• Earth is a crucial source of natural capital including essential metals, fuels, and plant
nutrients.
• These earth resources are used in various natural and human processes.
• Earth is also an important repository of wastes enriching soil fertility.
• Unfortunately, recycling process is not uniform around the globe.
• In some locations, waste is accumulated creating hazardous environment. Whereas, some essential nutrients are deprived requiring the addition of synthetic chemicals such as agrochemicals.
• Leaching of hazardous substances from the accumulated wastes contributed to degrade the soil fertility and threatens the existence of different forms of life Sources of soil pollution
Household wastes
• Includes the food waste, human excretes, waste water, garden debris, plastics Agrochemicals
Pesticides
• Pesticide is a substance used for controlling, preventing, destroying, repelling or mitigating any pests. There are two main classes of pesticides used.
Natural pesticides
• Neem (Kohomba) extract is an example for a natural pesticide.
Synthetic pesticides.
• The main types of pesticides used are weedicides and insecticides.
• Weedicides (weed killers) kill plants that would otherwise compete with crop for light and nutrients.
• Insecticides kill insects that would damage the crop.
• Insect pests can reduce the yield in two main ways. They might eat the part of the plants that the farmer wants to harvest. By damaging leaves they reduce photosynthesis which affects the food production.
• Insecticides used against insect pest are of three types (Based on their action).
Three main groups of synthetic insecticides are known.
• Chlorinated hydrocarbons – eg. DDT – (Dichlorodiphenyltrichloroethane).
• Organophosphorus – eg. Melathion.
• Heavy metal salts – eg. Copper dithiocarbomates.
An ideal pesticide should have the following properties
• Should kill only the target pest.
• Should biodegrade easily in the environment or soil water system.
• The pest should not develop any tolerance to the pesticide.
• Should be cheap, abundant and non-toxic to humans.
Problems of using pesticides
• Pesticides can be deposited on our food. They can harm people as well. If the dose is
large enough it could poison us.
• Bio accumulation of persistent pesticides leads to concentration at each level of the
food chains. The concentration at the end of the food chain may reach very high levels.
• They damage the environment. Pesticides often kill harmless or even beneficial species as well as pests.
• Pests can become resistant to pesticides over a period of time. Repeated use of same
pesticide increases the resistance to it through natural selection. Then the pesticide becomes less effective. Natural predators are killed by the pesticide. This may cause a worse outbreak than before.
L.D. value – Lethal dose value LD50.
The chemical dose needed to kill 50% of the population of one species under test is called LD50
Fertilizers
• Fertilizers make plant grow faster because they give the plant essential minerals and
nutrients. eg. NPK
• The most important mineral ions are nitrate, phosphate and potassium. But there are
some trace elements needed in small amounts. NPK content of a fertilizer is expressed as N%, P2O5 %, K2O%.
There are two main types of fertilizers. Each has its own advantages.
• Natural fertilizers are organic matter. They include manure, sewage and sludge.
• Natural fertilizers supply a wide range of nutrients and release them slowly with long lasting effects. They are less harmful to the environment and are suitable for “organic” farming.
• Natural fertilizers are cheap.
• Natural fertilizers can improve the soil structure (texture).
• Natural fertilizers are expensive to transport and to apply and might not have ideal balance of nutrients.
• Artificial fertilizers are inorganic. They contain pure chemicals (eg. NH4NO3) as powders or pellets.
• Artificial fertilizers are fast acting and easy to transport and supply.
• Artificial fertilizers can be used to target particular mineral ions needed and the amount of each mineral supplied can be accurately controlled.
• Artificial fertilizerscan affect the balance of the soil and are more easily washed out of the soil leading to eutrophication of surface water bodies.
• Artificial fertilizers can affect the quality of ground water.
eg. Nitrate content.
Heavy metals
• Used and scrapped metals, used equipments, vehicles
• Heavy metals are leached in to drinking water and contaminate soil
• Uptake of heavy metals through drinking or food can cause numerous health problems
• Heavy metals such as lead can accumulate in body lowering the intelligence e-waste
• The term “e-waste” is used to identify all the waste originated from electronic and
electrical equipments and related accessories including used or outdated computers,
electronic equipments, mobile phones, televisions, sound systems, CFL bulbs, electric
and electronic accessories.
• The impact of e-waste has already witnessed by the developed countries and they are
attempting to mitigate the problem by dumping them to poor countries.
• Rapid technology change, low initial cost, high obsolescence rate have resulted the ewaste to be the fastest growing problem making yesterday’s electronic dream machines to become today’s environmental nightmare.
• The average obsolescence rate for a computer is estimated to be 7 years, and it is 15
years for a television or a refrigerator or a washing machine while a mobile phone has a life span of 1.5 years only.
• Common list hazardous chemicals from e-waste include metallic lead (in batteries, circuit boards, cathode ray tubes in TV), mercury (in thermometers, thermostats, discharge lamps, sensors, relay and switches), cadmium (in batteries, mobile phones), beryllium(in computer, telecommunication equipments, and automotive electronics), arsenic (inlight emitting diodes), polyvinyl chlorides (in computer casings and cables),
polychlorinated biphenyls (in transformers)
• Also form hazardous fumes upon burning the PVC containing e-waste.
3R Systems (Reduce, Reuse and Recycle)
• Reduce, Reuse
Most effetive way to reduce waste is to not create it in the first place. Making a new
product requires a lot of materials and energy: raw materials must be extracted from theearth, and the product must be fabricated and then transported to wherever it will be sold.As a result, reduction and reuse are the most effective ways you can save natural resources,protect the environment and save money.Using as raw materials for the other productions
• Solid wastes can be used to produce various materials.
• Chromium wastes in a tannery effluent can be precipitated as Cr(OH)3 using MgO and is reused in all leather tannery processes.
Using as raw materials for energy generation
• Dry garbage is a fuel. In Sri Lanka about 80% of the garbage is organic material. They
can be converted to obtain energy.
(CHO)n + O2(g) → CO2(g) + H2O(g) + heat
Heat can be used in industries .
• Recycling
Recycling is the process of collecting and processing materials that would otherwise be
thrown away as trash and turning them into new products. Recycling can benefit your community and the environment.
• Many countries have established the recycling of domestic and industrial waste water.Since a large quantity of ground water is used by some industries in Sri Lanka, it is important to encourage them to reuse the water in the same industry. Since the composition of garbage in Sri Lanka is over 80% organic matter, the solid waste can easily be used as a fuel to generate electricity.
• Metals are valuable resources. Instead of burying metal waste it makes sense to collect it and recycle the metals. There are two savings, for instance when scrap iron is collected, melted and re-used, it saves earths reserves of iron ore. In addition the energy required to mine ore, transport it and smelt it is several times greater than the energy required to recycle scrap iron.
• Glass, paper and plastic also can be recycled.
• These materials can be recycled if they are collected and separated at the sources.
Benefits of the recycling process
• Saving in energy
• Saving in natural resources
• Saving in refuse disposal costs
• A source of income for local authorities
• Composting
Fresh plant biomass has a C:N ratio of 100:1. Organic matter is decomposed in solid by
bacteria and fungi (microorganisms) to form humus with a C:N ratio of 10:1. If the C:N ratio of the organic matter in the soil is too high, nitrogen may be the limiting factor in the growth of organisms which decompose organic matter and recycle nutrients. If straw (C:N=80:1) is ploughed in to the soil, a nitrogenous fertilizer is usually applied to lower the C:N ratio.
Composting can be used to reduce the C:N ratio. Storing organic matter in a compost pile with moisture and air allows carbon dioxide and water to escape, while nitrogen is retained as amino acids and proteins of microorganisms. Adding fertilizer to compost increases the population of microorganisms and speeds composting.
• Biogas production
Biogas typically refers to a gas produced by breakdown of organic matters in the absence of oxygen. Organic waste such as dead plants and animal materials, animal feces, and kitchen waste can be converted into a gaseous fuel called biogas. Biogas originates from biogenic material and is a type of bio fuel.
Biogas is produced by the anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green wastes, plant material and crops.Biogas comprises primarily methane, and carbon dioxide and may have small amounts of hydrogen sulphide, moisture, etc.
• Incineration
The incineration of waste needs a temperature at which complete combustion of oxidisable material will occur and ash, glass, metal and other materials remain. A temperature of 770-970 0C is used. In many incinerators the heat of combustion of the waste is used to help to maintain the temperature. It is always recommended that the solid wastes from hospitals should be subjected to incineration.
