عنوان مقاله [English]
Management of municipal wastes as well as their reuse is one of major concerns of researchers in recent decades due to the expansion of urbanization and increase in production of municipal waste. Composting and use of municipal waste is one of the solutions used in the management of these materials. Implementation of various additives to enrich and improve the properties of the produced compost is one of the common methods to increase the efficiency of produced compost. Different organic and inorganic compounds are used to enrich the produced compost. The aim of this study was to investigate the effect of two organic compounds (blood powder and bone powder) and a mineral compound (phosphate soil) on the composting properties of municipal waste. It was also our goal to find the effect of these treatments on growth characteristics and concentration of nutrients in shoot of spinach was evaluated.
Materials and Methods
This research was conducted in two stages. The purpose of the first part was to investigate the effect of organic and inorganic additives on the properties of municipal waste compost. Experimental factors included four types of composts including control compost (without additives); compost plus 1% blood powder; compost plus 1% bone powder and compost plus 5% phosphate soil. After sieving the waste and removing the waste leachate, about 60 kg of waste was weighed for each treatment and placed in plastic barrels with a volume of 100 liters for better control of aeration conditions. The compost ripening factors were stable after 90 days, when it was screened and materials were separated, then some of its properties include acidity, electrical conductivity, organic carbon, total nitrogen, C/N ratio, iron, humic acid, fulvic acid, and other parameters including humification ratio, humification index and degree of polymerisation were measured. In the second phase, the effect of compost enriched with blood powder, bone powder and phosphate soil treatments was compared with control treatment (without compost) on growth characteristics and nutrient concentrations in spinach shoots in a greenhouse experiment. For this purpose, pots (with a diameter of 25 cm and a height of 30 cm) were packed with 8 kg of soil in which enriched composts was mixed in 5 g compost/kg of soil ratio. After preparing the pot, the humidity reached 65% of the field capacity and after 25 days, 6 spinach seeds (Spinacia oleracea L.) were planted. After 50 days of planting, the plants were harvested and parameters such as shoot dry weight, leaf area, nitrogen, iron and phosphorus were measured.
Results and Discussion
Results of enriched compost showed that the highest amount of reduction in EC (with 14.5%) and OC (with 8.9%) was resulted in phosphate soil treatment and the highest reduction in C/N ratio (with 46.8%) was related to blood powder treatment. Regarding to the other variables, the highest N and Fe concentrations was related to the blood powder treatment with 2.5% and 706.6 mg/Kg and the highest P content with 1.66% was observed in phosphate soil treatment which had a significant difference with control. Regarding to the Humification indices the highest difference with the control treatment in Fulvic acid content with 24.5% was related to bone powder treatment, that of Humic acid content with 32.4% and Polymerization rate with 43% was related to phosphate soil. In this experiment, the amount of organic carbon was expected to increase in blood powder and bone powder treatments, which was not the case. This may be due to the effect of these treatments on increasing microbial activity such as microbial respiration and increasing the decomposition of organic carbon which ultimately leads to a decrease in the amount of organic carbon. The increase in EC in organic treatments compared to inorganic treatments may be due to weight loss of organic matter and release of various mineral salts. The effect of experimental treatments in the greenhouse section also showed that highest difference in plant dry weight compared to the control was related to the blood powder treatment with 59% increase and regarding to the leaf area with 31.9% increase through application of the blood powder and phosphate treatments. The highest amount of Fe and N absorption in spinach shoots was also observed in blood powder treatment with 1177 mg/Kg and 3.13% respectively. Phosphate soil with high amounts of phosphorus increased the amount of this element in the shoots of spinach. The two combinations of blood powder and bone powder caused a significant increase in these elements in the compost and in most of the measured parameters, due to their high amounts of nitrogen and iron. These two organic substances were significantly different from the control.
The results of this study showed that the enrichment of municipal waste compost using organic and inorganic additives can compensate for the lack of some elements in the compost and further increase the growth of spinach. Adding blood powder increased the concentration of iron and nitrogen in the shoot and decreased the C/N ratio compared to the control treatment. Also, the positive effect of phosphate soil and bone powder are effective in increasing the phosphorus content of compost. In addition, the combination of phosphate soil with municipal waste compost due to the formation of more stable materials such as humic acid and folic acid prevents their subsequent wastage. Finally, it can be concluded that in this experiment, two treatments of blood powder and phosphate soil have the best effect on enrichment and they had increased growth characteristics of spinach and in general, and blood powder was selected as the best treatment.