Sludge Pre-thickener and Automatic Sludge Thickener "AZK"


Produced excess sludge in wastewater treatment plants is stored and it is desirable to have minimum water content. Sludge pre-thickener is used for sludge dewatering to ca. 2 – 3 weight percentage, automatic sludge thickener AZK dewaters sludge to ca. 10 – 20 weight percentage.


1. Discharge of excess sludge from oxical aeration compartment: When discharging the excess sludge from oxical aeration compartment polyphospates are removed from sludge water in a greater extent and thus it reduces phosphate content in the whole treatment process.
2. Excess sludge is discharged with higher concentration than the operational concentration exists: Operational concentration of activated sludge of common sewage treatment plant ranges from 2 – 5 g/l, the pre-thickener makes the concentration up to 20 – 30 g/l. Less amount of sludge water is pumped off, which results in less demand of polycoagulant in further dewatering.
3. Application of automatic sludge thickener: Automatic sludge thickener makes sludge concentration to 10 – 20 weight percentage. No special filter clothes are needed. The equipment is fitted with a metal filter and thickened suspension is pumped out to a container.


Sludge pre-thickener is a plastic and/or rust-resistant steel tank emerged in the aeration zone and fitted inside with a pump. Automatic sludge thickener AZK is made of stainless steel.

System Description

Plastic or rust-resistant steel tank of sludge pre-thickener is fitted on its top and middle part with slide gates controlling the flow of thickened sludge suspension. A pump is installed in the tank bottom part and is controlled with a time switch and pumps the thickened sludge suspension out to a container. Sludge suspension pumped to an automatic sludge thickener AZK is mixed with a solution of auxiliary organic flocculant. When suspension becomes filterable it passes on to automatic sludge thickener AZK where sludge water is separated and it returns back to treatment process. Separated sludge when thickened reasonably is pumped out with a screw pump to a container for storage and further thickening.

Thickened, Dewatered Sludge

Based on laboratory analyses the thickened sludge from a container is disposed of either with dumping, composting or burning.