Questions And Answers On Hazardous Wastes Environmental Sciences Essay

Explain what is meant by a ‘secure’ and a ‘sanitary’ landfill. What advantages to they have over open pit landfills? Landfills which are disposing of hazardous waste on land can either be classed as secure or sanitary. A secure landfill is where a liner that may be either a permeable clay or plastic is used. This prevents leakage from occurring (notes ref). This type of Landfill is monitored to make sure that the surrounding ground water is not severely impacted on.

A Sanitary landfill is a different type of landfill. This landfill is where waste is ‘compacted and then covered daily’ (notes ref). By doing this it prevents odours from being released into the environment and also minimises any health issues. A disadvantage is that groundwater contamination may occur if there is leakage, nevertheless a large amount of waste can be disposed of using this method (Bank, 2000).

An open pit landfill is practically a large hole in the ground which is filled with rubbish (Answers.com, 2010). Sometimes the pit is lined with clay (Answers.com, 2010). The advantages a secure and sanitary landfill has over open pit landfills are that they do not provide breeding grounds for insects and rodents which may affect the surrounding environment (Centre, 2010). Due to the exposure open pit landfills have to the environment, they create air pollution, and they may also contaminate ground water and create run off pollution (Centre, 2010).

Question 2 What is ‘fixation’ when applied to pre-treatment of wastes going to landfill. Why is it applied? What would be an appropriate fixation method for an aqueous waste contaminated with lead?

When hazardous materials are disposed of in landfills it must be ensured that these materials are safe (notes ref). If they are not they may require pre treatment. If the unsafe material ‘dissolves and escapes from the landfill site it may contaminate groundwater’ (notes ref). In order to prevent this, immobilisation techniques can be used. These techniques are also called fixation. Fixation is a technique that prevents leachate from escaping the landfill site (notes ref). As previously stated it is used to ensure that groundwater is not contaminated.

An appropriate fixation method for an aqueous waste contaminated with lead is using phosphate rocks (Qi Ying Ma, 1995). Phosphate rocks react and immobilise the lead in the aqueous solution (Qi Ying Ma, 1995).

Question 3 What types of waste can be discharged to the sewer? What restrictions need to be put on these discharges? Why are restrictions necessary?

Usually biological waste is disposed of in the sewage system, however ‘industries can be licensed to discharge to the sewer’ (notes ref). Other types of waste that can be discharged into the sewer must be types of waste that will not block the system nor cause harm to the environment. There are parameters that restrict the amount of discharge that occurs daily and also the actual properties of the waste determine whether it is suitable to discharge within the sewage system. These restrictions include things like the pH levels of the liquid waste, temperature, mercury levels and other contaminant levels (ref notes). This is done to ensure that the sewage system does not transport this substance to an environment where it will harm humans or damage its surroundings.

Question 4 A rotary kiln is one type of incinerator used for wastes. Describe the operation of a rotary kiln. What kinds of wastes can be treated using this process?

A rotary kiln rotates about its own axis and has material fed into the kiln, which is a cylindrical body (Wikipedia, 2010b). Material is fed into the kiln where it is incinerated within the chamber. The waste is fed in at the highest end of the cylinder and slowly travels through the chamber to experience higher temperatures (Group, 2010). At the bottom of the kiln the waste that has been incinerated is removed as ash. It must also have a static post combustion chamber to ensure that all of the flue gases are treated before releasing them into the atmosphere (Group, 2010).

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A vast variety of wastes can be treated using this process. Some of these types of waste are liquids, solids and fumes, as long as they are properly incinerated and undergo post treatment to ensure flue gases released will not harm the environment (Advameg, 2009).

Question 5 How is cyanide used in the mining industry? Where has it been used? What problems does it cause and how can cyanide wastes be treated?

Cyanide is used mainly in the gold mining sector. ‘More than 90% of the gold extracted annually is done so with the aid of cyanide’ (Centre, 2009). Crushed rock is sprayed with sodium cyanide solution and this solution helps extract the gold within the crushed rock pile out as it slowly makes its way through (Centre, 2009). Using cyanide allows gold particles too small for human eyes to detect to be collected using this chemical (Centre, 2009). This method has been used all around the world in countries such as Greece, Ghana, USA, Krgyzstan and Guyana (Centre, 2009). This type of solution causes many problems to the environment due to its toxic nature. Methods that can be used for treating cyanide wastes are chlorination, acidification and chemical precipitation (Richard G. Tyler, 1951).

Question 6 Describe what kinds of pre-treatment could be used for aqueous wastes contaminated with oils. What advantages and disadvantages would these methods have?

Question 7 What is the Basel Convention and why was it set up? What is its significance in Hazardous Waste treatment?

The Basel Convention is an international treaty (Wikipedia, 2010a) which was developed by the United National Environment Program (Australian Government; Department of Sustainability, 2008). It was established to monitor and try and prevent “toxic traders” from profiting (Convention, 2005). What these “toxic traders” do is try to find manners in which to ship toxic waste offshore to another nation where they can dump waste for a cheaper price (Convention, 2005). Its significance in Hazardous Waste treatment is that this convention encourages the production of less hazardous waste and also sets regulations onto how hazardous waste is controlled by monitoring its method of disposal (Australian Government; Department of Sustainability, 2008).

Question 8 Describe one method that has been used to dispose of a scheduled waste. If possible, give an example where this method has been applied.

Methods used to dispose of a schedule waste are molten media processes. This type of processing involves such processes like molten metal, molten slag or molten salt (Australian Government; Department of Environment, 1997). One of the processes involving using molten metal has been used in Australia by Molten Metal Technology Inc. (Australian Government; Department of Environment, 1997). ‘The molten metal process is called “Catalytic Extraction Processing”‘ (Australian Government; Department of Environment, 1997). This type of process uses molten metal bath at a temperature above the liquid’s melting point is used to ‘dissociate wastes into their atomic constituents’ (Australian Government; Department of Environment, 1997). The waste is inserted into a reactor usually using oxygen to feed it in. In this reactor lies the molten metal and the waste is fed through the bottom of the reactor (Australian Government; Department of Environment, 1997). It means that using this method only certain types of waste can be disposed of in this method, such as gases or liquids or very fine particles (solids) (Australian Government; Department of Environment, 1997). This type of method was proposed to be established in Botany, however this type of method has been established in Fall River, Massachusetts on a commercial level (Australian Government; Department of Environment, 1997).

Question 9 What are the relative advantages and disadvantages of methods available to remediate contaminated soil (consider only non-biological methods)?

Question 10 What is ‘bioremediation’ and what are its advantages? Are there limitations on where it can be applied?

Bioremediation in a method used to treat hazardous waste. It is a process ‘that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition’ (Ltd, 2005). This process contains various different subgroups of microbes that can be used depending on the type of waste that will be treated. It has numerous advantages, such as being a method that can reach locations that are normally difficult to get to (Ltd, 2005). However this method is not suitable for all situations, such as situations where there is too much moisture and not enough oxygen, or if pH levels or temperature are not within the range needed for this process to occur (Ref notes 2). Competing organisms or toxicity will also greatly influence whether this type of treatment can be employed (ref notes 2).