Pretreatment Design for Pucará, Perú

Posted: August 27th, 2021

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Pretreatment Design for Pucará, Perú

Screenings Production

In municipal wastewater treatment, it is important to initiate pretreatment to measure filtering materials that did not get removed biologically during the first unit processes.

Types of Removed Materials

1. There are coarse solids like paper, plastics, rags, and cloth, which get suspended in raw wastewater, depending on bar spacing human excreta.
2. There are also inorganic solids like sand and gravel which enter the sewerage system. Such inorganic solids, also known as grit, enter via sewer connections as well as inspection covers. They varybased on local soil characteristics since they have much specific and greater gravity than the organic solids in wastewater.

In many small-to-medium-sized towns, manual bar screens and horizontal flow grit chambers are the most appropriate methods for removing coarse solids and grit(Capitulo 3). Thus, Parshall flume controls the horizontal velocity measuring the flow-rates.

Volumes Produced Per Unit Flow

Coarse solids are removed by inserting bar screens transversely to the flow direction as water passes through the bars. Studies in Peru have established that the mounts of retained coarse solids range from 0.008 to 0.038 cubic meters per 1,000 cubic meters in screens coupled with openings that range from 20 to 50 mm. Therefore, based on these estimates at a flow per person of 120 L per capita-d and 10,000 residents, the production volumes of retained material per unit flow would be from 0.01 to 0.05 cubic meter per diameter.

Final Disposal of Screenings

Screenings seem highly dirtied with nasty and odiferous pathogens; therefore, they need to be buried daily by the facility operator (Capitulo 3). The pretreatment facility’s designing should consist of a reserved area close to the pretreatment. In this case, therefore, it is easy for the facility operator buries screenings with minimum handling.
Short Term Drying

This is a short-term sedimentation basin for screening and removing grits so that they do not contaminate the environment. Hence, grits are done via excreta disposal and further left to dry and decompose for at least two years before the contents could be safely emptied.Onsite Burial

Onsite burial is done for highly hazardous biomedical materials through landfills, surface impoundments, and underground injection to decompose the biomedical materials.Offsite Disposal Options

An off-site disposal option entails transferring toxic chemicals in wastewater to geographically separated facilities away from the wastewater treatment plant. Therefore, disposals are channeled to off-site facilities for recycling, energy recovery, or treatment. In the exception of the off-site transfers to disposal, these amounts of materials do not essentiallyimply entry of the hazardous chemical into the environment.

Summary Table and Drawings of Bar Screen and Approach Channel(Plan and Profile)

Table 1. Design specifications for manual bar screens

Parameter	Recommendation
Shape	Rectangular
Width	5-15 mm
Thickness	25-40 mm
Spacing between bars	25-50 mm, whereas 50 mm seemedsuggested for human feces.
Inclination from horizontal	45-600
Drainage platform
By-pass channel
Bar screens and drainage platform materials
Approach velocity	0.45 m/s
Hydraulic retention time in the approach	³ 3 s
Approach channel length	³ 1.35 m
Velocity through bars	£ 0.6 m/s for average flow and £ 0.9 m/s for maximum flow
Maximum Head loss through bars	0.15 m
Quantities of screenings (volume per flow)	0.008 – 0.038 m3 /1,000 m3
Final disposal of screenings	Disposed onsite in respect with daily cover

Figure 1. Drawings of bar screens

Approach Channel

It is designed with the following equations in that the maximum depth P_MAX is established when designing the grit chamber, as illustrated by figure 2 below.

Figure 2. Approach channel

Figure 3. Google Earth of the disposal materials in Pucara Pretreatment Design in Peru

Works Cited

Capitulo 3. “Chapter 3: Pretreatment and Flow Measurement.” pp 1-31.