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Item Understanding the mechanisms involved in Escherichia coli decay during wastewater treatment in High Rate Algal Ponds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2019) Chambonnière, PaulLittle is known about the mechanisms and magnitude of pathogen disinfection in High Rate Algal Ponds (HRAPs). However, maturation ponds are used worldwide for wastewater disinfection, and pathogens can experience similar environmental conditions in maturation ponds and HRAPs. The literature suggests that pathogen removal in maturation ponds is primarily supported by sunlight-mediated mechanisms (direct DNA damage, endogenous photo-oxidation, and exogenous photo-oxidation), and a range of poorly characterized ―dark‖ mechanisms. Based on this evidence, and knowing HRAPs are specifically designed to optimize light supply into the broth, there is reason to believe sunlight mediated disinfection mechanisms should be significant in HRAPs. This thesis therefore aimed at identifying and quantifying the mechanisms responsible for Escherichia coli (E. coli) decay in HRAPs under the hypothesis that understanding the mechanisms involved in disinfection during wastewater treatment in HRAPs can provide the scientific foundation needed to optimize the design and operation for this critical wastewater treatment service. E. coli was selected for being an established indicator of the removal of faecal contamination during wastewater treatment. Two pilot scale HRAPs (0.88 m3) were commissioned and monitored over 1-2 years, showing a mean E. coli decay coefficient of 11.90 d-1 (std = 24.05 d-1, N = 128), equivalent to a mean E. coli log removal of 1.77 (std = 0.538, N = 128) when operated at a hydraulic retention time (HRT) of 10.3 d (std = 2.01 d, N = 139). Hourly monitoring showed high daily variations of E. coli log removal (up to 2.6 log10 amplitude) during the warmest summer days, with the lowest E. coli cell counts observed in the late afternoon, when the broth pH, dissolved oxygen concentration, and temperature typically reached peak values in the HRAP. No mechanisms driving E. coli removal in HRAP could be identified during the monitoring of pilot scale HRAPs so a mechanistic study of E. coli decay was performed at laboratory and bench scale to individually quantify potential mechanisms. At laboratory scale under various conditions (e.g. darkness vs sunlight exposure, neutral pH vs alkaline pH, RO water vs filtered HRAP broth), direct DNA damage, endogenous photo-oxidation, and high-pH toxicity were identified as the main mechanisms contributing to E. coli decay. Exposure to potentially toxic algal metabolites and exogenous photo-oxidation were not found to be significant under the conditions tested. Natural decay (i.e. decay in conditions identified not to be detrimental to E. coli survival) was never significant. The impact of predation could not be investigated due to technical challenges although pilot scale observations suggested this mechanism may be significant in certain conditions. Subsequent bench-scale tests conducted in HRAP broth indicated that temperature-dependent uncharacterized dark decay (i.e. decay in conditions not known to be detrimental to E. coli survival) was likely to be the dominant mechanism of E. coli removal under conditions relevant to full-scale operation. Temperature-dependent high-pH toxicity was confirmed to further increase E. coli decay at pH levels commonly reached in HRAPs. The contribution of sunlight mediated mechanisms was however not significant. Exposure to toxic algal metabolites was suspected to cause significant E. coli decay at times of extreme photosynthetic activity, but more research is needed to confirm this mechanism and its true significance. Results from laboratory scale and bench scale experiments enabled the development of a model capable of predicting E. coli decay in HRAP broth according to pH, temperature, and sunlight intensity distribution. A model predicting HRAP broth temperature and pH according to design and weather data was also developed and validated against data from the pilot scale HRAPs monitored during this study for temperature (average absolute error of predictions 1.35°C, N = 25,906) and pH (average absolute error of predictions 0.501 pH unit, N = 23,817). Coupling the E. coli decay model with the environmental model enabled long term predictions of E. coli removal performances in HRAP for various weather conditions, design, and operational regimes. Simulations predicted that a 3-HRAPs series would sustain average yearly E. coli log-removal of 3.1 in Palmerston North, New Zealand when operated in conditions similar to the pilot scale HRAPs used in the present study. Such performance would deliver year round compliance with local microbial quality guidelines. Disinfection performance could be further improved by increasing the hydraulic retention time, lowering the depth, or collecting the effluent once daily in the late afternoon while letting HRAP depth fluctuate. Overall, this research challenges the common belief that sunlight mediated disinfection mechanisms contribute the most to pathogen removal in HRAPs. Instead, uncharacterized dark decay was predicted to cause 87% of the total E. coli decay over one year simulation. High-pH toxicity may significantly contribute to overall E. coli decay in specific conditions (e.g. low depth where high-pH toxicity was predicted to account for 33% of total yearly E. coli decay), while sunlight mediated disinfection was limited under all simulated designs and operations (highest contribution predicted being 16% of total yearly E. coli decay). Because this study also confirmed the potential of HRAP to achieve sustained wastewater disinfection, further research is needed to better characterize dark decay mechanisms (for E. coli and other key indicators) as this knowledge has the potential to further improve HRAP design and operations for wastewater disinfection.Item Elevating phosphorus accumulation in waste stabilisation pond algae : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2019) Sells, MatthewFacultative waste stabilisation ponds (WSP) are used globally for wastewater treatment due to their low cost and simple operation. While WSPs can be effective at removing organic pollutants and pathogens, phosphorus removal is typically poor. Algae that are common in WSPs are known to accumulate phosphorus and increase their phosphorus content in the biomass from 1% up to 3.8% (gP/gSS), which is believed to be from the production of intracellular polyphosphate granules. This phenomenon, known as luxury uptake, may be possible to manipulate to improve phosphorus removal in WSPs; however, its occurrence is sporadic and poorly understood. This PhD thesis was undertaken to investigate the conditions that influence phosphorus accumulation in WSP algae. Phosphorus accumulation was quantified using two methods: (1) the traditional phosphorus content in the biomass (gP/gSS), and (2) a new image analysis method developed in this thesis that quantifies stained polyphosphate granules within individual algal cells (μm2 granule/μm2 cell). Following a literature review and screening experiments that sought to identify variables that could affect the phosphorus content in the biomass (gP/gSS), six variables: temperature, phosphorus concentration, light intensity, mixing intensity, organic load, and pH were comprehensively examined using 40 batch factorial experiments (26-1) and a mixed genus culture from a full-scale WSP. Nine variables and interactions had a significant effect on the phosphorus content in the biomass and were incorporated into a regression equation. This ‘mixed genus’ regression equation was tested against literature data, where seven out of the eight batch experiments from the literature were successfully predicted. In order to identify if the batch findings could be applied to a continuous process, which is more typical of full-scale WSPs, a bench-scale novel ‘luxury uptake’ process was designed, built, and operated under five different scenarios. The regression equation successfully predicted the experimental results for three of the five conditions examined. It was theorised that differences in behaviour at the genus level might explain why all five conditions were not successfully predicted. In an attempt to improve the prediction capability, the ‘black-box’ of mixed genus analysis was ‘opened’ to allow the effects of variables on phosphorus accumulation at the genus level to be directly examined. To achieve this, a new image analysis method was developed that quantified stained polyphosphate granules in individual algal cells. To ensure the granules being measured were indeed polyphosphate, algal cells were analysed using transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, which confirmed the granules contained higher levels of phosphorus compared to the remaining cell. The image analysis method was then used to quantify stained polyphosphate granules in individual cells from the 40 batch factorial experiments mentioned previously. The results using the image analysis method showed that, for the five most abundant algal genera, Micractinium/Microcystis had the highest average accumulation of polyphosphate granules (17% μm2 granule/μm2 cell), followed by Scenedesmus (12%), Pediastrum (11%), Monoraphidium (8%), and Actinastrum (4%). Although none of the genera studied had the same combination of significant variables, all five genera preferred a high phosphorus concentration to elevate polyphosphate granule accumulation. Furthermore, a high light intensity, high organic load, or high temperature was preferred by the algae if the variable was significant for that genus. The culture used in the bench-scale continuous flow ‘luxury uptake’ process originated from a mixed genus WSP culture; however, it had become dominated by the Scenedesmus genus. Therefore, the regression equation was refined to use the batch data for this genus alone. This new Scenedesmus regression equation was compared against the experimental data from the ‘luxury uptake’ process previously mentioned. Polyphosphate granule accumulation was now successfully predicted in all five experimental conditions at the 95% confidence level. This improved prediction capability indicates that an understanding of the algal genus present in a WSP system is required for accurate predictions of the phosphorus accumulation to be obtained, and the batch data can indeed be applied to a continuous process. An unexpected result of the research was that, contrary to what was believed in the literature, an increase in the phosphorus content in the biomass did not necessarily increase the polyphosphate granule accumulation. Further examination identified that individual cells from the same algal species had varying polyphosphate granule contents from 0% to over 20% (μm2 granule/μm2 cell) when exposed to the same conditions. This variation was hypothesised to be from cellular functions influencing the granules differently depending on the individual alga’s cell cycle. In addition, when the phosphorus content in the biomass was increased above 2.1% (gP/gSS), no significant effect on the average quantity of polyphosphate granules was observed. This finding indicates that other forms of phosphorus storage must be responsible for attaining a highly elevated phosphorus content in the biomass.Item Evaluation of baffles for optimisation of waste stabilisation ponds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Environmental Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2003) Harrison, JillWaste stabilisation ponds are a common form of treating wastewater throughout the world and they provide a reliable, low-cost, low-maintenance treatment system. A literature review undertaken highlighted the need for improved understanding of the hydraulics of such systems, and their upgrade. In particular, the application of baffles is not well understood beyond the use of longer, traditional baffles to increase the approximation to plug flow. The mechanisms and interactions behind baffles are not generally understood. The work involved the use of CFD modelling to assess various pond designs. In addition to this, traditional tracer studies were carried out on a physical laboratory model, and on a full-scale field pond. These traditional studies highlighted the success of the computer modelling approach. CFD modelling was used to model twenty pond designs, utilising various baffle lengths, number and position. These cases also studied inlet type and outlet position. In the second phase of the work, six of the CFD designs were tested in the laboratory setting. The final phase of work involved two tracer studies carried out on a field pond, utilising a modified inlet, then a combination of a modified inlet and the inclusion of a short (stub) baffle. CFD modelling has shown to be an effective investigative and design tool. The addition of results from laboratory and field studies further emphasises the benefits of the CFD modelling. The work has also provided an understanding of key flow mechanisms and interactions that have previously been attributed to other factors. Single baffles are not generally effective, and a minimum of two baffles will generally be required to achieve significant treatment improvements. The potential of short (stub) baffles has been shown, however they are sensitive to design changes and should be further researched. Previous research has looked at the pond using a 'black-box' approach, this work seeks to open and explain the flow patterns within that 'black-box'.Item Effects of carbon dioxide addition on algae and treatment performance of high rate algal ponds : a thesis presented in partial fulfilment of the requirements of the degree of Master of Engineering in Environmental Engineering at Massey University(Massey University, 2006) Heubeck, StephanWaste stabilisation ponds have been used for treating a great variety of wastewaters around the world for many decades. More advanced systems combine anaerobic or advanced facultative ponds with high rate algal ponds (HRAP) followed by a number of algae settling ponds and maturation ponds to achieve enhanced and more reliable removal of wastewater pollutants, while yielding possibly valuable by-products such as biogas and algal biomass. In recent years a growing number of scientists and engineers have proposed the use of HRAP treating domestic wastewater for carbon dioxide (CO2) scrubbing from biogas and CO2 sequestration. The experiments presented in this thesis sought to determine if the treatment performance of HRAP is affected by the addition of CO2 and subsequent reduction of pond pH. Experiments with algae cultures grown on domestic wastewater in laboratory microcosms, outside mesocosms and outside pilot-scale HRAP were conducted. Carbon dioxide addition to algae wastewater cultures restricted the maximum pH level to ~8. Key wastewater quality parameters of CO2 added cultures, were compared to control cultures without CO2 addition. The wastewater quality parameters monitored include temperature, pH, and concentrations of total suspended solids (TSS), ammoniacal-nitrogen (NH4-N), dissolved reactive phosphorus (DRP), filtered biochemical oxygen demand (fBOD5) and the faecal indicator Escherichia coli (E. coli). Carbon dioxide addition to algae wastewater cultures was found to promote algal growth and increased the TSS concentrations. Over 8 day culture length CO2 addition in laboratory and outside batch experiments increased algal growth (indicated by TSS) by up to 76% and 53%, respectively. During semi-continuous outside experiments CO2 addition increased algal growth by ~20% in comparison to the control cultures. Despite enhancing algal growth (TSS), CO2 addition appeared to have little effect on algae cell morphology, species composition and zooplankton activity in the algae wastewater cultures. Monitoring of the key nutrients NH4-N and DRP in cultures with and without CO2 addition indicated that CO2 addition can lead to an increase or a decrease in nutrient removal. Under culture conditions which allowed the control cultures to achieve high day-time pH levels CO2 addition, and subsequent pH restriction, appeared to reduce overall nutrient removal. Only slight changes or an increase in nutrient removal as a result of CO2 addition were observed under culture conditions which allowed only for a moderate or small elevation of the control culture pH. However, the increases in algal biomass, observed in all CO2 added cultures indicate a greater potential for the reclamation of potentially valuable wastewater nutrients in the form of algal biomass. Monitoring of fBOD5 levels during several outside experiments showed that CO2 addition had no effect on the fBOD5 removal by the algae wastewater cultures under those conditions. During several outside batch experiments (of up to 8 day culture length) the removal of the faecal indicator bacteria E. coli was monitored. It was shown that CO2 addition reduced E. coli removal by 1.4 to 4.9 log units compared to control cultures. Basic modelling of carbon flows indicated that under New Zealand conditions the CO2 volumes required for the changes described above would be available from the biogas produced in a wastewater pond system treating wastewater with a volatile solids (VS) concentration of ~ 500 mg/L. In systems treating weaker wastewaters additional CO2 could be made available through the onsite combustion of biogas. In summary, the obtained results suggest that CO2 addition to a field-scale HRAP could increase algal biomass growth year-round and slightly enhance nutrient removal during winter, but might reduce nutrient removal during summer, and reduce E. coli removal year-round, while having no effect on fBOD5 removal. The reduction in nutrient treatment performance during summer, and especially the losses in E. coli removal resulting form CO2 addition may require more sophisticated downstream processing of the HRAP effluent, like increase retention times in maturation ponds. Such remedial measures have to be evaluated on a case by case basis, and are dependent on the given regulations and discharge regimes of the system. This study indicates that in general HRAP can be employed for biogas purification and provide a useful sink for CO2 rich waste streams. The beneficial effects of CO2 addition to HRAP do not appear to allow for any design or management changes within the system, while it was indicated that most detrimental effects of CO2 addition could be accommodated without major alternations, although in some cases significant remedial measures may be required for correcting the losses in disinfection and nutrient removal performance.Item Studies into the hydraulics of waste stabilisation ponds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering at Massey University, Turitea Campus, Palmerston North, New Zealand(Massey University, 2001) Shilton, AndyWastewater stabilisation ponds are used extensively to provide wastewater treatment throughout the world. A review of the literature indicated that, while understanding the hydraulics of waste stabilisation ponds is critical to their optimisation, the research in this area has been relatively limited and that there is a poor mechanistic understanding of the flow behaviour that exists within these systems. Traditional tracer studies were used in this study but, in addition, new methodologies were developed involving drogue-tracking techniques to directly quantify the internal flow pattern. The investigation included study of physical scale models in the laboratory, operational ponds in the field and the simulation of both using computational fluid dynamics (CFD) mathematical modelling. Twenty experimental configurations were tested in the laboratory with the variables being: retention time; outlet position; inlet type and position; and the influence of a baffle. Ten of these experimental cases were then mathematically modelled and, in general, the simulations had close similarity to the experimental data. In the next phase of the work, the tracer and drogue tracking techniques were applied on two full-scale waste stabilisation ponds in the field. For one of the ponds a large scale model was also constructed. Mathematical modelling was again performed and a high degree of similarity was achieved. The study then finished with a broad review of wind effects and an investigation of integrating a biodegradation equation within the CFD model. While it was concluded that a CFD model cannot always be expected to precisely predict the performance of a field pond, this work has validated its use to the extent that it can be pragmatically applied for the systematic evaluation of alternative baffle, inlet and outlet configurations, thereby, addressing a major knowledge gap in waste stabilisation pond design.