9 Struvite Crystallization: An Effective Technology …
155
However, the presence of K causes less interference with NH 4 −N recovery than
that of Ca. According to Huang et al. (2011a, b), a slight drop in NH 4 −N removal from
synthetic piggery wastewater was observed when K:Mg molar ratio was increased
from 0 to 0.75. Besides, the effect of K was illustrated in previous researches, which
targeted the recovery of K from source-separated urine in the form of MPP (Kstruvite). Wilsenach et al. (2007) reported that MAP has more tendency to be formed
than MPP. In the same context, for P and K recovery from synthetic urine, it was
demonstrated that, when NH 4 −N concentration was increased from 0 to 500 mg/L,
the efficiency of MPP precipitation, as well as NH 4 −N removal, was decreased
from 77% to 65% and from 97% to 77%, respectively, (K 0 = 52.4 mM/L, pH 10,
Mg:K:P = 2:1:2) (Xu et al. 2011). These studies indicated that the effect of K is
less significant than Ca; however, it should be taken into consideration in the cases
of high concentrations of K, such as those reported for LL (Di Iaconi et al. 2010;
Huang et al. 2014 and Kochany and Lipczynska-Kochany 2009).
Wastewater may contain high concentrations of heavy metals that could affect
the purity of struvite. For agronomic field applications, the incorporation of heavy
metals, such as chromium (Cr), is a vital issue if struvite is to be used as a fertilizer
(Rouff 2012a, b). Minute levels of some heavy metals, such as arsenic (As) in urine
(Ronteltap et al. 2007) and sewage sludge effluent (Uysal et al. 2010), were found
co-precipitated with struvite. Liu et al. (2013a, b) found a lower limit of heavy metals
in struvite obtained from swine wastewater. The authors reported that this struvite is
safer compared to struvite recovered from LL or some other industrial wastewaters.
However, for sustainable agriculture, the potential accumulation of heavy metals in
soil and plants is undesirable as heavy metals may consequently cause hazardous
effects for humans and animals. Table 9.5 shows the effect of some heavy metals
on MAP recovery. Heavy metals have shown two sorption mechanisms during MAP
crystallization, i.e. co-precipitation and adsorption. Co-precipitation was found to be
the sorption mechanism of As(V) (Ma and Rouff 2012) and Al
3+ (Acelas et al. 2015),
while other metals like Cu
2+ and Zn
2+ (Muryanto and Bayuseno 2014), and As(III)
(Ma and Rouff 2012) were found to be adsorbed on struvite surface. Table 9.5 shows
that some heavy metals such as aluminium (Al
3+ ), copper (Cu
2+ ) and zinc (Zn
2+ ),
which are highly concentrated in swine wastewater and sludge digestion liquors,
have the ability to cause inhibition on struvite formation (Acelas et al. 2015; Liu
et al. 2011a, b), while the sorption of either Cr(III) or Cr(VI) on struvite has several
environmental implications related to agriculture sustainability and human health.
The effects of many other heavy metals (e.g. Ni and Cd) were not investigated in
literature, although high concentrations are commonly found in different types of
wastewater such as LL.
9.4.3.6 Mixing Conditions
Struvite crystallization (nuclei generation and growth) is significantly influenced by
mixing intensity value (G value) and mixing duration (t d ). While the generation
of crystal nuclei depends on the initial value of G, crystals’ growth relies on t d
155
However, the presence of K causes less interference with NH 4 −N recovery than
that of Ca. According to Huang et al. (2011a, b), a slight drop in NH 4 −N removal from
synthetic piggery wastewater was observed when K:Mg molar ratio was increased
from 0 to 0.75. Besides, the effect of K was illustrated in previous researches, which
targeted the recovery of K from source-separated urine in the form of MPP (Kstruvite). Wilsenach et al. (2007) reported that MAP has more tendency to be formed
than MPP. In the same context, for P and K recovery from synthetic urine, it was
demonstrated that, when NH 4 −N concentration was increased from 0 to 500 mg/L,
the efficiency of MPP precipitation, as well as NH 4 −N removal, was decreased
from 77% to 65% and from 97% to 77%, respectively, (K 0 = 52.4 mM/L, pH 10,
Mg:K:P = 2:1:2) (Xu et al. 2011). These studies indicated that the effect of K is
less significant than Ca; however, it should be taken into consideration in the cases
of high concentrations of K, such as those reported for LL (Di Iaconi et al. 2010;
Huang et al. 2014 and Kochany and Lipczynska-Kochany 2009).
Wastewater may contain high concentrations of heavy metals that could affect
the purity of struvite. For agronomic field applications, the incorporation of heavy
metals, such as chromium (Cr), is a vital issue if struvite is to be used as a fertilizer
(Rouff 2012a, b). Minute levels of some heavy metals, such as arsenic (As) in urine
(Ronteltap et al. 2007) and sewage sludge effluent (Uysal et al. 2010), were found
co-precipitated with struvite. Liu et al. (2013a, b) found a lower limit of heavy metals
in struvite obtained from swine wastewater. The authors reported that this struvite is
safer compared to struvite recovered from LL or some other industrial wastewaters.
However, for sustainable agriculture, the potential accumulation of heavy metals in
soil and plants is undesirable as heavy metals may consequently cause hazardous
effects for humans and animals. Table 9.5 shows the effect of some heavy metals
on MAP recovery. Heavy metals have shown two sorption mechanisms during MAP
crystallization, i.e. co-precipitation and adsorption. Co-precipitation was found to be
the sorption mechanism of As(V) (Ma and Rouff 2012) and Al
3+ (Acelas et al. 2015),
while other metals like Cu
2+ and Zn
2+ (Muryanto and Bayuseno 2014), and As(III)
(Ma and Rouff 2012) were found to be adsorbed on struvite surface. Table 9.5 shows
that some heavy metals such as aluminium (Al
3+ ), copper (Cu
2+ ) and zinc (Zn
2+ ),
which are highly concentrated in swine wastewater and sludge digestion liquors,
have the ability to cause inhibition on struvite formation (Acelas et al. 2015; Liu
et al. 2011a, b), while the sorption of either Cr(III) or Cr(VI) on struvite has several
environmental implications related to agriculture sustainability and human health.
The effects of many other heavy metals (e.g. Ni and Cd) were not investigated in
literature, although high concentrations are commonly found in different types of
wastewater such as LL.
9.4.3.6 Mixing Conditions
Struvite crystallization (nuclei generation and growth) is significantly influenced by
mixing intensity value (G value) and mixing duration (t d ). While the generation
of crystal nuclei depends on the initial value of G, crystals’ growth relies on t d