Supervisor: Professor Chris Greenwell (Durham University)
BACKGROUND AND RATIONALE
If wastewater treatment plants could effectively reprocess the ammonium and phosphate groups found in struvite this could reduce the shortage of these compounds in the fertiliser industry. Within wastewater treatment plants, anaerobic digestion is a favourable method of treating solid waste as the gas collected is returned to the gas network and the liquid product is recirculated for treatment because it has a high nutrient content.1 The solid sludge waste, post digestion, is given to farmers to spread onto their land as a soil improver. This is not the most effective or safe use of this solid waste as it does also not account for the possibility of heavy metals present.2 If the solids produced by the process were more effectively utilised, it would decrease the waste from the plant. It is a green source of ammonium and phosphate groups, from which effective fertilisers can be produced, reducing the amount of food poverty globally.3
Ammonium and phosphate recovery from struvite precipitation has been undertaken before, although using methods that differ from those outlined in this research project. Struvite precipitation has been achieved using spent refractory brick from the steel industry.4 However, this method removes the magnesium cations using nitric acid. Research has also been conducted recovering ammonium and phosphate as struvite, utilising hydrolysis and incineration of sewage sludge. This yielded a concentrated ammonium solution and a phosphate group rich sewage sludge ash. 5 However, once the heavy metals have been removed, a 1:10 ratio of sewage sludge ash to aqueous hydrochloric acid is formed which is an unsustainable amount of hydrochloric acid for the quantity of sewage sludge ash being dissolved.
OBJECTIVES OF THE RESEARCH
A report and poster detailing:
- The experimental methods applied to recover ammonium and phosphate groups from struvite.
- The purity of the ammonium and phosphate examples recorded.
- The monitoring the amount of phosphate group exchanged in the ion-ion exchange process.
- The percentage yield of ammonium and phosphate.
- The detailing of the equipment set-up used in this experiment.
- Is there an effective method by which ammonium (NH4+) and phosphate groups (PO34-) can be recovered from the mineral struvite?
- Does this process recover a high yield of ammonium and the phosphate groups?
- How can the ammonium and the phosphate groups be recovered in a useable form for redistribution and the consumer?
- Can this process be easy to implement in ongoing waste-water treatment plants and new waste-water treatment plants being built.
- What is the most sustainable and ethical way for this research to be undertaken?
Ammonium could be bubbled off and stored in canisters from the process already used by the Greenwell group to extract magnesium cations, for the synthesis of Layered Double Hydroxides, which is a catalyst for the formation of biofuels.6
The present understanding of the chemical structure and geometry of Layered Double Hydroxides is that the phosphate, the interlayer anion, allows the formations of the layers in the Layered Double Hydroxides, but is in fact not a critical part of the structure. Consequently, it could be recovered using an ion-ion exchange, using a carbonate anion to take the place of the phosphate.7
The recovered phosphate group would then be reacted to form a useful phosphate salt or could be reacted with the recovered ammonium to form ammonium phosphate, both being easily stored and transportable.
This method is advantageous as it does use environmentally friendly chemical methods and reagents, it does not use of an excess of liquid to dissolve the product, it also breaks down the struvite into three useful components, magnesium cations, ammonium and phosphate.
REFERENCES ( Royal Society of Chemistry Style)
- European Environmental Agency: Urban wastewater treatment for 21st century challenges,
(Accessed December 2022)
- L. Lake, P. W. W. Kirk, J. N. Lester, Journal of Environmental Quality, 1984 13, 175-183
- World Food Programme: Projected increase in acute food insecurity due to war in Ukraine,
(Accessed December 2022)
- Dong-Ying Li, Yi-Chin Cho, Ming Huang Hsu, Yi-Pin Lin, Journal of Environmental Management, 2022, 302, https://doi.org/10.1016/j.jenvman.2021.114110
- Moh Moh ThantZin, Diwakar Tiwari, Dong-Jin Kim, Journal of Water Process Engineering, 2021, 39, https://doi.org/10.1016/j.jwpe.2020.101697
- L. Joyce Kwok, Hongri Suo, Chunping Chen, D. W. Justin Leung, Jean-Charles Buffet, Dermot O’Hare, Green Chem., 2021, 23, 1616-1620
- Britannica: Ion-exchange reaction,
(Accessed November 2022)
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