The Use Of Sewage Sludge As A Fertilizer Environmental Sciences Essay

Fertilizers necessary for the maintenance and increase of soil productivity are classified into two categories: 1) organic fertilizers consisted of crop residues, sludge and manure, and 2) inorganic fertilizers which are synthetic fertilizers consisted of 3 key elements: nitrogen, phosphorous and potassium (Merrington, 2002).

Organic Fertilizers

Sludge

Sewage sludge also known as bio-solid is the remainder product of domestic or urban waste water cleaning at waste water treatment plants. It has high levels of organic content as well as plant nutrients. Although it would make a good fertilizer, the pollutant capability of sewage sludge is high as it is also composed of industrial waste (Merrington, 2002).

The process where sewage sludge or materials obtained from it are sprayed, injected or spread on land is defined as land application. It is applied on or below agricultural land surface, forests and lawns because it is high in nutrient content and can enhance soil quality (EPA, 1994).

In addition, it serves as a fertilizer supplying the necessary nutrients for crops and other vegetation. Sewage is applied in bulk meaning in large amounts by commercial and municipal appliers for various purposes such as agriculture, golf courses and recovery of mining sites (EPA, 1994). In sites such as mining sites which are completely destroyed and barely have soil substrate for vegetation, nitrogen and organic material content need to be higher than normal level before the site is seeded. For the use of sewage sludge in home gardens or lawns, it is available in a bag or small container intended for small-scale use (EPA, 1994).

In the use of sewage sludge, it is crucial to keep in mind the negative impacts it can have if not utilized properly. Nitrates which are easily soluble and have high potential for contamination make up majority of the sewage sludge components (EPA, 1994). As a result, great care is taken in its application and the applier as to fulfill requirements set by the government. Although sewage sludge is applied on land to enhance quality of soil, it is also used as a technique for disposing land (EPA, 1994). Sewage sludge is supplied by water companies for famers to use on their land. Although it contains toxic elements, it still has beneficial effects. According to a study done, farmers who use sewage sludge as fertiliser have a saving of 15 million pounds yearly as it contains high levels of nitrogen and phosphorous as well as necessary micronutrients. In addition, it enhances the structure as well as water retention capacity of soil through the organic matter it supplies (Stout, 1979).

Usage of sewage sludge as a fertilizer is not a concept that is applied in many regions of the world. Although before application of sludge on land, it undergoes treatment such as anaerobic digestion to have low pathogen count it still contains potentially dangerous contaminants such as copper, cadmium, zinc, PAH’s and PCB’s. The amount of contaminants present in sewage sludge is dependent upon the source of the sludge (Merrington, 2002). Toxic metals forming a large component of sludge is a well known fact however, the level at which those metals become harmful is the point of debate (Renner, 2001). As a result, some countries are becoming more restricting or banning to protect the health of individuals.

Research compiled indicates that individuals who live in areas within 1 km of land-application sites have been found to show irritation of the eyes, throat, skin and lungs preceding exposure to wind from fields that have had sludge applied. It was found that Staphylococcus aureus was the bacteria involved in the irritations observed on exposed individuals. Although sewage sludge may be low in pathogen count, it is crucial to take into consideration possible interaction of pathogen with chemical contaminants and as a result becoming unsafe for the health of individuals (Lewis, 2002).

Manure

Manure is composed of three key elements; nitrogen, phosphorus and potassium. These elements are a necessity for the growth of plants as well as the enhancement of soil quality through increasing organic matter and water-holding capacity. In addition, acidity is neutralized and compaction is reduced. Manure serves as a great substitute for synthetic fertilizers whose prices increased dramatically in the recent years (MacDonald, 2009). Land application of manure is possible either by grazing animals or transportation from manure storage facilities. Study found that nitrogenous commercial fertilizer doubled in prices in the 2000- 2007 timeframe and then increased again by 62% in between December 2007 and September 2008. Moreover, phosphate commercial fertilizer prices have increased by 115% in the 2000- 2007 timeframe followed by 177% increase between December 2007 and September 2008 (MacDonald, 2009).

Although those high prices make manure more appealing, there are limitations that come along with the use of manure. Manure transportation is pricey even if it is not transported very far. (MacDonald, 2009) In addition, manure may not be composed of the exact combination of nutrients required for the growth of specific crops or fields. Moreover, waste that can be transmitted through runoff of nutrients, pathogens and organic matter from land to surface water pose great environmental as well as health risks. Leaching of nutrients and pathogens to ground water, volatile gases and odours contaminating the atmosphere are additional problems faced (MacDonald, 2009).

According to the regulations, industrialized livestock production cannot concentrate manure on limited acres as that would exceed the acceptable limits. As a result, it becomes necessary to distribute manure into larger land which in turn requires better transportation as well as application techniques. Storage of manure before it is applied on land can result in problems such as flooding, manure odour and seepage (MacDonald, 2009).

Inorganic Fertilizers

Nitrogen

Nitrogenous fertilizers are a result of combining atmospheric nitrogen with hydrogen to yield final product ammonia. Ammonia is the base found in at least 90% of fertilizers. It is found in the U.S.A. 38% of the ammonia produced is used for fertilizers while the remaining is utilized for the production of Urea. Urea production has increased over the years with an 11% increase from 1967 to 1973 and has become reliable nitrogen source. Hydrogen required can be obtained from varied sources such as natural gas, fuel oil, coal, naphtha and hydrolized water (Stout, 1981).

The following chemical equation represents formation of nitrogenous fertilizers

2N + 3H2 – – -> 2NH3

There is a continuous increase in the use of inorganic fertilizers despite the fact that they require large quantity of energy to produce. Table 11 below displays the use of oil and natural gas for nitrogen fertilizers worldwide. Developed countries utilized approximately four times as much oil and natural gas for nitrogen fertilizer in 1975 (Stout, 1981). Research has shown the greater use of fertilizers in the developed nations has increased yields per hectare.

Phosphate

Phosphate fertilizers are produced by the use of phosphoric acid, sulphuric acid or nitric acid to decompose phosphate rock. If nitric acid is used further treatment with ammonia is required for it to be utilized as a fertilizer. Although there is lots of phosphate rock available, there are environmental problems associated with mining of those rocks for the production of fertilizers. The sulphur necessary for carrying out the process is obtained from ore-deposit or a by-product of other process. Use of sulphuric acid is very efficient but has the downside of producing large amount of sulphate waste resulting in environmental problems. In addition, world reserve of ore is being depleted and obtaining sulphur from the by-products of other processes is very costly (Stout, 1981).

Research shows there is a minimum of 90 * 10^8 metric tons of phosphate rock found in the world and because production in 1972 was only about 13* 10^6 metric tons, there is no concern that phosphate reserves will be diminishing for a while. However, there are environmental problems associated in the mining of phosphate rock such as temporary demolition of land and soil erosion (Stout, 1981).

According to the table below it can be seen that phosphate recovery is relatively cheap in North America and Africa followed by Europe while obtaining phosphorous from region such as Oceania, South America and Asia is more costly.

Potassium

Potassium is the 7th most abundant element in the world and is widely dispersed throughout the world. It is found in soils, rivers, lakes and rocks. Studies have shown that 95% of potash required for production of potassium fertilizers is obtained from underground mines where deposits are 3, 000 feet below the surface in Saskatchewan and 2,500 feet below the surface (Production and Use of Potassium, 1998). There are potassium deposits that are isolated in few parts of the world. Canada, Germany and U.S.S.R. are the top three countries with the highest level of potassium resources. Consumption of potash has exceeded demand over the years (Production and Use of Potassium, 1998). However, research shows that will change in the future and Canada having high potash resources is willing to increase production to meet demand requirements (Stout, 1981). The following table depicts potash distribution in various regions of the world with Canada having the highest in mine production as well as reserve base.

Comparisons Between Organic and Inorganic Fertilizers

Manure Versus Inorganic Fertilizers

Organic and inorganic fertilizers both have their advantages and disadvantages. The following table compares the nutrient content of manure and inorganic fertilizer. It is observed that the level of nitrogen, phosphorous and potassium are significantly higher in fertilizer as opposed to manure. Animal and human excrements contain lower levels of the key 3 elements required for growth. The nutrient content of animal excrement is variable and is dependent upon factors such as type of species and the type of nutrient of feed (Stout, 1981).

Sludge Versus Inorganic Fertilizer (Nitrogen Fertilizer)

Many studies have been done to test the effect of sludges, synthetic fertilizers and manures on the final yield of crops. Given the same level of water and nutrients, the use of sludges, fertilizers or manure did not have any large impact on crop yield. However, in the long term, due to the presence of micronutrients in sludges, there is potential for damage if metals such as copper, nickel and zinc accumulate (Harrison, 2003).

A study was performed to determine the amount of bio-solids necessary to replace nitrogen fertilizer. Different rates of sewage sludge and nitrogen fertilizer were applied in 6 different farms through discing a technique used to turn and loosen the soil in order to prevent the loss of ammonia – nitrogen as much as possible. It is important to apply other nutrients to all areas to ensure nitrogen as the only limiting nutrient (Binder, 2009).

The above graph shows that sites receiving more sludge (site four and six) had higher yields in comparison to sites that received nitrogen fertilizer. It can be observed that there was minute response to nitrogen fertilizers in all three sites. Results can be explained by the presence of nutrients found in sludge that are not present in nitrogen fertilizers (Binder, 2009).

Advantages and Disadvantages

Advantages of organic fertilizers

Rapid decomposition of organic fertilizers makes nutrients highly available. Organic fertilizers are bulky and readily available. Energy is not directly needed in the manufacturing process and they are highly renewable. In addition, they also have little direct cost and provide a method to dispose waste. Although they don’t have high amounts of the three key elements they have other minerals that are not found in synthetic fertilizers that contribute in increased water retention capability of soil, its structure and its resistance to erosion. (Morris, 2007)

Disadvantage of organic fertilizers

Organic fertilizers are not very high in nutrient and analysis of components is not very precise. Decomposition of organic material cannot be controlled as it is dependent on temperature and soil moisture. This results in the release of nutrients when they are not needed. It is very difficult to meet necessary nutrient levels for crop growth solely through the use of organic fertilizers. Waste from humans and animals consist of disease causing microorganisms and therefore need to be disposed of safely (Morris, 2007).

Advantage of inorganic fertilizers

Inorganic fertilizers on the other hand are very high in nutrient concentration and transportation of handling is fairly easy. In addition, it is analysis of content is very precise and can utilize waste from other manufacturing process (Morris, 2007).

Disadvantage of inorganic fertilizers

Inorganic fertilizers have increasing cost and are produced from finite resources. It requires large use of energy for manufacturing. Unlike organic fertilizers, availability is dependent on production, cost and region. Moreover, inorganic fertilizers create waste in processing. Although both organic and inorganic fertilizers contribute to water pollution, the manufacturing process of inorganic fertilizers alone results in water pollution. Nitrates pose a big threat due to the increased algae growth in lakes and water supplies. Phosphate fertilizers also have fluorides and sulphur oxides as a by-product (Morris, 2007).

Regulations and Safety

Although animal manure serves as a great fertiliser and soil amendment it has risks associated with it as it can exceed limits resulting in severe environmental problems. To deal with these problems government has ensured to have regulation and conservation programs. In some states there have been lawsuits initiated against livestock operations as a result of damaging water resources from manure (MacDonald, 2009).

To meet the requirements of those regulations the livestock operations have to deal with increased costs and as a result it is predicted there will be changes made to manure use. Prices are dependent on the excess manure that needs to be disposed. In addition, if farmers are not willing to take in manure for use in their cropland livestock producers must transport the excess manure farther to use for their crop (MacDonald, 2009).

It is absolutely necessary to ensure that sewage sludge applied does not cause any harm to the environment or humans. To ensure safety, requirements that must be met before application have been prepared although they differ from region to region. The following table presents the requirements set by Maryland Department of Environment for application of sewage sludge (O’Malley, 2009).

In addition, acceptable maximum concentrations of contaminants found in sludge to be applied in land have also been set by the NYSDEC. Cumulative limits represent the maximum level of chemical that can be applied in land repeatedly and over time. The following table displays acceptable limits for various types of contaminants (Harrison, 2003).

Restrictions set by NYSDEC for applying Class B sludge’s makes certain that appliers obtain permits specifically for the sites they want to utilize which also includes acceptable limits of contaminants. Nitrogen levels should also not exceed limits. A mandatory waiting period of 14 months in the case of above ground crops and 38 months in the case of below ground crops have been set by NYSDEC. It is recommended that appliers check with their local regulations as it may vary from region to region (Harrison, 2003).

Conclusion

In this section we have talked about how organic fertilizers are compared to inorganic fertilizers, including the advantages and disadvantages of each. Sewage sludge is categorized as an organic fertilizer. It is a good fertilizer because of the amount of nutrients it contains. However, regulations are made to ensure that its application is safe to us, animals, and the environment because sewage sludge also contains many dangerous contaminants.

In Conclusion

The purpose of this report is to provide information about the compositions, the treatments, and the applications of sewage sludge. Sewage sludge comes from wastewater filtration and is often perceived as environmental waste that needs to be eliminated. However, sewage sludge can be used as a fertilizer in agriculture because of the nutrients it contains. The only downside is that sewage sludge also contains many toxic and dangerous substances that must be limited or removed before it can be safely used. Many treatments were developed to limit these toxins and pathogens. Government also made regulations on the applications of sewage sludge to protect the environment. Overall, sewage sludge plays a role in our life and environment. Understanding the importance of sewage sludge makes us appreciate its existence as more than just a mere waste.

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