Physico-chemical treatments of waste waters Purpose

Ph-c plants are planned in such a manner that the maximum amount of recyclable materials can be separated so that a minimum amount of auxiliary materials is used. The purposes of physico-chemical treatment plants are to:

• enable delivery of environmental protection goals, in particular, water quality management.

In Ph-c plants, materials which may be hazardous to water are either treated, withheld and/or converted to a non-hazardous form

• enable the correct disposal of large quantities of, in general, aqueous liquid waste and waste requiring special controls

• separate the oil or the organic fraction to be used as fuel.

The procedures serve the specific application of physico-chemical reactions for material conver-sion (e.g. neutralisation, oxidation, reduction) and for material separation (e.g. filtration, sedi-mentation, distillation, ion exchange).

Principle of operation

During the physico-chemical treatment of contaminated waste water, water is separated and processed for discharge to sewerage systems or water bodies. This processed water becomes subject to various water legislation as soon as it is discharged.

Feed and output streams

The waste treated in Ph-c plants is aqueous liquid. Ph-c plants generally treat waste liquids or sludges with a relatively high water content (>80 w/w-%). Regardless of their origin and their relationship to their material characteristics, the wastes commonly treated by these plants are:

• emulsions/cooling lubricants

• acids (e.g. picking acids from surface treatments. Some information on STM BREF)

• alkaline solutions

• concentrates/saline solutions containing metals

• wash-water

• waste water containing a gasoline/oil separator

• solvent mixtures

• sludges

• aqueous liquid wastes with high concentrations of biodegradable materials

• aqueous marine waste.

An indication of the type of wastes accepted at sites in the UK is given in Table 2.6.

Waste stream Percentage of sites accepting each type of waste (%) Neutral aqueous inorganics 69

Acids 62 Oils 62 Alkalis 54 Neutral aqueous organics 54

Contaminated containers 23

Cyanides 23

Organic sludges 8 Water reactive chemicals 8

Table 2.6: Waste types accepted at physico-chemical treatment plants in the UK [56, Babtie Group Ltd, 2002]

Process description

Ph-c plants are configured on a case-by-case basis depending on requirements and/or applica-tion. Each Ph-c plant has a specific individual technological and operational concept; this is geared to the waste to be treated. For this reason, there is no ‘standard’ physico-chemical treat-ment plant. Although all plants have inspection and process laboratories and tend to have a neu-tralisation function, the range of pretreatment processes, sludge handling methods and the com-bination of input waste streams makes each a unique operation. The modes of operation of Ph-c plants are:

• continuous operation: particularly suitable for large throughputs, waste of relatively con-stant composition and for automated operation

• batch operation: particularly well suited to the very variable characteristics/reaction of the waste to be treated.

Table 2.7 shows some differences between different Ph-c plants.

Treatment of

emulsions

emulsions and oil/water mixtures

emulsions

and waste with contents to be detoxi-cated

liquid and aqueous waste with some or-ganic solvents

liquid and aqueous waste containing or-ganic solvents and tensides

Sieving

Sedimentation

Ultrafiltration

Evaporation

Heating up

Stripping

Acid splitting

Organic splitting

Oxidation/reduction

Membrane filtration

Flocculation/precipitation

Sedimentation

Draining

Sulphuric precipitation

Filtration

Ion exchanger

Neutralisation

Note: Dark grey: required process, light grey: Optional process

Table 2.7: Analysis of some representative types of physico-chemical treatment plants Based on [121, Schmidt and Institute for environmental and waste management, 2002]

The unit operations typically used are sieving, storage/accumulation, neutralisation, sedimenta-tion, precipitation/flocculasedimenta-tion, ion exchange, oxidation/reducsedimenta-tion, sorption (adsorp-tion/absorption), evaporation/distillation, membrane filtration, stripping, extraction, filtra-tion/draining, acid splitting of emulsions and the organic splitting of emulsions.

Frequently several unit operations will have to be used to correctly treat a specific waste. The unit operations procedure combination (type of procedure, sequence of their application, con-trols) is specified by the Ph-c plant laboratory, on the basis of the composition of the waste and its reaction behaviour.

The following equipment is typically available for reactors in order to control reactions:

• storage vessels for separate storage, depending on the type of treatment

• reaction containers with adjustable agitators and temperature indicators

• sedimentation containers

• metering equipment

• receiver and storage tanks for chemicals

• storage tanks and reservoirs for the waste to be treated

• dosing equipment

• material resistant to acids and alkalis

• control of pH value for the chemicals

• containers for settling and mixing ancillary agents

• measurement and automatic controls

• ventilation and filtering of the reaction tanks with facilities for cleaning the exhaust air.

Users

From 25 to 30 % of all hazardous waste in Germany is disposed of by Ph-c plants. Some exam-ples of the operations carried out via a Ph-c plant are:

• treatment of emulsions

• treatment of emulsions and waste with contents to be detoxified

• treatment of liquids, aqueous wastes with some organic solvents

• treatment of emulsions and oil/water mixtures

• treatment of liquids, aqueous wastes containing organic solvents and tensides

• detoxification (oxidation/reduction) of waste containing nitrites, Cr(VI), cyanide (as pre-treatment).

The wastes processed are usually from various industrial and commercial production processes, and from maintenance, repair and cleaning activities. Some specific industrial sectors served are the printing and photographic industries. These are an example of those sites, which provide a service to a particular industrial sector, taking away a wide range of wastes and transferring those that cannot be treated or recycled in-house.

Figure 2.7 shows the treatment of aqueous marine waste.

Waste water containing chemicals

If possible recovery/re-use Chemical

Waste water containing oil

Oil separation

Pretreatment (emulsion

splitting, precipitation

and neutralisation)

Flocculation/f lotation

Biological treatment

Effluent

Sludge

Sludge processing

Dewatered sludge

Oil

Re-use as fuel Incineration Chemical

separation

Oil

Figure 2.7: Treatment of aqueous marine waste [156, VROM, 2004]

Im Dokument Integrierte Vermeidung und Verminderung der Umweltverschmutzung (IVU) (Seite 95-98)