Phosphorus recovery from urine by adding difference sources of magnesium ion, applying for rural, coastal and island areas in Vietnam

In coastal areas and islands, farmlands often lack of nutrients. This research assessed the precipitation of phosphorus presenting in urine in the form of struvite of magnesium ammonium phosphate (MAP) by adding of supplement of Mg2+ ion from MgCl2 solution contained in seawater (Cat Ba island area). The urine and seawater have been mixed at different ratios.

Journal of Science and Technology in Civil Engineering NUCE 2019 13 (1): 66–77 PHOSPHORUS RECOVERY FROM URINE BY ADDING DIFFERENCE SOURCES OF MAGNESIUM ION, APPLYING FOR RURAL, COASTAL AND ISLAND AREAS IN VIETNAM Do Hong Anha,∗, Nguyen Viet Anha a Faculty of Environmental Engineering, National University of Civil Engineering, 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam Article history: Received 24 October 2018, Revised 23 December 2018, Accepted 29 January 2019 Abstract In coastal areas and islands, farmlands often lack of nutrients This research assessed the precipitation of phosphorus presenting in urine in the form of struvite of magnesium ammonium phosphate (MAP) by adding of supplement of Mg2+ ion from MgCl2 solution contained in seawater (Cat Ba island area) The urine and seawater have been mixed at different ratios The results have shown [Mg]:[PO4 ] ratios ranging from 0.75 to 5.26 allowed the precipitation of more than 90% of the phosphorus in the urine Seawater – to – urine ratios of 0.67/1, 1.3/1, 3.2/1, 5/1, 7/1 and 9/1 in volume would give phosphorus recovery efficiency of 99%, 92%, 96%, 96%, 95% and 99%, respectively Seawater in the studied area could be an appropriate Mg2+ ion source to produce MAP from urine diverting dry toilets Recovered phosphorus can be used as slow releasing fertilize for farming Keywords: MAP: phosphorus recovery; seawater; urine; struvite https://doi.org/10.31814/stce.nuce2019-13(1)-07 © 2019 National University of Civil Engineering Introduction According to General statistic office of Vietnam, there are 65% of population living in rural areas including coastal and island areas [1] Almost of them have main source of income from agriculture activities Modern agriculture is highly dependent on artificial fertilizers Many reports warn for the depletion of phosphorus, one of the key elements in artificial fertilizers The reserves may already have been depleted for about 50 to 100 years [2] For this reason, the recovery and recycling of phosphorus become essential to cope with the rapidly increasing demand In rural areas expecially coastal and island areas, crop soil need more nutriens because their geolosical conditions are mainly sand and gravel Wolgast and Jonsson [3, 4] estimated that the average annual per capita urine production was 500 L In additionally, 90% of the tot-N, 60-65% of tot-P and 50-80% of K are partitioned by the human body and excreted in the urine More recently, in a survey of three case study locations across South Thailand, Schouw [5] observed the per capita daily production rates for urine and faeces to be 0.6-1.2 L and 120-400 g, respectively A Vietnamese case study condected by Polprasert et al [6] estimated the production of urine as 0.82-1.2 kg person – d – and faeces as 130-140 g person−1 d−1 ∗ Corresponding author E-mail address: anhdh@nuce.edu.vn (Anh, D H.) 66 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering Antonini et al [7] reported that they used magnesium oxide as the precipitant and dosed it at a molar ratio of 1.5 mol Mg mol P – The mechanism for phosphorus precipitation was shown in the equation below Mg2+ + NH4 + + HPO4 2− + H2 O −−−→ MgNH4 PO4 · H2 O ↓ + H+ The precipitate was later collected in a filter bag attached to the outflow of the reactor The phosphate removal was as high as 98% [7] Abegglen [8] dosed magnesium at a molar ratio of 1.8 mol Mg mol P – and observed phosphate removal efficiencies higher than 95% The reactor type used in the above studies has proven to be very suitable for pilot studies with a reliable power supply, but the investment costs are still rather high In our study, we wanted to build struvite reactors, which conform to the requirements of low-cost sanitation systems in rural areas in Vietnam, i.e where the struvite process uses only locally available inputs, without in-depth technical knowledge, and without continuous electricity supply Besides the results with MgO and MgCl2 as external magnesium sources for struvite precipitation from urine are promising (e.g [9, 10]) Seawater is an infinite alternative source of water and ions [11– 13] The salinity of seawater is usually 35 parts per thousand in most marine areas The interesting thing about this dissolved salt is that it is always made up of the same types of salts and they are always in the same proportion to each other (even if the salinity is different from or higher than the average) According to field survey data collected by Institute of Environmental Science and Engineering (IESE) from 2016 to 2018, in Cat Ba island’s costal area, seawater salinity was low ranging from 20% to 25% It was much lower than previous result [11, 14] Furthermore, seawater can also facilitate phosphorus recovery from urine through chemical precipitation due to the presence of key ions like magnesium and calcium [11–13] Tran Duc Ha [14] reported that, the magnesium content in most marine areas is in concentration of 1.295 ‰ equal to 1295 mg/l approximately, accounting for 3.68% of total salt, Kumashiro [13] also reported that, magnesium in seawater was contained around 1250 mg/l Tran Duc Ha [14] reported that, in coastal areas in Nam Dinh and Hai Phong, ions concentration in seawater were 1080 mg/l and 1160 mg/l of Mg2+ , respectively and 330 mg/l and 334 mg/l of Ca2+ , respectively Tran Duc Ha also reported that, some marine areas in the Central of Vietnam have high salinity of 30 – 35 ‰, for example, Deo Ngang, Da Nang, Sa Huynh, Dzung Quat, Quy Nhon, Nha Trang areas The other areas which have lower salinity, often appear near river estuary with salinity range of 12 and 25 ‰ [15] The study conducted by Liu et al [16] reported that, struvite recovery condition inSUPR (Seawater – caltalysed Urine P Recovery) with completely ureolysed urine plus seawater at the volume ratios of 1:2 and 1:5 Rubio-Rincón et al., 2014 reported that up to 99% phosphorus removal was observed at seawater-to-urine volume ratios below 3.3:1.0 (as the ones reached by water-less and water-saving urinals) Above this ratio the hydrolysis process in non-hydrolyzed urine is inhibited Phosphorus removal occurred through the formation and precipitation of struvite; less struvite crystals were observed at Ca/PO4 -P ratios higher than 0.8 The process was pH dependent and requires a pH of around 8.5 (whereas the initial pH of urine is around 6.0) [9, 17] Thus, it relies on the (partial) hydrolysis of urea which contributed to the increase of the pH and the concentration of ammonium [18] The latter was favoring the precipitation of phosphate crystals [19] However, the high salt content of seawater could hinder the ability of the enzyme urease to attach to the urea, inhibiting the (biological) hydrolysis process [20, 21] Hence, suitable seawater-to urine mixing ratios need to be defined It has already shown to be a promising solution to contribute to alleviate expenses of magnesium chemical for people living in low income areas, especially in the island areas where seawater are 67 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering available sources For the purpose of investigating either the appropriate mixing ratio of magnesium ion to phosphate or impact of present ions in seawater for highly efficient recovery of phosphorus, applying to coastal areas where salinity in seawater vary from 20% - 25% [11], the research team conducted experiments with two types of magnesium sources, MgCl2 solution and synthetic offshore water Therefore, this study aims to assess the feasibility of phosphorus recovery from urine This study is aimed at investigating: 1) the effectiveness of ion Mg2+ from difference sources (artificial water with chemical mixture, synthetic offshore water) as precipitants for phosphate precipitation from urine and its precipitation rate; 2) the optimal conditions for the phosphate precipitation including pH and the offshore water to urine ratio; 3) the quality of the precipitates; and 4) evaluation of nitrogen remaining after reaction, 5) application of phosphorus recovery by seawater from Cat Ba island Material and methods 2.1 Location of pilot testing The military barracks of Cat Ba island was choosen as a location for pilot testing because 02 urine diverting public toilets (UDT) were constructed there, for recovery of excreta and urine as nutrient for garden There is also available seawater sources for seting up experiment on phosphate precipitation from urine by adding Mg2+ ion source from seawater 2.2 Material Urine (UU): Urine was collected from UDT at Catba military barracks The urinal was connected with a urine container and storerage time in one month to produce ureolysed urine (UU) The ureolysed urine applied in entire study was collected from container and transfer to Hanoi within a day and stored at room temperature to achive a stabel ammoina concentration It was ascertained by [17], when seawater was added after 10 hours of hydrolysis, the salt contained in seawater did not represent the main inhibitor of urine hydrolysis Thus, possibly the early additions of seawater and/or rapid release of ammonium in the beginning of hydrolysis process might hinder the hydrolysis of urea, to ensure full P-removal, seawater should be added hydrolysis of urea was achieved [17] The UU had a final concentration of 2060 PO4 – mg L – 1, 4141 TN – mg L – MgCl2 solution: a 20-mM magnesium (Mg2+ ) solution were prepared by using 1litre of deionized water included: 18.8 mg MgCl2 , after mixing the solution had a concentration of 18.8 mg MgCl2 L – was used for experiment Offshore water (OW): The synthetic offshore water use in experiments was preapared base on the composition reported by Anderson, 2008, [11] and produced by adding sea salt collected from coastal salt field to simulate seawater The synthetic offshore water had Mg2+ concentration of 1,385 mg L – 1, Ca2+ concentration of 427 mg L – 1, an electrical conductivity of 68.8 mS/cm, pH of 8.09 Seawater (SW): 40 liters of real seawater was collected from the beach at Cat Ba island and transfer to Hanoi within a day and stored at 4◦ C prior to use Prior to use, seawater was filtered through sive with pore size of 100 µm to remove any debris present The initial pH and electricial conductivity of seawater were 801 and 425 mS/cm, respectively The seawater had concentration of 927 mg Mg L – 1, 272 mg Ca L – It is similar to [14] The Mg2+ and Ca2+ contains in seawater around Cat Ba island were lower than results reported in [13] and [11] It can be due to the fact that the seawater near beach was diluted with rainfall, river water or wastewater 68 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering 2.3 Reasearch approach The experiments were excuted to assess the feasibility to use difference sources of magnesium ion for phosphorus recovery from urine as struvite in rural areas The experiments conducted to compare the urine P recovery efficiency with different precipitant sources, including magnesium solution and offshore water Magnesium solution or offshore water was mixed with UU respectively at difference volumetric mixing ratios so the Mg/P molar ratios were set at 0.08, 0.15, 0.37, 0.75, 1.88, 3.01, 4.14, 5.26 and 100 respectively; ultrapure water (UPW) was used as the control solution The precipitates formed in the last of each ratios of Mg/P with difference magnesium sources were characterized accordingly Some good results of Mg to P molar ratio for highly phosphorus recovery will be test with real seawater from Cat Ba island to verify the findings 2.4 Experimental setup and chemical analyses All experiment were performed in beakers of 600 ml with maximum working volume of 500 ml They were continuously mixed with a magnetic stirrer for hours, covered with tin sheet which only opened after the test completion Experiments were performed at room temperature (at round 33◦ C) Samples were taken at the start of the test, five minutes after magnesium ion source solutions was added and at the end of the test (after hours) Samples were collected by twice For the determination of soluble compound, 0.45 µm pore size filters were used, and total soluble phosphorus (TSP) analysis undertaken All samples were analyzed at laboratory immediately All the precipitates formed at each beaker was filtered out through 0.45 µm syringe filter and dried at 46◦ C for 48 hours – 72 hours to minimize struvite decomposition [22, 23] Then, the weights of syringe filter were carried out before and after filtrations to determine the amount of struvite precipitation Working solutions with adding of magnesium ion sources from MgCl2 solution (Seri A), offshore water (Seri C) and seawater (Seri D) are shown in Tables 1, and 4, respectively Seri B experiment uses mixture solution of ultra pure water and UU for control, is shown in Table Table Parameter applied in P precipitate with MgCl2 solution Seri A A4 A5 A6 A7 A8 A9 A10 A11 A12 VUU , ml VMgCl2 , ml [Mg]:[PO4 ] VMgCl2 : VUU 200 0.08 1:40 200 10 0.15 1:20 200 25 0.37 1:8 200 50 0.75 1:4 200 125 1.88 1:1.6 200 200 3.01 1:1 200 275 4.14 1.375:1 200 350 5.26 1.75:1 500 100 37:1 Table Parameter applied in P precipitate with deionized water as the control solution Seri B Vurine , ml Vultrapure water , ml Vultrapure water : VUU B0 B6 B7 B8 B9 200 0:200 200 25 1:8 200 50 1:4 200 125 1:1.6 200 200 1:1 The analytical determination of ammonia and orthophosphate was performed in accordance to standard methods TSP was measured by reaction of orthophosphate ions with an acid solution containing molybdate and antimony ions to form an antimony phosphomolybdate complex Reduction 69 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering Table Parameter applied in P precipitate with sythentic offshore water Seri C VUU , ml VOW , ml [Mg]:[PO4 ] [Ca]:[PO4 ] VOW : VUU C4 C5 C6 C7 C8 C9 C10 C11 C12 400 26 0.08 0.01 1:16 400 52 0.15 0.03 1:8 300 97.5 0.37 0.07 1:3 200 130 0.75 0.14 1:1.5 100 162.5 1.88 0.35 1.63:1 75 195 3.01 0.56 2.6:1 50 178.8 4.14 0.77 3.6:1 50 227.5 5.26 0.98 5.6:1 259.3 100 18.20 86:1 Table Parameter applied in P precipitate with real seawater Seri D D6 D7 D8 D9 D10 D11 VUU , ml VSW , ml [Mg]:[PO4 ] [Ca]:[PO4 ] VSW : VUU 300 194.2 0.37 0.07 1:1.5 200 258.9 0.75 0.13 1.3:1 100 323.6 1.88 0.33 3.2:1 75 388.3 3.01 0.53 5:1 50 356.0 4.14 0.73 7:1 50 453.1 5.26 0.93 9:1 of the complex with ascorbic acid to form a strongly coloured molybdenum blue complex Measurement of the absorbance of this complex to determine the concentration of orthophosphate present by spectrometer with wavelength of 880 nm (UV-VIS DR/890) NH3 was measured by reaction of ammonia compounds combine with chlorine to form monochloramine Monochloramine reacts with salicylate to form 5-aminosalicylate The aminosalicylate is oxidized in the presence of a sodium nitroprusside catalyst to form a blue colored compound The blue color is masked by the yellow color from the excess reagent present to give a green colored solution The measurement wavelength is 650 nm for spectrophotometers (UV-VIS DR/890) pH and electrical conductivity were measured with a multifunctional portable meter (HQ40D, Hach, USA) 2.5 Calculations TSP was calculated as the difference between the initial and the final ortho-phosphate concentrations from the tests (TSPinitial , TSPfinal , respectively) The initial ortho-phosphate concentration was corrected according to the dilution used in the experiment The maximum P recovery efficiency was determined from Eq (1) TSPfinal ∗ V s %P = − (1) TSPinitial ∗ Vu where % P is the percentage of ortho-phosphate precipitated; TSPinitial and TSPfinal are the initial and final concentrations of soluble ortho-phosphate, respectively; and, Vu and V s are the initial volume of urine and the final volume of the soluble, respectively The concentration of ortho-phosphate precipitated in the experiment (PO4 – -P) was used to estimate the potential formation of struvite assuming that for struvite formation, mol PO4 – -P to mol NH4 -N is needed per mol of struvite formed In order to estimate the concentrations of struvite or magnesium ammonia-phosphate (MAP) precipitated during the execution of the experiments, a similar approach to that applied by Hao et al [24] was applied Then, it was assumed that struvite was the only crystal of ammonia formed Thus, the 45 mg of crystals formed in the experiments were 70 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering redissolved fully by adding volume of ml 2M HCl to lower the pH to around 2.0 The solution was Tạpchí chíKhoa Khoahọc họcCơng Cơngnghệ nghệXây Xâydựng dựngNUCE NUCE2018 2018 Tạp transferred to beaker of 250 ml, added more deionized water for increasing of pH Then, the concen𝑀𝑀𝑁𝐻 [𝑃𝑂 [𝑃𝑂 −𝑃] 𝑃𝑂 trations of ammonia (NH3 -N) and ortho-phosphate (PO 𝑃𝑂 𝑁𝐻 44−𝑃] 44 33 -P) were measured and the molar ratios of = ∗ (2) = ∗ (2) NH3 -N/PO4 -P were calculated from Eq (2) Thereafter, [𝑁𝐻 −𝑁] 𝑁𝐻 [𝑁𝐻 𝑀𝑀𝑃𝑂 𝑁𝐻 𝑃𝑂 33−𝑁] 33 the concentration of struvite or MAP formed 44 was estimated based on the struvite composition (MgNH4 PO4 · H2 O) wherePO PO44and andNH NH33are arethe theortho-phosphate ortho-phosphateand andammonia ammoniaconcentration concentrationofofstruvite struvitererewhere [PO4 − P] PO4 MNH3 = M dissolvingsolution, solution,respectively; respectively;and, and,M MNH3 and MPO4 aremolar molarmass massofofortho-phosphate ortho-phosphate(2) dissolving NH3and PO4∗are [NH3 − N] MPO4 NH3 and andammonia, ammonia,respectively respectively where PO4 and NH3 are the ortho-phosphate and ammonia concentration of struvite re-dissolving and discussion 3.Results Results and discussion solution, respectively; and, MNH3 and MPO4 are molar mass of ortho-phosphate and ammonia, respectively 3.1 3.1.Phosphorus Phosphorusand andammonium ammoniumrecovery recoveryefficiency efficiency Results and discussion Fig 1(a) showns the Fig 1(a) showns the final final pH, pH, the the measured measured the the removed removed percentage percentage ofof TSP TSP after after 2+ 3exprementing time with different molecular exprementing timeand with different molecular ratios ofof Mg Mg2+ toto PO PO4 43-, , and and different different 3.1 Phosphorus ammonium recovery efficiencyratios magnesium sources ItIt also that, pH are stable magnesium ion shows sources also shows that, the theremoved pH inin mixed mixed solutions solutions areexprementing stable inin all all Fig ion 1(a) the final pH,shows the measured the percentage of TSP after 2+ 3– beakers, between 88 and 9,9, ititof was forming ofofmagnesium struvite [26], to PO4 for , and different ion sources also timerange with different molecular Mgsuitable beakers, range between andratios was suitable for forming struviteMAP MAP [26],Itthe thePP showsincreased that, the pH in mixed areto stable in all beakers, range and to 9,toitlower was suitable recovery from less than than 90% The pH values recovery increased from lesssolutions than20% 20% tomore more than 90% Thebetween pHshifted shifted lower values for forming of struvite MAP [25], the P recovery increased from less than 20% to more than 90% 2+ 3-32+ for increase of Mg totoPO ratio from 0.08 toto5.26, the ofofpH depended foran an increase ofthe thelower Mg values PO ratio from 0.08 5.26, thelevel levelfrom pH 44 molar 3– The pH shifted to for anmolar increase of the Mg2+ to PO molar ratio 0.08depended to 5.26, 2+ 32+ 32+ to 3– on PO due struvite precipitation totoKorchef etetal, on the the Mg topH POdepended molaronratio ratio due struvite precipitation andsimilar similar Korchef al, 44 molar theMg level to of the Mg totoPO molar ratio due to and struvite precipitation and similar to Korchef et al., 2011 [26] 2011 2011 [27] [27] pH 1212 pH 100 100 100 100 9090 1010 8080 7070 88 6060 5050 66 4040 44 3030 2020 22 1010 00 00 0.08 0.08 0.15 0.15 0.38 0.38 0.75 0.75 1.88 1.88 3.01 3.01 4.14 4.14 5.26 5.26 100 100[Mg]:[PO4] [Mg]:[PO4] MgCl2 MgCl2 OW OW pH (MgCl2) pH (MgCl2) (a)TSP TSP (a) (a) TSP pH (OW) pH (OW) 8080 TN removal efficiency (%) TN removal efficiency (%) TSP recovery efficiency (%) TSP recovery efficiency (%) 9090 7070 6060 5050 4040 3030 2020 1010 00 0.37 0.37 0.75 0.75 SW SW 1.88 1.88 OW OW 3.01 [Mg]:[PO4] 3.01 [Mg]:[PO4] (b) TN (b) (b)TN TN Figure efficiencies Recovery efficiencies of “MgCl tobe be comparable withwith “OW” Fig of toto “OW” solution” 22solution” Fig.11Recovery Recovery efficiencies of“MgCl “MgCl solution” becomparable comparable with “OW” Fig Fig.1(a) 1(a)also alsoshows showsthat, that,aadecreasing decreasingtrend trendwas wasobserved observedininTSP TSPremoval removalasasMg MgtotoPPmolar molar Fig 1(a) also shows that, a decreasing trend was observed in TSP removal as Mg to P molar ratio increased, although, TSP removal was approximately constant between 0.75 – 5.26 ratio ratio increased, although, TSPremoval removal approximately between – 5.26 increased, although, TSP waswas approximately constantconstant between 0.75 – 5.26.0.75 Mg-to-PO Mg-to-PO ratio of 0.38 and 5.26 to 1.0 removed up to 90% TSP, similar to previous 44 molar Mg-to-PO molar ratio of 0.38 and 5.26 to 1.0 removed up to 90% TSP, similar to previous molar ratio of 0.38 and 5.26 to 1.0 removed up to 90% TSP, similar to previous studies on P recovery studies on by [28], ratios ofof 1.15 and 5.48 4 molar studies on PPbyrecovery recovery reported by ratios [28], at Mg Mg to PO PO molarremoval ratios increased 1.15from and70% 5.48 reported [27], at Mgreported to PO4 molar of at 1.15 and to 5.48 phosphorus phosphorus removal increased from 70% to more than 95%, and P removal did not increase phosphorus removal increased from 70% to more than 95%, and PMg-to-PO removal4 did increase to more than 95%, and P removal did not increase significantly at higher I wasnot consistent significantly atat higher Mg-to-PO 4.IIwas consistent with the [28] the significantly higher Mg-to-PO consistent witheven theresult resultby byimpressly [28]ininatwhich which the4PP with the result by [27] in which4the Pwas removal efficiencies decrease Mg-to-PO removal efficiencies even decrease impressly at Mg-to-PO molar ratio of 100 With 4 removal molarefficiencies ratio of 100 With same molar ratios of at Mg-to-PO efficiency in experiment removal eventhe decrease impressly Mg-to-PO molar ratio of 100 Withthe the , the same molar ratios of Mg-to-PO , the removal efficiency in experiment which added MgCl which added MgCl solution is litle higher than experiment with OW, it can be impacted by present same molar ratios of 2Mg-to-PO4, the removal efficiency in experiment which added MgCl2 of calcium to form of experiment precipitation previous study reported by Haoof et al [24] solution isis litle higher than with OW, be by solution litleion higher than experimentMAP, withsimilar OW,itittocan can beimpacted impacted bypresent present ofcalcium calcium ion to form of precipitation MAP, similar to previous study reported by Hao et al, ion to form of precipitation MAP, similar to71previous study reported by Hao et al,2008 2008 [25] At Mg-to-PO molar ratio of 100, P removal efficiencies in series A, C achieved [25] At Mg-to-PO4 molar ratio of 100, P removal efficiencies in series A, C achievedthe the same same results results of of 60,6% 60,6% and and 60%, 60%, respectively respectively.At AtMg-to-PO Mg-to-PO44molar molarratio ratioofof0.38 0.38and and3.01 3.01 TN TN removal removalefficiencies efficienciesare aremuch muchlower lowerthan thanTSP TSPone, one,for forthe theexperiment experimentseri seriD, D,Fig Fig.1(b) 1(b) Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering At Mg-to-PO4 molar ratio of 100, P removal efficiencies in series A, C achieved the same results of 60.6% and 60%, respectively At Mg-to-PO4 molar ratio of 0.38 and 3.01 TN removal efficiencies are much lower than TSP one, for the experiment seri D, Fig 1(b) showed only slight ammonium removals of 10.1%, 8.6%, 15.4% and 27.5%, respectively It can be caused by Mg2+ that could favor Tạp chí(HAPKhoa học Cơng4nghệ Xây dựngK-struvite NUCE 2018 the formation of hydroxyapatite CaCông )6 (OH) (MgKPO4 · H2 O) 10 (PO ) and NUCE Tạp chíchí Khoa học Tạp Khoa học Cơngnghệ nghệXây Xâydựng dựng NUCE2018 2018 100 100 -20 -20 TSP recovery efficiency (%) 80 70 60 50 40 30 20 10 TSP recovery efficiency TSP recovery efficiency (%) (%) 90 1:8 1:8 1:4 1:4 1:4 MgCl2 UPW MgCl2 MgCl2 UPWUPW 1:1.6 1.4:1 1:1.6 1:1.6 1.4:11.4:1 V MgCl2/upw: Vuu (a) 1.75:1 1.75:1 1.75:1 37:1 37:137:1 100 90 100 90 80 90 80 70 80 70 60 70 50 60 60 40 50 50 30 40 40 20 30 30 10 20 20 10 10 -10 0 -20 -10-10 TSP recovery efficiency (%) TSP recovery efficiency (%) (%) TSP recovery efficiency -10 90 100 80 90 70 80 60 70 50 60 40 50 30 40 20 30 10 20 10 -10 -20 1:8 -10 100 OW OW OW 1:8 1:81:8 1:3 1:1.5 1:3 1:3 UPW UPW UPW 1.63:1 1:1.5 1.63:1 1:1.5 1.63:1 V ow/upw:Vuu (b) 2.6:1 2.6:1 86:1 86:1 86:1 -20-20 V MgCl2/upw: Vuu (a) V MgCl2/upw: Vuu (a) ow/upw:Vuu(b) (b) VVow/upw:Vuu (a) MgCl (a)with With MgCl solution solution With MgCl solution (a)(a) With MgCl solution 100 TSP recovery efficiency (%) (%) TSP recovery efficiency TSP recovery efficiency (%) 90 100 100 80 90 90 70 80 80 60 70 70 50 60 60 40 50 50 30 40 40 20 30 30 10 20 20 100 10 0 (b)(b) withwith offshore water offshore water (b)with with offshore offshore water (b) MgCl2 0.89 0.89 0.89 OW MgCl2 OW MgCl2 OW 0.79 0.61 0.44 0.24 Vuu:Vmixture (c) 0.79 0.61 0.44 0.24 0.79 0.61 0.44(c) 0.24 Vuu:Vmixture Vuu:Vmixture (c) (c) mixture (c)in in mixture 0.01 0.01 0.01 (c) in mixture (c) in mixture Figure Relationship between TSP recovery efficiencies and volume ratios of UU and Figure Relationship between TSP recovery efficiencies Figure Relationship between TSP recovery efficiencies and volume ratios of UU and and between volumediference ratios of UU and diference magnesium ionvolume sources ratios magnesium ion sources Figure Relationship TSP recovery efficiencies and of UU and diference magnesium ion sources diferencedid magnesium ion sources Figure that,the theprecipitation precipitation didhappen not happened when addedwater ultrapure water Fig.22 shows shows that, not when added ultrapure into UU, even into it Figure shows that, the precipitation did not happened when added ultrapure water into makes present solid inpresent UU to dissolve intoUU solution In experiment B, TSP concentration in theB,final UU, it makes solid in to dissolve intowhen solution experiment TSP Figure 2even shows that, the precipitation did not happened addedInultrapure water into UU, evenwas it higher makesthan present in almost UU toTSP dissolve solution.of In B, was TSP solution initialsolid one so removalinto efficiencies Seriexperiment B below zero, in the finalsolid solution wastohigher thaninto initial one so almost TSP B, removal UU,concentration even it indicating makes present in UU dissolve solution Inalmost experiment TSP observed thatfinal no Psolution precipitates formthan in the absence Mg or Ca (Table 2) The concentration in the waswould higher initial oneof so TSP removal efficiencies of Seri B below was indicating no P precipitates would results in (c)in mixture Fig.solution zero, confirm thatobserved offshore water can bethat anone effective precipitant for urineform P concentration the final was higher indicating than initial almost TSP removal efficiencies ofinSeri B below zero, was observed that no Psoprecipitates would form in the absence of Mg or Ca (Table 2a, b) The results in (c) in mixture Figure confirm that precipitation As long as volume ratio UU fraction is between 24% and 61% However, at 99% UU efficiencies of Seri below was indicating no P precipitates would form infraction, the absence of B Mg ordropped Cazero, (Table 2a,observed b) The in (c)that inMg mixture Figure confirm that 2+ 2+ the efficiency to only 60%, dueresults to insufficient and Ca According to the offshore water can be an effective precipitant for urine P precipitation As long as volume in the absence of ratio Mg or 2a,precipitant b) results in of (c)PUU in mixture Figure for confirm that offshore water can of bePCa an effective forratio urine precipitation As long ascomplete volume stoichiometric to (Table Mg in MAP, the The maximum to OW should be 4.7 ratio UU fraction is between 24% and 61% However, at 99% UU fraction, the efficiency offshore water can be effective precipitant Patprecipitation Asdilution long volume P recovery, corresponding to an24% 83% UU fraction Onurine the other hand,UU excessive of UU by ratio UU fraction is an between and 61% for However, 99% fraction, the as efficiency 2+ 2+ dropped to only 60%, due to insufficient Mg and Ca According to the stoichiometric OW leads toisreduction of to the P recovery, inMg mixture of UU MgCl OW, UUefficiency fraction 2+ solution, ratio UUalso fraction between 24% and 61% However, UU fraction, the dropped to only 60%, due insufficient and Caat2+and 99% According to the stoichiometric to 1% theinP MAP, recovery 60% and 70%, respectively Moreover, when the P concentration ratio of reduced P to Mg theto maximum ratio of UU to OW should be 4.7 for complete P 2+ dropped toPonly 60%, due tothe insufficient Mg and Cato2+.OW According to 4.7 the for stoichiometric ratio of to Mg in MAP, maximum ratio of UU should be complete P is relatively low, calcium and may fraction complete against andexcessive phosphate for site in of recovery, corresponding to carbonate an 83% UU On themagnesium other hand, dilution ratio of Pcrystal to corresponding Mgstructures, in MAP, the maximum ratio of UU totheOW should beexcessive 4.7with for Vietnamese complete recovery, tohindering an 83%the UU fraction Ongrowth other hand, dilution ofP MAP thus effective crystal [28] In summary, UU by OW also leads to reduction of characteristic, the P recovery, in mixture of UU and MgCl2 solution, specific condition of nutrition and OW high urine hand, Pofrecovery can beof recovery, corresponding to reduction an 83% UU fraction Onin the other UU by OW also leads to of the P recovery, in mixture UUexcessive andefficiency MgCldilution solution, OW, UU fraction to 1% reduced the P recovery to 60% and 70%, respectively Moreover, UU also fraction reduced of thethe P recovery to 60% and 70%, respectively UUOW, by OW leadstoto1% reduction P recovery, in mixture of UU and MgClMoreover, solution, when the P concentration is relatively low,72calcium and carbonate may complete against when P concentration is relatively low, calcium andand carbonate may complete against OW, UUthe fraction to 1% reduced the P recovery to 60% 70%, respectively Moreover, magnesium and phosphate for site in MAP crystal structures, thus hindering the effective magnesium and phosphate site in low, MAPcalcium crystal structures, thus hindering the effective when the P concentration is for relatively and carbonate may complete against crystal growth [29] In summary, with Vietnamese specific condition of nutrition and OW crystal growth [29] In summary, Vietnamese specific condition of nutrition and OW magnesium and phosphate for site inwith MAP crystal structures, thus hindering the effective characteristic, in high urine P recovery efficiency can be achieved when 24 – 79% UU ity which populate in most areas Vietnamese island, the experiment was carried g urine and real seawater taken from the beach of Cat Ba island (Seri D) Thus, the molar ratios result for highly phosphorus recover of 0.38, 0.75; 1.88; 3.01; 4.14; Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering e selected (Table 4) Figure shows the same result with previous experiment achieved when 24 – 79% UU fraction is applied in mixture of UU and OW hetic subsance, recovery efficiencies were high, ranging between All the phosphorus previous experiment were performed with magnesium ionstill sources taken from synthetic substance To validate the obtained results with urine and seawater with lower salinity which populate 100% The final concentrations of soluble phosphate were below 100 mg/l (Tabl in most areas Vietnamese island, the experiment was carried out using urine and real seawater taken the beach of Catthan Ba island (Seri D) Thus,standard the Mg to P molar for highly phosphorus wever, it from is still higher Vietnamese levelratios of result QCVN 14/2008 on wastew recover of 0.38, 0.75; 1.88; 3.01; 4.14; 5.26 were selected (Table 4) Fig shows the same result ity, accepting Mg experiment to P molar ratio ofsubsance, 5.26 phosphorus This result wasefficiencies much lower with previous with synthetic recovery were stillthan high, experim ranging between 90% and 100% The final concentrations of soluble phosphate were below 100 mg/l lts with chlorine magnesium solution and synthetic offshore water It certified that a (Table 5) However, it is still higher than Vietnamese standard level of QCVN 14/2008 on wastewater quality, acceptingion Mg to P molar ratio of 5.26 This result was muchcalcium lower than experiment results unt of phosphorus was precipitated with present ion in seawater, sim with chlorine magnesium solution and synthetic offshore water It certified that a big amount of rman study, 2009 [30] phosphorus ion was precipitated with present calcium ion in seawater, similar to the study [29] 12 pH 100 TSP recovery efficiency (%) 90 10 80 70 60 50 40 30 20 10 0.38 0.75 1.88 TSP 3.01 4.14 pH 5.26[Mg]:[PO4] Figure TSP recovery efficiencies in the mixture of urine and real seawater Figure TSP recovery efficiencies in the mixture of urine and real seawater After experimenting time, the final solution contains high concentration of total nitrogen (Ta- r experimenting time, the final concentration total nitro ble 5), it shown that, struvite formingsolution process gavecontains low nitrogenhigh recovery, similar results withof previous study [30] and [31] Moreever, Maurer et al [32] investigated composititon of urine in difference le 5), it urine shown that, struvite forming process gave low nitrogen recovery, similar re collection systems, there is much more ammonium than phosphate present in urine on a molar basis As a Ganrot consequence, 3% of the nitrogen be eliminated magnesium addition onlyMaurer e previous study et about al, 2007, Lind et can al 2000 [31],by [32] More ever, so that the effect on the pH value is small [32] Etter et al [12] had shown the similar results, the investigated urine in difference urine collection systems, ther recovery ofcomposititon ammonium throughof struvite precipitation may be only 5% and other macronutrients may not be recovered; the authors, using the case of study of Nepal also emphasized that the struvite allows h more ammonium than phosphate present in urine on a molar basis As a conseque harnessing only 13% monetary value of urine as a fertilizer ut 3% of the nitrogen can be eliminated by magnesium addition only so that the e 3.2 Struvite Precipitation characteristic he pH valueTheisresult small [33] Etter et al, [12] had shown the similar result, the recover has been shown in Fig an observation, comparatively, the recover efficiency of precipitant achieved theprecipitation highest result withmay precipitation of mixture of UUother and SW, it happened in monium through struvite be only 5% and macronutrients may almost range of Mg to P molar ratios Maximum amount of precipitant was observed with the mixture ecovered;solution the authors, using of study of mg/ml NepalUU), also emphasized of UU and SW at Mgthe to P case molar ratio of 5.26 (40 while UU-Mg solutionthat and the stru UU-OW achieved maximum precipitate recoveries of and 26 mg/ml UU at Mg-P molar ratios of ws harnessing only 13% monetary value of urine as a fertilizer 3.01 and 100, respectively ]:[PO4] iA Table Nutrien concentration in final solution 0.08 A4 0.15 A5 0.37 A6 73 0.75 A7 1.88 A8 3.01 A9 4.14 A10 5.26 A11 l (mg/l) l (mg/l) 3,216 72 2,350 17 1,183 11 692 12 Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering ite Precipitation characteristic Table Nutrien concentration in final solution 0.08 0.15 0.75 1.88comparatively, 3.01 4.14 5.26the 100 t has been[Mg]:[PO shown an 0.37 observation, recover eff ] in Figure Seri A A4 A5 A6 A7 A8 A9 A10 A11 A12 itant achieved the highest result with precipitation of mixture of UU and TSP final (mg/l) 1939 1364 493 88 84 80 59 18 T-N final (mg/l)of Mg to P molar 6250 5300 in almost range ratios.4000 Maximum amount of precipit Seri C C4 C5 C6 C7 C8 C9 C10 C11 C12 final (mg/l) 1181 194UU129 55 25 P molar 16 13 with the TSP mixture solution of and SW at24Mg to ratio 7of 5.26 (4 T-N final (mg/l) 3000 5000 3867 2700 2067 le UU-Mg Seri solution and UU-OW recoveri D D6 achieved D7 D8maximum D9 D10precipitate D11 TSP final (mg/l) 72 17 11 12 g/ml UUT-N at final Mg-P 3.012350 and 100, (mg/l)molar ratios of 3216 1183 respectively 692 50 45 mg Precipitant /ml UU 40 35 30 25 20 15 10 0.08 0.15 0.38 0.75 MgCl2 1.88 3.01 SW OW 4.14 5.26 100 [Mg]:[PO4] Figure Struvite recovery efficiencies Figure Struvite recovery efficiencies + Urine and seawater mixtures contain various ions such as Mg2+ , Ca2+ , NH2+ (Na+ ), potas4 , sodium 2+ + in sium (K+ ), phosphate (PO4 – ) sulphate) (SO4 – ) and bicarbonate (HCO3 – ) potentially resulting the formation of diverse precipitates and possible impurities 32- Characterization of these precipitates is 4 thus deemed necessary in order to confirm the potential use of MAP products produced from a sys- tem as a P fertilizer Hence, the precipitates from UU and OW/SM mixtures with different volumetric ratios were characterized Comparatively, the composition of the precipitates formed in the mixtures of OW and SW with difference urine fraction (Seri A, Seri C, Seri D) at Mg to P molar ratios of 0.38, 0.75, 1.88 and 5.26 are shown in Table The precipitate forming in mixture of UU and 20 mM magnesium solution (A7, A8) has PO4 to NH3 molar ratios were 1:1 approximately, similar to the stoichiometric While, the amount of PO4 content of precipitant was higher than NH3 content, indicating some of P in the mixture of OW and SW precipitated out as calcium and magnesium ion to form MKP (magnesium kali phosphate) and HAP (hydroxyapatite – Ca10 (PO4 )6 (OH)2 )) [18, 33] With the same of Mg to PO4 molar ratio of 1.88 in mixtures of A8, C8, D8 beakers, mixture in A8 had N content higher than C8 and D8 respectively, indicating that, the present of other ion in d seawater mixtures contain various ions such as Mg , Ca , NH , sodium m (K+), phosphate (PO ) sulphate) (SO ) and bicarbonate (HCO ) pot in the formation of diverse precipitates and possible impurities Characteriz cipitates is thus deemed necessary in order to confirm the potential use o produced from a system as a P fertilizer Hence, the precipitates from U mixtures with different volumetric ratios were characterized ively, the composition of the precipitates formed in the mixtures of OW a rence urine fraction (Seri A, Seri C, Seri D) at Mg to P molar ratios of 0.3 74 5.26 are show in Table The precipitate forming in mixture of UU and m solution (A7, A8) has PO4 to NH3 molar ratios were 1:1 approximately, iometric While, the amount of PO4 content of precipitant were higher th Anh, D H., Anh, N V / Journal of Science and Technology in Civil Engineering Table Struvite precipitate characteristic C6 D6 A7 C7 D7 A8 C8 D8 C11 D11 [Mg]:[P] [PO4 ] [NH3 ] Molar ratio in precipitate 0.38 0.38 0.75 0.75 0.75 1.88 1.88 1.88 5.26 5.26 0.00014 0.00022 0.00027 0.00010 0.00011 0.00024 0.00013 0.00017 0.00099 0.00009 0.00011 0.00021 0.00025 7.353E-05 0.00009 0.00021 8.82353E-05 0.00011 0 1.24 1.05 1.07 1.46 1.26 1.10 1.50 1.58 OW/SW impacted to form struvite A lower UU fraction reduce contents in the struvite in the urine and OW/SW mixtures (Table 6), at Mg to P ratio of 5.26 there is not any N contents in the precipitate, indicating of the precipitate exsits forming of calcium or/and magnesium compound Conclusions and recomendations Urine from eco-san toilet which is the urine diverting dry toilet can be used for recover nutrien as high nutrien content of slow release fertilizer under crystal forming (MAP, MKP, HAP ) By this way, it can help for easier storage and transportation Ureolysed urine with high pH (8-9) creates optimal conditon in mixture of urine and seawater for the phosphorus precipitation Adding of magnesium ion into ureolysed urine to achieve Mg to PO4 – molar ratio between 0.75 and 5.26 can recover more than 90% of phosphorus The ion source from offshore water can give phosphate recover efficiencies of 89.04; 94.1; 95.86; 94.06; 95.25; 95.31% at offshore water to ureolysis urine 0.33; 0.65; 1.63; 2.6; 3.58; 5.56 :1, respectively According to above result, the phosphorus recover rate was hightest result when volumetric ratios of offshore water to UU were 0.65: or 5.56:1 The increasing of Mg to P molar ratio decreases MAP content in precipitate Mg to P molar ratios of 0.38, 0.75, 1.88 will pricipitate struvite with high MAP content, while there is not any MAP content in precipitate when this ratio is 5.26 The crystalizied precipitate should be filtered then dired in atmosphere condition before storage and enduse Seawater also can be used as a source of ions (magnesium and calcium) for struvite precipitation for recover phosphorus from urine which collected from dry eco-san toilet Phosphate removal efficiencies of 99.31; 92.01; 96.49; 96.5; 95.25; 99.26%, achieved at seawater to ureolysis urine volumetric ratios of 0.67; 1.3; 3.2; 5; 7; 9:1, respectively The highest recover efficiency of phosphorus had been achieved when volume ratios of seawater to UU were 0.67:1 or 9:1 Resulting that, the coastal areas can use seawater to add to urine tank with volumetric ratio above to recover/precipitation of phosphorus for reuse as fertilizer Nitrogen recover efficiency stoped at low level The highest remove rate of nitrogen was 30% and 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