Pretreatment Design for Pucara, Peru
Posted: August 27th, 2021
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Pretreatment Design for Pucara, Peru
Final Disposal of Grit
Wastewater is recognized to contain high amounts of inorganic solids like sand, gravel, and cinders. It might contain organic components like eggshells, seeds, and closely-held coffee grounds with a specific gravity varying from 1.5 to 2.65. With Grit’s production in the sewer system, its amount is highly inconstant. This is because it depends on varied factors like rates of sewer infiltration, the collection system, topography, type of soils, and percentage of either paved or unpaved streets. Therefore, the amount of Grit varies substantially during wet and dry periods.
On-site Storage for Pathogen Reduction
The conventional on-site storage is important for undertaking the final sedimentation process. During the process, suspended solids coupled with viruses, bacteria, and protozoa are eventually removed. The removal of pathogens happens slowly due to sedimentation and retention of the pathogens over settling flocs. Indeed, a minor percentage of pathogens would be retained in flocs by adsorption or entrapment within the floc matrix. Nonetheless, a majority of the exit occurs in the primary effluent. Apart from that, critical factors limit the design overflow rates and the equivalent settling velocities, such as the size of the primary sedimentation tanks. Hence, some segments of pathogens attached to solids have a direct effect on the removal process.
Long Term Disposal or Reuse Options
The need for long-term disposal or reuse of Grit is dependent on the directives of Wastewater Treatment plans. In particular, there might be minimum standards that seek to safeguard the local community against the wastewater environment. For example, there are decisions regarding the acceptable amount of discharges from an effluent being emptied into the water. Such decisions are made based on regional confined topographical and hydrological factors like discharge points and regions where there is a mixing of discharges with water bodies. These directives of wastewater need to consider the usefulness of effluents disposal to improve water resource recovery. Notably, the reuse option may add up the environmental water uses, which could provide agricultural or industrial purposes.
Burial-Onsite or Offsite
Burial on-site or offsite entails the fecal sludge sanitized before being transported and emptied closer to or away from the wastewater treatment plant. Offsite burial consists of the amount of sludge that is being lost through leakages in sewers. In contrast, on-site burial encompasses the quantity of sludge emptied into a general sanitization facility.
Fill Material
Wastewater grit is considered the best landfill material, for it does not cause harm to humans. Likewise, most of the grit landfills might be rechanneled to make green pothole fills as a replacement for asphalt. Grit fill material is widely regarded as eco-friendly.
Summary Table and Drawing of Grit Chamber and Parshall Flume
Table 1: Summary table for variations of Free Flow Parshall Flume
Table 2: Parameters involving the design for horizontal grit chambers
| Parameter | Design Recommendations |
| Horizontal velocity | Vmax = 0.3 m/s Vmin ³ 0.24 m/s |
| Sedimentation velocity | 0.02 m/s (particles with 0.2 mm diameter) |
| The transverse section in the canal | Rectangular coupled with a hydraulic drop from the base of the canal towards the base of Parshall flume |
| Hydraulic retention time | Vmin £60s Vmax ³45s |
| Length of canal | L = 25Pmax |
| Velocity control | Parshall flume experiencing downstream free flow |
| Hydraulic head in canal downstream from Parshall flume associated with free-flow | Hydraulic head for the grit chamber canal at £60% |
| Number of canals | Two no. of canals lying parallel with drainage to downstream treatment (One for operation and another for cleaning) |
Figure 1: Example of an installed Parshall flume across a horizontal Flow grit chamber
Plan for Grit Chamber and Parshall Flume
From the plan, the flow rate involving the Parshall flume is expressed mathematically in the following way.
Q = 2.27 x W(Ha)1.5
Where; Q is the flow rate in m3/s
W is the throat width in Parshall flume in meters
Ha is the depth of water on the Hydraulic Head at point 2/3 A (fig.2), which is established from the Parshall flume base in meters.
Figure 2: Plan drawing for Parshall flame
Figure 3: Profile for Grit chambers and Parshall flume
Works Cited
Capitulo 3. “Chapter 3: Pretreatment and Flow Measurement.” pp 1-31.
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