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Solid-Liquid Separation

Treating Wastewater Effectively: New System for Solid-Liquid Separation

| Author / Editor: Dr Girish R Pophali / Dominik Stephan

In water and wastewater treatment, solid-liquid separation is imperative. The new system will enhance the functioning of treatment plants and make them more sustainable.
In water and wastewater treatment, solid-liquid separation is imperative. The new system will enhance the functioning of treatment plants and make them more sustainable. (Picture: www.depositphotos.com/lightsource. Taken from PROCESS India February 2014)

Treating wastewater by employing solid-liquid separation technique poses major challenges in the water management industry. Scientists from CSIR-National Environmental Engineering Research Institute (CSIR-NEERI) have come up with a solution in the form of a new wastewater management system to simplify the process.

In the wastewater management sector, treating water containing solids is one of the major areas of concern. Many plants use primary and secondary clarifiers to resolve the problem; however, this solution comes with multiple drawbacks. Release of water from the top in the conventional secondary clarifiers creates turbulence in the clarification zone (Figure 1).

Figure 1: Conventional secondary clarifier
Figure 1: Conventional secondary clarifier (Picture: CSIR-NEERI)

The hydraulic energy of the incoming flow is also not dissipated to the extent that it is desirable and hence, creates turbulence in the clarifier. Some other shortcomings of the conventional system include:

  • Flocculation of solids hardly occurs in the clarifier unless a flocculating well is provided
  • The settled sludge is collected into a sludge sump-cum-pump house through rotating scraper mechanism, which brings some solids in re-suspension
  • A separate unit for sludge recycling and/or sludge wastage is essentially required; this increases the capital cost

As a result, conventional clarifiers are either too large or often fail to meet permissible effluent discharge standards prescribed by regulatory bodies. In order to help plants obviate these drawbacks of clarifiers, CSIR-National Environmental Engineering Research Institute has developed a novel circular secondary clarifier, named Hydroplume (Figure 2).

Figure 2: Functioning of Hydroplume
Figure 2: Functioning of Hydroplume (Picture: CSIR-NEERI)

Achieving Natural Flocculation for Better Solid–Liquid Separation

The new system provides natural flocculation through plume formation and produces excellent effluent quality (98-99 per cent suspended solids removal) and hence, helps in attaining prescribed discharge standards of treated effluent. It also removes sludge through a specially designed suction mechanism, which is fabricated to remove sludge from all around the clarifier and discharge it from the stationary outlet.

Function of Hydroplume in Waste-Water Treatment

The newly developed concept includes a low level gradually enlarged inlet, which ensures hydraulic energy dissipation through reduction in upflow velocity. It also allows plume formation just above the inlet and leads towards frictional resistance, which is normally caused by the dense flocs within the plume. Plume is nothing but a cloud of sludge, which is formed in the clarifier. Additionally, the system features an outward sloped clarifier bottom and a specially designed sludge removal system that uses suction mechanism. Another advantage of the plume formation is that it helps in flocculation of particles.

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