Processes involving heavy metals

[1, Hunger, 2003, 6, Ullmann, 2001, 16, Winnacker and Kuechler, 1982, 51, UBA, 2004],

*018A,I*, *015D,I,O,B*

Heavy metals are involved in chemical synthesis:

• if the feedstock or product contains heavy metals

• if the heavy metals are used as auxiliaries (e.g. catalysts, redox partners).

Table 2.16 gives an impression of the type of processes involving heavy metals.

Metal Solvents Agent

Metallisation to form chelated metals

1:1 or 1:2

complexes to form azo dyes

Hydrogenation Nickel Raney nickel

Catalysts

Metals, metal oxides, chlorides or acetates, carbonyls

Table 2.16: Typical processes involving heavy metals

Environmental issues

Table 2.17 gives some example data of the waste streams from processes involving heavy metals.

Heavy metals are not degradable but are adsorbed to the sludge or passed through the WWTP.

Heavy metal loadings in sewage sludge cause problems for disposal and, therefore, the increased costs of disposal or treatment have to be taken into account.

Catalysts containing precious metals are to be sent advantageously to recycling companies.

The usual measure applied to prevent dilution and sludge contamination/emission is the pretreatment of the concentrated waste water streams by means such as:

• ion-exchange

• precipitation/filtration

• reactive extraction.

Catalytic reduction with Raney Ni *018A,I*

Mother liquor after

filtration Nickel 1.84 kg per batch 0.92 mg/l ⁱ

i Calculated concentration after dilution to a total effluent of 2000 m³ without pretreatment

Table 2.17: Example data for a waste stream from processes involving heavy metals

Chapter 2

68 Dezember 2005 OFC_BREF

2.6 Fermentation

[2, Onken, 1996, 15, Köppke, 2000, 18, CEFIC, 2003, 25, Kruse, 2001]

The term “fermentation” means process operations that utilise a chemical change induced by a living organism or enzyme, specifically, bacteria, or the micro-organisms occurring in yeast, moulds, or fungi to produce a specified product. Most industrial microbiological processes are enhancements or modifications of metabolic reactions that micro-organisms already carry out.

Some applications of fermentation are the production or modification of the β-lactam antibiotics, penicillins and cephalosporins, tetracyclines, and also alkaloids and amino acids.

The industrial production of antibiotics begins with screening for antibiotic producers. A new antibiotic producer may be genetically modified to increase yields to levels acceptable for commercial development. These “Genetically Modified Organisms” (GMOs) require specific measures under Directive 90/219/EEC and Directive 90/220/EEC and are excluded from the substance definition of the IPPC Directive. They (with exceptions) have to be inactivated before they are disposed of. In practice, the manufacturing process after the fermentation stage causes the destruction of the production organism so that it is incapable of survival in the environment.

If this is not achieved, then a separate deactivation step may be necessary, for example by steam sterilisation or chemical inactivation.

Fermentation technology sometimes uses pathogenic micro-organisms.

2.6.1 Operations

Figure 2.32 shows the typical sequences of operations for fermentations, some possible input materials and their associated waste streams.

Raw materials and seed stage

In the large scale fermentation of antibiotics, there are a number of stages, termed “seed stages”, leading to the final production stage. The objective of the seed stages is simply to develop an ever larger and more vigorous population of micro-organisms, with no attempt being made at this stage to produce any antibiotic. Each seed stage is used to innoculate the next, with process times for the individual seed stages usually being less than the final production stage.

The early seed stages are carried out on a laboratory scale and involve the preparation of starter cultures, which are then used to innoculate larger fermenter vessels (from some m³ to 50 m³ or more) containing a sterile medium.

The raw materials used as the growth medium in the fermentation process are primarily liquids stored in bulk, for example corn steep liquor, rapeseed oil and starch hydrolysate. These types of raw materials are non-volatile and there are no special precautions required for the transfer and batching into fermenter vessels. Bulk storage tanks for these materials are usually provided with secondary containment and high level alarms to prevent overfilling. Other batched solid raw materials are dispensed from bags and are dosed into the fermenter medium at low levels.

The batching area is provided with an air extraction system for the protection of the operators, with the extracted air passing to a dust scrubber before being released to the air. Alternatively, the batching area is designed with closed systems, which are dust free and therefore not hazardous to the operators. Equipment and growth medium are sterilised above 120 °C for 20 minutes.

Fermentation stage

The fermentation stage is carried out in a large stirred fermenter (from some m³ to 200 m³ or more) and is an aerated, batch-fed process. The batched medium is designed to support only a limited amount of further growth and is steam-sterilised within the fermenter. After sterilisation, it is inoculated with the final seed stage broth. Further sterilised nutrients are added continuously (“fed”) during the fermentation in such a way that the growth of the micro-organism is precisely controlled and the conditions made favourable for antibiotic production.

The process lasts up to eight days.

Seed stage

Figure 2.32: Typical sequences of operations for fermentations and downstream work-up Possible input materials (on the left) and the associated waste streams (grey background)

Product work-up

The following work-up steps depend on the properties and location of the product. The products are obtained by separation of the biomass from the broth by:

• filtration (conventional or ultrafiltration) and extraction of the filtered broth with an organic solvent and pH adjustment (e.g. penicillin G) or extraction of the biomass with organic solvents (e.g. steroids)

• filtration (conventional or ultrafiltration) and product precipitation from the filtered broth by adjusting the pH and/or by the addition of auxiliaries (e.g. tetracyclines)

• pH adjustment and processing of the unfiltered broth over an ion-exchanger (alkaloids, amino acids)

• direct spray drying of the unfiltered broth (e.g. for feed industry purposes).

Intracellular products need an additional mechanical step of cell destruction before extraction.

Chapter 2

70 Dezember 2005 OFC_BREF Further steps can also be carried out in order to optimise the purity or concentration. The choice

of methods are:

• evaporation

• ultrafiltration

• chromatography and/or ion-exchange

• reverse osmosis.

After purification, the product is obtained by conventional crystallisation and drying.