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

Constructed wetlands for wastewater treatment and reuse: Two decades of experience from China

Constructed wetlands (CWs) can be used for water purification and ecological restoration through the synergistic effects of substrates, aquatic plants, and microorganisms. This study explored a bibliometric approach to quantitatively evaluate the recent research progress and applications of CWs in China by synthetically analyzing publication output characteristics, research hotspots and quantified China's unique contributions to global CW applications. The results indicated that the number of papers published in the field of CWs has shown an overall upward trend in the past two decades, and the research hotspots mainly focus on the nitrogen and phosphorus removal, microbial community. China has actively supported the investigation and application of CWs for wastewater treatment and reuse. More than 40 species of plants and over 30 types of substrates have been employed in CWs for treating different types of wastewater, such as domestic sewage, industrial effluents, river water, and drinking water. Several successful case studies of full-scale CWs have been selected and summarized to highlight the extensive application of CWs in China and provided a CW localized design framework.

Intensifying intermittent aeration for optimizing nutrient and hormone removal in vertical-flow constructed wetlands filled with aerated concrete

Operational strategies have been applied in constructed wetlands to optimize the removal of nutrients and hormones that are still a concern in wastewater treatment. The strategy of intensifying intermittent aeration was investigated in two microcosm-scale vertical-flow constructed wetlands (VFCWs) planted with Eichhornia crassipes onto autoclaved aerated concrete (AC) in the removal of nutrients, estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2). CW-1 (2.4 LO2 min-1) and CW-2 (1.4 LO2 min-1) were fed with synthetic wastewater in sequencing-batch mode (cycles 48-48-72 h) and intermittently aerated for 1 h, followed by 7 h without aeration for 377 days. Combined with the intensification strategy, the use of planted free-floating macrophytes and concrete-based material (emergent) as filtering media stand out as the innovation and originality aspects of this study. Despite the hormone addition, intensifying aeration enhanced the efficiencies since CW-1 achieved the highest removals with 91% COD, 77% TN, 74% TAN, 60% nitrate, and 97% TP in Stage I (no hormone addition) and 90% COD, 80% TN, 93% TAN, 63% nitrate, and 82% TP in Stage II (with hormone addition). CW-1 achieved the highest removal efficiencies of E1 (84%), E2 (95%), and EE2 (73%). Conversely, the efficiencies decreased under the lower aeration rate (in CW-2) for all parameters. Macrophyte uptake and adsorption stood out for TN (>60.25%) and TP (>27.6%) removal as the main mechanisms in the VFCWs. The characteristics of AC favored ion exchange and precipitation, reinforcing the potential of this material as filtering media in VFCWs. Intensification of intermittent aeration combined with hormone addition diverse and riched the microbial community with the presence of Thauera, Lentimicrobium (denitrification), Candidatus Accumulibacter (phosphorus removal), Pseudomonas, Fusibacter, and Azoarcus (EE2 degradation). Intensifying intermittent aeration was an important strategy to enhance the simultaneous removal of nutrients and hormones in the VFCWs under the evaluated operational conditions.

Application of New Filling Material Based on Combined Heat and Power Waste for Sewage Treatment in Constructed Wetlands

The filling of constructed wetlands (CWs) affects the efficiency of sewage treatment and proper operation. Mineral aggregates are most often used as filling materials. Significant environmental burdens from mineral mining operations justify the search for waste fill. This study aimed to determine the possibility of increasing the efficiency of CW by using a Certyd aggregate as a new filling. Certyd is produced in the sintering process of coal ash, a waste from combined heat and power (CHP) plant operation. Comprehensive two-year studies were conducted using two real-scale subsurface vertical flow (SS VF) CWs supplied with domestic sewage. One bed was filled with a Certyd and the other was filled with appropriate fractions of a mineral aggregate. Both beds worked in parallel, and to compare their effectiveness, account seasonality was taken into account. The SS-VF Certyd-filled bed achieved an average efficiency of 88.0% for biological oxygen demand (BOD5), 80.2% for chemical oxygen demand (COD), 80.4% for suspended solids (SSs), 80.2 for ammonia nitrogen (N-NH4), 72.2% for total nitrogen (TN), and 55.3% for total phosphorus (TP), while the gravel-filled bed achieved 84.5%, 77.0%, 86.9%, 74.2%, 69.4%, and 57.8% for the whole research period, respectively. A higher effect of the removed unit load was achieved in the bed filled with Certyd (36.2 g BOD5 m-2 d-1, 50.0 g COD m-2 d-1, 5.88 g SS m-2 d-1, 7.1 g TN m-2 d-1, 7.9 g N-NH4 m-2 d-1, 0.79 g TP m-2 d-1) compared to the gravel-filled bed (34.7 g BOD5 m-2 d-1, 47.0 g COD, 6.35 g SS m-2 d-1, 6.9 g TN m-2 d-1, 7.3 g m-2 d-1 N-NH4, 0.83 g TP m-2 d-1).

Biodegradation and sorption of nutrients and endocrine disruptors in a novel concrete-based substrate in vertical-flow constructed wetlands

Removing phosphorus and endocrine-disruptors (EDC) is still challenging for low-cost sewage treatment systems. This study investigated the efficiency of three vertical-flow constructed wetlands (VFCW) vegetated with Eichhornia crassipes onto red clay (CW-RC), autoclaved aerated concrete (CW-AC), and composite from the chemical activation of autoclaved aerated concrete with white cement (CW-AAC) in the removal of organic matter, nutrients, and estrone, 17β-estradiol, and 17α-ethinylestradiol. The novelty aspect of this study is related to selecting these clay and cementitious-based materials in removing endocrine disruptors and nutrients in VFCW. The subsurface VFCW were operated in sequencing-batch mode (cycles of 48-48-72 h), treating synthetic wastewater for 308 days. The operation consisted of Stages I and II, different by adding EDC in Stage II. The presence of EDC increased the competition for dissolved oxygen (DO) and reduced the active sites available for adsorption, diminishing the removal efficiencies of TKN and TAN and total phosphorus in the systems. CW-RC showed a significant increase in COD removal from 65% to 91%, while CW-AC and CW-AAC maintained stable COD removal (84%-82% and 78%-81%, respectively). Overall, the substrates proved effective in removing EDC, with CW-AC and CW-AAC achieving >60% of removal. Bacteria Candidatus Brocadia and Candidatus Jettenia, responsible for carrying out the Anammox process, were identified in assessing the microbial community structure. According to the mass balance analysis, adsorption is the main mechanism for removing TP in CW-AC and CW-AAC, while other losses were predominant in CW-RC. Conversely, for TN removal, the adsorption is more representative in CW-RC, and the different metabolic routes of microorganisms, biofilm assimilation, and partial ammonia volatilization in CW-AC and CW-AAC. The results suggest that the composite AAC is the most suitable material for enhancing the simultaneous removal of organic matter, nutrients, and EDC in VFCW under the evaluated operational conditions.

Technical structure and influencing factors of nitrogen and phosphorus removal in constructed wetlands

Constructed wetlands purify water quality by synergistically removing nitrogen and phosphorus pollutants from water, among other pollutants such as organic matter through a physical, chemical, and biological composite remediation mechanism formed between plants, fillers, and microorganisms. Compared with large-scale centralized wastewater treatment systems with high cost and energy consumption, the construction and operation costs of artificial wetlands are relatively low, do not require large-scale equipment and high energy consumption treatment processes, and have the characteristics of green, environmental protection, and sustainability. Gradually, constructed wetlands are widely used to treat nitrogen and phosphorus substances in wastewater. Therefore, this article discusses in detail the role and interaction of the main technical structures (plants, microorganisms, and fillers) involved in nitrogen and phosphorus removal in constructed wetlands. At the same time, it analyses the impact of main environmental parameters (such as pH and temperature) and operating conditions (such as hydraulic load and hydraulic retention time, forced ventilation, influent carbon/nitrogen ratio, and feeding patterns) on nitrogen and phosphorus removal in wetland systems, and addresses the problems currently existing in relevant research, the future research directions are prospected in order to provide theoretical references for scholars' research.

Use of sponge iron dosing in baffled subsurface-flow constructed wetlands for treatment of wastewater treatment plant effluents during autumn and winter

Sponge iron (SI) is widely used in water treatment. As effluents from wastewater treatment plant (WWTP) require advanced treatment methodology, three forms of constructed wetlands (CWs): wetlands with sponge iron (SI), copper sulfate modified sponge iron (Cu/SI), and sponge iron coupled with solid carbon sources (C/SI), have been investigated in this paper for the removal effects of organic matter and nutrients in WWTP effluents, and the corresponding mechanisms have been analyzed. The results showed the effect of baffled subsurface-flow constructed wetland (BSFCW) with SI dosing to purify the WWTP effluents after the stable operation. The water flow of this BSFCW is the repeated combination of upward flow and downward flow, which can provide a longer treatment pathway and microbial exposure time. The average removal rates of total inorganic nitrogen (TIN) were 27.80%, 30.17%, and 44.83%, and the average removal rates of chemical oxygen demand (COD) were 19.96%, 23.73%, and 18.38%. The average removal rates of total phosphorus (TP) were 85.94%, 82.14%, and 83.95%. Cu/SI improved the dissolution of iron, C/SI improved denitrification, and a winter indoor temperature retention measure was adopted to increase the effectiveness of wetland treatment during the winter months. After comprehensively analyzing X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and two-dimensional numerical simulation diagrams, a plausible conjecture that microbes use electrons from SI for autotrophic denitrification is presented. Moreover, the stress effect of wetlands dosed with SI on plants decreased stepwise along the course since C/SI used on wetlands had less impact on plant stress.

Distribution coefficients of nitrogen pollutants between water and sediment and their environmental risks in Lingang hybrid constructed wetland fed by industrial tailwater, Tianjin, China

Exploring the fate of nitrogen pollutants in constructed wetlands (CWs) fed by industrial tailwater is significant to strengthen its pollution control and promoting the development of CWs in the field of micro-polluted water treatment. In this study, the distribution coefficients and the environmental risks of nitrogen pollutants between water and sediment of the hybrid CW in Tianjin were systematically investigated. From a spatial perspective, the nitrogen pollutants could be removed in this hybrid CW, and subsurface flow wetland played a key role in nitrogen pollutant removal. From a temporal perspective, the concentration of nitrogen pollutants was largely affected by the dissolved oxygen (DO) and temperature. The distribution coefficient of nitrogen pollutants between water and sediment was further clarified, suggesting that NH₄⁺-N was more likely to be enriched in sediments due to microbial process. The overall level of pollution in hybrid CW was moderate according to the nutritional pollution index (NPI) analysis. The risk assessment indicated that timely dredging control measures should be considered to maintain the performance of hybrid CW.

Field-scale baffled and biorack hybrid constructed wetland: effect of fluctuating loading rates and recirculation for domestic wastewater treatment

The conventionally used constructed wetlands require modification/s to minimize clogging problems and space requirement. In this study, a field-scale baffled and biorack hybrid constructed wetland (BBHCW) was developed as a part of 42 KLD decentralized wastewater treatment (DWT) system at Walchand College of Engineering, Sangli (M.S.), India for domestic wastewater. Brickbats were used as support medium in the baffled portion and corrugated sheets in biorack. Mixed vegetation of Typha angustifolia and Canna indica was used in both baffled and biorack portions. BBHCW was operated under the dynamic conditions of flow (0.60-9.89 m³/m² day) and strength (0.12-2.12 kg COD/m² day) for 8 months. The performance was assessed for the removal of organic carbon and nitrogen with and without recirculation of treated effluent. Tracer studies showed that the hydraulic efficiency was satisfactory. COD, BOD₃, and TKN removal is possible to an extent of 26.30 ± 1.36, 29.08 ± 2.43, and 19.39 ± 2.27%, respectively, under dynamic conditions. Recirculation enhances the removal efficiency of COD by 5.00-10.00%. However, TKN removal was not significant with or without recirculation. Morphological study showed that vegetation growth was well supported in BBHCW. The discarded corrugated sheets in BR and brickbats in BSFW are the most appropriate low-cost options. The clogging problem is reduced significantly. BBHCW is sturdy enough to absorb shock loading and space requirement can be reduced by judicious choice of HLR and OLR. BBHCW is an alternative to conventionally used sub-surface constructed wetland as a part of DWT. Novelty statementDevelopment of newly configured baffled and biorack hybrid dual-species constructed wetland (BBHCW) for field scale application.Use of discarded brickbat and cement sheets as a new support medium and bioracks.Performance assessment of field-scale BBHCW for the removal of organic carbon (expressed as COD and BOD₃), and nitrogen (expressed as TKN) from domestic wastewater under highly dynamic conditions induced by fluctuating hydraulic loading rate (0.60-9.89 m³/m² day) and organic loading rate (0.12-2.12 kg COD/m² day).