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Operating experiences of a treatment plant designed for biological nutrient removal by pilot trials and mathematical modelling
Resources, Conservation and Recycling 27 (1999) 117–124
Operating experiences of a treatment plant designed for biological nutrient removal by pilot trials and mathematical modelling Terry O’Flynn Banks Douglas En6ironmental Scientists, Seabright, Shore Road, Rostre6or, Co. Down, BT34 3EQ, UK
Abstract An existing rendering plant wastewater treatment facility had to be up-graded to comply with new more stringent discharge consent standards. The rendering plant processes slaughterhouse waste materials to produce animal feed additives. The wastewater contains biodegradable organic substances, mainly organic acids and ammonia. The treated effluent is discharged to an adjacent river which feeds into nearby Lough Neagh. The revised consent standards required the removal of ammonia and new reduced standards for total-N and total-P are pending. The site trials indicated influent levels of BOD 1500 – 5000 mg/l and ammonia 250–750 mg/l. The discharge requirements were 20 mg/l BOD and 10 mg/l ammonia. The pilot trial results were tested against a mathematical model to verify the suitability of the treatment process and predict performance under full-scale conditions. An activated sludge plant with anoxic stage was constructed to provide nitrification-denitrification with phosphate removal by post-precipitation. This paper focuses on a comparison of predicted performance with the actual performance over an extended period. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Wastewater treatment; Activated sludge; Pilot plant; Mathematical model; Nitrogen removal; Rendering plant
0921-3449/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 3 4 4 9 ( 9 8 ) 0 0 0 9 1 - 3
118
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
1. Introduction In 1992 a commitment was undertaken to upgrade the effluent treatment facility at Ulster Farm By-Products (UFBP). The UFBP operation renders slaughterhouse offal to produce bone-meal and tallow. This process generates a liquid effluent with high levels of organic contamination, mainly acids and ammonia. The treated effluent is discharged to a small river which feeds to a nearby lake. This lake, Lough Neagh, is classified as ‘environmentally sensitive’ and is a major drinking water supply source. The discharge consent was reviewed and restrictions were placed on ammonia levels. The regulators indicated that total nitrogen and phosphate limits were also pending and the project brief was extended to include these (Table 1). A total-P discharge level of 10 mg/l was expected and allowed for in the design. The future application of the E.C. Wastewater Directive would result in total-N limits of 15 mg/l being required —the new plant must also include denitrification. The existing biofilter treatment plant was studied and found to be unable to be upgraded to meet the new standards. It was necessary to design a new treatment plant — biological nitrification/denitrification in an activated sludge system was selected with post precipitation of phosphate. Given the very high levels of ammonia (500–1000 mg/l) associated with this type of waste and the absence of relevant published information, it was deemed prudent to evaluate the treatment process by pilot plant trials.
2. Pilot plant To produce basic design data for the new plant, a pilot plant was constructed for on-site treatment experiments. A schematic layout of this unit is outlined in Fig. 1. A number of 3-week operating cycles were carried out with an acclimatised sludge using differing influent concentrations to simulate performance with a range of inflow qualities (Table 2).
Table 1 Consent standards Parameter
units
BOD SS NH4–N pH
20 mg/l 30 mg/1 10 mg/l1 6–9
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
119
Fig. 1. Pilot plant schematic layout.
3. Mathematical modelling A mathematical model of the pilot plant was developed to generalise experimental results and predict plant performance under full-scale conditions. The model was generated in GPS-X, a Canadian produced modular object package. The model was run in a steady state mode and was optimised until a good fit was achieved. The simulated and measured treated effluent concentrations are summarised in Table 3.
4. Plant design Based on the results of the pilot trials and model simulations, the full-scale plant design parameters were calculated and the plant was designed to treat 350 m3/dav of effluent containing 2500 mg/l BOD and 600 mg/l TKN to consent standard [1]. A schematic layout of the plant is outlined in Fig. 2. Table 2 Experimental data Cycle
Parameters (mg/l) Influent
1 2 3 4
Effluent
COD
BOD
NH4–N
PO4–P
COD
BOD
NH4–N
PO4–P
1992 3440 4615 7820
1410 2420 3300 5500
372 508 593 891
31.1 43.4 52.2 75.4
60 54 68 140
12 9 15 25
0.79 0.94 2.27 4.63
19.1 15.0 33.4 34.3
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
120
Table 3 Simulated versus modelled effluent values Cycle
1 2 3 4
Parameters (mg/l) Pilot
Model
COD
BOD
NH4–N
NO3–N
COD
BOD
NH4–N
NO3–N
60 54 68 140
12 9 15 25
0.79 0.94 2.27 4.63
57.5 0.38 12.6 3.78
53 58 65 71
11 9 12 17
0.50 1.10 2.50 4.10
54.3 1.70 10.5 6.30
5. Plant operation The plant operator benefited from considerable experience operating the effluent plant which was now redundant. A daily program was already in place and was modified for the new plant, supported by in-house laboratory testing facilities ([2], Table 4). Dissolved oxygen was controlled automatically by oxygen probe in the aeration tank and maintained at around 2 mg/l. The pH in the aeration tank was also monitored by pH probe —the pH can drop during nitrification due to destruction of alkalinity by the oxidation of ammonia—lime was added manually occasionally as needed until the nitrification/denitrification process became balanced. Over time it became clear that the key parameter for successful plant operation was the aeration tank MLSS—the solids level was critical as the SVI
Fig. 2. Full scale plant schematic layout.
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
121
Table 4 Performance results 1994 (in house monitoring) Month
MLSS
COD
BOD
NH4–N
NO3–N
PO3–P
Jan/Feb Mar/Apr May/Jun Jul/Aug Sep/Oct Nov/Dec
3793 5229 3136 3425 2833 3497
136 115 89 78 166 100
12.9 6.7 9.2 3.8 21.3 9.9
66 7 0.6 0.2 0.1 0.2
0.54 2.37 3.78 1.57 2.56 7.05
14.78 10.9 13.3 7.8 15.1 7.4
remained generally in the range 200–300 and exceeding the MLSS design figure of 3500 mg/l would result in solids loss from the clarifier (Figs. 3–5).
6. Discussion The performance of the plant was monitored through an in-house sampling and analysis program with independent monthly sampling by the Department of Environment (Table 5). These tests demonstrate a stable process and consistent performance. There have been occasional problems, notably when the factory was
Fig. 3. Comparative COD results.
122
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
Fig. 4. Comparative BOD results.
Fig. 5. Comparative NH4 – N results.
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
123
Table 5 Performance results (Dept. of Environment monitoring) Date
BOD
SS
Tot-Pa
NH4–N (mg/l)
27.01.94 28.02.94 29.03.94 28.04.94 24.05.94 27.06.94 21.07.94 28.09.94 31.10.94 29.11.94 12.12.94 25.01.95 24.02.95 21.03.95 26.04.95 23.05.95 27.06.95 26.07.95 28.09.95 23.10.95 24.11.95 12.12.95 05.01.96 10.09.96
14 4.4 5.9 4.9 14 3.1 2.4 15.5 19 3.6 7.1 3.2 5.3 7.2 2.6 6.5 15 8.9 7 4.5 29 6.1 9.4 7.1
14 4 12 11 14 10 16 6.9 47 10 8 7 6 14 4 15 20 47 10 10 35 14 15 17
8.97 7.65 12.34 0.48 1.08 20.27 2.13 12.8 2.24 3.93 5.61 16.78 13.79 15.6 12.08 18.6 29.6 9.53 1.1 8.83 9.84 5.68 4.72 0.78
63 14 11 1.4 0.44 0.09 0.11 0.14 0.62 0.18 0.36 0.1 0.23 0.08 0.24 0.23 2.6 0.66 0.08 0.4 0.14 0.l 0.32 0.68
a
Tot-P for information only.
required to process a large number of whole chickens which were destroyed during an outbreak of Newcastle Disease. The disinfectant that had been sprayed on the chickens upset the plant resulting in a deterioration in treated effluent quality—the plant recovered in a matter of days. In the absence at present of consent requirements for total-P and total-N these parameters were only recorded during the first year of plant operation to prove the plant performance The phosphate removal system is only operated intermittently for servicing purposes.
7. Conclusion The absence of published data on the treatment of effluents containing very high levels of ammonia required the development of a demonstration unit to establish design parameters prior to construction of a full-scale plant. At a later stage in the study, a computer model based on IAWQ Model No.1 [3] became available. It was calibrated on the pilot plant and a simulation was run to try and predict plant performance under full-scale conditions. There was reasonably good correlation between measured data and simulated values.
124
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
The treatment plant resulting from these studies has operated over an extended period and under a wide range of loadings. The treated effluent has generally equalled and often exceeded predictions and expectations. It has been shown in this study that a pilot demonstration unit can be an invaluable tool in the designing of treatment plants for unusual waste streams. The development of improved mathematical models provides useful support information but the difficulty in modelling complex biological processes means that these models should complement rather than replace experimental units.
References [1] Dobolyi E, Takacs T. Pilot-scale, high strength industrial wastewater treatment evaluation by mathematical modelling. In: Selected proceedings of the 17th Biennial Conference of the International Association on Water Quality, Budapest, 1994, 1994:119 – 28. [2] Clescen LS, Greenberg AI, Trussel RR, editors. Standard methods for examination of water and wastewater, 17th ed. APHA, AWWA, WPCS, 1989. [3] Henze M, Grady CPL, Gujer W, Marais GVR, Matsuo T. Activated sludge model no. 1, IAWPRC Science and Technology Report no. 1. IAWPRC, London, 1987
.
Operating experiences of a treatment plant designed for biological nutrient removal by pilot trials and mathematical modelling Terry O’Flynn Banks Douglas En6ironmental Scientists, Seabright, Shore Road, Rostre6or, Co. Down, BT34 3EQ, UK
Abstract An existing rendering plant wastewater treatment facility had to be up-graded to comply with new more stringent discharge consent standards. The rendering plant processes slaughterhouse waste materials to produce animal feed additives. The wastewater contains biodegradable organic substances, mainly organic acids and ammonia. The treated effluent is discharged to an adjacent river which feeds into nearby Lough Neagh. The revised consent standards required the removal of ammonia and new reduced standards for total-N and total-P are pending. The site trials indicated influent levels of BOD 1500 – 5000 mg/l and ammonia 250–750 mg/l. The discharge requirements were 20 mg/l BOD and 10 mg/l ammonia. The pilot trial results were tested against a mathematical model to verify the suitability of the treatment process and predict performance under full-scale conditions. An activated sludge plant with anoxic stage was constructed to provide nitrification-denitrification with phosphate removal by post-precipitation. This paper focuses on a comparison of predicted performance with the actual performance over an extended period. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Wastewater treatment; Activated sludge; Pilot plant; Mathematical model; Nitrogen removal; Rendering plant
0921-3449/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 3 4 4 9 ( 9 8 ) 0 0 0 9 1 - 3
118
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
1. Introduction In 1992 a commitment was undertaken to upgrade the effluent treatment facility at Ulster Farm By-Products (UFBP). The UFBP operation renders slaughterhouse offal to produce bone-meal and tallow. This process generates a liquid effluent with high levels of organic contamination, mainly acids and ammonia. The treated effluent is discharged to a small river which feeds to a nearby lake. This lake, Lough Neagh, is classified as ‘environmentally sensitive’ and is a major drinking water supply source. The discharge consent was reviewed and restrictions were placed on ammonia levels. The regulators indicated that total nitrogen and phosphate limits were also pending and the project brief was extended to include these (Table 1). A total-P discharge level of 10 mg/l was expected and allowed for in the design. The future application of the E.C. Wastewater Directive would result in total-N limits of 15 mg/l being required —the new plant must also include denitrification. The existing biofilter treatment plant was studied and found to be unable to be upgraded to meet the new standards. It was necessary to design a new treatment plant — biological nitrification/denitrification in an activated sludge system was selected with post precipitation of phosphate. Given the very high levels of ammonia (500–1000 mg/l) associated with this type of waste and the absence of relevant published information, it was deemed prudent to evaluate the treatment process by pilot plant trials.
2. Pilot plant To produce basic design data for the new plant, a pilot plant was constructed for on-site treatment experiments. A schematic layout of this unit is outlined in Fig. 1. A number of 3-week operating cycles were carried out with an acclimatised sludge using differing influent concentrations to simulate performance with a range of inflow qualities (Table 2).
Table 1 Consent standards Parameter
units
BOD SS NH4–N pH
20 mg/l 30 mg/1 10 mg/l1 6–9
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
119
Fig. 1. Pilot plant schematic layout.
3. Mathematical modelling A mathematical model of the pilot plant was developed to generalise experimental results and predict plant performance under full-scale conditions. The model was generated in GPS-X, a Canadian produced modular object package. The model was run in a steady state mode and was optimised until a good fit was achieved. The simulated and measured treated effluent concentrations are summarised in Table 3.
4. Plant design Based on the results of the pilot trials and model simulations, the full-scale plant design parameters were calculated and the plant was designed to treat 350 m3/dav of effluent containing 2500 mg/l BOD and 600 mg/l TKN to consent standard [1]. A schematic layout of the plant is outlined in Fig. 2. Table 2 Experimental data Cycle
Parameters (mg/l) Influent
1 2 3 4
Effluent
COD
BOD
NH4–N
PO4–P
COD
BOD
NH4–N
PO4–P
1992 3440 4615 7820
1410 2420 3300 5500
372 508 593 891
31.1 43.4 52.2 75.4
60 54 68 140
12 9 15 25
0.79 0.94 2.27 4.63
19.1 15.0 33.4 34.3
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
120
Table 3 Simulated versus modelled effluent values Cycle
1 2 3 4
Parameters (mg/l) Pilot
Model
COD
BOD
NH4–N
NO3–N
COD
BOD
NH4–N
NO3–N
60 54 68 140
12 9 15 25
0.79 0.94 2.27 4.63
57.5 0.38 12.6 3.78
53 58 65 71
11 9 12 17
0.50 1.10 2.50 4.10
54.3 1.70 10.5 6.30
5. Plant operation The plant operator benefited from considerable experience operating the effluent plant which was now redundant. A daily program was already in place and was modified for the new plant, supported by in-house laboratory testing facilities ([2], Table 4). Dissolved oxygen was controlled automatically by oxygen probe in the aeration tank and maintained at around 2 mg/l. The pH in the aeration tank was also monitored by pH probe —the pH can drop during nitrification due to destruction of alkalinity by the oxidation of ammonia—lime was added manually occasionally as needed until the nitrification/denitrification process became balanced. Over time it became clear that the key parameter for successful plant operation was the aeration tank MLSS—the solids level was critical as the SVI
Fig. 2. Full scale plant schematic layout.
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
121
Table 4 Performance results 1994 (in house monitoring) Month
MLSS
COD
BOD
NH4–N
NO3–N
PO3–P
Jan/Feb Mar/Apr May/Jun Jul/Aug Sep/Oct Nov/Dec
3793 5229 3136 3425 2833 3497
136 115 89 78 166 100
12.9 6.7 9.2 3.8 21.3 9.9
66 7 0.6 0.2 0.1 0.2
0.54 2.37 3.78 1.57 2.56 7.05
14.78 10.9 13.3 7.8 15.1 7.4
remained generally in the range 200–300 and exceeding the MLSS design figure of 3500 mg/l would result in solids loss from the clarifier (Figs. 3–5).
6. Discussion The performance of the plant was monitored through an in-house sampling and analysis program with independent monthly sampling by the Department of Environment (Table 5). These tests demonstrate a stable process and consistent performance. There have been occasional problems, notably when the factory was
Fig. 3. Comparative COD results.
122
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
Fig. 4. Comparative BOD results.
Fig. 5. Comparative NH4 – N results.
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
123
Table 5 Performance results (Dept. of Environment monitoring) Date
BOD
SS
Tot-Pa
NH4–N (mg/l)
27.01.94 28.02.94 29.03.94 28.04.94 24.05.94 27.06.94 21.07.94 28.09.94 31.10.94 29.11.94 12.12.94 25.01.95 24.02.95 21.03.95 26.04.95 23.05.95 27.06.95 26.07.95 28.09.95 23.10.95 24.11.95 12.12.95 05.01.96 10.09.96
14 4.4 5.9 4.9 14 3.1 2.4 15.5 19 3.6 7.1 3.2 5.3 7.2 2.6 6.5 15 8.9 7 4.5 29 6.1 9.4 7.1
14 4 12 11 14 10 16 6.9 47 10 8 7 6 14 4 15 20 47 10 10 35 14 15 17
8.97 7.65 12.34 0.48 1.08 20.27 2.13 12.8 2.24 3.93 5.61 16.78 13.79 15.6 12.08 18.6 29.6 9.53 1.1 8.83 9.84 5.68 4.72 0.78
63 14 11 1.4 0.44 0.09 0.11 0.14 0.62 0.18 0.36 0.1 0.23 0.08 0.24 0.23 2.6 0.66 0.08 0.4 0.14 0.l 0.32 0.68
a
Tot-P for information only.
required to process a large number of whole chickens which were destroyed during an outbreak of Newcastle Disease. The disinfectant that had been sprayed on the chickens upset the plant resulting in a deterioration in treated effluent quality—the plant recovered in a matter of days. In the absence at present of consent requirements for total-P and total-N these parameters were only recorded during the first year of plant operation to prove the plant performance The phosphate removal system is only operated intermittently for servicing purposes.
7. Conclusion The absence of published data on the treatment of effluents containing very high levels of ammonia required the development of a demonstration unit to establish design parameters prior to construction of a full-scale plant. At a later stage in the study, a computer model based on IAWQ Model No.1 [3] became available. It was calibrated on the pilot plant and a simulation was run to try and predict plant performance under full-scale conditions. There was reasonably good correlation between measured data and simulated values.
124
T. O’Flynn / Resources, Conser6ation and Recycling 27 (1999) 117–124
The treatment plant resulting from these studies has operated over an extended period and under a wide range of loadings. The treated effluent has generally equalled and often exceeded predictions and expectations. It has been shown in this study that a pilot demonstration unit can be an invaluable tool in the designing of treatment plants for unusual waste streams. The development of improved mathematical models provides useful support information but the difficulty in modelling complex biological processes means that these models should complement rather than replace experimental units.
References [1] Dobolyi E, Takacs T. Pilot-scale, high strength industrial wastewater treatment evaluation by mathematical modelling. In: Selected proceedings of the 17th Biennial Conference of the International Association on Water Quality, Budapest, 1994, 1994:119 – 28. [2] Clescen LS, Greenberg AI, Trussel RR, editors. Standard methods for examination of water and wastewater, 17th ed. APHA, AWWA, WPCS, 1989. [3] Henze M, Grady CPL, Gujer W, Marais GVR, Matsuo T. Activated sludge model no. 1, IAWPRC Science and Technology Report no. 1. IAWPRC, London, 1987
.