolite (1:4) effectively purified NH₄⁺-N and phosphorus in secondary WWTP effluent, with removal efficiency exceeding 39% and 27%, respectively. A sequential experiment was performed to optimize packing substrates ratios in CW with volcanic rock and anthracite, ceramsite and yellow earth, and manganese sand and activated carbon. When the quantity of the substrate was doubled, most packing substrates adsorb more than 50% phosphorus and NH₄⁺-N of the standard 1B WWTP synthetic wastewater. Considering the removal efficiency of packing substrates on phosphorus and NH₄⁺-N, it is suggested that manganese sand and activated carbon (1:3), volcanic rock and anthracite (2:1), and yellow earth are appropriate substrates for CW in WWTP effluent advanced treatment.

Recent Advances in the Application, Design, and Operations & Maintenance of Aerated Treatment Wetlands

This paper outlines recent advances in the design, application, and operations and maintenance (O&M) of aerated treatment wetland systems as well as current research trends. We provide the first-ever comprehensive estimate of the number and geographical distribution of aerated treatment wetlands worldwide and review new developments in aerated wetland design and application. This paper also presents and discusses first-hand experiences and challenges with the O&M of full-scale aerated treatment wetland systems, which is an important aspect that is currently not well reported in the literature. Knowledge gaps and suggestions for future research on aerated treatment wetlands are provided.

The Improvement of Pollutant Removal in the Ferric-Carbon Micro-Electrolysis Constructed Wetland by Partial Aeration

Subsurface flow constructed wetland (SSFCW) has been applied for wastewater treatment for several decades. In recent years, the combination of ferric-carbon micro-electrolysis (Fe/C-M/E) and SSFCW was proven to be an effective method of multifarious sewage treatment. However, Ferric substrate created a relatively reductive condition, decreased the oxidation efficiency of NH4+-N, and blocked the following denitrification process, which led to the low removal efficiencies of NH4+-N and total nitrogen (TN). In this study, partial aeration was introduced into the ferric-carbon micro-electrolysis SSFCW (Fe/C-M/E CW) system to solve the problem above. The water quality and nitrogen-related functional genes of bacteria on the surface of substrate were measured for mechanism exploration. The results showed that, the removal efficiencies of NH4+-N and total phosphorus (TP) in an aerated Fe/C-M/E CW system were 96.97% ± 6.06% and 84.62% ± 8.47%, much higher than 43.33% ± 11.27% and 60.16% ± 2.95% in the unaerated Fe/C-M/E CW systems. However, the TN removal in Fe/C-M/E CW system was not enhanced by aeration, which could be optimized by extending more anoxic section for denitrification.

The configuration, purification effect and mechanism of intensified constructed wetland for wastewater treatment from the aspect of nitrogen removal: A review

Constructed wetland (CW) for wastewater treatment has attracted increasing attention. In this review, the system configuration optimization, purification effect and general mechanisms of nitrogen removal in CW are systematically summarized and discussed. Ammonia oxidation is a crucial and primary process for total nitrogen (TN) removal in domestic or livestock wastewater treatment. Aeration, waterdrop influent and tidal operation are three main methods to strengthen the oxygen supplement and nitrification process in CW. Aeration significantly increases the ammonia removal rate (almost 100%), followed by the removal of chemical oxygen demand (COD) and TN. Solid carbon source, iron and anode material can be filled as electron donor for the denitrification process. The co-adjustment of oxygen and carbon/electron donor can form different conditions for different nitrogen removal pathways (e.g. the simultaneous nitrification-denitrification, the partial nitrification-denitrification and the anammox process), and achieve the optimal removal of nitrogen.