PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

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PRACTICAL GUIDE ON THE SELECTION
OF PROCESS TECHNOLOGY FOR THE
TREATMENT OF AQUEOUS ORGANIC
EFFLUENT STREAMS
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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR
THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS
CONTENTS
0 INTRODUCTION/PURPOSE
1 SCOPE
2 FIELD OF APPLICATION
3 DEFINITIONS
3.1 IPU
3.2 AOS
3.3 BODs
3.4 COD
3.5 TOC
3.6 Toxicity
3.7 Refractory Organics/Hard COD
3.8 Heavy Metals
3.9 EA
3.10 Biological Treatment Terms
3.11 BATNEEC
3.12 BPEO
3.13 EQS/LV
3.14 IPC
3.15 VOC
3.16 F/M Ratio
3.17 MLSS
3.18 MLVSS
4 DESIGN/ECONOMIC GUIDELINES

5 EUROPEAN LEGISLATION
5.1 General
5.2 Integrated Pollution Control (IPC)
5.3 Best Available Techniques Not Entailing Excessive Costs (BATNEEC)
5.4 Best Practicable Environmental Option (BPEO)
5.5 Environmental Quality Standards(EQS)
6 IPU EXIT CONCENTRATION
7 SITE/LOCAL REQUIREMENTS
8 PROCESS SELECTION PROCEDURE
8.1 Waste Minimization Techniques (WMT)
8.2 AOS Stream Definition
8.3 Technical Check List
8.4 Preliminary Selection of Suitable Technologies
8.5 Process Sequences
8.6 Economic Evaluation
8.7 Process Selection
APPENDICES
A DIRECTIVE 76/464/EEC - LIST 1
B DIRECTIVE 76/464/EEC - LIST 2
C THE EUROPEAN COMMISSION PRIORITY CANDIDATE LIST
D THE UK RED LIST
E CURRENT VALUES FOR EUROPEAN COMMUNITY ENVIRONMENTAL
QUALITY STANDARDS AND CORRESPONDING LIMIT VALUES
F ESTABLISHED TECHNOLOGIES
G EMERGING TECHNOLOGY
H PROPRIETARY/LESS COMMON TECHNOLOGIES
J COMPARATIVE COST DATA

FIGURES
1 INTERMEDIATE PROCESS UNIT SYSTEM
2 AOS TREATMENT - SELECTION PROCEDURE (INLET
CONCENTRATION)
3 AOS TREATMENT - SELECTION PROCEDURE (OUTLET
CONCENTRATION)
4 LIQUID WASTE TREATMENT PROCESSES

0 INTRODUCTION/PURPOSE
This Guide is one in the series of GBHE's Environmental Technical Practice Guides. Its
purpose is to provide the practicing Process Engineer with:
(a) A brief, simple environmental framework within which initial process design work
handling aqueous organic streams (AOS) can proceed efficiently.
(b) A structured selection procedure which will facilitate the generation of a small
number of competing flowsheet schemes. These options will then be further
refined prior to selection of the preferred process.
(c) A summary of the commercially proven and emerging technologies for the
treatment of Aqueous Organic Streams.
1 SCOPE
This Guide presents in outline those key factors which need to be
addressed by the chemical engineer when faced with the task of
generating preliminary flowsheet schemes for the treatment of AOS. The
guide does not present technical data to be used for design purposes, nor
does it attempt to replicate detailed descriptions of alternate technologies.
This information should be sought in Research reports, from in-house
specialists, in the literature and from contractors.
2 FIELD OF APPLICATION
This Guide is available to Process Engineers in GBH Enterprises
Worldwide.
3 DEFINITIONS
3.1 IPU
An Intermediate Process Unit utilizes any suitable technology to treat plant
Aqueous Organic Streams in such a way that all water, surplus to
production requirements, is exported from the plant as Product streams.
Such streams may require further treatment prior to discharge to receiving
waters. Further treatment may be on site or off site (e.g. a biological
treatment unit), (see Figure1).

The IPU system will be designed to achieve the best overall economics
while meeting environmental constraints focusing on:
(a) Recycle of material back into the process either for reuse or
destruction.
(b) Technical and economic integration with any downstream biological
unit, e.g. selective removal of those chemicals which are not to
enter receiving waters but are impractical or more expensive to
remove either by biological treatment or subsequent tertiary
treatment.
(c) Achievement of adequate quality control of the exported aqueous
product stream.
All AOS should be listed as candidates for treatment by an IPU system.
3.2 AOS
Aqueous Organic Streams are single phase, contain dissolved organics,
and are surplus to process requirements, (see 8.3).
3.3 BODs
The chemical oxygen demand is determined by a batch reactor test in
which microbes are allowed to degrade organic matter in the presence of
oxygen over a period of 5 days at 20°C.
3.4 COD
The chemical oxygen demand is determined by a procedure in which a
chemical oxidizing agent is added to the sample and refluxed for 2 hours.
The amount of oxidizing agent destroyed in the test is proportional to the
COD of the sample. The COD value will normally be higher than the
BODs.

3.5 TOC
Total organic carbon is measured by converting all of the carbon present
in the sample into carbon dioxide by combusting the sample in a high
temperature furnace and measuring the carbon dioxide formed by infrared
spectroscopy.
3.6 Toxicity
The definition of toxicity raises complex issues beyond the scope of this
Guide.
The considerable concern that waste waters can convey hazardous
materials into the environment has led to legislation in virtually every
country. In the EC and U.K., lists of dangerous substances (see 5.1) have
been issued under legislation with selection based on considerations of
toxicity, persistence and bio-accumulation. In the U.S.A. the situation is
similar, but greater emphasis is placed on acute toxicity tests.
The key test for acute toxicity is LC50 which means that approximately
50% of the aquatic species (usually fish) used in the test will die under the
conditions of concentration and time given. The term TLm (Median
Tolerance Limit) means that approximately 50% of the fish will show
abnormal behavior (including death) under the conditions given.
Legislation, which may be different from one country to another, is moving
toward "toxicity based consent" based on identified species. In cases of
discharges to municipal treatment plants, the toxicity of the discharged
effluent to the microbes in the treatment process has to be determined.
3.7 Refractory Organics/Hard COD
These are organic chemicals which resist biodegradation. Examples
include some halogenated hydrocarbons and chlorinated pesticides.
3.8 Heavy Metals
Any cation having an atomic weight greater than 23 should be considered
to be a heavy metal. These are persistent and can be toxic/carcinogenic.

3.9 EA
Environment Agency
3.10 Biological Treatment Terms
"Equalization" is the provision of storage capacity for effluent in order to
reduce the variability of waste water flow rates and composition to
acceptable levels which protect the treatment plant from shock pollutants
and hydraulic loadings. These variations may occur, for example, due to
cyclical process operations, unsteady state process operation,
spillage, plant maintenance operations, fire-water and storm-water.
"Primary Treatment" means the first major operation in a waste water
treatment works in which a substantial proportion of the suspended solids
contained within the incoming waste water are removed, usually by
sedimentation.
"Secondary Treatment" means treatment by biological methods and is
usually preceded by primary treatment.
"Tertiary or Advanced Treatment" processes control specific organic and
inorganic pollutants. The more common processes are used for the
removal of nitrogen and phosphorus nutrients. Other more special-
purpose processes include carbon adsorption, ion exchange and reverse
osmosis.
3.11 BATNEEC
Best Available Techniques Not Entailing Excessive Costs.
3.12 BPEO
Best Practicable Environmental Option.
3.13 EQS/LV
Environmental Quality Standards, this is usually expressed as an annual
average. Limit Value.

3.14 IPC
Integrated Pollution Control.
3.15 VOC
Volatile Organic Compounds.
3.16 F/M Ratio
Feed to biomass ratio usually expressed in (g/day)/g.
3.17 MLSS
"Mixed-Liquor Suspended Solids"; the concentration of suspended solids
in the "mixed-liquor", measured by filtration and drying. Beware: dissolved
salts can lead to misleading results. The value includes active biosolids,
inactive biosolids and inert non-biosolids.
3.18 MLVSS
"Mixed-Liquor Volatile Suspended Solids"; the concentration of suspended
solids in the "mixed-liquor" which are capable of being vaporized in at
500°C. Measured by filtration on ashless paper and incineration in a
muffle-furnace. Commonly used to estimate (MLSS - inorganic inerts); not
equal to active biomass.
4 DESIGN/ECONOMIC GUIDELINES
During the design of any plant the following recommendations should be
considered by the process engineer:
(a) Check out the Project philosophy regarding "Cleaner Technology"
and contribute to its formulation as appropriate.
(b) Rigorously apply waste minimization techniques by avoiding the
production of waste or reducing its rate of production

Note: AOS may contain material that could be profitably upgraded and
sold as a byproduct.
(c) Assess the selection of process technology/operating conditions and
methods of process control with a view to eliminating/reducing AOS.
(d) Assess the design of equipment with a view to minimizing AOS produced
during start-up, shutdowns, product changes, plant maintenance and
equipment cleaning operations.
(e) The AOS produced in the process should not be flow sheeted to enter the
site drainage system except where specific approval is given by Site
Environmental Group.
(f) AOS produced in a plant should not be mixed with each other unless there
is a clear economic case for treating several AOS in a single IPU. In most
cases, it is more economic to treat a concentrated stream at source.
(g) All on-plot plant AOS, including intermittent discharges, should be piped
above ground to an IPU, except where this can be shown to be
unnecessary.
(h) Special consideration should be given to the case for removing any
volatile compounds contained in AOS in an IPU.
(j) Each on-plot effluent stream leaving an IPU should have Product Status
and therefore a specification to show that it meets the requirements of the
Site Drainage system and the input conditions of any downstream
biological treatment that may be required.

The specification should include definition of:
(1) Flow Rate
(2) Composition
(3) Temperature
(4) BOD/COD/TOC
(5) pH
(6) Volatiles
(7) Color
(8) Suspended/dissolved solids/salts
(9) Toxicity
(10) Metals
(11) Stream availability/variability
(k) Any project economic evaluation should include the cost involved in
treatment of AOS to meet the Site and legal requirements.
(l) Work on preliminary flowsheet schemes should assume that EA
authorization will take into account the effect of any downstream treatment
stages through which the plant effluent would pass. In consequence, the
process engineer should make an early check on existing/planned on-site
or off-site facilities and establish through the Project Team the technical
basis on which these facilities could be utilized.
5 EUROPEAN LEGISLATION
5.1 General
Most EC Directives relating to the discharge of "dangerous substances" to
water are based on the framework Directive 76/464/EEC. The aim of this
Directive is to cause a reduction in the level of pollution of Community
water by defined "dangerous substances". The most harmful of these
substances were selected on the basis of their toxicity, persistence in the
environment and bio-accumulation and are included in List 1 of the
Directive (Appendix A), known as the "Black List". The less harmful
substances were selected because they have a deleterious effect on the
aquatic environment and are included in List 2, the " Grey List"
(Appendix B).

It should be understood that List 1 and List 2 contain both individual
substances and families and groups of substances from which specific
substances will be identified and characterized in subsequent daughter
Directives but this is proving to be a slow process. Daughter Directives
have been issued for mercury, cadmium plus some pesticides and
chlorinated organic compounds. The European Commission has
established a priority list of 132 substances (Appendix C) which are
candidates for inclusion under the Directive.
"The Red List" was defined in the United Kingdom North Sea Action Plan
1985-1995. The Trade Effluent Regulations 1989 and 1992 require special
control of the discharge of Red List substances (plus carbon tetrachloride
and trichloroethylene) to sewer. The Red List was used as a basis for
defining prescribed substances to water under the Environmental
Protection Act 1990. Appendix D is the original Red List.
5.2 Integrated Pollution Control (IPC)
Release of prescribed substances is subject to integrated pollution control
(IPC) measures as required by the Environmental Protection Act 1990 and
in line with the EC Directive's requirement that any discharge of List 1 or
List 2 substances into the aquatic environment should be subject to
prior authorization.
In practice, IPC covers the whole of the chemical industry. For the
purposes of this guide its most important requirements are covered by 5.3
to 5.5.
5.3 Best Available Techniques Not Entailing Excessive Costs
(BATNEEC)
Ensure that best available techniques not entailing excessive costs
(BATNEEC) will be utilized to:
(a) Prevent the release of prescribed substances or, where that is not
practicable, reduce the release of such substances to a minimum
and sufficiently low level which is judged to be harmless.
(b) Similarly render harmless any other substances which might cause
harm if released.

5.4 Best Practicable Environmental Option (BPEO)
Ensure that BATNEEC will be used for minimizing the pollution which may
be caused by releases to the environment taken as a whole having regard
to the best practicable environmental option (BPEO) available.
5.5 Environmental Quality Standards(EQS)
Compliance with any Environmental Quality Standards(EQS) prescribed
by the Secretary of State.
Whereas the EQS (or quality objective in EC terminology) approach
applies to List 2 substances throughout the European Community,
Member States have a choice of two methods of control for discharges of
List 1 substances. The U.K. favors the use of EQS which specify
concentration limits in the receiving water. Therefore, the chemical
engineer should seek guidance from the Site Environmental Adviser
regarding the degree of dilution between the discharge point and the
receiving water before using EQS. The alternative Limit Value (LV)
approach utilizes fixed maximum emission quantities/concentrations which
are specific to a given sector of industry. In consequence, these LVs can
be used directly to arrive at an exit stream design specification.
Unfortunately, from the viewpoint of the chemical engineer, the number of
substances for which LVs have been issued is limited (see Appendix E).
6 IPU EXIT CONCENTRATION
Determining for design purposes the quantity and composition of Product leaving each
IPU is a complex exercise. The following factors should be taken into account:
(a) Project Team directed discussion with GBHE has the expertise to advise on
environmental matters.
(b) Process definition and performance of BATNEEC.
(c) Assessment of BPEO options.
(d) Receiving waters - more than one option?
(e) Downstream treatment options:
(1) plant Works or Site bio unit;
(2) municipal sewerage undertaker;
(3) direct discharge to receiving waters;
(4) tertiary treatment.

(f) Relevant Environmental Quality Standards and Limit Values (see!5.5).
(g) Toxicological test results.
(h) Existing and projected EA authorization and NRA/RPB consent requirements
and conditions.
7 SITE/LOCAL REQUIREMENTS
It is recommended that all project flowsheet proposals should be
discussed at an early stage with:
(a) Site Environmental Group.
(b) GBH Enterprises
In consequence, the Project Team may then decide to obtain further
information from external sources as appropriate.
In the case of projects not preceded by a research stage, these
discussions should be part of the work undertaken to generate basic
flowsheet options.
All ongoing research projects should review their future work program
periodically in this way as part of an environmental impact assessment.
This may require some experimental evaluation of the specific toxicity of
the individual components of the effluent stream which, together with the
discharge rates, may be an important factor in the selection of treatment
processes.
8 PROCESS SELECTION PROCEDURE
The recommended procedure for selection of candidate processes for use
by an IPU includes seven stages. See 8.1 to 8.7.
8.1 Waste Minimization Techniques (WMT)
Apply WMT to achieve waste elimination, recovery and recycle within the
process to minimize the size of an AOS. [See Ref 1].

8.2 AOS Stream Definition
Define each AOS in terms of:
(a) Chemical analysis/VOC
(b) Toxicological tests
(c) Temperature/pressure
(d) pH, BOD, COD, TOC
(e) Flow rate/availability pattern
(f) Variability
Once the composition and key toxic components are known, it is
necessary to form an initial view of the allowable final emission levels from
the IPU for each of the parameters listed above (see Clause 6).
8.3 Technical Check List
8.3.1 Parameters
Apply the following technical check list. These parameters, if present in
the AOS, can influence substantially the choice of treatment technology.
(a) Foams
(b) Emulsions
(c) Suspended solids
(d) Immiscible liquids
(e) Azeotropes
(f) Color
(g) Volatile organics
(h) Salts/Complexes

8.3.2 Other Factors
In multi-step treatment processes the progressive change in AOS
composition may cause problems to occur in subsequent stages e.g.:
(a) A stream suitable for Bio-treatment may become unsuitable
following extraction with a solvent which is toxic to the bio-
organism.
(b) A change in pH may precipitate some soluble organics or metals.
(c) Acids may form during an oxidation step and cause corrosion.
(d) The properties of a non-foaming liquid may be changed in such a
way that it will generate frothing.
8.4 Preliminary Selection of Suitable Technologies
8.4.1 General
Review the Established Technologies and Emerging Technologies listed
in 8.4.2 and 8.4.3 and expanded in Appendices F and G respectively, then
select a short list of technology options. This activity may be assisted by
utilizing Figures 2 and 3 which differentiate treatment technologies by
applying two criteria:
(a) Initial concentration of dissolved Organics in the water (Figure 2).
(b) The final concentration required (Figure 3).
In addition, reference should be made to Appendix H and Figure 4 which
categorize liquid waste treatment processes by application.

8.4.2 Established Technologies
The technologies listed below are described in outline in Appendix F.
(a) Bio Treatment: Aerobic: - Activated Sludge
- VITOX
- Deep Shaft
- Bio Towers
Anaerobic
(b) Physical Separation
(1) Coagulation/Flocculation
(2) Distillation
(3) Stripping
(4) Steam Stripping
(5) Air Stripping
(6) Liquid/Liquid extraction
(7) Adsorption: - General
- Granular Carbon
- Powder Carbon
- Charcoal
- Zeolites/polymeric
- Ion exchange
(c) Membrane processes - General
- Microfiltration
- Ultra filtration
- Reverse Osmosis
- Pervaporation
- Electro dialysis
(d) Chemical Oxidation - Wet Air Oxidation
- U.V. Light
- U.V. Light + H2O2
- Ozone
- H2O2/Fe
- Other
(e) Thermal Oxidation - Total (Incinerators)
- Partial (Oil-Gas process)

8.4.3 Emerging Technologies
The technologies listed below are described in outline in Appendix G.
(a) Supercritical Water Oxidation
(b) Liquid Membranes
(c) Reed Beds
8.5 Process Sequences
In some cases it will not be possible or desirable to achieve the required
design objective by using a single technology, and several treatment steps
may have to be designed to operate in sequence.
In addition, the most suitable options for treating each individual AOS can
be listed as a basis for generating alternative process flow schemes which
combine the several AOS in different ways. A comparative evaluation will
then lead to a short list of preferred options. These should be assessed in
more detail by following up appropriate references and discussion with
GBHE specialists/contractors.
8.6 Economic Evaluation
Economic evaluation data obtained from sources external to the Project
Team should be treated with caution. In this first issue of the Guide no
internally generated economic assessment data has been provided.
However, some published comparative cost data has been appended (see
Appendix J) which shows the variability of costs as a function of the
specific chemical composition of each stream.
An example of the type of problem commonly met in this area are cost
comparisons which, when examined in detail, are found to apply to
different technical definitions (e.g. items of equipment are omitted or
feed/product qualities are different.)

8.7 Process Selection
The main objective at this final stage is to identify those options which
perform strongly when judged against the following criteria:
(a) Compliance with legislation.
(b) Compliance with GBHE rules and requirements.
(c) Low capital cost.
(d) Low operating cost.
(e) High reliability.
(f) Compatibility with existing and projected Site operations.
The process engineer should then justify to the Project Team his/her
selection of preferred options. It is likely that considerable Project effort
will then be applied to refine the preliminary selection referred to here in
order to select a preferred process. In some cases it may also be
necessary to reassess other factors, for example, the chemistry of the
process or the location of the plant.

APPENDIX A DIRECTIVE 76/464/EEC - LIST 1
List 1 contains individual substances which belong to the following families and
groups of substances, selected mainly on the basis of their toxicity, persistence
and bio-accumulation with the exception of those which are biologically harmless
or which are rapidly converted into substances which are biologically harmless.
(1) Organo-halogen compounds and substances which may form such
compounds in the aqueous environment.
(2) Organo-phosphorus compounds.
(3) Organotin compounds.
(4) Substances in respect of which it has been proved that they possess
carcinogenic properties in or via the aquatic environment. (Where certain
substances in List 2 are carcinogenic they are included in this category).
(5) Mercury and its compounds.
(6) Cadmium and its compounds.
(7) Persistent mineral oils and hydrocarbons of mineral origin, and for the
purposes of implementing Articles 2, 8, 9 and 14 of this Directive.
(8) Persistent synthetic substances which may float, remain in suspension or
sink and which may interfere with any use of the waters

APPENDIX B DIRECTIVE 76/464/EEC - LIST 2
List 2 contains:
(a) Substances belonging to the families and groups of substances in List 1
for which the limit values referred to in Article 6 of the Directive have not
been determined.
(b) Certain individual substances and categories of substances belonging to
the families and groups of substances listed below, and which have a
deleterious effect on the aquatic environment, which can, however, be
confined to a given area and which depend on the characteristics and
location of the water into which they are discharged.
Families and groups of substances referred to in the second indent:
(1) The following metalloids and metals and their compounds:
1 Zinc 8 Antimony 15 Uranium
2 Copper 9 Molybdenum 16 Vanadium
3 Nickel 10 Titanium 17 Cobalt
4 Chromium 11 Tin 18 Thallium
5 Lead 12 Barium 19 Tellurium
6 Selenium 13 Beryllium 20 Silver
7 Arsenic 14 Boron
(2) Biocides and their derivatives not appearing in List 1.
(3) Substances which have a deleterious effect on the taste and/or smell of
the products for human consumption derived from the aquatic
environment, and compounds liable to give rise to such substances in
water.
(4) Toxic or persistent organic compounds of silicon and substances which
may give rise to such compounds in water, excluding those which are
biologically harmless or are rapidly converted in water into harmless
substances.
(5) Inorganic compounds of phosphorus and elemental phosphorus.
(6) Non persistent mineral oils and hydrocarbons of petroleum origin.
(7) Cyanides and fluorides.

(8) Substances which have an adverse effect on the oxygen balance,
particularly: ammonia, nitrites.

APPENDIX F ESTABLISHED TECHNOLOGIES
Table of Contents
F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS
F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS
F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT
F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS
F.5 BIO TREATMENT: ANAEROBIC PROCESSES
F.6 COAGULATION/FLOCCULATION
F.7 DISTILLATION
F.8 STRIPPING
F.9 AIR STRIPPING: PACKED COLUMNS
F.10 AIR STRIPPING: HIGEE
F.11 LIQUID/LIQUID EXTRACTION
F.12 ADSORPTION - GENERAL
F.13 ADSORPTION: GRANULAR CARBON
F.14 ADSORPTION: POWDER CARBON
F.15 ADSORPTION: BONE CHARCOAL
F.16 ADSORPTION: POLYMERIC/ZEOLITES
F.17 ADSORPTION: ION EXCHANGE
F.18 MEMBRANE PROCESSES (GENERAL)
F.19 MEMBRANE PROCESSES: MICROFILTRATION

F.20 MEMBRANE PROCESSES: ULTRAFILTRATION
F.21 MEMBRANE PROCESSES: REVERSE OSMOSIS
F.22 MEMBRANE PROCESSES: PERVAPORATION
F.23 MEMBRANE PROCESSES: ELECTRODIALYSIS
F.24 CHEMICAL OXIDATION: WET AIR OXIDATION (WAO)
F.25 CHEMICAL OXIDATION: U.V. LIGHT
F.26 CHEMICAL OXIDATION: U.V. LIGHT + H202
F.27 CHEMICAL OXIDATION: OZONE
F.28 CHEMICAL OXIDATION: H2O2/Fe (FENTON'S REAGENT)
F.29 CHEMICAL OXIDATION: OTHERS
F.30 TOTAL THERMAL OXIDATION: INCINERATION
F.31 PARTIAL THERMAL OXIDATION: OIL-GAS PROCESS

F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS
F.1.1 Introduction
Aerobic biological waste water treatment is the process by which
microorganisms consume biodegradable organic compounds and free
oxygen to produce cell growth, CO2 and water.
Bio treatment can only destroy biodegradable compounds and therefore
those chemicals which are not biodegradable (hard COD) will pass
through and will require additional treatment. Not all the biodegradable
material is oxidized and the BOD5 leaving the treatment beds depends on
the design of the process, the technology employed and the residence
time, and can vary from 5 to 40% of the original BODs.
F.1.2 Process Description
Several types of bio treatment processes have been operated over the
years. Differentiation between these requires a careful assessment of cost
and performance on a project by project basis.
A bio treatment process may include the following additive stages:
(a) Primary treatment:
(1) An equalization stage to minimize concentration and
temperature fluctuations (typical operating temperature 10 to
37°C)
(2) A pH adjustment and nutrients dosing stage to prepare the
feed for the process. (typical pH range 5.5 to 9).
(3) A Suspended Solids removal stage.
(b) Secondary treatment:
(1) The aeration tanks which are agitated to maintain the
biomass in suspension and where air or oxygen is injected.
The sizes of the tanks depend on the stream mass flow, the
type and concentration of chemicals present and the exit
BOD/COD levels required (i.e. standards and legislation).

(2) A sedimentation stage to separate the biomass from the
water and allow recycle of the biomass to the aeration tanks.
(3) A sludge thickening stage. This is applied to surplus sludge
to reduce its water content to a level suitable for further
treatment or landfill.
(c) Tertiary treatment:
Removal of specific organic or inorganic pollutant such as hard
COD/metals and excess nutrients (phosphorus and nitrogen
compounds if they have not been removed in the
nitrification/ denitrification section of a secondary treatment).
(d) Sludge disposal:
An appropriate sludge disposal stage: for example, landfill, land
spread, incineration, digestion in aerobic or anaerobic digesters or
Wet Air Oxidation.
F.1.3 Process Requirements/Limitations
(a) A substantial amount of land is required to locate the equipment,
although it can be reduced by using Deep Shaft and similar "tower"
processes.
(b) Electric power is required to ensure adequate mixing/the
` suspension of the solids if necessary and oxygen/air mass transfer.
There are several generic and proprietary methods for dispersing
the air and maintaining solids suspension (e.g. surface aerators,
liquid jet aerators, fine bubble diffusers, venting aerators, etc.). The
total power requirement is one of the main factors in the choice of
process. Typical values are 0.05 kW/m3
with an oxygen transfer
capability of 2 kgO2/kW.h.
(c) In the absence of a specific treatment stage:
(1) Heavy metals will either remain dissolved in the water or will
accumulate in the biomass and may create subsequent
sludge disposal problems.

(2) The non-biodegradable chemicals will not be oxidized, and if
allowed to remain in the effluent may result in toxic
effect/COD problems in receiving waters.
] (d) The performance of a conventional activated sludge bio treatment
plant can be improved by the addition of powdered activated
carbon. This technology is well established and marketed as the
PACT process by Zimpro Passavant. The main benefits derived
from the combined adsorption/biological oxidation are:
(1) It buffers the system against shock loads of biologically toxic
or inhibitory compounds.
(2) Improved removal of compounds which exhibit only partial or
slow biodegradability.
(3) Improved COD reduction and color removal by adsorption of
Refractory Organics.
(4) Increased hydraulic capacity of an existing facility.
(5) Reduced VOC losses from the aeration basin. However,
VOC could be present in the off-gas from the Wet Air
Regeneration process.
(6) Improved sludge settling capacity.
The choice of carbon is important, but generally speaking the
cheaper "low" activity waste water carbons are more commonly
used.
The economics and elegance of the PACT process may be
improved by adopting Wet Air Regeneration (WAR) of the spent
carbon contained in the surplus biomass. In this manner, excess
biomass is oxidized (the high COD providing autogenous operation
of the reactor) and contained carbon may be regenerated for
recycle. Virgin carbon make-up is required to compensate for
physical losses and deterioration of carbon activity on repeated
regeneration.

(e) The amount of sludge produced per tonne of BODs is a function of
the type of process used and the operating conditions [feed to
biomass ratio (F/M)] but it ranges from about 0.5 tonne/tonne on a
dry weight basis with F/M of 1.0 down to less than 0.1 tonne/tonne
with F/M lower than 0.2.
(f) During plant shutdown periods the biomass should be sustained by
an alternative feed supply. In addition, the design should cater for
the required turndown.
(g) Start-up of a bio treatment system normally takes several days
before BOD removal is effective. In consequence, its design usually
incorporates protection against any identified risk to the biomass
health. This is usually a combination of operating procedures and
detection by analysis which enable unacceptable feed to be
dumped into holding tanks/lagoons. This material can then be
blended into the feed at an acceptable rate.
(h) Temperature influences the rate of reaction but is limited to a
maximum of 40°C in most cases.
(j) The kinetic constants of the biological reactions become dependent
on the mode of operation of the system, as well as the chemical
nature of the waste, and should be determined experimentally.
(k) Minor nutrient (e.g. Fe, K, Mg, Zn, Mn) are also required for
optimum performance.

F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS
F.2.1 Introduction
The VITOX process is a bio treatment process developed by BOC for the
treatment of effluents. Its distinguishing feature is the use of oxygen
instead of air.
The operation of a VITOX process is very similar to the traditional
activated sludge process. However, BOC makes several specific claims:
(a) The use of oxygen allows the process to operate at a higher
biomass concentration "M" and therefore a smaller size biological
treatment tank is required for the same duty.
(b) In the case of existing plants, the extra capacity can be used either
to increase the overall treatment capability by maintaining the F/M
ratio or, alternatively, to reduce the final DOB of the discharge by
operating at a lower F/M.
(c) If the process is operated at low F/M ratios, then the rate of
production of excess biomass can be reduced. In some cases, this
rate can be so low that it is possible to discharge the excess
biomass mixed with the treatment effluent without exceeding the
suspended solid specification of the receiving waters.
(a) It requires a supply of oxygen at a suitable price.
(b) The VITOX process is normally designed to operate with a low F/M
ratio, high "M" concentrations and a low rate of sludge export.
(c) I t may need a larger clarifier because the high operating "M" can
produce hindered settling.
(d) The low sludge production may result in progressive build up of
inert solids (e.g. metals and inorganic salts).

F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT
F.3.1 Introduction
The Deep Shaft process is a specific aerobic process utilizing air as
oxidant and developed by ICI for the treatment of effluents. Its main
difference from a traditional activated sludge process is its design as a
tower which is located underground and therefore it provides a very
compact arrangement.
Each shaft is divided into a down comer and a riser. Compressed gas is
injected into the down comer to induce liquid circulation by an air lift effect,
to create turbulence and supply oxygen to the microorganisms. (During
start-up, air is injected into the riser to establish circulation).
The good mixing, long bubble residence times and large hydrostatic head
create a high oxygen transfer rate, and so with increased availability of
nutrients the BOD degradation rate is maximized. As with conventional
processes, a treatability study is commonly needed for detailed design
purposes.
Gas bubbles disengage in the head tank at the shaft top, and the clarifier
feed is taken from here. Excess sludge is removed from the clarifier.
There are several specific claims for the Deep Shaft process:
(a) A very small land requirement for the biological bed.
(b) An intensified process due to the high hydrostatic pressure
generated at the bottom of the shaft which increases the oxygen
transfer rate.
(c) An enclosed system which can be located in sensitive areas like
building basements and proximity to domestic housing.
(d) Lower power input than traditional designs.

To date, the Deep Shaft has been operated with air, and air/oxygen
mixtures.
Anti-froth agents may need to be added to avoid frothing in the head tank.

F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS
F.4.1 Introduction
The bio-tower technology is an alternative to the conventional activated
sludge plants which uses enclosed tanks of up to 30 m height instead of
open basins. This results in a more compact design and, in some cases,
lower capital and energy costs.
The aeration is provided by the injection of air into the waste water stream.
The mixture of air and waste water is then injected at several points at the
bottom of the tower to achieve uniform distribution of the air. The height of
the tower determines the hydrostatic pressure and the solubility of oxygen
at the point of injection. This results in a much higher oxygen efficiency
than that achieved by conventional activated sludge plants.
Additional claims for the bio-tower design (compared with a conventional
activated sludge process) are:
Volume of air required 20%
Energy required 40-50%
Land area required 20%
The closed tank design facilitates elimination of pollution by fumes and
aerosols.

F.5 BIO TREATMENT: ANAEROBIC PROCESSES
F.5.1 Introduction
Anaerobic treatment is a biological process in which microorganisms
convert organic compounds in the presence of water into methane, CO2,
cellular materials and other organic compounds.
Anaerobic processes do not require the introduction of air or oxygen.
Some microorganisms are able to operate both under aerobic or
anaerobic conditions while other are specifically anaerobic.
There are three basic types of reactor systems:
(a) Deep lagoons - often used as pretreatment but which can have an
odor problem.
(b) Enclosed vessels with suspended growth - with separation and
recycle of the suspended solids.
(c) Enclosed vessels with fixed growth - in which the microbial growth
is attached to solid surfaces provided in the form of packing or
particles in the case of a fluidized bed system.
Anaerobic treatment has the following characteristics:
(a) Suitable for:
(1) pretreatment of high strength waste streams;
(2) waste water sludge destruction.
(b) Low sludge production rate.
(c) Energy potential of the off-gas produced.

(d) Reaction rate is slow compared with aerobic processes and needs
higher temperatures.
(e) Anaerobic treatment can destroy some chemicals which are not
degradable by an aerobic process.
(f) Effluent from anaerobic processes usually requires further
treatment prior to discharge to receiving waters.
(g) Very sensitive to variations in incoming effluent composition and
flow rate.
(h) Sulfates in the effluents are reduced to H2S which may require
corrosion resistant materials of construction.

F.6 COAGULATION/FLOCCULATION
F.6.1 Introduction
Coagulation and flocculation are well established methods for removing
soluble and insoluble organic compounds from water and are generically
known as Physical - Chemical processes. They are mainly used prior to
biological processes to partially remove suspended solids, colloidal
particles and dissolved substances (dyes and other hard COD
compounds).
The treatment, which in most cases is specific to the organic compounds
to be removed, requires the pH to be adjusted to insure the optimum
performance of the coagulation and flocculation stages.
The coagulation process involves the addition of a coagulant to the
aqueous stream to destabilize the colloidal suspensions and allow the
organic matter to come out of solution. In most cases a flocculant is also
added to promote the formation of large flocs which can then be separated
by settling.
The most widely used coagulants are iron or aluminum salts although
synthetic cationic polyelectrolyte's can also be used. The inorganic salts
are generally used together with lime or caustic to produce a hydroxide
precipitate.
When using ferrous salts it is possible to use their reducing power to break
the azoic link in some dye molecules and render them colorless.
Coagulants are mainly synthetic organic polymers of acrylamide and
acrylic acid and, depending on their composition, can be cationic, anionic
or neutral. Natural organic polymers, starches and alginates and inorganic
coagulants, activated silica, alumino silicates and clays are also used.
The settling time required depends on the sedimentation rate of the flocs
obtained. The clear liquid is separated from the top of the settling tank and
the concentrated sludge is removed from the bottom and then further de-
watered in a pressure filter before disposal by a suitable method; normally
to landfill, depending on the toxicity of the chemicals present.

The size of the coagulation, flocculation and settling stages depends on
the nature of the physical and chemical reactions taking place and the
type, composition and quantity of the reagents used.
This process requires the addition of specific coagulating and flocculating
chemicals which need to be identified and evaluated during laboratory
trials. Depending on the coagulating chemicals used, the pH may need to
be increased to 9 or 10 using caustic or lime and then neutralized with a
mineral acid or CO2.
In most cases, for economic reasons, the process is operated to achieve
only a partial removal of the BOD and COD and is then followed by a
Biological Treatment Stage to achieve the required discharge values.

F.7 DISTILLATION
F.7.1 Introduction
Distillation as a recovery technique is generally limited to separating
compounds more volatile than water from water itself.
A distillation column consists of two sections:
(a) A stripping section below the feed entry which can be designed to
control the final concentration of volatile organics in the aqueous
product stream.
(b) A rectifying section above the feed which, combined with the choice
of reflux, allows control of the concentration of water in the
recovered organic product stream.
(a) Distillation is used for the recovery of individual organic compounds
or groups of compounds from aqueous streams only if:
(1) their concentration is high enough to make economic sense,
generally greater than 5%, and the water content of the
recovered stream is acceptable either for recycle or
subsequent processing or export;
(2) it is the most cost effective process for removal of
compounds which are highly toxic and have to be separated
to facilitate subsequent treatment of the aqueous stream or
for disposal as a concentrated stream (e.g. by incineration);
(3) relative volatility of organics with water exceeds 1.2. Below
1.2, it is generally more economic to remove high
concentrations of organics by liquid-liquid extraction (see
F.11).
(b) The overhead stream, mainly organics, may require further
treatment or purification if it is to be returned to the process.

F.8 STRIPPING
F.8.1 Introduction
The stripping process is a variant of conventional distillation, utilizing
either a reboiler for steam generation or direct injection of steam from an
outside source. Even relatively high boiling compounds can be removed
efficiently by this method, e.g. Phenol (Boiling point 182°C).
A stripping column consists of one section below the feed designed to
achieve the required low level of organics in the water.
It can operate on a batch or continuous mode.
(a) The overheads are recovered as a mixture of organics in water
which will separate into two phases if immiscible and the
distribution of the organic compounds between the organic and
the water layer will be determined by solubility levels.
(b) Both layers may need to be further treated before disposal or
recycle. In some cases the water layer can be recycled back to the
column.
(c) Removal of high boiling point components is assisted by operation
under vacuum.

F.9 AIR STRIPPING: PACKED COLUMNS
F.9.1 Introduction
Air stripping is the countercurrent contacting in a column of an AOS with a
gas stream usually air or N2, although natural gas has also been used to
strip methanol from water.
It is only useful for volatile organics, that is, compounds with a boiling point
less than 100°C. It can reduce the final COD to less than 0.001ppm and
can remove up to 99.9% of the organics present.
Air stripping is performed in packed columns and requires a substantial
volume of air which then has to be disposed of in an acceptable way to
prevent the organics reaching the environment.
If the columns are operating continuously, the packing may get fouled and
require a continuous or intermittent supply of biocide at a level of 50 to
500 ppm which will be discharged in the water.
Batch operation may need 2 columns and regular cleaning to control
fouling.

F.10 AIR STRIPPING: ICI HIGEE
F.10.1 Introduction
The Higee process intensifies mass transfer between a gas stream and a
liquid stream by means of high "g" forces generated by rotation. For
example, in this way the height of packing required to reach equilibrium for
the EDC/water system is reduced from about 0.8 m per stage in a packed
column to less than 0.06 m achieved in the Higee machine.
The packing has the form of a hollow cylinder which rotates on its axis.
The liquid is distributed on the inside surface and travels through the
packing by centrifugal force. The stripping gas is fed to the outside of the
rotating cylinder and travels through the packing counter currently with the
liquid and is discharged from the centre.
The thickness of the packing, and therefore the outside diameter of the
rotor, is a function of the number of stages required (at about 50 to 70 mm
per stage) and the axial length of the cylinder is determined by the liquid
flow.
The machine operates in the range of 100 to 1000 times terrestrial "g" and
therefore a very small volume of packing is required when compared with
a packed tower.
The standard stacked rings Sherwood correlation for the calculation of
flooding has been found to apply to the rotating packing.
Fouling of various types may develop in the packing.

F.11 LIQUID/LIQUID EXTRACTION
F.11.1 Introduction
Liquid/liquid extraction's main application is to remove organic
components which are present in high concentration (1 to 25%) and the
relative volatility to water is less than 1.2 (otherwise distillation may be
more appropriate)
An organic, low toxicity, preferably biodegradable solvent with very low
water solubility is required.
The process involves the countercurrent contact of the AOS with a water
immiscible, selective organic solvent which is then phase separated from
the treated water.
The loaded organic solvent is then separated from the contained organics
by distillation before recycling it to the extractor. A solvent purge is
normally removed for purification.
The organic solvent will be present in small amounts in the treated water
and, depending on its toxicity, solubility and cost, will have to be removed
for recovery or destruction by a suitable treatment.

F.12 ADSORPTION - GENERAL
F.12.1 Introduction
Adsorption is a well established process for the removal of organic
compounds from industrial waste waters and potable waters. Although a
variety of adsorbents are available commercially, activated carbon is by
far the most popular. This is a broad spectrum adsorbent with a wide pore
size distribution which makes it very attractive for AOS treatment.
Activated carbon is available in two basic forms, viz. powder (PAC) or
granular (GAC). PAC is the cheapest, for example, at about $2/kg
compared with $4-6/kg for a GAC of similar activity, and achieves a higher
adsorption rate but is less amenable to regeneration.
F.12.2 PAC
Fresh PAC is normally added to the aqueous waste in the last stirred tank
in a series. Then, after filtration at each stage, it is transferred through the
remaining tanks countercurrent to the AOS to achieve maximum use of
adsorptive capacity. Regeneration may not be cost effective.
F.12.3 GAC
The use of GAC in fixed beds requires less material handling than PAC.
However, the moving bed version is likely to be more problematical in this
respect. When the adsorption capacity of the carbon is exhausted, the
spent GAC is usually discharged prior to regeneration/reactivation and the
adsorber reloaded with active material. Spent GAC is usually regenerated
and reactivated in large plant using multiple-hearth furnaces.
Regeneration/reactivation losses are typically 5-10% and the
reactivated carbon has different adsorption characteristics to virgin carbon
in part due to enlarged pore sizes caused by the Pyrolysis step. A contract
regeneration/reactivation service is available (e.g. Chemviron Carbons).
Alternatively, it can be incinerated.
If on-line regeneration is feasible, for example by steam stripping, then this
may be preferred.

F.12.4 Key Points
Adsorption is used mainly for the removal of dissolved organics that are
present in small amounts and are difficult to remove by biological
methods. For a given adsorbent/adsorbate system the adsorption
capacity, as defined by the adsorption isotherm, is influenced by many
factors including temperature, solubility, pH, size of adsorbate molecule,
adsorbent pore structure, etc. but the most important factor is the
adsorbate concentration in the aqueous phase. For example, the capacity
of a GAC (expressed as weight adsorbate/weight adsorbent) is expected
to be about 45% when in equilibrium with an aqueous solution containing
2000 ppm Aniline whereas at 1-10 ppm the capacity falls to less than 1%.
The bed life will, however, be appreciable because the quantity of
adsorbate present is so small.
GAC is regenerated by four methods:
(1) Steam Stripping - applied in situations where the
molecular weight of the adsorbate
(in situ) is generally less than 200;
separation usually allows recycle of the
organic layer with the aqueous layer
discharged either to receiving waters or
to biotreatment or recycled to adsorber
feed.
(2) Chemical - e.g. caustic washing to remove Phenol.
(in situ)
(3) Solvent Extraction - e.g. elution of dyestuffs.
(in situ)
(4) Thermal - is used principally at waste water
treatment plants and usually includes
multiple-hearth furnaces. The process
includes drying, volatilization, Pyrolysis,
and reactivation stages. GAC weight
loss is typically 5-10%. Most modern
units employ afterburners operating at
1200/1300°C to destroy any dioxins that
may have been formed.

The bed size in terms of its length/diameter ratio is influenced by the
shape of the adsorption profile through the bed and whether the bed is
regenerated or used on a once-through basis. For example, the more
favorable adsorption profile achieved by chlorobenzene allows the use of
a lower L/D ratio than with dyestuffs while still achieving efficient utilization
of the carbon bed. In the case of dyestuffs adsorption the bed should be
sized for a minimum of two weeks operation on-line compared with only a
few hours for chlorobenzene, depending on the regeneration time.
Hydraulic loadings are usually in the range 1-6 m3
/m2
with the lowest
loadings selected for adsorbates that are slow to adsorb such as
dyestuffs.
Carbon adsorption is commonly used to treat AOS containing from a few
ppb to 2000!ppm of dissolved organics.
If the AOS contains suspended solids then the adsorption bed should be
preceded by a filtration stage.

F.13 ADSORPTION: GRANULAR CARBON
F.13.1 Introduction
Granular carbon is a treatment process for the removal of small amounts
of dissolved, refractory organic compounds from water. It is used when
high quality process water is required for reuse or when the organic
compounds are so toxic that they have to be removed before the effluent
water is finally discharged to receiving waters.
Granular carbon is used in fixed packed beds which operate with
continuous liquid feed until they are economically loaded, at which point
they have to be taken off-line and the carbon either regenerated or
replaced with fresh material.
Various series/parallel equipment arrangements are needed to achieve
the required technical performance and reliability.
In most cases, granular carbon is only economic if the organic compounds
can be removed and the carbon regenerated and reused several times.
The most commonly used methods of regeneration are steam stripping,
solvent extraction and partial combustion, or a combination of these.
Laboratory tests are advisable since:
(a) Some organic compound present in minor amounts in a stream may
interfere with the adsorption of the key component and drastically reduce
the efficiency of the beds.

(b) The presence of inorganic salts may cause an irreversible deactivation of
the carbon which will then have to be replaced.
(c) The reliable calculation of steady-state rate of carbon make-up to a
specific adsorption/regeneration process requires the use of practical
data. During regeneration there is always a mass loss due to attrition and
partial combustion which needs to be compensated by addition of fresh
carbon. However, a further purge and addition of carbon may be
necessary to compensate any progressive irreversible loss of adsorption
capacity.
Granular carbon is usually only suitable economically if it can be readily
regenerated.
The size of the bed has to be calculated so that it takes a reasonable time
to achieve economic loading.
F.13.4 Carbon Properties
Data sheets on carbon properties can be obtained from the following
suppliers:-
NORIT
CHEMVIRON
SUTCLIFFE SPEAKMAN

PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS