Biodegradability

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When a compound biodegrades, it returns to compounds found in nature. So, that completes the cycle right? Good. How can we make this happen? Let’s see.

Molecular features generally increasing resistance to aerobic biodegradation are given as follows:

  1. Halogens : Especially Cl and F.
  2. Chain branching, especially Quaternary C and N or extensive branching such as in surfactants derived from tri- or tera-propylene.
  3. Nitro, nitroso, azo and arylamino groups.
  4. Polycyclic residues, especially with more than 3 rings.
  5. Heterocyclic residues, for example, pyridine rings.
  6. Aliphatic ethers.

Biodegradability may be in direct contrast to the functionality/performances of the chemical. Can somebody explain to me, how this works?

Biodegradability enhancing factors:

  1. Presence of potential sites of enzymatic hydrolysis, for example, esters and amides.
  2. Introduction of oxygen in the form of hydroxyl, aldehydic or carboxylic groups. Now, this is the most important one, since during the biodegradation of many compounds, the biodegradation of say, hydrocarbons, starts with the enzymatic insertion of oxygen into the structure.
  3. Presence of unsubstituted linear alkyl chains (>=4 C) and phenyl rings.
  4. Water solubility. Let’s talk about the effects of solubility in biodegradation.

Effects of solubility in biodegradation:

  1. Microbial bioavailability: Insoluble compounds tend to remain partitioned in the activated sludge, sediments and soil.
  2. Rate of solubilization: Many microorganisms secrete biosurfactants that enhance the rate of solublization.
  3. Low aqueous phase concentration is responsible for inefficient performance by cellular enzymes.

Examples of Biodegradable chemicals:

  1. LABS (Sodium dodecylbenzenesulfonate)
  2. Dialkyl Quaternaries (dialkyl dimethyl ammonium salts, imidazolium quaternary)

Biodegradability increases in the following order: Linear molecule, branched ortho, para.

Since microbial degradation is the major loss mechanism for most organic chemicals in soil, water and sewage treatment, biodegradability should be induced as a factor in product design along with function and economics.

Biodegradability should lead to non-toxic products. I wonder if biodegradability leads to toxic products in any case? Does it? It should break down into simplest forms, right?

Doesn’t all this inevitably leads you to ponder about plastics? Ah, yes. Let’s talk about plastics. I’ve got some interesting things to share. We almost always talk about how to replace plastic bags with paper bags, right? Well,  there are some other alternatives too.

  1. Liquid Wood (Arboform):

The liquid wood technology is capable of replacing plastic and providing mankind with new materials for many years ahead. Norbert Eisenfreich, a senior researcher at the Faunhofer Institute for Chemical Technology in Germany (ICT), said that arboform, the new material, is made of lignin, which can be derived from soft tissues of wood. Once mixed with several other ingredients, the substance turns into solid and non-toxic alternative for plastics. Arboform is already used for the production of car parts which require extra strength. However, the new invention does not enjoy an extensive use due to the high content of sulphur in it. German researchers believe that they will be able to reduce the amount of sulphur by 90 percent very soon to make arboform usable for home needs.

  1. New Material Made From Paper Sludge Could Replace Plastic Packaging:

Recycling paper to obtain more paper or cardboard has been a common process for many years. However, the production of a new, highly resistant, versatile and environmentally friendly material from the unwanted waste of this process is a completely new idea. This is achieved in the most productive way possible, as each kilogram of paper produces a kilogram of the new material, which has numerous applications in various industry and production sectors. This researcher has devised a new biotechnology method that she has used to modify the chemical and structural properties of the cellulose materials that are left over from the paper recycling process. Thus, she has created a new compact, mouldable, fire resistant, impermeable, strong, porous material that could, in many cases, replace materials that are not environmentally friendly or that are more expensive, such as plastics, wood derivatives or rubber. This is achieved in the most productive way possible, as each kilogram of paper produces a kilogram of the new material, which has numerous applications in various industry and production sectors.

  1. Elastic Water:

Bernama, a part of the Malaysian National News Agency, reports that Japanese scientists have created “elastic water.” Developed at the Tokyo University, the new material consists mostly of water–95-percent–with an added two grams of clay and organic material. The resulting substance resembles jelly, but is extremely elastic and transparent. According to the article, the new material is quite safe for the environment and humans, and may be a “long-term” tool in medical technology, possibly to help wounded or surgically cut tissue to remain closed.

We talked about replacing plastic, how about reusing the existing plastic? Read on.

PET Bottle recycle:

SODIS

Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable method for household water treatment and safe storage. SODIS is already applied in numerous developing countries. Educational pamphlets on the method are available in many languages, each equivalent to the English language version.

Exposure to sunlight has been shown to deactivate diarrhea-causing organisms in polluted drinking water. Three effects of solar radiation are believed to contribute to the inactivation of pathogenic organisms:

  • UV-A interferes directly with the metabolism and destroys cell structures of bacteria.

  • UV-A (wavelength 320-400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides), that are believed to also damage pathogens.

  • Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperature rises above 50°C, the disinfection process is three times faster.

At a water temperature of about 30°C (86°F), a threshold solar irradiance of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350 nm-450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.

At water temperatures higher than 45°C (113°F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.

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