154
M. Darwish et al.
ores that are estimated to last about 50–100 years (Driver et al. (1999). However,
despite the scarcity and the high cost of P sources, only a few studies have been
conducted to find alternative sources of P to date. Bone-meal waste (a by-product of
meat-waste thermal treatment, 61.6% PO 4
3− ) was utilized as a low-cost source of
P by Siciliano et al. (2013) and Siciliano and De Rosa (2014) for NH 4 −N recovery
in LL and calf manure digestates, respectively. Additionally, Huang et al. (2014)
applied wasted H 3 PO 4 to treat NH 4 −N in LL. In these studies, high efficiencies
of NH 4 −N recovery were achieved, relatively similar to those achieved when pure
chemicals were used. Recently, using fish waste bone ash as an alternative source of
P has demonstrated considerable recovery of NH 4 −N (≈90%) in synthetic solution
(Darwish et al. (2017). Practically, P can be found in many kinds of waste materials
such as food waste and animals waste bones. In addition to the economic benefit
that could be derived from struvite recovery, using alternative Mg and P sources
contributes to waste minimization and utilization simultaneously, hence enhances
the sustainability of struvite recovery process.
9.4.3.5 Effect of Foreign Ions
The process of NH 4 −N recovery via MAP precipitation is highly competed due
to the presence of different sorts of foreign ions. Previous literatures showed that
calcium (Ca
2+ ) is one of the main elements that hinders MAP formation, because Ca
2+
has high potential to compete with Mg
2+ , forming amorphous calcium phosphates
(Ca 3 (PO 4 ) 2 ). This process is controlled by pH and initial concentrations of P, N
and Mg (Ca/Mg ratio) in wastewater. In general, molar ratios of Ca:Mg higher than
0.5 were noticed to enhance the reaction between Ca and PO 4 ions, hence lowering
the efficiency of NH 4 −N recovery (Lee et al. 2013; Song et al. 2011). Huang et al.
(2011a, b) depicted that when the molar ratio of Ca:Mg was raised from 0 to 0.75 (Mg
= 985 mg/L), NH 4 −N recovery was drastically decreased from 88 to 58% (initial
NH 4 = 985 mg/L).
Based on the reported characteristics of LL in literature, it was found that LL
usually contains low amounts of Ca such that when struvite precipitation is applied,
the molar ratio of Ca:Mg becomes less than 0.1 (Huang et al. 2014; Siciliano et al.
2013). Therefore, Ca is not considered as a major problem when recovering NH 4 −N
from LL by struvite precipitation.
High concentrations of K can be found in different types of wastewater such as
human urine (Liu et al. 2008). In previous work, K was shown to co-precipitate
in parallel with struvite crystals, especially at low NH 4 −N concentrations, forming
MgKPO 4 .6H 2 O (MPP), which is called “Struvite-K” or “Potassium-struvite” (Di
Iaconi et al. 2010; Wilsenach et al. 2007). Struvite-K is one of the struvite analogues
and the behaviour of the formation could be explained by Eq. (9.4) (Wilsenach et al.
2007).
(9.4)
M. Darwish et al.
ores that are estimated to last about 50–100 years (Driver et al. (1999). However,
despite the scarcity and the high cost of P sources, only a few studies have been
conducted to find alternative sources of P to date. Bone-meal waste (a by-product of
meat-waste thermal treatment, 61.6% PO 4
3− ) was utilized as a low-cost source of
P by Siciliano et al. (2013) and Siciliano and De Rosa (2014) for NH 4 −N recovery
in LL and calf manure digestates, respectively. Additionally, Huang et al. (2014)
applied wasted H 3 PO 4 to treat NH 4 −N in LL. In these studies, high efficiencies
of NH 4 −N recovery were achieved, relatively similar to those achieved when pure
chemicals were used. Recently, using fish waste bone ash as an alternative source of
P has demonstrated considerable recovery of NH 4 −N (≈90%) in synthetic solution
(Darwish et al. (2017). Practically, P can be found in many kinds of waste materials
such as food waste and animals waste bones. In addition to the economic benefit
that could be derived from struvite recovery, using alternative Mg and P sources
contributes to waste minimization and utilization simultaneously, hence enhances
the sustainability of struvite recovery process.
9.4.3.5 Effect of Foreign Ions
The process of NH 4 −N recovery via MAP precipitation is highly competed due
to the presence of different sorts of foreign ions. Previous literatures showed that
calcium (Ca
2+ ) is one of the main elements that hinders MAP formation, because Ca
2+
has high potential to compete with Mg
2+ , forming amorphous calcium phosphates
(Ca 3 (PO 4 ) 2 ). This process is controlled by pH and initial concentrations of P, N
and Mg (Ca/Mg ratio) in wastewater. In general, molar ratios of Ca:Mg higher than
0.5 were noticed to enhance the reaction between Ca and PO 4 ions, hence lowering
the efficiency of NH 4 −N recovery (Lee et al. 2013; Song et al. 2011). Huang et al.
(2011a, b) depicted that when the molar ratio of Ca:Mg was raised from 0 to 0.75 (Mg
= 985 mg/L), NH 4 −N recovery was drastically decreased from 88 to 58% (initial
NH 4 = 985 mg/L).
Based on the reported characteristics of LL in literature, it was found that LL
usually contains low amounts of Ca such that when struvite precipitation is applied,
the molar ratio of Ca:Mg becomes less than 0.1 (Huang et al. 2014; Siciliano et al.
2013). Therefore, Ca is not considered as a major problem when recovering NH 4 −N
from LL by struvite precipitation.
High concentrations of K can be found in different types of wastewater such as
human urine (Liu et al. 2008). In previous work, K was shown to co-precipitate
in parallel with struvite crystals, especially at low NH 4 −N concentrations, forming
MgKPO 4 .6H 2 O (MPP), which is called “Struvite-K” or “Potassium-struvite” (Di
Iaconi et al. 2010; Wilsenach et al. 2007). Struvite-K is one of the struvite analogues
and the behaviour of the formation could be explained by Eq. (9.4) (Wilsenach et al.
2007).
(9.4)