Recycling in aerobic and anaerobic treatment

Recycling in aerobic and anaerobic treatment


I. Bio-recycling and reuse in aerobic treatment

The decomposition in composting treatment is aerobic decomposition, and the “Standardization of Experimental Methods for Evaluating the Degree of Biodegradability” of this decomposition method has contributed to the development and expansion of the market for environmental products.

In order to establish the “Standardization of Biodegradability Evaluation Test Method”, BPS spent 3 years in Japan to verify the test method using a biodegradation instrument (MODA method) and submitted this test method to the Japan Plastics Industry Federation as an ISO specification. TC61/SC5/WG22 MAASTRICHT International Conference (Netherlands, September 30, 2003), and it was adopted. The results revealed differences in the degree of biodegradation between countries due to differences in moisture retention and organic matter content.

The biodegradability of plastics under composting conditions was determined by the production of CO The mixture of compost and plastic test material was biodegraded at 58°C under aerobic conditions and measured within 6 months. The decomposition is shown in the figure. As can be seen from the figure, after the induction phase (lag phase: the biodegradation rate reaches 10% of the theoretical value), the biodegradation phase (biodegradation phase), and the stabilization phase (plateau phase) after 150 days, the total time of measurement was 6 months (180 days).

Recycling in aerobic and anaerobic treatment
Biodegradability curve

The results of the validation tests conducted in Sweden, Italy, China, India, and Japan are shown in Figure 8-17. As can be seen from Figure 8-17, including geographical differences and experimental errors, the R2 = 0.8191 of the biodegradability curve of PCL after 45 days was within 20% deviation and the confidence level was 82%. The deviation within countries (n = 2) was below 5% (data omitted).

Recycling in aerobic and anaerobic treatment
Biodegradability curve of PCL

The following conclusions can be drawn from this result.

①Shortening of induction period

②Improve water retention

Consider these as future technical research topics and continue with the next phase of validation tests.

2.the anaerobic treatment in the biological recycling reuse

Another promising biorecycling process is the generation of biogas. Since this process yields methane that can be used as a gaseous fuel, it can also be considered as a type of chemical recycling. This method, like composting, is a traditional technique that existed from a long time ago, but after the oil crisis, new improvements have been made, such as low efficiency, vulnerability to external environmental impacts and other disadvantages. Recently, a number of new attempts have been made in Europe, such as making organic wastewater flow upward or downward on fixed plates of methane bacteria and conducting high temperature methane fermentation near 55°C at the same time. As mentioned before in Figure 8-12, the use as a fluid fuel ranks higher than as a fertilizer, and the further combination with fuel cells to become easier to use electricity or turn into gaseous fuel is again a more tempting direction. This decomposition is anaerobic biodegradation, through which energy can be recovered in the form of methane, and is a noteworthy area in the future.

Methane fermentation is a microbial reaction that is more prevalent in anaerobic environments, where organic compounds are decomposed by the combined action of large numbers of anaerobic bacteria to produce methane and carbon dioxide. The production of methane under microbial action goes through three stages as shown in the figure.

Recycling in aerobic and anaerobic treatment
Route of methane generation under microbial action

The decomposition takes place in two stages (Fig.) The first stage is the decomposition of complex compounds into simple compounds, particularly lower fatty acid esters; the second stage is the further decomposition of these compounds into methane and carbon dioxide. Academically, the second stage of decomposition is referred to as methane fermentation, and the bacteria involved in the decomposition are collectively referred to as methanogens. a. M. Buswell (1930), H. A. Barker (1936), and others cultured various methanogens individually, which led to the understanding of the mechanism of methane fermentation as shown in the chemical formula below.

Recycling in aerobic and anaerobic treatment
Recycling in aerobic and anaerobic treatment

Methane fermentation fermentation includes both medium-temperature fermentation (about 38°C) used when raw liquids such as sewer sludge and urine are discharged at room temperature, and high-temperature fermentation used when factory wastewater (such as distillation drainage of alcohols) is discharged at 60 to 70°C.

The above two treatment methods are summarized as shown in Figure 8-19. Our country is more advanced in this area, so we should actively propose to the international. Biodegradable plastics, as the capital of our country to strengthen the competitiveness of our industry, are very important for the international advantage of our technology, our position in the international market, and the popularity of the research and development results from a globalization standpoint.

In order to respond to the needs of society, it is important to establish experimental evaluation methods that support a common base plate for industrial competitiveness. In addition, in order to obtain objective evaluation through verification tests in overseas programs and make it a worldwide standard, it is necessary to study and discuss new problems that may occur. since 1989, BPS has been working to establish experimental and evaluation methods for biodegradable plastics, and it is hoped that an ISO standard for Japanese distribution can be established in the future.

In recent years, the type of PLA foam generation has been introduced to the fish box market in the city of precision, and empirical experiments have been conducted to recover biogas by subjecting broken fish boxes and food scraps together to methane fermentation at medium temperature (about 38°C). The product also has problems such as high weight and insufficient strength due to its low foaming rate. The method of crushing the material and the mixing ratio with the food residue are still debatable, but it did undergo biodegradation and conversion into biogas.

Composting, methane fermentation and burial in the soil, and slow decomposition rates compared to food scraps and livestock manure are common features of this type of material. Figure shows the decomposability of biodegradable plastics (PBS, derived from petroleum) compared to bio-based polymers (PLA) in a composting environment. Although there are also differences between the two, the decomposition rate is very slow and the time required (days) is very long compared to household waste (2-5 days) and livestock manure (5-7 days). It is not at all expected to use plastic as the main raw material in the mix, so the right mixing ratio must be grasped.

3.the prospect of bio-recycling and reuse

For bio-based chemicals, the apparent consumption of succinic acid was about 100,000 tons in 2015, which is expected to reach a market demand of $800 million worth of succinic acid in 2018, according to a report released by Transparency Market Research in 2013. the apparent consumption of global lactic acid was about 400,000 tons in 2014, and the domestic production capacity of lactic acid was over 200,000 tons but the actual apparent consumption was only about 60,000 tons. Although there has been a significant imbalance between domestic supply and demand, there are still companies ready to go on lactic acid production projects, which must be a cause for concern.

Bio-based plastics have been developing rapidly in recent years, with breakthroughs in key technologies, rapid growth in product variety and enhanced product economics, and are becoming a hot spot for industrial investment, showing strong momentum, with dozens of production lines of more than 10,000 tons already under construction or under construction. In the short term, due to the high cost of bio-based plastics, some functional applications will develop faster, such as biodegradable plastics due to the biodegradable properties and in line with the requirements of the ban on plastic in Europe and the United States, even if the cost is high, there is a large market space. In the long run, in addition to the development of bio-based plastics with biodegradable function, some bio-based nylon, bio-based polyethylene, bio-based polyethylene terephthalate and other non-biodegradable plastics may have a larger scale of application in the international arena. However, in China, because these materials are not yet available on a pilot scale, they will not be developed on a very large scale in the near future. The bio-based materials industry is in the stage of laboratory research and development into the stage of industrial production and large-scale application, gradually becoming industrialized bulk materials, but there is still a need for continuous progress in microbial synthetic strains, raw materials research and development, product molding and processing technology and equipment, and large-scale application demonstration.

Taking bio-recycling and reuse of bio-based polymers as an example, we look forward to the prospect of bio-recycling and reuse of biodegradable plastics or bio-based polymers. In the process of popularization and promotion, the main problem facing biorecycling of bio-based polymers is to ensure the performance and reduce the price. How to significantly reduce the price and enhance the competitiveness with conventional commercial plastics in the popularization of bio-based polymers is directly related to its future. The Japan Organic Resources Association calculates that the production cost of 50,000 tons of PLA per year is 450 yen/kg, assuming the same production-related conditions as today, and that 70% is consumed in the process of fermenting raw materials to obtain lactic acid monomers. This shows that it is difficult to produce PLA economically in Japan from domestic biomass. However, the reuse and recycling of PLA through microorganisms that break down PLA into lactic acid oligomers and enzymes for monomers, and also chemical recycling through bio-recycling and reuse, is expected to rival conventional plastics in terms of manufacturing and recycling costs after polymerization.

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