Preparation Of Coated Slow Releasing Fertilizer Using Swill-cooked Oil And Municipal Waste Sludge

The objective of this thesis was to preparethe coated slow releasing fertilizer using swill-cooked oil(SCO)and municipal waste sludge(MWS)as raw materials.The SCOwas refined and modified before duo reaction.The reaction product was mixedwith fine ground MWS powder before beingcoated to large granular urea particle surface.The effects of various factors on the slow release of coated slow-release fertilizer were studied to with the ultimate purpose of optimizing the manufacturing process.The main findings are as follows:(1)Refining of SWO : The delicate process included pickling,water washing,decoloration and deodorization,filtration,drying.The refining conditions were: specific p H value by means of acid pickling to be 1 ~ 2 by adding sulfuricdrops by drops.The amount of water used was 50 % of the SCO and the water washing process was repeated 5 times;The white active clay was decolorized by being stirred and heated at 80 ℃ before being filtered using 0.25 nm filter paper.The filtered SCOwas stored in a vacuum bag for drying.(2)SCOwas modified by polyol(glycerin)in order to achieve the required reaction conditions where the mass ratio ofSCO versus polyol was 1: 2,the reaction temperature was 170 ℃,and the pressure was kept constant for 2.5 hours.(3)The ratio of gutter oil po lyol and duo: di polyol: duo(mass ratio)should be kept as 1.5: 1 in order to achieve the best coated slow-release fertilizer.(4)The common drum granulator was used for coating.The best coating process was determined by orthogonal test(L): the number of coating layer was greater than or equal to 4;Temperature was 80 ℃;MWS powderwas 300 mesh: the dosage was 20 %-30 % of the urea mass,the rotational speed was greater than 30 r / min.The mass ratio of di polyol to duo was 1.5: 1.When the dosage of coating is 5 %,the effect of coated fertilizer couldqualify the national standard.(5)The internal structure of coating film was characterized by SEM.The results showed that the coated slow-release fertilizer had three-layer structure including the core layer(urea particles),waterproof layer(polyurethane film),and cortex(mixed material of polyurethane and sludge).Itwas different from the traditional coating of two-layer structure,which only depended on the thick cortex to achieve waterproof slow-release effect.There were two layers of barriers in such fertilizer to prevent water from entering fertilizer where the cortex was the main waterproof layer and the outer layer not only functioned as waterproof layer but also increased the hardness of fertilizer particles,including organic substances,pores etc.(6)The final coated slow-release fertilizer satisfied GB /T 23348 standards where the percent of nitrogen content was 30.61 % and water contentwas 1.2 %.The grain size was 91.24%.The release cycle was more than 60 days and the initial nutrient release rate was 4.25 %,accumulated nutrient release rate was 28 %,nutrient release was 95.31 %.