Evaluation of Septic Tank and Subsurface Wetland for

More documents

Recommendations

Info

Biological Nitrification Reaction (Crites et al., 1998). NH4 + +1.731O2 +1.962HCO3 - → 0.038C5H7NO2 +0.962NO3 - +1.077H2O +1.769H2CO3 Biological Denitrification Reaction (Crites et al., 1998). NO3 - + 1.183CH3OH + 0.273H2CO3 0.091C5H7NO2 + 0.454N2 + 1.820H2O + HCO3 - → Biologically nitrifying 1.0 g of ammonia nitrogen consumes 7.01 g of alkalinity and denitrifying 1.0 g of nitrate nitrogen produces 3.57 g alkalinity (Crites et al., 1998). Following the above reactions, if 1.0 g of ammonia nitrogen is nitrified then 3.57g CaCO3 0.962g NO3-N 1.0g NO3-N × or 3.43 g of alkalinity is produced during denitrification. The 7.01 g of alkalinity consumed in nitrification minus the 3.43 g of alkalinity produced by denitrification yields a net 3.58 grams of alkalinity consumed for every gram of ammonia nitrogen converted to cell tissue and nitrogen gas. Therefore the required mass ratio of alkalinity to ammonia is 3.58:1 assuming all nitrate converts to nitrogen gas. At Pisgah the 8.1 mg/l alkalinity to 58 mg/l ammonia ratio of 0.14:1 is sufficient for converting only 2.3 mg/l of ammonia. This is based on the assumption that the toilet flushing water is the sole source of alkalinity to the system. The Retrieve wetland influent alkalinity to ammonia ratio of 210:5.8 (36:1) is adequate for complete conversion. Therefore the primary mechanism for ammonia removal at Pisgah was not biological nitrification and denitrification but must have been uptake by the wild cane and adsorption by the rock media. Ammonia removal at Retrieve may have been a combination of biological removal, plant uptake and perhaps media absorption. Total Phosphorus The results for the total phosphorus tests are presented in Table 5-7. The average total phosphorus concentrations in the Pisgah sanitation system were measured to be 12.8 mg/l entering the septic tanks, 9.6 mg/l entering the wetland and 0.4 mg/l at the mid-wetland sample point. The average total phosphorus concentrations in the Retrieve sanitation 47
system were measured to be 3.3 mg/l entering the septic tanks, 1.5 mg/l entering the wetland and 1.2 mg/l exiting the wetland. The average mass load of phosphorus on the wetlands was 0.28 kg/ha-d (0.25 lb/ac-d ) at Pisgah and 1.5 kg/ha-d (1.3 lb/ac-d) at Retrieve. Average phosphorus removal was determined to be 97% for the Pisgah sanitation system and 64% for the Retrieve system. The septic tank removal efficiencies of 25% at Pisgah and 55% at Retrieve were within the typical phosphate removal efficiency range of 20 – 65% (Seabloom et al., 1982; Rahman et al., 1999). Removal efficiency for wetland influent phosphorus was determined to be 96% at Pisgah and 20% at Retrieve. These results are outside the removal efficiency range of 26.7 – 65.0% reported in literature for SSF wetlands (Vymazal, 2002). The harvest of the wild cane from the Pisgah wetland contributed to the high phosphorus uptake. The high solids accumulation in the Retrieve wetland effluent caused by the sampling method could have contributed to the low phosphorus uptake that was measured. Table 5-7 Total Phosphorus (P) for Pisgah and Retrieve Sanitation Systems ________________________________________________________________________ Sample Arithmetic Mean 90% Confidence Sample ( X ) mg/l Interval mg/l Size (n) Pisgah First Septic Tank 12.8 X ± 7.6 5 Pisgah Wetland Influent 9.6 X ± 6.6 5 Pisgah Wetland Effluent 0.4 X ± 0.2 4 Retrieve First Septic Tank 3.3 X ± 1.6 6 Retrieve Wetland Influent 1.5 X ± 0.5 6 Retrieve Wetland Effluent 1.2 X ± 0.5 7 Long term phosphorus removal should not be expected for a wetland unless regular plant harvesting is performed which can yield a maximum of 0.25 kg/ha-d (0.22 lb/ac-d) phosphorus removal (EPA, 2000). The removal of phosphorus was determined to be 0.27 kg/ha-d (0.24 lb/ac-d) at Pisgah and 0.0088 kg/ha-d (0.0079 lb/ac-d) at Retrieve. 48
Page 1 and 2:
Evaluation of Septic Tank and Subsu
Page 3 and 4:
Abstract Locally designed wastewate
Page 5 and 6: Acknowledgments Major funding was p
Page 7 and 8: Chapter 6 - Costs ……………
Page 9 and 10: Table 5-6 Parameters Influencing Bi
Page 11 and 12: The predominant geological formatio
Page 13 and 14: plants discharging a volume of 20m
Page 15 and 16: lack access to acceptable excreta d
Page 17 and 18: Critical design parameters for sept
Page 19 and 20: Subsurface Flow Constructed Wetland
Page 21 and 22: inging larger rock from a distant q
Page 23 and 24: Chapter 3 - Site Descriptions Figur
Page 25 and 26: Wetland inlet sample point Flush to
Page 27 and 28: Figure 3-4 Pisgah wetland beds befo
Page 29 and 30: times over a two-week period, grew
Page 31 and 32: Figure 3-7 Retrieve youth in front
Page 33 and 34: Chapter 4 - Methodology Field Data
Page 35 and 36: out (see Figure 4-2). Locating the
Page 37 and 38: Figure 4-3 Media porosity measureme
Page 39 and 40: Laboratory Water Quality Analysis A
Page 41 and 42: NEPA laboratory also does not test
Page 43 and 44: Since evapotranspiration decreases
Page 45 and 46: The water level in the middle of th
Page 47 and 48: BOD was determined to be 53% at Pis
Page 49 and 50: solids than a sample point that pul
Page 51 and 52: Table 5-4 Ammonia (NH3-N) for Pisga
Page 53 and 54: Table 5-5 Nitrate (NO3-N) for Pisga
Page 55: o Alkalinity Nitrification and deni
Page 59 and 60: coliform by 88%. The Retrieve septi
Page 61 and 62: Chapter 6 - Cost of Pisgah and Retr
Page 63 and 64: The septic tanks will have to be pu
Page 65 and 66: Jamaica may refer to the hydraulic
Page 67 and 68: Chapter 8 - References APHA (Americ
Page 69 and 70: Pennant, Joseph, (2005), Assistant
Page 71 and 72: Chapter 9 - Appendices Appendix 1 -
Page 73 and 74: 7-Dec- 2004 SET FIVE Sample BOD TSS
Page 75 and 76: Appendix 3 - Determination of 90% C
Page 77 and 78: Appendix 4 - Conductance of Water C
Page 79 and 80: Appendix 6 - Total Dissolved Nitrog
Page 81 and 82: Appendix 8 - Evapotranspiration Det
show all

Evaluation of Septic Tank and Subsurface Wetland for

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?