Phytoremediation capabilities of Salvinia molesta, water hyacinth, water lettuce, and duckweed to reduce phosphorus in rice mill wastewater

Experiments and modeling to develop a Pistia stratiotes based Floating Vegetated System (FVS) for the removal of heavy metals (Pb, Zn, Cr, Cu, Ni)

Floating Vegetated System (FVS) emerged as a green and sustainable technology, presenting a viable solution for treating heavy metals (HMs) contaminated water without disrupting the food web. Pistia stratiotes has been used in the design of FVS due to its abundance of aerenchyma tissues, which contribute to its ability to remain buoyant. FVS exhibited significant HMs removal efficiencies, with Pb top at average 84.4 %, followed by Zn (81.1 %), Cr (78.5 %), Cu (76.5 %) and Ni (73 %). Bio-concentration Factor (BCF) and Translocation Factor (TF) values evaluated the plant's adeptness in metal uptake. For plants treated with Cu, the highest post-treatment chlorophyll content of 9 ± 1 mg.ml-1 was observed while Zn induced plant shows the lowest content of 7.1 ± 0.4 mg.ml-1. Using Box-Behnken Design (BBD), the system achieved 81.48 % Pb removal under optimized conditions such as initial Pb conc. of 9.25 mg. l-1, HRT of 24.49 days and a water depth of 26.52 cm. ANOVA analysis highlighted the significant impact of all the factors such as initial HM conc., HRT and wastewater depth on FVS performance. Kinetic analysis estimated a closer observance to the zero-order model, supported by high determination coefficient (R2) values. In conclusion, the FVS, as one of the most eco-friendly technologies, demonstrates higher potential for treating polluted water bodies, offering a sustainable remedy to global metal pollution challenges. Research on FVS for HMs removal is an area of ongoing interest and there are several potential future studies that could be pursued to further understand and optimize their effectiveness such as optimization of plant species, enhancement of plant-metal interactions, effects of environmental factors, economic feasibility studies, disposal of heavy metals accumulated plant, scale-up and application in real-world settings, etc.

Heavy metals/-metalloids (As) phytoremediation with Landoltia punctata and Lemna sp. (duckweeds): coupling with biorefinery prospects for sustainable phytotechnologies

Heavy metals/-metalloids can result in serious human health hazards. Phytoremediation is green bioresource technology for the remediation of heavy metals and arsenic (As). However, there exists a knowledge gap and systematic information on duckweed-based metal phytoremediation in an eco-sustainable way. Therefore, the present review offers a critical discussion on the effective use of duckweeds (genera Landoltia and Lemna)-based phytoremediation to decontaminate metallic contaminants from wastewater. Phytoextraction and rhizofiltration were the major mechanism in 'duckweed bioreactors' that can be dependent on physico-chemical factors and plant-microbe interactions. The biotechnological advances such as gene manipulations can accelerate the duckweed-based phytoremediation process. High starch and protein contents of the metal-loaded duckweed biomass facilitate their use as feedstock in biorefinery. Biorefinery prospects such as bioenergy production, value-added products, and biofertilizers can augment the circular economy approach. Coupling duckweed-based phytoremediation with biorefinery can help achieve Sustainable Development Goals (SDGs) and human well-being.

Biodegradable chelating agents for enhancing phytoremediation: Mechanisms, market feasibility, and future studies

Heavy metals in soil significantly threaten human health, and their remediation is essential. Among the various techniques used, phytoremediation is one of the safest, most innovative, and effective. In recent years, the use of biodegradable chelators to assist plants in improving their remediation efficiency has gained popularity. These biodegradable chelators aid in the transformation of metal ions or metalloids, thereby facilitating their mobilization and uptake by plants. Developed countries are increasingly adopting biodegradable chelators for phytoremediation, with a growing emphasis on green manufacturing and technological innovation in the chelating agent market. Therefore, it is crucial to gain a comprehensive understanding of the mechanisms and market prospects of biodegradable chelators for phytoremediation. This review focuses on elucidating the uptake, translocation, and detoxification mechanisms of chelators in plants. In this study, we focused on the effects of biodegradable chelators on the growth and environmental development of plants treated with phytoremediation agents. Finally, the potential risks associated with biodegradable chelator-assisted phytoremediation are presented in terms of their availability and application prospects in the market. This study provides a valuable reference for future research in this field.

Rice mill wastewater management in the era of circular economy

Several nations around the world use rice as their primary food staple because of its tremendous nutritional value. India's expanding population has sparked a proliferation of rice mills as a result of the country's growing rice demand. However, small and medium-scale industries lack adequate facilities for processing effluents and other waste generated. Paddy is typically processed by parboiling, which involves soaking it in water, boiling it with steam, and then drying and milling. Around 1-1.5 L of water is necessary to partially cook 1 kg of unhusked rice, with approximately half of this water being discharged as effluent. Disposal of rice mill effluent (RME) in water bodies or on the land causes severe damage to soil and water. An inclusive examination of diverse approaches for the treatment and stabilization of partially cooked rice milling effluents is provided. Moreover, the document provides a concise overview of contemporary and environmentally friendly technologies for treating RME. Adsorption, electrocoagulation, chemical coagulation, and bioremediation using microbes, plants, and microalgae are all included in these methods. This manuscript discusses the concept of a circular economy, which is focused on enhancing environmental sustainability through the recycling and repurposing of generated waste into raw materials for the creation of new products. In addition, this review aims to focus on the impact of RME on soils and water species and the status of sustainable management at the point of circular economy with RME bioenergy production (bioelectricity, biomethane, and bio-hydrogen).

Performance evaluation of hybrid constructed wetlands for nitrogen removal and statistical approaches

Nitrogen pollution in water bodies has become a pressing environmental and public health issue worldwide, demanding the implementation of effective nitrogen removal strategies. This research paper delves into the performance evaluation of hybrid constructed wetlands (HCWs) as a sustainable and innovative approach for nitrogen removal, employing a comprehensive year-long dataset gathered from a practical setup. The study collected data under diverse operating conditions to investigate the effectiveness of HCWs in removing nitrogen. Results revealed that HCWs achieved nitrogen removal efficiencies ranging from 28% to 65%, influenced by temperature and hydraulic retention time. Optimal removal occurred at an average temperature of 28°C and a 4-day hydraulic retention time. Notably, performance declined during colder periods, with temperatures below 15°C. The study also aims to predict nitrogen removal by three modeling techniques, that is, artificial neural networks (ANNs), support vector machines Pearson VII kernel function (SVM PUK), and multiple linear regression (MLR). Prediction has been done considering temperature (TEMP), hydraulic loading rate (HLR), initial concentration of chemical oxygen demand (COD) (CODin), initial concentration of total nitrogen (TNin ), initial concentration of total phosphorous (TPin ), and initial concentration of turbidity (TBin ) as input parameters, whereas reduction of total nitrogen (RED TN) is regarded as output parameter. The performance of the soft computing techniques has been compared in terms of coefficient of determination (R2 ), root mean square error (RMSE), and mean absolute error (MAE). The analysis revealed that the performance of the SVM (PUK) model (R2 : 0.572, RMSE: 0.0359, MAE: 0.0294) for the prediction of TN reduction is superior followed by MLR (R2 : 0.562, RMSE: 0.0365, MAE: 0.0294) and ANN (R2 : 0.597, RMSE: 0.0377, MAE: 0.0301). The present study concludes that the treated effluent by the HCWs, using water hyacinth and water lettuce, is of fair quality, thus having potential application for the treatment of rice mill wastewater in warmer climates. Further, machine learning approaches employed in estimating the total nitrogen reduction by HCWs technology have shown promising applicability and utilization in such studies. PRACTITIONER POINTS: Hybrid constructed wetlands (HCWs) are effective in removing nitrogen from wastewater. The performance of HCWs in nitrogen removal can vary due to physical, chemical, and biological processes. The performance of the HCWs highly depends on temperature and hydraulic retention time. Artificial neural networks (ANNs) and support vector machines (SVMs) provided better predictions of nitrogen removal with high accuracy and low root mean square error.

The ppk-expressing transgenic rice floating bed improves P removal in slightly polluted water

With significant economic advantages, the plant floating bed has been widely utilized in the ecological remediation of eutrophic water because of the excessive phosphorus (P) and nitrogen discharge in China. Previous research has demonstrated that polyphosphate kinase (ppk)-expressing transgenic rice (Oryza sativa L. ssp. japonica) (ETR) can increase the P absorption capacity to support rice growth and boost rice yield. In this study, the floating beds of ETR with single copy line (ETRS) and double copy line (ETRD) are built to investigate their capacity to remove aqueous P in slightly polluted water. Compared with the wild type Nipponbare (WT) floating bed, the ETR floating beds greatly reduce the total P concentration in slightly polluted water though the ETR floating beds have the same removal rates of chlorophyll-a, NO3--N, and total nitrogen in slightly polluted water. The P uptake rate of ETRD on the floating bed is 72.37% in slightly polluted water, which is higher than that of ETRS and WT on the floating beds. Polyphosphate (polyP) synthesis is a critical factor for the excessive phosphate uptake of ETR on the floating beds. The synthesis of polyP decreases the level of free intracellular phosphate (Pi) in ETR on the floating beds, simulating the phosphate starvation signaling. The OsPHR2 expression in the shoot and root of ETR on the floating bed increased, and the corresponding P metabolism gene expression in ETR was changed, which promoted Pi uptake by ETR in slightly polluted water. The Pi accumulation further promoted the growth of ETR on the floating beds. These findings highlight that the ETR floating beds, especially ETRD floating bed, have significant potential for P removal and can be exploited as a novel method for phytoremediation in slightly polluted water.

Improving the efficacy of different life-form macrophytes in phytoremediation of artificial eutrophic water by combined planting

Phytoremediation of the eutrophic water bodies by using various macrophytes has long been considered effective and economical. However, the understanding of combining macrophytes to maximize efficacy in the restoration is still limited. In this study, three different life-form macrophytes were employed to explore the optimal plant combination of eutrophic water purification, including Pontederia cordata L. (E: emergent), Pistia stratiotes L. (F: floating), and Hydrilla verticillata (L. f.) Royle (S: submerged). The effects on water quality, removal of the excess nutrients (TN, NH₃-N, NO₃-N, and TP) in the water, along with the growth response and the nutrient accumulation of the macrophytes were investigated both individually and in combination. The phytoremediation of every single macrophyte was significantly improved by combined planting and increasing the diversity of the combination led to better enhancements. In general, the treatment with macrophytes in three life forms (EFS) not only resulted in the highest removal rates of the TN, NH₃-N, NO₃-N, and TP (40.89, 33.50, 46.81, and 43.55%, respectively) but also decreased the turbidity and increased the dissolved oxygen more effectively and efficiently. Furthermore, EFS mitigated the environmental stress of plants and promoted the accumulation of TN and TP in them, especially the emergent macrophyte P. cordata. The combinations with macrophyte in two life forms (EF, ES, and FS) also exhibited unique strengths: the removal efficacy of TN (39.25%) and TP (46.16%) in FS, and NO₃-N in EF (48.54%) and ES (49.90%) were also at the forefront; the biomass and nutrient content of the submerged macrophyte H. verticillata in ES were the highest. Moreover, a strong correlation between the eutrophic factors and the plant physiological indexes was observed. These findings highlighted the role of combined planting in phytoremediation and provided a valuable reference for the development of ecological restoration for eutrophic ecosystems.

Process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system

Phytofiltration is an eco-friendly and cost-effective approach to the management of pollutants in aquatic system. The present study aimed at elucidating the process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system. The invasion of macrophytes, such as Pistia stratiotes, of water bodies is an undesirable experience because of the challenges synonymous with their occurrence. Owing to the unfettered proliferation, high and rich biomass generation, and nutrient uptake capability, these macrophytes outcompete the native vegetation and reduce the distinctiveness of the biological communities at various scales. However, these same intrinsic features positioned them as an ideal phytofiltration species for the decontamination of polluted aqua systems. Herein, we provided an overview of the process of phytofiltration in an aquatic system, and the need to create a balanced ecological system through the exploitation of the potentials of macrophytes as phytoremediators. The translocation factor, type, and concentration of pollutants in the matrix, pH value, type of macrophyte employed are among the factors identified as determinants of the success or failure of invasive macrophytes as pollutant remediators in the aqua system. Therefore, the optimization of these variables, to enhance the phytoremediation potentials of the different macrophytes were critically appraised.

Evaluation for phosphorus accumulation and removal capability of nine species in the Polygonaceae to excavate amphibious superstars used for phosphorus-phytoextraction

Reducing excessive phosphorus (P) from both soils and eutrophic waters is attractive to achieve environmental P balance, and P-phytoextraction by amphibious plants with great biomass and P uptake is an amazing method, as already reported for P-accumulating plant, Polygonum hydropiper. However, it is still unknown how widespread high P tolerance and great P accumulation is among species in the Polygonaceae, and if there are new amphibious superstars used for P-phytoextraction. We used six Polygonum species and three non-Polygonum species to compare P accumulation and removal capability in hydroponics and soils with different P treatments. In high P hydroponics, all species showed superiority in growth and P accumulation without P toxicity, except for F. multiflora. In high P soils, all species showed much better growth performance with green leaves at 8 weeks, with shoot biomass being 3.60-29.49 g plant^-1. At 8 weeks, Polygonum species displayed obviously higher shoot P accumulation (31.32-152.37 mg plant^-1), P extraction ratio (3.16%-15.36%), maximum potential P removal (13.89-67.59 kg ha^-1), and much lower plant effective number (7-32) than non-Polygonum species under high P soils. Besides, P. lapathifolium, P. divaricatum and P. orientale ranked the top three in growth with P concentration more than 10 mg g^-1 dry weight in hydroponics and showed dominant advantage in P accumulation and P removal from high P soils. Through the cluster analysis, P. lapathifolium was always separated into a class, and P. divaricatum and P. orientale more likely clustered together. It is therefore that P. lapathifolium, P. divaricatum and P. orientale are tolerant to high P and attractive in P accumulation and P removal from high P waters and soils, and thus can be used as new amphibious superstars for P-phytoextraction, particularly P. lapathifolium.

Physiological defense and metabolic strategy of Pistia stratiotes in response to zinc-cadmium co-pollution

Pistia stratiotes is a cadmium (Cd) hyperaccumulating plant with strong bioaccumulation and translocation capacity for Cd. A hydroponic experiment was used to evaluate the combined effect of Zinc (Zn) and Cd at different concentrations on leaf growth and metabolism of P. stratiotes. This study revealed the physiological defense and metabolic strategy of responses to Zn-Cd co-pollution. With the Zn₅₀Cd₁, Zn₅₀Cd₁₀, Zn₁₀₀Cd_1, and Zn₁₀₀Cd₁₀ treatments for 9 d, the relative crown diameter, relative leave number, and ramet number of the plant had no significant difference with the control. Under the compound treatments containing Zn₅₀Cd₅₀ and Zn₁₀₀Cd₅₀, the activity of the glyoxalase system and amino acid metabolism in the leaves were inhibited. The leaf photosynthetic apparatus increased heat dissipation to reduce the damage to the photosystem II (PS II) reaction center caused by excess excitation energy under Zn-Cd stress. This safeguarded the balance between the absorption and utilization of light energy. Compared to the control, the Zn and Cd co-pollution for 9 d had no effect on the reduced glutathione (GSH) and oxidized glutathione (GSSG) contents. There was no effect on the dehydroascorbate reductase (DHAR) and glutathione reductase (GR) activities, but there was increased ascorbate peroxidase (APX) activity and oxidized ascorbic acid (DHA) content. These increased the antioxidant capacity of the ascorbate-glutathione (AsA-GSH) cycle. The treated plants also had increased levels of carnosol and substances related to lipid metabolism including 9, 10-Dihydroxystearate, Prostaglandin G2, Sphingosine, and 13-L-Hydroperoxylinoleic acid, maintaining the cell stability and resistance to the Zn-Cd stress.

Tolerance mechanism and phytoremediation potential of Pistia stratiotes to zinc and cadmium co-contamination

Pistia stratiotes can not only effectively remediate eutrophic water, but also displays strong absorption and bioaccumulation abilities for heavy metals. However, it has not been well-understood how the plant resists the combined stress of heavy metals. In these experiments, the morphophysiological traits, the ascorbate-glutathione (AsA-GSH) cycle, the glyoxalase system, and the contents of zinc (Zn) and cadmium (Cd) were investigated under Zn and Cd co-pollution. The AsA-GSH cycle and glyoxalase system could coordinately alleviate the oxidative and carbonyl stress, which was identified as an important tolerance mechanism. With Zn₅₀Cd₁, Zn₅₀Cd₁₀, Zn₁₀₀Cd₁, and Zn₁₀₀Cd₁₀ treatments for 18 days, 90.75-93.69% of Zn and 88.13-96.96% Cd accumulated in the roots. Treatments with Zn₅₀Cd₅₀, and Zn₁₀₀Cd₅₀ for 18 days resulted in a decrease of stress tolerance and chlorophyll content in leaves, an increase in plasma membrane permeability, a massive accumulation of methylglyoxal (MG), and visible toxic symptoms. Additionally, the bioaccumulation factor (BCF) for roots and shoots and the translocation factor (TF) were >1, and the content of Cd in shoots was no <100 mg·kg^-1. This indicated P. stratiotes was a Cd hyperaccumulator and have great potential for the phytoremediation of heavy metal contaminated water.Novelty statement Pistia stratiotes, a cadmium hyperaccumulator, has great application potential for the phytoremediation of zinc and cadmium co-polluted water.

Differential efficacy of water lily cultivars in phytoremediation of eutrophic water contaminated with phosphorus and nitrogen

Excessive inputs of phosphorus (P) and nitrogen (N) trigger eutrophication of the water bodies, which promotes the undesirable growth of algal bloom and deterioration of the water quality, and aquatic biodiversity. Macrophytes provide an environmentally benign and economically viable paradigm for the ecological restoration of eutrophic aquatic ecosystems. Water lily (Nymphaea) is largely used as ornamental plant for landscaping, and it has been documented that water lily possesses the potentiality in mitigating polluted aquatic environments. In the present study, water lily cultivars Nymphaea Texas Dawn (NTD), Nymphaea Colorado (NC), Nymphaea Madame Wilfron Gonnère (NMWG), and Nymphaea Sunshine Princess (NSP) were investigated for their potency in alleviating the eutrophication. The concentrations of total P and total N were significantly higher in the leaves of NC and NSP compared with NTD and NMWG. Therefore, NC and NSP were selected for subsequent studies to decipher their recuperation efficacy on eutrophic waters at different growth stages. NC and NSP significantly reduced the concentrations of eutrophication indicators i.e., total P, NH₄⁺-N, and chemical oxygen demand in different gradients of the simulated eutrophic water in a growth-dependent manner. On the contrary, NC and NSP triggered a significant increase in the concentration of dissolved oxygen particularly at the seedling stage. Notably, the concentrations of total P (shoot and root) and total N (root) were relatively higher in NSP than NC. The study thus revealed a growth-dependent differential efficacy of NSP and NC in mitigating the different eutrophic waters.

Heavy Metals Assimilation by Native and Non-Native Aquatic Macrophyte Species: A Case Study of a River in the Eastern Cape Province of South Africa

There is continuous deterioration of freshwater systems globally due to excessive anthropogenic inputs, which severely affect important socio-economic and ecological services. We investigated the water and sediment quality at 10 sites along the severely modified Swartkops River system in the Eastern Cape Province of South Africa and then quantified the phytoremediation potential by native and non-native macrophyte species over a period of 6 months. We hypothesized that the presence of semi and permanent native and non-native macrophytes mats would reduce water and sediment contamination through assimilation downriver. Our results were variable and, thus, inconsistent with our hypotheses; there were no clear trends in water and sediment quality improvement along the Swartkops River. Although variable, the free-floating non-native macrophyte, Pontederia (=Eichhornia) crassipes recorded the highest assimilation potential of heavy metals in water (e.g., Fe and Cu) and sediments (e.g., Fe and Zn), followed by a submerged native macrophyte, Stuckenia pectinatus, and three native emergent species, Typha capensis, Cyperus sexangularis, and Phragmites australis. Pollution indices clearly showed the promising assimilation by native and non-native macrophytes species; however, the Swartkops River was heavily influenced by multiple non-point sources along the system, compromising the assimilation effect. Furthermore, we emphasise that excessive anthropogenic inputs compromise the system's ability to assimilate heavy metals inputs leading to water quality deterioration.

Recent developments and applications of floating treatment wetlands for treating different source waters: a review

Most water bodies around the world suffer from pollution to varying degrees. Floating treatment wetlands (FTWs) are a simple and efficient ecological treatment technology and have been widely studied and applied as a sustainable solution for different source waters. Based on the analysis of abundant literature in the last ten years, this paper systematically reviews the history and the latest development of FTWs. Meanwhile, the treatment performance and pollutant removal mechanisms of FTWs on the natural water, stormwater, domestic wastewater, industrial wastewater, and agricultural runoff are analyzed. In particular, very interesting information is provided, such as water depth, water surface coverage, the ratio of dissolved to total phosphorous (DRP/TP), the ratio of nitrogen to phosphorous (N/P), BOD/COD ratio, and its effects on the efficiency and removal mechanisms of FTWs. This information will provide useful references and guidance for optimizing the design of FTW and pollutant treatment efficiency of different source waters. This paper also provides an objective review of the limitations of FTWs. Subsequently, the enhancements of FTW technology which are recognized to be effective, including aeration, adding functional fillers or obligate degrading bacteria, and construction of hybrid FTWs, are summarized and recommendations are made for further research.

An experimental investigation on phytoremediation performance of water lettuce (Pistia stratiotes L.) for pollutants removal from paper mill effluent

The present study describes the phytoremediation performance of water lettuce (Pistia stratiotes L.) for physicochemical pollutants elimination from paper mill effluent (PME). For this, pot (glass aquarium) experiments were conducted using 0% (BWW: borewell water), 25%, 50%, 75%, and 100% treatments of PME under natural day/light regime. Results of the experiments showed that the highest removal of pH (10.75%), electrical conductivity (EC: 63.82%), total dissolved solids (TDS: 71.20%) biological oxygen demand (BOD: 85.03%), chemical oxygen demand (COD: 80.46%), total Kjeldahl's nitrogen (TKN: 93.03%), phosphorus (P: 85.56%), sodium (Na: 91.89%), potassium (K: 84.04%), calcium (Ca: 84.75%), and magnesium (Mg: 83.62%), most probable number (MPN: 77.63%), and standard plate count (SPC: 74.43%) was noted in 75% treatment of PME after treatment by P. stratiotes. PCA showed the best vector length for TKN, Na, and Ca. The maximum plant growth parameters including, total fresh biomass (81.30 ± 0.28 g), chlorophyll content (3.67 ± 0.05 mg g^-1  f.wt), and relative growth rate (0.0051 gg^-1  d^-1 ) was also measured in 75% PME treatment after phytoremediation experiments. The findings of this study make useful insight into the biological management of PME through plant-based pollutant eradication while leftover biomass may be used as a feedstock for low-cost bioenergy production. PRACTITIONER POINTS: Biological treatment of paper mill effluent using water lettuce is presented. Best reduction of physicochemical and microbiological pollutants was attained in 75% treatment. Maximum production of chlorophyll, plant biomass, and highest growth rate was also observed in 75% treatment.

Invasive Water Hyacinth: Ecology, Impacts and Prospects for the Rural Economy

Water hyacinth (WH) is notorious for causing severe environmental degradation and being an economic burden to manage. However, it offers substantial prospects if exploited, especially by rural communities. High temperatures, eutrophic conditions and other environmental factors promote the proliferation of the plant in regions where it has been introduced. Regarded as among the world's worst invasive weeds, WH is nearly impossible to control and eradicate without an integrated approach and community participation. The effectiveness of control methods varies, yet sustained community involvement determines the long-term success of these methods. Reproducing rapidly, WH has the resource capacity to support a unique microeconomic ecosystem, incentivising WH control by generating sustainable income. The WH ecology, the socioeconomic impacts of its invasion and its various applications are reviewed, and revenue generation and cost-saving options are highlighted. A circular microeconomic model is proposed by integrating WH valorisation into the general limitations of a rural community. Empowering locals with opportunities and enticing them with potential economic gains can be a nudge towards a pro-environment behavioural change in managing WH. This would aid in upgrading local livelihoods and could foster resilience within the community in tackling both environmental problems and economic setbacks through the management of WH invasions.

Performance of Salvinia molesta plants in tertiary treatment of domestic wastewater

The objective of this study was to investigate the performance of different weight of Salvinia molesta plants in biological treatment of domestic wastewater. Three treatment systems containing 280g (GS1), 140g (GS2) and 70g (GS3) of S. molesta plants were used for the phytoremediation process. Physicochemical analysis such as pH, colour, chemical oxygen demand (COD), and biological oxygen demand (BOD₅) of the influent and effluent water samples were performed according to spectrophotometric methods. The outcome of the study demonstrated that the different weight of S. molesta plants played a significant role in improving the quality of the wastewater samples, in which GS1 removed 96.8% (colour), 91% (BOD₅), and 82.6% (COD). While up to 88.6% (colour), 87.1% (BOD₅), and 81.1% (COD) reduction was observed for GS2 treatment systems, and GS3 was efficient in removing 85.5% (colour), 86.1% (BOD₅), and 68.3% (COD). Also, a pH value of 6.29–7.19, 5.97–7.07, and 6.17–7.42 was obtained from GS1, GS2 and GS3 treatment systems, respectively. Thus, the treatment system with the highest quantity of S. molesta (GS1) demonstrated better performance compared to the other two systems (GS2 and GS3). The findings of this research can be applied in addressing the goals of sustainable development through the use of green technology to reduce the threat of water pollution in natural water bodies. Perhaps existing and future water scarcity can be resolved through the use of phytoremediation technology.

A review on current techniques used in India for rice mill wastewater treatment and emerging techniques with valuable by-products

Parboiling rice mills produce a large amount of wastewater. The effluent from the rice mill contains high concentration of organic and inorganic compounds. Continuous discharge of this wastewater from rice mills could be a major cause of eutrophication of the water bodies, leading to a robust and undesirable growth of vegetation and algal bloom. Eutrophication leads to deoxygenation of water bodies, resulting in the mortality of aquatic flora and fauna. It is therefore very important to treat wastewater and ensure safe disposal. There are various types of processes already in existence, but the most important thing is to select a cost-effective technique. Phytoremediation technique has shown promising results for low-income countries like India. It is useful for the small-scale industrial and domestic wastewater treatment. It is a slow process, requiring a large area of land. It is an eco-friendly approach and ideal for rural areas where there is ample land availability. This paper addresses the techniques used by various researchers for rice mill wastewater treatment and also focuses on reusing and recycling of waste from rice mills. The performance of every technique is discussed in detail with its specific advantages and disadvantages. This paper also focuses on the advanced techniques of water treatment with valuable by-products such as silica, activated adsorbent, electricity and methane gas.

Assessing the impact of vegetation coverage ratio in a floating water treatment bed of Pistia stratiotes

Floating bed (FB) is one of the low cost and efficient system to treat polluted water bodies in rural as well as urban area. It requires less space compared to other macrophyte based treatment system. Vegetation coverage is an effective factor as atmospheric oxygen diffusion to water body depends upon this. When a water body is fully covered by vegetation, it prevents the diffusion of atmospheric oxygen, which is a major source of dissolved oxygen (DO). An optimum vegetation coverage is necessary to obtain maximum treatment efficiency and to verify this a laboratory scale experiment was performed with various vegetation coverage ratio (VCR) of 0, 0.25, 0.5, 0.75, 1. Organics and nutrient removal were measured corresponding to initial floating bed VCR. COD removal for VCR 1.0, 0.75, 0.5, 0.25 and 0 were 86.4%, 93.6%, 96.2%, 85.4% and 60.8%, respectively. The roots of macrophyte (Pistia stratiotes) supports growth of microorganism, which perform biodegradation of organics as well as uptake nutrients. Maximum NH4+-N and PO43−-P removal were observed at VCR of 0.75 and 1.0, respectively. In the tanks with VCR of 0.25, 0.5 and 0.75, the final DO was more than 4 mg/L, which is the requisite DO value for survival of aquatic organism.

Responses of phytoremediation in urban wastewater with water hyacinths to extreme precipitation

Climate change not only intensifies eutrophication and enhances the rainfall, but also elevates the contents of greenhouse gases, which can further increase the intensity and frequency of extreme precipitation events. The effectivity of phytoremediation of urban wastewaters by water hyacinths under an extreme rainfall event (up to 380 mm d^-1) was investigated using self-designed fabrications with six flow rates (2-15 m³ d^-1) in situ on pilot scale for 30 days. The results suggest that water hyacinths had high N and P removal capacities even under adverse conditions such as low dissolved oxygen concentrations (DO, <1 mg L^-1) and high ammonium concentrations (NH₄⁺-N, >7 mg L^-1). Specifically, the highest removal yields of N and P were 13.14 ± 0.47 g N·m^-2·d^-1 and 2.12 ± 0.04 g P·m^-2·d^-1, respectively. The results indicate that water hyacinths can be used for water treatment to reduce the amounts of NH₄⁺-N, dissolved organic nitrogen (DON) and phosphate (PO₄^3-) even during extreme precipitation events. Moreover, DO increased due to wet deposition, runoff and surface flows during the extreme rainfall event, resulting in shifts between nitrification and denitrification processes which significantly altered nitrogen forms in urban wastewater. Results of this study suggest that water hyacinths could be recommended as a cost-effective and eco-friendly technology for urban wastewater phytoremediation in areas suffering from frequent extreme precipitation events.