Floating Islands Supported by LED Lighting: an Ecological Solution of Nutrients Removal from Municipal Wastewater?

Abstract

Abstract The aim of the study was to evaluate removal efficiency of nitrogen and phosphorus compounds by floating islands with macrophytes and influence of LED lights imitating the photosynthetically active radiation (PAR) on that effectiveness. Improving removal efficiency is crucial, thanks to ever-tightening legal requirements. Main reason for that is growing problem of eutrophication phenomenon. Nowadays, this problem is visible not only in lakes and ponds but also in water courses and coastal water. Study was conducted during time of 15 weeks. In that time, listed parameters were tested: pH, conductivity, total nitrogen, organic nitrogen, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, total phosphorus, and phosphates. Each tank was filled with same amount of biologically treated wastewater; ambient temperature and dissolved oxygen concentrations were kept in same range for the time of experiment. Average concentrations of main pollutants in tanks with LED lighting have reached: conductivity, 936 μS/cm; TN, 8.55 mg/dm3; P-PO4, 0.74 mg/dm3; TP, 2.57 mg/dm3. In case of no LED lighting, concentrations of main pollutants have reached: conductivity, 949 μS/cm; TN, 12.85 mg/dm3; P-PO4, 1.28 mg/dm3; TP, 2.54 mg/dm3. Based on observations and analyses, it can be concluded that the use of LED lighting imitating PAR radiation has positive effect on removal efficiency of total nitrogen and phosphates. Data suggests optimal time for treatment with floating islands as 13 weeks, extending that time to 15 weeks leads to degradation of treated wastewater quality instead improving it. Highlights • Floating islands supported with LED lighting are an alternative solution for nutrients removal. • LED light intensifies nitrogen and phosphorus removal from municipal wastewater. • The use of macrophytes in third stage of wastewater purification may result in increased nutrient removal efficiency.