Raw water clarification and sludge thickening in drinking water treatment plant (DWTP)

Scenario

ABENGOA was contracted to design and build the expansion and upgrade of the REUS DWTP with a capacity of 30 ML/d (250,000 PE). The DWTP has two clarification-filtration treatment lines and a sludge treatment line.

In the improvement works, a new pretreatment was added that includes a physical-chemical treatment followed by dissolved air flotation to remove suspended matter and eventually algae present in the water. SIGMADAF supplied the flotation process equipment for the clarification of the raw water and thickening of the sludge generated in the DWTP, including the surface skimmer, the air saturator and bubble aerators, the air supply units and the rest of the equipment to complete the system.

The SIGMADAF FPAC is a large surface area flotation system with piston flow (longitudinal) separation, designed to treat heavily solids-laden wastewater streams that require sufficient surface area for successful solids removal. In this project the DAF tank is constructed in concrete.

Feed water enters at the front of the tank and flows to the outlet at the opposite front of the tank. Solids float along the water flow path aided by air bubbles and the foam layer formed is removed by the longitudinal scraper in a collection hopper in the tank.

Before DAF, the water is flocculated with the aid of chemicals in coagulation-flocculation tanks with mechanical agitation. A coagulant (alumina sulfate) and polyelectrolyte are added to facilitate the formation of flocs with better flotation properties; retention times in these two tanks are 2 min for coagulation and 20 min for flocculation.

SIGMADAF designed and supplied all the equipment for the two (2) FPAC600 CW units working as primary clarifiers at the DWTP, installed in newly constructed concrete tanks, including: surface chain scraper, recirculation pumps (2 + 1R), air compressors (1 + 1R), air saturators with depressurization system with nozzles, settled sludge purge valves, pneumatic control panel, piping, valves and fittings, instrumentation, spare parts, technical documentation and manuals.

The DAF unit has dimensions L 10800 x W 7500 x H 4940 mm. with a usable area of 81^m2. The recirculation flow rate was set at 70 ^m3/h per DAF (12%) with (2 + 1R) centrifugal pumps and an air flow rate of 100 l/min at 6 bar pressure.

COLLECTOR

To sweep the sludge floated on the surface of the tank, there is a chain-type scraper with dimensions L 10500 x W 7500 mm made of AISI316 with a 1.1 kW drive motor. This device sweeps the sludge into an extraction hopper at the tank outlet.

AERATION SYSTEM

The aeration system includes a saturation pressure vessel (2 pcs) with a volume of 2300 lts (Ø1400 x L 1500 mm) with 8 air supply manifolds and submerged nozzles for depressurization. The air is supplied by a piston type air compressor (1 + 1R) with a capacity of 1000 lts/min (5.5 kW motor) and a 500 lt. air accumulator.

SIGMADAF FPAC-CPL20 FOR SLUDGE THICKENER

SIGMADAF also supplied the flotation units for the thickening of sludge produced in the DWTP as a result of water treatment, 2 units FPAC-CPL20 with a capacity of 10 ^m3/h each built in AISI304 and 1 polymer preparation unit PFL10 were supplied. These DAF thickening units are supplied complete with all the necessary equipment, such as recirculation pumps, aeration vessels and depressurization valves, air compressor, etc.

Performance