Combined application of induced MAP (Magnesium Ammonium Phosphate) precipitation and adsorption through natural zeolites for reducing NH4+ and PO43- in swine wastewaters
Authors: Tescaro Nicola , Galamini Giulio , Ferretti Giacomo , Faccini Barbara , Eftekhari Negar , Coltorti Massimo 
Published: March 2020

&lt;p&gt;&lt;strong&gt;Combined application of induced MAP (Magnesium Ammonium Phosphate) precipitation and adsorption through natural zeolites for reducing NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; in swine wastewaters&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Nicola Tescaro*1, Giulio Galamini1, Giacomo Ferretti1, Barbara Faccini, Negar &lt;/strong&gt;&lt;strong&gt;Eftekhari&lt;/strong&gt;&lt;strong&gt;, Massimo Coltorti &lt;/strong&gt;&lt;/p&gt;&lt;p&gt;* Corresponding author&lt;/p&gt;&lt;p&gt;1) Department of Physics and Earth Science, University of Ferrara, Ferrara Via Saragat 1 44122, Italy.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Modern agriculture, in response to the constantly increasing need of high crop production, requires application of high levels of N and P fertilizers to soil. These substances are mainly composed by nutrients such as NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; and are often applied in strong excess in order to assure high crop yield. The nutrients applied through fertilizers and not exploited by crops (estimated on average around 50%) can considerably impairs &amp;#160;environmental quality through nitrogen losses in atmosphere (N&lt;sub&gt;2&lt;/sub&gt;O, NO&lt;sub&gt;x&lt;/sub&gt;, NH&lt;sub&gt;3&lt;/sub&gt;) and eutrophication of water bodies.&lt;/p&gt;&lt;p&gt;In this work, a new method for reducing NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; in swine wastewaters (commonly used as organic fertilizer) was studied. The aim is to reduce their environmental impact and concomitantly create a new slow-release fertilizer.&lt;/p&gt;&lt;p&gt;Two techniques have been combined: the induced MAP precipitation (magnesium ammonium phosphate) and natural zeolite ammonium adsorption for removing the NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+ &lt;/sup&gt;excess that generally remains in solution after MAP precipitation. Given the complexity of working with real wastewaters, in this preliminary phase a synthetic analogue was used in order to better evaluate the efficiency of this method. Two synthetic wastewaters with different Mg&lt;sup&gt;2+&lt;/sup&gt; : NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; : PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; molar ratio were tested:&amp;#160; MR1 (1:1,5:1) and MR2 (2:1:1), which according to the literature give the best reductions of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt;. &amp;#160;Since swine wastewater are naturally rich of both NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and K&lt;sup&gt;+&lt;/sup&gt;, isotherm studies were conducted on natural zeolites for evaluating their adsorption capacity of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; under different levels of K&lt;sup&gt;+&lt;/sup&gt; competition. Results showed that&amp;#160; the potential in NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; adsorption decreased while competition with K&lt;sup&gt;+&lt;/sup&gt; increased. &amp;#160;The combination of MAP precipitation and NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; adsorption by natural zeolite has been tested in 2 ways: 1) zeolite was added before inducing MAP precipitation 2) zeolite was added after inducing MAP precipitation. &amp;#160;These two treatments were compared to a blank in which only MAP precipitation technique was used.&lt;/p&gt;&lt;p&gt;The amount of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; was monitored in various steps during the experiments as well as&amp;#160; SEM observations were conducted on precipitated obtained. Results showed that adding zeolites before MAP precipitation induce a variation in the &amp;#160;Mg&lt;sup&gt;2+&lt;/sup&gt; : NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; : PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; ratio due to cation exchange processes before MAP precipitation which introduce interfering ions such as Ca&lt;sup&gt;2+&lt;/sup&gt; favoring calcium phosphates precipitation instead of MAP. The best test conditions, which produced the 75,1% of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and 99,9% of PO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;3-&lt;/sup&gt; reductions, occurred when zeolites have been added after MAP precipitation using the MR2. &amp;#160;This new material obtained&amp;#160; combines good N and P concentration and have therefore potentialities to be a high-quality slow-release fertilizer.&lt;/p&gt;