SUMGAIT PRIVATE TURKISH HIGH
SCHOOL
SEWAGE TREATMENT TECHNOLOGIESNEW APROACH
Authors:
Bahram Suleymanov &
Elshan Shiraliyev
Sumgait private Turkish high school,
st 20 January, 6, 14 dst, Sumgait, Azerbaijan
Tel: +99450 6307171
Fax: 99412 4479616
E-mail: bahram.suleymanov@gmail.com
elsen.sireliyev@gmail.com
2007- April
CONTENT
Project objectivities .................................................................................................................3
Introduction .............................................................................................................................3
Methods of project ...................................................................................................................3
3.1
Sources and Chemical composition of sewage water ......................................................3
3.1.1
Pathogens .................................................................................................................4
3.1.2
Nutrients ..................................................................................................................5
3.1.3
Floatables .................................................................................................................5
3.1.4
Toxic contaminants .................................................................................................5
3.1.5
Organic materials (BOD).........................................................................................5
3.1.6
Total suspended solids (TSS) ..................................................................................6
3.2
Elements of STP ..............................................................................................................6
3.2.1
Preliminary treatment ..............................................................................................6
3.2.2
Secondary treatment ................................................................................................7
3.2.3
Activated sludge ......................................................................................................8
3.2.4
Filter beds (oxidizing beds) .....................................................................................8
3.2.5
Biological aerated filters ..........................................................................................8
3.2.6
Membrane biological reactors .................................................................................8
3.2.7
Secondary sedimentation .........................................................................................8
3.2.8
Rotating Biological Contractors ..............................................................................8
3.2.9
Tertiary treatment ....................................................................................................9
3.2.10
Filtration ..................................................................................................................9
3.2.11
Lagooning ................................................................................................................9
3.2.12
Constructed wetlands ...............................................................................................9
3.2.13
Waste removal .........................................................................................................9
3.2.14
Nitrogen and phosphorius effects ............................................................................9
3.2.15
Disinfection importancy ........................................................................................10
3.2.16
Disinfection by chlorine ........................................................................................10
3.2.17
Disinfection by UV and Ultrasound irradiation ....................................................10
3.2.18
Disinfection by Ozone ...........................................................................................11
3.2.19
Package plants and batch reactors .........................................................................12
3.2.20
Sludge treatment and disposal ...............................................................................12
3.2.21
Anaerobic digestion ...............................................................................................12
3.2.22
Aerobic digestion ...................................................................................................13
4 Conclusion .............................................................................................................................14
5 Next years planning ...............................................................................................................14
6 References .............................................................................................................................14
1
2
3
LIST OF FIGURES
Fig. 1 Main pollutants in sewage water ...........................................................................................4
Fig. 2 Sewage bacterias ...................................................................................................................5
Fig. 3 Prelinary treatment step .........................................................................................................7
Fig. 4 Nitrogen effects in sewage treatments ................................................................................10
Fig. 5 Desinfection by application of UV and ultrasound .............................................................11
Fig. 6 Ozone disinfection scheme .................................................................................................11
Fig. 7 Anaerobic digestion ............................................................................................................13
Fig. 8 Proposed optimal scheme of STP .......................................................................................14
LIST OF TABLES
Tab. 1 Composition of sewage water and effluent standards ..........................................................4
1
Project objectivities
The objectivities of project are to analyze of modern sewage treatment technologies and propose
of optimal design of sewage treatment plant.
2
Introduction
It is important to remove pollution and kill disease-causing organisms from wastewater. There
are many types of pollutants, if not properly treated, that can cause environmental problems
which could affect our lives.
E.g., the city populated with 100000 citizen can produce around of 40000 m3 sewages daily. For
year this will be more than 14.6 million m3 sewages which can content of more than 14600 ton
organics and suspended matter which need to remove from water and utilize separately. Main
requirements for sewage treatment plant are following:
- Sewage treatment plant (STP) could be capable to receive of all water from city
- Effluent from STP can satisfy for environmental standard to discharge of these waters to
rivers or seas.
- Huge amount of biosolids which will be removed from sewages need to be utilized by
appropriate ways
- Exploitation cost of STP could be minimized without decreasing of effluent standards
- Working conditions for personals need to be satisfied for occupational healthy standards
Below elements of STP were developed to satisfy for above requirements.
- Preliminary
- Primary
- Secondary
- Filtration and disinfection
- Biosolid treatment
- Biosolid utilization
This project aimed to collect of most successful solutions for STP and propose of optimal design
of STP.
3
Methods of project
Following methods were used during working under project.
- There were studied sources to form of municipal sewage water
- It is given characterization of main chemicals need to treat in sewages
- There were investigated of basic technology components of STP
- It is made evaluation of difference STP technologies on base of information from internet
and specialized books
- There was proposed of optimal STP scheme
3.1 Sources and Chemical composition of sewage water
Water pollution can come from many sources. Depending on the source, pollution may be
treated or released in rivers and streams. Below are some examples of sources for water
pollution:
 Home
 Toilets: human waste, toilet paper, cleaning chemicals, food
 Shower/Bathtub: hair, soap, germs, dirt
 Sinks: grease, garbage, food
 Washing machine: detergent, lint, dirt, grease, bleach, coins
 Factories & Offices: Industrial chemicals in wastewater may include anything from solvents
to metals. Industrial chemicals can cause cancers or other disease.




Atmospheric deposition: Particles from industrial processes and from burning fossil fuels fall
down to the ground. The particles include toxic metals (mercury and lead) and combustion
products like soot and cancer-causing chemicals.
Street Run-Off: Rain washes pollution from the soil, streets, and other surfaces into storm
drains. Storm drains empty into rivers or the harbor. Street run off (also called storm water)
is hard to clean up. But citizens can help out by not dumping, spilling, or pouring waste on
the ground and by cleaning up after pets.
Farms & Landscaping: Animals may contribute to water pollution when their droppings enter
the water stream. Also, animals may erode stream banks, breaking down natural pollution
barriers. Fertilizers, pesticides and even irrigation may contribute to pollution.
Lawn & Gardens: Excess fertilizer, insecticides and weed killers may all wash down into the
sewerage system or into the ground water or surface water which then flows into rivers,
lakes, or the ocean.
It is important to remove pollution and kill disease-causing organisms from wastewater. There
are many types of pollutants, if not properly treated, that can cause environmental problems
which could affect our lives.
Fig. 1 Main pollutants in sewage water
Tab. 1 have demonstrated examples for composition of sewage water and effluent standard.
Tab. 1 Composition of sewage water and effluent standards
Some information about the components
of waste waters
Caliform bacteria
BOD (concentration of organic
compounds which can split by
microbiological ways)
COD (concentration of matters which can
be oxidized chemically
The concentration of suspended solids
Other toxic metals (for instance: Heavy
metals Cd, Hg, Pb, Cu, Zn....)
Unit
unit/mL
mg/L
Before
refining
>1000
>250
Refining
standards
<2
<6
mg/L
>500
<30
mg/L
mg/L
>250
>5
<30
<0.01
3.1.1 Pathogens
Definition: Disease-causing viruses, parasites, and bacteria. Monitoring for pathogens in water is
usually done with a test for the presence of indicator bacteria such as fecal coliform, E.coli, and
entercoccus (Fig. 2).
Environmental Problems: May cause unsafe swimming, boating and shellfishing.
Treatment procedures:
-Disinfection occurs here where longer holding time kills pathogens more reliably.
-Secondary treatment removes particles which pathogens adhere to. This process makes the
disinfection more effective.
Fig. 2 Sewage bacterias
3.1.2 Nutrients
Definition: A source of nourishment that is essential for the growth of organisms, big and small.
Examples include nitrogen and phosphorous.
Environmental Problems: An excessive amount of nutrients, especially nitrogen, can be harmful
as it encourages the overgrowth of phytoplankton and seaweed. Consequently, this overgrowth
can cause discoloration of the water, bad odors, depletion of dissolved oxygen in the water and
the sediment, shading out of sea grasses, and less biodiversity in bottom-dwelling communities.
Together with other pollutants such as organic matter and suspended solids, nutrients can
encourage the growth of nuisance algal blooms.
Treatment: Primary and secondary treatment remove only about 10% of nutrients. The treatment
plant actually contributes to 90% of the nitrogen entering the ocean.
3.1.3 Floatables
Definition: Plastics and other floating debris (e.g. oil, grease, toilet paper).
Environmental Problems: Aesthetically offensive to observe in the water.
Treatment:
-Preliminary treatment can filter out floatables using the bar screens.
-Pumping improvements reduces combine sewer overflows which carry floatables into the
harbor.
-Secondary treatment breaks down oil and grease.
3.1.4 Toxic contaminants
Definition: Heavy metals such as copper, mercury, lead; PCBs, pesticides, petroleum
hydrocarbons, chlorine.
Environmental Problems:
-Contaminates seafood consumed by humans.
-Detrimental effects on the marine ecosystem; many organisms can absorb toxic contaminants
through their skin while others can not live in contaminated sediments.
-At high doses, it can be carcinogenic to humans.
Treatment: Settling during primary and secondary treatment removes most contaminant solids.
Industrial pre-treatment programs, secondary treatment and a long outfall means less chlorine is
needed for disinfection.
3.1.5 Organic materials (BOD)
Definition: Organic Material can include food residues, human waste, plant matter. It can be
dissolved, a solid, or a liquid. As it decays, organic material use up dissolved oxygen (DO)
which marine and aquatic life need to breathe. The amount of DO used when a given amount of
wastewater decays is called the Biochemical Oxygen Demand or BOD.
Environmental Problems: Large amounts can deplete dissolved oxygen in the water, endangering
marine and aquatic life.
Treatment: Secondary treatment removes about 85% of BOD
3.1.6 Total suspended solids (TSS)
Definition: Mixture of organic particles, silt, and sand suspended in the water.
Environmental Problems: Clouds water which can prevent adequate light from reaching
important plant species on the sea floor. Contaminants can also adhere to other particles and
eventually settle to the bottom, potentially inhibiting growth and reproduction of bottomdwelling organisms.
3.2 Elements of STP
Main elements (steps) of sewage treatment plants are followings:
 Mechanical treatment;
 Influx (Influent)
 Removal of large objects
 Removal of sand and grit
 Pre-precipitation
 Biological treatment;
 Oxidation bed (oxidizing bed) or aeration system
 Post precipitation
 Chemical treatment (this step is usually combined with settling and other processes to
remove solids, such as filtration.
 Discharge of effluent (cleaned water)
3.2.1 Preliminary treatment
Primary treatment is to reduce oils, grease, fats, sand, grit, and coarse (settle able) solids. This
step is done entirely with machinery, hence the name mechanical treatment. Influx (influent) and
removal of large objects (Fig. 3)
In the mechanical treatment, the influx (influent) of sewage water is strained to remove all large
objects that are deposited in the sewer system, such as rags, sticks, cans, fruit, etc. This is most
commonly done with a manual or automated mechanically raked screen. This type of waste is
removed because it can damage the sensitive equipment in the sewage treatment plant.
Sand and grit removal is main for this stage. This stage typically includes a sand or grit channel
where the velocity of the incoming wastewater is carefully controlled to allow sand grit and
stones to settle but still maintain the majority of the organic material within the flow. This
equipment is called a detractor or sand catcher. Sand grit and stones need to be removed early in
the process to avoid damage to pumps and other equipment in the remaining treatment stages.
Sometimes there is a sand washer (grit classifier) followed by a conveyor that transports the sand
to a container for disposal. The contents from the sand catcher may be fed into the incinerator in
a sludge processing plant, but in many cases, the sand and grit is sent to a land-fill.
Screening and maceration (raw sewage pumping)
The grit free liquid is then passed through fixed or rotating screens to remove floating and larger
material such as rags and smaller particulates such as peas and corn. Screenings are collected and
may be returned to the sludge treatment plant or may be disposed of off site by land-filling or
incineration. Maceration, in which solids are cut into small particles through the use of rotating
knife edges mounted on a revolving cylinder, is used in plants that are able to process this
particulate waste.
Fig. 3 Preliminary treatment step
Many plants have a sedimentation stage where the sewage is allowed to pass slowly through
large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks". The tanks
are large enough that faecal solids can settle and floating material such as grease and plastics can
rise to the surface and be skimmed off. The main purpose of the primary stage is to produce a
generally homogeneous liquid capable of being treated biologically and a sludge that can be
separately treated or processed. Primary settlement tanks are usually equipped with mechanically
driven scrapers that continually drive the collected sludge towards a hopper in the base of the
tank from where it can be pumped to further sludge treatment stages.
3.2.2 Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of the sewage
such as are derived from human waste, food waste, soaps and detergent. The majority of
municipal and industrial plants treat the settled sewage liquor using aerobic biological processes.
For this to be effective, the biota require both oxygen and a substrate on which to live. There are
number of ways in which this is done. In all these methods, the bacteria and protozoa consume
biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon
molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment
systems are classified as fixed film or suspended growth, such as rock filters where the biomass
grows on media and the sewage passes over its surface. In suspended growth systems - such as
activated sludge - the biomass is well mixed with the sewage & can be operated in a smaller
space than fixed film systems that treat the same amount of water. However, fixed film systems
are more able to cope with drastic changes in the amount of biological material and can provide
higher removal rates for organic material and suspended solids than suspended growth systems.
Roughing filters are intended to treat particularly strong or variable organic loads, typically
industrial, to allow them to then be treated by conventional secondary treatment processes.
Characteristics include typically tall, circular filters filled with open synthetic filter media to
which sewage is applied at a relatively high rate. Designed to allow high hydraulic loading and a
high flow-through of air. On larger installations, air is forced through the media using blowers.
The resultant liquor is usually within the normal range for conventional treatment processes.
3.2.3 Activated sludge
Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen to
promote the growth of biological floc that substantially removes organic material. It also traps
particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate
ultimately to nitrogen gas.
3.2.4 Filter beds (oxidizing beds)
In older plants and plants receiving more variable loads, trickling filter beds are used where the
settled sewage liquor is spread onto the surface and of a deep bed made up of coke (carbonized
coal), limestone chips or specially fabricated plastic media. Such media must have high surface
areas to support the biofilms that form. The liquor is distributed through perforated rotating arms
radiating from a central pivot. The distributed liquor trickles through this bed and is collected in
drains at the base. These drains also provide a source of air which percolates up through the bed,
keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces
and eat or otherwise reduce the organic content. This biofilm is grazed by insect larvae and
worms which help maintain an optimal thickness. Overloading of beds increases the thickness of
the film leading to clogging of the filter media and ponding on the surface.
3.2.5 Biological aerated filters
Biological Aerated (or Anoxic) Filter (BAF) combines filtration with biological carbon
reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter
media. The media is either in suspension or supported by a gravel layer at the foot of the filter.
The dual purpose of this media is to support highly active biomass that is attached to it and to
filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and
sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is
operated either in upflow or downflow configuration depending on design specified by
manufacturer.
3.2.6 Membrane biological reactors
Membrane biological reactors (MBR) combines activated sludge treatment with a membrane
liquid-solid separation process. The membrane component utilizes low pressure microfiltration
or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The
limitation of MBR systems is directly proportional to nutrient reduction efficiency of the
activated sludge process. The cost of building and operating a MBR is usually higher than
conventional wastewater treatment. However, in developed urban areas where the footprint of
the treatment plant is considered a limiting factor MBR Facilities can be considered a desirable
option.
3.2.7 Secondary sedimentation
The final step in the secondary treatment stage is to settle out the biological floc or filter material
and produce sewage water containing very low levels of organic material and suspended matter.
3.2.8 Rotating Biological Contractors
Rotating Biological Contactors (RBCs) are mechanical secondary treatment systems, which are
robust and capable of withstanding surges in organic load. The rotating disks support the growth
of bacteria and micro-organisms present in the sewage, which breakdown and stabilize organic
pollutants. To be successful, micro-organisms need both oxygen to live and food to grow.
Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they
build up on the media until they are sloughed off due to shear forces provided by the rotating
discs in the sewage.
Effluent from the RBC is then passed through final clarifiers where the micro-organisms in
suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.
3.2.9 Tertiary treatment
Tertiary treatment provides a final stage to raise the effluent quality to the standard required
before it is discharged to the receiving environment (sea, river, lake, ground, etc.) More than one
tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is
always the final process. It is also called "effluent polishing".
3.2.10 Filtration
Sand filtration removes much of the residual suspended matter. Filtration over activated carbon
removes residual toxins.
3.2.11 Lagooning
Lagooning provides settlement and further biological improvement through storage in large manmade ponds or lagoons. These lagoons are highly aerobic and colonization by native
macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as
Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates.
3.2.12 Constructed wetlands
Constructed wetlands include engineered reedbeds and a range of similar methodologies, all of
which provide a high degree of aerobic biological improvement and can often be used instead of
secondary treatment for small communities, also see phytoremediation. One example is a small
reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England.
3.2.13 Waste removal
Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release
to the environment can lead to a build up of nutrients, called eutrophication, which can in turn
encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause
an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable
and eventually most of them die. The decomposition of the algae by bacteria uses up so much of
oxygen in the water that most or all of the animals die, which creates more organic matter for the
bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins
that contaminate drinking water supplies.
3.2.14 Nitrogen and phosphorous effects
The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia
(nitrification) to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas.
Nitrogen gas is released to the atmosphere and thus removed from the water.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of
bacteria. The oxidation of ammonia (NH3) to nitrite (NO2−) is most often facilitated by
Nitrosomonas spp. (nitroso=ammonium). Nitrite oxidation to nitrate (NO3−), though traditionally
believed to be facilitated by Nitrobacter spp. (nitro=nitrite), is now known to be facilitated in the
environment almost exclusively by Nitrospira spp..
Denitrification requires anoxic conditions to encourage the appropriate biological communities
to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can
all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job
the most easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron
donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide,
or an added donor like methanol. Sometimes the conversion of toxic ammonia to nitratealone is
referred to as tertiary treatment. (Fig. 4).
Fig. 4 Nitrogen effects in sewage treatments
Phosphorus can be removed biologically in a process called enhanced biological phosphorus
removal. In this process, specific bacteria, called polyphosphate accumulating organisms, are
selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20%
of their mass). When the biomass enriched in these bacteria is separated from the treated water,
these biosolids have a high fertilizer value.
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron
(e.g. ferric chloride) or aluminum (e.g. alum). The resulting chemical sludge is difficult to handle
and the added chemicals can be expensive. Despite this, chemical phosphorus removal requires
significantly smaller equipment footprint than biological removal, is easier to operate and can be
more reliable in areas that have wastewater compositions that make biological phosphorus
removal difficult (Fig. 4).
3.2.15 Disinfection importance
The purpose of disinfection in the treatment of wastewater is to substantially reduce the number
of microorganisms in the water to be discharged back into the environment. The effectiveness of
disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type
of disinfection being used, the disinfectant dosage (concentration and time), and other
environmental variables. Cloudy water will be treated less successfully since solid matter can
shield organisms, especially from ultraviolet light or if contact times are low. Generally, short
contact times, low doses and high flows all militate against effective disinfection. Common
methods of disinfection include ozone, chlorine, or ultraviolet light & ultrasound irradiation.
Chloramines, which is used for drinking water, is not used in wastewater treatment because of its
persistence.
3.2.16 Disinfection by chlorine
Chlorination remains the most common form of wastewater disinfection in North America due to
its low cost and long-term history of effectiveness. One disadvantage is that chlorination of
residual organic material can generate chlorinated-organic compounds that may be carcinogenic
or harmful to the environment. Residual chlorine or chloramines may also be capable of
chlorinating organic material in the natural aquatic environment. Further, because residual
chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated,
adding to the complexity and cost of treatment.
3.2.17 Disinfection by UV and Ultrasound irradiation
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no
chemicals are used, the treated water's taste is more natural and pure as compared to other
methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other
pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection
are the need for frequent lamp maintenance and replacement and the need for a highly treated
effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any
solids present in the treated effluent may protect microorganisms from the UV light). Because of
frequent replacement ultrasound can be used with UV. Ultrasound make micro bombs in the
system, at this time, not only bacteria are destroyed but also walls of the system is escaped from
sludge settlers. And from this we do not need frequent replacement of UV lamp. Light is
becoming the most common means of disinfection because of the concerns about the impacts of
chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the
receiving water. (Fig. 5).
Fig. 5 Disinfection by application of UV and ultrasound
3.2.18 Disinfection by Ozone
Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third
oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and
oxidizes most organic material it comes in contact with, thereby destroying many pathogenic
microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which
has to be stored on site (highly poisonous in the event of an accidental release), ozone is
generated onsite as needed. Ozonation also produces fewer disinfection by-products than
chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation
equipment and the requirements for highly skilled operators. (Fig. 6)
Fig. 6 Ozone disinfection scheme
3.2.19 Package plants and batch reactors
In order to use less space, treat difficult waste, deal with intermittent flow or achieve higher
environmental standards, a number of designs of hybrid treatment plants have been produced.
Such plants often combine all or at least two stages of the three main treatment stages into one
combined stage. Where a large number of sewage treatment plants serve small populations,
package plants are a viable alternative to building discrete structures for each process stage.
The most advanced packaged treatment plant according to a study treating waste and nutrients
(phosphorus and nitrogen) in one step economically is the USBFTM (Upflow Sludge Blanket
Filter). The USBFTM process is a modification of the conventional activated sludge process that
incorporates an anoxic selector zone and an upflow sludge blanket filtration clarifier all in one
integrated bioreactor vessel. The treatment includes efficient reduction of BOD5 and TSS but
also biological nutrient removal (BNR) by the processes of denitrification and "biological luxury
uptake".
The ensuing compact, modular system takes up less space and contains very few moving parts.
The result is an efficient, highly affordable wastewater treatment plant with low maintenance and
operating costs.
USBFTM technology has no inherent capacity limits and is used in a wide range of applications
from subdivisions resorts and municipalities, to agricultural and industrial sites. Plants can be
retrofitted and expanded from existing sites reducing capital costs. Since there are no mechanical
parts and no chemicals needed, operations cost are much less than sequencing batch reactor BR
and membrane bio reactor MBR systems.
Another type of process which combines secondary treatment and settlement is the sequencing
batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage and mixed
and aerated. The resultant mixture is then allowed to settle producing a high quality effluent. The
settled sludge is run off and re-aerated before a proportion is returned to the head of the works..
The disadvantage of such processes is that precise control of timing, mixing and aeration is
required. This precision is usually achieved by computer controls linked to many sensors in the
plant. Such a complex, fragile system is unsuited to places where such controls may be
unreliable, or poorly maintained, or where the power supply may be intermittent.
Package plants may be referred to as high charged or low charged. This refers to the way the
biological load is processed. In high charged systems, the biological stage is presented with a
high organic load and the combined floc and organic material is then oxygenated for a few hours
before being charged again with a new load. In the low charged system the biological stage
contains a low organic load and is combined with floculate for a relatively long time.
3.2.20 Sludge treatment and disposal
The sludge accumulated in a wastewater treatment process must be treated and disposed of in a
safe and effective manner. The purpose of digestion is to reduce the amount of organic matter
and the number of disease-causing microorganisms present in the solids. The most common
treatment options include anaerobic digestion, aerobic digestion, and composting.
The choice of a wastewater solid treatment method depends on the amount of solids generated
and other site-specific conditions. However, in general, composting is most often applied to
smaller-scale applications followed by aerobic digestion and then lastly anaerobic digestion for
the larger-scale municipal applications.
3.2.21 Anaerobic digestion
Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The
process can either be thermophilic digestion, in which sludge is fermented in tanks at a
temperature of 55°C, or mesophilic, at a temperature of around 36°C. Though allowing shorter
retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of
energy consumption for heating the sludge.
One major feature of anaerobic digestion is the production of biogas (Fig. 7), which can be used
in generators for electricity production and/or in boilers for heating purposes.
Fig. 7 Anaerobic digestion
Biosolids separated from sewage could be used as fertilizer in agriculture. This biosolids may be
in the form of compost, sterilized or dried materials. To kill of hazardous viruses and
microorganisms biosolids have to treat between 60-70 0C.
Existence of the organics in the biosolids allow to use them as alternative fuel. It is calculated
that 350 thousand ton biosolids can give energy equal energy from 700 thousand barrel oil
(42168 ton) or 175 thousand ton coal.
In case of existence toxic substances (heavy metals, persistence organic matter and so on) in
content of biosolids it is restricted to use them. Such type of waste can be burred in special
landfill equipped with special geomembrane at the bottom.
3.2.22 Aerobic digestion
Aerobic digestion is a bacterial process occurring in the presence of oxygen. Under aerobic
conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. The
operating costs are characteristically much greater than for anaerobic digestion because of the
energy costs needed to add oxygen to the process.
Composting
Composting is also an aerobic process that involves mixing the wastewater solids with sources of
carbon such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest both the
wastewater solids and the added carbon source and, in doing so, produce a large amount of heat.
Thermal depolymerization
Thermal depolymerization uses hydrous pyrolysis to convert reduced complex organics to oil.
Sludge disposal
When a liquid sludge is produced, further treatment may be required to make it suitable for final
disposal. Typically, sludge is thickened (dewatered) to reduce the volumes transported off-site
for disposal. There is no process which completely eliminates the need to dispose of biosolids.
4
Conclusion
Analyzing of STP technologies have demonstrated existence difference approaches. For our
opinion it is necessary to develop optimal STP to satisfy al requirements. Our approach base on
applying computer controlling of all processes, applying of new type sensors for distance
collection of water quality data and modeling for minimize of process cost and efficiency
utilization of separated biosolids.
Our approaches involve:
 To use distance water quality measuring sensors for influent sewage water and in all
stages of STP
 To develop process optimization software to increase efficiency of STP systems
 To apply technologies appropriate for minimize human works
 To apply technologies to minimize energy cost
 To apply technologies to produce biosolids ready to use in agriculture
STP control system
Influent
STP
Biosolid regeneration
Effluent
Agriculture application
Fig. 8 Proposed optimal scheme of STP
5
Next years planning
2007 develop of application of new sensors for distance collection of water quality data
2007-2008 develop of optimization software to manage which STP technology steps
2007-2008 develop of models to minimize of process costs
2008 develop of models to optimize biosolid utilization
6
References
Shun Dar Lin and C. C. Lee,Water and Wastewater Calculations Manual,2001
Franklin L. Burton, and H. David Stensel, Wastewater Engineering: Treatment and Reuse by
George Tchobanoglous, 2002
Water Quality & Treatment Handbook by American Water Works Association, 1999
Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2003
David Hendricks, Water Treatment Unit Processes: Physical and Chemical (Civil and
Environmental Engineering), 2006
Susumu Kawamura, Integrated Design and Operation of Water Treatment Facilities, 2000
Frank R. Spellman, Mathematics Manual for Water and Wastewater Treatment Plant Operators,
2004
Pettrucci, Harwood, Herring, Madura General Chemistry: Principles modern applications, 2007