The HOG Project includes the construction of new facilities for the collection and processing of grit and screenings to provide a 50 percent minimum solids concentration in the final dewatered products. The project also includes modification of existing facilities and addition of new existing odor control facilities to improve odorous air collection and treatment of the headworks, aerated grit removal tanks, primary sedimentation basins, and new buildings associated with the HOG Project. In addition, the project incorporates a new digesters/influent tunnel cleaning station, and a partially designed scum concentrating facility. All screenings, grit, and scum processing facilities are intended to be incorporated into a centralized facility to minimize odor treatment requirements and maximize utilization of available land at the existing headworks site.
The recommended improvements to the screening, odorous air, and future scum processing facilities contained several unresolved issues which required further investigation to identify the recommended options, solutions and/or mitigation methods, as well as, to establish the basis for the final design. These issues included:
maintaining the operation of the existing screening, odor control and scum facilities during construction of new HOG and scum facilities determining the optimum location of the new bar screens in the existing screening channels and any identifying any required structural modifications determining the effects of the impact of rocks, having a diameter greater than three inches, on the influent screens and on the screenings washing and compaction equipment.
Dean Ryan also determined the feasibility of screening raw and /or concentrated scum, the number and location of scum, screens and compacted scum screenings disposal method to use, such as direct discharge into the screenings hoppers via a reversible conveyor.
Dean Ryan staff participated in the field and desktop evaluations which were performed on the existing screening, odor control and grit processing facilities to identify operation changes and recommended new equipment or facilities for improved performance. The information developed from these evaluations was augmented through workshops conducted to develop and refine the recommended HOG Project.
Headworks modifications: Raw wastewater entering the Point Loma Wastewater Treatment Plant was first mechanically screened at the head of the plant, consisting of four screens and a screening collection system. An additional screen and modifications to the screening collection system were added in 1988.
Bar Screen modifications: Each of the five existing screens is a 15-mm mesh, mechanically self-cleaning, traveling filter type screen. The screens are installed side-by-side in separate 7-foot wide channels. A slide gate is located upstream and downstream of each screen in the channels for wastewater flow isolation. Each channel can also be isolated, thereby providing access.