The effect of carbon source on nitrate and ammonium removal from drinking water by immobilised Chlorella sorokiniana

The feasibility of alginate-immobilised Chlorella sorokiniana for nitrate and ammonium removal from drinking water in regard to carbon source effects was studied in this paper. Three different natural carbon sources were tested in batch experiments with nitrate as nitrogen source: sucrose, grape juice and acacia honey. The nitrate removal efficiencies achieved at 50 mg/L of initial nitrate concentration under sucrose, grape juice and acacia honey were 93, 99 and 94 %, respectively. At 100 mg/L of nitrate, comparable efficiencies were obtained after approximately 3 days, whilst for acacia honey at 50 mg/L, it took only 2 days of cultivation and 3 days for the other two carbon sources. Grape juice and acacia honey showed better performances than sucrose, which must be linked to their chemical compositions. The study of the impact of biosorbent quantity on nitrate removal efficiency showed that sufficient nitrate removal efficiencies could be achieved with a beads/water ratio of 1:6.7 (v/v) or smaller. In addition, the beads’ ages significantly impacted the nitrate removal. The removal of ammonium was studied in the presence of nitrate with acacia honey as carbon source. At the highest concentrations being tested (ammonium- 30 mg/L and nitrate-50 mg/L), ammonium was completely removed in <3 days and nitrate by 81 % in 4 days, whereby the suitable beads/water ratio was 1:5. The priority of ammonium assimilation was noticed when compared to nitrate. According to the results, the alginateimmobilised C. sorokiniana represents a promising tool for the removal of nitrogen from drinking water sources.

Keywords
Algae; Ammonium; Carbon source; Chlorella sorokiniana; Drinking water; Nitrate