| The rapid development of the animal breeding industry has been necessary to meet the growing demand for food,but has led to the production of a large amount of waste,which has become a severe environmental problem in countries such as China.Biogas technology is the main technical means of harmless treatment and resource utilization of animal manure.However recently in China,in order to adapt to the intensive development of the swine industry,biogas plants are having to continually increase in size,resulting in more digestate being produced in one place.The disposal of liquid digestate is becoming one of the bottleneck problems restricting the development of biogas technology and even the development of livestock and poultry breeding industry in China.Livestock and poultry waste liquid digestate contains a certain amount of nitrogen and phosphorus,humic acid,trace elements and other nutrients,which can be used as fertilizer.Direct utilization the nutrients in the liquid digestate may exceed the carrying capacity of lands nearby.However,liquid digestate has lower value density and higher utilization cost as a liquid fertilizer.How to improve the value density of liquid digestate and realize efficient utilization is the difficulty of liquid digestate utilization technical.Membrane separation technology has become an important way to realize treatment and utilization of liquid digestate due to its characteristics of small area,convenient operation and high treatment efficiency.However,due to the high turbidity and ammonia nitrogen content in liquid digestate,reverse osmosis membrane(RO)was used to treat liquid digestate will lead to membrane pollution and high ammonia nitrogen concentration of RO permeate.The membrane bioreactor(MBR)coupled with RO membrane can combine the treatment of liquid digestate with the utilization of resources,to solve the above problems.However,there are few studies on the fertilizer utilization of its concentrate.This study focuses on liquid digestate concentrate from membrane bioreactor(MBR)coupled with RO membrane was used to formulate liquid fertilizer and its fertilizer efficiency and safety on pakchoi(Brassica chinensis L.)The following results are obtained:(1)The bioreactor component of the system was able to reduce the pH of the liquid digestate to 6.5.A dissolved oxygen(DO)concentration of 4.0 mg/L,under the condition of sludge inoculum 12.0g /L,2 days of hydraulic retention time,was found to lead to the highest quality of effluent.The UF component of the MBR had an obvious effect on removing suspended solids and reducing turbidity,protecting the subsequent RO membrane.(2)RO membrane was used to concentrate liquid digestate by 1-10 times,and it was found that the nutrient in the concentrated solution of liquid digestate increased with the increase of concentration times.Higher concentrations of nutrients and humic acid were found in the 10 times RO concentrated liquid digestate.According to the characteristics of 10 times liquid digestate concentration,the nutrient elements were added to re-formulated to meet the standard of liquid fertilizer.(3)Liquid digestate concentration fertilizer was used as test fertilizer,and solid compound fertilizer and concentrated nutrient solution were used as control fertilizer.The results showed that under the same amount of nitrogen application,liquid digestate concentrate fertilizer could significantly increase the yield,chlorophyll content,soluble sugar content and vitamin C content,and reduce the risk of nitrate and heavy metal accumulation in pakchoi.The liquid digestate concentrate fertilizer had superior fertilizer efficiency and low risk for pakchoi.In the experiment of liquid digestate concentration fertilizer with different dilution ratio,with the increase of dilution ratio of liquid digestate concentration fertilizer,the yield and nutrient content of Pakchoi increased first and then decreased. |
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