1. Can only biodegradable plastic be composted?
This is not necessarily case. Biodegradable plastics can biodegrade under composting conditions, and can also biodegrade under other conditions, such as anaerobic digestion equipment, and can also biodegrade under natural conditions, such as soil, sea water, etc., but specific chemical structure of plastic and composition product And so on and environmental degradation. Generally speaking, it is wrong to say that biodegradable plastic can only be recycled through composting.
Materials such as PHA and PBAT are relatively easily biodegradable in seawater, soil, and composting conditions, while PLA is relatively easily biodegradable in composting conditions, and degradation cycle or rate is relatively slow in seawater conditions and soil.
2. Can biodegradable plastic be completely biodegradable in an anaerobic digester?
The main reason why biodegradable plastics can be biodegraded is because their chemical structure is different from traditional plastics, so they can be biodegradable. Most currently known biodegradable materials can be biodegraded in an anaerobic digester.
3.Can biodegradable plastic be completely biodegradable in soil?
Because conditions such as temperature, humidity, and micro-organisms are uncontrollable in natural soil, these conditions are relatively uncontrollable compared to controlled conditions in composting process. At present, based on application of biodegradable mulch film and results of laboratory and field degradation experiments, most biodegradable plastics are biodegradable in field soil conditions such as PBAT, PHA, PCL, PBS, etc. under normal climatic conditions for 5 months . can be completely decomposed under condition of burying soil and will not affect plants; materials such as PLA decompose relatively slowly and take a long time, but after mixing with PBAT and other materials, according to results of experiments, they can also degrade within about half a year completely degrade. The picture below is observation result after we used natural soil to bury PBAT, PBAT/PLA and PLA film in Mentouga. From photo, it can be seen that biodegradable plastics are suitable for spring, summer and autumn in north, when soil moisture is sufficient, it can decompose natural way.
4. Can biodegradable plastic be completely biodegradable in seawater?
There are also microorganisms adapted to high salt content of seawater. Materials such as PHA and PBAT can be completely degraded in about 30-60 days in seawater conditions at 25°C±3°C. Specific photographs of observation of experimental process can be seen in figure below.
5. Will degradation or degradation products of biodegradable plastics cause a secondary environmental hazard?
Everyone is especially concerned about whether degradation products of biodegradable plastics will cause secondary harm to environment, so heavy metal content index has been added to requirements for degradation performance of biodegradable plastics, and strict requirements have been introduced.
Ecotoxicity tests, including phytotoxicity tests and earthworm toxicity tests, were conducted on composted compost made from compostable plastics.
For soil-degradable biodegradable mulching films, in addition to degradability and heavy metal content, new international standards also provide for ecotoxicity and other standards.
Therefore, from present point of view, biodegradable plastics that meet requirements of standard will not cause secondary harm to environment after decomposition.
To be continued...