Composting of bio degradeable waste

Composting is the purposeful biodegradation of organic matter, such as yard and food waste. The decomposition is performed by micro-organisms, mostly bacteria, but also yeasts and fungi.[1] In low temperature phases a number of macro-organisms, such as springtails, ants, nematodes, isopods and earthworms also contribute to the process, as well as soldier fly, fruit flies and fungus gnats. There are a wide range of organisms in the decomposer community.
A biodegradable material is capable of being completely broken down under the action of microorganisms into carbon dioxide, water and biomass. It may take a very long time for some material to biodegrade depending on its environment (e.g. wood in an arid area versus paper in water), but it ultimately breaks down completely. Many contaminating materials not dealt with in common composting are in fact "biodegradeable", and may be dealt with via bioremediation, or other special composting approaches.
Stable bedding after shredding and three weeks of hot aerobic composting.A compostable material biodegrades substantially under specific composting conditions. It is metabolized by the microorganisms, being incorporated into the organisms or converted into humus. The size of the material is a factor in determining compostability, and mechanical particle size reduction can speed the process. Large pieces of hardwood may not be compostable under a specific set of composting conditions, whereas sawdust of the same type of wood may be. Some biodegradeable materials are only compostable under very specific conditions, usually with an industrial process.
Contents [hide]
1 Importance
2 Materials
3 Approaches
3.1 Active (aerobic)
3.2 Passive (anaerobic)
4 In nature
5 Vermicomposting
6 Industrial systems
7 Agriculture
8 See also
9 References
10 External links



[edit] Importance
Composting upcycles organic kitchen and yard waste and manures into an extremely useful humus-like, soil end product, permitting the return of vital organic matter, nutrients, and particularly bacteria, that are vital to plant nutrition to the soil. Managed aerobic composting arranges environmental conditions so they are optimal for the natural processes to take place. There is a popular expression: "compost happens", but it is helpful to engineer the best possible circumstances for large amounts of organic waste to decompose quickly and efficiently, with the greatest conservation of useful nutrients and mass. Uncontrolled composting is when compost "happens", and although that may be functional in some circumstances, as with forest floor detritus, a neglected heap of kitchen and yard wastes will more likely result in "smells happen", or "rodents happen" long before useful compost does.

Long used in subsistence farming and home gardening for creating garden-ready soil, composting is becoming increasingly important and better understood as a tool for reducing municipal solid waste,[4] and reducing the amount of green waste going into landfills. The decomposition of organic material sent to landfills is a principal cause of methane, an important greenhouse gas, making reduction of organic waste being landfilled a key element in the fight against climate change. In suburban and rural areas, much of the organic waste could be removed from the waste stream by promoting home composting, where consumers compost their yard waste and kitchen scraps on their own land, regardless of whether the material is ever actively re-used as "soil".[5] In urban areas with dwellings predominantly lacking individual yard space, there are indoor small scale composting alternatives, such as vermicomposting and bokashi composting.[6]


[edit] Materials

Posters for compost education (European)Composting organisms require four equally important things to work effectively:

Carbon ("C" or carbohydrates), for energy - the microbial oxidation of carbon produces the heat.
High carbon materials tend to be brown and dry.
Nitrogen ("N" or protein), to grow and reproduce more organisms to oxidize the carbon.
High nitrogen materials tend to be green (or colorful, like fruits and vegetables) and wet.[7]
Oxygen, for oxidizing the carbon, the decomposition process.
Water, in the right amounts to maintain activity without causing anaerobic conditions.
Certain ratios of these elements will provide beneficial bacteria with the nutrients to work at a rate that will heat up the pile. In that process much water will be released as vapor ("steam"), and the oxygen will be quickly depleted, explaining the need to actively manage the pile. The hotter the pile gets, the more often added air and water is necessary; the air/water balance is critical to maintaining high temperatures until the materials are broken down. At the same time, too much air or water also slows the process, as does too much C (or too little N).

The most efficient composting occurs with a C:N mix of about 30 to 1. All organics have both carbon and nitrogen, but amounts vary widely, with characteristics noted above (dry/wet, brown/green).[8] Fresh grass clippings have an average ratio of about 15 to 1 and dry autumn leaves about 50 to 1 depending on species. Mixing equal parts by volume approximates the ideal C:N range. Few individual situations will provide the ideal mix of materials at any point in time - in this respect, home composting is like horseshoes, perfect is great, but close still works. Observation of amounts, and consideration of different materials[9] as a pile is built over time can quickly achieve a workable technique for the individual situation.


Home compost barrel in the Escuela Barreales, Chile.Ingredients that are primarily carbon include:

Dry, straw-type material, such as cereal straws and corn stalks
Dry leaves (best shredded, as with a rotary mower, to prevent matting)
Wood, as coarse or fine (may compact) sawdust, or ground wood waste
Paper, corrugated cardboard, box board, and office paper or newsprint (soy-based inks)
Ingredients with relatively high nitrogen content include:

Green plant material, like crop residues, hay (especially alfalfa), grass clippings and weeds.
Manure from poultry, and herbivorous animals such as horses, cows and llamas.
Kitchen waste - fruit and vegetable cooked waste and trimmings, juicing-pulp residue, tea and coffee grounds.
For "back yard" composting, mixing the materials as they are added increases the rate of decomposition, as does reduced particle size (ie, chopped, shredded), or materials can be added in alternating layers, about 15 centimeters (6 in) thick. Keeping a carbon "cache" handy to the pile for covering and mixing with fresh wet additions (lawn clippings, kitchen scraps) is simplest. Special additions or activators are not necessary, although some sprinklings of good garden loam as a first pile is built will aid more rapid working by inoculating it with beneficial soil bacteria, and some of the material from the first finished batch can be used in the subsequent mixes. Agricultural lime is not necessary - the bacteria prefer a slightly acidic pH, and their processing invariably results in a near-neutral product.[10] Seaweed meal, rock dust or rock flour, and other trace element amendments are best added to the finished compost, or directly to the garden.


[edit] Approaches

[edit] Active (aerobic)

An active compost heap, steaming on a cool morning. The heap is kept warm by the exothermic action of the bacteria as they decompose the organic matter.Hot thermophilic composting is essential with some materials, such as meat and other animal products, dairy products, eggs, grease, cooking oil, manure of non-herbivores, and residuals from the treatment of wastewater, in order to kill pathogens; but these materials are not generally recommended in home composting because of the likelihood of creating odors and attracting rodents. Human waste can be composted by industrial methods as well as composting toilets. When high temperatures are reached, the resulting compost can be safely used for agricultural or horticultural purposes, providing local health regulations are met. Humanure fertilizer (as opposed to night soil) is used throughout the developing world and is becoming more accepted as a garden amendment in the developed world.

Hot, aerobic composting is conducted at close to the ideal conditions noted above, allowing thermophilic bacteria to thrive. These aerobic bacteria break down material faster, producing less odor, fewer pathogens, and less greenhouse gas than cool, uncontrolled, or accidental anaerobic methods. Commercial scale composting operations actively control the composting conditions (C:N ration, moisture level and air), usually in a closed environment (in-vessel composting, tunnel composting or aerated static pile composting), where air is fan forced through the mass, and moisture added with sprayers, or conserved via the enclosure, with computer monitored probes detecting conditions.

In Thailand an aerated static pile system is in use by farmer groups at over 400 sites. The process needs only 30 days to finish without manual turning, with 10 metric tons of compost produced per month. A 38 centimetres (15 in) squirrel-cage blower with 2.2 kilowatts (3.0 hp) motor is used to force air through 10 covered static piles of compost twice a day. The raw materials consist of agricultural wastes and animal manure in the ratio of 3:1 by volume.[11]

High temperatures destroy insects, larvae, and weed seeds, but no compost will be totally sterilized by high temperatures alone. In a hot compost where the temperature exceeds 55 °C (131 °F) for several days, the ability of most organisms to survive is compromised, and there are temperature standards[12] set by various regulating authorities for commercial products[13] Nevertheless, many organisms in nature can survive extreme temperatures, including extremophiles such as Thermus thermophilus which play an important role in thermogenic composting,[14] as well as pathogens such as Clostridium. The necessary second stage of hot composting is maturation, a period allowing the dissipation of any phyto-toxins[15] remaining from the process or contaminating ingredients (eg: chemical residues), and achieving a state of nutrient stability (low C:N ratio) that will not have an impact on Nitrogen availability in the receiving soil.[16]


An alternative to manual turning, the "Wing Ding" compost aeratorFor backyard composters, carbon and nitrogen ratios in various ingredients and the calculations required to get the ideal mixture can be intimidating, so rules of thumb exist for approximating it by ingredient types and condition, as mentioned in Materials above. If the pile is built in a short period, and has a good mix of materials (C:N) and a coarse structure, with about 50% moisture ("like a squeezed out sponge"), the temperature should rise within days to as high as 60 °C (140 °F). When the temperature begins to fall, more air is needed, usually added by turning the pile or using an agitating tool, and moisture may be needed at the same time. Turning or other aeration is usually needed about every 6–10 days to maintain the highest heat levels until the material is fairly uniformly broken down to unrecognizability, and temperatures no longer rebound. A pile that has been maintained at peak temperatures may be ready for maturing in as little as 30 days. Another 30–60 days maturing should suffice to allow passing the "germination test".[17]

To achieve thermophilic decomposition, a compost bin is best about 1 cubic metre (1.3 cu yd), or 1 metre (3 ft) wide, 1 metre (3 ft) tall, and as long as desired for windrow composting. This provides enough insulating mass to build up heat but also allows oxygen infiltration. The center of the pile heats up the most, so regular turning/mixing is needed for insuring all material spends some time in the hottest area. When turning the pile results in no further temperature rise, the active aerobic phase is complete, and the mass may be turned out to a maturing pile. When the matured material has a dark brown crumbly appearance and the smell of rich damp earth, it is ready to use.


Turning a home compost binThe natural sequence of the decomposition community involved will be:

0-15 °C (32-59 °F) - psychrophiles predominate, beginning the heating process as they multiply
15-40 °C (60-104 °F) - mesophiles take over, psychrophiles die off or are relegated to the borders
40-70 °C (105-160 °F) - thermophiles work at their peak, including consuming many other bacteria
At the lower temperatures and around the borders, there will also be various fungal activity, as well as larger organisms, getting their share - a very dry, cooler pile may be attractive to ants, and gastropods may visit very wet piles. As the temperature returns to ambient at the end of the process, the sequence reverses, including new organisms that prefer the more degraded materials. Added heat and pile insulation may be useful in the coldest weather, but is not ordinarily necessary, and is not desirable if it interferes with aeration or natural convective evaporation. Keeping the top dry and burying fresh additions in the center of a pile will be effective during winter conditions until heating resumes in spring.


[edit] Passive (anaerobic)
Cool or ambient temperature composting, when the level of physical intervention is minimal, usually results in temperatures never reaching above 30°C (86°F). It is slower but effective, and is the more common type of composting in domestic gardening. Such composting systems may be in open or closed containers of wood or plastic, or in open exposed piles. Kitchen scraps are put in the garden compost bin and left untended. This scrap bin can have a very high water content which reduces aeration, and may become odorous. To improve drainage and airflow, and reduce odor, carbon-rich materials, or 'browns', such as wood chips, shredded bark, leaves, or twigs may be added to mix and cover each wet addition, or holes made occasionally in the pile. The amount of attention may vary from none through occasional to "regular".


[edit] In nature
An unusual form of composting in nature is seen in the case of the mound-builders (megapodes) of the Australasian region. These Megapodes are fowl-sized birds famous for building nests in the form of compost heaps containing organic litter, in which they incubate their eggs. The male birds work assiduously to maintain the correct incubation temperatures, by adding and removing litter from the compost pile.

Forest floor detritus is the natural fertilizing material in temperate forests. Soil dwelling organisms slowly decompose the continuously deposited litter from below, returning the nutrients to the soil for bacterial conversion to forms useful to the native vegation. This is a natural form of mulching or sheet composting. While some may be tempted to gather this rich, partially decomposed litter for use in a home garden, it is best left to the use of the forest.


[edit] Vermicomposting
Worm composting or vermicomposting is a method using Red Wiggler worms in a container to process kitchen waste. Moistened high-carbon bedding such as shredded paper is used as a base to which the food waste is added, and the worms and micro-organisms convert the materials to rich compost called worm castings, a nutrient and microbially rich material. Worm composting can be done indoors, allowing year-round composting, and providing apartment dwellers with a means of recycling food waste.


[edit] Industrial systems
Industrial composting systems are increasingly being installed as a waste management alternative to landfills, along with other advanced waste processing systems. Mechanical sorting of mixed waste streams combined with anaerobic digestion or in-vessel composting, is called mechanical biological treatment, increasingly used in developed countries due to regulations controlling the amount of organic matter allowed in landfills. Treating biodegradable waste before it enters a landfill reduces global warming from fugitive methane; untreated waste breaks down anaerobically in a landfill, producing landfill gas that contains methane, a potent greenhouse gas.

Large-scale composting systems are used by many urban centers around the world. Co-composting is a technique which combines solid waste with de-watered biosolids, although difficulties controlling inert and plastic contamination from Municipal solid waste makes this approach less attractive. The world's largest MSW co-composter is the Edmonton Composting Facility in Edmonton, Alberta, Canada, which turns 220,000 tonnes of residential solid waste and 22,500 dry tonnes of biosolids per year into 80,000 tonnes of compost. The facility is 38,690 meters2 (416,500 ft2), equivalent to 4½ Canadian football fields, and the operating structure is the largest stainless steel building in North America, the size of 14 NHL rinks.[18]


[edit] Agriculture
Compost is an important source of nutrients commonly used in modern agriculture. Through steaming compost can be sanitized and prepared for further use.

INTERVIEW FAQs and their answers

Now that you know what mistakes to avoid during an interview here are top 10 most commonly asked questions during an interview and how to answer them impressively.

1. Tell me something about your self
This is usually the first question you face in an interview. The purpose of this question is to:
a) Put the candidate at ease and b) Initiate a discussion.
The answer to this question should cover a little information about your work experience, educational qualifications and family background. Your answer to this question can help you take the interview in whichever direction you want. The key to this is to put a full stop to your answer at the right place to provoke the second question you want.

2. Why have you applied for this job?

A good way to answer this question in practical way is to talk about the requirements of the job, relate your skills and experience to it. To do this, you need to carefully go through the job requirements and ask yourself how your skills fit into the requirement.
Your CV will be your best companion to identify your skills and match them with the requirements.
It won't be much helpful to talk about the career, progression and the challenges this job offers.

3. Why do you want to leave your present job or why did you leave your last job?

You can switch jobs for numerous reasons which can be you are not happy with your profile, you don't get well along with your boss, the salary they pay is less etc. The key to this question lies in 3Es.
When asked this question, you can simply say : for better prospects in terms of experience, exposure and earnings.
In current market situation, lay offs are common everywhere and owing to them people are looking out for jobs. If this is the case with you, chose your words carefully so that you do not leave an impression that it was only you who was laid off.
You can say something like: As you know, in the current economic situation, almost everybody is trying to cut costs. A lot of restructuring has been happening in my company also over the last X months and finally "Y" jobs were made redundant. One of them was mine. Leave the answer here with out giving too much importance to the fact that you were "laid off". It can happen with anyone and need not necessarily be your fault.

4. What is your greatest strength?

Take this question as "Why should we hire you?"
Sell them a strength or two which they are ready to buy. It can be anything directly related to the requirements of job under discussion.
Identify the qualities the job needs a person to have and how your skills fit into them. To do this you will need to:
· Understand the requirements of the job
· Identify your skills and match the two


5. What is your greatest weakness?

There are three ways to answer this question depending on the environment in which the discussion is going on. Understand the environment and use one of them:
Use your sense of humor and say something cool like "movies". This has to be accompanied by a right body language. This method would work if the discussion is going on in a light environment.
If you need to answer this question seriously offer a weakness which doesn't relate to the job immediately under discussion. It would be foolish to say that "I am slow at taking notes or typing" if you are applying for a secretarial job.
If you have applied for a job in marketing and you do not know cooking properly, you can say something like I have been using a microwave since last two years but I still can't bake a good cake.
Turn your weakness into your strength: frame your words in a way that they convey, others accuse you of having this weakness but you actually treat it as your strength. For example: my friends accuse me of being too people friendly but I think being in marketing I need to develop a good social network and I think this people friendliness takes me a long way.

6. You have switched many jobs, why?

Switching many jobs makes you a job hopper and gives an impression that the candidate is unreliable.
To answer this question, you can say something like to broaden your experience.


7. You do not have all the experience we are seeking for this position

It is not necessary that the candidate who knows everything about the job would be the best fit for the job. It is the person's willingness to learn which matters more.
Understand the job requirements properly and if you meet most of the requirements, you can say that you meet most of the requirements and you will be happy to learn whatever you don't know.
Moreover, there might be some new things in the job in future and your willingness to learn will help you do the job well. You can accompany this with an example where you learnt new things and implemented them successfully in the past.

8. Where do you see yourself five years from now?

The purpose of this question is to understand how ambitious the candidate is.
You can say something like, I see myself in a more responsible position where I can make important decisions for the company and am treated as an asset. I hope I can get both these things in this job.

9. Your expected salary?

This is the trickiest question in the interview to answer.
Try not to be the first one to throw a figure in the court. Ask the interviewer, what is it that they offer for a position like this? Know your baseline below which you can't go and try to negotiate above that. Also, make sure that you know your market value so that you do not try to negotiate too much and finally lose the opportunity.
If you have to give a figure, mention a range rather than the exact figure and don't keep the range too broad. If you offer a very broad range, you will be offered something towards the lower end. Say something like: I'll be comfortable with something around mid-forties.


10. Do you want to ask us something about the company?

Don't come out like a dumb when you are given an opportunity to ask questions.
Research a bit about the company and ask some intelligent questions like the expansion plan, opportunity for you to grow in the company, anything for which the company has been in news recently etc