The functioning of a mobile sewage treatment plant equals that of a stationary one, because the demand for the technological standard determines the treatment process. The difference results from differences in design as well as the need for a con-struction that is as light and compact as possible. The fully automatic control of the entire process is based upon a Siemens SPS, it can contain several treatment programmes. The following steps are the most important ones in the process technology.

Neutralization:
Mordant dyes and sewage of dry cleaners could be acidic or alkaline, they will be set pH controlled by using either hydrochloric acid or caustic-soda solution. In order to accelerate the settling rate or the precipitation of fluoride or phosphate a milk-of-lime dosing station is offered, too.


Precipitation:
Dissolved substances are converted into slightly soluble compounds. The usual precipitants are iron(III) salt or aluminium salts (e. g. PAC) and synthetic polymeres to split dispersions or emulsions. Continuously operated plants have got a separate reaction chamber for neutralization and precipitation.


Flocculation:
The dosage of flocculation aids - these are synthetic polymeres with various charge densities - is most of the times necessary to achieve sufficiently large flocs for a satisfactory ability of sedimentation and floatation. Continuously operated plants get a second reaction chamber for flocculation.


Gravity separation:
Batch plants contain a sedimentor. Continuously operated plants could be optionally equipped with an inclined lamella clarifier for sedimentation or floatation. Sedimented thin sludge is collected in a funnel and periodically removed. The microbubbles needed for floatation are generated by pressure/relief by means of a non-corroding multi-phase pump. The floatation sludge is separated by means of a sludge scraper. There is also a construction unit available that allows both separation processes.

 
Thin sludge treatment:
The drainage of the thin sludge to produce a filter cake that can be disposed of is done by means of a band filter.
Further dosing stations: The more universal the application of the plant should be the more different dosing stations could be needed, e. g. organosulphide solution for increased arsenic/antimony values, combination of synthetic polymeres to handle specific problems, and much more. WAT helps you in choosing the suitable configuration.


Afterpurification of the clear phase:
For a purification according to the effluent standards and to the level of technology further purification processes are needed for manyfold problems. “WAT Mobile Plants” are designed in modules and can be equipped with different peripheral units as for instance:
Continuously self-cleansing sand filter for separating pulp matters;
Selective ion-exchanger for the fine purification of heavy metals;

    * Active charcoal filter for separating KW, PCB and AOX
    * Spray degasifiers for removing LHKW and BTX
    * Ultraviolet wet oxidation to reduce CSB and AOX

The indirect discharge of industrial sewage into the sewage sluice requires a pretreatment according to the effluent standards of the regions or communities. Per-manently incurring sewages and freights are purified in stationary plants. But often highly contaminated sewa-ges incur temporarily e. g. during construction and reorganization measures, in cleanings or during distur-bances. These sewages can be collected, taken away and centrally purified. In most of the cases a de-centralized treatment in a mobile plant, which is well-equipped for the specific problems, is more cost-efficient. Smaller amounts of sewage can be processed  in a batch process, larger amounts require a continu-ously working plant.

The most important fields of appli-cation for mobile plants are:

    * Purifications to be performed in various places
    * Disturbances having various reasons
    * Collection of continuously incurring small amounts of sewage and de-centralized treatment