Solubility products of magnesium ammonium and magnesium potassium phosphates

Taylor, A. W.; Frazier, A. W.; Gurney, E. L.

doi:10.1039/tf9635901580

Cited by 167 publications

(84 citation statements)

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“…The inorganic complex P concentration was almost half of the total P concentration in the sludge at control conditions (250 mg L -1 ). A larger portion of the inorganic complex P was solubilized at acidic pH conditions, which was in accordance to the previous finding of (Taylor, Frazier et al 1963). The low pH conditions triggered release of Ca and Mg from the inorganic complexes in the digestate as shown in Fig.…”

Section: Nutrient Forms and Concentrationssupporting

confidence: 80%

Enhanced phosphorus solubility during anaerobic digestion

Latif¹

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Worldwide phosphorus (P) consumption has increased massively over the last century, to overcome soil nutrient constraints, and to feed an increasing population with an increasing level of urbanization.However, current P reserves are limited and are expected to deplete in 50-120 years. Hence, new techniques to source P from alternative resources are essential. Waste streams are the largest alternative resource of P, with much of the organic wastes containing P treated by anaerobic digestion (AD). However, P recovery from the digested waste streams is limited by in-reactor P precipitation, and inaccessibility of soil available P in sludge biosolids. In-reactor P precipitation increases the operational costs of a treatment facility due to scaling and precipitation, there are strong advantages in being able to recover P as a purified mineral product. In such circumstances, keeping high PO4 concentration during AD is vital to enhance its recovery post AD.This thesis aims to assess two different techniques to enhance PO4 concentration during AD from waste activated sludge (WAS): low pH and high pressure (enabling low pH). Low pH single stage AD was tested in both batch and continuous mode. In the batch study, biochemical methane potential tests were conducted for 51 days at a pH range of 5.0 to 7.2 in two separate sets (two different WAS samples collected from municipal WWTP). Low pH (< 5.7) caused a significant loss in the methane potential (B0) of up to 33%, with 3.6 times increase in PO4 concentration compared to the neutral pH (7 -7.7), but with no major change in methane production rate coefficient (khyd). The loss in methane yield was mainly due to decrease in hydrolytic capability rather than inhibition of methanogenesis with volatile fatty acids (VFAs) being < 300 mgCOD L -1 and soluble COD < 1300 mgCOD L -1 even at low pH. While pH did not influence the acetoclastic community (Methanosaeta dominated), it was the primary driver for the remaining community, and caused a loss of diversity and shift to Clostridia.To validate the results from batch conditions, continuous low pH AD was performed using similar substrate and pH conditions. The influence of the pH on PO4 concentration was similar in continuous and batch. It was found that the low pH (5.5) caused a significant increase in PO4 concentration up to 79% of the total P, while methane yield was reduced by 50%. VFAs and SCOD concentrations increased from 40 to 504 mg L -1 and 600 to 2017 mg L -1 respectively, as the pH was reduced from 7.0 to 5.5. Higher concentration of propionic acid (370 -430 mg L -1 ) was recorded at low pH (< 5.5).The reduction in methane yield was associated with a shift in microbial community and decreased destruction of particulate organics. Acidogens dominated at low pH (< 6.0), while methanogens decreased by 88% at pH 5.5 compared to neutral pH. Apart from the loss in methanogenic and hydrolytic capacity, continuous acid dosing to maintain low pH condition was identified as a key limitation with this technology. To assess an...

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Section: Nutrient Forms and Concentrationssupporting

confidence: 80%

Enhanced phosphorus solubility during anaerobic digestion

Latif¹

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“…3b, both remain well above the pK sp of 10.62, showing no precipitation of potassium with orthophosphate. This is likely to be the case, as KMP precipitates at high pHs (about 10, Wilsenach et al,2007;Taylor et al, 1963).…”

Section: High-tss Digestermentioning

confidence: 99%

“…Newberyite (MgHPO 4 ) and bobierite (Mg 3 (PO 4 ) 2 ·8H 2 O) are indicated to precipitate from around Day 8 based on measured concentrations and pH. Other points of interest are (i) struvite (MgNH 4 PO 4 ) did not appear to precipitate, because in aerobic digestion the ammonia released is nitrified leaving little residual ammonia available to precipitate, (ii) potassium magnesium phosphate (KMP, MgKPO 4 ) also did not appear to precipitate -it generally precipitates at higher pHs (Taylor et al, 1963, Wilsenach et al, 2007, and (iii) calcium phosphate (Ca 3 (PO 4 ) 2 ) did not appear to precipitate due to the low calcium content of the polyP.…”

Section: Batch Test 2 (Bt2)mentioning

confidence: 99%

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

M¹,

Ikumi²,

Ekama³

2016

WSA

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Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3-6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/ℓ (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/ℓ ) and the other fed diluted WAS (3 g TSS/ℓ). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (b GP ) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (b G ) of phosphorus accumulating organics (PAO), i.e. b GP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO 4 ·3H 2 O) and amorphous tricalcium phosphate (ACP or TCP, Ca 3 (PO 4 ) 2 ·xH 2 O) are found to be the most common phosphate precipitates.

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“…If desorption of P was conducted using a high concentration NaOH solution, evaporation of the solvent would be required to solidify tri-sodium phosphate. Moreover, using a relatively low concentration of NaOH solution, KMP precipitate can be easily obtained because of its low solubility product (Taylor et al 1963). In this study, 0.05-0.1 M NaOH solutions were used to avoid the effect of sodium in the formation of the KMP precipitate/crystal.…”

Section: Desorption Of P With Naohmentioning

confidence: 99%

Simultaneous solidification of potassium and phosphorus using rice straw charcoal and saturated phosphorus adsorbent

Koutarou

Seigo

Harada

et al. 2015

Int J Recycl Org Waste Agricult

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Phosphorus (P) ore is an expensive and limited resource that will be depleted in a few decades if the current global consumption rate continues. Japan, one of the most developed countries in the world, relies completely on imported phosphate rock for P. Potassium (K) ore, which is equally important for continuous development, is also becoming increasingly expensive. The recovery of P and K is therefore important for continuous and sustainable development. In this study, concentrated P (obtained from eluent) and K (obtained through alkali leaching of rice straw charcoal) were recovered as potassium magnesium phosphate (PMP) through the controlled addition of magnesium (Mg). A PMP crystal was produced when an equimolar (with respect to P) Mg solution was added to the leaching solution (rich in P and K) at a pH range of 11-12. Thus, the production of PMP in a crystalline form demonstrates the huge scope for the recycling of limited resources.

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Solubility products of magnesium ammonium and magnesium potassium phosphates

Cited by 167 publications

References 0 publications

Enhanced phosphorus solubility during anaerobic digestion

Enhanced phosphorus solubility during anaerobic digestion

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Simultaneous solidification of potassium and phosphorus using rice straw charcoal and saturated phosphorus adsorbent

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