'Halophyte filters': the potential of constructed wetlands for application in saline aquaculture

Efficacy of Juncus maritimus floating treatment saltmarsh as anti-contamination barrier for saltwater aquaculture pollution control

Floating treatment saltmarsh (FTS) is a new concept proposed to name floating treatment wetlands made of estuarine halophytes especially engineered for the control of contamination in brackish and saline waterbodies. The first full-scale FTS was implemented in 2018 to create an anti-contamination barrier for saline aquaculture wastewater treatment in an estuarine tidal lagoon. Results of a two-year investigation validated 'Phytobatea' modular technology for floating wetlands implementation and operation. Juncus maritimus crossflow FTS efficiency on main mariculture wastewater constituents' removal under low hydraulic retention time was remarkable, i.e., total phosphorus (86%), total suspended solids (82%), biochemical oxygen demand (78%), total organic carbon (55%), turbidity (53%), Escherichia coli (30%), and dissolved oxygen increased (19%). Key features of the native halophyte Juncus maritimus were determined to ensure 75-100% survival under high water salinities up to 38 g/L. A scientific literature review confirmed strategic sectors' growing interest in Juncus maritimus as raw material, supporting its possible cultivation as an added-value by-product within integrated aquaculture systems. Plants' root systems colonization by crabs, shrimps, and young individuals of the critically endangered European eel (Anguilla anguilla), revealed the role of FTS for biodiversity conservation, and its potential as functional habitat, nursery, and refuge for aquatic fauna species in contaminated waterbodies.

Current available treatment technologies for saline wastewater and land-based treatment as an emerging environment-friendly technology: A review

Different industrial activities such as agro-food processing and manufacturing, leather manufacturing, and paper and pulp production generate highly saline wastewater. Direct discharge of saline wastewater has resulted in pollution of waterbodies by very high magnitudes. Consequently, an enormous number of pollutants such as heavy metals, salts, and organic matter are also released into the environment threatening the survival of human and biota. Saline wastewater also has significant effects on survival of plants, agricultural activities, and groundwater systems. Several treatments and disposal technologies are available for saline wastewater, but the selection of the most appropriate treatment and disposal technology still remains a major challenge with respect to the economic or technical constraints. Considering the sustainable management of saline wastewater, the present review is an attempt to compile the existing and emerging technologies for the treatment of saline wastewater. Among all the individual and hybrid technologies, land-based treatment systems are proven to be the most efficient technologies considering the energy demands, economic, and treatment efficiencies. Likewise, new and sustainable technologies are the need of hour integrating both the treatment and management and the resource recovery factors along with the ultimate goal of the protection in terms of human health and environmental aspect. PRACTITIONER POINTS: Physico-chemical treatment technologies for saline wastewater. Combined/Hybrid technologies for the treatment of saline wastewater. Land-based treatments as the environment friendly and sustainable method for saline wastewater treatment and disposal. Role of phytoremediation in land-based treatment.

Constructed wetland, an eco-technology for wastewater treatment: A review on types of wastewater treated and components of the technology (macrophyte, biolfilm and substrate)

Constructed wetland (CW) represents an efficient eco-technological conglomerate interweaving water security, energy possibility and environmental protection. In the context of wastewater treatment technologies requiring substantial efficiency at reduced cost, chemical input and low environmental impact, applications of CW is being demonstrated at laboratory and field level with reasonably high contaminant removal efficiency and ecological benefits. However, along with the scope of applications, role of individual wetland component has to be re-emphasized through related research interventions. Hence, this review distinctively explores the concerns for extracting maximum benefit of macrophyte (focusing on interface of pollutant removal, root radial oxygen loss, root iron plaque, endophyte-macrophyte assisted treatment in CW, and prospects of energy harvesting from macrophyte) and role of biofilm (effect on treatment efficiency, composition and factors affecting) in a CW. Another focus of the review is on recent advances and developments in alternative low-cost substrate materials (including conventional type, industrial by-products, organic waste, mineral based and hybrid type) and their effect on target pollutants. The remainder of this review is organized to discuss the concerns of CW with respect to wastewater type (municipal, industrial, agricultural and farm wastewater). Attempt is made to analyze the practical relevance and significance of these aspects incorporating all recent developments in the areas to help making informed decisions about future directions for research and development related to CW.

Aquaponics using a fish farm effluent shifts bacterial communities profile in halophytes rhizosphere and endosphere

The intensification of marine aquaculture raises multiple sustainability issues, namely the handling of nutrient-rich effluents that can adversely impact ecosystems. As integrated multi-trophic aquaculture (IMTA) gains momentum, the use of halophyte plants to phytoremediate aquaculture effluents has received growing attention, particularly in aquaponics. It is, therefore, important to obtain a more in-depth knowledge of the microbial communities present in the root systems of these plants, both in their natural environment (sediment) and in aquaponics, in order to understand their nutrient removal potential. The present study used denaturing gradient gel electrophoresis (DGGE) and barcoded pyrosequencing to assess the bacterial community present in the endosphere and rhizosphere of three halophyte plants: Halimione portulacoides, Salicornia ramosissima and Sarcocornia perennis. Species-specific effects were recorded in the profile and diversity of the bacterial communities present in halophyte roots, with significant differences also recorded for the same halophyte species grown in contrasting environments (sediment vs. aquaponics). In aquaponics the most abundant groups belonged to the orders Rhodocyclales, Campylobacterales, Rhodobacterales and Desulfobacterales, while in the natural environment (sediment) the most abundant groups belonged to the orders Rhizobiales, Sphingomonadales and Alteromonadales. An overall enrichment in bacterial taxa involved in nutrient cycling was recorded in the roots of halophytes grown in aquaponics (such as Denitromonas, Mesorhizobium, Colwellia, Dokdonella and Arcobacter), thereby highlighting their potential to reduce the nutrient loads from aquaculture effluents.

Enhanced removal mechanism of iron carbon micro-electrolysis constructed wetland on C, N, and P in salty permitted effluent of wastewater treatment plant

In this study, the combination of a constructed wetland (CW) with iron-carbon (Fe-C) system was used to enhance the simultaneous removal of carbon, nitrogen and phosphorus in salty permitted effluent of wastewater treatment plant (SPE-WTP). The removal mechanism of Fe-C micro-electrolysis CWs with different salinity (0.027, 0.308, and 0.511%) for treating SPE-WTP was investigated, including chemical oxygen demand (COD), phosphorus and nitrogen removal, the mass balance, as well as the changes in the microbial community structure. The results showed the salinity has a certain influence on the contaminant removals, and can enhance nitrogen removal under certain conditions. When the salinity increased from 0.308% to 0.511%, the removal of COD decreased from 68.20% to 62.69%, whereas the removal of total nitrogen (TN) increased from 72.02% to 81.21% in the ICCW-p system (including P. australis as the plant and gravel doped with 3% iron-carbon as the matrix). Microbial degradation, including the electrochemical effect (the degradation by iron-carbon micro-electrolysis) was the main N removal pathway in the ICCW-p system. The ICCW-p system always achieved higher removal rates (such as 81.21% TN and 62.69% COD removals at 0.511% salinity) than that in ICCW-n system (without plants and gravel doped with 3% iron-carbon as the matrix, 63.76% TN and 56.31% COD removals, respectively) and CW-n (without plants and gravel as the matrix, 14.90% TN and 22.39% COD removals, respectively). In addition, high-throughput sequencing analysis revealed that high salinity increased the abundance of N-removing bacteria in the ICCW-p system. Furthermore, with the introduction of iron-carbon in CWs, the removal methods in ICCW-p were diverse, which has enough ability to resist the impact of salinity. Fe electrolysis produced different valence states that acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions, which enhanced the simultaneous removal of carbon, nitrogen and phosphorus.

Removal of nutrients in saline wastewater using constructed wetlands: Plant species, influent loads and salinity levels as influencing factors

This study aims to evaluate how plant species, influent loads and salinity levels affect the removal of nutrients from saline wastewater using constructed wetlands (CWs). CWs planted with Canna indica showed the greatest removal percentages among the four tested species for nitrogen (N) (∼100%) at both low and high influent loads, and ∼100% and 93.8% for phosphorus (P) at low and high influent loads, respectively at an electrical conductivity (EC) of 7 mS/cm (25 °C). The influence of different salinity levels on plant assimilation of N and P varied with their respective concentrations; salinity (e.g., EC at 7, 10 and 15 mS/cm) even enhanced plant absorption of N and P under specific conditions. In conclusion, CWs planted with selected species can be used for the removal of N and P under a range of different salinity levels (e.g., EC at 7, 10 and 15 mS/cm, 25 °C).

Salt tolerant plants increase nitrogen removal from biofiltration systems affected by saline stormwater

Biofiltration systems are used in urban areas to reduce the concentration and load of nutrient pollutants and heavy metals entering waterways through stormwater runoff. Biofilters can, however be exposed to salt water, through intrusion of seawater in coastal areas which could decrease their ability to intercept and retain pollutants. We measured the effect of adding saline stormwater on pollutant removal by six monocotyledonous species with different levels of salt-tolerance. Carex appressa, Carex bichenoviana, Ficinia nodosa, Gahnia filum, Juncus kraussii and Juncus usitatus were exposed to six concentrations of saline stormwater, equivalent to electrical conductivity readings of: 0.09, 2.3, 5.5, 10.4, 20.0 and 37.6 mS cm(-1). Salt-sensitive species: C. appressa, C. bichenoviana and J. usitatus did not survive ≥10.4 mS cm(-1), removing their ability to take up nitrogen (N). Salt-tolerant species, such as F. nodosa and J. kraussii, maintained N-removal even at the highest salt concentration. However, their levels of water stress and stomatal conductance suggest that N-removal would not be sustained at concentrations ≥10.4 mS cm(-1). Increasing salt concentration indirectly increased phosphorus (P) removal, by converting dissolved forms of P to particulate forms which were retained by filter media. Salt concentrations ≥10 mS cm(-1) also reduced removal efficiency of zinc, manganese and cadmium, but increased removal of iron and lead, regardless of plant species. Our results suggest that biofiltration systems exposed to saline stormwater ≤10 mS cm(-1) can only maintain N-removal when planted with salt-tolerant species, while P removal and immobilisation of heavy metals is less affected by species selection.

Potential of Spartina maritima in restored salt marshes for phytoremediation of metals in a highly polluted estuary

Sedimentary abiotic environment, and concentration and stock of nine metals were analyzed in vegetation and sediments to evaluate the phytoremediation capacity of restored Spartina maritima prairies in the highly polluted Odiel Marshes (SW Iberian Peninsula). Samples were collected in two 10 -m long rows parallel to the tidal line at two sediments depths (0-2 cm and 2-20 cm). Metal concentrations were measured by inductively coupled plasma spectroscopy. Iron, aluminum, copper, and zinc were the most concentrated metals. Every metal, except nickel, showed higher concentration in the root zone than at the sediment surface, with values as high as ca. 70 g Fe kg(-1). The highest metal concentrations in S. maritima tissues were recorded in its roots (maximum for iron in Spartina roots: 4160.2 +/- 945.3 mg kg(-1)). Concentrations of aluminum and iron in leaves and roots were higher than in superficial sediments. Rhizosediments showed higher concentrations of every metal than plant tissues, except for nickel. Sediment metal stock in the first 20 cm deep was ca. 170.89 t ha(-1). Restored S. maritima prairies, with relative cover of 62 +/- 6%, accumulated ca. 22 kg metals ha(-1). Our results show S. maritima to be an useful biotool for phytoremediation projects in European salt marshes.