Biological wastewater treatment plants are presented with a recurring pattern, which provides at least three phases of treatment: primary treatments, of which the primary sedimentation, biological treatment and secondary sedimentation are part of. Sludge scrapers are used for the removal of decanted solids in sedimentation tanks.

The chain sludge scrapers offered by MITA Water Technologies were designed for the installation in a rectangular tank. By choosing non-metallic materials for the construction of the main components, our machines are corrosion proof.

Actions to control or repair corrosion damage are among the most frequent and costly needs for performing maintenance. The service life of the scraper is limited by these problems, which are evident mostly on traction and scraping systems.

In terms of process, the chain scraper allows for a steady decanted sludge removal without any accumulations. Furthermore, the scraper is more efficient for the removal of floating sludge.

The chain scrapers are made of plastic and are offered either for newly built plants or for the renewal of existing installations. They are used for:

• rectangular primary, secondary and tertiary settling tanks, alone or combined with the reed valves
• flotation tanks
• silting tanks

The plastic chain scraper system is designed to be installed in rectangular settling tanks. The choice of this solution has many advantages:

• durability, lightness and self-lubricating
• minimum energy requirements
• easy installation even in existing tanks for the replacement of obsolete systems or deteriorated by corrosion

The chain scrapers carry out both the additional function of surface drains for the removal of any supernatant substances.

The main components are made with non-metallic materials making them corrosion resistant. The chain links are made of reinforced polyester resin, a highly resistant material, the shafts and scraping bars are made of fiberglass, whereas the gears are made of Cast Nylon-6
The service life of this type of scraper is much longer with an extremely low maintenance.

Components

A – Shaft

• The idler pinion is made of Cast Nylon-6, with a self-lubricating bearing in PE and shaft in stainless steel

B – Chain NCS-720-S

• Chain with 6″ pitch in polyester resin + fiberglass
• Fiberglass scraper blades
• Coupling element to chain in stainless steel
• Scraping pads in Cast Nylon-6

C – Fiberglass wall-mounted rail

• Track wear in PE with high molecular weight, low friction and self lubricating
• Wall holding bracket in stainless steel

D – Drive shaft non-metallic

• Telescopic shaft in fiberglass with bi-axial winding supported by truncated pins in stainless steel and held in place by non-metallic collars and interconnection keys.

E – Control crown gear

• Toothed gear transmission in Cast Nylon-6 for chain drive NH-78
• Sprocket wheels in Cast Nylon-6 for conveyor chain NCS-720-S mounted on the telescopic drive shaft

F –Toothed pinion

• Toothed pinion in Cast Nylon-6 for NH-78 chain drive mounted on Cast Nylon-6 hub and complete with safety shear pin

G – Scraper blades

Scraper blades in fiberglass, type:

• “Standard” type: width = 8 m
• “Ultra”: width = 12 m

System advantages

• Durability and light weight
• Self-lubricating properties
• Minimum energy requirements
• Easy installation even in existing tanks (for replacement of obsolete or corroded systems)
• Telescopic shaft, extremely light support splines and collars lubricated by water; they do not require a crane for installation and they are corrosion resistant
• Scraper blades available in several models, for tanks up to 12 m wide with high sludge loads

Application fields

• Primary and secondary settling tanks in biological treatment plants: in case longitudinal flow sedimentation tanks are provided for the primary and secondary settling inside the wastewater process, the use of plastic chain scrapers becomes very interesting. They carry out effectively the continuous transfer and accumulation of settleable solids and floating foams/oils in the areas of the tanks which can be easily removed for recycling or definite disposal.
• Clari-flocculation in rectangular tanks: in wastewater treatment plants, downstream of secondary treatments, a tertiary treatment is often requested and provided for the final stage with the aim to reduce the SST content and/or phosphorus residues. Appropriate chemical reagents are dosed with the clari-flocculation which combine solid suspended particles in larger sludge flakes. They are then separated in settling tanks that, if in rectangular sections, can be equipped with plastic chain scrapers that offer big advantages.
• Rectangular settling tanks with lamella packs technology: in new plants where available space is limited or existing plants with no additional usable space available, lamella packs for sedimentation are widely used because they offer effective treatments with reduced spaces. The rectangular settling tanks with lamella packs can be easily mechanized with plastic chain scrapers to facilitate and maximize efficiency of the steady removal of sludge deposited below the packs.
• Dissolved air flotation process (DAF system) in rectangular tanks: the dissolved air flotation for the separation of suspended solids contained in industrial waters or wastewater to be purified are always provided with equipment that remove the sludge mass accumulated on the surface of the water. Even for this application, in the case of site-built DAF rectangular tanks, the plastic scrapers can be used with excellent results particularly for medium-high capacity equipment.
• Sand trapping in rectangular tanks: sand trapping is a pre-treatment of wastewater sewage mix used for separating solids and heavy sands before subsequent treatment stages of a purification plant. The material deposited at the bottom of the sand trap must be handled and removed while the tank is full.MITA Water Technologies offers a rectangular tank system based on the usage of chain scrapers with a few changes that take into account the weight and the abrasive power of the solid. This system permits to either move the sand at the bottom of the tank and to send it towards appropriate hoppers.