Industrial organic wastewater often contains high levels of toxic substances. How can we reduce the harm to microorganisms?

 

What is 'strain acclimation,' and what is 'pretreatment'?

 

   Biological treatment of wastewater involves using the metabolic activity of microorganisms to convert organic compounds into simpler inorganic forms. In simple terms, it's using the life processes of microorganisms to transform pollutants, ultimately achieving harmlessness. This method can be divided into aerobic and anaerobic biological treatment, depending on the types of microorganisms involved.

 

   With industrial development, wastewater compositions have become increasingly complex, containing more difficult-to-degrade organic compounds and toxic substances. Simple physical or chemical treatment methods are insufficient. Microbial treatment methods are needed to utilize the metabolic processes of microorganisms to remove nutrients from wastewater and purify organic pollutants.

 

   Biological wastewater treatment boasts low operating costs and easy operational management. However, microorganisms have specific requirements for nutrient levels, temperature, pH, etc. This method isn't easily adaptable to the rapid changes, diverse compositions, strong toxicity, and difficulty in degradation of industrial organic wastewater. Solely relying on biological methods for treating industrial wastewater to meet standards is challenging. Therefore, the integration of biological, physical, or biochemical treatment methods is an inevitable trend in industrial organic wastewater treatment.

 

▲Industrial organic wastewater treatment exhibits three main characteristics:

 

1.Wastewater with easily biodegradable organic matter and minimal toxic substances. Examples include domestic sewage and wastewater from agricultural and animal products.

 

2.Wastewater with easily biodegradable organic matter and a significant amount of toxic substances. Examples include dyeing and tanning wastewater.

 

3.Wastewater containing organic matter that is difficult to degrade (very slow biodegradation). Examples include papermaking and pharmaceutical wastewater.

 

Toxic Substances and Their Mechanisms of Action

 

Chemicals that can delay or completely inhibit microbial growth in industrial wastewater are collectively referred to as toxic substances. These toxins can be categorized into organic and inorganic substances. From a treatment perspective, they can be divided into substances that can be biologically treated or transformed (such as H2S and phenol) and those that cannot be biologically treated or transformed (such as NaCl, mercury, and copper).

 

The mechanisms of toxic substances on microorganisms mainly include:

 

1.Damaging cell structure components and the cell membrane. For example, 70% ethanol can coagulate proteins to achieve sterilization. Phenols, cresols, and surfactants act on the cell membrane, disrupting its permeability.

 

2.Inhibiting enzymes and important metabolic processes. Some heavy metals (copper, silver, mercury, etc.) have potential toxic effects on enzymes, even at very low concentrations. Their salts and organic compounds can bind to enzyme -SH groups, altering the tertiary and quaternary structures of these proteins.

 

3.Competitive inhibition. When wastewater contains an organic compound structurally similar to a metabolite, competitive inhibition occurs. Because both substances can bind to the enzyme's active site, their competition inhibits the formation of intermediate products, reducing the catalytic reaction rate.

 

4.Inhibition of cellular component synthesis processes. When certain chemicals have a structure similar to cellular components, they are absorbed and assimilated by the cell, resulting in the synthesis of non-functional coenzymes or growth cessation. The classic example is sulfa drugs.

 

5.Inhibition of nucleic acid by antibiotics. Many antibiotics specifically inhibit the protein synthesis of prokaryotes. For example, streptomycin selectively inhibits amino acid correct binding to peptides.

 

6.Inhibition of nucleic acid synthesis. For example, actinomycin selectively inhibits DNA synthesis, thereby inhibiting microbial growth.

 

7.Inhibition of cell wall synthesis. For example, penicillin interferes with cell wall synthesis, inhibiting microbial growth.

 

  To ensure stable microbial growth, strain acclimation is necessary. Many strains of microorganisms can tolerate common metabolic toxins, some of which can even utilize them as an energy source. The inhibitory effects of chemical substances on microorganisms are directly related to their concentration and change with microbial acclimation. The adaptability of microorganisms to toxic substances gradually strengthens through acclimation.

 

  Although acclimation is a fundamental method in biological treatment to deal with toxins, every microorganism has its limits. When toxin concentrations exceed the permitted limit, pretreatment is necessary.

 

  Currently, pretreatment methods mainly include dilution, conversion, and separation:

 

1.Dilution method: When toxin concentrations in wastewater exceed the permissible limit for biological treatment, a simple dilution method can be used to reduce the toxin concentration to below the limit. Depending on the stability of the toxins in the wastewater and the actual situation, three different dilution methods can be adopted: sewage dilution, treated effluent dilution, and clean water dilution.

 

2.Conversion method: Some chemicals exhibit toxicity only under specific conditions. For example, nitrobenzene is highly toxic, but its toxicity decreases significantly after conversion to aniline. Chromium (VI) has high toxicity but is reduced to chromium (III), significantly reducing toxicity. By chemically converting toxic substances in organic wastewater to nontoxic or less toxic substances, normal biological treatment can proceed. This method is suitable for both stable and unstable toxins.

 

3.Separation method: By using separation methods, toxins in wastewater are transferred to the gas phase or solid phase to ensure the normal operation of biological wastewater treatment. This is the principle of the separation method. This method is suitable for both stable and unstable toxins.