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Subject: search.filters.subject.Phosphate removal

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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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    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, Matthew
    Facultative 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.
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    Luxury uptake of phosphorus by microalgae in New Zealand waste stabilisation ponds : a thesis presented in partial fulfilment of the requirements for the degree of Masters in Engineering at Massey University, Manawatu, New Zealand
    (Massey University, 2015) Crimp, Aidan Jeremy
    The discharge of phosphorus to waterways within wastewater effluent causes significant environmental damage through microalgal blooms and eutrophication. This is a particular problem for wastewater treatment plants that rely on waste stabilisation ponds (WSPs) for the bulk of their treatment. While having simple designs and low running costs, WSPs are mostly ineffective at phosphorus removal, with only 15 – 50% removal achieved on average according to some studies. The luxury uptake phenomenon within microalgae has been identified as one mechanism that could improve WSP phosphorus removal. This occurs when microalgae store phosphorus beyond what is required for their metabolism as polyphosphate, leading to phosphorus contents above the standard 1 %P/g VSS for microalgae. However, studies on this subject in full scale WSPs to date have been limited to just two different ponds. To improve knowledge on this mechanism, this study aimed to assess the impact of environmental conditions, climatic region and pond type on microalgal luxury uptake, as well as determine which specific microalgal and cyanobacterial genera were best able to perform this mechanism. To achieve these objectives, a yearlong study was conducted on 13 different WSPs from 7 sites within various climatological regions within New Zealand, as well as two pilot scale High Rate Algal Ponds (HRAPs). From this study, it was found that luxury uptake was found to occur in 56% of the WSP, with a peak phosphorus content of 3.8 %P/g VSS. Conversely, only one sample taken from the HRAPs was found to exhibit luxury uptake. Total dissolved phosphorus (TDP) concentration and rainfall were found to have a significant effect on biomass phosphorus content at a 95% confidence level, while the WSP climate was found not have an influence. There were no significant differences between the biomass phosphorus contents in primary and secondary ponds, with averages of 1.31 %P/g VSS and 1.21 %P/g VSS respectively, while HRAPs (0.71 %P/g VSS) were significantly lower due to the low TDP concentrations experienced by these ponds. 22 of the 23 identified microalgal and cyanobacterial genera were found to perform luxury uptake, at varying frequencies. The cyanobacterium Planktothrix was most effective, storing polyphosphate as granules in 84% of the samples it was identified in. Scenedesmus, Pediastrum, and Schroederia were also effective, at frequencies of 73%, 82% and 79% respectively. There was some correlation between storage of phosphorus as polyphosphate and enhanced phosphorus contents in the biomass, with nearly all samples containing no visually identifiable polyphosphate granules exhibiting phosphorus contents below 1 %P/g VSS. However, there were only limited correlations between the amount of polyphosphate and the levels of the significant variables identified previously. This research provides valuable insight into the phosphorus uptake behaviour of microalgae and cyanobacteria, and shows that there is some potential for development of a new engineered process targeting improved phosphorus removal. If the phosphorus content of biomass in this new process could consistently attain a level of 3 %P/g VSS, phosphorus removal from wastewater for an average community of 500 people could be increased from 31% to 93%, thus greatly reducing the impact of wastewater discharge on the receiving environment.