Simple method for control of phosphate level of manure using magnesium oxide

الملخص EN

A simple method is described for the reduction of available phosphate released from soaking manure in water.

The method involves the indirect contact of magnesium oxide, MgO, with manure soaked in water for pre-specified time.

Preliminary study indicated that phosphate could be removed effectively by MgO addition and the precipitation is accelerated by NH4Cl addition.

Thus, and for economic reasons, the study was continued using only MgO.

Two sets of experiments were carried out.

Water was used for the extraction of manure by shaking for 2 h followed by press filtration.

The aqueous phase was used for phosphate removal experiments.

The weighed amount of MgO was placed in a cotton bag fixed to the stirring bar of a jar tester.

The concentration of phosphate was monitored after equilibration for 0, 7, 30, 50, 89, 100, 120, 150 and 192 hours.

In the other set of experiments, weighed amount of manure powder (Less than 2 mm diameter particles) was placed in 50-mL capacity capped plastic bottles (50 bottles) with various amounts of MgO : 0, 0.4, 0.8, 1.4 and 2.0% (by weight MgO:Manure) in 9 bottles each.

Water was added to the bottles to make 40 mL.

The bottles were shaken on a rotary shaker at 250 rpm.

One set of bottles containing the different amounts of MgO was removed from the shaker after 2 hours.

The other sets were removed after 7, 10, 25, 24, 36, 48, 72 and 120 hours.

Phosphate was determined in the filtered aqueous samples.

The first seven hours was enough to cause a removal of 65-70% of phosphate from solution.

The removal of the remaining part of phosphate required as long as 9 days.

It was concluded that MgO in clothing bags may be suspended and moved inside manure-water suspension for 10 hours to extract the majority of the phosphate.

The remaining manure may be used for fertilization with harmless phosphate content that may not result in the growth of undesirable water environment plants.

The reacted oxide in the bags can then be used later as a slowly released phosphate source (Struvite) for plant application a matter that increase the economy of the method.