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    Accounting of nitrogen attenuation in agricultural catchments : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2018) Elwan, Ahmed
    The transport and fate of the nitrate that leaches from the root zone of farms, via groundwaters, to receiving surface waters is poorly understood, particularly for New Zealand’s agricultural catchments. Monitoring nitrate concentrations in rivers clearly demonstrates that not all of the nitrate leached across the catchment enters the river. As nitrate moves from land to receiving waters there is potential for subsurface denitrification and hence the attenuation of the nitrate flux to receiving surface waters. A good understanding of the influence of catchment characteristics on the spatial variations of nitrate attenuation is essential for targeted and effective water quality outcomes across agricultural landscapes. This thesis analysed large datasets of geographical information (land use, soils and geology) and water quality records at 20 sites in two large agricultural catchments, the Tararua and Rangitikei, which are located in the lower parts of the North Island New Zealand. The results demonstrated that the influence of land use on river soluble inorganic nitrogen (SIN) concentrations in the Tararua catchment was outweighed by other catchment characteristics such as soil type and hydrological indices. A simple approach, that is not data-intensive, was developed and applied to quantify the capacity of a catchment to attenuate nitrogen. The nitrogen attenuation factor (AFN) is a key component of this approach. AFN is defined as the average annual land use nitrogen leaching losses minus the average annual river SIN river loads, divided by the average annual land use nitrogen leaching losses. AFN was determined for 5 and 15 sub-catchments in the Rangitikei and Tararua catchments, respectively, and was found to be highly spatially variable with values ranging from 0.14 to 0.94. To assess the uncertainty associated with AFN, the uncertainty in the average annual river SIN loads was evaluated. Five load calculation methods (global mean GM, rating curve RC, ratio estimator RE, flow-stratified FS, and flow-weighted FW) and four sampling frequencies (2 days, weekly, fortnightly, and monthly) were investigated to calculate average annual river loads at one of the long-term, representative water quality monitoring sites in the study catchment. The FS method using a monthly sampling frequency resulted in the lowest bias (0.9%) for average annual river SIN loads and therefore was used in the quantification of AFN across the study catchments. A robust uncertainty analysis of AFN showed two distinct groups of sub-catchments; sub-catchments with higher (>0.7) and less uncertain nitrogen attenuation factors, and sub-catchments with lower (<0.4) and more uncertain nitrogen attenuation factors. This supports the use and applicability of AFN as a sub-catchment descriptor of the capacity of a sub-catchment to attenuate nitrogen. AFN was positively related to poorly drained soils and mudstones, and negatively related to well-drained soils and gravels in the study catchments. A novel but simple hydrogeologic-based model was developed to evaluate the potential to use soil and rock indices to predict average annual river SIN loads from different land uses in a catchment. Four different versions of the model (uniform nitrogen attenuation, variable nitrogen attenuation based on soil indices only; variable nitrogen attenuation based on rock indices only; and variable nitrogen attenuation based on both soil and rock indices) were developed. Accounting for the spatial distribution of the nitrogen attenuation capacities of both soils and rocks resulted in markedly better predictions of river SIN loads in the Tararua and Rangitikei sub-catchments. The novel findings of this thesis clearly suggest that effective and targeted measures to improve water quality at a catchment scale should account not only for land use but also for other catchment characteristics, such as the subsurface nitrogen attenuation capacity. This new knowledge will be instrumental in the future development of the models and planning tools required to reduce the detrimental impacts of agriculture, by aligning spatially intensive land use practices with high nitrogen attenuation pathways in sensitive agricultural catchments.
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    Nitrogen removal in a foam media biofilter for on-site wastewater treatment systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Environmental Engineering at Massey University
    (Massey University, 2005) Miller, David Rei
    Discharges of nitrogen can contaminate groundwater, and cause algal blooms or eutrophication in surface waters. On-site wastewater treatment systems (OWTS) have been identified as significant sources of nitrogen. Homeowners and manufacturers are under increasing pressure to install OWTS capable of effective nitrogen removal. Biological nitrogen removal in OWTS usually takes place in a fixed growth biofilter, following primary treatment in a septic tank arrangement. Three configurations of OWTS using foam media biofilters were assessed in the field. Foam media has advantages over sand, as high porosity and large air gaps allow the simultaneous flow of wastewater and air, thus reducing clogging and allowing higher loading rates. Septic tank effluent had lower concentrations of TSS, COD and TN in configurations with larger tank volume. Biofilters provided additional removal of TSS and COD to give effluent concentrations as low as 9 mg/L and 36 mg/L respectively. TN concentration in the effluent varied from 41-53 mg/L depending on configuration. The least nitrogen removal occurred in the configuration with the highest loading rate (in terms of L/m2/d). A bench-scale biofilter constructed using a single foam block (200 x 160 x 60 mm) achieved TN removal up to 10.7 mg/L (0.024 g-N/d at a dosing rate of 2.2 L/d). It was observed that nitrification and denitrification can both occur in a single foam block. Assimilation was also a significant nitrogen removal mechanism, accounting for up to 49 % of total removal. DO concentrations at microenvironments within the bench-scale biofilter were determined using a miniature membrane electrode. A syringe needle and custom-made plunger with the electrode fitted inside allowed DO concentration to be determined in sample volumes as small as 1 mL. The empirical equation derived to calculate DO concentration was accurate to within ± 2.9 %. The extent of nitrification was greatest after an overnight rest period. At microenvironments within the bench-scale biofilter, nitrification increased at longer hydraulic residence time. Nitrification increased at high feed concentrations of carbon, which was not expected, and did not decrease at DO concentrations as low as 0.88 mg/L. Denitrification was greatest when feed was high in carbon and low in DO, but was not affected by DO concentrations as high as 2.70 mg/L. The effects of loading rate, biofilter depth, recirculation ratio and flooding need to be investigated further to optimise the design of biofilters in the field.
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    COD removal and nitrification of piggery wastewater in a sequencing batch reactor : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Technology in Environmental Engineering
    (Massey University, 1998) Wong, Wing Nga
    Piggery wastewaters are particularly problematic when released untreated into the environment. They contain high levels of chemical oxygen demand (COD) and also nutrients such as nitrogen and phosphorus which can cause eutrophication in surface waters. The sequencing batch reactor is a form of biological treatment in a completely mixed reactor with aerobic and anoxic periods to facilitate nutrient removal. In this study nitrogen removal of piggery wastewater in a SBR by nitrification and denitrification was investigated. Screened raw piggery effluent was used in this study. Average non filtered feed contained a chemical oxygen demand of 12,679 mg/l. The average of the non filtered feed TKN was 1103 mg/l with its largest component being ammonia having an average concentration of 681 mg/l (non filtered feed). Initial experiments with solids retention time (SRT) of 15 days and the hydraulic retention time (HRT) was 5 and 3.3 days for 9 and 4 weeks respectively during Stage 1. No significant nitrification activity was observed during this period. The reactor cycle time was then increased to 2 days which effectively increased the SRT to 30 days and HRT to 6.7 days (Stage 2). The new environment allowed the nitrifying population to develop and nitrification was observed with the formation of nitrite and nitrate. The heterotrophic kinetic constants determined the yield coefficient as 0.49. The maximum specific growth rate (μ max) was 6.8 day-1 and half saturation constant (Ks) was 293.6 mg/l. The COD removal of the feed in the SBR started from around 70% in weeks 6-10 during Stage 1 and reached 92.7% in week 29. Ammonia removal was not significant in the first 17 weeks due to no significant nitrification activity during that time. After initiating a 2 day reactor cycle, ammonia removal rates increased to over 90%. Batch tests indicated that most of the ammonia needed to be removed in the first aerobic period. This allows nitrite and nitrate concentrations to build up and be removed by the subsequent anoxic period. This was when there was enough readily degradable COD as not to inhibit denitrification. The reactor cycle time which achieved full nitrification and the highest nitrate removal by denitrification was observed in the batch test on day 256. The first 6 hour aerobic period removed 81.1% of the ammonia. Subsequent anoxic periods reduced the nitrate concentration in the effluent to 11.0 mg N/l. The nitrification rates increased in the reactor over time as the nitrifying population acclimatised to the piggery effluent. In fact the highest nitrate formation and ammonia oxidation rate was 15.5 mg N/l. h and 24.6 mg N/l.h measured during the last test on day 270. Nitrite formation rates peaked at 11.5 mg N/l.h. The SBR biomass population was able to remove nitrate efficiently as batch tests showed that denitrification rates could reach 22.1 mg N/l.h. The relationship between effluent nitrate levels and COD: ammonia concentration ratio was assessed in order to determine the importance of these chemical characteristics important in controlling the nitrification and denitrification activity in the SBR. Results showed that as the COD: ammonia concentration ratio increases, the effluent nitrate levels decreases. The study found that the SBR was suitable in removing COD and Nitrogen from piggery wastewater.
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    Nitrogen and phosphorus removal from dairyshed effluent using a sequencing batch reactor : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Applied Science at Massey University
    (Massey University, 1997) Ellwood, Brian
    It is apparent that present dairyshed effluent treatment systems are not capable of complying with regulations generated by Regional Councils implementing the Resource Management Act 1991. This has created a need for research into dairyshed effluent treatment. To develop an improved treatment system for dairyshed effluent, research was conducted with two main study objectives; to characterise effluent from the dairyshed holding yard and anaerobic pond, and to develop a sequencing batch reactor (SBR) for the removal of nitrogen and phosphorus. The carbon characterisation showed that there was a large difference between dairyshed effluent and domestic effluent in the proportion of carbon in each fraction. When treating dairyshed wastewater to reduce BOD, nitrogen and phosphorus concentrations it was not possible to treat either the yard effluent or the anaerobic effluent without addition of external materials. The BOD reaction rate constant for the yard effluent at 0.2 d -1 was similar to a typical domestic wastewater value of 0.23 d -1 . The anaerobic pond effluent BOD reaction rate constant of 0.16 d -1 was lower than the yard effluent value indicating that the anaerobically treated effluent was hard to treat aerobically. A pilot scale SBR treating dairyshed effluent was operated for 75 days. Startup procedure used a 50/50 mixture of anaerobic pond and aerobic pond effluents which was successful in establishing a biomass capable of nitrifying anaerobic pond effluent. The startup time to establish a nitrifying population was 17 days. The sludge was found to settle well, with a maximum sludge volume index of 54 ml/g measured during the SBR operation. Sludge bulking was not seen as a problem. Nitrification performance a large proportion of the bacteria were lost took only 5 days to recover. With the addition of alkalinity nitrification reliably reduced the effluent ammonia concentration to 5 mg/l. From the cycle analysis the first order reaction rate constants for nitrification were; ammonia reduction 0.7 hr -1 , TKN reduction 0.4 hr -1 and nitrate formation 0.2 hr -1. These constants could be used in future work to optimise stage times. KEYWORDS: Sequencing Batch Reactor; Dairyshed effluent characterisation; readily available carbon; nitrogen and phosphorus removal; activated sludge; venturi aerator; Sludge Volume Index.