2. General characteristics of wastewater

1.2. Composition and properties of wastewater

polluted
industrial wastewater (as
usually process water) contain
various impurities and can be separated
In this regard, into three groups:

• polluted
  predominantly mineral impurities
  (metallurgical enterprises,
  engineering, mining
  industries; manufacturing plants
  mineral fertilizers, acids,
  building materials, etc.)

• polluted
  predominantly organic impurities
  (enterprises of food, pulp and paper,
  microbiological industry;
  plastics factories,
  rubber, etc.);

• polluted
  mineral and organic impurities
  (oil companies,
  oil refining, pharmaceutical
  industries; manufacturing plants
  canned food, sugar, organic products
  synthesis, paper, vitamins, etc.)

Depending on the
pollutant concentrations
industrial wastewater can
present in 4 groups: 1 - 500; 500 - 5000; 5000
- 30000; and more than 30000 mg / l.

By degree
aggressiveness are:

• slightly aggressive
  (slightly acidic with pH=6.06.5
  and weakly alkaline with pH=89);

• highly aggressive
  (strongly acidic with pH9);

• non-aggressive
  (with pH=6.5
  8,0).

Moreover,
contaminated industrial waste
water is classified according to the content
toxic and dangerous in the epidemiological
the ratio of substances and impurities; by availability
concentrated production waste,
not subject to release into the wastewater
net; on the physical properties of pollutants
their organic impurities.

Composition and properties
industrial wastewater are determined
specific conditions for their formation.
Even in enterprises with the same
these technological processes
specifications will vary. Besides
In addition, the modes will differ
wastewater disposal and specific water consumption
per unit of output.

Basic meaning
in the formation of the composition of production
wastewater has the form of recyclable
raw materials, as well as technological processes,
intermediate products produced
products, composition and properties of fresh
water, etc.

When developing
sewerage schemes, as well as in assessing
reuse opportunities
water or when creating circulating systems
water supply, you need to know
composition and mode of disposal of wastewater.
For this, it is necessary to analyze
physical and chemical indicators and regimes
receipts of various types of waste
waters generated at the enterprise
individual industries and workshops, and in
some cases - on separate
technological processes and devices.
In wastewater, the following should be determined:

content
components specific to this
production;

• general
  amount of organic matter
  expressed in terms of BOD_full(BOD₅)
  and COD;

• active
  reaction (pH);

• degree
  mineralization;

• Availability
  biogenic elements.

Depending on the
specifics of production and technological
processes analysis of the composition and properties
wastewater can be produced by
one-time hourly, average shift and
average daily proportional samples.
You should also draw up charts
fluctuations in contaminant concentrations
shift hours, days, days of the week. Necessary
set options like
kinetics of sedimentation and surfacing of mechanical
impurities and their volume; opportunity
coagulation of impurities, etc. with the aim of
determining the most appropriate
and economically viable systems
wastewater and treatment technologies
wastewater at this enterprise.

Significant
impact on the quality and composition of production
wastewater render features
water supply systems. The more
water is used in circulation cycles
or again (at the same enterprise
or on the neighboring one), the smaller the absolute
the amount of wastewater and the higher
their content of contaminants.

Compound

The solid components of sediments at the bottom are organic substances, which occupy 60-80% of the total volume. The main components are fat components, protein elements and carbohydrates. They occupy 80-85 percent of the total volume of organic matter. The rest of the volume is lignin-humus components.

The main types of sedimentary deposits:

• with a mineral composition;
• with organic components;
• mixed.

The wet sediments at the bottom of the treatment chambers contain useful substances such as nitrogen, potassium and phosphorus. Although these components can serve as fertilizers, they are rather poorly absorbed by plants.

Raw deposits rot very quickly and can be unsafe in terms of sanitation, because they contain viruses, fungi, bacteria and helminth eggs. If such substances remain for a long time in the settling tanks and chambers of the treatment plant, they will quickly cause decay of the sediments with the release of gases. As a result, sewage sludge can float to the surface in the sump and disrupt sedimentation processes. That is why the elimination of sewage sludge must be carried out in a timely manner, that is, their cleaning from the chamber, dehydration and disinfection.

Sludge from industrial and domestic wastewater can be divided into several types depending on the treatment method used:

• sedimentary deposits from gratings;
• sand deposits from sand traps;
• heavy waste from primary settling tanks (wet sludge);
• bottom sediments from settling tanks with flocculants and coagulants;
• activated sludge from biological treatment chambers in aerotanks;
• biological film from biofilters;
• activated sludge, which contains flocculants and coagulants;
• a mixture of activated sludge and heavy components of wastewater.

Composition and properties of ship wastewater

Wastewater (WW) generated on ships is conventionally divided into economic and fecal and household.

Ship domestic and fecal wastewater includes:

• - drains and other outlets from all types of toilets, urinals, toilet bowls, as well as scuppers located in common latrines;
• - drains from sinks, bathtubs, showers and scuppers located in medical premises;
• - runoff from premises where animals are kept;
• — other effluents, if they are mixed with the effluents listed above.

Domestic wastewater includes: drains from washbasins, showers, bathtubs, scuppers of residential and sanitary facilities, from sinks and galley equipment and other catering facilities. If domestic and WW are not mixed with domestic and fecal waters, then their collection and processing by the requirements of the MARPOL-73/78 convention are not provided.

In terms of composition, household faecal WW consists of 58% organic and 42% mineral substances (of which 20% are insoluble substances in the form of suspended particles), which contain the following five main pollutants:

• - a large number of bacteria, parasites, and possibly viruses that infect marine animals and people;
• — dissolved organic and suspended components with a medium high biochemical oxygen demand;
• - solid particles (organic and inorganic), settling to the bottom and absorbing oxygen during their biochemical decomposition;
• — floating particles (organic and inorganic) that float on the surface of the water and represent a serious problem in terms of the usability of marine recreational pools;
• - high concentrations of nutrients (mainly phosphorus and nitrogen compounds).

In cases of excessive or permanent pollution of the aquatic environment with SW, the amount of oxygen dissolved in it decreases, which in turn leads to a disruption in the process of natural self-purification and, as a result, to a change in the entire ecological character of the water area. A low concentration of dissolved oxygen and a high concentration of organic matter create unfavorable conditions for the existence of fish, which either die or leave the contaminated area.

So far, no criterion has been established that would be recognized by all states as universal, satisfying the assessment of the contamination of WW discharged from ships in terms of their harmful effects on the marine environment. Under these conditions, in different countries, the safe degree of pollution is limited by different values ​​of the main indicators, which fluctuate over a wide range.

The following main indicators are usually used to determine the degree of WW pollution:

BOD₅- biochemical oxygen demand for 5 days. This is the amount of oxygen (mg / l) that is required for the aerobic biochemical decomposition of organic substances contained in water for 5 days at a temperature of 20 ° C without access to air and light. The biochemical oxygen demand does not take into account persistent organic substances that are not affected by the biochemical process, and part of the substances used for bacterial growth;

COD — chemical oxygen demand. This is the amount of oxygen (mg / l) that is required for the complete chemical oxidation of organic and mineral substances contained in water under the action of oxidizing agents;

TVV- suspended solids. This is the amount of floating or suspended solids (mg/l);

If index- this is the number of bacteria of the Escherichia coli ("coli") group per unit volume per 1 liter of water or 1 kg of substrate (a quantitative indicator of water pollution is no more than 3 in 1 liter). The presence of these bacteria is an indication of the possibility of the presence of disease-causing (pathogenic) microorganisms.

Practice shows that pathogenic bacteria survive much longer at low sea water temperatures than in warm waters. But in any case, these bacteria and viruses survive in the aquatic environment for a long time, sufficient for direct transmission of infection to humans, entry into the body of marine animals and damage to their vital functions.

1.1.Classification of wastewater

Waste water from
industrial enterprises, depending
from the conditions of education, subdivide
into three main groups:

—
Production
wastewater.
Their presence is directly related to
product release or provision
operation of technological equipment.
These waters, in turn, should be divided
for technical and technological.

Technical waste
water are a consequence of the use
water to ensure normal operation
technological equipment (for example,
cooling).

Technological
wastewater
formed as a result of the use
water in technological processes
(for example: hydrotransport, solutions
reagents, etc.)

—
household
wastewater.
Formed as a result of using
water for domestic purposes (i.e. water from
sanitary facilities, showers, etc.)

—
atmospheric
(surface) sewage.
are the result of precipitation
(rain and melt). This group should
carry water used for irrigation
lawns, driveways, as well as for washing
buildings, etc.

By degree
sewage pollution can be
two categories:

—
polluted,
those. the discharge of which into a water body or
sewerage network of the settlement
without pre-treatment is prohibited;

—
uncontaminated
(conditionally clean),
those. the discharge of which into a water body or
sewerage network of the settlement,
under these conditions, permitted without
pre-processing.

Depending on the
destination, water in production systems
water supplies are divided into 4 categories:

I
category - water is used for
liquid cooling and condensation
gaseous products in heat exchangers
devices without contact with
product, as well as the water used
for process cooling
equipment; the water gets hot, but
practically not polluted (pollution
chemicals in such water
observed as a result of accidents or
malfunctions of heat exchangers
and technological equipment);

II
category - water is used as
medium that absorbs various insoluble
(mechanical) and dissolved impurities;
does not heat up, but gets dirty
mechanical and dissolved impurities
(for example: mineral processing,
hydrotransport);

III
category - water is also used,
like water II
categories; while polluting and
heats up (for example: trapping and
gas cleaning in scrubbers, extinguishing
coke, etc.)

IV
category - water is used as
reagent solvent or extractant
(for example: during flotation enrichment
natural resources), etc.

Sediment processing

The treatment of sewage sludge from enterprises and domestic effluents begins with a thickening or compaction stage. At this stage, free moisture is removed. This stage is necessary for all technological purification schemes. During thickening, about 60 percent of the free water is removed. As a result, the volume of deposits decreases by more than 2 times. The following methods are used for sealing:

• vibration;
• centrifugal;
• gravity;
• flotation;
• filtration;
• combined methods.

Gravity technique is suitable for compaction of digested sediments and activated sludge. This is a fairly simple and economical technique. To implement the method, radial and vertical settling tanks are used. The procedure time depends on the characteristics of the deposits and is 5-24 hours. To speed up the process, coagulation using ferric chloride, heating to 90 degrees, compaction with other types of deposits or mixing is used.

The flotation technique is based on the fact that activated sludge particles can stick to air bubbles and float to the surface. The speed of the process is higher than when using gravity. The process is easy to control by increasing or decreasing the air supply. The most commonly used is pressure flotation.

Stabilization is used to decompose complex organic compounds into water, methane and carbon dioxide. This process takes place under anaerobic and aerobic conditions:

1. Anaerobic conditions are created in septic tanks, clarifiers, two-tier settling tanks and special digesters. At the same time, septic tanks and settling tanks are suitable for small volumes of wastewater, that is, for private use. For large volumes of effluents, digesters are used.
2. Aerobic stabilization takes place in aeration tanks. It is based on continuous aeration of the sludge. This technique is simpler than anaerobic digestion. It is characterized by simplicity, no emission of explosive gases, stability and low cost. After the decomposition of biodegradable organic components, the rest of the substances lose their ability to rot, that is, the sediment stabilizes.

In order to improve mechanical dewatering, sediments need to be prepared. For this, air conditioning is used. In this case, the form and structure of the water bond changes.

In the reagent method, lime, aluminum and iron salts are used as coagulants. Along with coagulants, flocculants are also used. Reagent-free technique implies:

• heat treatment;
• freezing and thawing;
• radiation exposure;
• electrocoagulation.

Typically, dewatering of sediments is carried out in sludge beds or using mechanical methods. Silt pads are areas of territory with earthen ramparts along the edges. Here, the dehydration process is very slow, but the technique is quite simple and does not require high operating costs.

Mechanical methods of dehydration are carried out using:

• vacuum filters;
• filter presses;
• centrifuges;
• vibration filters.

Also used is the thermal treatment of precipitation, which consists in their drying. For this, flue gases, steam or hot air are used. Dryers of different designs are involved in the technique.

The most promising direction in the disposal of sedimentary deposits is pyrolysis. This is the process of processing substances that contain carbon by heating without oxygen at high temperatures. After pyrolysis, a powder is formed that can be used in industry, disposed of as a fuel, or used to produce phosphorus and nitrogen. The primary tar formed during pyrolysis, after fractional distillation, makes it possible to obtain carboxylic acids, paraffin, phenols, organic bases, and coke dust.