Sustained Phosphorus Removal by Calcareous Materials in Long-Term (Two Years) Column Experiment

(1) Phosphorus (P) removal has proven difficult in decentralized wastewater treatment systems, and external filters installed with a highly P sorbent material have been proposed to improve the P removal. In particular, calcium (Ca) rich materials have shown promising results. (2) Eight materials (five calcareous materials, one quartz sand, and two Sol-Gel coated calcareous materials) were tested in columns fed with P-spiked tap water for two years. The experiment was operated under four periods with increased P concentration from 3.3 to 21.5 mg P L-1, and with increased surface loading rate from 18 to 227 mm d(-1). After termination, the element content was measured in four column height fractions. (3) Initially, all columns removed P effectively and the calcareous materials (CAT, CAT A, and CAT C) maintained an effective removal until termination, while increases in effluent P concentration were detected already after 7 weeks for SAN and after 80-90 weeks for OPO, PHO, CAL, and HYG. The highest P content for materials were measured for the bottom fraction closest to the inlet distribution. For most materials, we observed a good agreement between the maximum sorption capacity (Q(max)) and the P content in the bottom fraction; however, a discrepancy was observed for CAL, CAT A, and CAT C. (4) In conclusion, the calcareous materials provided a consistent P removal for all 24 months. Additionally, the Sol-Gel coating had a minimal effect on the P removal capacity contrary to previous findings in batch experiments for the coated materials.

Automated summary

Phosphorus removal has always been a challenge in decentralized wastewater treatment systems. This study found that installing external filters with highly sorbent materials can improve phosphorus removal. Eight materials were tested over two years, and the calcareous materials showed the most promising results.