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    Evaluating woodchip bioreactors for mitigating drainage nitrate levels from a municipal wastewater land treatment site : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences at Massey University, Palmerston North, New Zealand
    (Massey University, 2024-09-23) Romero Ramírez, Stefanía Yanina
    Woodchips bioreactors are a well-established end-of-drain treatment technology that has been widely used to reduce nitrate (NO₃-) from agricultural drainage water. However, their application to municipal wastewater land treatment sites remains less explored, despite potential advantages. In New Zealand, land application of pre-treated wastewater is a growing practice to mitigate excessive nutrient discharges to the aquatic environment. Land treatment can prove effective when operated correctly, but challenges arise when large volumes of wastewater, and small areas available for irrigation, necessitate high application rates, which can result in NO₃- enrichment of drainage water. The Levin Wastewater Land Treatment Site (LWLTS) is an example of where relatively high annual volumes of municipal wastewater are irrigated over an under-sized application area, resulting in high application depths (4667 mm/year). Consequently, surface drains and shallow groundwater transfer NO₃- to the Waiwiri Stream continually all year. In order to reduce the impact of the LWLTS on the water quality of the Waiwiri Stream, one of its resource consent requirements involves reducing the NO₃- levels in the Waiwiri Stream, downstream from the site. The objective of this thesis was to evaluate the potential use of woodchip bioreactors for reducing NO₃- concentrations in drainage water from LWLTS, including an assessment of the ability of soluble C dosing to enhance NO₃- removal. Initial experiments used small-scale column woodchips bioreactors, which simulated similar water temperatures and NO₃- concentrations to those at the LWLTS. The effect of different water hydraulic retention times (HRT) and the use of dosing with two soluble C sources, liquid sugar, and ethanol, were assessed. Under warm temperature conditions, the column bioreactors achieved 99% NO₃- removal efficiency with a 10-hour HRT. In contrast, under cool water temperatures at the same HRT, the NO₃- removal efficiency decreased to 31%. Soluble C dosing was an effective strategy for enhancing NO₃- removal, with the choice of C source proving to be crucial. Ethanol demonstrated to be more efficient than liquid sugar. Additionally, it was determined that dosing with ethanol at a C:N dosing rate of 1.5:1 achieved high removal efficiencies of 77% under warm conditions and at a 3.3-hour HRT, and 82% under cool conditions and at a 10-hour HRT. Based on the results of the column bioreactor study, the performance of pilot-scale woodchip bioreactors at reducing NO₃- levels in drainage water were evaluated at the LWLTS under field conditions. These experiments involved quantifying the effects of different HRTs and dosing with ethanol at different C:N ratios. Operating the bioreactors, at a 10-hour HRT achieved average NO₃- removal efficiencies of 43% and 59% during the cool and warm seasons, respectively. While, at a 20-hour HRT, the removal efficiencies were 69% and 85%, respectively. The variations in NO₃- removal efficiency between both seasons demonstrated that during the cool season the bioreactors were on average about one-third less effective. When bioreactors, operating at 6.6-hour HRT in cool conditions, were dosed with ethanol at a C:N ratio of 0.75:1, the NO₃- removal efficiency improved from 24% to 93%. This result demonstrates that under field conditions ethanol dosing proved to be a higher effective strategy for enhancing the performance of woodchip bioreactors, particularly during cool periods. Based on the findings of the pilot-scale bioreactors, two woodchip bioreactor designs were proposed for the LWLTS: a non-dosed woodchip bioreactor of 645 m³ operating at a long HRT (20 hours), and an ethanol-dosed woodchip bioreactor of 197 m³ operating at a short HRT (6.6 hours). The two proposed designs provide contrasting approaches, although both are expected to achieve the same annual NO₃- load removal (1174 kg N/year) and have similar annualised NO₃- removal costs ($6.90 and $6.50/kg N, respectively). In the long term, it is expected that the NO₃- removal of the larger non-dosed bioreactor will decline at a faster rate compared to the ethanol-dosed bioreactor due to relying solely of woodchips as the C source. However, it would be less susceptible to the risk of bioclogging and has greater capacity to increase NO₃- removal. In addition, ethanol dosing could be introduced to the larger non-dosed bioreactor in the future, when a decline in NO₃- removal efficiency is observed. Therefore, the overall flexibility of the larger bioreactor design is an advantage but comes with higher initial set-up cost. The results of this research demonstrate that woodchips bioreactors are effective treatment methods for mitigating drain water NO₃- levels at a municipal wastewater land application site. Additionally, C dosing using ethanol proved to be a promising cost-effective alternative to enhance bioreactor performance, allowing the use of relatively short HRTs, especially during cool conditions. This increases the daily volume of water that can be effectively treated.
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    Removal of dissolved reactive phosphorus from municipal and dairy factory wastewater using allophanic soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Cheuyglintase, Sasikunya
    Many of New Zealand’s sewage treatment plants (STPs) and rural factories discharge treated or partially treated sewage, which is rich in dissolved reactive phosphorus (DRP), into rivers and streams. A large number of these STPs are not able to comply with the current DRP river standards because conventional treatment methods are cost-prohibitive. There is an abundance of Allophanic soils with high phosphorus (P) sorption capacities located in the central North Island of New Zealand that have potential for use as low-cost filter material for removing DRP from wastewaters. For Allophanic soil filters to be a viable treatment option, the soil, in addition to having a high P sorption capacity, should be both accessible and plentiful. The main aims of this study were to assess and improve the effectiveness of Allophanic soil filters at removing DRP from wastewaters and to evaluate the agronomic value of P-enriched soils as a P source for plant growth. It also sought to contribute to a better understanding of the feasibility and important design characteristics of fullscale soil-based treatment systems. Five quarry sites in the Waikato Region were soil sampled to identify soils with high P retention values. Only the Te Mata Quarry (TQ) soil in the, northwestern Waikato Region, had a high P retention value at or close to 100% as assessed using the standard (5 g) anion storage capacity (ASC) test. The modified (1 g) ASC test revealed P retention values of 47 – 91% for samples taken from different soil depths at TQ. All of the soil depths down to 600 cm, except for the 125 – 175 cm depth, had modified (1 g) ASC test values >58%. This indicated that the TQ soil had P sorption capacities that would potentially make it a suitable material for filtering DRP from wastewater and, therefore, it warranted further evaluation using real wastewater. Wastewater pH has a marked influence on the P sorption capacity of soil filters, with the sorption capacity expected to increase as wastewater pH is decreased, from being alkaline to acidic. The laboratory soil column experiment quantified the effect of the level of acid dosing and the type of acid used on the capacity of soils to remove P from wastewater. Columns of soil, taken from a quarry at Ohakune (OQ), and treated with wastewater adjusted to pH 5.5 removed the greatest amount of DRP. A total of 8.9 mg P/g oven-dried soil was removed at an average removal efficiency of 75%. In comparison, the soil columns treated with wastewater without pH adjustment, removed only 4.5 mg P/g oven-dried soil at the same removal efficiency of 75%. This highlights the merits of lowering wastewater pH to increase DRP removal capacity. The performance pilot-scale soil filters at the Dannevirke STP and Fonterra Te Rapa WTP were evaluated, under field conditions, for a total operational period of 440 and 376 days, respectively. Each filter contained the OQ soil and had a surface area of 1 m². The OQ soil had an overall P removal efficiency of 67% and 71% at the STP and WTP sites, respectively. The OQ soil filters at Dannevirke STP removed a total of 6.4 mg P/g oven-dried soil, while the OQ soil filters at the Fonterra Te Rapa WTP removed a total of 1.87 mg P/g ovendried soil. This discrepancy in performance was due to the difference in wastewater type and pH adjustment, initial P concentrations, and soil pretreatment (i.e. the soil used at Dannevirke was sieved). A cost/benefit analysis suggested that if the STP was 225 km from the soil source then the cost of acid dosing is about ten times greater than the cost of supplying additional soil to achieve the same amount of P removal. Therefore, it is unlikely that acid dosing will be cost competitive for most wastewater treatment sites in the central North Island of New Zealand. The wastewater treated soil (WTS) obtained from the Dannevirke STP pilotscale filter experiment was evaluated for its agronomic effectiveness in a glasshouse pot experiment. The ability of WTS to supply P for ryegrass growth (Lolium multiflorum) was compared with a soluble phosphorus source (monocalcium phosphate, MCP). The WTS was highly effective at increasing available P in the soil, as measured by the Olsen P soil test, ryegrass yield and ryegrass P uptake. The soluble fertiliser P value of WTS was estimated to be equivalent to 61% of MCP applied at the same rate. Therefore, the results show that WTS is an effective P source for plant growth and its application to soil has the potential to recycle both the soil and the P it contains.
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    Tracer studies of a subsurface flow wetland : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Technology in Environmental Engineering, Massey University
    (Massey University, 1996) Prasad, Julius Narendra
    The use of constructed wetlands represents an innovative approach to wastewater treatment. However, the treatment performance of constructed wetlands has been variable due to an incomplete knowledge of the hydraulic characteristics. Current design methods idealise constructed wetlands as plug flow reactors ignoring the existence of longitudinal dispersion, short-circuiting and stagnant regions. The overall effect will be a reduction of treatment efficiency at the outlet. This thesis investigates the hydraulic characteristics of a subsurface flow wetland using a fluorescence dye tracer so as to determine the difference between theoretical and actual retention times and their effect on treatment efficiency. A thorough review of the literature is undertaken, firstly examining wetland systems and their treatment mechanisms, it then reviews their hydraulic characteristics and design considerations while finally discussing dye tracing studies. A series of dye tracing trials were undertaken on a pilot scale gravel bed wetland with a theoretical retention time of four days. The results from this research are presented as plots of dye concentration versus time at the outlet. These results are analysed in terms of chemical reactor theory and their implications on performance of various treatment mechanisms is discussed.
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    Wetland wastewater treatment systems : a New Zealand based review : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Massey University
    (Massey University, 1990) Shilton, Andrew Nicholas
    Natural and constructed wetlands have proven capable of providing a high standard of renovation to wastewater and their use as engineered treatment systems is rapidly developing in New Zealand and overseas. This thesis begins by examining the nature or the wetland environment and outlines the renovating processes it contains. The different types of wetland treatment systems are reviewed. Discussion continues into design and management principles which include physical and process design and hydrological and biotic considerations. Finally a review is made of the application of wetlands to the treatment of domestic sewage, non-point pollution, and industrial wastewaters. The conclusion is reached that wetland treatment systems offers an innovative and appropriate solution to a wide range of New Zealand's waste treatment problems and are likely to become an increasingly common treatment option in this country.