Parisa Mashayekhi; Hosein Sharifi
Abstract
Introduction: In recent years, the increased water, soil, and environmental degradation, due to the excessive use of chemicals, has encouraged researchers into organic farming. Despite all the positive effects associated with the consumption of sewage sludge and municipal compost on the soil physical ...
Read More
Introduction: In recent years, the increased water, soil, and environmental degradation, due to the excessive use of chemicals, has encouraged researchers into organic farming. Despite all the positive effects associated with the consumption of sewage sludge and municipal compost on the soil physical and chemical properties, there is still a great concern in terms of the environment, agriculture and health. Depending on the source, composts often contain relatively large amounts of heavy metals, and thus accurate measurement of heavy metal contents in these compounds is important.Material and methods: In this study, 20 compost samples from different sources, including manure, municipal waste and sewage sludge sources were selected. Five methods of digestion in three replicates were used to extract the heavy metals of the compost samples, including nitric acid, dry ashing, nitric–perchloric acid, sulfuric acid and sulfosalicylic acid methods. The elements were Cd, Pb, Ni, Cr, Co, Cu, Zn, Mn, and Fe.Results and discussion: Analytical results indicated that the nitric–perchloric acid procedure was the most efficient for recovering Cd, Pb and Cr from the organic samples. After that, dry ashing method extracted the highest amount of Cd, Pb and Cr from all compost samples (on average). Since perchloric acid is potentially hazardous during digestion procedure, dry ashing was recommended as an alternative method. The recovery of Cd and Pb in the organic compounds is affected not only by the digestion method, but also by the type of compost. For example, the nitric–perchloric acid procedure recovered more Cd and Pb from municipal waste and sewage sludge than manure and Poultry fertilizers. In the case of other elements including Ni, Co, Cu, Mn, Zn and Fe, sulfosalicylic acid has the highest efficiency in extracting these elements from compost samples. Extraction of these elements was only affected by the type of extraction method and the type of organic composition had no effect on it.Conclusion: Different digestion methods and also different compost sources that were tested had a very significant effect on the extraction of all heavy metals. Despite the fact that the organic compounds used in this experiment had a relatively wide range in terms of various structural and chemical properties, the digestion methods used for the heavy and micronutrient elements in these compounds had a relatively specific trend in terms of the extraction potential of these elements. In general, in the case of heavy metals, Cd, Pb and Cr, nitric acid + perchloric acid and then dry digestion method, had the best efficiency in extracting these elements. For the other elements including Ni, Co, Cu, Mn, Zn and Fe, sulfosalicylic acid was the most effective in extracting these elements from compost samples.
Alireza Marjovvi; Parisa Mashayekhi
Abstract
Introduction: The increasing trend of water, soil and environmental degradation caused by the excessive use of chemicals material has encouraged researchers into organic farming in recent years. Despite all the positive effects associated with the consumption of municipal compost and sewage sludge on ...
Read More
Introduction: The increasing trend of water, soil and environmental degradation caused by the excessive use of chemicals material has encouraged researchers into organic farming in recent years. Despite all the positive effects associated with the consumption of municipal compost and sewage sludge on the physical and chemical properties of soils, there are still many concerns about environmental and health issues. Therefore, the aim of this study was to investigate the effect of accumulation of heavy elements in soil and plant by different amounts of organic fertilizers on municipal compost and sewage sludge in stable plots after 5 years. Material and methods: This research was carried out in stable plots (dimensions of each plot was 40 m2) at Ruddasht irrigation and drainage research station in Isfahan with four organic manure treatments including municipal compost and sewage sludge fertilizer with control in a randomized complete block design with three replications and five consecutive year. The treatments were: a) without the use of any organic fertilizers the experimental periods (control). B) treatment of 25 tons per hectare of municipal compost fertilizer. C-treatment of 50 tons per hectare of municipal compost fertilizer. D) Treatment of 15 tons per hectare of sewage sludge. E) Treatment of 30 tons per hectare of sewage sludge. Results and discussion: The results showed that organic fertilizer application increased soil organic matter. Also, the use of both types of organic fertilizers, especially at higher levels, caused a significant increase in phosphorus, potassium, iron, copper, manganese, zinc and lead in soil. The use of organic treatments had no effect on the increase of lead and cadmium in the soil in the first stage; however, the consumption of several consecutive years of municipal compost (treatment of 50 tons per hectare) increased the available lead in the soil, in the second stage. Application of organic fertilizers increased the macro (e. g. N, P, K) and micro nutrients (e. g. Fe, Zn, Mn and Cu) in the onion shoot. The highest amounts of nutrient elements was observed in treatment of 50 ton / ha municipal compost, in onion shoot. In most cases, there was no significant difference between 50 ton / ha municipal compost treatment and 30 ton / ha sewage sludge treatment. The concentration of these elements increased significantly with the use of organic fertilizers by five years. In the case of copper, this trend was reversed, and the rate of absorption of this element in the second stage was lower than that of the first stage due to the increase in the concentration of other elements such as phosphorus and the competition between the various elements in the absorption by the plant. Conversely, the rate of copper was reduced uptake in the second stage. This was due to increase of other elements concentrations, such as phosphorus, and the competition between different elements to be absorbed by the plant. The use of different fertilizer treatments in the first stage only increased the amount of zinc in the onion bulb, but in the second stage, as a result of several years of waste compost and sewage sludge consumption, the concentrations of nitrogen, potassium, copper, iron and zinc in the onion bulb increased significantly. The concentration of lead and cadmium in the plant was low in different treatments, which was not measurable by atomic absorption. Conclusion: In general, municipal compost and sewage sludge, at the studied levels, increased soil organic matter and the concentration of nutrients in the plant, especially in terms of micronutrients such as zinc and iron.
