Sewage Sludge Applied to Agricultural Soil
Sewage Sludge Applied to Agricultural Soil
The increase in population, urbanization, and industrialization in the world has resulted to increased levels of waste products that the relevant authorities have to deal with to prevent the adverse effects associated with these waste materials. In most cases, the local governments in most towns have constructed sewerage systems with consolidating the waste product in one region for treatment and recycling of wastewaters. The recycled water is reused again for domestic purposes by the city and town dwellers during the by-product of treatment, sludge may be used for other purposes majorly in agriculture. Sewage sludge may be defined as the semi-solid residuals produced as a by-product during sewage treatment of industrial or municipal wastewater. This paper will explain the sewage sludge applied in agricultural soil, its economic benefit, merits, and demerits.
Due to the increasing amount of sewage sludge over time, industries and municipals have adopted various methods of disposing of the sludge. According to Saabye (1997), the various method used for disposing of the sewage sludge included; land-filling that has been the major method in Europe constituting about 50-75% while the remaining percent has been disposed of in Agricultural lands. The latter method has been encouraged since it is the modest way of recycling the waste although incineration has been viewed as the worst procedure due to high levels of pollution. When the wastewater arrives at sewerage treatment plant, it passes via physical, biological, and chemical a process that purifies the wastewater and eliminates the solids that are termed as sludge (Fao, 2015). Due to the foul smell in the solids, the pH of the solids is raised remove the odor using lime and the wastewater is sanitized to control the pathogens in solids.
Since the wastewater in the sewage is a composition of large effluent from industries, households, and run-off, the sludge may contain heavy metals that might be toxic to plant and human health. Therefore, EU countries have been restricted on the use of the sludge in agricultural activities until tested for the chemical composition. To utilize safely the sewage sludge in agricultural soil, the raw sludge must undergo the treatment and processing to form Biosolids. According to United States Environmental Protection Agency (2012), Biosolids are the resulting materials after the treatment and processing of the raw sewage sludge that contains organic nutrients. These left over are applied as fertilizers in agricultural fields after they have been ascertained to be within the regulatory requirement.
The uses of treated sewage sludge, Biosolid, have various economic benefits. Since the Biosolids contains essential minerals such as nitrogen, phosphorous and various micronutrients, it has greatly reduced the cost the farmers would have incurred in purchasing the fertilizers with all these nutrients. Additionally, Biosolids fertilizer is cheaper compared to inorganic fertilizers and readily available to the farmer. Therefore, they have significantly led to a reduction in production cost of crops, which have enabled the produce to compete effectively in the market. Also, the use of Biosolids has improved the yield of some crops which has resulted to increased revenue due to increased sale of the produce. In addition, the improved yields have enabled farmers t export the produce to other countries at relative prices that have helped the country in the balance of payment.
Moreover, application of treated sewage sludge in agricultural fields has helped in reducing the cost of disposing of the by-product of wastewater. In the past, most European countries were disposing the sludge in the ocean, abandoned lands, and landfill disposals among others that were environmentally unfriendly (Saabye, 1997). Due to increasing level of waste, these methods proved expensive in term of transportation of sludge and management. Therefore, treatment of sludge for application in soil was a cheaper an environmentally friendly alternative of disposing of the by-product that has greatly reduced these costs. Furthermore, since the governments used to set aside a huge amount for rehabilitating the damaged environment, this money has reduced and hence being utilized in another sector for the growth of the economy.
Due to continued reduction in utilization of inorganic fertilizers by the farmers, the governments has benefited due to the reduced importation of chemical used for manufacturing these fertilizers. This is essential in the economy for the balance of trade between imports and exports. Similarly, the applications of sewage wastes in agricultural soils have saved the government and municipal funds that could have been used in the purchase of land for disposal of sludge. This has allowed these authorities to utilize these funds in other sectors that could benefit the farmers. Furthermore, due to the reduced cost of production and increase in output, the agriculture sector has attracted many individuals hence reducing the level of unemployment in the country.
Treated sewage sludge also has other benefits apart from an economic perspective. According to Bishop (1995), disposal of sludge in agricultural soil has greatly aided in the reduction of minimization of energy utilization and air pollution. This is because some of the methods used in the past such as incineration heavily polluted the air. He also claimed the land application of sludge has reduced other pollution threat such as water pollution as well as protecting the aquatic life. This is because municipals used to dispose of by-product in oceans or other coastal waters that are the habitat of marine animals. The other benefit is that application of sludge in the soils over time has improved the soil properties. According to Roig, Marti, Nadal, Sierra, Schumacher, and Domingo (2012), sludge enhances soil acidity, nitrogen levels, organic carbon measures, organic matters, and other microbial activities in the soil. Consequently, this has improved some soil structures regarding aeration, permeability, as well as water holding capacity.
In addition, enhanced soil structure has an advantage of minimizing the risk of soil erosion that is highly contributed by surface run-off. Another merit is that sewage Biosolids are readily available at a considerable price. Since the wastewater has been increasing due to growth in urban migration and increase in industrial activities, the amount of sludge has also increased hence benefiting the farmers with both small and large-scale production. Also, the transportation of Biosolids to the farms is cheaper as compared to the primary untreated sludge that is more fluid and has a bad smell.
However, before application of the Biosolids in agriculture soil, several measures must be adhered to obtain the permission to use the sludge. The factors that are required to be fulfilled include the following; first, the soil must be within the required buffers in areas around the stream and wells. Secondly, the composition of metal and nutrients in the Biosolids must be with the specifications of EU policy. Thirdly, the farmers or gardeners have to produce the test results of the soil in their farms. This aids in determining the level of nutrients and metals already in the soil to avoid increasing them to toxic levels that might affect plant or even human health. The test results are accomplished by calculation of the right agronomic rate. Lastly, the farmer must exhibit the calculations of the amount of Biosolids to be applied in each specific field and maintain the records of the amount of Biosolids that has been on those fields. These records will assist in determining the accumulation of nutrients and other metals in the soil for safety control.
Nonetheless, although the sewage sludge has a wide range of benefits, it has several disadvantages that should be looked into. According to Gaskin, Risse, Segars, and Harris (2012), these demerits may be categorized with respect to odor, availability of specific metals, pathogen concerns and the risk of over-application of some nutrients. First, although treated and processed, Biosolids may also have a foul smell with may be an issue of concern to the public. However, to curb this issue, some techniques have been employed to reduce these odors. They include; use of buffer vegetation, Biosolids incorporation in the soil, timely planning of the application, etc. Secondly, some metals in the sludge may be of quantities hence toxic to plants, animal health, and even the human health. In pursuit of mitigating the risk, the 503 regulations by EU has set the maximum limit to be complied with during the application of the sewage sludge to reduce the risk. Thirdly, over-application of Biosolids can lead to increase in levels of some nutrients, which can contaminate surface and underground water. For instance, excess phosphorous can and nitrogen. Therefore, the application of nutrients should be limited to requirements of plants and soils. Lastly, there may be some pathogens causing diseases in the Biosolids. The presence of the pathogens can be reduced by extensively treating the sludge (Gaskin, Risse, Segars, & Harris, 2012).
In conclusion, it is clear that as the population of the world is growing exponentially, the way to curb the increasing wastewater from urban centers and industries can be utilized effectively and in an environmentally friendly manner. After recycling the water, the by-product of treatment that used to cause the problem to many municipals can now be utilized to make fertilizers that have benefited the farmers in the agriculture sector. After treatment of the sludge, it has become economical to apply the Biosolids to the farms hence reducing the cost of its disposal and consequently reducing the cost of production of farm produce. Additionally, this alternative disposal of sewage sludge has reduced pollution in air and water that have been a major problem in the past methods of disposal. However, caution should be taken in the application of Biosolids to reduce the chances of the pathogen, over-application of some nutrients and metals that may be harmful to plant, animals, and even human beings.
Bishop, P. (1997). Municipal sewage sludge: Management, processing, and disposal. Boca Raton: CRC Press.
FAO (2015). Agricultural use of sewage sludge. Retrieved from http://www.fao.org/docrep/t0551e/t0551e08.htm#6.4%20effects%20of%20sludge%20on%20soils%20and%20crops
Gaskin, J., Risse, M., Segars, B and Harris, G. (2012). Beneficial Reuse of Municipal Biosolids in Agriculture. Retrieved from http://extension.uga.edu/publications/files/pdf/SB%2027_3.PDF
Roig, N., Sierra, J., Martí, E., Nadal, M., Schumacher, M. & Doming, J. L. (2012). Long-term amendment of Spanish soils with sewage sludge: Effects on soil functioning. Agriculture, ecosystems, and environment, 158, 41-48.
Saabye, A. (1997). Sludge treatment and disposal: Management approaches and experiences. European Environmental Agency, 7, 1-54.
United States Environmental Protection Agency, (2012). Water: Sewage Sludge (Biosolids). Retrieved from http://water.epa.gov/polwaste/wastewater/treatment/biosolids/genqa.cfm