Waste Management Flashcards

Question

What are the different stages that take place in a Materials Recovery Facility (MRF)

Answer 1

Stage 1 – Quality Inspection - To ensure that only those materials required for recycling are moved onto the next stage of the process. The waste material is pushed onto conveyors where it first enters a pre-sort cabin. Here personnel remove any unwanted items. State 2 – Separation – A series of systems and technologies are used to separate the glass, cans and plastic bottles into single waste streams ready for recycling. This has a number of different stages;  Over-band magnet separates out any steel cans.  Glass bottles and jars are identified through a breaker screen and passed into a clean-up system for further refinement and separation by size.  Eddy current separator can be used to remove aluminium foil and cans.  The plastic bottles go into another separator until that has the capability to divide them into the following different types: HDPE, PET and unwanted mixed plastic. Stage 3 – The separate streams of plastic are sent for quality control before handling to be punctured and squashed, ready for bailing. 3 - The MRF process can be highly efficient, 95% of the material that enters the MRF can be recycled, the remaining 5% of waste gets sent for energy recovery. It also of course generates jobs, in what some people call the new ‘green economy

Answer 2

An open hole in the ground where waste is buried and that has various animals (rats, mice, birds) swarming around.

Answer 3

Landfill – Carefully designed structure built into or on top of the ground in which MSW is isolated from the surrounding environment (groundwater, air and rain). This isolation is accomplished with a bottom liner and a daily covering of soil.

Answer 4

The bottom liner prevents the trash from coming into contact with the outside soil, particularly the groundwater. In MSW landfills, the liner is usually some type of durable, puncture resistant synthetic plastic (PE, HDPE or PVC). It is usually 30 to 100mm thick. This liner may also be surrounded on either side by a fabric mat (geotextile mat) that will help keep the plastic from tearing or puncturing from sharp rock or stones.

Answer 5

Leachate collection system – The leachate is allowed to filter down to the bottom liner system where perforated pipes (pipes with holes in them) drain the leachate to a sump (just a hole at low level, so fluid falls to this point). Then the leachate can be pumped to a collection pond. Some systems can use gravity of allow the leachate to flow to the collection pond. The leachate in the ponds is then tested for various chemicals (biological and chemical oxygen demands, organic chemicals, pH, calcium, magnesium, iron, sulphate and chloride) and allowed to settle. After testing, the leachate must be treated like any other sewage / wastewater. This can sometimes occur onsite or off site. The capping layer (which will be discussed in more detail below) id designed to prevent rainwater from entering the landfill, but some will always pass down through adding to the volume of leachate.

Answer 6

It’s important to keep the landfill as dry as possible to reduce the amount of leachate. This can be achieved in two ways; Option 1 – Exclude liquids from the solid waste. Solid waste must be tested for liquids before entering the landfill. This is done by passing samples of the waste through standard paint filters. If no liquid comes through the sample after 10 minutes, then the trash is accepted into the landfill. Option 2 – Keep rainwater out of the landfill. To exclude rainwater, the landfill has a storm drainage system. Plastic drainage pipes and storm liners collect water from areas of the landfill and channel it to drainage ditches surrounding the landfills base. The ditches are either concrete or gravel lined and carry water to collection ponds to the side of the landfill. In the collection ponds, suspended soil particles are allowed to settle and the water is tested for leachate chemicals. Once the steeling has occurred and the water has passed tests, it is then pumped or allowed to flow off site. The storm drainage system is designed to stop storm water from entering the waste, but it does not stop all water from entering.

Answer 7

Bacteria in the landfill break down the trash in the absence of oxygen (anaerobic) because the landfill is airtight. A byproduct of this AD breakdown is LFG which as we have seen contains approx. 50% methane and 50% CO2, with small traces of nitrogen and oxygen. Additionally the methane provides an additional hazard in that it can explode. So this LFG must be removed. To do this a series of pipes are embedded within the landfill to collect the gas. In some landfills, this gas is vented or burned. This LFG can be collected and separated, after which the methane can be used as a fuel. The methane could be used for heating purposes, but as a landfills tend to be reasonable distances from mass populations, use for electricity tends to be the most frequent choice

Answer 8

Cells (Old and New). Trash is compacted into cells. These cells only contain one days waste. Cells may be approx. 15m x 15m area x 4m in depth. It is seriously compressed to reduce the volume of the waste. This of course means that more material can be put into a specific landfill site. The compression is done by heavy equipment (tractors, bulldozers, rollers). At the end of the day when a cell is made, it is covered in approx. 6 inches of soil and compacted further. These cells are arranged in rows. Cells in the same row are called a lift. The compression of the waste is aided by the removal of certain waste types such as carpets, mattresses, foam and yard waste.

Answer 9

Covering or cap. – a 6 inch layer of compacted soil added to cover a cell on a daily basis (in recent times tarps and spray coverings of paper or cement /paper emulsions are being utilised to reduce volume) Each cell is covered daily with six inches of compacted soil. This covering seals the compacted waste from the air and prevents pests (birds, mice, flying insects) from getting to the waste. This soil takes up quite a bit of space and because space is a valuable commodity in a landfill in more recent times landfills have experimented with tarps or spray coverings of paper or cement / paper emulsions. These still cover the waste but take up only ¼ of an inch in comparison to the 6 inches of the soil layer

Answer 10

Cap – a 40mm plastic cover added to the top of the landfill when it is full. Covered in approx. 2ft to 3ft of compacted soil and grass / trees with shallow roots planted to retain the soils integrity.

Answer 11

Bioreactor landfill can be defined as, ‘Any permitted landfill or landfill cell where liquid or air is injected in a controlled fashion into the waste mass in order to accelerate or enhance biostabilisation of the waste’.

Answer 12

A bioreactor landfill operates to rapidly transform and degrade organic waste. The increase in waste degradation and stabilisation is accomplished through the addition of liquid and air to enhance microbial processes

Answer 13

Aerobic – In an aerobic bioreactor landfill, leachate is removed from the bottom layer, piped to liquid storage tanks, and recirculated into the landfill in a controlled manner. Air is injected into the waste mass, using vertical or horizontal wells, to promote aerobic activity and accelerate stabilisation.

Answer 14

In an anaerobic bioreactor landfill, moisture is added to the waste mass in the form of re-circulated leachate and other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. LFG primarily methane, can be captured to minimise greenhouse gas emissions and for energy recovery

Answer 15

Hybrid – (Aerobic & Anaerobic) – The hybrid bioreactor landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly degrade organics in the upper sections of the landfill and collect gas from he lower sections.

Answer 16

Bioreactors often need other liquids such as storm water, wastewater and wastewater treatment plant sludges to supplement leachate to enhance the microbiological process. It does this by purposeful control of the moisture content and differs from a landfill that simply recirculates leachate for liquid management. Landfills that simply recirculate leachate may not necessarily operate as optimised bioreactors (they simply want to reduce the volume of leachate which needs to be transferred to be treated, thus saving money). - Moisture content is the single most important factor that promotes the accelerated decomposition. The bioreactor technology relies on maintaining optimal moisture content (mc) which should be between 35-65% and liquids need to be added when required to maintain this % mc. – The moisture content, combined with the biological action of naturally occurring microbes decomposes the waste. The microbes can be either aerobic or anaerobic depending upon the presence of oxygen.

Answer 17

- Decomposition and biological stabilisation in years vs. decades in a dry tomb. - Lower waste toxicity due to both anaerobic and aerobic conditions. - Reduced leachate disposal costs. - A 15 to 30% gain in landfill space due to an increase in density of waste mass (the waste mass can be compressed more). - In the initial years a significant increase in the generation of LFG that can be captured and used of energy use of resold. - Reduced post closure care.

Answer 18

With a restriction on exposure to oxygen, decomposition takes place through 4 phases. Phase 1 – Aerobic biodegradation takes place; oxygen is gradually removed and replaced by CO2 Phase 2 – Substances such as cellulose, proteins and fats decompose to produce substrates for further biodegradation that provide short fatty acids, CO2 and H2 . This process can take two weeks to become established. During this phase methane bacteria begin to establish themselves in the waste. Phase 3 – Landfill gas begins to be produced in significant quantities. This phase takes three to four months to become established. The rate of gas production stabilises within two to three years. Phase 4 – The site will produce gas over a long period of time.

Answer 19

0 – 10% active waste > Qualifies at the lower rate of tax. 11 – 100% active waste > Standard rate.