title: Landfill leachate treatment: Using sequencing batch reactor technology to remove high ammonium concentration

authors: Lu, Philip Andrew

subjects: landfill leachate

abstract: Landfilling requires various consents and regulations in order to operate most effectively and cause minimal environmental issues to its immediate surroundings. The contaminated liquid produced from precipitation seeping through the layers of waste in landfills are generally called landfill leachate or leachate. Sequencing batch reactors (SBR) are fill-and-draw activated sludge systems that facilitate wastewater treatment in a singular reactor, while utilizing a sequence of different phases to create aerobic, anoxic, and sometimes anaerobic conditions. Multiple studies have been done that demonstrate the capacity of SBRs to treat wastewater for varying strengths of wastewater and concentration of contaminants, including ammonium. The objectives of the research are to: 1. run a lab-scale sequencing batch reactor to treat ammonium concentrations similar to that of landfill leachate; 2. design a full-scale sequencing batch reactor for landfills based on the bench-scale reactor’s ammonium removal potential; and 3. analyse the viability and economic feasibility of a SBR for treating landfill leachate.

Two lab-scale SBRs are used in the experiment. SBR 1 was run for 250 days of operation, while SBR 2 was run for only 130 days. These achieved ammonium removal at influent ammonium loading as high as 720 mg/L, and the SBR achieved ammonium removal efficiency of 90% to 100% with a TSS of 17 to 18 g/L during this most stable period of operation. pH control was required at higher influent ammonium loadings above 300 mg/L. Removal rates over the stable periods of operation are calculated to be at 1.65 and 1.55 mg NH4+ removed/g TSS/ per cycle for SBR 1 and 2, respectively. An ammonium removal rate of 0.0508 mg NH4+/L/min is calculated based on measurements using an ammonium ISE probe. Inhibition in ammonium removal due to low pH is observed. With extended aeration and pH control the ammonium removal continued as long as pH is maintained above 6.5. The oxygen consumption rate is also found to be at 0.01 mg DO/L/min, while the average mass transfer coefficient of O2 at 0.0144 min-1, and the percentage of oxygen transferred from gas to the mixed liquor calculated to be at 14.8%.

The full-scale SBR design is based on rates calculated from the experimental set-up and approximate leachate flow rate, based on precipitation, in the Waikato region. An area of 49 hectares landfilled is considered, which is similar to one of the class 1 municipal sanitary landfills in the region. A landfill leachate ammonium concentration range of 600 to 1500 mg/L is considered for the full-scale SBR design. The full-scale SBR is calculated to require a working volume of 8168 m3. The capital and operating cost of which shows high economic feasibility, and is estimated to be cost-effective compared to the cost of offsite treatment.

text: Landfill leachate treatment: Using sequencing batch reactor technology to remove high ammonium concentration Landfilling requires various consents and regulations in order to operate most effectively and cause minimal environmental issues to its immediate surroundings. The contaminated liquid produced from precipitation seeping through the layers of waste in landfills are generally called landfill leachate or leachate. Sequencing batch reactors (SBR) are fill-and-draw activated sludge systems that facilitate wastewater treatment in a singular reactor, while utilizing a sequence of different phases to create aerobic, anoxic, and sometimes anaerobic conditions. Multiple studies have been done that demonstrate the capacity of SBRs to treat wastewater for varying strengths of wastewater and concentration of contaminants, including ammonium. The objectives of the research are to: 1. run a lab-scale sequencing batch reactor to treat ammonium concentrations similar to that of landfill leachate; 2. design a full-scale sequencing batch reactor for landfills based on the bench-scale reactor’s ammonium removal potential; and 3. analyse the viability and economic feasibility of a SBR for treating landfill leachate.

Two lab-scale SBRs are used in the experiment. SBR 1 was run for 250 days of operation, while SBR 2 was run for only 130 days. These achieved ammonium removal at influent ammonium loading as high as 720 mg/L, and the SBR achieved ammonium removal efficiency of 90% to 100% with a TSS of 17 to 18 g/L during this most stable period of operation. pH control was required at higher influent ammonium loadings above 300 mg/L. Removal rates over the stable periods of operation are calculated to be at 1.65 and 1.55 mg NH4+ removed/g TSS/ per cycle for SBR 1 and 2, respectively. An ammonium removal rate of 0.0508 mg NH4+/L/min is calculated based on measurements using an ammonium ISE probe. Inhibition in ammonium removal due to low pH is observed. With extended aeration and pH control the ammonium removal continued as long as pH is maintained above 6.5. The oxygen consumption rate is also found to be at 0.01 mg DO/L/min, while the average mass transfer coefficient of O2 at 0.0144 min-1, and the percentage of oxygen transferred from gas to the mixed liquor calculated to be at 14.8%.

The full-scale SBR design is based on rates calculated from the experimental set-up and approximate leachate flow rate, based on precipitation, in the Waikato region. An area of 49 hectares landfilled is considered, which is similar to one of the class 1 municipal sanitary landfills in the region. A landfill leachate ammonium concentration range of 600 to 1500 mg/L is considered for the full-scale SBR design. The full-scale SBR is calculated to require a working volume of 8168 m3. The capital and operating cost of which shows high economic feasibility, and is estimated to be cost-effective compared to the cost of offsite treatment.

year: 2024-02-20

title: Approximation of non-linear cost functions in p-graph structures

authors: Ong, Benjamin H.Y.

abstract: P-graph employs combinatorial and optimisation algorithms to solve process network synthesis (PNS) problem. However, the P-graph framework requires linear cost functions when optimising PNS problems. As a result, a high error between the user-input linear cost function and the actual non-linear cost function is likely to occur. This paper presents a new method to incorporate multiple linear cost functions in parallel for raw materials, operating units and products in P-graph problems to accurately approximate the non-linear functional form of most cost estimation functions. This was achieved by dividing the original cost functions into multiple equal segments that then could be individually represented by linear sub-functions. Application of the new method to a simple wood-to-fuel processing example influences the optimal P-graph process structure such that a previously uneconomic side-product route (pyrolysis) becomes economic and increases the overall profit. The results also demonstrate that the linear approximation error decreases with increasing numbers of segments and linear cost sub-functions. The time increase to solve the new problem structure, which has over threefold more operating units, is negligible for this simple case, but may be significant for more complex problems.

text: Approximation of non-linear cost functions in p-graph structures P-graph employs combinatorial and optimisation algorithms to solve process network synthesis (PNS) problem. However, the P-graph framework requires linear cost functions when optimising PNS problems. As a result, a high error between the user-input linear cost function and the actual non-linear cost function is likely to occur. This paper presents a new method to incorporate multiple linear cost functions in parallel for raw materials, operating units and products in P-graph problems to accurately approximate the non-linear functional form of most cost estimation functions. This was achieved by dividing the original cost functions into multiple equal segments that then could be individually represented by linear sub-functions. Application of the new method to a simple wood-to-fuel processing example influences the optimal P-graph process structure such that a previously uneconomic side-product route (pyrolysis) becomes economic and increases the overall profit. The results also demonstrate that the linear approximation error decreases with increasing numbers of segments and linear cost sub-functions. The time increase to solve the new problem structure, which has over threefold more operating units, is negligible for this simple case, but may be significant for more complex problems.

year: 2016

title: Cooperation in Maori and European children

authors: Vercoe, Glynis Price

subjects: Maori children

abstract: The object of this study is to compare the cooperative behaviour of Maori and European children and to investigate and compare the effects, upon the performance of the two ethnic groups, of working under cooperative conditions and under competitive conditions. Certain differences are expected to exist between the two ethnic groups as a result of the different child rearing practices employed by the Maoris and by the Europeans.

text: Cooperation in Maori and European children The object of this study is to compare the cooperative behaviour of Maori and European children and to investigate and compare the effects, upon the performance of the two ethnic groups, of working under cooperative conditions and under competitive conditions. Certain differences are expected to exist between the two ethnic groups as a result of the different child rearing practices employed by the Maoris and by the Europeans.

year: 1971