| Abstract | This study aimed to determine phosphorus (P) removal in charcoal-filled in vertical flow constructed wetland (VFCW) beds treating fecal sludge (FS). Main substrata in four lab-scale CW units consisted of small charcoal with size of 10-15 nun (CW-SC1 and CW-SC2), large charcoal with size of 30-50 mm (CW-LC1 and CW-LC2). Lab-scale (CW-G) and pilot-scale (CW-PS) units used small gravel (10-25 mm) as substrata were used to compare treatment performance with charcoal-filled units. Cattails (Typha augustifolia) were planted in these experimental units to determine role of plant in P removal. To determine the effected of loading rate to P removal, solid loading rate (SRL) of 125 kgTS/m².yr (phase I) and 250 kgTS/m².yr (phase II) was fed into CW-G, CW-SC1, CW-LC1, and 180 kgTS/m².yr and 360 kgTS/m2.yr for CW-SC2 and CW-LC2. Pilot-scale CW units was fed at constant FS volume rate of 8 m³/wk, corresponding to SLR of 292-319 kgTS/m².yr. Batch and column tests were conducted to observe P adsorption. Maximum P adsorbed by charcoal (2.78 mgig for large charcoal, and 3.03 mgig for small charcoal) was higher than sand (1.09 mgig) and gravel (0.78 mgig for large gravel, and 0.83 mgig for small gravel) in batch test. This was also different considerably between small and large size of both charcoal and gravel. Likely due to smaller size had higher specific surface area for P adsorption. Column test was conducted for charcoal with setup proportion to lab-scale in thickness of material, loading rate, and concentration. Four units that had accumulated sludge on the top of filter media was 0, 2.5, 5, and 10 cm. Ratio of concentration in effluent and influent (Ce/Co) was reached 0.95 at 20th day of operation in unit filled with sludge on substrata. However, this ratio was lower 0.95 at the end of experiment (25th day) in unit that had without sludge. P mass adsorbed by this test (0.66-1.03 g) was of 22-32% of maximum adsorption capacity (3.40 g) with the same material weight. Nevertheless, after 25 days of operation, P mass adsorbed in unit that had no sludge on the top was nearly the same that of in batch test when concentration was the same. Raw FS had high concentration of pollutant was used as influent into system. TS and SS removal efficiency based on flux were of 89.7-95.1 % and 97.5-99.4%, that was of 96.9-99.3% and 95.9-98.7% for COD and BOD₅, respectively. Units filled with charcoal showed better removal of TS, SS, COD, BOD₅, as well as TP than one filled with gravel when fed with the same SLR. TP removal efficiency based on flux of charcoal-filled units was in range of 96.3-98.3%, while gravel-filled unit was of 88.5-97.5%. Removal efficiency of these parameters were decreased when applied higher SLR. However, P removal efficiency of small and large charcoal feeding same SLR did not show clearly trend. It was of 96.3-97.4% and 97.2-98.3% in CW-SC1 and CW-LC1, and 93.9-98.3% and 91.3-94.4% in CW-SC2 and CW-LC2, respectively. P removal efficiency decreased when increased SLR in all lab-scale units, it was 94.4-98.3% at phase I, and 91.3-97.2% at phase II. Pilot-scale unit with longer time of operation showed contrary trend, P removal efficiency was decreased significantly (92.5% at phase I, and 88.5% at phase II) even P flux in influent was reduced by time (53.6 and 51.9 g/m². wk at phase I and phase II, respectively). Based on the P mass balance in all CW units, P uptake by plant (0.2-0.4%) played minor role of P removal. Most of P mass was accumulated in sludge where on substrata was of 57.9-70.9% and 2.3-4.9% was kept in accumulated sludge within substrata. P adsorption in filter material was of 17.9-27.0%. The rest one was uncounted TP mass (2.7-9.6%). The results of this study showed P uptake by cattail was minor role in CWs with high P concentration applied. Charcoal has potential of P removal, but removal efficiency of charcoal and gravel filled units showed little difference in a short time of operation. In addition, P removal efficiency of small charcoal and large charcoal was less clearly. Therefore, long term study P removal by charcoal is necessary before transfer to practice application. |