Effects of influent nitrogen loads on nitrogen and COD removal in horizontal subsurface flow constructed wetlands during different growth periods of Phragmites australis

Assessing the nutrient removal performance from rice-crayfish paddy fields by an ecological ditch-wetland system

Agricultural drainage from catchments significantly impacts aquatic ecosystems due to high nitrogen and phosphorus concentrations in runoff. While original ecological ditches and wetlands have demonstrated effectiveness in nutrient load removal, the overall impact of an ecological ditch-wetland system (EDWS) on agricultural nutrient removal has received limited attention. This study conducted a field experiment to investigate the physicochemical conditions and nutrient removal efficiency of an EDWS for purifying nutrient discharge from rice-crayfish paddy fields. Variations in water temperature (WT), dissolved oxygen (DO), pH, and total suspended solids (TSS) within the EDWS were assessed. Nutrient concentrations-including total nitrogen (TN), ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), total phosphorus (TP), and soluble reactive phosphorus (SRP)-were monitored from the tillering to the ripening stage of the rice growth cycle. The evaluation of nutrient removal efficiencies in the EDWS revealed that ecological ditches exhibited higher removal efficiencies compared to wetlands. The average total removal efficiencies for TN, NH4-N, NO3-N, TP, and SRP were 37.50 %, 39.38 %, 38.62 %, 37.94 %, and 39.51 %, respectively, with peak removal efficiencies observed at specific growth stages of the rice crop. Furthermore, the study explored the influence of hydraulic retention time on nutrient removal efficiency in the EDWS, indicating higher nutrient discharge removal efficiencies under low water discharge rates. Linear regression analysis identified water discharge, influent nutrient loads, and TSS as significant factors affecting nutrient removal efficiency in the EDWS. This study provides valuable insights into the effectiveness of EDWS in purifying nutrient discharge from rice-crayfish paddy fields, highlighting their potential as sustainable solutions for nutrient management in agricultural landscapes.

Performance of vertical flow constructed wetland for the treatment of effluent from a brassware industry in city of Fez, Morocco: a laboratory scale study

Brassware industry constitutes the second most polluting industrial sector in Fez city, Morocco, owing to its high heavy metal load. The aim of this study is to examine and evaluate the performance of vertical flow constructed wetlands in treating brassware effluents using various plant species. Ten treatment systems were planted with four types of plants: Chrysopogon zizanioides, Typha latifolia, Phragmites australis, and Vitex agnus-castus, while another system remained unplanted. These systems underwent evaluation by measuring various parameters, including pH, electrical conductivity, suspended solids, chemical oxygen demand, biological oxygen demand, sulfates, orthophosphates, total Kjeldhal nitrogen, ammonium, nitrates, nitrites, and heavy metals such as silver, copper, and nickel, using standard methods over of ten weeks. The results obtained demonstrate effectiveness of these systems. When planted with Ch. zizanioides, the systems achieved elimination rates of 83.64%, 98.55%, 91.48%, 86.82%, 80.31%, 96.54%, 98%, and 98.82% for suspended solids, ammonium, nitrites, BOD5, sulfates, orthophosphates, silver, and nickel, respectively. System with V. agnus-castus showed significant reductions in nitrate and copper, with rates of 84.48% and 99.10%, respectively. Considerable decrease in pH and electrical conductivity values was observed in all systems, with a notable difference between planted and control systems regarding effectiveness of treatment for other parameters.

Relationships between denitrification rates and functional gene abundance in a wetland: The roles of single- and multiple-species plant communities

Wetland soil denitrification removes excess inorganic nitrogen (N) and prevents eutrophication in aquatic ecosystems. Wetland plants have been considered the key factors determining the capacity of wetland soil denitrification to remove N pollutants in aquatic ecosystems. However, the influences of various plant communities on wetland soil denitrification remain unknown. In the present study, we measured variations in soil denitrification under different herbaceous plant communities including single Phragmites karka (PK), single Paspalum thunbergia (PT), single Zizania latifolia (ZL), a mixture of Paspalum thunbergia plus Phragmites karka (PTPK), a mixture of Paspalum thunbergia plus Zizania latifolia (PTZL), and bare soil (CK) in the Estuary of Nantiaoxi River, the largest tributary of Qingshan Lake in Hangzhou, China. The soil denitrification rate was significantly higher in the surface (0-10 cm) than the subsurface (10-20 cm) layer. Wetland plant growth increased the soil denitrification rate by significantly increasing the soil water content, nitrate concentration, and ln(nirS) + ln(nirK). A structural equation model (SEM) showed that wetland plants indirectly regulated soil denitrification by altering the aboveground and belowground plant biomass, nitrate concentration, abundances of denitrifying functional genes, and denitrification potential. There was no significant difference in soil denitrification rates among PT, PK and ZL. The soil denitrification rate was significantly lower in PTZL than PTPK. Two-plant communities did not necessarily enhance the denitrification rate compared to single planting, the former had a greater competitiveness on N uptake and consequently reduced the amount of nitrate available for denitrification. As PTPK had the highest denitrification rate, co-planting P. thunbergia and P. karka could effectively improve N removal efficiency and help mitigate eutrophication in adjacent aquatic ecosystems. The results of this investigation provide useful information guiding the selection of appropriate wetland herbaceous plant species for wetland construction and the removal of N pollutants in aquatic ecosystems.

Optimization of constructed wetlands on purifying black-odorous water and their potential purification mechanism

Black-odorous water has become a common and widespread problem in recent decades. In this study, nine constructed wetlands (CWs) with different flow types, filters, plants, and hydraulic loadings were designed according to an orthogonal array (L₉ (3⁴), and were used for the purification of black-odorous water in summer and winter. The results showed that CWs are regarded as effective to purify black-odorous water in both seasons. Microbial degradation is the major removal pathway of pollutants in CWs during summer, while the joint effect of biodegradation and adsorption is the main treatment route during winter. Flow type and hydraulic loading appear to be the most important factors impacting the purification performance of CWs, by changing the redox condition of systems and retention time of contaminants, respectively. 'Vertical flow-zeolite filter-high loading' is proposed as the best parameter selection for CWs on the purification of black-odorous water: among them, CWs with vertical flow have better oxygen transport capacity that is conductive to aerobic processes of pollutants, zeolite substrates may adsorb more nitrogen via ion exchange, higher hydraulic loadings can extend the contact time between contaminants and filters, and regulate the water temperature for microbial activity.

Research on removal of fluoroquinolones in rural domestic wastewater by vertical flow constructed wetlands under different hydraulic loads

Antibiotics had attracted more and more attention in recent years due to their harmfulness. Fluoroquinolones (FQs), one class of antibiotics widely used in human and veterinary medicine, were found in various water bodies in China. Therefore, in order to found an efficient method for removing FQs in rural domestic wastewater and optimize the process parameters, ceramsite and soil were applied in vertical flow constructed wetlands (VFCWs) to study the effects of different hydraulic loads and different substrates on the removal of FQs and conventional pollutants. The results showed the VFCW-D filled with 45 cm soil layer and 15 cm ceramasite layer had the highest removal efficiency of conventional pollutants and FQs under low hydraulic load. Nevertheless, the removal efficiency of conventional pollutants was significantly declined for the VFCWs which contained soil substrates under high hydraulic load due to the soil pores were clogged by the accumulation of organic matter. Finally, VFCW-A filled with 60 cm ceramasite layer revealed good ability to remove conventional pollutants and FQs under high hydraulic load. Deinococcus played a vital role here due to its excellent removal effect on conventional pollutants. The microbial composition in the substrate changed greatly after adding antibiotics under high hydraulic load. Devosia, Pseudorhodoferax, Cellvibrio, Bosea, Caulobacter, Acinetobacter, Zoogloea, Arcobacter, Dechloromonas, Flavobacterium, Nakamurella, Chloroplast, Clostridium_sensu_stricto_1, Pelosinus, UTCFX1 and Hypnocyclicus became the new dominated genera and were essential to remove pollutants. In summary, VFCW was an effective system to remove fluoroquinolones in rural domestic wastewater.

Performance optimization and microbial community evaluation for domestic wastewater treatment in a constructed wetland-microbial fuel cell

Constructed wetland-microbial fuel cell system (CW-MFC), an attractive technology still under study, has shown to improve domestic wastewater treatment efficiency and generate bioelectricity. This work investigated the effect of multiple factors on the performance optimization for the pollutants removal and bioelectricity production compared to a traditional CW, including influent chemical oxygen demand (COD) concentration, hydraulic retention time (HRT) and external resistance. The results showed that the optimal operating conditions of COD concentration, HRT and external resistance for CW-MFC were 200 mg/L, 24 h and 1000 Ω, respectively. The average COD, NH₄⁺-N, NO₃^--N and TP removal efficiencies were 6.06%, 3.85%, 3.68% and 3.68% higher than these in CW system, respectively. Meanwhile, the maximum output voltage and power density of CW-MFC were 388 ± 12 mV and 107.54 mW/m³. In addition, the microbial community analysis indicated that the pollution removal and bioelectricity generation might benefit from the gradual enrichment of electroactive bacteria (Tolumonas) and denitrifying bacteria (Denitratisoma, Methylotenera and Sulfuritales). The findings can provide the optimum operation parameters and mechanism insight for the performance of CW-MFC systems.

Investigation of dissimilatory nitrate reduction to ammonium (DNRA) in urban river network along the Huangpu River, China: rates, abundances, and microbial communities

Dissimilatory nitrate reduction to ammonium (DNRA) is an essential intermediate step in the nitrogen cycle, and different sediment physicochemical properties can affect the DNRA process. But the detailed research on the environmental nitrogen cycling in urban river networks based on DNRA communities and the functional gene nrfA is lacking. In this study, the flow line of the Huangpu River in Shanghai was analyzed using isotope tracer, quantitative real-time PCR, and high-throughput sequencing techniques to evaluate the role of DNRA on the stability of the river network and marine. The significant positive correlation between the rate of DNRA and sediment organic carbon was identified. At the genus level, Anaeromyxobacter is the most dominant. Notably, both heterotrophic and autotrophic DNRA species were discovered. This study added diversity to the scope of urban freshwater river network ecosystem studies by investigating the distribution of DNRA bacteria along the Huangpu River. It provided new insights into the biological nitrogen cycle of typical urban inland rivers in eastern China.

Efficiency and plant indication of nitrogen and phosphorus removal in constructed wetlands: A field-scale study in a frost-free area

Frost-free areas have suitable climate for wetland plant growth and constructed wetlands (CW) technology. Information on the quantification of plant biomass and uptake efficiency in field-scale CWs is limited in these climates. The removal efficiency of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), and total suspended solids (TSS) in wastewater from sewage plants, domestic sewage, and an industrial park in 15 rural and urban CWs in Guangdong Province, China, with an average temperature of 30 °C was evaluated. The effects of influent concentration, hydraulic load, the wastewater's physicochemical properties, operating conditions, and plant uptake were analysed. The mean removal rates were 40.0%, 45.2%, 41.1%, and 71.7% for TN, TP, COD, and TSS, respectively, which were higher than the removal load of the field-scale CWs in temperate regions. Removal loads of TN, TP, COD, and TSS were highest in CWs that have been operating for 5-6 years, treating wastewater volumes of over 1 m³/m²·d. The removal efficiency was mainly related to the inflow concentration and less affected by the type of CWs. Nutrient accumulation trends were primarily linked to influent concentrations (TN: r² = 0.89, P = 0.007; TP: r² = 0.96, P = 0.001) and plant biomass (TN: r² = 0.96, P = 0.001; TP: r² = 0.92, P = 0.004). Plant biomass contributed 2%-29% and 2%-70%, respectively, to removing N and P in CWs. The average uptake concentration of N and P in aboveground plant organs (15.66 ± 4.44 mg N/g, 2.15 ± 1.18 mg P/g) was generally higher than that of other temperate plants. A strong relationship between TN and TP in the biomass was also observed; however, the relationship is only restricted by the influent TP concentration. Arundo donax is well-adapted for nutrient accumulation and adaptation and is an ideal wetland plant to purify wastewater in frost-free climates.

A comparison of the mechanisms and performances of Acorus calamus, Pontederia cordata and Alisma plantagoaquatica in removing nitrogen from farmland wastewater

This study examined the performances of Acorus calamus, Pontederia cordata, and Alisma plantagoaquatica in removing nitrogen (N) from farmland wastewater. P. cordata showed the fastest rate of N removal, followed by A. plantagoaquatica, whereas that of A. calamus was slowest. P. cordata and A. plantagoaquatica achieving a greater rate of TN reduction in soil than that by A. calamus. A. plantagoaquatica demonstrated the highest N adsorption capacity, 32.6% and 392.1% higher than that of P. cordata and A. calamus, respectively. The higher potential nitrification and denitrification rate, and abundance of functional genes in the P. cordata microcosm resulted in a stronger process of nitrification-denitrification, which accounted for 65.99% of TN loss. Plant uptake and nitrification-denitrification were responsible for 50.06% and 49.94% of TN removed within the A. plantagoaquatica. Nitrification-denitrification accounted for 86.35% of TN loss in A. calamus. These findings helped to insight into N removal mechanisms in different plants.

Alkylphenols and Chlorophenols Remediation in Vertical Flow Constructed Wetlands: Removal Efficiency and Microbial Community Response

This study aims to investigate the effect of two different groups of phenolic compounds (the alkylphenols nonylphenol (NP) and octylphenol (OP), and the chlorophenol pentachlorophenol (PCP)) on constructed wetlands (CWs) performance, including on organic matter, nutrients and contaminants removal efficiency, and on microbial community structure in the plant bed substrate. CWs were assembled at lab scale simulating a vertical flow configuration and irrigated along eight weeks with Ribeira de Joane (an urban stream) water not doped (control) or doped with a mixture of NP and OP or with PCP (at a 100 μg·L−1 concentration each). The presence of the phenolic contaminants did not interfere in the removal of organic matter or nutrients in CWs in the long term. Removals of NP and OP were >99%, whereas PCP removals varied between 87% and 98%, mainly due to biodegradation. Microbial richness, diversity and dominance in CWs substrate were generally not affected by phenolic compounds, with only PCP decreasing diversity. Microbial community structure, however, showed that there was an adaptation of the microbial community to the presence of each contaminant, with several specialist genera being enriched following exposure. The three more abundant specialist genera were Methylotenera and Methylophilus (methylophilaceae family) and Hyphomicrobium (hyphomicrobiaceae family) when the systems were exposed to a mixture of NP and OP. When exposed to PCP, the three more abundant genera were Denitromonas (Rhodocyclaceae family), Xenococcus_PCC_7305 (Xenococcaceae family) and Rhodocyclaceae_uncultured (Rhodocyclaceae family). To increase CWs efficiency in the elimination of phenolic compounds, namely PCP which was not totally removed, strategies to stimulate (namely biostimulation) or increase (namely bioaugmentation) the presence of these bacteria should be explore. This study clearly shows the potential of vertical flow CWs for the removal of phenolic compounds, a still little explored subject, contributing to promote the use of CWs as nature-based solutions to remediate water contaminated with different families of persistent and/or emergent contaminants.

Assessing wetland nitrogen removal and reed (Phragmites australis) nutrient responses for the selection of optimal harvest time

Wetlands play an important role in reducing the impact of nitrogen pollution on natural aquatic environments. However, during the plant wilting period (winter) there will inevitably be a reduction in nitrogen removal from wetlands. Understanding optimum harvest time will allow the use of management practices to balance the trade-off between nitrogen removal and the sustainability of wetlands. In this study, we investigated wetland nitrogen removal and reed (Phragmites australis) nutrient responses for two years [first year: influent total nitrogen (TN) 17.6-34.7 mg L^-1; second year: influent TN 3.2-10.0 mg L^-1] to identify the optimal harvest time: before wilting, mid-wilting, or late wilting. Harvesting decreased wetland nitrogen removal in both years, with later harvest time producing a smaller decrease in TN and ammonium-nitrogen (NH₄⁺-N) removal. In addition to harvest before wilting, aboveground reed harvest at mid-wilting harvested more nutrients [carbon (C) 7.9%, nitrogen (N) 46.6% and phosphorus (P) 43.6%] in the first year, while harvest at late wilting harvested more nutrients (C 4.9%, N 7.8% and P 24.1%) in the second year, although this was not statistically significant. The late wilting harvest caused fewer disturbances to root stoichiometric homeostasis in the first year, while mid-wilting harvest promoted root nutrient availability in the second year. In addition, redundancy analysis (RDA) showed that root stoichiometry was interrelated with wetland nitrogen removal. Our results suggest that optimal harvest time was late wilting on the basis of wetland nitrogen removal, or either mid- or late wilting according to reed nutrient response to influent nitrogen concentration in some years. Our results provide crucial information for winter wetlands management.

Bacterially mediated release and mobilization of As/Fe coupled to nitrate reduction in a sediment environment

Metal-reducing bacteria play an important role in the release and mobilization of arsenic from sediments into groundwater. This study aimed to investigate the influence of nitrate on arsenic bio-release. Microcosm experiments consisting of high arsenic sediments and indigenous bacterium Bacillus sp. D2201 were conducted and the effects of nitrate on the mobilization of As/Fe determined. The results show arsenic release is triggered by iron reduction, which is regulated by nitrate. Increasing the nitrate concentration from 0 to 1 and 3 mM decreased Fe(III) reduction by 62.5% and 16.9% and decreased As(V) bio-release by 41.5% and 85.5%, respectively. Moreover, the results of step-wise Wenzel sequential extractions indicate nitrate addition prevents the transformation of poorly crystalline iron oxides to well crystalline iron oxides. Overall, nitrate appears to have a dual effect, inhibiting both iron reduction and arsenic release by incubation strain D2201. This study offers new insights regarding the biogeochemistry of arsenic in groundwater systems.

Mathematical Modeling of a Domestic Wastewater Treatment System Combining a Septic Tank, an Up Flow Anaerobic Filter, and a Constructed Wetland

Systems combining anaerobic bioreactors with constructed wetlands (CW) have proven to be adequate and efficient for wastewater treatment. Detailed knowledge of removal dynamics of contaminants can ensure positive results for engineering and design. Mathematical modeling is a useful approach to studying the dynamics of contaminant removal in wastewater. In this study, water quality monitoring was performed in a system composed of a septic tank (ST), an up flow anaerobic filter (UAF), and a horizontal flow constructed wetland (HFCW). Biological oxygen demand (BOD5), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), NH3, organic nitrogen (ON), total suspended solids (TSS), NO2−, and NO3− were measured biweekly during a 3-month period. First-order kinetics, multiple linear regression, and mass balance models were applied for data adjustment. First-order models were useful to predict the outlet concentration of pollutants (R2 > 0.87). Relevant multiple linear regression models were found, which could be applied to facilitate the system’s monitoring and provide valuable information to control and improve biological and physical processes necessary for wastewater treatment. Finally, the values of important parameters (μmax, Ks,  and Yx/s) in mass-balance models were determined with the aid of a differential neural network (DNN) and an optimization algorithm. The estimated parameters indicated the high robustness of the treatment system since performance stability was found despite variations in wastewater composition.

Enhanced nitrogen removal in filled-and-drained vertical flow constructed wetlands: microbial responses to aeration mode and carbon source

For the purpose of enhancing the removal rate of nitrogen (N) and organic matters, intermittent aeration and carbon source were used in filled-and-drained vertical flow constructed wetlands (VFCWs). The results showed that the best removal of COD (74.16%), NH₄⁺-N (93.56%), TN (86.88%), and NO₃^--N (79.65%) was achieved in VFCW1 (aerated with carbon source system). Illumina MiSeq300 high-throughput sequencing showed that carbon source aerated system increases the diversity and richness of the microbial community. The copy numbers of nitrification functional genes (nxrA, amoA), denitrification functional genes (nirS, nirK, nosZ), and anammox functional gene (anammox 16S rRNA) displayed various changes when applied different aeration modes and additional carbon source to each system. An increase of the DO concentration and carbon source facilitated the absolute abundance of microbial nitrification and denitrification functional genes, respectively. All in all, these results demonstrate that carbon source combined with intermittent aeration is valid to improve the pollutant treatment performance in these systems.

Function and biomass production of willow wetlands applied in the polishing phase of sewage treatment in cold climate conditions

Willow wetlands can offer a low-cost solution for recovery of nutrients contained in sewage water and simultaneously produce plant biomass, which can be used in energy production. Willow (Salix spp.) is considered an excellent crop for this purpose, due to its good nutrient uptake and biomass production. Although willow wetlands have been used in sewage treatment in e.g. Denmark, Sweden and southern Finland, their use in northern regions is challenging due to the detrimental effects cold climate conditions can have on plant survival rates and wastewater purification efficiency. In this study, a pilot constructed wetland in northern Finland receiving effluent from a small-scale wastewater treatment plant was investigated. Four willow varieties were planted (Gudrun, Karin, Klara and one local variety) and retention of nutrients in the wetland and willow plant survival rate, biomass production and nutrient uptake were evaluated. Good retention of nutrients (e.g. Tot. N 66-86% and Tot. P 30-87%) was achieved throughout the study period. After two growing seasons, the variety Gudrun showed the best survival rate and significantly higher biomass production (5.7 t/ha) than Karin, Klara and the local variety (1.7, 3.0 and 0.02 t/ha, respectively). Thus, willow wetlands are suitable systems for nutrient recovery from pre-treated wastewater in cold climate regions. However, the willow variety used should be chosen carefully, as there can be significant differences in survival rate and biomass production between varieties.

Contrasting Patterns in Diversity and Community Assembly of Phragmites australis Root-Associated Bacterial Communities from Different Seasons

The common reed (Phragmites australis), a cosmopolitan aquatic macrophyte, plays an important role in the structure and function of aquatic ecosystems. We compared bacterial community compositions (BCCs) and their assembly processes in the root-associated compartments (i.e., rhizosphere and endosphere) of reed and bulk sediment between summer and winter. The BCCs were analyzed using high-throughput sequencing of the bacterial 16S rRNA gene; meanwhile, null-model analysis was employed to characterize their assembly mechanisms. The sources of the endosphere BCCs were quantitatively examined using SourceTracker from bulk sediment, rhizosphere, and seed. We observed the highest α-diversity and the lowest β-diversity of BCCs in the rhizosphere in both seasons. We also found a significant increase in α- and β-diversity in summer compared to that in winter among the three compartments. It was demonstrated that rhizosphere sediments were the main source (∼70%) of root endosphere bacteria during both seasons. Null-model tests indicated that stochastic processes primarily affected endosphere BCCs, whereas both deterministic and stochastic processes dictated bacterial assemblages of the rhizosphere, with the relative importance of stochastic versus deterministic processes depending on the season. This study suggests that multiple mechanisms of bacterial selection and community assembly exist both inside and outside P. australis roots in different seasons.IMPORTANCE Understanding the composition and assembly mechanisms of root-associated microbial communities of plants is crucial for understanding the interactions between plants and soil. Most previous studies of the plant root-associated microbiome focused on model and economic plants, with fewer temporal or seasonal investigations. The assembly mechanisms of root-associated bacterial communities in different seasons remain poorly known, especially for the aquatic macrophytes. In this study, we compared the diversity, composition, and relative importance of two different assembly processes (stochastic and deterministic processes) of bacterial communities associated with bulk sediment and the rhizosphere and endosphere of Phragmites australis in summer and winter. While we found apparent differences in composition, diversity, and assembly processes of bacterial communities among different compartments, season played important roles in determining BCCs and their diversity patterns and assemblages. We also found that endosphere bacteria mainly originated from the rhizosphere. The results add new knowledge regarding the plant-microbe interactions in aquatic ecosystems.

Nitrogen removal efficiency of surface flow constructed wetland for treating slightly polluted river water

Restoration and water quality improvement of malodorous as well as slightly polluted rivers have been the global focus for environmental protection research and the development and construction of sponge cities. To date, constructed wetlands have been proven to be one of efficient methods to improve water quality. Nitrogen removal efficiency is a crucial indicator for the performance evaluation in slightly polluted river water treatment. Therefore, current study aimed to investigate the N removal efficiency of 3-stage surface flow constructed wetlands for water treatment. Results show that after a prolonged operation period, constructed wetlands were able to remove NH₄⁺-N, NO₃^--N, and TN by 38.4%, 22.3%, and 29.1%, respectively. Further investigations were carried out to investigate the removal efficiency of various N species in the 3-stage wetlands. Findings reveal that NH₄⁺-N was mainly treated in wetland #1 (W1) and wetland #2 (W2), while NO₃^--N and TN were in wetland #2 (W2) and wetland #3 (W3). Results also reveal that the influencing factors such as hydraulic retention time (HRT), water temperature (WT), and additional carbon source have significant effect on the removal performance of constructed wetlands.

Optimized fuzzy inference system to enhance prediction accuracy for influent characteristics of a sewage treatment plant

Sewage treatment plants (STPs) keep sewage contamination within safe levels and minimize the risk of environmental disasters. To achieve optimum operation of an STP, it is necessary for influent parameters to be measured or estimated precisely. In this research, six well-known influent chemical and biological characteristics, i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD), Ammoniacal Nitrogen (NH₃-N), pH, oil and grease (OG) and suspended solids (SS), were modeled and predicted using the Sugeno fuzzy logic model. The membership function range of the fuzzy model was optimized by ANFIS, the integrated Genetic algorithms (GA), and the integrated particle swarm optimization (PSO) algorithms. The results were evaluated by different indices to find the accuracy of each algorithm. To ensure prediction accuracy, outliers in the predicted data were found and replaced with reasonable values. The results showed that both integrated GA-FIS and PSO-FIS algorithms performed at almost the same level and both had fewer errors than ANFIS. As the GA-FIS algorithm predicts BOD with fewer errors than PSO-FIS and the aim of this study is to provide an accurate prediction of missing data, GA-FIS was only used to predict the BOD parameter; the other parameters were predicted by PSO-FIS algorithm. As a result, the model successfully could provide outstanding performance for predicting the BOD, COD, NH₃-N, OG, pH and SS with MAE equal to 3.79, 5.14, 0.4, 0.27, 0.02, and 3.16, respectively.

New solution to build constructed wetland in cold climatic region

Constructed wetland is an efficient and convenient wastewater treatment technology that has been widely used in China and elsewhere. However, seasonal frozen soil is easily formed in the cold regions of northern China. The local wetlands are in the frozen soil layer, causing the pollutants from wastewater not to be removed well. Therefore, a new constructed wetland structure that uses shallow geothermal energy to keep the wetland not frozen in the winter is proposed in this paper. The results of the experiment show that the average removal rates of total nitrogen, ammonium ion, and total phosphorus in the multistage constructed wetland system are 54.8%, 44.5%, and 77.7%, respectively. This performance is substantially better than that of conventional wetlands in winter. The proposed wetland structure can be applied to conventional wetlands and avoid the conventional wetlands being idle during cold seasons, which is conducive to the popularization of constructed wetlands (CWs) in cold regions.

High rates of ammonium recycling in northwestern Lake Taihu and adjacent rivers: An important pathway of nutrient supply in a water column

The ammonium (NH₄⁺) pool in the water column of eutrophic lakes is dynamic and undergoes tightly coupled production and consumption processes because of the metabolism of bacterial and algal communities, particularly in summer. However, NH₄⁺ recycling rates along nutrient gradients at river-lake transitional zones and the extent to which NH₄⁺ regeneration can compensate for consumption have been poorly studied. In August (flood period) and November (normal period), 2016, NH₄⁺ regeneration rates (REGs) and potential uptake rates (U_pots) were measured in northwestern Lake Taihu and adjacent rivers. Results showed that the REGs ranged from 0.09 to 3.30 μmol N L^-1 h^-1 and the U_pots ranged from 0.20 to 4.88 μmol N L^-1 h^-1, with higher recycling rates occurring at the river sites. Yet, the lake sites showed significantly higher water column NH₄⁺ demand (WCAD) than that of the adjacent river sites during both seasons (p < 0.05), probably as a result of the low REGs and the lack of exogenous nitrogen (N) inputs. The flood period showed significantly higher REG and U_pot values than those of the normal period (p < 0.05), probably controlled by higher water temperature and algal biomass. This study confirms that regenerated NH₄⁺ was more important than the ambient NH₄⁺ for sustaining cyanobacterial blooms in northwestern Lake Taihu and indicates that the river-lake transitional zones are key areas for N control in this hypereutrophic system.

Biogardens as constructed wetlands in tropical climate: A case study in the Central Pacific Coast of Costa Rica

In Costa Rica, <10% of wastewater is treated before its discharge. This generates a significant impact on the environment, public health, and tourism industry, which is one of the country's main economic activities. Biogardens, subsurface flow artificial wetlands, are alternative systems for the treatment of wastewater. The present study evaluated the removal of organic matter and nutrients in a biogarden located at a hotel in the Central Pacific Coast of Costa Rica between 2012 and 2017. Pretreatment involved septic tanks and grease traps for sewage and gray water, respectively. The biogarden, which is composed of seven wetlands with an average area of 12 m² and a depth of 0.7 m, contains river cobble as support material, gravel as bed, and Cyperus papyrus and Heliconia sp. plants. Removal of the biochemical oxygen demand (BOD), the chemical oxygen demand (COD), and the total suspended solids (TSS) on average were 80%, 66%, and 72%, respectively, thus producing an effluent in compliance with current national legislation. Furthermore, the biogarden did not emit noxious odors or display an excessive presence of mosquitoes. The results showed consistent and efficient removal of organic matter and nutrients from the wastewater throughout different seasons and pollutant loads, verifying that such systems can be used in decentralized locations (e.g., tourist areas) in tropical climates.