Biodegradation is the decomposition of organic compounds into simple compounds, carried out by living organisms, e.g. bacteria, protozoa, fungi, and algae. These organisms are common in sewage, soil, and groundwater. Biodegradation can be anaerobic, in the absence of air: less common, and less effective, leading to the formation of methane, carbon dioxide, and water. This process, which takes place with the participation of oxygen, is called aerobic biodegradation, in which the material finally decomposes into carbon dioxide, water, and biomass.
Composting is an accelerated biodegradation process under controlled conditions, mainly characterized by forced aeration and natural heat generation due to the biological activity inside the material. The product of this process, compost, contains valuable nutrients and can act as a soil improver.
Home compostable products are made of components and materials that fully decompose into the soil. This includes any printing ink and adhesives when it comes to goods such as packaging.
Industrial composting is a controlled process that converts organic waste into stable, decontaminated products that can be used in agriculture. It occurs under certain, controlled conditions (in the presence of heat, moisture, and oxygen) in industrial composting plants.
There are three techniques used in industrial composting: pile composting, tank composting, and aerated static composting
Pile Composting is an outdoor process in which the compost material is placed in long piles of about 5 feet high, known as “piles”. These piles are turned over regularly to ensure that all compost material remains for some time in the warm, moist center of the pile, where bacterial activity generates heat that favors further decomposition. As stockpile composting takes place in the open air, it is mainly used in garden and with garden waste to help control odors.
Tank Composting is a process that takes place in a closed environment. Composting inside the tank can process large amounts of waste without taking up as much space as the prism method, and it can handle virtually any type of organic waste – for example, meat, animal excrement, bio-solids, and food scraps. This method involves introducing organic materials into a drum, silo, concrete trench, or similar space. This makes it possible to effectively control environmental conditions such as temperature, humidity, and airflow. The material is mechanically rotated or agitated to ensure the material is aerated to stimulate bacterial activity. The size of the pan may vary in size and capacity.
It takes weeks or months for composting in a tank to be ready for use as microbial activity has to balance and the stockpile has to cool down. Waste is left in these bins for seven days and the temperature probes provide enough heat to kill any dangerous bacteria – they must reach a temperature of 60 ° C for at least two consecutive days. The waste is then transferred to a maturation pad in the final stage of composting.
Aerated static composting produces compost relatively quickly, usually within three to six months. It is suitable for a relatively homogeneous mixture of organic waste and works well with larger municipal compostable generators such as government agencies and commercial solid waste such as food scraps, paper products, and bioplastics.
In composting with an aerated static pile, the organic waste is mixed in a large pile. To air the pile, layers of loosely laid filler substances such as wood shavings and shredded newspapers are added so that the air can pass from the bottom to the top of the pile. The stacks can also be placed above the network of pipes so as to create airflow to and from the stack by means of air blowers, that can be triggered by a timer or temperature sensors.
Recycling – is a system of activities and processes aimed at recovering and reusing waste with the lowest possible energy input. The basis of recycling is the proper selection of waste, and then it is processed into new products and used to the maximum extent. A resource is recovered as many times as possible, by working it again after each subsequent use, until it loses its potential. A material that can be reused after processing is called a secondary raw material.
Chemical recycling – known also as feedstock or advanced recycling is the method of reprocessing the (plastic) waste into valuable products, where chemical structure of the original material is changed. According to ISO Standard 15270, chemical recycling is limited to following processes: cracking, gasification and depolymerization. During these processes, polymer chains of plastics are degraded into shorter chain structures that can be further processed into different products. Types of processes as well as types of products that can be obtained from chemical recycling of plastics depends on the type of polymer.
For example, depolymerization processes can be used for polyesters, like PET. On the other hand, polyolefins (PE, PP) are used as a feedstock for cracking (pyrolysis). Chemical recycling products can be divided into three groups: fuels/fuel components, monomers and other products. Following the Waste Framework Directive, production of fuels and fuel components are not considered as a recycling in Europe – it falls under the energy recovery processes. Monomers are mainly obtained from depolymerization processes. Then plastic waste can become pure virgin polymer. Chemical recycling of polyethylene and polypropylene, apart from monomers production, can lead to other products based on hydrocarbons, like waxes, oils and solvents used by many industries.
Mechanical recycling – this is the traditional recycling, where mechanical processes are used for waste treatment, and where no intentional influence on the chemical structure of polymers takes place. Basically, mechanical recycling consists of such units like: sorting, shredding, washing, drying and re-melting. As during these processes some degradation of polymer can take place as well as to improve mechanical and visual properties of the product, many additives are added, like UV stabilizers, pigments or other fillers.
Plastic obtained from mechanical recycling can be used in many applications – for example recycled PET can be used again for production of beverage bottles and PE can become a plastic bucket. Mechanical recycling is limited to the highest quality plastic waste streams, as it requires polymers of same type, preferably similar color and cannot be used indefinitely because of reduction of mechanical properties of the polymer with each circle.
This term covers technologies that use physical separation for purification of plastic waste. The major process that is used is dissolution, which benefits from differences in solubility in different solvents between polymers. In this case special compositions of solvents at proper process conditions are used to separate the polymer from additives (fillers, pigments etc.) and other polymers in a form of dissolution. Then, after evaporation of solvent, clean polymer can be obtained, potentially of virgin quality. Thereafter solvent can be condensated and circulated in the system.
An ecological system that includes a living and inanimate part of a certain space of the natural environment. There are many relationships between organisms that inhabit a given inanimate environment, which allow them to function in harmony and balance. An ecosystem, also known as a biosystem or ecological system, is based on the flow and exchange of matter and energy between organisms that inhabit it and between organisms and their surroundings.