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N and P removal from wastewater: a novel approach by developing innovative media augmented by sequencing batch reactor technology (SBR-CBA) : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

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  • Title:
    N and P removal from wastewater: a novel approach by developing innovative media augmented by sequencing batch reactor technology (SBR-CBA) : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
  • Author: Mohajeri, Parsa
  • Subjects: adsorption ; ANZSRC::05 Environmental Sciences ; ANZSRC::0501 Ecological Applications ; ANZSRC::0502 Environmental Science and Management ; ANZSRC::050204 Environmental Impact Assessment ; ANZSRC::050205 Environmental Management ; ANZSRC::050299 Environmental Science and Management not elsewhere classified ; ANZSRC::0907 Environmental Engineering ; biological reduction ; nitrate ; nutrient contamination ; phosphate ; wastewater treatment ; water management ; water process engineering
  • Description: The agriculture sector has many challenges: how to feed a growing global population, and also to mitigate negative impacts on the environment. How can we protect the environment, while producing food and fibre in a sustainable way? Discharge of different contaminants from agricultural, industrial and residential sources threatens the surrounding environment and ecosystems. One of the biggest environmental issues facing New Zealand, and our planet Earth, is N and P contamination of freshwater. Two novel methods in water process engineering were identified and evaluated in this PhD: 1. A powdered media was developed from locally sourced soil minerals and byproducts of the wood processing industry. After use, the novel media can be used as a soil conditioner. The physiochemical properties of ALLODUST were adjusted for the target contaminants. It provided a high area for adsorption and active sites for binding phosphate along with a desirable surfaces and pores for the denitrifier biofilm development. It was able to convert nitrate and phosphate applied to the system in concentrations up to 120 mg L-1 and 300 mg L-1, respectively, into passive forms. Field monitoring, regulation guidelines from Environment Canterbury, consultancies reports, and government publications suggest that the media would be suitable for waste water treatment in most commonly encountered NZ conditions. 2. The bioreactor has been designed and constructed with a focus on on user-friendly operation and cost effective components. The bioreactor’s agitation system was designed with a novel aeration and stirring design at the bottom of the reactor, which can save a significant amounts of energy, during the operation of the technology. In Chapter 3, two novel media were developed and the phosphate adsorption capacity of each was determined. In order to explain the adsorption mechanism, a series of the physiochemical experiments along with a morphology study were used. ALLODUST and ALLOCHAR consisted of allophanic soil mineral material sourced from either Horotiu soil or Craigieburn soil , two unique soils that are known to contain allophane minerals. Central Composite Design and Response Surface Methodology were used to design the experiment and model the nature of the response surface of the novel media in the experimental design and to analyze the optimum operational conditions. A Single Batch Aerobic Reactor with Couple Bottom Aertion was constructed at lab scale. The reactor design was optimized for three ranges of P contamination: 1-50 mg L-1 (low range); 51-175 (mid-range); and 176-300 (high range). The ALLODUST novel media demonstrated a higher P adsorption capacity compared to the ALLOCHAR media and Allophane compound itself. The ALLODUST adsorbent dosage of 3 g L-1 was the optimum: being able to remove 100% of P up to 50 mg L-1 in 30 minutes with the lowest aeration rate (1.5 L min-1) and remove 76% of P up to 300 mg L-1 in 450 minutes with the highest aeration rate (7.5 L min-1). In Chapter 4, the phosphate adsorption results from chapter 3 were optimised. The ALLODUST was designed to be able to neutralise phosphate concentrations representative of contamination from diffuse- and point sources. An elution experiment was used to investigate the adsorption cycle capacity of the media. Both Freundlich and Langmuir adsorption isotherms were used to describe the adsorption behavior of the ALLODUST with phosphate contaminated water. The BET experiment could support the high adsorption capacity of the ALLODUST while the total pore volume was increased by 70% compared to Horotiu soil itself. After seven continuous cycles, ALLODUST could still adsorb a high concentration of the phosphorous with only 13% desorption. The BET experiment could support the high adsorption capacity of the ALLODUST while the total pore volume was increased by 70% compared to Horotiu soil itself. This result can prove the high adsorption capacity of the ALLODUST in a fixed mode which the legacy phosphorous release could be expected in the lowest amount when it’s been used as a filter for the drainage pipes, fluidized media for the reactors, or floating media on the phosphorous contaminated lakes. In Chapter 5, the mechanisms that underpin the reduction of nitrate concentrations and nitrous oxide (N2O) emission were investigated in the presence of ALLODUST in an activated sludge process. Two anaerobic-aerobic batch reactors were developed, where the coupled bottom aeration method was used for efficient agitation and aeration in the aerobic reactor. The reactor was run at high nitrate concentrations (110 mg L-1), under anaerobic conditions at low- to long-term contact times (2, 12, and 22 h), while the aerobic period was constant for all the experimental designs (2 h). ALLODUST retained its integrity and stability over the long term operation. The allophanic soil material is a porous media with a high soil microbial population in anaerobic respiration. Also sawdust will provide an additional habitat for microbial colonization. Surface protonation by a chemical-acidic treatment lead to the development of positive surface charge density and also provided more microsites and nanosites which enhanced the specific surface area favourable for the microorganism’s growth. Ions, water, and organic compounds can be retained by the polar sites on the surface. The very low N2O concentration that was observed in the reactors containing ALLODUST might be the result of N2O diffusion back into the aqueous phase from the headspace, during the denitrification process. So, it will be available to the bacterial communities on the media’s surface for the reduction to N2 by denitrifiers. The high specific surface area, pore sizes and the porous structure of the media could enhance the N2O emission control. ALLODUST retained its integrity and stability over the long-term operation. Low ALLODUST concentrations (5.95 g L-1) removed 87% of the NO-3-N from the wastewater within 12 h. Further exploration revealed that the same amount of the media was optimal for decreasing N2O emissions from the anaerobic activated sludge reactor by 80%. In Chapter 6, the nutrient uptake efficiency of Carex virgata was monitored. The main aim of this chapter was to investigate what rate of N and P concentration can enter a wastewater treatment pond after completing the removal processes in chapters 3-5 and how the Carex virgata can contribute to the treatment process as a Floating Treatment Wetland system. A mesocosm batch experiment was performed at three different N and P concentrations, where 20 buckets were planted with Carex virgata and then the plants were left to grow for three months. The nitrate and phosphorous removal experiment was conducted in three ranges of contamination. Low-range buckets were set up by adding 10 mg d-1 L-1 NO3-N and 0.5 mg d-1 L-1 PO4-P. These amounts were 20 mg d-1 L-1 NO3-N and 1 mg d-1 L-1 PO4-P for average range and 30 mg d-1 L-1 NO3-N and 1.5 mg d-1 L-1 PO4-P for high-range. The role of the plant uptake in the FTW treatment system was the major in uptake the nitrate and phosphate from wastewater. i.e, 87% of TN and 82% of TP removal resulted from plant uptake. In Chapter 7, an overall discussion and conclusion of all the chapters is presented.
  • Publisher: Lincoln University
  • Creation Date: 2020
  • Language: English
  • Source: Lincoln University Research Archive
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