Treatment efficiency of a hybrid constructed wetland system for municipal wastewater and its suitability for crop irrigation

Phytoextraction Options

Wastewaters often contain an array of economically valuable elements, including elements considered critical raw materials and elements for fertilizer production. Plant-based treatment approaches in constructed wetlands, open ponds, or hydroponic systems represent an eco-friendly and economical way to remove potentially toxic metal(loid)s from wastewater (phytoextraction). Concomitantly, the element-enriched biomass represents an important secondary raw material for bioenergy generation and the recovery of raw materials from the harvested plant biomass (phytomining). At present, phytoextraction in constructed wetlands is still considered a nascent technology that still requires more fundamental and applied research before it can be commercially applied. This chapter discusses the different roles of plants in constructed wetlands during the phytoextraction of economically valuable elements. It sheds light on the utilization of plant biomass in the recovery of raw materials from wastewater streams. Here, we consider phytoextraction of the commonly studied water pollutants (N, P, Zn, Cd, Pb, Cr) and expand this concept to a group of rather exotic metal(loid)s (Ge, REE, PGM) highlighting the role of phytoextraction in the face of climate change and finite resources of high-tech metals.

An integrated decision making approach for selecting a sustainable waste water treatment technology

Growing global energy demand and the depletion of fossil fuels have highlighted the need for alternate and environmentally benign energy sources. The volume of untreated waste water being disposed of straight into fresh water is becoming a major concern. An integrated treatment method can address the problems of bio-energy generation and wastewater management as both processes can use wastewater as a substrate. Linear diophantine fuzzy sets help handle the uncertainty and difficulties that arise while deciding on an effective treatment technique. The use of control parameters makes these fuzzy sets unique and superior to other existing fuzzy sets. A modified strategy incorporating the Pivot pairwise relative criteria importance assessment and Interactive multi-criteria decision making methodologies is proposed for the linear diophantine fuzzy environment. The applicability and effectiveness of the developed model are established by choosing an appropriate wastewater treatment technology in the context of linear diophantine fuzzy sets. In addition, sensitivity analysis is used in this study to determine the stability of the developed framework. Further, comparison analysis is also addressed to assess the validity of the acquired results.

Heavy metals phytofiltration potential of Hydrocotyle umbellata from Nullah Lai wastewater and its environmental risk

This study aims to examine the heavy metal phytofiltration potential of Hydrocotyle umbellata from Nullah Lai wastewater and its environmental risk. Wastewater was initially analyzed for heavy metals and physicochemical parameters and compared with irrigation water standards. The phytofiltration potential of H. umbellata was determined by periodically monitoring heavy metal concentrations at time points T1 (day 05), T2 (day10), T3 (day 15), and T4 (day 20). This study shows that some water parameters reached the permissible limits after treatment with H. umbellata. Results of the risk analysis reveal a significant discharge (kg d^-y) of heavy metals to arable land. Phytofiltration efficiency of H. umbellata for water quality parameters was in order of Ni (98.75%), Cr (98.11%), Cd (95.84%), Pb (94.90%), Cu (94.10%), Zn (85.34%), BOD (53.67%), TDS (29.28%), EC (27.31%), Cl (6.65%), and SAR (6.34%). The growth of H. umbellata in wastewater resulted in heavy metal bioaccumulation in both roots and shoots of the plant. Less than 01 translocation factor (TF) values for cadmium, copper, lead, chromium, and zinc showed the metal tolerance ability of the tested plant. These results demonstrated that treated water could be used in water-deficient peri-urban areas as supplementary irrigation.

Phytoremediation of heavy metals and total petroleum hydrocarbon and nutrients enhancement of Typha latifolia in petroleum secondary effluent for biomass growth

Phytoremediation is an innovative tool which can be used for the treatment of industrial and agricultural wastewater. Typha latifolia (T. latifolia) is an aquatic plant used for phytoremediation of heavy metals (HMs) like cadmium (Cd), cobalt (Co), manganese (Mn), and TPH (total petroleum hydrocarbon) for the treatment of petroleum secondary effluent (PSE). During this experiment, the growth of T. latifolia in biomass, nutrient concentrations, and heavy metals were studied. The results indicated that T. latifolia was more tolerant to Cd, Co, and Mn due to its transfer index (TI) which was found to be greater than 2.9. The enrichment coefficients of the metals, Cd and Co present in the root were found to be higher than 3.31 to 2.56 and 5.35 to 3.55, respectively unlike the stem of T. latifolia. But, the enrichment coefficient of Mn was found to be 1.98 which was expected to be 3.51 at 75%. Similarly, the enrichment coefficients of all the metals, except for Co, in roots of T. latifolia were higher than 5.36. (TI) for Co (2.95) and Mn (2.55) which is better as compared to the enrichment coefficients of Cd (2.35) and TPH (3.45) in PSE. Thus, there is a possibility that PSE could be a source of important nutrients.

Materials in constructed wetlands for wastewater remediation: A review

The wastewater treatment industry is constantly evolving to abate emerging contaminants and to meet stringent legislative requirements. The existing technologies need to be modified, or new innovative treatment techniques need to be developed to ensure environmental protection and secure sustainability in the future. Emphasis is mainly on nutrient recovery, energy-efficient systems, zero waste generation, and environmentally friendly techniques. Constructed wetlands (CWs) have evolved as natural, eco-friendly, economical, and low-maintenance alternatives for wastewater remediation. These wetlands employ several materials as adsorbents for the treatment, commonly known as media/substrate. This review paper presents an assessment of various materials that can be used as substrates in CWs for the efficient removal of organic and non-biodegradable pollutants in different types of wastewaters. The effect of pH, mineral composition, specific surface area, and porosity of various natural materials and agricultural and industrial wastes used as media in CWs for wastewater remediation was discussed. The study showed that different substrates like alum sludge, limestone, coal slags, rice husk, and sand had removal efficiency for chemical oxygen demand (COD): 71.8%-82%, total phosphorous (TP): 77%-80%, and total nitrogen (TN): 52%-82% for different types of wastewaters. It also highlights the challenges related to the long-term sustainability of these materials. PRACTITIONER POINTS: Physicochemical characteristics influence the removal efficiency of the materials Life of media is also important along with removal efficiency and cost The sustainability of materials is very crucial for the overall performance of the system.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

Metal accumulation potential, human health risks, and yield attributes of hundred bread wheat genotypes on irrigation with municipal and remediated wastewater

This study was carried out to screen historical diversity panel of bread wheat against municipal wastewater (MW) and remediated wastewater (RW) irrigation to find tolerant and sensitive genotypes and their impact on yield attributes. The experiment was conducted in randomized complete block design (RCBD) with three water treatments, i.e., tap water (TW), RW, and MW. Yield attributes, health risk assessment, water and soil chemistry were recorded. Principal component analysis (PCA) was used to identify tolerant and sensitive genotypes of wheat on the basis of metal accumulation. Metal accumulation in grains increased in pattern K > Fe > Zn in all irrigation treatments. Tolerant genotypes in MW showed lowest hazard quotient (HQ) and hazard index (HI) values (adults 0.62; children 0.67) for Fe and Zn as compared to sensitive genotypes (adults 1.53; children 1.70). However, HI values in sensitive and tolerant genotypes of RW were recorded < 1. Mean values of yield attributes, i.e., plant height, spike length, spikelet per spike, grains per plant, biological yield, grain yield, and thousand kernel weight, were recorded in pattern, i.e., MW > RW > TW. In this study, yield attributes and human health are affected in both cases of higher and lower concentration of Fe and Zn metal. It is suggested that tolerant genotypes can prove useful for cultivation in areas receiving MW and also provide molecular breeding opportunities for seeking tolerance against metal stresses.

Wastewater Discharge through a Stream into a Mediterranean Ramsar Wetland: Evaluation and Proposal of a Nature-Based Treatment System

Impacts on wetlands are becoming more pressing every day. Among them, habitat loss, overexploitation of aquifers and changes in land use are considered the most important. However, the impacts linked to wastewater discharges are increasing worldwide. In this context, this study analyses the impacts of input of wastewater to a Mediterranean Ramsar temporary wetland (Fuente de Piedra, south of Spain). To this end, systematic sampling was carried out in the Charcón stream which receives water from a wastewater treatment plant (WWTP) and discharges it into the wetland. The results showed a slight decrease in the nutrient concentrations, particularly for nitrogen compounds. Heterotrophic and fecal bacteria concentration, as well as phytoplankton and zooplankton abundance and biomass, all significantly decreased from the treatment plant to the wetland. When comparing the effect of this discharge with other similar occurring to the same wetland, it was evident that the Charcón stream was responsible for a greater impact. At this point, it is relevant to note that the main difference among both treated wastewater discharges lies in the different water retention time once the wastewater was released from the WWTP. In fact, we recommend an increase in the water retention time by building seminatural ponds, together with the use of biofilters, which will notably contribute to improve the processes of assimilation of nutrients and to decrease the impact generated in the wetland by this spill.

Heavy metal phyto-accretion, biochemical responses and non-carcinogenic human health risks of genetically diverse wheat genotypes cultivated with sewage of municipal origin

Current study explored the effects of municipal sewage (MS) irrigation on heavy metal phyto-accretion, biochemical responses and human health risks of diverse wheat genotypes along with recycled municipal sewage (RMS). Mean concentrations of PO₄^3-, NO₃^--N, chemical oxygen demand, biological oxygen demand, K, Co, Cu, Cd, Cr and Ni were found higher in MS than irrigation criteria. This led to significant increase in heavy metal contents in roots, stem and grains of MS irrigated wheat genotypes compared to RMS and control treatments. No adverse health risk effects for individual or multiple metals were recorded in RMS irrigated wheat genotypes on grounds of lowest heavy metal accumulation. Multivariate techniques i.e. principal component analyses (PCA) and hierarchical agglomerative cluster analyses (HACA) identified tolerant (inefficient metal accumulators) and sensitive (efficient metal accumulators) wheat genotypes in MS and RMS. Tolerant wheat genotypes showed lowest accumulation of heavy metals, efficient biochemical mechanisms to combat oxidative stress and lower health risks to adults/children. Cultivation of identified tolerant wheat genotypes is recommended in areas receiving municipal wastes to reduce human and environmental health risks. Moreover, genetic potential of identified tolerant wheat genotypes from MS and RMS can be utilized in breeding heavy metal tolerant wheat germplasm worldwide.

The Importance of Biological and Ecological Properties of Phragmites Australis (Cav.) Trin. Ex Steud., in Phytoremendiation of Aquatic Ecosystems—The Review

Phragmites australis (common reed) is one of the most extensively distributed species of emergent plant worldwide. The adaptive features of this plant show its competitive character. Owing to high intraspecific diversity of common reed, as well as its phenotypic plasticity, the plant shows a broad ecological amplitude. Moreover, the plant exhibits a high capacity for acclimatization to environmental conditions which are considered adverse. This plant has been used for many years in phytoremediation to purify various types of wastewater. Phragmites australis has a high ability to accumulate various nutrients, heavy metals, and micropollutants, and in this respect, it is superior to other aquatic plants. This review examines the existing literature on the biological and ecological properties of common reed, the use of common reed in wastewater treatment for removing pollutants and tolerance for metals, and in hydrophyte treatment systems. It seems vital to conduct further research on the physiology and biochemistry of the common reed, with the aim of increasing the plant’s efficiency for pollutants removal.

A small-scale study of plant orientation in treatment performance of vertical flow constructed wetland in continuous flow

In constructed wetland (CW) ecology, plants play a vital role in wastewater treatment. The plants provide an adequate surface to various microorganisms, transfers oxygen and uptake nutrients to treat wastewater. This study deals with the treatment of greywater by using vertical flow constructed wetland system (VFCW). In the present study, two reactors were prepared for two different orientations in monoculture (S-1) and mixed culture (S-2) by using four types of macrophytes (Canna indica, Colocasia, Hymenocallis littoralis, and Phragmites australis). The reactors were operated in continuous mode for 90 days by maintaining the 10 mL/min flow rate and 1-day retention time. The mean removal efficiency of S-1 is 40.70, 33.69, 27.13, 48.17, 66.76, and 50.82% for ammonia, total kjeldahl nitrogen (TKN), phosphate, sulfate, turbidity, and chemical oxygen demand (COD), respectively. The mean removal efficiency of S-2 CW is 53.06, 34.54, 37.49, 48.64, 69.26, and 58.26% for ammonia, TKN, phosphate, sulfate, turbidity, and COD, respectively. ANOVA showed significant differences among both VFCWs in removal efficiency for all measured parameters. The performance of the two systems was compared with each other with the significance level of p = 0.05. The results indicated that the orientation of plant plays a major role in the removal of various physicochemical parameters.

Nitrogen Removal from Domestic Wastewater and the Development of Tropical Ornamental Plants in Partially Saturated Mesocosm-Scale Constructed Wetlands

Vertical partially saturated (VPS) constructed wetlands (CWs) are a novel wastewater treatment system for which little information is known about its design parameters and performance under tropical climates. The objective of this study is to evaluate the nitrogen removal process from domestic wastewater and the production of tropical ornamental plants (Canna hybrids and Zantedeschia aethiopica) in VPS CWs at a mesocosms scale. Nine VPS CWs, with a free-flow zone of 16 cm and a saturated zone of 16 cm, were used as experimental units. Three units were planted with Canna hybrids., and three, with Zantedeschia aethiopica (one plant per unit); the remaining three units were established as controls without vegetation. They were fed with domestic wastewater intermittently and evaluated for the elimination of COD, N-NH₄, N-NO₃, Norg, NT, and PT. The results showed an increase in the removal for some pollutants in the vegetated systems, i.e., N-NH₄ (35%), Norg (16%), TN (25%), and TP (47%) in comparison to the unvegetated systems. While N-NO₃ removal showed better removal in 10% of the systems without vegetation, no significant differences were found (p > 0.05) for COD removal. The aerobic and anaerobic conditions in the VPS CWs favor the elimination of pollutants in the systems, and also the development of the tropical species evaluated in this study; good development was exhibited by a high growth rate and biomass production.

Heavy metal phyto-accumulation in leafy vegetables irrigated with municipal wastewater and human health risk repercussions

In this study, heavy metal phyto-accumulation potential of selected cultivars of two leafy vegetables on irrigation with municipal wastewater and human health risks were investigated. Municipal wastewater chemistry was recorded significantly different from groundwater control and led to the two-fold high enrichment of soil heavy metal contents (Ni, 19.46; Pb, 23.94; Co, 4.68; Cd, 1.4 in mg/kg, respectively). Interactive effects for phyto-accumulation of most heavy metals were also recorded significant at p < 0.001 in four vegetable cultivars. Heatmap revealed higher accumulation of heavy metals (Fe, Zn, Mn, Cu, Pb, Cr, Co) in spinach cultivars than lettuce cultivars creating elevated health risk index (HRI) and hazard index (HI) values for adults and children. Highest HI was recorded for Lahori palak (adults, 1.42; children, 2.58) and lowest for iceberg (adults, 0.04; children, 0.07). The NPK supplementation improved mineral composition of leafy vegetables within safer human health limits in control treatments. However, in municipal wastewater treatments, NPK fertilization decreased heavy metal uptake and phyto-accumulation in S2 (Lahori palak) than remaining vegetable cultivars leading to reduced health risk values. Because of higher heavy metal phyto-accumulation and health risks, cultivation of spinach cultivars must be discouraged in agro-ecologies receiving municipal wastes, whereas lettuce cultivars should be promoted.