The Efficiency and Reliability of Pollutant Removal in a Hybrid Constructed Wetland with Common Reed, Manna Grass, and Virginia Mallow

Abstract

In this paper, the pollutant removal efficiency and the reliability of a vertical and horizontal flow hybrid constructed wetland (CW) planted with common reed, manna grass, and Virginia mallow were analyzed. The wastewater treatment plant, located in south-eastern Poland, treated domestic sewage at an average flow rate of 2.5 m3/d. The tests were carried out during five years of its operation (2014–2018). The following parameters were measured: biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids, total nitrogen, and total phosphorus. The results showed that more than 95% of BOD5, COD, and total phosphorus was removed in the tested CW system. The average effectiveness of removal of total suspended solids and total nitrogen exceeded 86%. A reliability analysis performed using the Weibull probability model showed that the removal reliability in the tested CW was very high for BOD5, COD, total suspended solids, and total phosphorus (100%). The probability that the total nitrogen concentration in the treated effluents would reach the limit value (30 mg/L) established for effluents discharged from a treatment plant of less than 2000 PE (population equivalent) to standing waters was 94%. The values of all the pollution indicators in wastewater discharged to the receiver were significantly lower than the limit values required in Poland. The investigated hybrid CW system with common reed, manna grass, and Virginia mallow guaranteed stable low values of BOD5, COD, total suspended solids, and total phosphorus in the treated wastewater, which meant it was highly likely to be positively evaluated in case of an inspection.

Reliability and Efficiency of Pollutant Removal in Four-Stage Constructed Wetland of SSVF-SSHF-SSHF-SSVF Type

“…The reliability levels we obtained were lower even than those recorded for single-stage constructed wetlands [3]. A clearly higher level of reliability of nitrogen removal treatment (32%) was obtained for a hybrid system by Marzec and colleagues [51,52]. However, compared to the wetland analyzed in this present article, the SSVF-SSHF plant they studied had a significantly lower reliability of total phosphorus removal treatment (28%).…”

“…Throughout the study period, wastewater discharged from the facility contained stable, low concentrations of BOD 5 , TSS and COD. Reports by other authors confirm that constructed wetlands provide a high degree of reliability with regard to the removal of organic pollutants [4,35,51,52]. The reliability of the SSVF-SSHF-SSHF-SSVF constructed wetland was higher than reliabilities reported for single-stage systems [3,4] and similar to those reported for two-stage systems [51,52].…”

“…Reports by other authors confirm that constructed wetlands provide a high degree of reliability with regard to the removal of organic pollutants [4,35,51,52]. The reliability of the SSVF-SSHF-SSHF-SSVF constructed wetland was higher than reliabilities reported for single-stage systems [3,4] and similar to those reported for two-stage systems [51,52]. In facilities using other technological solutions for wastewater treatment, such as activated sludge, a biological filter bed or a hybrid reactor, removal reliability levels for organic pollutants expressed by BOD 5 and COD ranged between 60 and 88% as well as 89 and 92%, respectively, and in some extreme cases were as low as 30% [33,84,85].…”

“…The first stage of purification (the reed bed) created favorable conditions for the biodegradation of organic pollutants and moderately good conditions for the removal of biogenic contaminants. Several factors may have affected those processes, among others the way the bed was fed with sewage, and determinants directly associated with it, such as the availability of oxygen, hydraulic load and pollutant load of the bed, as well as the plant species used [51,52]. In addition, cyclic dosing of wastewater to the SSVF bed with reed and the alternating occurrence of dry and wet periods may have significantly increased the diffusion of atmospheric oxygen and improved the conditions for the oxidation of organic pollutants and nitrification, as observed in previous research [53,54].…”

A Preliminary Study on A Novel Water Treatment Pond Design Using Dredged Sediment, Shrub Willow and Recycling Hand Pumps for the Restoration of Water Pollution

“…At the same time, a water treatment system can play a valuable role in intercepting the runoff of pollutants from the land into the water and protecting the bank from erosive tides, waves, and storms [10].Because the bankside area habitat is labile to be affected by water surface fluctuations, it is necessary to select plants that can adapt to such an environment. Herbaceous wetland plants are the main species used in creating the pond system [11,12], but they often need to be harvested in a timely manner to avoid plant tissue decomposition in autumn. Therefore, other water-tolerant, high-biomass woody plant species should be considered, especially in the colder, northern regions.…”