Carson Ph., Mumford C. Hazardous Chemicals Handbook (Справочник по опасным химическим веществам)

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High-

efficiency

cyclone

Self-induced

spray de-

duster

Electrostatic

precipitator

High-energy

venturi

scrubber

Fabric filter

Medium

efficiency

cyclone

100

50 10 5 1 0.5 0.1

Particle diameter (µm)

Collection efficiency (%)

in droplet diameter. The range of droplet diameters associated with various processes, and the

types of equipment used for their separation, are exemplified in Figure 17.4.

Processes for the control of atmospheric emissions are summarized in Table 17.9. Some of

these involve the types of chemical engineering operations referred to in Chapter 7; the added

complications are:

• the inlet pollutant concentrations may be quite low;

• the total stream flowrates may be large;

• the target outlet concentrations are probably subject to stringent regulation to very low levels.

As with pollution control equipment generally, a high degree of reliability is required.

Liquid effluent treatment operations

Any of the variety of chemical engineering operations or unit processes listed in Table 17.10 may

be used to treat aqueous effluents. Oxidation includes both chemical and biological processes;

the latter include trickling filters or an activated sludge bed.

Process operation and the storage and handling of effluents and chemicals involve potential

chemical and biological hazards (Chapter 5). Safeguards of the type outlined in Chapters 12 and

13 are essential, particularly since the activities are often on a site’s periphery and have low

manning levels.

EC policy is that waste oils from use as lubricants should be recycled or used as fuel as far as

possible. Some EC countries have a more regulated organizational framework for collection and

Figure 17.3

Particle arrestment efficiencies for different equipment

LIQUID EFFLUENT TREATMENT OPERATIONS 529

530 CHEMICALS AND THE ENVIRONMENT

carry-over from

water cooling and

spray cooling towers

Rain drops

Drizzle Mist

baffle, louvre

separators

knitted-mesh

demisters

knock-out drums/collectors with knitted-mesh

condensate from high-pressure

compression plant

condensate

from gas coolers

condensate from

intercoolers ion

compression plant

spray produced by bubbles at a liquid

vapour interface

entrainment from

evaporators, distillation and

absorption columns

cyclones, centrifugal

separators

Process applications

1000

500 200 100 50 20 10 5 2 1 0.5

Droplet diameter (µm)

Operating

range of

equipment

Fog

demisters

recycling of used oil. Used oil can be drained from machinery during routine servicing and should

be stored in a central store using suitable leak-proof containers. Different types of oil should be

stored separately. Used oils must not be disposed of into soakaways, watercourses, drains and

sewers. The requirement of ‘no visible oil’ is often specified for releases to water, usually taken

to mean no more than 20 ppm depending on droplet size. Used oils should only be disposed of to

registered waste oil carriers. Alternatively waste oil can be burnt for heating provided that approval

is given by the local authority Environmental Health Department for the installation of the burner.

The disposal of waste oils is largely governed in the UK by the EPA 90. Waste oils are a

‘Special Waste’ covered by Special Waste Regulations. Establishments handling more than 500

litres per annum have a duty to maintain records. There are also requirements for record keeping

where waste oils contain toxic impurities and so become ‘Special Waste’.

PCBs and PCTs are particularly troublesome liquids because of their toxicity and persistence

in the environment. They are defined as polychlorinated biphenyls, polychlorinated terphenyls,

monomethyl-dibromo-diphenyl methane, monomethyl-dichloro-diphenyl methane or monomethyl-

tetrachlorodiphenyl methane. With low electrical conductivity and heat resistance they found

wide use as dielectric fluids and were formerly used as hydraulic fluids. PCBs have not been

made in the UK since 1977 and whilst most new uses for the substance are banned in most

countries, around two-thirds of the 1.5 million tonnes manufactured in Europe and the US prior

to 1985 still remain in equipment such as transformers. PCTs have been used in the past in a

restricted range of specialist industrial applications.

Figure 17.4

Mists and sprays; applications of separators

Table 17.9 Treatment methods for gaseous waste

General methods Alternatives

Centrifugal techniques Centrifuge

Cyclone

Coalescence

Condensation

Destruction Chemical reaction

Incineration

Direct recycle

Dispersion

Electrostatic precipitation

Filtration Needle bonded fabric

Reverse jet

Reverse pressure

Shaker type

Gravity settlement

Total enclosure

Wet scrubbing Absorption tower

Fluidized bed scrubber

Impingement scrubber

Irrigated target scrubber

Pressure spray scrubber

Rotary scrubber

Self-induced spray scrubber

Spray tower

Venturi scrubber

Waste gas treatment system

Dry methods Pollutant Wet methods

Absorption Gas Wet scrubbing

Destruction

Direct recycling

Dispersion

Total enclosure

Destruction Liquid Centrifugal techniques

Coalescence

Destruction

Gravity settlement

Total enclosure

Wet scrubbing

Centrifugal techniques Solid Electrostatic precipitation

Destruction Wet scrubbing

Direct recycling

Electrostatic precipitation

Filtration

Gravity settlement

Total enclosure

LIQUID EFFLUENT TREATMENT OPERATIONS 531

532 CHEMICALS AND THE ENVIRONMENT

Table 17.10 Treatment methods for liquid effluent

Treatment method Example

Chemical

Cementation Copper recovery

Chlorination Cyanide oxidation

Coagulation,

see

Flocculation

Electrolytic processes Metal recovery

Emulsion breaking Soluble oil recovery

Flocculation Sewage treatment

Hydrolysis Cellulose waste

Incineration Waste oils

Ion exchange Metal recovery

Leaching Metal-bearing sludges

Neutralization Waste acid, waste alkali

Oxidation Phenol removal

Ozonization Cyanide oxidation

Precipitation Metals

Reduction Hexavalent chromium

Thermal decomposition Recycling hydrochloric acid

Physical

Adsorption Removal of volatile organics

Cooling Water reuse

Crystallization Recovery of inorganic salts

Dewatering,

see

Filtration

Dialysis Desalination

Distillation Solvent recovery

Drying Pig manure

Electrodialysis Desalination

Evaporation Sulphuric acid recovery

Filtration Sewage sludge

Flotation Dairy wastes

Foam fractionation Metal separation

Fractionation,

see

Distillation

Freezing Desalination

Heating Demulsification

Phase separation Oily wastes, hydrocarbons

Reverse osmosis Desalination

Screening Sewage

Sedimentation Suspended solids removal

Solvent extraction Metal recovery

Stripping Ammonia removal, solvent removal

Ultrafiltration,

see

Dialysis, Reverse osmosis

Biological

Activated sludge Sewage

Anaerobic digestion Food wastes

Chemical production Ethanol

Disinfection Sewage plant effluent

High-rate filtration Phenol removal

Oxidation,

see

Activated sludge, High-rate

filtration, Trickling filter

Reduction,

see

Anaerobic digestion

Single-cell protein production Organic waste

Trickling filter Sewage

Under the requirements of the Environmental Protection (Disposal of Polychlorinated Biphenyls

and other Dangerous Substances) (England and Wales) Regulations, SI 2000/1043, equipment

containing PCBs is now required to be: identified, registered with the Environment Agency,

labelled so that the PCB presence can be identified, and decontaminated without endangering

health and safety to reduce the level of PCBs in equipment to less than 50 ppm (less than 0.005%

in weight). It was, however, regarded as acceptable to achieve a level between 50 and 500 ppm

and to dispose of equipment by 31 December 2000 unless the exemptions set out under the

Environmental Protection (Disposal of Polychlorinated Biphenyls and other Dangerous Substances)

Regulations, apply.

Control of solid waste

The overall stages in handling waste are summarized in Figure 16.2. The treatment methods

applicable to it are listed in Table 17.11.

The range of precautions required during handling, transfer, and disposal, e.g. by landfill,

depend upon the risk including the nature and degree of contamination and the work to be

undertaken.

It will, however, encompass personal protective equipment: a high standard of personal hygiene;

enclosure, possibly pressurization and regular cleaning of vehicle cabs; vehicle washing facilities;

site security, and control of designated dirty areas. Air monitoring and medical surveillance may

be required.

Monitoring and auditing

Auditing

The basic database for the control of environmental pollution is a pollution inventory, viz. a

tabulation of emissions, discharges and wastes from the factory or activity covering all operating

phases. This includes:

• atmospheric emissions; continuous, occasional and fugitive emissions during normal operation,

start-up, shutdown, etc.;

• aqueous discharges; to sewers, direct to controlled waters, etc.;

• solid wastes; by type, origins, routes;

• noise; by reference to environmental noise surveys with identification of special features, tonal

characteristics and intermittency;

• transport; normal plus any hazardous cargoes.

An environmental audit is a systematic, documented, periodic and objective evaluation of how

well environmental organization, management and equipment are performing. The aim is to help

safeguard the environment by:

• assessing compliance with company policies, including compliance with all regulatory

requirements; and

• facilitating management control of environmental practices.

MONITORING AND AUDITING 533

534 CHEMICALS AND THE ENVIRONMENT

Table 17.11 Treatment methods for solid waste

Treatment method Examples/comments

Chemical

Calcination Gypsum

Chlorination Tin removal

Cooking Inedible offal

Froth flotation Coal recovery

Glass

Hydrolysis Household refuse

Vegetable waste

Incineration Household refuse, rubber tyres

Leaching Gives an aqueous solution for treatment as liquid waste

(Table 17.4)

Oxidation Weathering

Pyrolysis Household refuse

Polystyrene

Sintering Colliery spoil

Millscale

Physical

Adhesion Household refuse

Agglomeration Pulverized fuel ash

Ballistic separation Household refuse

Baling Cans, paper, cardboard

Centrifugation Animal oil separation

De-oiling swarf

Classification (air) Household refuse

Classification (wet) Plastic

Comminution Mining wastes

Motor vehicles

Compaction Household refuse

Dewatering Sewage sludge

Dissolution Forms a liquid waste for treatment as in Table 17.4

Drying Filter cake

Electrostatic separation Household refuse

Foaming Slag

Freezing Meat products

Granulation Slag

Impalement Household refuse

Jigging Household refuse

Magnetic treatment Iron removal from slag

Household refuse

Melting Selective non-ferrous metal recovery

Pelletization Iron and steel fines

Pulverization Household refuse

Swarf

Quenching Incinerator residues

Screening Clinker

Settlement China clay wastes

Shape separation Household refuse

Sliding separation Household refuse, agricultural wastes

Biological

Anaerobic digestion Farm waste

Bacterial leaching Low-grade copper ore

Composting Household refuse

Degradation Plastic

Fermentation Requires solution or dilute slurry,

see

Table 17.4

Audits may differ. Some concentrate on particular facets, e.g. waste minimization, energy

conservation. A management audit will probably cover organizational structures and relationships,

communications, procedures acceptance and implementation, training and quality assurance. A

technical audit will consider the performance of plant and equipment, monitoring and inspection

programmes. Items for inclusion in auditing are listed in Table 17.12.

Table 17.12 Some items in a typical environmental pollution audit

• Checks on environmental policy, organization and responsibilities, legislation, training records, emergency plans, performance

targets, means of investigating incidents and written work instructions.

• Listing gaseous emissions, concentrations, smoke characteristics; prevailing winds and exposed zones; toxicity or nuisance

potential; effects of synergism or poor atmospheric dispersing conditions. Consent limits. Compliance record keeping.

• Querying the adequacy of chimneys and stacks, scrubbers and particulates collection equipment (e.g. filters, cyclones).

• Listing effluents, their analyses and discharge from processes. Querying flammability, corrosivity, toxicity, miscibility,

reactivity. Checking the reliability of treatment and analysis. Consent limits. Compliance record keeping.

• Listing of ‘solid’ wastes, quantities, analyses and physical form (e.g. solid, slurry, suspension, sludge); ‘toxicity’ and

flammability. Checking the reliability and legality of waste disposal options, including any transportation offsite. Record

keeping.

• Bunding of storage areas, segregation of waste storage areas, security of landfill sites, etc.

• Soil contamination.

• Monitoring (preferably continuous). Record keeping (on- and off-site).

• Checking for land contamination, e.g. analysis of soil samples. Record keeping.

• Checks on waste removal. (Whilst a producer is under no obligation to audit his waste’s final destination, such a visit is

a prudent means of demonstrating the steps taken to prevent subsequent illegal treatment of the waste.)

• Checking noise levels (on- and off-site).

Specific attention is given to auditing for compliance with legislation, including the requirements

of IPC, BATNEEC and BPEO.

Monitoring

Monitoring of emissions, discharges and disposals is a prerequisite of control. Depending upon

the waste stream, sampling and analysis may be continuous or periodic. Measurement methods

for physico-chemical properties and chemical analysis of waste streams are very diverse. The data

obtained are used both for monitoring to ensure adequate control and compliance with legislation,

and for process plant design and operation – including recycling and recovery. A selective list of

methods for physico-chemical properties is given in Table 17.13 and for chemical analysis in

Table 17.14.

All the parameters on which various consents (or permissions to dispose of, waste streams) are

based must be reliably measured and recorded. This is easier to achieve with gaseous emissions

(Chapter 10) and liquid effluents than with heterogeneous solid wastes. Systematic analysis of

solid wastes will cover as a minimum the information in Table 17.15.

The gold standard for environment management systems is BS EN ISO 14001 as summarized

by Table 17.16.

MONITORING AND AUDITING 535

536 CHEMICALS AND THE ENVIRONMENT

Table 17.13 Methods for measurement of physico-chemical properties

(R = routine test)

Gaseous wastes

Property For consideration Methods

Gases generally

Calorific value Incineration with/without heat Calculation from published data

recovery Calorimeters

Concentration of gaseous (R) Disposal constraints Chemical analysis (q.v.)

pollutant Design of treatment/disposal/ Chromatography

recovery plant

Density Dispersion Chancel flask, or effusiometer

Design of disposal/treatment

plant

Dewpoint Design of treatment/disposal/ Tabulated

recovery plant Hygrometer ASTM method

Condensation

Flammable limits Fire and explosion hazard Tabulated

Control of combustion

Flammability Fire and explosion hazard s

Calorific value and

Control of combustion Flammable limits

ASTM methods

Ignition temperature Fire and explosion hazard Adiabatic compression

Control of combustion Concentric tube

Tabulated

Moisture content

see

Dewpoint Subjective testing

Potential nuisance ASTM methods

Disposal Proprietary meters

Necessity for treatment

Pressure Design of treatment/disposal/ Gauges

recovery plant Transducer

Manometer

Solubility of pollutant (R) Design of separation/ Wide range

treatment plant ASTM methods

Tabulated

Temperature (R) Corrosion resistance Thermometer

Design of treatment/disposal Thermocouple

plant Resistance treatment

Materials of construction Pyrometer

ASTM methods

Velocity (R) Design of disposal/treatment Pitot tube

plant Anemometer

Orifice plate, etc.

Rotameter

Gas meters

ASTM method

Viscosity Design of disposal/treatment Calculated or tabulated

plant

Liquids suspended in gases

(