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Article

Treatment of High Nutrient-Loaded Wastewater in a Constructed Floating Wetland with Different Configurations: Role of Lantana Biochar Addition

by
Preeti Parihar
1,
Naveen Chand
2 and
Surindra Suthar
1,*
1
School of Environment & Natural Resources, Doon University, Dehradun 248001, India
2
Environmental Engineering Research Group, National Institute of Technology Delhi, New Delhi 110040, India
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(23), 16049; https://doi.org/10.3390/su142316049
Submission received: 16 October 2022 / Revised: 10 November 2022 / Accepted: 27 November 2022 / Published: 1 December 2022
(This article belongs to the Special Issue Cutting-Edge Technologies for Wastewater Management and Environmental Protection)
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Abstract

:
Constructed wetlands (CW) with carbon stock in substrate matrix show high efficiency in wastewater nutrient removals. In this study, five batch-scale CW setups with varying Lantana weed biochar (BC) doses (5, 10, and 15%) in substrate matrix were established and changes in high nutrient-loaded wastewater parameters, ammonium N (NH4+-N), chemical oxygen demand (COD), nitrate (NO3-N), sulfate (SO4−2), and phosphate (PO4−3), were monitored for 240 h hydraulic retention time (HRT). BC amount directly affected the removal mechanism of CWs and a significant reduction in COD (>92.71%) was recorded. CW setup with a 15% BC dose showed the maximum removal of PO4−3 (79.06%), NH4+-N (78.79%), SO4−2 (67.93%), and NO3-N (77.42%) from wastewater. The theory of BC facilitated physical removal, microbial facilitation, and chemical kinetics improvements are proposed for better removal of wastewater nutrients in studied CWs. Research results could be utilized to design a low-cost domestic wastewater treatment facility using BC for rural areas under a decentralized water treatment program.

1. Introduction

The usage of eco-sustainable and economical solutions to treat wastewater has been encouraged in many nations all over the world [1,2,3]. Out of various technologies for low-cost wastewater treatment, CW is considered to be a sustainability-recognized process. CWs have been utilized for a long time for treating both disseminated and point-source pollutants, such as metals, pathogens, wastewater nutrients, suspended solids, organic compounds, etc., from wastewater [2,3,4,5]. Under this approach, the macrophytes-based floating CW system could be a sustainable approach to treating nutrient-rich urban wastewater with multiple benefits, such as groundwater recharge, pollution removal, biomass production, aesthetic beautification of wastelands, and development of habitats for aquatic animals and birds, etc. [6,7,8,9]. Aquatic macrophytes (duckweed) and/or microalgae in the floating system help in the reduction of wastewater nutrients through the phytoremediation process, which involves various mechanisms such as phytodegradation, volatilization, and phytoaccumulation [10,11,12]. Further, through photosynthesis, some of the wastewater nutrients are bio-converted into phytomass, which could be utilized as a valuable lignocellulose feedstock for alternative green-energy resources. Recent studies indicate the efficiency of floating macrophytes in the removal of various kinds of water pollutants, heavy metals, and pharmaceutical compounds. For example, Toyama et al. [13] used four species of duckweed (Lemna minor, Lemna gibba, Spirodela polyrhiza, and Landoltia punctate) to anaerobically treat pre-treated swine wastewater for four days under a free-flow water setup and they found that Spirodela polyrhiza has the maximum capacity of 2.0 to 10.8 mg L−1 d−1 for the removal of dissolved inorganic nitrogen with a biomass production rate of 52.6–70.3 mg (dry weight) L−1 d−1. Another study by Zhou et al. [14], with duckweed (Lemna aequinoctialis matK), showed the removal of 84% of NH3-N and 98% of TP by growing duckweeds in anaerobically digested swine wastewater after 25 d of the inoculations. Dinh et al. [15] reported the significance of the duckweed (Lemna minor) in the removal of COD in anaerobically treated wastewater, and they found 74% and 71% COD reduction with and without duckweed, respectively. Adhikari et al. [16], in duckweed-based CWs with subsurface and surface flow, found the maximum removal of COD (81%) in dairy wastewater mainly driven by a phytoremediation mechanism. Further, an investigation by Verma and Suthar [10] revealed the importance of duckweed for the reduction of NO3−N in which they reported efficacy in the range of 42–64%.
The majority of previous studies on floating CWs were performed without substrate filling in the reactor system, which can be modified through various ways to enhance the removal rates in such floating CWs. The substrate matrix composition and its heterogeneity play a highly significant role in the working capacity of floating CWs [17,18]. Till now, substrate matrices, such as aluminum mud [19], zeolite, slag [4,20], or composite materials [21], etc., have been used widely for the designing of the filling substratum for the CWs. It is found that the supply of external carbon stock in the substrate matrix could be a viable approach not only to feed active microbial communities [2,22] but also to enhance the adsorptive capacity of filling beds in CWs [22]. In this context, BC has been utilized widely as a carbon substance in the composite substrate matrix in the CWs due to its fine ability to adsorb various types of organic and inorganic pollutants [16,23,24] and support the growth of microbial communities in the substrate matrix [20,25]. The characteristics of BC, such as high porosity, broad surface area, significant cation exchange capacity, etc., make BC a vital substance for enhanced performance by CWs [3,22,26]. The application of BC in floating CW has not been widely examined by previous researchers. However, a recent study by Parihar et al. [9] revealed the potential of floating CW with Spirodela polyrhiza topping layer and biochar-aided substratum columns in the removal of wastewater nutrients and found significant removal of PO4−3 (68.43%), NH4 +-N (66.41%), SO4−2 (60.48%), and COD (58.02%) after 168 h of the treatment. They concluded that BC addition in the substrate matrix not only enhanced the adsorptive removal of wastewater pollutants but also helped in retaining dissolved oxygen (DO) in floating CWs. Recent studies indicate the potential of BC in substrate matrix in nutrient removals in vertical flow constructed wetlands (VFCWs). For example, A study by Chand et al. [27], found that after the introduction of cattle dung BC in the substrate matrix, the removal of nutrients from sewage water enhanced in a significant way. In another study, Chand et al. [3] demonstrated that cow dung BC amendment in the substrate matrix of VFCWs not only enhanced the nutrient removals in such setups but also reduced the coliform population to a safe level as decided by regulatory agencies. Bolton et al. [23] concluded that BC addition in CW enhances phosphorus removal from wastewater significantly through its adsorptive properties. Zhong et al. [28] found enhanced nitrogen removal in VFCWs amended with BC through enhanced denitrification, which was directly supported by BC presence in the substrate.
Lantana-based BC has been utilized successfully in various environmental processes, such as soil restoration [29], toxic chemical adsorption [30,31], heavy metal immobilization in soils [29], etc. Lantana weed-based BC is a low-cost substitute for commercial wood-based BC having similar properties to be applied for various environmental operations under the waste-to-wealth approach. Lantana is an invasive weed in India and widely distributed in all types of land use systems and poses a serious threat to local biodiversity and crop productivity. Thus, utilizing weed as feedstock for BC preparation could solve two issues simultaneously: low-cost weed biomass management and environmental pollution abetments under a circular economy approach.
Therefore, this research is another step toward developing a low-cost treatment of high nutrient-loaded wastewater using a floating CW system with Wolfia sp. Wolfia, one of the promising species of duckweeds, is a free-floating, tiny, and flowering aquatic plant that commonly occurs in a wide range of tropical and temperate environments. Wolfia sp. has been used widely as a promising floating plant for the phytoremediation of heavy metals [32] and wastewater nutrients [33]. However, the use of Wolfia in floating CW is hardly studied by any previous researcher. Therefore, this study includes the domestic wastewater treatment in a BC-packed sand-gravel reactor with Wolfia. The current investigation targets the impact of BC dosing in the conventional substrate matrix for the removal of wastewater nutrients/organic load (NH4+-N; COD; NO3-N; SO4−2; PO4−3) from domestic wastewater. The obtained results of the present study will provide an understanding of the role of BC and its dosing on the phtyo-remediation process in CWs.

2. Materials and Methods

2.1. Biochar Preparation, Plant, and Wastewater Collection

The BC was prepared from the terrestrial weed Lantana camara wood, which was collected from the university campus. The woody parts of the Lantana shrub were cut into small pieces (1–2 cm) and brought to the laboratory, then sun-dried for 7 days. Before pyrolysis, the sun-dried wood was placed at 80 °C (48 h) in a hot air oven to dry it completely. Dried biomass was grounded to powder and then filled in a metal container (500 mL) tightly and covered with a lid. BC was prepared through slow pyrolysis at 350 °C (heating rate 26.5 °C min−1) for 4 h in a muffle furnace equipped with an N2 supply system by following the procedure described in Chand et al. [3]. We used slow pyrolysis because of its advantages such as energy efficiency, low ash values, and also helpful in retaining valuable nutrients in BC as revealed in previous studies [34,35]. The charred biomass was crushed into fine powder to a particle size of 0.25–1 mm. Finally, the prepared BC was stored in an airtight container for further usage in experiments. The proximate, ultimate, and chemical analysis of BC was performed, and the results are presented in Table S1.
Life specimens of Wolfia were collected from a local water body located nearby the university campus using a plankton net, and the entire set of collected specimens was transferred to the laboratory. The Wolfia mass was washed thoroughly under tap water for the removal of the attached deposit and other particles. After this, the process involved culturing specimens in a pre-sterilized container, which led to the attainment of the second generation of Wolfia, free from any contamination. When sufficient populations of Wolfia sp. were achieved, the sub-culture was harvested to be used for floating CW experimental procedures.
For this study, the grab sample (20 L) of wastewater was collected daily for one week (the daily sample was stored at 4 °C to be used for the experiments) from the inlet unit of a sewage treatment facility located near the university campus, and a composite sample of sewage water was used as inlet water for experimental setups. The chemical characteristics of inlet water were determined using the standard protocol described by APHA [36], and the results are described in Table 1.

2.2. Setup Preparation and Observations

For floating CW, a column-based arrangement with BC dosing and the duckweed was established in the Doon University laboratory. A circular plastic column (30 cm in length), built-in with flow control plugs, was used. The configuration of setups is described in Figure 1. The bottom substrate was made of coarse gravel (8–12 mm) layer of 5 cm followed by (bottom-to-top), fine gravels (9–6 cm), and top river bottom sand layer (5 cm). Three doses of BC (5, 10, and 15%) in the top sand layer (S) were used to prepare setups: S + BC5%, S + BC10%, and S + BC15%. Further, two distinct columns as a control were used without BC: first with sand, fine gravel, and coarse gravels (5 cm each, as described above), and second with coarse gravels (5 cm) and fine gravel (5 cm). These control setups were designed to check the role of coarse gravel and sand in the removal mechanism. All setups were inoculated with fresh specimens of Wolfia after calculating the optimal density as described by Verma and Suthar [10]. Every setup was run four times and average removal was recorded for each selected wastewater parameter. All setups were kept for 1 week by damping the column material with distilled water till there was the attainment of an even condition in setups. Once the setups were established, the wastewater observation was started and it was monitored continuously for 40 d. Further, the outlet samples were taken at intervals of 24 h to 240 h. After each cycle of 10 d, the wastewater was replaced with fresh wastewater as per the detailed methodology described in Chand et al. [3]. For the analysis wastewater sample (25 mL) was taken from the bottom drain plug of the experimental setups during evening hours as per the procedure described in our previous work.

2.3. Analytical Procedure

The inlet and outlet water in each setup was analyzed for pH, COD, SO4−2, PO4−3, NH4+-N, and NO3− using the methodology described in APHA [36]. In addition, 99% pure AR chemicals from Merck (Germany) were used during the study for the preparation of reagents and standards for various analytical work.

2.4. Statistical Analysis

Raw data were analyzed for mean and standard deviation values for all observed data sets using IBM SPSS 20 (Chicago, IL, USA) software. One-way ANOVA was performed to check statistically significant differences among different reactors for various physicochemical parameters. HSD Turkey’s t-test was performed for the segregation of homogenous sub-sets of mean values.

3. Results and Discussion

3.1. COD Removal in Different Treatment Setups

The average influent COD level was 419.66 mg L−1 and that reduced to a range of 58.80 ± 17.04–293.67 ± 26.78 mg L−1, 46.80 ± 16.23–281.02 ± 19.60 mg L−1, 30.60 ± 6.09–261.29 ± 30.52 mg L−1, 175.90 ± 23.43–330.34 ± 35.58 mg L−1, and 265.80 ± 22.66–378.12 ± 17.50 mg L−1 in S + BC5%, S + BC10%, S + BC15%, S + GR and GR setups, respectively (ANOVA: F = 242.194, p < 0.001) (Figure 2). The maximum COD reduction was recorded in S + BC15% (92.71%), followed by S + BC10% (88.85%), S + BC5% (85.98%), S + GR (58.09%), and GR (36.66%) CW units. HSD test suggests no difference among CWs with different BC doses (ANOVA: Tukey’s t-test, p = 0.064) for COD removal. COD reduction showed a direct relationship with BC dosing in the CWs in our study, and that could be attributed to its porous morphology, which enriches the substrate with oxygen packets [37], helping in microbial-mediated oxidative reduction of organic pollutants in the substratum. A study by Zhou et al. [38] also suggested the significance of BC addition in substrate matrix and they achieved a higher COD reduction, i.e., 91.80% in BC amended setups than that of non-BC setups (83.49%). Further, Chand et al. [37] also documented a high COD reduction (92.6%) in BC-amended CWs, suggesting a direct role of BC amendments in DO supply in CWs. BC has been seen as a valuable addition due to its diverse advantages, which can be described as: (a) BC provides a heterogeneous surface apart from a porous surface which provides more DO in the substrate; (b) furthermore, researchers have acknowledged that the addition of porous carbon-rich material in the substrate matrix helps in the growth of beneficial microbes in substrate matrix thus helping in the reduction of pollutants through metabolic oxidations [39]; (c) the presence of Wolfia in floating CWs might have also played an important part in achieving the overall removal of COD. Previous studies have also found the role of aquatic plants in COD removals. For example, Dinh et al. [15] in their study found the significance of the Lemna minor in wastewater treatment in which they reported 74% and 71% COD reduction with and without duckweed, respectively. Adhikari et al. [16] reported a COD removal efficacy of 81% in CWs operated with dairy wastewater. S + GR and GR floating CW setups showed poor COD reduction acknowledging the direct role of BC, which probably enriches microbial growth [38]; improves adsorption rates [8,38]; activates electrostatic attraction/or shock, intermolecular-hydrogen holding, and π–π interaction foundations [2]. Probably all these factors could be involved in the higher reduction of COD.

3.2. Dynamics in NH4+-N and N-NO3− Load in Different CW Setups

The influent NO3-N and the NH4+-N loads were 95.25 ± 7.65 mg L−1 and 33.48 ± 2.93 mg L−1, respectively, which reduced rapidly during treatment by CWs (Figure 3 and Figure 4). The maximum NH4+-N reduction efficacy was found to be 64.28, 69.99, 78.79, 45.78, and 25.43% in S + BC5%, S + BC 10%, S + BC15%, S + GR, and GR reactor units, respectively. NH4+-N reduction rate showed statistically significant differences among setups (ANOVA: F = 201.908, p < 0.001); however, HSD test suggests no difference between S + BC5%, and S + BC10% setups (ANOVA: Tukey’s t-test, p = 0.213). The effective removal in BC-aided setups could be due to the NH4+-N adsorption potential of BC, as evidenced in previous reports [9,40]. The reduction of NH4+-N through the nitrification process could be the main mechanism under an anaerobic environment in CWs, which is supported by the supply of oxygen through atmospheric diffusion and duckweed-mediated root respiration. In addition, porous morphology and cracks/holes in BC might have enriched CW bed layers with high DO [38]. The morphological advantage in BC also provides habitats to microbial groups, which drive the reduction of N in the substrates [41]. Plant uptake is considered another valid reason for the loss of NH4+-N in the DW-supported CW setups [10]. Phytoremediation is another possible mechanism responsible for the removal of the NH4+-N as acknowledged by previous researchers. For instance, Toyama et al. [13] found the removal of 2.0–10.8 mg total dissolved N from a high N loading (20–50 mL) wastewater using four different types of duckweed ponds, and their study revealed that bio-transformation was the key process for N loss during the treatment by duckweed. Further, a low removal of NH4+-N by S + GR and GR setups could be related to insufficient oxygen in such systems as oxygen becomes competitive for oxidative removal of COD and N in the later phase of treatment [3]. Better NH4+-N reduction in BC-amended reactors could be attributed to the collective influence of plant uptake, sand, BC, adsorption rate in the substrate, ammonia loss, and trade of cations for ammonium [42,43].
NO3-N reduction during the first 24 h showed a negative response in all the reactor units. This phenomenon could be understood by the nitrification process (i.e., NH4+-N converted into liable forms, i.e., NO3-N), by virtue of which an increase can be seen in the NO3-N load [25]. NO3-N reduction efficacy was found to be a maximum of 39.31, 53.75, 77.42, 19.37, and 9.37% in S + BC5%, S + BC10%, S + BC15%, S + GR, and GR reactor units, respectively. NO3-N reduction showed statistically significant (ANOVA: F = 115.733, p < 0.001) difference among experimental setups, but the HSD test suggests no difference between S + GR and GR units (ANOVA: Tukey’s t-test, p = 0.163). NO3-N reduction showed a close relationship with BC dosing in CWs. Chand et al. [3] demonstrated the role of BC in the removal of the NO3-N via adsorption when the two CWs (with and without BC addition) were compared. Furthermore, the factors responsible for the remediation of NO3-N could be microbial denitrification, plant take-up, organism catabolism, adsorption, etc. [23,25,44]. Le Zhong [28] in their study found that BC addition in CW promotes the population of heterotrophic and autotrophic denitrifiers, which plays an important role in N metabolism in CWs. It is also important that when domestic wastewater contains SO4−2 and NO3-N, NO3-N reduce primarily due to low energy requirement during the oxidative reduction of such substance [43]. The role of duckweed in NO3-N reduction through uptake cannot be overruled.

3.3. PO4−3 Removals in Different Setups

PO4−3 concentration in the influent was 72.37 ± 4.89 mg L−1, which was reduced significantly in all the reactor units (Figure 5). The maximum removal was recorded at 69.39, 70.77, 79.06, 51.44, and 23.84% in S + BC5%, S + BC10%, S + BC15%, S + GR, and GR setups, respectively. PO4-P reduction showed a statistically significant difference among studied floating CWs (ANOVA: F = 237.323, p < 0.001), but the HSD test suggested no difference among BC setups (ANOVA: Tukey’s t-test, p = 0.681). The previous literature has documented the evidence of PO4−3 reduction via adsorption, precipitation, or build-up processes in substrate medium [23,24,45]. The role of BC in P removals through adsorption is also documented in a previous study by Lise Bolton [23], who found that mineral phases on BC surface play a vital role in P removal from wastewater when treated with a CW amended with BC in substrate matrix. Duckweed setups with BC showed a major difference in PO4−3 removals, possibly due to the BC inhabiting microbes, which probably boosted the bioconversion of P into microbial mass. Porous structures in BC also hold P salts as feed for inhabited microbial communities. In an investigation, Kizito et al. [2] revealed that alteration in media apart from the conventional ones could enhance the reduction of PO4−3-P, which also seems to be one of the possible mechanisms in our study, especially in reactor units with conventional substrates. Further phytoaccumulation of available P could be one of the reasons for PO4−3-P loss in the effluent. Few earlier studies have shown accumulation of P in planted biomass of CWs: 0.01–19 g P m−2 [7]; 2.6–5 g P m−2 [46]; 0.155–0.344 [47]; 7.8–12.3 P m−2 [3], suggesting the role of plant stand in P removal mechanisms. Apart from this, other factors controlling PO4−3-P reduction could be temperature, interaction with redox potential, and pH in substrates during CW operations [10].

3.4. SO4−2 Removal

Throughout the experimental period, the influent SO4−2 concentration was 15.81 ± 1.98 mg L−1 which reduced significantly in all setups over the experimental period. The maximum of SO4−2 removal was 42.38, 55.28, 67.93, 22.65, and 10.0% in S + BC5%, S + BC10%, S + BC15%, S + GR and GR reactor units, respectively (Figure 6). The SO4−2 reduction showed a significant difference among different CWs (ANOVA: F = 91.676, p < 0.001); however, the HSD test suggests no difference between S + GR and GR units (ANOVA: Tukey’s t-test, p = 0.056). The previous literature suggested phenomena such as uptake by the plant, nitrate reduction, deposition in chelated forms, etc., for removal of SO4−2 during wastewater treatment [48]. Studies also suggested metabolism by sulfate-reducing bacteria [49] and plant uptake [10], another important route for SO4−2 reduction in wastewater when treated by CWs. However, the co-removal of NO3 and SO4-S during sulfur oxidation in CW is also reported in the literature [1]. In summary, BC addition supported the SO4−2 removals in CWs, but metabolism by aquatic macrophytes was the prime mechanism of the SO4−2 removals in CWs.

4. Conclusions

The experiment illustrated that a BC-packed sand-gravel reactor with Wolfia sp. is capable of treating domestic wastewater efficiently. The removal of wastewater nutrients showed a direct relationship with BC doses, and 15% BC dose showed better removal rates by studied CWs. The highest removal of COD, PO4−3, NH4+-N, SO4−2, and NO3-N was found to be 92.71, 79.06, 78.79, 67.93, and 77.42%, respectively, in 15% biochar amended CW setups. The adsorption by biochar and phytoremediation process could be proposed as a possible theory of wastewater nutrient removal by floating CWs with Wolfia toppings. This study is a preliminary (lab-scale) observation, and future studies on the role of operation mode, ambient conditions, and plant density can be performed to develop a commercial-scale floating CW for decentralized urban wastewater treatment. In summary, floating CW could be a cost-effective, energy-efficient, and easy-to-operate method to treat urban wastewater sources.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su142316049/s1, Table S1: Biochar characterization (mean ± SD, n = 3) used for experimentations.

Author Contributions

P.P. was involved in data collection and conducted all experiments. N.C. assisted with experiments, statistical analysis, and writing of the initial draft. S.S. designed the research setup, supervised the research, and was involved in writing the final manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The study did not report any data.

Acknowledgments

The authors acknowledge the support and facilities provided by the Doon University administration for conducting the research.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Layout of treatment setups designed for the current study: the first CW (top layer—sand + biochar (5 to 15%), middle layer—fine gravels, and bottom layer—coarse gravels; second CW (top layer—sand, middle layer—fine gravels, bottom layer—coarse gravels; third CW (top layer—fine gravel and bottom layer—coarse gravels).
Figure 1. Layout of treatment setups designed for the current study: the first CW (top layer—sand + biochar (5 to 15%), middle layer—fine gravels, and bottom layer—coarse gravels; second CW (top layer—sand, middle layer—fine gravels, bottom layer—coarse gravels; third CW (top layer—fine gravel and bottom layer—coarse gravels).
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Figure 2. Changes in COD (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of COD in different reactor setups after 240 h HRT (b).
Figure 2. Changes in COD (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of COD in different reactor setups after 240 h HRT (b).
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Figure 3. Changes in NH4+-N (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of NH4+-N in different reactors setups after 240 h HRT (b).
Figure 3. Changes in NH4+-N (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of NH4+-N in different reactors setups after 240 h HRT (b).
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Figure 4. Changes in NO3-N (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of NO3-N in different reactors setups after 240 h HRT (b).
Figure 4. Changes in NO3-N (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of NO3-N in different reactors setups after 240 h HRT (b).
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Figure 5. Changes in PO4-P (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of PO4-P in different reactors setups after 240 h HRT (b).
Figure 5. Changes in PO4-P (mean ± SD, n= 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of PO4-P in different reactors setups after 240 h HRT (b).
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Figure 6. Changes in SO4−2 (mean ± SD, n = 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of SO4−2 in different reactor setups after 240 h HRT (b).
Figure 6. Changes in SO4−2 (mean ± SD, n = 3) load in wastewater over different HRT in different setups (a), and Whisker plots of total percent removal of SO4−2 in different reactor setups after 240 h HRT (b).
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Table
Table 1. The influent-, effluent characteristics, and the maximum removals in different treatment setups. The results are mean ± SD (n = 3).
Table 1. The influent-, effluent characteristics, and the maximum removals in different treatment setups. The results are mean ± SD (n = 3).
Wastewater ParametersInfluentEffluent
S + BC5%S + BC10%S + BC15%S + GRGR
pH8.77 ± 0.127.87 ± 0.817.60 ± 0.117.70 ± 0.167.50 ± 0.087.60 ± 0.11
COD (mg L−1)419.66 ± 11.9358.80 ± 17.0446.80 ± 16.7330.60 ± 6.09175.90 ± 23.43 265.80 ± 22.66
% REmax (HRT) 1 85.85 (240 h)88.88 (192 h)92.71 (216 h)58.09 (216 h)36.66 (216 h)
PO4-P (mg L−1)72.37 ± 4.8922.15 ± 2.5521.15 ± 3.1915.15 ± 2.23 35.14 ± 3.4455.12 ± 1.21
% REmax (HRT) 69.39 (192 h)70.77 (72 h)79.06 (72 h)51.44 (96)23.84 (168 h)
SO4−2 (mg L−1)15.81 ± 1.989.11 ± 1.837.07 ± 1.035.07 ± 1.0112.23 ± 2.3514.23 ± 1.77
% REmax (HRT) 42.38 (144 h)55.28 (144 h)67.93 (144 h)22.65 (144 h)10.00 (192 h)
NO3− (mg L−1)95.25 ± 7.6557.80 ± 8.8144.05 ± 8.7421.50 ± 7.9876.80 ± 4.1086.32 ± 5.77
% REmax (HRT) 39.31(240 h)53.75 (240 h)77.42 (240 h)19.37 (240 h)9.37 (240 h)
NH4+-N (mg L−1)33.62 ± 2.9312.01 ± 1.53 10.09 ± 1.817.13 ± 1.6318.23 ± 1.3225.07 ± 0.95
% REmax (HRT) 64.28 (168)69.99 (168 h)78.79 (168 h)45.78 (144 h)25.43 (144 h)
1 Maximum removal efficiency (REmax) at hydraulic retention time (HRT).
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Parihar, P.; Chand, N.; Suthar, S. Treatment of High Nutrient-Loaded Wastewater in a Constructed Floating Wetland with Different Configurations: Role of Lantana Biochar Addition. Sustainability 2022, 14, 16049. https://doi.org/10.3390/su142316049

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Parihar P, Chand N, Suthar S. Treatment of High Nutrient-Loaded Wastewater in a Constructed Floating Wetland with Different Configurations: Role of Lantana Biochar Addition. Sustainability. 2022; 14(23):16049. https://doi.org/10.3390/su142316049

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Parihar, Preeti, Naveen Chand, and Surindra Suthar. 2022. "Treatment of High Nutrient-Loaded Wastewater in a Constructed Floating Wetland with Different Configurations: Role of Lantana Biochar Addition" Sustainability 14, no. 23: 16049. https://doi.org/10.3390/su142316049

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