160
M. Darwish et al.
maximum N uptake by plants and minimum N loss. Application of MAP fertilizer would also reduce greenhouse gas emission, mainly due to the gradual release
of nutrients. Rahman et al. (2011) found that leaching loss of N from MAP-treated
soil (1.98–2.05%) was lower than that from urea-treated soil (6.47–7.82%). The
leaching rate of P was also very low for both soils, hence, making MAP an efficient
and eco-friendly N fertilizer.
9.6.1 Low-Cost Sources of Magnesium and Phosphorus
in Struvite Crystallization Process
Several research works have evaluated the feasibility of utilizing low-cost sources of
Mg and/or P in order to reduce the recovery cost. The cost of struvite recovery from
LL using conventional sources of Mg and P (MgO and H 3 PO 4 ) is approximately
$24–28/m
3 leachate (Di Iaconi et al. 2010; Gunay et al. 2008b). Gunay et al. (2008b)
reported that using natural magnesium carbonate (MgCO 3 ) saved nearly 18% of
struvite recovery cost (from $28 to 22/m
3 leachate). However, a better cost saving
could be achieved by applying low-cost sources of Mg and P together. As illustrated
by a few studies, the use of by-products of Mg and P together could reduce the costs
of struvite recovery by 43–68% (Huang et al. 2014; Siciliano and De Rosa 2014;
Siciliano et al. 2013). Hence, more studies are required to explore other alternative
sources of P, particularly such as those from food industries.
9.6.2 Reuse as Source of Magnesium and Phosphorus
The main idea of reusing struvite is based on eliminating NH 4 from struvite matrix
and reproducing Mg and P compounds that can be usable for NH 4 −N recovery. Five
main techniques have been recently studied for MAP reuse, namely pyrogenation
(heating under alkali conditions), distillation with alkaline addition, electrolysis,
breakpoint chlorination and microwave decomposition. The procedures and related
details have been thoroughly discussed elsewhere (Liu et al. 2013a, b; Türker and
Çelen 2007). Researches on pyrogenation demonstrated that such technology could
reduce the chemicals costs by 67% (Huang et al. 2016a, b). Later, Huang et al. (2016a,
b) developed a new pyrogenation process that used low temperature and negative
pressure. The authors were able to save around 86% of treatment cost, compared
to the cost of using pure chemicals without recycling. By applying distillation with
caustic addition, Türker and Çelen (2007) reached 100% vaporization of NH 3 and
achieved around 41.6% cost reduction. Electrolysis technique was investigated by
Liu et al. (2011a, b), at which the researchers achieved more than 65% cost reduction.
Recently, Huang et al. (2015) developed a novel approach of struvite recycling, based
on chlorination decomposition of struvite. Using sodium hypochlorite (NaClO), 98%
M. Darwish et al.
maximum N uptake by plants and minimum N loss. Application of MAP fertilizer would also reduce greenhouse gas emission, mainly due to the gradual release
of nutrients. Rahman et al. (2011) found that leaching loss of N from MAP-treated
soil (1.98–2.05%) was lower than that from urea-treated soil (6.47–7.82%). The
leaching rate of P was also very low for both soils, hence, making MAP an efficient
and eco-friendly N fertilizer.
9.6.1 Low-Cost Sources of Magnesium and Phosphorus
in Struvite Crystallization Process
Several research works have evaluated the feasibility of utilizing low-cost sources of
Mg and/or P in order to reduce the recovery cost. The cost of struvite recovery from
LL using conventional sources of Mg and P (MgO and H 3 PO 4 ) is approximately
$24–28/m
3 leachate (Di Iaconi et al. 2010; Gunay et al. 2008b). Gunay et al. (2008b)
reported that using natural magnesium carbonate (MgCO 3 ) saved nearly 18% of
struvite recovery cost (from $28 to 22/m
3 leachate). However, a better cost saving
could be achieved by applying low-cost sources of Mg and P together. As illustrated
by a few studies, the use of by-products of Mg and P together could reduce the costs
of struvite recovery by 43–68% (Huang et al. 2014; Siciliano and De Rosa 2014;
Siciliano et al. 2013). Hence, more studies are required to explore other alternative
sources of P, particularly such as those from food industries.
9.6.2 Reuse as Source of Magnesium and Phosphorus
The main idea of reusing struvite is based on eliminating NH 4 from struvite matrix
and reproducing Mg and P compounds that can be usable for NH 4 −N recovery. Five
main techniques have been recently studied for MAP reuse, namely pyrogenation
(heating under alkali conditions), distillation with alkaline addition, electrolysis,
breakpoint chlorination and microwave decomposition. The procedures and related
details have been thoroughly discussed elsewhere (Liu et al. 2013a, b; Türker and
Çelen 2007). Researches on pyrogenation demonstrated that such technology could
reduce the chemicals costs by 67% (Huang et al. 2016a, b). Later, Huang et al. (2016a,
b) developed a new pyrogenation process that used low temperature and negative
pressure. The authors were able to save around 86% of treatment cost, compared
to the cost of using pure chemicals without recycling. By applying distillation with
caustic addition, Türker and Çelen (2007) reached 100% vaporization of NH 3 and
achieved around 41.6% cost reduction. Electrolysis technique was investigated by
Liu et al. (2011a, b), at which the researchers achieved more than 65% cost reduction.
Recently, Huang et al. (2015) developed a novel approach of struvite recycling, based
on chlorination decomposition of struvite. Using sodium hypochlorite (NaClO), 98%