Master's Thesis
Department of Civil-Environmental Engineering
Abstract
Garbage is one of the environmental pollutants that cause many problems including the spread of pollution in water, air and soil and transmission to humans and animals directly or indirectly. Today, with the increasing expansion of urban and industrial societies, we are witnessing the widening of the amount of these pollutants.
On the other hand, the urban wastewater treatment plant of the aerobic type produces significant amounts of excess sludge, which if these increasing amounts are not properly managed, it will cause environmental problems in water, soil, and air and the possibility of diseases for urban communities. Considering the importance of the two mentioned issues, urban waste and sludge, by combining these two in a process, co-composting can be obtained, which will solve the problem of urban waste and treatment plants, and finally produce fertilizer for agricultural purposes. be used In this research, with the aim of investigating the effective factors in the production of mixed compost, such as aeration rate, particle size, moisture percentage, heavy metals and so on. It was done in two pelexiglass pilots with a height of 1 meter and a diameter of 20 cm. In each step, a 1:1:3 combination of waste to sludge to wood chips was used (to create proper porosity). In the first stage, which was launched in the winter season, the particle size was less than 10 mm, the initial moisture percentage was 78%, the mass without turning over and different aeration rates were studied. In the second stage, which was launched in the summer season, the aeration rate was 3 times, the humidity was reduced by 10% compared to the first stage, and the particle size increased up to 4 times in the first stage. Due to the high rate of decomposition, the process of turning the materials every 4-6 days was studied. The results of the investigation showed that the composting time in summer conditions was four days less than the first stage and the reduction rate was also recorded faster than the first stage, and on the other hand, the combination of waste with sewage sludge in the ratio of 1:3 is a suitable condition for the composting process. With the increase in the size of the particles, the aeration process of the compost increased and finally the maturity time of the compost increased to 12.5%. Due to the increase in temperature in the second stage, the possibility of the compost becoming stinky or anaerobic was prevented by increasing the aeration rate. The results of the sludge showed that the amount of organic matter in the first and second stages was reduced by 30 and 25%, respectively, and the amount of heavy metals in the combined compost showed that the produced product was within the standard range.
Chapter One
Introduction
1-1- Generalities
Today, in all parts of the world, we are witnessing the increasing progress of various nations in all fields, especially economic. In no era has the world seen such rapid transformation. One of the characteristics of this new system is more production, which results in widespread consumption. This consumption will not result in mass production of unwanted materials or in simpler terms, waste. Garbage in urban societies, especially large cities where the population is concentrated, is defined as an unwanted and hated product that should be removed from the personal living environment as soon as possible. Today, after long experiences and experiments, it has been determined that the most valuable and effective fertilizers and enhancers are obtained from humans. The Chinese before us observed this principle and returned human excrement to their land [33]. The fact is that environmental crises, by causing irreparable losses of life and money, warn people that the self-healing power of nature's tired body has been exhausted. With this belief for a long time, in order to protect the environment, advanced countries have made it mandatory to treat waste materials such as sewage before disposal [32]. Wastewater treatment is always associated with the production of two separate parts, sewage and sludge, of which sewage often has a favorable quality for disposal into the environment, while sludge needs further purification and stabilization due to high pollution. In an urban wastewater treatment plant, sludge treatment and stabilization facilities are far more sensitive, specialized and expensive than other units, for example, about 30% of the total construction cost of the Gorgan treatment plant was allocated to the sludge stabilization unit. Based on this, special attention should be paid to the technical and economic optimization of sludge purification and stabilization methods [32]..
In developed countries, research has been started for several years to choose the optimal model for sludge treatment and stabilization. This should be taken care of by officials and experts in our country along with the expansion of the sewage industry. Considering the importance of the two mentioned issues, that is, urban waste and sludge, by combining these two during the process, co-composting can be obtained, which solves the problem of urban waste and treatment plants.
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1-2- Necessity of conducting research
One of the effective methods in neutralizing the adverse effects of waste and sludge is to convert them into compost and reuse them as organic fertilizers. (vegetable) in agriculture. In most countries of the world, the economic efficiency of this method compared to other methods has been proven, especially in agricultural areas and around small towns (in non-industrial ways), where even the low cost of transportation, the abundance of organic materials, and cheap manpower can be very economical[10]. Of course, it is necessary to mention that mixed compost must be prepared and consumed in appropriate and hygienic conditions, because waste is an inhomogeneous mixture and all its components are not capable of being composted, and on the other hand, some materials If the waste components are mixed with the soil, it will cause its quality to decrease, and some of them will cause soil pollution, and will be transferred to humans and animals through absorption in plants, which will cause irreparable losses, and the sludge also contains a large amount of heavy metals, which will cause the quality of the sludge to decrease [10]. Unsuitability of municipal waste and sludge problems in treatment plants will grow and develop in the near future. Composting is an easy process. It is simple because it does not require complex electronic and mechanical devices and equipment, and it can be implemented with minimal facilities in all regions with different climates and with any capacity, and it is prohibited because the process is a biological process. It means that you have to deal with living organisms and you have to provide the right conditions for their nutrition and growth. Therefore, knowing the factors and factors affecting the life, nutrition and growth of these organisms is very basic and important, and the slightest ignorance of this will cause the production of unwanted products in the combined composting process, which is our main topic in this treatise.
3) The effect of turning over on the performance of combined compost
4) The effect of summer and winter seasons on the performance of combined compost
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Chapter Two
Subject Literature
2-1-Knowledge of combined compost
One of the effective methods in neutralizing the adverse effects of waste and sludge is to convert them into compost and use It is one of them as vegetable fertilizer in agriculture. In most countries of the world, the economic efficiency of this method has been proven compared to other methods, especially in agricultural areas and around small towns (in non-industrial ways), where even the low cost of transportation, the abundance of organic materials, and cheap manpower can be very economical [10].
Of course, it is necessary to mention this fact that mixed compost must be prepared and consumed under appropriate and hygienic conditions, because waste is an inhomogeneous mixture and all its components are not capable of being composted, and on the other hand, some If the waste materials are mixed with the soil, it causes its quality to decrease, and some of them cause soil pollution and are transferred to humans and animals through absorption in plants, which causes irreparable losses, and the sludge also contains a large amount of heavy metals, which causes the quality of the sludge to decrease [10]. [
Therefore, before entering into the main discussion, i.e. turning waste and sludge into fertilizer, it is necessary to know the various sources of waste producers and their compounds.