Biotechnology - Yu.O. Sazykin 2006

General Biotechnology
Environmental Aspects of Biotechnology
Environmental Aspects of Biotechnological Production

It should be emphasized that Anthropogenic impact on the biosphere is inseparable from The Development of civilization. The plowing of land, deforestation, and the "trampling" of steppes have constantly accompanied human history. It is also worth recalling the eradication of certain animal and plant species and the Introduction of some species far from their native habitats.

Given the particular urgency of the problem regarding the industry's impact on the biosphere, let us examine how biotechnological production stands in this regard. First of all, it is knowledge-intensive and, compared to chemical-technological manufacturing, significantly more efficient, since the producer Cell (bioobject) represents a "balanced complex of biocatalysts" that operates more productively than systems of sequential Chemical Reactions with inorganic catalysts.

The consumption of energy resources and Water by the biotechnological industry accounts for a fraction of a percent of that consumed by the modern chemical industry. Gaseous emissions from biotechnological facilities do not exceed even a tenth of a percent of total industrial emissions. While biotechnological production is undoubtedly the most acceptable option under modern conditions, it nevertheless faces specific environmental challenges and is accordingly being improved in the following directions:

✵ creating and utilizing more active producer bioobjects (resulting in less waste per unit of product!);

✵ replacing MEDIA AND Reagents with less scarce alternatives;

✵ immobilizing bioobjects (both Cells and Enzymes) and reusing them multiple times to reduce waste;

✵ implementing membrane technology at the target product Isolation and Purification stages (reducing The amount of organic Solvents used to avoid harsh conditions at certain Stages of the production process);

✵ adhering to GMP guidelines.

Let us briefly review the issues related to the disposal (utilization) or Treatment of industrial waste from a traditional biotechnological enterprise.

Solid waste. First and foremost, this includes the producer's mycelium (biomass) after its Separation from the culture liquid and the target product. To gain a clear picture of the volume of mycelium involved, one can consider that the discharge volume of an industrial fermenter is 50–100 m³ of a thick, viscous liquid (due to the presence of mycelium). Given that a facility operates multiple fermenters and a Fermentation cycle lasts about a week, one can conclude that this type of solid waste at a single (large-scale) enterprise amounts to hundreds of tons per year. Furthermore, it must be taken into account that the mycelium contains residual amounts of the target product, which are typically highly BIOLOGICALLY ACTIVE SUBSTANCES.

Currently, solid waste is eliminated through mycelium Processing. It is mixed with soil and placed in pits with concrete linings. Each such pit is left sealed for several years. During this time, soil microorganisms subject the organic substances of the mycelium to enzymatic degradation, utilizing them to build "their own" biomass. Effectively, compost is formed, and the organic fraction of the mycelium is decomposed in the process. The concrete lining in such "compost pits" is necessary to prevent yet-undecomposed soluble organic substances of the mycelium from leaching into groundwater and rainwater reservoirs. Typically, special areas on the enterprise grounds are designated for compost pits. It should be noted that transporting dried mycelium (whose mass is reduced by a factor of 10–100 compared to the original) to municipal landfills is prohibited.

Attempts to apply mycelium for various purposes have generally not met with success so far; however, low-waste technology has already been developed under laboratory conditions. The total lipid fraction was extracted from the mycelium of a tetracycline-producing actinomycete and used as an antifoaming agent in the subsequent production cycle for obtaining tetracycline produced by a strain of the same strain. In some cases (where pastureland is limited), sterilized and ground biomass of certain microorganisms is used as a feed additive for farm animals. Fungal and actinomycete mycelium (byproducts of antibiotic production) can improve the quality of certain building Materials (dite concrete slabs, bricks, etc.), increasing their strength. However, for economic reasons, manufacturing these materials is impractical.

Liquid waste. In the case of biotechnological production, liquid waste consists of effluents and wastewater—primarily the culture liquid after the separation of the mycelium and the extraction of the target product. The total annual volume of culture liquid requiring treatment amounts to tens of thousands of cubic meters for a single enterprise. The degree of purification, monitored by various Methods, must be sufficient to allow the treated liquid to be discharged into open water bodies.

Various treatment schemes exist. In almost all of them, microorganisms play a key role (biological treatment). Let us consider one such scheme (Fig. 12). The first component of the treatment system is a reinforced concrete settling tank, where the spent culture liquid flows. Pipes are laid at the bottom of the tank through which sludge is sucked out. At this stage, approximately 40% of the contaminants are removed from the culture liquid. The next section of the treatment system consists of one or more successive aeration tanks—basins with pipes running along the bottom from which air emerges as bubbles passing through the entire thickness of the liquid, thereby saturating it with oxygen. The air promotes the intensive progression of oxidation processes. A key feature of the aeration tank is the presence of so-called "activated sludge" (an artificial biocenosis—a community of microorganisms that oxidize organic substances dissolved in the liquid into CO₂ and H₂O), which gradually forms during the enterprise's operation.

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Fig. 12. Scheme of biological treatment of liquid waste:

1, 3 — Primary and secondary reinforced concrete settling tanks, respectively; 2 — aeration tank; 4 — tertiary treatment unit

The species COMPOSITION OF THE activated sludge biocenosis may vary slightly across different enterprises, as the latter depends on the substrates being oxidized. As a rule, Representatives of the genus Pseudomonas dominate (70%). These are followed by microorganisms grouped into the genus Bacterium (20%). The remaining 10% are representatives of the genera Bacillus, Sarcina, and other microorganisms. Characterizing activated sludge as a biocenosis or as a supra-organismal interspecific community in the context of treating wastewater from biotechnological production, three important circumstances should be noted.

First, strains of the genus Pseudomonas play a fundamental role here; however, this genus should not be reduced solely to the species Pseudomonas aeruginosa—a well-known CAUSATIVE AGENT OF dangerous wound infections. Under natural conditions, the genus Pseudomonas is represented by A large number of species that are harmless to humans. It is precisely these non-pathogenic strains that make up the activated sludge. These microorganisms are characterized by a wide array of oxidative enzymes. Preparations consisting of Pseudomonas cells are used in cleaning up pollution caused by oil spills. Figuratively speaking, even exotic substrates, such as cyclic Hydrocarbons, undergo oxidation. In addition, The Cell wall of saprophytic Pseudomonas species included in the activated sludge has unique features at the porin channel level that facilitate substrate access to oxidative enzymes.

Second, The conversion of certain substrates into CO₂ and H₂O is achieved through the sequential action of enzymes from different microorganisms. In other words, one enzyme system converts a specific compound into intermediate products, while another catalyzes the further degradation of these intermediates. This emphasizes that activated sludge Functions as a complex microbial community.

Third, it should be kept in mind that wastewater from certain industries (particularly the antibiotic manufacturing sector) may contain residual amounts of antimicrobial substances. This means that microorganisms in aeration tanks are in constant contact with them, creating conditions for the Selection of resistant forms. However, instances cannot be excluded where the concentration of antimicrobial substances in the treated liquid waste might prove unusually high and cause the death of activated sludge cells.

This necessitates monitoring the condition of the activated sludge. Following the section with the aeration tank (or several aeration tanks arranged in series) and the secondary settling tank, a crucially important component of the liquid waste system is the "tertiary treatment unit." In this unit, the culture liquid—which still retains approximately 10% of its initial organic matter content (typically recalcitrant, hard-to-oxidize substances)—is passed through biofilters consisting of films with immobilized cells of microorganisms possessing the highest oxidative activity. Frequently, these cells belong to genetically engineered strains harboring Plasmids that carry genes for oxidative enzymes (degradation enzymes). Such purposefully developed "degrader strains" are capable of oxidizing refractory compounds and eliminating the remaining 10% of contaminants in the treated liquid.

The immobilization of cells from such strains in biofilms is rational because, during free proliferation, this artificially enhanced oxidative activity might be lost due to back Mutations or plasmid loss. In this case, the "tertiary treatment unit" essentially "combines" Genetic Engineering and enzyme engineering. The liquid emerging from the "tertiary treatment unit," which meets official drinking water criteria (one of the accepted toxicity control methods in this case being the suppression of the viability of the microscopic crustacean Daphnia magna), is chlorinated and subsequently discharged into open water bodies.

Addressing the operation of biological wastewater treatment systems under various modes, it should be noted that maximum ("Shock") loads can cause various difficulties. During such operational periods, highly active degrader strains ("bacterial starters") are introduced into the aeration tanks, which significantly boosts the throughput capacity of the liquid waste treatment system. For this purpose, specialized preparations are recommended for biotechnological plants of various profiles: "Phenobac" for hydrocarbon utilization, "Thermobac" for polysaccharide oxidation, "Polibac" for eliminating synthetic detergents, and so on. The approximate dose of the living-cell "bacterial starter" is about 100 mg per 1 m³ of wastewater.

In Conclusion, we should note the potential diversity of biological liquid waste treatment schemes. Thus, In addition to aerobic treatment, the scheme may incorporate: an anaerobic treatment stage, stages utilizing sorbents (activated carbon, zeolites, etc.), and stages employing electrochemical methods (e.g., electrocoagulation).

Gaseous waste. Waste gases are purified from Organic compounds at temperatures ranging from 300 to 1000 °С in columns packed with inorganic catalysts. In this process, volatile organics are converted into СО₂. In some cases, biological filters utilizing microorganisms that oxidize organic substances to СО₂ are employed.

Review Questions

1. What is the overall contribution of biotechnology to solving modern environmental problems?

2. What constitutes biotechnological waste?

3. What are the primary types of microorganisms present in activated sludge?

4. What treatment schemes exist for solid, liquid, and gaseous wastes?

5. What is The Role of Genetic Engineering in environmental science?

6. What are signaling and communicative molecules in supraorganismal systems, and what are the Prospects for their application in environmental management?

7. What types of pheromones exist?

3. What are the Specific characteristics of biotechnological production regarding its waste output?

9. Which commercial preparations are used as bacterial starter cultures?

10. In what ways can biotechnological manufacturing be improved in terms of environmental safety?