Effect of Aeration and Mixed Culture of Eichhornia Crassipes and Salvinia Natans On Removal of Wastewater Pollutants

Ecological Engineering 62 (2014) 48–53

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Effect of aeration and mixed culture of Eichhornia crassipes and Salvinia natans on removal of wastewater pollutants Menka Kumari a , B.D. Tripathi b,∗ a b

Pollution Ecology Research Laboratory, Department of Botany, Banaras Hindu University, Varanasi 221005, India Department of Botany, Banaras Hindu University, Varanasi 221005, India

a r t i c l e

i n f o

Article history: Received 31 May 2013 Received in revised form 27 September 2013 Accepted 12 October 2013 Available online 15 November 2013 Keywords: Aeration Eichhornia crassipes Removal Salvinia natans Wastewater pollutants

a b s t r a c t An attempt was made to investigate the impact of aeration and mixed culture of Eichhornia crassipes and Salvinia natans on the removal of both organic and inorganic pollutants from municipal wastewater. Since treatment of wastewater generated from industrial and domestic sources have made mandatory before its release to rivers, ponds or streams. This study focused on the comparison between removal potentials of non-aerated and aerated cultures of E. crassipes and S. natans grown individually and in mixed culture. Highest removal potential of aerated and mixed plant culture was recorded as 84.5% of biochemical oxygen demand (BOD5 ), 83.2% of chemical oxygen demand (COD), 26.6% of nitrate-nitrogen (NO3 − -N), 53.0% of total Kjeldahl nitrogen (TKN) and 56.6% of phosphate-phosphorous (PO4 3− -P). A positive and significant relationship was established between percent removal of the pollutants and retention time. It was observed that 36 h of retention time was sufficient to minimize BOD5 from 154.5 ± 1.36 to 23.9 ± 0.94 mg L−1 and COD from 309.0 ± 2.2 to 51.9 ± 3.9 mg L−1 , which were for below permissible levels of 30 mg L−1 BOD and 250 mg L−1 COD. Thus, a culture of E. crassipes and S. natans might be utilized for the removal of organic (BOD and COD) and inorganic (NO3 − -N, TKN and PO4 3− -P) pollutants from municipal wastewater. In addition, a removal of pollutant may further be enhanced with the aeration (0.5 L min−1 ) of wastewater. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Due to water scarcity and increasingly stringent regulations for the release of wastewater generated from industrial and domestic sources proper treatment and safe disposal of wastewater has become one of the major concerns of wastewater discharge regulatory authorities. Release of organic and inorganic pollutants including nitrogen and phosphorus into water bodies causes eutrophication invariable, which may deplete dissolved oxygen content of the water body, posing a serious threat to both aquatic life and human health (Pramanik et al., 2012). The conventional sewage treatment plants are not adequate to remove pollutants from wastewater. Therefore, it is imperative to suggest an appropriate wastewater treatment technology. Bio-filtration systems are natural machineries that are used worldwide to improve the quality of effluents from domestic and industrial sources. These bio-filtration systems consist of aquatic plants, which act as bio-filters by providing a larger surface area

∗ Corresponding author. Tel.: +91 9415225011; fax: +91 542 2369139. E-mail addresses: [email protected] (M. Kumari), [email protected] (B.D. Tripathi). 0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.10.007

for the microbial degradation of organic materials (Brix, 1997; Dong and Sun, 2007; Tripathi and Shukla, 1991; Upadhyay et al., 2007). In recent years, bio-filtration systems or constructed wetlands with rooted, emergent and free floating aquatic plants have been used extensively for the treatment of municipal and industrial wastewater (Calheiros et al., 2007; Jayaweera et al., 2008; Klomjek and Nitisoravut, 2005; Song et al., 2006; Thomas et al., 1995; Vymazal, 2007). During removal of organic and inorganic pollutants including nitrogen aeration is often a limiting factor (Huang et al., 2000; Huett et al., 2005). In a non-aerated biofiltration system nitrifying microorganisms often show slow growth rate as compared to heterotrophic microorganisms, which would hamper the removal of organic and inorganic pollutants from the wastewater. Aeration facilitates aerobic degradation of organic materials by maintaining oxygen concentration in the wastewater. The conversion of NH4 + -N to NO3 − -N and free nitrogen through nitrification and denitrification is also enhanced in limited aeration. Therefore, in order to enhance the removal of organic and inorganic pollutants including nitrogen from municipal and industrial wastewater, aeration is often used. Several studies have been conducted to improve the quality of effluent from domestic and industrial sources using aerated bio-filtration systems (Boyd, 1998; Dong et al., 2012;

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Ouellet-Plamondon et al., 2006; Kadlec and Wallace, 2009; Tripathi and Tripathi, 2011; Zhang et al., 2010; Zimmels et al., 2009). However, in previous studies, aeration was applied in individually grown aquatic plants including Eichhornia crassipes, Lemna minor (Zimmels et al., 2009). Systematic data on removal of organic and inorganic pollutants by aerated mixed culture is scarce. Therefore, it was imperative to evaluate the effect of aeration and mixed culture of the selected aquatic plants on the removal of organic and inorganic pollutants from municipal wastewater. In present study, free floating aquatic plants were selected for the removal of organic and inorganic pollutants because they have higher removal efficiencies as compared to rooted emergent plants. This may attributed to the fact that free floating plants float freely in aquatic system and cover more area for absorption as compared to the fixed emergent plants. Among free floating aquatic plants, E. crassipes (Mart.) has greater capacity to remove pollutants because of their higher growth rate and extensive root system for microbial growth, which make it an attractive filter for nutrients and suspended particles (Zimmels et al., 2006). E. crassipes has been used for the removal of organic, inorganic and toxic pollutants from wastewater by a number of previous researchers (Agunbiade et al., 2009; Ayyasamy et al., 2009; Chen et al., 2010; Deng et al., 2012; Ebel et al., 2007; Kony et al., 2013; Lu et al., 2008; Módenes et al., 2011; Nesterenko-Malkovskaya et al., 2012; Thomas et al., 1995; Wang et al., 2012). Several studies were also conducted on the removal of pollutants by Salvinia sp (Baral et al., 2008; Espinoza˜ Quinones et al., 2009; Prado et al., 2010). Therefore, in this study, E. crassipes and Salvinia natans (L.) Hoffm have been used as an experimental plant species. In mixed culture, broad leaved (E. crassipes) and short leaved (S. natans) aquatic plant species enhance the utilization of nutrients from all possible niches. In this study, a bio-filtration system consisting aquatic plants E. crassipes and S. natans aerated through multi-pore fine bubble aeration system, has been developed for the treatment of municipal wastewater. 1.1. Research aim and objectives The aim of this study was to evaluate the effect of aeration and mixed culture of selected plant species on the removal of organic and inorganic pollutants from municipal wastewater. Specific objectives were: (1) to determine the effect of aeration on removal of organic and inorganic materials in E. crassipes and S. natans and their mixed culture; (2) to compare removal of wastewater pollutants by E. crassipes and S. natans in aerated and non-aerated cultures; and (3) to evaluate the impact of aeration and mixed culture of E. crassipes and S. natans on the removal of the pollutants. A novel approach i.e. effect of combined aeration and mixed culture of selected plant species has been evaluated has been used to remove wastewater pollutants in this study. 2. Materials and methods 2.1. Experimental bio-filtration units Batch experiments were carried out in seven biofiltration units (Fig. 1a). Each unit has a dimension of 50 cm length, 50 cm width and 30 cm height (75 L). Three units were aerated with a multi-pore aeration system fitted at bottom with the PVC pipe of 50 cm length and 8 cm diameter (Fig. 1b). The air flow rate of 0.5 L min−1 was maintained. Other four units were kept non-aerated. Out of seven experimental units, three were aerated and three non-aerated units with the individual and mixed culture of E. crassipes and S. natans. However, remaining one unit was kept without plant culture and

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Fig. 1. (a) Layout of the seven experiment sets: NAEC (non-aerated E. crassipes culture); AEC (aerated E. crassipes culture; NASC: non-aerated S. natans culture); ASC (aerated S. natans culture); NAMC (non-aerated mixed culture of E. crassipes and S. natans; AMC (aerated mixed culture of E. crassipes and S. natans); NAUPS (non-aerated unplanted set); (b) experimental set up of aerated mixed culture of E. crassipes culture and S. natans. (DO: dissolved oxygen; dd: double distilled water).

aeration and treated as reference set for calculating the loss of nutrients through natural degradation process. Surface area of each experimental set was 0.25 m2 . Total planted surface area was 1.5 m2 (0.25 m2 × 6), out of which three sets of total 0.75 m2 area was aerated and rest was non-aerated. For both aerated and nonaerated monocultures, plant biomass of 73.0 ± 0.03 g dry weight per experimental set for each water hyacinth and floating fern was maintained. For both aerated and non-aerated mixed cultures, 36.5 ± 0.05 g dry weight per set for each of the water hyacinth and floating fern was taken. Total plant biomass in six planted experimental sets was 438.0 g dry weight of plant. Plant density was maintained at the rate of 146.0 g dry weight per m−2 for water hyacinth and floating fern in the mixed culture, while 292.0 g dry weight m−2 for each of the water hyacinth and floating fern in both aerated and non-aerated monocultures. 2.2. Operating conditions In order to minimize experimental error, bio-filtration units were configured thrice at monthly intervals from March 2012 to May 2012. The units were fed with 50 L of municipal wastewater, which was collected from the inlet point of a nearby Sewage Treatment Plant located at Bhagwanpur, Varanasi, India. Physicochemical characteristics of untreated wastewater have been shown in Table 1.

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Table 1 Physicochemical properties of municipal wastewater before treatment. Variable Temperature ( C) pH Electrical conductivity (␮S cm−1 ) Total alkalinity (CaCO3 mg L−1 ) Acidity (CaCO3 mg L−1 ) Dissolved oxygen DO (mg L−1 ) Biochemical oxygen demand BOD5 (mg L−1 ) Chemical oxygen demand COD (mg L−1 ) Nitrate nitrogen NO3 -N (mg L−1 ) Total Kjeldahl nitrogen TKN (mg L−1 ) Phosphate phosphorous PO4 -P (mg L−1 ) a

CPCB (1993) a

Value ◦

26.1 7.7 211.3 357.2 61.4 0.99 154.5 309.0 2.5 5.5 7.7

± ± ± ± ± ± ± ± ± ± ±

COD > PO4 3− P > TKN > NO3 − -N. The reduction of organic pollutants (BOD5 and COD) was maximum followed by inorganic pollutants (NO3 − -N, TKN and PO4 3− -P).

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higher area root zone of E. crassipes, which not only provide larger area for decomposers but also help in nutrient and other elemental absorption. Higher absorption of nutrients may be associated with accelerated microbial degradation of organic pollutants as a result to synergistic of action of both the plant species.

3.2. Role of plants in the removal of wastewater pollutants In view of the role of selected plant species in the removal of organic and inorganic pollutants, E. crassipes and S. natans alone and their mixed culture showed a higher removal of BOD5 , COD, NO3 − -N, TKN and PO4 3− -P than the unplanted and non-aerated culture (Table 2). Similar findings were also reported by Klomjek and Nitisoravut (2005), who noted higher reduction in BOD5 (72.4–78.9%) and total phosphorus (28.9–44.9%) in units planted with emergent plants as compared to the unplanted one. Present findings were also supported by Gikas and Tsihrintzis (2012), where planted constructed wetland showed higher removal of BOD5 (49.4%), COD (47.7%), TKN (45.3%) and orthophosphate (19.3%) as compared to unplanted wetlands. The possible reason for higher reduction of BOD and COD in the plant culture set might be due to plant root system, which acts as suitable media for microbial growth providing oxygenic condition in the rhizosphere for microbial degradation of organic pollutants. The higher reduction of NO3 − -N and TKN in the planted culture might be attributed to the mechanism for nitrogen removal includes microbial nitrification–denitrification processes as well as plant uptake. Regarding PO4 3− -P removal, the selected plant species play a significant role in addition to precipitation and adsorption as reported by Vymazal (2007). Regarding the performance of selected plant species, E. crassipes performed better than S. natans for the removal of BOD5 , COD, NO3 − -N, TKN and PO4 3− -P (Table 2). Higher removal of NO3 − -N from synthetic medium and ground water by E. crassipes as compared to Pistia stratiotes and Salvinia molesta has also been reported by Ayyasamy et al. (2009). The possible reason for higher removal of organic and inorganic pollutants by E. crassipes might be due to the specific morphology of E. crassipes with broader leaves and larger root zone area, which helped in higher absorption of nutrients as compared to smaller leaves and root zone of S. natans. In the present study, there was a significant enhancement in BOD5 , COD, NO3 − -N, TKN and PO4 3− -P removal in mixed E. crassipes and S. natans cultures as compared to individual culture of E. crassipes and S. natans (Table 2). Similar findings were reported by Tripathi and Upadhyay (2003), who observed that in the mixed culture of Eichhornia crassipes and L. minor, a greater reduction in nitrogen and phosphorus from the secondary treated dairy effluent was achieved. In the present study, 84.5% removal of COD in the mixed culture was higher than 58. 7% COD removal as reported by Tripathi and Tripathi (2011), this clearly reflects greater removal capacity of selected plant species. The possible reason for higher removal of pollutants by mixed E. crassipes and S. natans culture might be that during mixed culture experiment, low area root zone of S. natans is associated with the

Fig. 2. Relationship between retention time and (a) BOD; (b) TKN; and (c) PO4 3− P in non-aerated mixed cultures (NAMC) and aerated mixed culture (AMC) of E. crassipes and S. natans.

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3.3. Relationship between retention time and removal of pollutants There is a continuous decrease in BOD5 , TKN and PO4 3− -P concentration with retention time in the mixed culture of E. crassipes and S. natans irrespective of aeration during 72 h of experiment (Fig. 2). The reduction of BOD5 , COD, NO3 − -N, TKN and PO4 3− -P was also observed in the individual and mixed culture of E. crassipes and S. natans. These findings revealed a positive relationship between retention time and removal of BOD5 , COD, NO3 − -N, TKN and PO4 3− -P. Similar findings were reported by Mishra and Tripathi (2008) and Tripathi and Tripathi (2011), which support the present observation. It was observed that 36 h of retention time decreased the BOD5 from 154.5 ± 1.36 to 23.9 ± 0.94 mg L−1 and COD from 309.0 ± 2.2 to 51.9 ± 3.9 mg L−1 in the mixed aerated culture of E. crassipes and S. natans, which were for below the permissible limits of 30 mg L−1 of BOD and 250 mg L−1 of COD (CPCB, 1993). 3.4. Comparative study with conventional wetland system A small size horizontal flow conventional wetland system was studied using E. crassipes and S. natans. The volume of the conventional treatment system was kept same as the experimental set up. The aerated system require higher operational cost (723060 USD) than conventional wetland system (7533 USD), though the initial cost is similar. However, the aerated system provides a faster and efficient method for the removal of organic and inorganic pollutants. Short retention time of 72 h and higher removal of pollutants are the main advantages of the aerated system than the conventional wetland system. Being continuously aerated, there is no odour related problem. The conventional system is prone to clogging due to presence of soil, which is not a problem in the aerated system. 4. Conclusions This study has successfully demonstrated the removal of organic and inorganic pollutants from municipal wastewater by aerated mixed and individual cultures of E. crassipes and S. natans in 36 h of retention time. Based on the results obtained, following conclusions can be drawn: (1) aeration (0.5 L min−1 ) enhanced the removal of organic (BOD5 and COD) and inorganic (NO3 − -N, TKN and PO4 3− ) pollutants from municipal wastewater. (2) The mixed E. crassipes and S. natans culture outperformed as compared to their individual cultures, which revealed the synergistic effect of both plant species. (3) E. crassipes performed better than S. natans in aerated and nonaerated conditions. Hence, a mixed culture of E. crassipes and S. natans might be utilized for the removal of organic (BOD and COD) and inorganic (NO3 − -N, TKN and PO4 3− ) pollutants from municipal wastewater. Removal rate may further be enhanced with the aeration (0.5 L min−1 ) of wastewater. Acknowledgements The authors thank the University Grants Commission (UGC) for their financial support and the Head, Department of Botany, Banaras Hindu University for providing laboratory facilities.

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