Nitrogen (N) and phosphorus (P) pollution from aquaculture has increased dramatically in recent years, and it is urgent to develop a cost-effective method to clean these polluted waters. The objective of this study is to investigate N and P removal using a two-stage infiltration system based on NaCl modified clinoptilolite (NCLP) and thermally-treated calcium-rich attapulgite (TCAP). Results from a batch study indicated that the maximum ammonium sorption capacity of NCLPs was in the range of 6.64 to 7.27 mg. N/g and decreased slightly among the three particle sizes studied (0.2-0.5 mm, 0.5 mm-1.0 mm and 1-2 mm). A 150-day column experiment indicated that the two-stage infiltration system achieved an average removal efficiency of 99.4% N and 99.0% P, and a removal rate of 50.3 g N/m3/d and 8.83 g P/m3/d for an influent concentration of 50 mg N/L and 10 mg P/L with a hydraulic retention time (HRT) of 16 h. When the influent concentration increased to 100 mg N/L and 20 mg P/L, the average ammonium removal efficiency decreased to 65.3%, while the system can still keep a high average P removal efficiency of 97.9% for 72 days of the experiment. Longer HRT favored N and P removal efficiency, but short HRTs can oxygenate ammonium sorbed in the NCLP filter and thereby refresh its sorption capacity. The results also indicated that longer wet and dry cycles can enhance the N removal efficiency of the system, but had minor influence on P removal. The sorbed clays contained high N and P content and might have use as a slow-release fertilizer. The results of this study indicate that a reactive clay-based treatment system can be used for dual removal of N and P from aquaculture wastewaters, making possible the development of a sustainable aquaculture model.
Keywords: Aquaculture wastewaters; Dual N and P removal; NaCl modified clinoptilolite; Thermally-treated calcium-rich attapulgite; Two-stage infiltration system.
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