Phosphorus recovery from human urine using magnesium and calcium from natural and waste sources

Abstract

Non-renewable natural resource scarcity is one of the problems at present, which is mainly a result of its high consumption (i.e. fossil energy - oil and coal) to meet growing demands. The nature of a non- renewable resource is that it will eventually reach the peak and then decrease year by year, resulting in a wide gap between supply and demand. Non-renewable natural resources are not only fossil energy, but also including phosphorus (P). P is an important mineral nutrient and essential element to all life forms, because it involves in many basic processes, such as photosynthesis. P is a necessary element for every cell of living organisms and cannot be substituted by other elements. Moreover, many studies indicate that the existing phosphate rock reserves could be exhausted in the next 50- 100 years. Therefore, the recycling of P from wastewater or waste sources is a very important issue. Currently, there are various methods to recover P from wastewater or waste sources. Formation of struvite (ammonium magnesium phosphate or MAP, MgNH4PO4•6H2O) and hydroxyapatite (Cas(PO4h(OH)) are good alternative methods for the recovery of P, because struvite can be used as a slow-release fertilizer that is appropriate for plants and soil applications or in industrial processes as a P source. In the recovery of struvite from urine, it needs magnesium (Mg) and calcium (Ca) for struvite precipitation because they are the main compositions of struvite and hydroxyapatite. However, human urine contains low concentrations of Mg and Ca. That will increase the cost of production. Nowadays, many kinds of wastewater and waste sources, such as municipal wastewater, cattle manure, and human urine, are employed as raw materials for struvite and calcium phosphate production. The most interesting waste source is human urine, because it contains with a relatively high P and nitrogen (N). For saving chemical cost in struvite and calcium phosphate recovery from urine, this research used egg shells which are mainly calcium carbonate and sea water which contains a high concentration of Mg instead of conventional Ca and Mg chemicals. The effect of initial Mg and Ca concentration was examined for human urine by batch experiments. The experimental results showed that a good phosphorus recovery could be achieved by egg shells and sea water. The composition of precipitates and morphological appearance were also investigated and observed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS).