1. Microwave technology applications for industrial sludge treatment

Industrial sludge refers to the oil and water emulsions containing solid debris. Every year, as much as several billion tons of oily sludge is produced globally. Conventional sludge treatment process is: heating demulsification – centrifugal separation – landfill. When heating demulsification, we often use additives; therefore, the residue produced during the process is difficult to handle. After it is de-oiled, the amount of residue that needs to be buried is large and the landfill cost is also high. In the United States, oil-based sludge microwave de-oiling technology has been developed. This technology is to mix the sludge containing oil and metal with the additive, and then to do microwave irradiation 10 minutes in a flow system and finally by means of centrifugal separation to separate out solid matter (mainly Fe, FeOX), oil and water. The solid separated can be reused as a raw material for steelmaking and the oil can be sold as a fuel.

Research shows that the processing speed of microwave demulsification de-oiling system is 30 times faster than conventional de-oiling system, and the volume of the processing system is also reduced by 90%，that greatly reduces the amount of solid waste needed to landfill and landfill costs. If we use microwave de-oiling technology to deal with sludge from steel mills, the cost of treatment is 10 times lower than the conventional treatment.

In addition, to use sludge generated from sewage treatment plants as raw materials, we can produce sludge activated carbon by means of microwave irradiation. In some places, people would dry the mix sludge which mainly from primary sedimentation tank and secondary sedimentation tank in sewage treatment plant, and after activated with phosphoric acid solution, to use 400W microwave to irradiate them 260 seconds, then successful produces sludge activated carbon that Iodine value is 517.4 mg / g. We use this sludge activated carbon to treat TNT waste water the treatment efficiency is slightly higher than powdered activated carbon.

2. Microwave technology used in the sterilization of medical waste

The mechanism of microwave sterilization is that the microwave energy can be transformed into heat energy in the microorganism so as to raise the temperature of the organism itself so as to degenerate and solidify the protein in the body. The characteristics of this technology are low temperature, short time and secondary pollution. Under normal circumstances, as for mold and yeast and other common microorganisms, when they are radiated by microwave 1 minute and heated to 70 ~ 80 ℃, can be killed; In 65 ~ 66 ℃ or so, through using microwave irradiation in 2 minutes, penicillin spores can be killed. Microwave sterilization is hot and humid steam which is generated by microwave sterilization process and the whole process is based on steam. When we use microwave to do sterilization job to solid waste, first we should crash the waste and then send them to microwave oven to do steam rotary heating, their volume will be compressed at the same time as sterilization.

Relevant research shows that after the medical waste is soaked and smashed, we sterilize them by microwave, the toxin can be quickly eliminated and its volume can be reduced by 80%.

Every year a large amount of medical waste is generated around the world, that causes serious environmental pollution, in Italy alone, 250,000 tons of medical waste are generated each year.

If we use microwave technology to do sterilization, more than 60% of medical waste can be buried. Compared with the traditional incineration method, this method does not produce poisonous dioxins and secondary pollutants and the treatment time is short with good effect, low energy consumption.

3. Microwave technology used in waste tire recycling

The tire is a hybrid material which contains rubber, carbon black, steel and sulfur and other substances. The waste tires is treated by thermal decomposition, in contrast to incineration, the thermal decomposition under oxygen-deficient conditions can reduce NOX and SOX emissions and prevent the soot generation. However, due to the heating temperature is not enough, conventional thermal decomposition often fails to completely decompose the tire. If we use microwave heating, the temperature will rise steadily, quickly reached 2000 ℃. Moreover, microwave heating technology to deal with discarded tires can also achieve the recycling of rubber materials and energy recovery.

Some factories in the United Kingdom use microwave heating technology to soften scrap tire rubber to break CC and CS bonds in the rubber molecular structure and to recover 36% of the material (Including high-quality activated carbon and petroleum hydrocarbons and carbonized products). The remaining methane and hydrogen etc. can also be used for system heating. The heat treatment process must be carried out under strict confinement conditions to avoid the production of dioxins, soot and fly ash. 

4. Microwave technology used in the treatment of electronic waste

In recent years millions of pieces of electronic components and printed circuit boards which are from computers, cars, phones, TVs and other products have been discarded each year. The conventional treatment of these e-wastes is landfill, however, with the result that the harmful metals are seeped out and it polluted the groundwater. For this reason, Professor D.E.Clark in Florida University has researched and developed microwave technology which could recovery of precious metals from printed circuit boards. The technical process is to crush the waste circuit board and send them into one quartz crucible and heating these wastes 30—60 minutes in a microwave oven which inner wall is made of refractory material. The organic matter such as benzene and styrene among them are evaporated and carried by the carrier gas (compressed air) out of the first microwave oven into the second microwave oven to be decomposed. The remaining substances are coked at below 1000 ℃. We then raised the power of the microwave and the remainder (mostly glass and metal) melted at a high temperature of 1400 ° C to form a vitrified substance. After we cool this material, gold, silver and other metals are separated in beads shape and they can be recycled as raw materials for metal smelting and the remaining vitrified substance can be recycled to use as building materials.

To use microwave technology treating e-waste can reduce the volume of waste by 50% and as the process without using any additives, the whole process will not cause secondary pollution. At the same time, the harmful ingredients are firmly packed in the vitrified product and will not leak out and the precious metals are also recyclable, all of these could greatly reduce processing costs.

5. Microwave technology used in the treatment of construction waste

Construction waste is generated during the construction process or repair or demolition of old buildings. It mainly contains waste such as mortar, concrete, masonry, soil pile head, metal, and decoration and waste such as packaging materials. It is estimated that there are 40 million tons of construction waste produced in China’s just only in the area of construction each year. Therefore, comprehensive utilization of construction waste is an effective way to save resources and protect the ecology.

It is reported that microwave technology is an effective way to recycle and reuse construction waste.

CYCLEAN company from America can use microwave technology 100% recycle and re-use construction waste, even they can make the old asphalt road material regeneration. The quality of recycled pavement materials is the same as that of fresh asphalt pavement, meanwhile, the cost is also reduced by 1/3 and it also saves the cost of garbage removal and disposal.

Recycling of construction waste using microwave technology not only avoids the problems of secondary pollution, large investment and large area caused by conventional treatment methods such as composting, incineration, landfill, but also enables the waste to be recycled.

In short, the features of using microwave technology to treat solid waste are high efficiency, simple operation, low energy consumption, low cost and high resource recovery and utilization, the prospects must be broad, and most of the current work is limited to the level of laboratory research and industrial application is less. With the improvement of people’s awareness of environmental protection and the further improvement of microwave technology, as well as the research and development of microwave equipment used in pollution control field, microwave technology will be widely used in the treatment of solid waste and the entire pollution control field.