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.
Highlights
An important indicator of the civilizational development of a society is the state of the sanitary infrastructure [1,2]
The concentrations of organic pollutant, expressed as BOD5 and chemical oxygen demand (COD), and the concentrations of total suspended solids content (TSS), as well as total nitrogen and total phosphorus, in mechanically treated wastewater were close to the average values reported in the literature [37,38,39]
The content of ammonium nitrogen in sewage flowing out of the pumping station to the constructed wetland system was at an average level of 76 mg/L; the remaining forms of nitrogen were found in trace amounts: nitrate—0.99 mg/L, and nitrite—0.11 mg/L
Summary
An important indicator of the civilizational development of a society is the state of the sanitary infrastructure [1,2]. Water 2018, 10, 1445 efficiencies [6,7,8] An alternative to these solutions is constructed wetlands (CWs), which are characterized by simple operation, low operating costs, and resistance to changes in technological conditions [9,10,11,12,13,14]. These systems, mainly comprising vegetation, substrates, soils, microorganisms, and water, utilize complex physical, chemical, and biological processes to remove various contaminants or improve water quality [9,15,16,17]. In SSF systems, wastewater flows horizontally or vertically through the substrate which supports the growth of plants
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