Keywords

1 Introduction

The concept of aquatic plants-based treatment system is one of the smart ways to reduce the burden of pollution of water bodies and could be a possible way to reuse or achieve disposal standards for the municipal wastewater generated from smart city community. Lacking access to clean water and sanitation could be a common problem affecting human health throughout the smart cities like developing town. Centralized wastewater system, energy and cost-intensive technologies are ineffective to resolve the complex water-related problem [1]. There is a need to investigate and implement alternative treatment system for the current wastewater technology [2]. In the field of wastewater treatment, aquatic plants are one of the low-cost treatment concepts which have not been recognized yet for smart cities. The natural systems for the treatment of low-strength municipal wastewater are still one of the most economical and sustainable technologies widely used around the world due to its simple operation and user friendly [3, 4]. In general, these treatment concepts were used in a variety of geometrical shapes and sizes like constructed wetlands (CWs), lagoons waste stabilization ponds (WSPs) with or without aquatic weeds and frequently used for the treatment of municipal wastewater. This type of system is also effective to reduce the large amounts of nonpoint source pollutants that occurred by the rainfall and rain washing the village grounds and fields [5]. Researcher also reported that constructed and natural wetlands are often used for municipal wastewater effluent, i.e., single-residence septic tank effluent and at large municipal wastewater plants due to low cost of treatment [3, 6]. Various simultaneous processes like filtration, sedimentation, adsorption, bioconversion, combination of nitrification/denitrification, uptake by microorganism, wetland microphyte and microbial processes were occurring in natural systems for the removal of nutrients. The selection of aquatic plant in constructed wetlands should be based on strong vitality, pollution resistant, survive in aquatic and wet environment, diseases and pests [7]. Enormous studies are found in the literature on the performance evaluation of the constructed wetlands (CWs) based on geometry like dimension, area and substrate used. The role of plants is equally important but limited studied observed on fate of organic and nutrients removal for the treatment of municipal sewage [8].

An attempt was made to investigate the nutrient removal using four widespread aquatic plants, two emergent plants and two floating plants from municipal wastewater and feasibility for smart city.

2 Materials and Methods

2.1 Reactor Configuration

Five batch reactors were used for the present study. Each reactor was made of plastic material having cylindrical shape of diameter 35 cm and height of 51 cm. The effective volume of each reactor was 49 L. Various types of plants, i.e., emergent plants (Typha Latifolia and Phragmites Australis) and floating plants (Lemna gibba and Eichhornia crassipes), were introduced in four different batch reactors. For emergent plants, the density of plant was kept six, while for floating plants, planting coverage area was maintained half of the sewage surface. One batch reactor was treated as control without any plant.

Three layers of different strata/media, i.e., gravels (20–40 mm), at the bottom followed by fine gravels (1–2 mm) and sand mixed with mud (0.0039–0.065 mm) above it were made in each batch reactor that was obtained from vicinity of the campus of university. The gravels, coarse sand and silt were thoroughly washed with tap water until the supernatant solution was clear. The emerging plants, i.e., Typha latifolia and Phragmites australis, were procured from nursery, while floating plants, i.e., Lemna gibba and Eichhornia crassipes, were collected from Okhla barrage at Yamuna River near Kalindi Kunj, New Delhi. The collected aquatic plants were washed to remove dirt and other adhesive materials introduced in the reactors. The sewage was brought to laboratory from the sewer pumping station Batla House, New Delhi.

2.2 Experimental Protocol

Experimental setups (batch reactors) were operated at the ambient temperature varied from 20 to 32 ±5 °C, with a light intensity of 1500 Lx during day time. Initially, all the batch reactors were filled with municipal sewage and kept for fifteen days for the stabilization of plant. Later, sewage in the reactors was replaced with fresh municipal sewage. The present study was performed for 45 days. The depth of the municipal sewage above the top surface was maintained constant by keeping 60 mm height avoiding the evaporation intervention. During the course of the study, this height was maintained by adding freshwater in the reactors. The porosity of the reactors was found to be 40% which was calculated after the stabilization of plants in the reactors.

Analytical Procedure

Samples were analyzed to determine the concentration of ammonia (NH4+ -N), nitrate (NO3− -N) and phosphate (PO4-P) at an interval of three days. All samples were analyzed in triplicate according to the Standard Methods for Examination of Water and Wastewater [9].

3 Results and Discussions

3.1 Emergent Plant (Typha latifolia and Phragmites australis)

The influent and effluent concentrations and percent removal for NH4-N, NO3-N and PO4-P were monitored in the batch studies planted with Typha latifolia and Phragmites australis with an interval of three days.

NH4-N and NO3-N

Figures 1 and 3 show the variation of ammonium concentration in reactors planted by Typha latifolia and Phragmites australis and Temporal variation of NO3-N by Typha latifolia and Phrgamites australis respectively. The result indicates that there is a significant reduction in NH4-N and NO3-N. The reduction in NH4-N reached to 7.5 and 11 mg/L from 38 mg/L in reactor planted by Typha latifolia and Phragmites australis, respectively, and similarly, NO3-N reduced to 1.48 and 1.76 mg/L from the initial value of 6 mg/L. The regression coefficient R2 = 0.85–0.89. Removal of ammonia and nitrate was influenced by temperature that varied from 20 to 38 °C. During start-up, the removal efficiency of NH4-N and NO3-N was significantly higher with both types of plants. From Figs. 1 and 2, removal of NH4-N was observed about 75–80% and NO3-N about 71% at HRT of 21 days by Typha latifolia and Phragmites australis planted reactor and 21–45 days, varied from 71 to 90%. The graph shows less variation in removal after 21 days, the reasons is dead lives or plant litter decomposition. Figure 2 shows the variation in removal of NH4-N and NO3-N in control reactor. Results were statistically found significant, and the percentage removal of nitrogenous pollutants in planted reactors is significant (p > 0.05) (Fig. 2).

Fig. 1
figure 1

Temporal variation in NH4-N by Typha latifolia and Phrgamites australis planted reactor

Full size image
Fig. 2
figure 2

Temporal variation of NH4-N and NO3-N by control reactor

Full size image
Fig. 3
figure 3

Temporal variation of NO3-N by Typha latifolia and Phrgamites australis planted reactor

Full size image

PO4-P

Figure 4 shows the variation of phosphorous removal in batch reactors having Typha latifolia and Phragmites australis; graph trends show 21 days retention time is an appropriate period for satisfactory removal. The removal of PO4-P was observed greater than 70% and reduces to 3 mg/L from the initial concentration of 12 mg/L at an HRT of 21 days. The removal efficiencies of PO4-P achieved in present study at an HRT of 21 days were 75 and 73% by Typha latifolia and Phragmites australis planted reactors were higher than the removal reported by [10] against of 50% removal efficiency in constructed wetland vertical type flow. The higher removal of PO4-P might be due to the high density of plant and high HRT. The highest removal may also be due to the PO4-P adsorbed in the media bed, rather than in the plant as sand used in this study contain oxides of Fe, Al and Ca. These minerals could enhance the phosphorous retention due to chemical adsorption and precipitation in wetlands. Other possible cause of PO4-P removal might be the adsorption in algal and microorganisms that utilize phosphorous as an essential nutrient and contain phosphorous in their tissues. Results of this study were well supported by one-way ANOVA with significant difference (p < 0.05) for removal of Typha latifolia and Phragmites australis-based reactor. The removal by Typha latifolia-based reactor was higher compared to Phragmites australis-based reactor. The overall phosphorous removal efficiency of Typha latifolia-based reactor was observed significantly good based on comparison with control reactor (Fig. 5).

Fig. 4
figure 4

Temporal variation of PO4-P by Typha latifolia and Phrgamites australis planted reactor

Full size image
Fig. 5
figure 5

Temporal variation of PO4-P by control reactor

Full size image

3.2 Floating Plants (Eichhornia crassipes and Lemna gibba)

In the batch studies planted with Eichhornia crassipes and Lemna gibba, the influent and effluent concentrations along with percent removal for NH4-N, NO3-N and PO4-P were analyzed.

Variation of NH4-N and NO3-N

Figures 6 and 8 shows the variation of NH4-N and NO3-N concentration in batch reactors planted two different plant species, viz. Lemna gibba and Eichhornia crassipes. Results show the removal of NH4-N and NO3-N was higher in Lemna gibba-based batch reactor compared with Eichhornia crassipes. The NH4-N removal efficiency in Lemna gibba-based batch reactor at HRT of 21 days observed 68%, and an initial concentration of 38 mg NH4-N/L reduced to 12 mg NH4-N/L with same reactor. The removal of NO3-N was 68%, and the final concentration was observed as 1.92 mg/L (Fig. 7).

Fig. 6
figure 6

Temporal variation in NH4-N by Eichhornia crassipes and Lemna gibba planted reactors

Full size image
Fig. 7
figure 7

Temporal variation of NH4-N and NO3-N by control reactor

Full size image
Fig. 8
figure 8

Temporal variation of NO3-N by Eichhornia crassipes and Lemna gibba planted reactor

Full size image

Results were well supported by statistically evaluation using single-way ANOVA and found that the removal of NH4-N and NO3-N significant (p > 0.05) difference from control reactor.

Variation of PO4-P

Figure 9 shows the variation of phosphorous removal by Lemna gibba and Eichhornia crassipes. Initially, the PO4-P concentration of municipal sewage was 12 mg/L and at retention time of three weeks. The concentration of PO4-P reduced to 4.4 and 5.7 mg/L in batch reactors having Lemna gibba and Eichhornia crassipes, respectively, with regression coefficient of R2 = 0.89–0.92. The removal efficiency was achieved as 63 and 53% by Lemna gibba and Eichhornia crassipes. The trend of nutrient removal during retention period of 21–45 days observed scantly due to dead leaves and plants.

Fig. 9
figure 9

Temporal variation in PO4-P by Eichhornia crassipes and Lemna gibba planted reactors

Full size image

4 Conclusions

Batch studies investigated the comparison of the performance of emergent and floating plant for the removal of nutrients from municipal sewage. The highest removal of nutrients in terms of NH4-N, NO3-N and PO4-P was observed in Typha latifolia plant species at an HRT of 21 days.

  • The highest removal of the NH4-N was 80, and NO3-N and PO4-P were 75%, and the final treated effluent concentration was reduced to 7.5, 1.48 and 3.0 mg/L, respectively.

Results inferred that the aquatic weeds are the promising option for the treatment of municipal sewage for small communities due to lower capital cost, easy operation and maintenance and highest removal in nutrients. However, further studies are required at demonstration scale in order to upscale the technology.

5 Acknowledgement

Authors are highly thankful to the Department of Science and Technology and UGC, Government of India to provide the financial support to carry out this study.