Primary water treatment

Primary treatment of sewage using the CirTec IntenSieve®

 The process of a sewage treatment plant (STP) can be divided into separate phases. 

  • Preliminary treatment: the removal of coarse particles, such as sand, sticks and bags
  • Primary treatment, the removal of suspended solids and organics
  • Secondary treatment: this involves the removal of dissolved nutrients and organics.
  • Tertiary treatment or effluent polishing

Small STPs often do not have a primary treatment step. The suspended solids are taken to the aeration tank where they are partially broken down. This takes up valuable energy due to higher oxygen demand. By installing a form of primary treatment, the capacity of the STP can be increased by up to 20%. The Intensieve is a rotary belt sieve (RBF) and an efficient form of primary treatment. The Intensieve removes 40-70% of the total suspended solids whilst having a small footprint and requiring little hydraulic height to function. The Intensieve can treat the same amount of water whilst only using 0,36% of the space used by a sedimentation tank. figure 2 shows the average removal efficiencies achieved with an RBF used as the primary treatment of sewage at different tested locations.

Removal Efficiency is dependent on the amount of bonded COD, BOD, TKN and TP to suspended solids

The sludge recovered by the Intensieve from sewage contains considerable amounts of cellulose, which can be reused for many applications and products.

Working principle of the IntenSieve®

  An IntenSieve® combines two critical processes into one compact unit – solids separation and solids thickening. The rotating filtermesh removes TSS and produces dewatered screenings. It is the preferred filter design that can replace conventional primary treatment.

With an almost unlimited design flow capacity and the option to install indoors or outdoors, an IntenSieve® system provides all the flexibility you need. An IntenSieve® system is cost-effective, compact, high-performing, chemical-free and sustainable.

Figure 1: IntenSieve® CT-170

The IntenSieve® is designed for high efficiency solids removal from sewage, aquaculture and industrial- and municipal (waste)water streams. It is particularly effective for removing suspended solids (TSS) from liquid streams, improving water quality, and recovering valuable material. The machine is designed to treat (waste)water streams which, next to solids, may contain high concentrations of fats, oils, or grease (FOG).

Figure 2: IntenSieve® working principle

 The IntenSieve®, depending on the application, is equipped with a filtermesh with one size mesh opening sizes that can range from 90 to 2000 microns. The feed water is continuously fed into the unit in which the filtrate escapes through the mesh. The suspended solids that are separated by the mesh form a pre-coat which increases the efficiency, by catching smaller particles. 

  The belt moves continuously, with a controlled speed based upon the water level within the machine. To improve separation of solids it is possible to add coagulants and/or flocculants.

The filtrate (free water) is collected behind the filter mesh in the frame from where it is discharged. The solids are removed from the filter cloth by means of a specific designed cleaning system.

Sewage treatment

Studies and practical experience with rotating belt fine sieves show the following:

  • Building a pre-coat on the filter mesh has a major effect on the solid’s removal efficiency. Even at high volumetric loads, particles that are smaller than the mesh pore size of the filter mesh are removed with high efficiencies.
  • The filtermesh has little influence on the removal efficiency. The built-up pre-coat is more decisive for the separation efficiency, although it should be noted that the larger mesh size does have a higher permeability (also with pre-coat) and therefore allows more water to pass through and allows a higher processing capacity.
  • To be able to make the right choice of the mesh size of the screen cloth, it is important to have insight into the particle size distribution of the suspended solids in the water.