Dynamics of organic matter, nitrogen and phosphorus removal and their interactions in a tidal operated constructed wetland

An insight on the plausible biological and non-biological detoxification of heavy metals in tannery waste: A comprehensive review

A key challenge for the tannery industries is the volume of tannery waste water (TWW) generated during the processing of leather, releasing various forms of toxic heavy metals resulting in uncontrolled discharge of tannery waste (TW) into the environment leading to pollution. The pollutants in TW includes heavy metals such as chromium (Cr), cadmium (Cd), lead (Pb) etc, when discharged above the permissible limit causes ill effects on humans. Therefore, several researchers have reported the application of biological and non-biological methods for the removal of pollutants in TW. This review provides insights on the global scenario of tannery industries and the harmful effects of heavy metal generated by tannery industry on micro and macroorganisms of the various ecological niches. It also provides information on the process, advantages and disadvantages of non-biological methods such as electrochemical oxidation, advanced oxidation processes, photon assisted catalytic remediation, adsorption and membrane technology. The various biological methods emphasised includes strategies such as constructed wetland, vermitechnology, phytoremediation, bioaugmentation, quorum sensing and biofilm in the remediation of heavy metals from tannery wastewater (TWW) with special emphasize on chromium.

Enhanced ammonia removal in tidal flow constructed wetland by incorporating steel slag: Performance, microbial community, and heavy metal release

Utilizing alkaline solid wastes, such as steel slag, as substrates in tidal flow constructed wetlands (TFCWs) can effectively neutralize the acidity generated by nitrification. However, the impacts of steel slag on microbial communities and the potential risk of heavy metal release remain poorly understood. To address these knowledge gaps, this study compared the performance and microbial community structure of TFCWs filled with a mixture of steel slag and zeolite (TFCW-S) to those filled with zeolite alone (TFCW-Z). TFCW-S exhibited a much higher NH4+-N removal efficiency (98.35 %) than TFCW-Z (55.26 %). Additionally, TFCW-S also achieved better TN and TP removal. The steel slag addition helped maintain the TFCW-S effluent pH at around 7.5, while the TFCW-Z effluent pH varied from 3.74 to 6.25. The nitrification and denitrification intensities in TFCW-S substrates were significantly higher than those in TFCW-Z, consistent with the observed removal performance. Moreover, steel slag did not cause excessive heavy metal release, as the effluent concentrations were below the standard limits. Microbial community analysis revealed that ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and complete ammonia-oxidizing bacteria coexisted in both TFCWs, albeit with different compositions. Furthermore, the enrichment of heterotrophic nitrification-aerobic denitrification bacteria in TFCW-S likely contributed to the high NH4+-N removal. In summary, these findings demonstrate that the combined use of steel slag and zeolite in TFCWs creates favorable pH conditions for ammonia-oxidizing microorganisms, leading to efficient ammonia removal in an environmentally friendly manner.

A survey on constructed wetland publications in the past three decades

Decentralised wastewater treatment systems, such as constructed wetlands, are becoming increasingly popular these days because they are more economical and cost-effective than conventional plants. The primary objective of this review paper is to determine the number of studies that have been conducted on constructed wetlands, specifically 'free water surface flow constructed wetlands', 'horizontal subsurface flow constructed wetlands', 'vertical subsurface flow constructed wetlands', and 'hybrid constructed wetlands'. In addition, the paper examines the status of research publications on constructed wetlands by country, author, and journal. Based on the review, it has been found that although constructed wetland technology is economical and cost-effective, it is still not among the top 10 effluent treatment methods. Compared to other constructed wetland systems, 'hybrid constructed wetlands' have received minimal attention. Based on the search results, 4639 documents published between 1989 and 2021 have been extracted from the online edition of SCI-EXPANDED, Web of Science. The documents associated with constructed wetlands are divided into eight main document types. Articles and proceedings papers are the most common document type, accounting for 93% of all publications, followed by reviews (4%), meeting abstracts (1.3%), corrections (0.56%), editorial materials (0.38%), news items (0.2%), letters (0.04%), and book reviews (0.02%).

Performance assessment of local aquatic macrophytes for domestic wastewater treatment in Nigerian communities: A review

The concept of treating wastewater before disposal is a global necessity. Recent mechanisms of doing this include the use of Constructed Wetland Systems (CWS). This technique is believed to be cost-effective and simpler compared to conventional methods. The application of this system is primarily dependent on the use of plants through the phytoremediation process. There is evidence of the potential of some locally found Nigerian aquatic plants such as water lettuce, water hyacinth and duckweed to be applicable for this purpose. However, there is little information on their performance level in remediating domestic wastewater. Thus, this review paper assessed the performance of these local macrophytes for domestic wastewater treatment and the potential of contributing the same in Nigerian communities. This was done by reviewing recent literature on the role of water lettuce, water hyacinth and duckweed, their occurrence and their efficiency in minimising different wastewater contaminants. Contaminant indicators such as total solids, electrical conductivity (EC), BOD, COD, dissolved oxygen, total phosphorous, total nitrogen, and heavy metals have been reduced using these macrophytes. The review indicates that the selected macrophytes do not only have the potential for wastewater purification but high efficiencies in doing so when applied appropriately in the Nigerian communities.

Study of the effect of pyrite and alkali-modified rice husk substrates on enhancing nitrogen and phosphorus removals in constructed wetlands

The combined effects and respective advantages of using pyrite and alkali-modified rice husk (RH) were studied as substrates for nitrogen and phosphorus removal from constructed wetlands, and the effects of the carbon to nitrogen (C/N) ratio and the tidal flow mode on system performance were explored. The results showed that alkali-modified RH, which enhances heterotrophic denitrification, had far more advantages than pyrite, which enhances autotrophic denitrification, and alkali-modified RH can be used for the treatment of sewage containing low C/N ratios. At a C/N ratio of 1.5, the total nitrogen (TN) removal rates exceeded 95%. However, the removal efficiency of the system with only pyrite only reached 76.90% when the influent C/N ratio was 6. Pyrite achieved a total phosphorus (TP) removal 10-20% higher than that of the control group. The tidal flow CWs showed enhanced nitrification, and the NH₄⁺-N removal rates increased by approximately 10%, but the increase in dissolved oxygen (DO) was still insufficient to meet the needs of the systems, leading to limited TP removal. The combination of pyrite and alkali-modified RH was optimal for improving the ability of constructed wetlands to treat wastewaters, simultaneously removing nitrogen and phosphorus from sewage containing low C/N ratios. Combined with the tidal flow mode strategy, the use of pyrite and alkali-modified RH as substrates showed substantial advantages for improving water quality.

Constructed wetlands as a sustainable technology for wastewater treatment with emphasis on chromium-rich tannery wastewater

Water scarcity is a major threat to agriculture and humans due to over abstraction of groundwater, rapid urbanization and improper use in industrial processes. Industrial consumption of water is lower than the abstraction rate, which ultimately produces large amounts of wastewater such as from tannery industry containing high concentration of chromium (Cr). Chromium-contaminated tannery industry wastewater is used for irrigation of food crops, resulting in food safety and public health issues globally. In contrast to conventional treatment technologies, constructed wetlands (CWs) are considered as an eco-friendly technique to treat various types of wastewaters, although their application and potential have not been discussed and elaborated for Cr treatment of tannery wastewater. This review briefly describes Cr occurrence, distribution and speciation in aquatic ecosystems. The significance of wetland plant species, microorganisms, various bedding media and adsorbents have been discussed with a particular emphasis on the removal and detoxification of Cr in CWs. Also, the efficiency of various types of CWs is elaborated for advancing our understanding on Cr removal efficiency and Cr partitioning in various compartments of the CWs. The review covers important aspects to use CWs for treatment of Cr-rich tannery wastewater that are key to meet UN's Sustainable Development Goals.

Constructed wetlands for rural domestic wastewater treatment: A coupling of tidal strategy, in-situ bio-regeneration of zeolite and Fe(Ⅱ)-oxygen denitrification

Constructed wetlands (CWs) offer a promising method to treat domestic wastewater in rural areas, but CWs usually limiting in nitrogen removal and large area. In this study, zeolite and pyrite were used to construct tidal wetlands to address the problems of insufficient oxygen supply and carbon source. The results show that the fully drained wetland achieved the highest ammonia removal load of 34.67 ± 1.72 g/(m²·d) with 8.57 ± 1.13 mg/L of effluent. Pyrite was found to compensate for the lack of carbon source in the denitrification process in half-drained wetland, which achieved a 78.36 ± 5.3% TN removal rate with 7.09 ± 1.85 mg/L effluent concentration. Pyrite released Fe(II) to promote nitrate reduction for denitrification in the subsequent flooded period. Microbial community analysis indicates that the tidal flow constructed wetlands simultaneously achieved nitrification and denitrification by the coupling of in-situ zeolite regeneration and Fe(II) oxidation denitrification.

Organic carbon quantity and quality jointly triggered the switch between dissimilatory nitrate reduction to ammonium (DNRA) and denitrification in biofilters

The effect of organic carbon (OC) quality and quantity on switch between dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (DEN) was studied in biofilter systems. High OC in matrix could promote significantly nitrate (NO₃^--N) removal due to the reinforce of DEN. Sodium acetate (SA) addition in influent further fueled NO₃^--N removal in groups with low OC in matrix but increased ammonium (NH₄⁺-N) and nitrite (NO₂^--N) accumulation in groups with high OC in matrix. This indicated that high OC combined different species, facilitated the DNRA over DEN. Compared to bagasse, corncob was the better suitable OC source in matrix for DEN due to slow and continuous release of OC. Hence, in order to promote NO₃^--N removal and decline NH₄⁺-N accumulation in biofilters, it is very important to screen suitable OC source (mixed utilization of multiple C sources is recommended) and regulate its dosage (below 80 mg L^-1).

The application of steel slag in a multistage pond constructed wetland to purify low-phosphorus polluted river water

To investigate the effect of a constructed wetland (CW) with steel slag as the filler on water contaminated by low phosphorus levels, a multistage pond CW system was designed in this study. Low-phosphorus polluted river water was used as the research object. This study explored the effects of using steel slag as a CW filler on phosphorus removal and the total phosphorus (TP) purification effect of the wetland system. The results showed that the TP removal rates in the ecological pond, oxidation pond, surface flow wetlands and submerged plant pond were 5.17%, 8.02%, 21.56%, and 16.31%, respectively. Intermittent increases in phosphorus concentration were observed in the reactors and were caused by the decay of plant tissues, which released pollutants. Because steel slag was added to the filler, the TP concentrations in the effluent of the first- and second-level horizontal subsurface CWs increased by 151.13% and 16.29%, respectively, compared to the influent concentration. The 20th to 40th days of the test run was a period of rapid phosphorus release of the system. The use of steel slag has a potential risk of phosphorus release when applied in CWs used to purify low-phosphorus contaminated water bodies.

The application of Marinobacter hydrocarbonoclasticus as a bioaugmentation agent for the enhanced treatment of non-sterile fish wastewater

Wastewaters generated by fish processing are characterised by salt concentrations similar to or greater than that of seawater together with high nutrient concentrations (e.g. organic carbon and total nitrogen) due to the presence of blood, oil, and fish tissues. Fish processing wastewater entering rivers and oceans have become a key factor leading to the pollution of receiving waters; the adequate treatment of this wastewater is, therefore, crucial to a sustainable fish industry. The present study aimed to determine whether augmentation of fish wastewater with either Marinirhabdus sp., Marinobacter hydrocarbonoclasticus or a consortium of the two halobacteria, could successfully enhance the removal of both chemical oxygen demand (COD) and total nitrogen (TN) from fish wastewater. Following 9 days of incubation, the bioaugmentation treatment resulted in a significant reduction in COD, 88%, 91%, and 92% in fish wastewater augmented with either Marinirhabdus sp., Marinobacter hydrocarbonoclasticus respectively, or a consortium of the two halobacteria compared with the control (non-bioaugmented) treatment (77% removal). In tall bioaugmentation treatments (79-88%) TN removal was also significantly greater than the control treatment (57%). After 9 days of incubation, the COD and TN in bioaugmentation reached the European Union's (EU) wastewater discharge standard (Level B, COD < 120 mg L^-1, TN < 70 mg L^-1). The addition of monoculture was effective in enhancing the removal of COD, while co-culture significantly improved TN removal. Results of 16S rDNA sequence analysis investigating the survival of these introduced bacteria showed that only Marinobacter hydrocarbonoclasticus was detected at the end of the treatment, constituting 36% of the total bacterial population when added alone to the wastewater. This study confirms the effectiveness of bioaugmentation in removing COD and TN in saline fish wastewater. The ability of Marinobacter hydrocarbonclasticus to enhance the treatment and dominate the bacterial community suggests the commercial potential of this organism for bioaugmentation of aquaculture wastewater without the need for further bioaugmentation.

Purification Efficiency of Three Combinations of Native Aquatic Macrophytes in Artificial Wastewater in Autumn

Water pollution caused by excessive nutrient and biological invasion is increasingly widespread in China, which can lead to problems with drinking water as well as serious damage to the ecosystem if not be properly treated. Aquatic plant restoration (phytoremediation) has become a promising and increasingly popular solution. In this study, eight native species of low-temperature-tolerant aquatic macrophytes were chosen to construct three combinations of aquatic macrophytes to study their purification efficiency on eutrophic water in large open tanks during autumn in Guangzhou City. The total nitrogen (TN) removal rates of group A (Vallisneria natans + Ludwigia adscendens + Monochoria vaginalis + Saururus chinensis), group B (V. natans + Ipomoea aquatica + Acorus calamus + Typha orientalis), and group C (V. natans + L. adscendens + Schoenoplectus juncoides + T. orientalis) were 79.10%, 46.39%, and 67.46%, respectively. The total phosphorus (TP) removal rates were 89.39%, 88.37%, and 91.96% in groups A, B, and C, respectively, while the chemical oxygen demand (COD) removal rates were 93.91%, 96.48%, and 92.78%, respectively. In the control group (CK), the removal rates of TN, TP, and COD were 70.42%, 86.59%, and 87.94%, respectively. The overall removal rates of TN, TP, and COD in the plant groups were only slightly higher than that in CK group, which did not show a significant advantage. This may be related to the leaf decay of some aquatic plants during the experiment, whereby the decay of V. natans was the most obvious. The results suggest that a proper amount of plant residue will not lead to a significant deterioration of water quality.

Influence of the flooded time on the performance of a tidal flow constructed wetland treating urban stream water

A vertical subsuperficial tidal flow constructed wetland (TFCW) operated under flooded time (FT) variation, was evaluated in the removal of carbonaceous, nitrogenous, and phosphorous matter from urban stream water. The TFCW downflow (117 L) was filled with bricks (44% porosity) and vegetated with Althernanthera philoxeroides (32 plants m^-2). The TFCW was operated under different flooded times - Stage A (48 h), B (36 h), C (24 h), and D (12 h), organic loading rates of 19.58-43.83 gCOD m^-2 d^-1, 3.68-6.94 gTN m^-2 d^-1 and 0.93-2.00 gTP m^-2 d^-1 and volumetric load rates of 46.8, 58.5, 78.0 and 11.7 L d^-1. No significant differences were observed in the removal efficiencies to Chemical Oxygen Demand (COD 66 to 94%), Total Ammonia Nitrogen (TAN 58 to 87%), and Total Nitrogen (TN 53 to 78%) among the stages, and nitrate concentrations lower than 6 mg L^-1 in the effluent. High Total Phosphorus removal was obtained in FT of 48 h (TP 79%). Total phosphorus loading rate was a limiting factor in TP removal, which reduced along with the reduction of FT. The nitrifying community was present over time since ammonia-oxidizing bacteria (Nitrosospira) and nitrite-oxidizing bacteria (Nitrobacter and Nitrospira) were identified in operational stages with variation in relative abundance, but TAN removal efficiency did not show significant differences. There was no change in the denitrifying community structure, indicating that FT did not influence the TN removal. A. philoxeroides was responsible for phytoextraction of 2.1% of TN and 2.7% of TP from the total removed by TFCW. TN removal (65%) was attributed to adsorption in the filtering material and microbial metabolism during the rest time. The findings of this study suggest FT of 12 h to remove COD and TN, and equal to or higher than 48 h to remove TP.

Characteristics of Dissolved Organic Matter and Its Role in Lake Eutrophication at the Early Stage of Algal Blooms—A Case Study of Lake Taihu, China

Decaying algal blooms in eutrophic lakes can introduce organic matter into the water and change nutrient concentrations in the water column. The spatial distribution and composition characteristics, sources, and contribution to eutrophication of dissolved organic matter (DOM) in the overlying water of Lake Taihu, a typical eutrophic lake in China, were analyzed by ultraviolet–visible spectra and three-dimensional fluorescence excitation–emission matrix spectra combined with the statistical decomposition technique, parallel factor analysis. The concentration of DOM was represented by dissolved organic carbon (DOC), and DOC in overlying water of Lake Taihu was 2.86–11.83 mg/L. The colored DOM (CDOM) was characterized by an absorption coefficient at 280 nm (a280) and 350 nm (a350), which were 6.63–29.87 and 1.84–10.41 m−1, respectively. These values showed an increasing trend from southeast to northwest, and the high values were concentrated in the northwest and northern lake areas. The parallel factor analysis (PARAFAC) identified two protein-like (C1: tyrosine-like and C2: tryptophan-like) and one humic-like (C3: humic acid and fulvic acid) fluorescence components for fluorescent DOM (FDOM). The most dominant components were protein-like components (C1 + C2), whose fluorescence intensity contributed 87.55% ± 3.39% to the total fluorescence intensity (Ft) of FDOM (3.38 R.U.). The mean value of the fluorescence index (FI) and index of recent autochthonous contribution (BIX) of DOM was 1.77 and 0.92, and DOC, a280 and fluorescence intensities of FDOM components were all significantly and positively correlated with chl. a, indicating that DOM, CDOM, and FDOM were all mainly derived from algal activities and metabolites. The average humification index of the DOM was 0.66, which indicated a low humification degree. The protein-like DOM was correlated with DON and DOP, and might make great contributions to the continuous occurrence of algal blooms.

Nitrogen Removal Ability and Characteristics of the Laboratory-Scale Tidal Flow Constructed Wetlands for Treating Ammonium-Nitrogen Contaminated Groundwater

Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (N) from wastewaters and contaminated environmental waters. However, the feasibility of CWs for ammonium-N (NH4+-N)-contaminated groundwater treatment is unclear. In this study, zeolite-based laboratory-scale CW was operated as a tidal flow CW with a cycle consisting of 21-h flooded and 3-h rest, and used to treat NH4+-N (30 mg L−1) contaminated groundwater. In addition to NH4+-N, nitrite (NO2−-N) and nitrate (NO3−-N) were also not detected in the effluents from the tidal flow CW. The N removal constant remained high for a longer period of time compared to the continuous flow CW. The higher and more sustainable N removal of the tidal flow CW was due to the in-situ biological regeneration of zeolite NH4+-N adsorption capacity. Vegetation of common reeds in tidal flow zeolite-based CW enhanced nitrification and heterotrophic denitrification activities, and increased the functional genes of nitrification (AOB-amoA and nxrA) and denitrification (narG, nirK, nirS, and nosZ) by 2‒3 orders of magnitude, compared to CW without vegetation. The results suggest that the combination of zeolite substrate, tidal flow, and vegetation is key for the highly efficient and sustainable N removal from NH4+-N contaminated groundwater.

Roles of biochar media and oxygen supply strategies in treatment performance, greenhouse gas emissions, and bacterial community features of subsurface-flow constructed wetlands

Biochar-based subsurface-flow constructed wetlands (CWs) with intermittent aeration (IA) or tidal flow (TF) oxygen supply strategies were established to treat domestic wastewater. The results showed that biochar achieved higher nutrient removal and lower greenhouse gas (GHG) emissions than ceramsite while supporting more diverse bacterial communities and higher abundances of functional taxa. Both IA and TF effectively enhanced nutrient removal, though the latter was more efficient and practical, and aeration conditions greatly influenced nutrient removal efficiency. GHG emissions were decreased by IA but were slightly increased by TF. Both oxygen supply methods significantly shaped the biofilm microbial communities and influenced biodiversity and richness, with observably higher proportions of potential nitrifiers and denitrifiers present in aerated CWs. Overall, biochar-based CWs operated with oxygen supply strategies provide superior treatment of decentralized wastewater.

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.

Effect of plant-based carbon source supplements on denitrification of synthetic wastewater: focus on the microbiology

The effects of plant-based carbon source addition on wastewater NO₃^--N removal and the involved microorganisms, especially denitrifying bacteria, were investigated. A synthetic wastewater (NO₃^--N, 15 mg/L) was treated through the batch experiment, which included three inoculation cycles (7 days/cycle), and was conducted at 25 °C. Four natural plant substrates, namely, rice straw (RS), wheat straw (WS), ryegrass (RG), and reed (RD), were used as carbon sources and supplemented at the rate of 1% (w/v). The results showed that both RS and WS performed well in promoting NO₃^--N removal (79.55-97.07%). While RG removed only 22.08% of NO₃^--N in the first cycle, the removal efficiency increased afterward (86.09-95.82%). Conversely, the NO₃^--N removal rate of RD decreased from 95.10 to 24.77% as a result of its low ability to supply carbon. With respect to the microorganisms, the RS treatment resulted in more bacteria and denitrifying genes such as narG, nirK, nirS, and norB than other treatments, while the highest number of nosZ gene copies was recorded in the WS treatment. Sequencing results revealed that Firmicutes (18.19-56.96%), Proteobacteria (38.82-74.80%), and Bacteroidetes (3.15-4.15%) were three dominant bacterial phyla for RS, WS, and RD treatments. Furthermore, the genera Enterobacter, Massilia, and Bacillus were the main denitrifying bacteria participating in the NO₃^--N removal. Furthermore, correlation analysis indicated that the denitrifying genus Sphingobacterium played an important role in enhancing nitrogen removal. This study suggested that RS is the superior plant-based carbon source for denitrifying bioreactors used in agricultural runoff treatment.

The structure of denitrifying microbial communities in constructed mangrove wetlands in response to fluctuating salinities

In this study, the experimental vertical-flow constructed wetland (CW) systems planted with the salt-tolerant mangrove species Kandelia candel were established to investigate the influence of salinity fluctuations on the denitrification performance and denitrifying microbial community structure of the CWs. The high-throughput sequencing analysis showed that 10-13 genera aerobic microbes had been enriched in the upper layer of wetland matrix in the depth of 10-25 cm, with the relative abundance accounting for 19.1 ± 7.9%. Although the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were inhibited significantly in the CW systems with salinity levels in the range of 0.9-1.8%, the aerobic denitrifying (AD) bacteria including Pseudomonas, Acinetobacter and Aeromonas, removed 99% of ammonia nitrogen from the influent by heterotrophic nitrification (HN) functions, and conducted denitrification at the same time to remove 90% of the TN in the system, indicating that the wetland test system successfully enriched a variety of aerobic denitrifying bacterial communities under different salinity conditions. Not only the nitrogen removal efficiency but also the adaptability of the wetland system to salinity fluctuations had been improved by the enriched HN-AD bacteria. In addition, HN-AD bacterial communities can conduct both nitrification and denitrification in the middle and upper layers of the vertical flow wetland, hereby saving the reaction space of the constructed wetland and reducing the construction cost.

Emulating natural wetlands oxygen conditions for the removal of N and P in agricultural wastewaters

The aim of this research was to evaluate a constructed wetland system (CW) operated under aerobic-anoxic-aerobic conditions to remove C, N and P from water with high concentrations of the last two nutrients. A series of three CW were operated continuously for 190 days. An aerobic vertical CW was used in the first and third stages and an anoxic horizontal CW was used in the second stage. The total nitrogen (TN) removal efficiency was 70 ± 1.5%. Similar removal efficiency behavior was observed in others nitrogen compounds, where a removal of 85 ± 1.5% for NO₃^--N and 97 ± 2.2% for NH₃⁺N were achieved. The combination of different oxygen conditions enhanced oxidation of nitrates and the assimilation of ammonium by vegetation. On the other hand, 54 ± 6.5% total phosphorus (TP) was removed in the entire system, which is higher than the reported in several investigations, including mechanized and controlled systems such as activated sludge. The phosphorous removal efficiency was attributed to the adequate design and configuration of CW, which facilitated dissolved oxygen (DO) conditions required for phosphorus capture. Despite in this investigation the CW was not designed for an optimal removal of organic matter the removal efficiency of this parameter was 64 ± 7.5%. The successful results suggest that the combination of aerobic-anoxic-aerobic stages is a technically suitable option for the treatment of agricultural wastewater with high content of N and P.

Wetlands for wastewater treatment and subsequent recycling of treated effluent: a review

Due to water scarcity challenges around the world, it is essential to think about non-conventional water resources to address the increased demand in clean freshwater. Environmental and public health problems may result from insufficient provision of sanitation and wastewater disposal facilities. Because of this, wastewater treatment and recycling methods will be vital to provide sufficient freshwater in the coming decades, since water resources are limited and more than 70% of water are consumed for irrigation purposes. Therefore, the application of treated wastewater for agricultural irrigation has much potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for plant production. Among the current treatment technologies applied in urban wastewater reuse for irrigation, wetlands were concluded to be the one of the most suitable ones in terms of pollutant removal and have advantages due to both low maintenance costs and required energy. Wetland behavior and efficiency concerning wastewater treatment is mainly linked to macrophyte composition, substrate, hydrology, surface loading rate, influent feeding mode, microorganism availability, and temperature. Constructed wetlands are very effective in removing organics and suspended solids, whereas the removal of nitrogen is relatively low, but could be improved by using a combination of various types of constructed wetlands meeting the irrigation reuse standards. The removal of phosphorus is usually low, unless special media with high sorption capacity are used. Pathogen removal from wetland effluent to meet irrigation reuse standards is a challenge unless supplementary lagoons or hybrid wetland systems are used.

Performance and bacterial community structure of a 10-years old constructed mangrove wetland

Constructed mangrove wetland has been used for wastewater treatment but its long-term performance has not been reported. One-year monitoring of a 10-years old horizontal subsurface-flow constructed mangrove wetland consisting of three belts, two with mangrove plants and one without, revealed that the system maintained high and stable removal percentages of organic matter and nutrients, and planted belts performed better than unplanted control. Substrates in belts planted with Aegiceras corniculatum or Kandelia obovata had higher abundance of ammonifiers, nitrifiers and denitrifiers but lower total heterotrophic bacteria than unplanted substrate. Denaturing gradient gel electrophoresis showed that microbial diversity in planted substrate was significantly lower than that in unplanted one. The bacteria in substrates, irrespective to belts, were phylogenetically related to Proteobacteria (most dominant), Acidobacteria, Firmicutes, Nitrospirae, Gemmatimonadetes, Chloroflexi and Cyanobacteria. The steady performance of this 10-year old constructed mangrove wetland was affected by the abundance and diversity of bacterial community in substrate.

Characterising stormwater gross pollutants captured in catch basin inserts

The accumulation of wash-off solid waste, termed gross pollutants (GPs), in drainage systems has become a major constraint for best management practices (BMPs) of stormwater. GPs should be captured at source before the material clogs the drainage network, seals the infiltration capacity of side entry pits or affects the aquatic life in receiving waters. BMPs intended to reduce stormwater pollutants include oil and grit separators, grassed swales, vegetated filter strips, retention ponds, and catch basin inserts (CBIs) are used to remove GP at the source and have no extra land use requirement because they are typically mounted within a catch basin (e.g. side entry pits; grate or gully pits). In this study, a new type of CBI, recently developed by Urban Stormwater Technologies (UST) was studied for its performance at a site in Gosnells, Western Australia. This new type of CBI can capture pollutants down to particle sizes of 150μm while retaining its shape and pollutant capturing capacity for at least 1year. Data on GP and associated water samples were collected during monthly servicing of CBIs for one year. The main component of GPs was found to be vegetation (93%): its accumulation showed a strong relationship (r²=0.9) with rainfall especially during the wet season. The average accumulation of total GP load for each CBI was 384kg/ha/yr (dry mass) with the GP moisture content ranging from 24 to 52.5%. Analysis of grain sizes of GPs captured in each CBI showed similar distributions in the different CBIs. The loading rate coefficient (K) calculated from runoff and GP load showed higher K-values for CBI located near trees. The UST developed CBI in this study showed higher potential to capture GPs down to 150μm in diameter than similar CBI devices described in previous studies.

Cold Temperature Effects on Long-Term Nitrogen Transformation Pathway in a Tidal Flow Constructed Wetland

The present study investigated long-term treatment performance and nitrogen transformation mechanisms in tidal flow constructed wetlands (TFCWs) under 4, 8, and 12 °C temperature regimes. High and stable ammonium (NH4(+)-N) removal efficiency (93-96%) was achieved in our TFCWs, whereas nitrate (NO3(-)-N) was accumulated at different levels under different temperatures. Quantitative response relationships showed anammox/amoA, (narG+napA)/amoA, and (narG+napA)/bacteria were the respective key functional gene groups determining 4, 8, and 12 °C NO3(-)-N reduction. Pathway analysis revealed the contribution of these functional gene groups along a depth gradient. In addition, denitrification process increased, while anammox process decreased consistent with a rise in temperature from 4 to 12 °C. Furthermore, cold temperatures exhibited different effects on anammox and denitrification and their long-term acclimatization capacities changed with temperature.

Enhanced long-term nitrogen removal and its quantitative molecular mechanism in tidal flow constructed wetlands

Tidal flow constructed wetlands (TF CWs) have recently been studied as a sustainable technology to achieve enhanced nitrogen removal; however, the underlying mechanisms responsible for removing ammonium (NH4(+)) and nitrate (NO3(-)) have not been compared and quantified at the molecular level (genes) in controlled TF CWs. In this study, two TF CWs T1 (treating NH4(+) wastewater) and T2 (treating NO3(-) wastewater) achieved high removal efficiencies for chemical oxygen demand (COD, 92 ± 2.7% and 95 ± 2.4%, respectively), NH4(+)/NO3(-) (76 ± 3.9% and 97 ± 2.2%, respectively), and total nitrogen (TN, 81 ± 3.5% and 93 ± 2.3%, respectively). Combined analyses revealed that the presence of simultaneous nitrification, anammox, and denitrification processes and the coupling of dissimilatory nitrate reduction to ammonium, ammonia oxidation, and anammox were the primary reason accounted for the robust treatment performance in T1 and T2, respectively. Results from stepwise regression analysis suggested that the NH4(+) removal rate in T1 was collectively controlled by amoA, nxrA, and anammox, while the NO3(-) removal rate in T2 was governed by nxrA and narG gene.