A comparative investigation on producing fertilizers from human urine through indirect routes

As the natural sources are not limitless, their sustainability has become a major problem for the past decades. Because of this problem, the term of recovery has become more important for a sustainable world. There must be a way to reuse natural sources after consuming them. Domestic wastewaster includes some pollutants that maybe be used further for other beneficial purposes. Specifically nutrients (nitrogen and phosphorus) in domestic wastewater causes eutrophication when discharged to the water bodies without any treatment. To control that problem recovering nitrogen and phosphorus is getting more important. Recovering those materials will serve both the environment and sustainability. Human urine takes only 1% of total volume of domestic wastewater however includes up to %80 of nitrogen and %60 of phosphorus. Due to these high concentrations, recovering nitrogen and phosphorus from urine is getting more attention. In this work recovery of nitrogen and phosphorus from urine with the usage of struvite precipitation, ion exchange/adsorption and stripping/absorption was investigated. Those three process were used and compared with each other single and combined stages. Seven dfferent combinations were used in total. Those are ıon exchange/adsorption, stripping/absorption and struvite precipitation as single stage; ion exchange/adsorption-ion exchange/adsorption, stripping/absorption-struvite precipitation, struvite precipitation-ion exchange/adsorption and struvite precipitation-stripping/absorption as combined stages Experiments were done in three stages. First of all urine was collected as a mixure and stored. During collection and storage period nitrogen and phosphorus concentrations, pH, salinity and conductivity changes in urine were monitored. In second stage of the work, nitrogen and phosphorus were recovered from stored urine through different alternative ways which were mentioned above. For the single stages, %10 of nitrogen and %99 of phosphorus was recovered through struvite precipitation while % 88 of nitrogen and %99 of phosphorus with ion exchange/adsorption and %99 of nitrogen were recovered with the usage of stripping/absorption processes. Single stage recovery results have shown that if only phosphorus recovery was needed then struvite precipitation is the best way, stipping/ absorption becomes prominent if only nitrogen recovery is needed. If the purpose is recovering both of the nutrients, than ion exchange/adsorption is the better option. Both of struvite precipitation and stripping/absorption processes have high efficiencies for only one element, and negligible results for the other one. Single stage applications have shown that 2.1 gr. of sturivte; 500 gr. of nutrient loaded clinoptilolite and 21 gr. of ammonium sulfate was produed through those processes. Residual liquid phase concentrations were measured as 5500mg/L nitrogen and 3mg/L phosphorus after sturivte precipitation; 800 mg/L nitrogen and 15mg/L phosphorus after ion exchange/adsorption; 60mg/L nitrogen and 260 mg/L phosphours after stripping/absorption. Combined recovery experiments were done to recover optimum amounts of nutrients and also reduce the remaining concentration in liquid phase. After struvite precipitation high amount of nitrogen remains in the liquid phase. To recover that nitrogen, ion exchange/adsorption and stripping/absorption processes were applied to the remaning liquid phase. By ion exchange/adsorption option %88 of nitrogen was recovered while this efficiency went up to %99 with the usage of stripping/absorption processes. Struvite precipitation was used to recover remaining phosphorus in the liqıid phase after stripping/absorption and %92 of phosphorus was recovered. Second stage of ion exchange/adsorption was also applied. %95 of nitrogen was recovered. Amounts of produced solid phases through combined stages were also compared. By two stage of ion exchange/adsorption process 615 g, through stripping/adsorption + struvite precipitation application 23g, with struvite precipitation + ion exchange/adsorption 475g and through struvite precipitation + stripping/absorption process 23 g of solid was produced. Remaining nitrogen and phosphorus concentrations in liquid phase were measured as 260 mg/L nitrogen and 12 mg/L phosphorus after 2 stage ion exchange/adsorption application, 50 mg/L nitrogen and 30 mg/L phosphorus after stripping/absorption + struvite precipitation, 800 mg/L nitrogen and 2 mg/L phosphorus after struvite precipitation + ion exchange/adsorption and 25 mg/L nitrogen and 3mg/L phosphorus after struvite precipitation + stripping/absorption. When those three processes were combined in pairs, stripping/absorption after struvite precipitation option has the highest (%99) recovery percentages for both nutrients. %88 of nitrogen and %99 of phosphours can be recovered with the usage of ion exchange/adsorption after struvite precpitation. When ıon exchange/adsorption process was used as two stages %95 nitrogen and up to %99 of phosphorus could be recovered. %92 of the remaining phosphorus after stripping/absorption was recovered through struvite precipitation. With the only %5 difference between the best and the worst option, this stage have shown that all of these combination could be used in proper conditions. Three different solids were produced as alternative fertilizers with those three processes; clinoptilolite loaded with nitrogen and phosphorus, ammonium sulfate and struvite. Those three solids were used on a pot trials as fertilizer to grow pepper and compared with the commercial synthetic fertilizers (ammonium nitrate, tri super phophate and 20:20 composite). Height of the plants were measured and number of flowers were counted. Results indicated that solid phases produced from human urine have almost the same and even better fertilizer capability as synthetic fertilizers.