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1OPTIMAL WAY OF USING SEWAGE SLUDGE IN UZBEKISTAN
Maxliyoxon Abdusattorova
Student of Namangan Presidential school
Sobirova Dilafruzxon Student of Ferghana Presidential school Shamsiddinov Shohjahon
Student of Nurafshan Presidential school
Abstract: The biosolid (biohumus) produced during wastewater treatment is accumulating in large quantities, often being stored in open-air sites. This practice promotes the growth of bacteria and pathogens, which can trigger various diseases. To mitigate this issue, it is essential to thoroughly evaluate the available treatment methods, select the most suitable option, and implement it effectively. Managing precipitate from sewage systems is increasingly critical in Uzbekistan, posing significant economic and ecological challenges. Drawing lessons from successful strategies in countries like the United States, Canada, and Germany, where organic-based compounds have proven effective, is essential. These compounds enhance soil quality and fertility and play an important role in energy generation. For instance, in the United States, organic-based compounds have boosted productivity by 25% compared to traditional fertilizers. European countries have similarly excelled, generating 40% of their electricity from organic-based reprocessing for over four decades. Implementing these proven practices can result in substantial economic benefits, develop agricultural productivity, reduce energy reliance, and foster ecological improvements in Uzbekistan's urban and rural areas.
Keywords: Anaerobic digestion, Air-drying, Aerobic digestion, Biosolid, Composting, Pyrolysis, Sustainable agriculture, Waste management.
Introduction
Managing precipitate from sewage systems is increasingly critical in Uzbekistan, posing significant economic and ecological challenges. Drawing lessons from successful strategies in countries like the United States, Canada, and Germany, where organic-based compounds have proven effective, is essential. These compounds enhance soil quality and fertility and play an important role in energy generation. For instance, in the United States, organic-based compounds have boosted productivity by 25% compared to traditional fertilizers. European countries
have similarly excelled, generating 40% of their electricity from organic-based reprocessing for over four decades(Smith, J. and others,2018). Implementing these proven practices can result in substantial economic benefits, develop agricultural productivity, reduce energy reliance, and foster ecological improvements in Uzbekistan's urban and rural areas.
Air-drying
Air-drying is a method that allows organic waste materials to dry and decompose in the open air naturally. The process begins with separating organic waste from metals and plastics. It is commonly employed for agricultural waste, organic matter, and other materials. Wet biosolids, separated from water, are spread out in thin layers and left exposed for a certain period. The drying surface must be uncontaminated and provide good air circulation. During this period, moisture containing organic and inorganic matter and microorganisms evaporates, reducing weight and odor as the biosolids mature. Depending on weather conditions, waste composition, and initial moisture content, the sludge can take weeks to months to dry optimally.
While air-drying effectively reduces moisture content in biowaste, additional treatments are typically required to optimize biosolids. Many countries utilize a combination of methods for sludge treatment. For example, in Japan, after air-drying, biowaste is composted or subjected to anaerobic digestion to produce biogas or compost. In Germany, sludge undergoes initial drying through thermal methods, followed by chemical stabilization to make fertilizer.
Moreover, this method cannot treat all materials. Sludges that have a high level of moisture or have a complex chemical texture should be treated by alternative methods. The method is reliable and easy to implement. It doesn't cost much as the process is simple and doesn't require extra labor. However, it requires a lot of space to implement. Another disadvantage of this method is vector attractions. The pathogens are transmitted by carriers to animals and humans. (Palmgren 2002). Some bacteria survive in biosolids after air-drying due to several reasons. Firstly, it can be because of technical errors such as incomplete drying, which can create spaces that retain moisture and thus provide a suitable environment for bacteria to survive; and ambient temperatures, which may not be high enough to kill all the bacteria in biosolid. Some of the bacteria that settle in the moist spaces and survive are E. coli and Enterococcus spp. Secondly, the biosolid contains organic matter that can be a source of food for bacteria to live and solids (aggregates, clumps) that can shield bacteria from drying effects. Lastly, bacteria can survive because of environmental
conditions, such as high humidity levels, which can slow down the drying process, and insufficient exposure to sunlight and UV radiation, which can result in incomplete disinfection of the biosolids. There are several methods used to overcome this problem. For example, STP Yemen used pesticides, but it led to the gathering of pesticides in the landsfUS EPA air-drying).
Composting
Composting is an essential method in waste management that utilizes natural decomposition to recycle organic waste into nutrient-rich compost. By collecting organic materials such as food scraps, yard waste, and paper products, and allowing microorganisms to break them down, composting effectively reduces the volume of waste sent to landfills.
First, a space in the yard is chosen for the compost pile. Then, the compost pile is built by adding ingredients that are organic waste products. Next comes the maintenance stage. There are 3 requirements that users have to be cautious about and keep track of all the time: moisture-pile will not work as actively if it is too dry, odor-unpleasant smell is a sign that the pile needs more air circulation, temperature-pile should heat up enough to work effectively. (Composting At Home | US EPA, 2023).
Composting entails several advantages for households, agriculture, and the environment. It significantly reduces the amount of trash, hence the potential health risks that it brings. It also enriches the soil with nutrients, so there will be less demand for chemical fertilizers. Composting prevents soil erosion by helping it retain moisture. (Trash to Treasure: The Incredible Benefits of Composting, 2019). Furthermore, this process mitigates methane emissions, a potent greenhouse gas produced in anaerobic landfill conditions, (Composting 101, 2020). Regularly turning and maintaining the pile speeds up the process.
However, composting takes time; a well-managed pile can produce compost in 3-5 months (Composting At Home | US EPA, 2023). It can attract unwanted pests and wildlife, which is likely to pose public health risks and damage property. Plus, improperly managed compost piles can emit strong odors, which might create problems for local residents and businesses. (Composting: Complications and Concerns - College of Business and Economics, 2023). Another limitation of the composting process is that not all areas of the compost pile may reach the sufficient temperature required to kill bacteria, particularly in the outer layers. E. coli is commonly found in composted biosolids that do not reach high enough temperatures. Short composting duration can also lead to the survival and spread of bacteria as not
all bacteria will be killed if the compost pile is not left for a long enough period. Furthermore, uneven aeration within the compost pile can cause anaerobic bacteria to thrive.
Since 1991, Germany has effectively been implementing a composting method in waste management. The amount of carbon dioxide emitted was roughly 3 times less in 2016 than it was before composting was used. Currently, about 50% of German households are involved in the collection of biowaste. Approximately 8 million tons of biowaste are treated in 800 composting plants to produce 5 million tons of compost. (Composting and Quality Assurance in Germany, n.d.)
Aerobic digestion
The tertiary sludge treatment process known as Autothermal Thermophilic Aerobic Digestion (ATAD) utilizes the heat produced by aerobic microbial digestion to make use of the sludge for agriculture. This method can be used to make use of a range of waste streams, including food waste, animal waste, and brewery abattoir waste. Nevertheless, the ATAD approach can reduce biological oxygen demand (BOD) to 95% and chemical oxygen demand (COD) to 99% when processing waste streams with high strength at increased temperatures. (J. T. Pembroke, M. P. Ryan, 2019). Organic matter breaks down into more basic chemicals during the process. (water, stable organic molecules, and carbon dioxide). This approach is unusual because of its auto thermal feature, which simply means it can achieve between 50 and 70°C without the need for external heating. In this situation, the heating is provided by microbial metabolites, particularly thermophilic nitriding during the process.
In addition to this, there are certain drawbacks. Keeping the required thermophilic temperatures (usually between 55 and 65°C) high enough to create a comfortable atmosphere for effective operation can be one of them, and it can have a significant impact on costs. (Smith et al., 2011). Furthermore, failure to appropriately control ATAD processes might result in process instability and decreased treatment efficiency due to their sensitivity to variations in feedstock properties (Pollmann et al., 2018). Aside from that, maintaining an ATAD system over its lifetime incurs additional costs due to the rigorous monitoring and control of operational parameters including pH, oxygen levels, and temperature. (Smith et al., 2011).
Along with these, the initial capital investment for ATAD systems is significant because of the advanced, sophisticated control systems. For smaller facilities, this can be a financial obstacle. (Remote Alarms & Monitoring).
Anaerobic digestion
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Anaerobic digestion is a biological process that breaks down organic matter in the absence of oxygen, producing biogas and digestate. This process is facilitated by a consortium of microorganisms, including bacteria and archaea, which degrade complex organic materials such as agricultural waste, food scraps, and sewage sludge. The resulting biogas, primarily composed of methane and carbon dioxide, can be harnessed as a renewable energy source for heating, electricity generation, and even as a vehicle fuel. The digestate, a nutrient-rich byproduct, can be used as a fertilizer, contributing to the circular economy by returning valuable nutrients to the soil.
The anaerobic digestion process occurs in a series of stages, starting with hydrolysis, where complex organic polymers are broken down into simpler monomers like sugars and amino acids. This is followed by angiogenesis, in which these monomers are further degraded into volatile fatty acids, alcohols, hydrogen, and carbon dioxide. Next is acetogenesis, where volatile fatty acids are converted into acetic acid, hydrogen, and carbon dioxide. Finally, methanogenesis takes place, where methanogenic archaea convert acetic acid and hydrogen into methane and carbon dioxide. Each of these stages is carried out by specialized microbial communities that thrive in the oxygen-free environment of the anaerobic digester.
Anaerobic digestion offers several environmental benefits, including the reduction of greenhouse gas emissions and waste volume. By capturing methane, a potent greenhouse gas, and using it as an energy source, anaerobic digestion helps mitigate climate change.
The digestate produced can improve soil health and reduce the need for synthetic fertilizers, which are energy-intensive to produce and can cause environmental harm. Overall, anaerobic digestion is a versatile and sustainable technology that supports waste management, renewable energy production, and agricultural practices.
However, it does have disadvantages regarding the amount of pathogenic bacteria left in biosolid after the anaerobic digestion process. One of the ways that bacteria can survive and reproduce in biosolids is incomplete digestion. Incomplete digestion can occur due to inadequate pH control, or fluctuations in organic loading rates. Secondly, most anaerobic processes use mesophilic conditions, which may not be sufficient to inactivate all pathogenic bacteria. Bacteria such as Salmonella and E. coli can survive under these conditions. Lastly, thermophilic conditions (50-60°C) are more efficient in reducing the amount of bacteria in biosolid after digestion. However, these conditions are rarely used due to higher energy requirements.
Pyrolysis
Pyrolysis, a process used to decompose biosolids and residues at temperatures ranging from 370 to 850 degrees Celsius, is revolutionizing waste management and sustainable practices worldwide (Lijie, 2014). Countries like India, Japan, the USA, the United Kingdom, Germany, and the Netherlands are utilizing this method, demonstrating an efficiency index of 60 to 80 depending on the accuracy of the recycling method.
Biochar is a residue of pyrolysis and is rich in carbon. It can be obtained from the thermal decomposition of wood, tires, domestic waste, and sewage sludge of wastewater treatment. High temperature creates pores/holes that extend the surface area for water and nutrient absorption creating better conditions for root and maintenance of the plant growth (Jabbarov, 2022,). Furthermore, biochar reduces greenhouse gas emissions due to the slow rate of decomposition of organic compounds which have already been converted into biochar as well and the stability within biochar prevents the release of CO2 into the environment extending the period that happens positively impacting the curve of global warming. In addition to that, it favors the growth of beneficial soil bacteria and microorganisms, affecting soil efficiency and plant health. (Biochar, n.d.)
This process converts organic materials and waste into useful products that are used for agricultural purposes, and biofuel to promote sustainable practices, resulting in a reduction of waste and creating room for recycling (Turning Waste Into Resources: Pyrolysis Vs Incineration Debate, n.d.). As a consequence of high temperature, bio-solid is fully decomposed killing all bacteria and germs which could lead to serious health conditions among citizens. Biochar produced is used in agriculture due to its nutrient-rich environment which creates the best conditions for plants to grow as well as leaving high yield in terms of quality and quantity behind.
For many years, the syngas generated from this method were seen as the only drawback since it includes mainly carbon dioxide, carbon monoxide, nitrogen compounds, hydrogen, methane, etc. There were situations where it led to respiratory diseases or a high probability of explosion raising concern among citizens and authorities (Ryczkowski, n.d.). However, for the last few decades, syngas have been converted into methanol, diesel, or many other products which may be directed to various businesses to use as a primary need prohibiting its direct release into the air. One of those ways is syngas fermentation where biological microorganisms including bacteria are naturally capable of consuming CO, CO2, and H2 to produce organic compounds such as ethanol, butanol, and acetate. Those are actively used in chemical
feedstock where they can be intermediate to produce other compounds or as a form of biofuel which is environmentally friendly as well as beneficial in implementing the Sustainable Development Goals (SDG) into real-world practices (Microbiology of Synthesis Gas Fermentation for Biofuel Production, n.d.). The other method is Fischer-Tropsch synthesis where syngas compounds may continue the process halfway through to produce diesel, kerosene, and naphtha which are essential in promoting green energy as well as global transportation and many other daily uses. (Syngas: What Is It, How Is It Made & Where Is It Used?, 2023)
Pyrolysis presents a promising solution for transforming waste into valuable products, supporting sustainable agricultural practices, and reducing environmental impact. By harnessing this technology, we can advance towards a more sustainable and efficient future.
Conclusion
In conclusion, through the 5 methods listed above obtaining two main products: fertilizer for agricultural purposes and renewable energy as a form of biofuels have been discussed. The methods: of air drying, composting, aerobic digestion, anaerobic digestion, and pyrolysis all have benefits as well as limiting factors. Those include pathogenic bacteria activation once the process is done leading to serious respiratory illnesses among citizens in the first three methods, air drying, composting, and aerobic digestion even though some of the methods are financially affordable. The next method which is anaerobic digestion is suitable in all terms, predominantly eliminating all bacteria and producing methane, and biofuel, however, it is not appropriate for Uzbekistan due to extreme weather conditions which may lead to an explosion of the methane tank. The last method, pyrolysis, is more suitable for our country since all pathogenic bacteria are killed due to high temperatures in pyrolysis plants. Moreover, it produces biochar which has pores, extending the surface area for nutrient and water absorption increasing soil fertility. Also, it is affordable as well as effective in comparison with the remaining alternatives.
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