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sewage systems

We can help in the following technologies encapsuling the area of Water Treatment and Sewage Systems

Anaerobic Digestion of Organic Wastes – Process Parameters and Balances in Practice

table of average loadings and their equivalents >>>>>>>>>>>
Activated sludge process >>>>>>>>>>>>

Main sewage processes

Diagrammatic representation of the process of sewage treatment

Small-Scale Sewage Treatment Facility
(Batch-Type Activated Sludge System)

Diagrammatic representation of sewage treatment at a small activated sludge plant

There are various types of treatment

Preliminary Treatment

In most sewage treatment systems of any size there will be some form of Preliminary Treatment.

In smaller treatment systems up to perhaps say 500 / 1000 population equivalent this stage may be omitted.

There are several stages within the preliminary treatment section and these are -


This stage removes all, large floating or suspended solids, rags, plastics, timber, animal carcasses. There are various types of screens from manual raked to mechanically raked.

The subsequent screenings have to be dealt with in a suitable manner for removal off site.

As an alternative it is sometimes possible to macerate the screenings to a much smaller size to be removed at later stages, but this may produce problems elsewhere.

Bild vergrößern

Grit Removal

This stage which usually happens at larger works, removes as much as possible of the - silt, sand, gravel, cinders, ashes, metal, glass and even razor blades in the sewage.

There are various types of grit removal systems from grit tanks, grit channels, and other mechanical systems.

The grit once removed has to be dealt with in a suitable manner for removal off site.

Flow Measurement

Flow of sewage to a works is measured to control and monitor treatment and to comply with consents. This can be undertaken by means of an open channel with perhaps a flume or V notch weir, or in a pipe with an external flow meter.

Storm Water Overflows

At some works where there is a high incidence of surface or storm water in the sewage (usually at works which serve older towns where the surface water readily enters the sewerage system) there is a need to separate the excess storm water flows out from the main sewage to be treated.

This storm water may be by-passed to a separate storm overflow to the watercourse or may be stored in storm tanks, for later treatment once the main storm has passed.

This separation is usually undertaken by means of storm overflow weirs.

If there are to be storm storage tanks then these need to be carefully designed as some settlement will occur in the tanks.

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Primary Settlement

Primary settlement of the sewage is necessary to remove heavy solids, remove grease and scum, balance the load, and performs some biological activity.

This is usually carried out by carefully designing tanks which are either of a, radial flow, upward flow, or horizontal flow type.

The type of tank used will depend on many circumstances and it has to be carefully designed with all the many factors to be taken into account.

From the primary settlement stage a lot of the coarser suspended solids will have been removed, and the biological content will have been reduced by between 25% and 50%.

However from this stage there will be quite a lot of sludge which must be removed from the tank very regularly, and in a large works probably continuously. Sludge can be removed by means of, manual, automated systems, or by tank emptying.

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Biological Treatment

The sewage after primary settlement still contains quite a large amount of biological pollutants.

The aim of the biological treatment stage is to purify the settled sewage by removing dissolved organic material, so that, after further settlement, in humus tanks, the effluent can be discharged to a watercourse.

Biological filtration is the oldest form of sewage treatment dating back to 1897.

The process relies upon Aerobic Bacteria and Micro-Organisms to break down the impurities in the settled sewage.

Other forms of life will also colonise the filter bed, for example, Protozoa, Worms, Fly and insect larvae, spiders, and even birds, each species feeding off smaller members in the food chain.

To live and purify settled sewage the bacteria and micro-organisms need

  • A Home
  • Adequate Oxygen
  • Adequate Food
  • A Comfortable Environment

Just like all human beings!

In a good and correctly designed biological filter bed all these conditions can exist.

A biological treatment system must however be correctly dosed with the sewage, and there are many different types of filtration system.

biologische Abwasser-Vorbehandlungsanlage, Industrie-Kläranlageor

Final or Humus Settlement

Final or Humus Settlement is usually carried out in tanks as they are a means of removing the smaller solids from filter effluent.

Filter effluent contains quantities of biological film which has been washed from the media, dead micro-organisms and worms.

These tanks are very similar in design to primary settlement tanks and can be either of a, radial flow, upward flow, or horizontal flow type.

From this stage there will be sludge which must be removed from the tank very regularly, and in a large works probably continuously. Sludge can be removed by means of, manual, automated systems, or by tank emptying.

The effluent from Humus Tanks will generally be about 90% to 95% clean, if the works are correctly designed and operated correctly.

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Tertiary Treatment

Tertiary treatment is aimed at improving the quality of effluent produced by a conventional biological treatment plant.

It is intended that tertiary treatment should polish a good quality effluent. It is not a substitute for inadequate secondary treatment processes.

Tertiary treatment can achieve a reduction in

  • Suspended solids
  • BOD
  • Ammonia

There are various types of tertiary treatment system, these being

  • Grass plots
  • Clarifiers
  • Sand Filters
  • Microstrainers
  • Drum Filters
  • Reed Beds
  • Lagoons
  • Nitrifying Filters

The type of system to be used will depend on many factors and the designer will have to make a technical decision on which to use.

Sewage Treatment Works with a Tertiary Reed Bed

Vertical and Horizontal Beds System

Flat Site

Sewage treatment processes simply explained

Sloping Site

Sewage treatment processes simply explained

It is normal in the U.K. in a sewage treatment plant to achieve an effluent quality of at least the following quality:

  • Suspended Solids (S.S.) = 30 mg/l.
  • Biochemical Oxygen Demand (BOD 5) = 20 mg/l.

Some plants offered may well achieve a higher quality of effluent.

Table of Loadings for Sewage Disposal Facilities

Situation Hydraulic Flow Litres/d Organic Loading
BOD5 grams/d
Organic Loading
Ammonia grams/d
Domestic Dwellings
Rural 180 60 8
Urban or high level of available services 200 60 8
Mobile home type caravans with full services 180 75 8
Office and/or factory without canteen 50 25 5
Office and/or factory with canteen 100 38 5
Open industrial site (e.g. Quarry,Coal) workings (excluding canteen) 60 25 5
Day staff 90 38 5
Part Time staff (4 hr shift) 45 25 3
Non-residential with canteen or cooking on site 90 38 5
Non-residential (no Canteen) 50 25 5
Boarding School:-
(i) Residents 200 75 10
(ii)Day Staff (includes mid day meal) 90 38 5
Guests (prestige hotels) 300 105 12
Guests (3* or 4* ) 250 94 10
Guests (Travel lodge type with no meals) 80 50 6
Residential training / conference guest (inclusive all meals) 350 150 15
Non residential conference guest 60 25 2.5
Resident Staff 180 75 10
Day Staff 90 38 5
Restaurant full meals -
Luxury catering 30 38 4
Pre-prepared catering 25 30 2.5
Snack bars & bar meals 15 19 2.5
Function Rooms including buffets 15 19 2.5
Fast Food (roadside restaurants) 12 12 2.5
Fast Food (burger chain or similar) 12 15 4
Students (accommodation only) 100 56 5
Pubs and Clubs
Residents 200 60 8
Day Staff 90 30 5
Bar Drinkers *1 12 15 5
Function rooms 15 15 5
Amenity Sites
Toilet blocks (per use) (or WC) 10 12 2.5
Toilet (urinal) 5 12 2.5
Toilet blocks in long stay car parks (ie Lorry Parks) 10 15 5
Golf Club 20 20 5
Shower (per use) 40 19 5
Local Community (Squash, Rugby, Football clubs) 40 25 6
Swimming (where a separate pool exists without an associated sports centre) 10 12 2.5
Health Club / Sports centre 50 20 4
Caravan Sites - (i) Touring 75 44 4
(ii) Static - not fully serviced 100 44 8
(iii) Static fully serviced 180 75 10
(iv) Tent sites 75 44 8
Residential old people 350 110 13
Residential old people plus nursing 300 90 12
Nursing home (convalescent) 350 100 12
Small Hospitals 450 140 20

Step-feed Anoxic/Aerobic Activated Sludge System

1. Outline of equipment

Recently, the problem of eutrophication of closed bodies of water is caused by the nutrient salts of nitrogen and phosphorus that can not be removed by such traditional methods as conventional activated sludge process without a large-scale renovation to the existing facilities. The step-feed anoxic/aerobic activated sludge process has been developed to enable efficient denitrification without a major renovation.
With the new system, the primary effluent is introduced by step-feed, providing effective distribution of BOD and reduction of nitrogen load. In addition, the inside of the reaction tank is made anoxic/aerobic to accelerate nitrification/denitrification, achieving effective and stable nitrogen removal.

2. Features

The step-feed anoxic/aerobic activated sludge process has the following features.
1. It has a high rate of denitrification.
By optimizing the conditions, BOD and T-N removal of 60-80% is possible.
2. It is of a compact design.
With the reduction in hydraulic retention time, the tank capacity is reduced to half that of a conventional circulating process.
3. It is energy-efficient.
As it no longer needs circulation of nitrification liquid, energy consumption has be cut to about 70% of the circulating process.
4. Existing facilities can be modified.
Modification to this advanced sewage treatment process can be carried out without sacrificing existing treatment capacity.
5. It is easy to operate.
It does not require complicated controls, and its maintenance is simple.

3. Performance

(1) Design hydrological retention time: 8 hours
(2) Denitrification Rate: 60-80%

4. Applications

1. Advanced treatment of sewage
The step-feed anoxic/aerobic activated sludge process can be built anew, or added to the existing conventional activated sludge plant by:
- installing partitions in the reaction tank, creating anoxic and aerobic zones, and
- adding distribution weir for the step-feed of the primary effluent
These modification will achieve high-efficiency nitrogen removal. If yet higher level of treatment is desired, we suggest adding an absolute anaerobic zone ahead of the reaction tank to biologically remove phosphorus, or installing movable bed type upward-flow continuous sand filter and flocculant dispensing unit downstream of final settling pond. This will carry out in-line coagulation filtration, removing phosphorus and SS.

Schematic Flow of Step-feed Anoxic/Aerobic Activated Sludge Process



Advanced Sewage Treatment System Using Low Pressure Reverse Osmosis

1. Purpose

In recent years, reclaimed sewage has been used to supply ponds and streams in urban areas as a part of a multipurpose utilization program. The reclaimed water must be sanitary and safe for people to touch or even put into their mouths, when it is used for a city stream or pond. In response to those demands, Kobe Steel offers an "Advanced Wastewater Treatment System Using Low Pressure Reverse Osmosis" to produce clear, safe and sanitary water.

2. Performance

Water Quality (Example of Analysis)

3. Characteristics

1) The low pressure reverse osmosis membranes remove color, odor, BOD, COD, MBAS (measure of foam-causing substance), N, P, bacteria, viruses, etc. Thus, very clear, safe and sanitary water is produced. Both the appearance and sanitary safety of the water is almost equal to that of tap water.
2) The cost of operation is low because of the low operating pressure (below 0.98MPa) and the sim-
3) The quality of the reclaimed water is stable, in spite of fluctuations in the raw water quality (secondary treated water).
4) Maintenance is easy because the system maintains itself automatically.

4. Principle

1) Pretreatment
(1) The coagulant (PAC) and the sodium hypochlorite to control the slime are injected to the raw feed water.
(2) Suspended solids which can obstruct the reverse osmosis membranes, are removed bay two media filters which are arranged consecutively.

2) Reverse Osmosis Treatment
(1) The reverse osmosis module is the spiral type. The spiral type has many advantages such as compactness, easy exchange of membrane elements and high resistance against the suspended particles in the feed water.
(2) The membranes are washed with the reclaimed water automatically to prevent a decrease in flow of the water.

5. Subject

Streams, fountains and ponds for playing, bathing, keeping fishes, etc.
Sewage reuse system
Fire fighting water
Sprinkling of the streets or trees

6. Figure

Flowchart of the Advanced Wastewater Treatment Using Low Pressure Reverse Osmosis


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