Introduction

Boron (B) is one of the necessary micronutrients for the usefulness of plant (Brown et al. 2002; Işık and Çalıseki 2017), often situated in growing concentrations in wastewater in consequence of domestic, industrial, and mining use (Hasenmueller and Criss 2013). Boron concentrations may become undesirable when present at different levels (Camacho-Cristóbal et al. 2008). While nutrient insufficiencies occur at comparatively low concentrations of B, toxic effects are seen at higher levels in plants (Camacho-Cristóbal et al. 2008). In plants, boron toxicity is related to both B concentrations in sediment solution and irrigation water, as well as tolerance mechanisms in plants. Hence, concentrations of boron in sediment solution and irrigation water should be at levels not passing 10 mg l−1 and 4 mg l−1, respectively (Nable et al. 1997). In accordance with the latest evidence, in 2009, the Drinking Water Quality Committee recommended 2.4 mg l−1 as the level of B in the water (Wolska and Bryjak 2013). It is necessary to limit B in the wastewater taking into account hard environmental production instructions and public health problems (Türker et al. 2017a). Boron toxicity is an important environmental problem for native and crop plants growing over semi-arid and arid zones with the inclusion of the USA, Australia, and North Africa (Nable et al. 1997; Türker et al. 2017b). Turkey has the biggest B reserves that find an important place in terms of B mining (Türe and Bell 2004). Turkey’s reserves Kirka (Eskisehir), Kestelek (Bursa), Emet (Kütahya), Sultançayır, and Bigadiç (Balikesir) are located within the boundaries (Kistler and Helvacı 1994; Böcük et al. 2013). Constructed wetland (CW) treatment systems, one of the phyto-engineering techniques, are described as an eco-friendly technology with low-cost, easy-operation/maintenance, and more sustainable technique for removing pollutants from wastewater (Türker et al. 2017c). Constructed wetlands using low energy are utilized in a wide perspective, from industrial to urban, irrigation and drainage from urban waters to agricultural and mine drainage (Vymazal 2014). In this study, we investigated the potential use of microcosm scale constructed wetlands (MCWs) with Carex divisa to purify boron (B) from simulated river water contaminated by boron.

Materials and methods

Wetland design

This article is part of the Topical Collection on Geo-Resources-Earth-Environmental SciencesThe research was carried out at Anadolu University, Department of Biology, Eskisehir, Turkey. The investigated area is under the influence of the semi-arid Mediterranean climate, with an average annual rainfall of 373.8 mm and a mean temperature of 10.8 °C. Four microcosm scale constructed wetlands (MCWs) (three replicate planted systems and one unplanted constructed wetlands) were produced and drafted utilizing plastic containers with 40-cm length, 30-cm width, and 28-cm depth for each system. MCWs were separated as C. divisa (with three replicate) [MCW1] and unplanted control (MCW2) according to the presence of vegetation in their matrices and positioned outside. Rhizomes of C. divisa were obtained from natural wetlands in Eskisehir, Turkey (39° 17′ N, 30° 30′ E), and the rhizomes were instantly sown in the respectively constructed wetlands in a vegetate density of approximately 16 rhizomes/m2. Before the experiment begins, constructed wetlands were grown for 30 days in a blend of domestic wastewater and Hoagland medium to promote the plant growth and improve microorganism (Türker et al. 2016).

Boron concentration and execution of wetland systems

With the completion of the 30-day culture period, the MCW systems were fully established for the bioremediation process of boron. This study conducted an investigation on the modified wastewater formed with river water polluted with six different boron concentrations changing from 4 to 128 mg /L (Table 2). This reason for choosing the modified wastewater similar contaminant level in the runoff water and certain sewerage in Turkey was made up (Türker et al. 2017c). The performance of the MCW treatment systems was assessed for 42 days under natural conditions in the Western Anatolia (Eskişehir, Turkey).

Wastewater sampling and analysis

Influent and effluent water samples from each wetland system were taken in accordance with the hydraulic retention time along the study period (7 days). pH, temperature, dissolved oxygen, redox potential, and electrical conductivity (EC) in wastewater samples were gauged with HACH HQ40D multi-parameter meter measuring instrument. Boron (B) concentrations in effluent and influent water were identified with respect to the carminic acid method (Adams 1990). The proportion of ammonium (NH4+) and nitrate (NO3−) in wastewater samples were determined by utilizing an ammonium electrode (INTELLICAL ISE ammonium electrode, 2406549) and nitrate electrode (INTELLICAL ISE Nitrate electrode, 2984790).

Equations

Boron (B), ammonium (NH4+), and nitrate (NO3−) removal efficiencies of MCWs in wastewater were calculated as:

$$ \mathrm{Removal}\ \mathrm{performance}\ \left(\%\right)=\left[\frac{Ci- Ce}{Ci}\right]\times 100 $$
(1)

where Ci and Ce are the B, NO3−, and NH4+ concentrations of wastewater samples in mg/L.

Results and discussion

Different boron doses were realized to the MCWs depending on the flow fluctuations to simulate the realistic wastewater composition. The outflow B concentrations were less than inflow in this research and showed that all wetland systems could remove B in wastewater samples (p < 0.05). The total boron treatment performance of the planted MCWs calculated to 57.7 % with a mean inlet boron concentration of 43.6 mg l−1. MCW systems with plant cover had better removal performance in comparison with unplanted systems, and B treatment performances in the study period were ranged from 29.9 to 70.6% for planted systems (MCWs) and from 21.3 to 44% for unplanted control. Table 2 shows the B concentration and B removal performances of the inlet and outlet water samples of MCWs in detail. In MCWs planted with C. divisa, the effluent removal efficiency was found to be relatively effective when compared to the productivity of planted CW systems for the treatment of B from wastewater. Ye et al. (2003) announced the B treatment performance of 32% for microcosm CWs with various wetland plants. Allende et al. (2012) obtained that microcosm scale CW vegetated with Phragmites australis refined 12.5% B from the wastewater at the 7 weeks. Kröpfelová et al. (2009) found 21.8% and 25.1% treatment performance of B in two SSFCW with P. australis planned to cure domestic wastewater. Türker et al. (2013) reported boron removal of 27.2%, 40.7 % from B mine wastewater in monoculture CWs. Türker et al. (2016) stated B removal of 53.7 % for CWs with Juncus gerardii. As a result, we found 57.7% boron removal with higher efficiency in MCWs which have vegetated C. divisa in this experiment.

Nitrification and denitrification operations ensure that the wetland system works efficiently by providing nitrogen removal. Nitrification just transforms nitrogen into various forms but did not remove nitrogen (Vymazal and Březinová 2015). Nitrate and ammonium concentrations were also monitored during the treatment period, and NO3− treatment performances were ranged from 84.58 to 90.38% and from 68.19 to 79.44% for MCWs and unplanted control, respectively. Ammonium treatment performances were ranged from 87.12 to 92.19% for treatment systems (MCWs) and from 77.98 to 81.36% for unplanted control, respectively. In the existence of vegetation aerobic environment formed a more convenient stage of nitrification, and thus, the ammonium treatment efficiency of planted wetland systems was higher than unplanted control systems. Water physicochemical parameters of the outflow samples from MCWs are shown in Table 1.

Table 1 Average physicochemical parameters in wastewater samples for MCW systems in the research period. Sign (±) denotes standard deviation
Full size table
Table 2 Boron concentrations in wastewater samples for MCW systems in the research period. Sign (±) denotes standard deviation
Full size table

Conclusions

The results obtained from the experiment suggested that MCWs with C. divisa treatment systems have a potential to treat B from contaminated river water, and thus, this type of systems could be used as an alternative treatment method for contaminated river water in Western Anatolia which has the biggest borax reserve in over the world.