Parameter optimization of preparation for biogas slurry based water-soluble liquid fertilizer containing humic acid

Abstract: Water-soluble liquid fertilizer containing humic acid is one of the important directions of liquid fertilizer development in the future. It not only has the high utilization efficiency and the abilities of water saving, environmental protection and increasing production, but also has the functions of enhancing plant resistance, promoting flower bud differentiation and development, and improving the quality of crops. According to the analysis, 90% of the nutrients of livestock and poultry manure and straw were preserved after biogas fermentation, and about 1/3 of nutrients entered biogas slurry. Using biogas liquid to develop liquid fertilizer could alleviate the problem of methane elimination and save water resources, besides producing high quality liquid fertilizer. In order to explore the feasible method for the development of water-soluble liquid fertilizer containing humic acid, in this paper, biogas slurry, formula fertilizer of cucumber, chelating agent, and stabilizer were used as the main raw materials, and the effects of different process parameters (amount of biogas slurry, amount of stabilizer, amount of chelating agent, reaction temperature and reaction time) on the performance of water-soluble liquid fertilizer containing humic acid were studied. The results showed that amount of biogas slurry, amount of chelating agent, amount of stabilizer, reaction temperature and reaction time had an important effect on the content of water insoluble substance in liquid fertilizer containing humic acid. In the case of the addition of certain amount of biogas solution, the impact importance of each factor was additive amount of stabilizer > reaction temperature > additive amount of chelating agent > reaction time. Adjusting amount of chelating agent, amount of stabilizer, reaction temperature and reaction time could reduce the concentration of water insoluble matter to a certain extent, and improve the total nutrient concentration in the liquid fertilizer. The excellent process parameters for preparing water-soluble liquid fertilizer were formula fertilizer of cucumber accounting for 39.6% of mixed material, biogas slurry 59%, stabilizer 0.4%, chelating agent 4%, reaction temperature of 40 ℃, and reaction time of 1.5 h. Under such conditions, the content of total nutrient was 220.47 g/L, humic acid was 33.25 g/L and insoluble matter was 18.6 g/L. The full utilization of biogas slurry was an important guarantee for the sustainable operation of biogas projects. From another point of view, under the premise of meeting the basic quality standard of liquid fertilizer, it was also of great practical significance to achieve maximum utilization of biogas slurry. The method not only realizes the full utilization of biogas slurry, but also has the advantages of high content of humic acid and nitrogen. It provides technical support for developing high quality water-soluble liquid fertilizer containing humic acid using biogas slurry.